Lasl subterrence program   rapid excavation by rock melting, 1976, 89p
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Lasl subterrence program   rapid excavation by rock melting, 1976, 89p Lasl subterrence program rapid excavation by rock melting, 1976, 89p Document Transcript

  • . .... : . * , . * .,.. .3& .*. . , : ..I I 4-5979-SRdO p UC-3 and UC-66c 775 Issued: February 1977 Rapid Excavation by Rock Melting == LASL Subterrene Program -= September 1973- June 1976 Compiled by R. J. Hanold Contributors J. H. Altseimer P. E. Armstrong H. N. Fisher M. C. Krupka scientific laboratory of the University of California LOS A L A M O S , NEW MEXICO 8 7 5 4 5 ffirmative Action/Equal Opportunity Employer a$ U N I T E D STATES E N E R G Y RESEARCH A N D D E V E L O P M E N T A D M I N I S T R A T I O N C O N T R A C T W-7405-ENG. 3 6 dSTRIBUTION OF THIS DOCUMENT I UNLlMlTED S
  • DISCLAIMERThis report was prepared as an account of work sponsored by anagency of the United States Government. Neither the United StatesGovernment nor any agency Thereof, nor any of their employees,makes any warranty, express or implied, or assumes any legalliability or responsibility for the accuracy, completeness, orusefulness of any information, apparatus, product, or processdisclosed, or represents that its use would not infringe privatelyowned rights. Reference herein to any specific commercial product,process, or service by trade name, trademark, manufacturer, orotherwise does not necessarily constitute or imply its endorsement,recommendation, or favoring by the United States Government or anyagency thereof. The views and opinions of authors expressed hereindo not necessarily state or reflect those of the United StatesGovernment or any agency thereof.
  • DISCLAIMERPortions of this document may be illegible inelectronic image products. Images are producedfrom the best available original document.
  • This work was supported by a grant from the National Science Foundation, Research Applied to National Needs (NSF-RA") and by the US EnergyI Research and Development Administration, Division of Geothermal Energy.I Printed in the United States of America. Available from National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfeld, VA 22161 Price: Printed Copy $5.00 Microfiche $3.00I
  • CONTENTS ABST~CT 1 I. INTRODUCTION AND SUMMARY 2 A. Objectives 2 B. Technical Approach 2= C. Sumnary 2 11. PROTOTYPE DESIGN AND TEST 6 A. Consolidation Penetrator Development 6 1. Introduction 6 2. S i g n i f i c a n t Technical Achievements 6 B. Extruding Penetrator Development 7 1. Introduction 7 2. 84-mn-diam Extended Surface Penetrator 8 3. High Advance Rate Extruder (HARE) 9 4. M e l t Flow Augmented Extruder 10 5. S i g n i f i c a n t Achievements 11 6. Penetration Rate Paradox 12 C. Coring Penetrator Development 13 D. Thermal Stress Rock F r a c t u r i n g Tool 14 E. G1ass-Formi ng Techno1ogy 15 F. D i r e c t M e l t Heating 17 1. Introduction 17 2. Me1t-Heating Experiments 17 G. S a l t Borehole Plugging by M e l t i n g 19 H. Plasma Arc Experiments 20 I. Rock Laboratory Test F a c i l i t y 111. POWER SOURCE DESIGN AND DIRECTED RESEARCH A. E l e c t r i c Power Sources 1. Intyoduction 2. Heater Development f o r Penetrator Research 3. A l t e r n a t i v e s t o Graphite Resistance Heating B. M a t e r i a l s Sc.ience and Technology 1. I n t r o d u c t i o n 2. Refractory A l l o y - Rock Melt I n t e r a c t i o n s 3.. Power Source M a t e r i a l s. 4. S t r u c t u r a l Glass L i n e r Results C. Refractory A l l o y F a b r i c a t i o n 1. Introduction-6eneral F a b r i c a t i o n Problems 2. High-Temperature Braze Development 3. Si1 i c o n Carbide Conversion Coatings D. Geosciences 1. Introduction 2. Me1t i n g Range Experiments 3. Molten Rock Property Studies . 4. Directed Research I .i i DISTRIBUTION OF THIS DOCUMENT ISUNLIMITED .$"r
  • IV. FIELD TEST AND DEMONSTRATIONS 40 A. Field-Demonstration Units 40 1. Introduction 40 2. Tunnel L i n i n g Experiment 40 B. Public Demonstrations 41 1. Washington, DC 41 2. Denver, CO 42 3. Tacma, blA 43 C. Mobile Experimental Field U n i t 43 1. Introduction 43 2. Stem Design and Performance 44 3. Proof-of-Concept Field Experiment 45 V. SYSTEMS ANALYSIS AND APPLICATIONS 47 A. Geothermal Well Technology 47 1. Introduction 47 2. Current Technological and Cost Status 47 3. Conceptual Applications of Subterrene Devices t o 50 Geothermal W11s e ‘4. Contacts Made t o Discuss Geothermal Well Drilling 52 Problems B. Geothermal Well Systems and Cost Analysis 53 1. Introduction 53 2. System Model 53 3. Study Results 56 4. Cost Analyses 57 C. Mathematical Modeling and Analysis 59 1. Introduction 59 2. The Thrust-Velocity Relationship for Extruding 61 Penetra tors 3 . Liquid Basalt Thermal Conductivity Investigation 66 4. Stem Cooling w i t h Particle Transport 69 5. M1 t-Heating Analysis e 70’ 6. Power Transmission Analysis of Subterrene Stem 77 D. Applications and Technology Transfer 78 V I . TECHNICAL REPORTS AND PRESENT~TIONS 80 A. Completed L S Technical Reports AL 80 B. Technical Presentations and Journal Articles 81 C. Reports Related t o Subterrene Technology Published by 83 Other Organizationsiv
  • RAPID EXCAVATION B ROCK MELTING Y -- LASL SUBTERRENE PROGRAM -- September 1973 - June 1976 Compi 1ed by R. J. Hanold Contributors J. H. Altseimer P. E. Armstrong H. N. Fisher M. C. Krupka ABSTRACT Research has been d i r e c t e d a t establishing the technical and economic feasi b i 1i y o f excavation systems based upon the rock-me1 t i n g (Subterrene) t concept. A series o f e l e c t r i c a l l y powered, small-diameter prototype me1t- i n g penetrators has been developed and tested. Research a c t i v i t i e s i n - clude optimizing penetrator configurations, designing high-performance heater systems, and improving r e f r a c t o r y metals technology. The properties o f the glass l i n i n g s t h a t are a u t o m a t i c a l l y formed on the melted holes have been investigated f o r a v a r i e t y o f rocks and s o i l s . Thermal and f l u i d - mechanics analyses o f the m e l t flows have been conducted w i t h the o b j e c t i v e o f optimizing penetrator designs. F i e l d t e s t s and demonstrations o f the prototype devices continue t o be performed i n a wide range o f rock and s o i l types. Primary emphasis has been placed on the development o f a penetrator designed f o r more economical e x t r a c t i o n o f geothermal energy and o f small- diameter penetrators which can be u t i l i z e d i n support o f geothermal energy exploration programs. The conceptual design o f a geothermal energy rock- m e l t i n g system w i l l d e f i n e the surface equipment, the stem, hole-forming. assembly, and debris removal subsystems.. Optimization o f we1 1 design, the t r a d e - o f f o f advance r a t e w i t h operating l i f e , the advantages o f using the melt-glass hole casing f o r well-bore seal-off, r i g automation, and the b e n e f i t s which r e s u l t from the i n s e n s i t i v i t y o f rock m e l t i n g t o formation temperatures and geologic v a r i a t i o n s have also been studied. Subsystem hardware development has been d i r e c t e d toward r e s o l u t i o n o f c r i t i c a l technical questions r e l a t e d t o penetrators f o r dense rock, debris handling, e l e c t r i c a l heater configuration, and e s t a b l i s h i n g pene- t r a t o r l i f e . Laboratory experiments and f i e l d t e s t s provide data f o r f i n a l system design o p t i m i i a t i o n s and i n d i c a t e proof o f a p p l i c a b i l i t y of the concept t o a geothermal w e l l hole-forming system. A f i e l d t e s t u n i t t o fonn r e l a t i v e l y shallow v e r t i c a l holes f o r heat f l o w surveys i n support o f geothermal exploration studies has been designed, fabricated, and f i e l d tested. Experience w i t h t h i s u n i t i s intended t o provide a basis f o r tech-.. nology t r a n s f e r t o the d r i l l i n g industry. P r a c t i c a l applications t o deep geothermal d r i l l i n g w i l l r e q u i r e an ex- tensive development program i n c o l l a b o r a t i o n w i t h the d r i l l i n g industry. progressive steps v i a smaller systems can p o t e n t i a l l y speed the transfer process. 1
  • I. INTRODUCTION AND SUMMARYA. Objectives Power Source Design and Directed Research The technical e f f o r t s and resources o f the LASL F i e l d Test and Demonstrationsrock-me1 t i n g (Subterrene) program have been d i s t r i b - Systems Analysis and Applications.uted t o y i e l d a balance o f prototype hardware o f i n - The s i g n i f i c a n t r e s u l t s and achievements i n t h ecreasing complexity and size, l a b o r a t o r y experi- research and development program are summarized f o rments, p r a c t i c a l f i e l d - t e s t experience, design and each o f these f o u r technical a c t i v i t i e s i n f o u reconomic analyses, e l e c t r i c heater development, ma- major sections o f t h i s r e p o r t f o r the period Septem-t e r i a l s development and applications, and t h e o r e t i - ber 1973 t o June 1976.c a l studies. The r e s u l t s o f these technical a c t i v - C. Summaryi t i e s were planned t o y i e l d : During the research p e r i o d covered by t h i s sta- The demonstration o f the basic f e a s i b i l i t y t u s report, a r e d i r e c t i o n o f technical e f f o r t was i n i - of rock m e l t i n g as a new excavation t o o l t i a t e d a t the request o f the programlsponsoring or- f o r a p p l i c a t i o n s up t o 400 mn (16 i n . ) i n ganizations. E f f o r t s d i r e c t e d toward the appl ica- diameter. t i o n o f rock m e l t i n g t o large-diameter tunneling Operational and f i e l d - t e s t data f r o m proto- systems were suspended. A vigorous research and de- type devices o f a range o f sizes and con- velopment program leading t o d e e p - d r i l l i n g capabil- i t y f o r geothermal energy systems was i n i t i a t e d i n - figurations, and the v e r i f i c a t i o n o f pre- l i m i n a r y t h e o r e t i c a l modeling needed t o c l u d i n g intermediate development o f equipment f o r scale t o l a r g e r diameters, p r e d i c t p e r f o r - shallow exploratory holes, development of h o l e sta- mance, make cost estimates, and optimize b i l i z a t i o n t o o l s , development and t e s t o f h o t rock advance r a t e and r e l i a b i l i t y . penetrators f o r magma taps, and development o f l a r g e r Refractory m a t e r i a l s technology s u f f i c i e n t l y diameter shallow-hole devices f o r a v a r i e t y o f po- established t o permit p r e d i c t i o n s o f compo- t e n t i a l applications. nent l i f e and t o generate m a t e r i a l s selec- Extruding penetrator systems have demonstrated t i o n c r i t e r i a f o r prototype development the basic features o f rock-melt f l o w handling w i t h needs and p r o j e c t i o n s o f service l i f e f o r debris produced i n the form o f chiTled glass pellets, systems i n p r a c t i c a l applications. glass rods,.or rock wool and c a r r i e d out of t h e stem F i e l d - t e s t experience and operational demon- by the coolant gas flow. Two l a r g e r diameter (84- s t r a t i o n s s u f f i c i e n t t o e x h i b i t the poten- and 86-mm), higher advance rate,molybdenum extruding t i a l u t i l i t y o f smaller diameter prototype penetrator systems were designed, fabricated, and devices and t o p r o j e c t commercial use i n t h e extensively tested i n both laboratory and f i e l d t e s t s . The f i r s t o f these designs incorporates mul- important p r a c t i c a l a p p l i c a t i o n s o f geo- t i p l e heater stacks, m u l t i p l e m e l t f l o w passages, and thermal energy e x p l o r a t i o n programs, econom- a penetrator configuration u t i l i z i n g extended sur- i c a l e x t r a c t i o n o f geothermal energy, and faces f o r enhanced heat t r a n s f e r surface area. This shallow h o r i z o n t a l hole emplacements i n penetrator was used w i t h t h e new Experimental F i e l d loose o r unconsolidated materials. U n i t (EFU) t o produce a 30m-deep hole i n a b a s a l t 0 Theoretical models and a n a l y t i c a l techniques 1edge near Los Alamos as a proof-of-concept experi- needed t o describe t h e heat- t r a n s f e r and ment. The second design incorporates a more conven- f l u i d mechanics o f the rock-melting and t i o n a l me1t i n g body capable o f producing t h i c k e r penetration processes f o r the purposes o f glass l i n i n g s i n dense rock, a s i n g l e annular r e s i s - o p t i m i z i n g configurations, and p r e d i c t i n g tance heater which d e l i v e r s a higher leading edge, performance. heat flux, and m e l t removal e n t i r e l y through t h e cen-B. Technical Approach t r a l e x t r u s i o n p o r t . S i g n i f i c a n t improvements have The technical e f f o r t i s organized i n t o f o u r been achieved i n extruding penetrators, i n c l u d i n g i m -technical a c t i v i t y areas whose functions are: Prototype Design and Test proved c o a x i a l - j e t debris removal systems, higher2
  • strength extractors, improved high-temperature opera- was d i r e c t e d toward the r e s u l t i n g physical properties i o n and s t a b i l i t y , and "designed i n " instrumentation of the plugs prepared i n t h i s manner. Another tech-qapability . The r e s u l t s from the successful t e s t i n g n i c a l approach investigated for Subterrene penetrators o f these extruding penetrator systems designed t o i n - involves the a p p l i c a t i o n o f plasma arc heating t o i n - vestigate s p e c i f i c aspects o f heater design, debris crease penetration r a t e s and handle the highest melt- removal, and viscous rock-melt f l o w t h a t w i l l lead t o ing-point rocks. While the observation has been higher penetration r a t e s were analyzed t o provide de- noted t h a t a plasma t o r c h r e a d i l y melts a rock sample, sign considerations f o r future penetrator systems. l i t t l e a t t e n t i o n has been given t o the task o f pro- Laboratory t e s t s i n Dresser b a s a l t heated t o 650 K v i d i n g a debris removal system for such a penetra- confirmed the a n a l y t i c a l l y predicted enhanced pene- t i o n device. t r a t i o n rates i n the hot basalt. Density consolida- R e s i s t i v e l y heated, pyrolytic-graphi t e heater t i o n penetrator designs have been developed t o the elements, which r a d i a t e energy t o the r e f r a c t o r y stage where compressed-air-cooled, oxidation-resis- metal penetrator body, have proven t o be most s a t i s - tant, e a s i l y replaceable penetrators a r e i n s a t i s - f a c t o r y f o r the development e f f o r t s . With heater f a c t o r y use f o r both laboratory experiments and f i e l d c a v i t i e s f i l l e d w i t h helium t o enhance the r a d i a l heat transfer, heat f l u x e s of up t o 2 MW/m 2 have been demonstrations i n a wide v a r i e t y o f porous materials i n c l u d i n g t u f f , alluvium, unconsolidated and layered obtained from p y r o l y t i c - g r a p h i t e radiant-heater ele- sediments, saturated ground, and b a s a l t i c gravel. A ments. Larger diameter annular-shaped p y r o l y t i c - high-temperature thermal stress rock f r a c t u r i n g probe graphite heaters have been used t o achieve higher based on rock-me1 t i n g Subterrene technology has been leading edge heat fluxes i n extruding penetrators, developed and made a v a i l a b l e f o r rock mechanics and and heater stacks whose energy generation per u n i t f r a c t u r i n g studies. A 114-mm-diam consolidating l e n g t h have been c a r e f u l l y matched t o the penetrator corer intended f o r use i n porous a l l u v i a l s o i l s has requirements through the use of a n a l y t i c a l modeling been designed, constructed, and laboratory tested. calculations are now routine. A new single-piece The core diameter i s 64 mn,and t h e melting body, carbon c l o t h composite heater has been developed which i s vacuum-arc-cgst molybdenum, i s f a b r i c a t e d which allows greater f l e x i b i l i t y i n heater configura- as a s i n g l e s t r u c t u r a l component. t i o n and has been successfully tested i n the thermal The p o s s i b i l i t y o f arranging the e l e c t r i c c i r - stress rock f r a c t u r i n g probe. Investigations o f new c u i t o f a rock-melting penetrator so t h a t c u r r e n t designs have been i n i t i a t e d , including high-tempera- passes through a molten region and deposits most o f t u r e l i q u i d metal heat pipes, the d i r e c t melt-heating the melting power d i r e c t l y i n t h e m e l t l a y e r j u s t concept, and t h e use o f higher resistance conduction adjacent t o the melting i n t e r f a c e has been recognized heaters which would lead t o s o l i d penetrators o f very f o r a long time. This mode o f rock melting has been high strength f o r use i n deep wells. A t the r e l a - investigated i n recent laboratory experiments and t i v e l y high temperatures encountered by rock-me1 t i n g The success o f a n a l y t i c a l modeling calculations. penetrator systems, most materials react with one an- these preliminary experiments has i n i t i a t e d f u r t h e r other t o some extent, and thermodynamic and k i n e t i c experimental and a n a l y t i c a l research t o d e f i n e the 1i f e t i m e 1i m i t a t i o n s have therefore been investigated. d e t a i l s of the heating mechanisms involved and the S t a t i c c o m p a t i b i l i t y laboratory t e s t s have been per- influence o f the t y p i c a l m e l t r e s i s t i v i t y vs tempera- formed t o determine the corrosion o r d i s s o l u t i o n r e - t u r e behavior on the process. An experimental study actions o f molybdenum and tungsten w i t h t u f f , Jemez of the f e a s i b i l i t y o f forming borehole plugs i n basalt, and g r a n i t i c rocks a t temperatures from 1700 underground s a l t deposits by m e l t i n g and r e s o l i d i - t o 2100 K. These experiments are designed t o inves- f y i n g s a l t s i m i l a r t o t h a t found i n the formation t i g a t e q u a n t i t a t i v e l y the e f f e c t s o f time and tempera- was conducted on the basis t h a t a plug w i t h physical t u r e on the reactions between r e f r a c t o r y metals and and chemical properties close t o those o f the forma- rock-glass me1ts. Techniques for rock-glass property t i o n could be formed by t h i s technique. Since melt- evaluation and optimization are under developmentwing and r e s o l i d i f i c a t i o n o f rock s a l t causes p r a c t i - w i t h the goal o f establishing rock-melt glass as an c a l l y no change i n the chemical properties, emphasis --t u i n si s t r u c t u r a l element t o serve as the hole 3
  • support d u r i n g penetration. Laboratory experiments field using a field-demonstration unit. A prototypehave confirmed a significant increase i n crush tunnel opening, 2 m h i g h , 2 m deep, and 1 m wide,wastrength and decrease i n permeability for rock-glass Li formed i n a loose alluvial d i r t f i l l . The roof andliners when compared to the original porous materials side walls were formed by melting a series of paral-from which they were formed i n situ. Petrological lel small-diameter horizontal holes i n the looseexaminations of parent rock and derived rock-glass soil f i l l using density consolidation penetrators.samples have been performed. Correlation of petro- The holes were placed sufficiently close togethergraphic information with physical properties and i t s that the glass linings fused and t h u s produced aextension to Subterrene design and performance is the double-walled lining reinforced by webs between thedesired goal. The melting ranges of approximately individual holes.15 different rock types were measured using hot- Efforts have been directed toward the develop-s t a t e microscopy. Penetrator fabrication techno1ogy ment of new analytical and numerical techniques forhas been vastly improved, particularly i n the areas analyzing the combined fluid dynamic and heat trans-of refractory metal forming, the development of mod- f e r performance of melting penetrators and the appli-erate-and high-temperature brazing techniques for dis- cation of these techniques to specific penetratorsimilar metals, and electron beam welding. designs and concepts. Numerical solutions of the The field-test program was expanded w i t h the coupled energy equation and the Navier-Stokes equa-design, construction, and utilization of two portable, tions, including the strong temperature dependencemodularized field-demonstration units (FDUs). These of the rock-melt viscosity, have been obtained. U t i -easily transportable units provided self-contained lizing this viscous rock flow computer program, de-systems for demonstrating smal 1-diameter rock-me1 t i n g tailed calculations have been performed on a varietypenetration system capabilities a t locations away of consolidating and extruding penetrator systems.from the Los Alamos area and were mobilized for pub- The validity of this powerful analytical tool hasl i c demonstrations of the rock-melting process before been established by comparisons with laboratory data,large audiences in Washington, DC; Denver, CO; and and design and scaling to larger diameters and dif-Tacoma, WA. Such field evaluations of penetrator ferent operating conditions can now be have served to acquaint excavation technolo- Analytical techniques have also been extended togists with the potential of rock melting and have pro- study the fluidized debris removal process in ex-vided valuable data and experience on reliability and truding penetrators. Calculations performed on ex-service l i f e . Numerous penetrations into various un- truding penetrator designs have also confirmed theconsolidated soil samples, including layered samples significant penetration rate increases associatedformed from different loose materials, have been con- with increasing in situ rock temperatures and theducted t o examine the resulting glass liners. The general trend toward higher penetrator efficienciesglass liners have been of good quality,and the smooth with increasing penetration rate, b o t h effects havingtransition across the layered samples was particu- been observed in the laboratory. Results from a two-larly encouraging. The LASL-designed mobile experi- dimensional heat conduction program have been instru-mental field unit (EFU) has been delivered, evaluated, mental in improving the thermal design of penetratorand operated in the field on basalt penetration tests. systems, particularly i n the areas of desired heaterT h i s unit, which can be used with penetrators from 50 performance, thermal control of the coaxial - j e t de-to 127 mn i n diameter, consists of a trailer-mounted bris removal zone, thermal control of the glass form-stem tower, hydraulic power supply, control functions, ing and conditioning zone, and i n evaluating theand a thruster that will support pipe stems 300 m thermal stress distributions and cooling requirementslong. The f i r s t field use of the EFU was i n the pro- in critical penetrator regions. The development ofduction of a planned 30-m-deep hole i n a basalt ledge analytical models has contributed t o the basic under-a t Ancho Canyon u s i n g 84-mn-diameter extruding pene- standing of specific relationships such as the lead-trators. The basic concept of Subterrene systems for i n g edge flux limitations and the thrust-velocity detunneling and excavating loosely compacted formations pendence. O major importance has been the theoret- fwas demonstrated by an experiment conducted i n the ical calculation of material properties when the 4
  • II experimental values were not appropriate or avail- hot rock penetrations for geothermal energy explora- U e l . The application of these models and techniques tion and production t o emplacements i n arctic perma- o specific designs and the interpretation of t e s t frost. The technology dissemination efforts expended results have received the largest portion of the anal- by members of the Subterrene program have been ex- ysis program effort. Analytical calculations have tensive in both scope and depth. O particular in- f also provided s u p p o r t for the laboratory experiments terest to the current program direction is a report investigating new penetration techniques , including entitled, "Geothermal Well Technology and Potential . direct melt heating and plasma arc heating. .. Applications of Subterrene Devices - A Status Review," The number of novel and conventional potential which has been completed and distributed. This re- applications of Subterrene technology that have been port reviews the past, present, and some future as- investigated continue t o increase and range from deep pects o f the geothermal energy industry w i t h special attention given to geothermal well drilling problems. 5
  • I 11. PROTOTYPE DESIGN AND TEST A. Consol idation Penetrator Development resulting hole liners were removed and examined. AI 1. Introduction. For porous rock or soft typical result from such a test i s shown i n Fig. ground, the density consol idation Subterrene can be 11-3. used to simplify the excavation process. In these materials, the glass lining formed when the rock- melt cools, i s significantly more dense and there- fore occupies a smaller volume than did the original porous rock. B melting out to a diameter larger y than that of the penetrator, the molten debris from the hole can be entirely consolidated i n the dense glass lining, completely eliminating the necessity for removing debris. Density consol idation pene- trator designs have been developed t o the stage where compressed-air-cooled, oxidation-resistant, easily replaceable penetrators are used satisfacto- r i l y for both laboratory experiments and field de- monstrations i n a wide variety of porous materials, including tuff, alluvium, unconsolidated and layered Fig. 11-1. Consolidating penetrator designs used f o r melting prototype tunnel opening sediments, saturated ground,and basaltic gravel. i n loose alluvial f i l l . . 2. Si gni f i cant Tec h n i ca 1 A h i evemen ts c A prototype tunnel opening (described i n detail i n Sec. IV. A ) was formed in.loose alluvial f i l l using two different 50-mm-diam consolidating penetrator designs. These penetrator designs, which employ replaceable graphite glass formers, are illus- trated i n Fig. 11-1. The solidified rock-melt layer which adheres t o the molybdenum penetrator body and provides oxidation resistance i s clearly visible. A considerable amount of operational field experi- ence was obtained i n this t e s t as over 100 m of sta- bilized hole were formed i n a loose f i l l including both vertical and horizontal penetrations. The a b i l i t y of consolidating penetrators t o produce glass-lined stabilized holes through vari- able, broken, and d i f f i c u l t rock samples was further verified by extensive testing i n a wide variety of samples. Figure 11-2 i l l u s t r a t e s a hole melted i n a conglomerate of Hanford alluvium. containing basal- t i c gravel and large cobbles. Penetration of the largest cobbles without debris removal is achieved by thermal stress fracturing and extrusion of por- tions of the rock melt into the resulting cracks. The a b i l i t y t o provide a continuous glass lining across nonhomogeneous samples was demonstrated i n tests i n which samples comprised of layers of allu- F i g . 11-2. Hole melted i n a conglomerate of Hanfor alluvium containing basaltic gravel and L large cobbles w i t h a consolidating pene- J viums, shales, and tuff were penetrated and the trator. 6
  • soil density and mechanical compaction. Results i n - dicate an extremely sharp drop i n penetration rate w i t h increasing soil density i n the range of densi- t i e s between 1.7 and 1.8 Mg/m 3 . Penetration of s o i l s w i t h b u l k densities greater than 1.8 by consolidating penetrators is very slow,and there i s l i t t l e possi- b i l i t y of significant mechanical compaction. Successful laboratory tests were conducted w i t h a 50-nnn-diam parabolic penetrator and a 60-mn- diam penetrator with a parabolic leading edge pro- f i l e joined t o a short cylindrical afterbody. Sig- nificant performance data were obtained from theseFig. 11-3. Continuous glass liner produced through tests,and penetration rates almost double the pre- a layered sample of unconsolidated allu- viums. vious rates for the double cone configuration were achieved . A design study was conducted indicating the During the research period covered by t h i s sta-feasibility of an integrated 76-mm-diam extruder- tus report, technical effort was redirected a t theconsol idator hole-forming system. T h i s proposed request of the program-sponsoring organization.system would take advantage of the simplicity of con- Efforts directed toward the development of densitysolidating penetrators, which eliminate the debris consol idation penetrators were terminated, and theremoval operation, for use in porous or low-density program emphasis was placed on the development ofrocks and soils. If hard rock were encountered, the hard rock extruding penetrator systems that could beuniversal stem would permit changing to an extruding applied t o the exploration and production of geother-penetrator for hole advancement u n t i l soft ground mal energy.conditions again prevailed. The emplacement of near- B. Extruding Penetrator Developmentsurface small-diameter u t i l i t y lines represents the 1. Introduction. Extrusion penetrators are re-main application for such an integrated system. quired i n dense materials and are designed to contin- Detailed viscous flow calculations have led uously remove the debris from the borehole. As i n -t o the development of a penetrator geometry incorpo- dicated in Fig. 11-4, the melt flow, confined by therating a parabolic leading edge segment joined t o a unmelted rock and the hot melting face of the pene-cy1 indrical afterbody. The parabolic leading edge trator, i s continuously extruded through a nozzle in the melting face. T h i s material is chilled and freezes shortly a f t e r the circulating cooling fluid impinges upon the extrudate exiting from the melt orifice. The flowing coolant then carries these small fragments up the stem t o the exhaust section. E x t r u d i n g penetrator systems have demonstrated the basic features of rock-melt flow handling w i t h debrissuited for the use of high-te produced in the form of chilled glass pellets, glass rods, or rock wool. These penetrators have been op-leading edge for en erated in the laboratory and in the field, i n verti-conceptual desi cal and horizontal orientations, and i n both hardrating these ad igneous rocks and porous tuffs and alluviums. Three larger diameter (84-to 89-mm) , higher advance rate,oerformance has been extended t o include the effect molybdenum extruding penetrator systems were design- mechanical compaction of the soil surrounding the ed, fabricated, and tested. Significant improvementsmelt zone. Calculations employing these methods show have been achieved i n current extruding penetrators,the dependence of consolidator penetration rates on including improved coaxial-jet debris removal systems, 7
  • rDEBRlS REMOVAL ZONE MOLYBDENUM Fig. 11-5. Cross section of the 84-m-diam extended surface penetrator me1 t i n g body. DENSE ROCKFig. 11-4. Extruding penetrator concept i l l u s t r a t - from the gas nozzle. The chilled debris is removed ing debris removal technique. through the debris carry-off tube and transported to the surface by the gas stream. A portion of theimproved high-temperature operation and stability, cooling gas flow enters the debris carry-off tubeand "designed-in" instrumentation. A maximum pene- through the gas orifices which provide a boundarytration rate of 0.28 m / s (3.31 f t / h ) in denseba- layer of cool gas along the tube surface reducing i t ss a l t has been demonstrated in the laboratory. temperature and minimizing any tendency for the cool- 2. 84-mn-diam Extended Surface Penetrator. ing rock melt to adhere t o i t s surface. Actual 84-This design introduced the concepts of mu1 t i p l e mm-diam hardware i s illustrated i n Fig. 11-6. Theheater stacks, multiple melt flow passages, and a upper penetrator i s unused,whereas the lower u n i tpenetrator configuration using extended surfaces for was tested in basalt and retains its protectiveenhanced heat transfer surface area. Based on theenhanced surface area, greater heater power, reducedoperating melt layer thickness, and high thrust ca-pability, this penetrator has melted hard rock a t asignificantly faster (- 3X) rate than the earlier66-mn design i t replaces. Figure 11-5 illustratesthe major components of this penetrator design. Theheater consists of three separate stacks of pyro-graphite resistance heater pellets and includeshigher power density pellets near the leading edgeto provide a higher heat flux in this critical re-gion. Electrical power i s supplied to the heatersby three tungsten electrodes. Energy distributionthroughout the penetrator is accomplished by radia-tion from the surface of the heater stacks t o thegraphite receptors and then by conduction throughthe h i g h thermal conductivity molybdenum meltingbody. Molten rock enters the rock nozzle from the Fig. 11-6. Extended surface penetrator hardwareaxial and radial rock flow passages and is rapidly comparing an as-fabricated melting body with an assembly that was tested inchilled by the high-veloc ty cooling gas exiting basalt.8
  • l a y e r o f s o l i d i f i e d b a s a l t melt. The f l u t e d o r ex- f i g u r a t i o n o f t h i s penetrator corresponds t o t h e de-u e n d e d surface c o n f i g u r a t i o n and t h e mu1t i p l e m e l t s i g n i l l u s t r a t e d i n Fig. 11-4, d e p i c t i n g t h e concept removal passages are c l e a r l y v i s i b l e i n t h i s photo- of extruding penetrator operation. This design was graph. 1 + based on t h e use o f a l a r g e d i a m e t e r annular pyro- This 84-mm-diam extended surface penetrator was graphite heating element which would provide t h e used t o produce a 30-m-deep f i e l d hole i n b a s a l t maximum surface area f o r r a d i a t i o n heat t r a n s f e r (see Sec. I V . C. 3). Design changes based on f i e l d near the c r i t i c a l leading edge region. The annular t e s t experience have eliminated e a r l y d i f f i c u l t i e s design eliminates the azimuthal temperature v a r i a - encountered i n the operation t o produce t h i s 30-m- t i o n s present w i t h t h e use o f three separate heater deep hole. Rock i n t r u s i o n has been eliminated by stacks (a!; i n the extended surface penetrator) and improved c o o l i n g of t h e glass-former region, and plug- f u r t h e r enhances the leading edge heating since both ging o f t h e debris carry-off tube has a l s o been elim- the i n n e r and outer surface of the heater can r a d i - i n a t e d by improved c o o l i n g o f t h e w a l l near t h e de- a t e w i t h equal f l u x density. I n addition, t h e mo- b r i s forming nozzle. The tube temperature i s held lybdenum penetrator body thickness was h e l d t o 5 m below 650 K t o prevent s t i c k i n g of h o t m e l t p a r t i - i n t h i s region t o minimize the temperature drop r e - cles. This has been accomplished by a combination s u l t i n g from heat conduction t o t h e molten rock l a y - of increased gas f l o w and improved coolant passage er. Approximately h a l f o f the t o t a l heater power i s design. Tests of t h i s penetrator system incorpo- developed i n t h e t h i n constant area section embedded r a t i n g a m e l t channel impedance, o r surge suppressor, i n the leading edge. Heater power i s s t e a d i l y r e - t h a t increased the pressure i n t h e molten l a y e r have duced away from the leading edge where t h e m e l t i n g been successful i n suppressing gas bubble production power requirements o f the penetrator are much less. i n t h e me1t and have produced remarkably improved This t a i l o r i n g o f the heater output i s based on de- smooth glass borehole l i n i n g s i n a d d i t i o n t o m i n i - t a i l e d coniputer c a l c u l a t i o n s which are discussed i n mizing any tendency o f t h e d e b r i s removal system t o the analysis section of t h i s report. Polycrystal- surge during t r a n s i e n t operations. Surging occurs 1ine-graphite r a d i a t i o n receptors are used t o i m - when a l a r g e m e l t pool i s formed and the penetrator prove t h e surface absorption c h a r a c t e r i s t i c s o f the i s suddenly pushed i n t o it. This causes a l a r g e heater c a v i t y which i s a l s o f i l l e d w i t h helium gas amount o f l i q u i d rock t o extrude r a p i d l y i n t o t h e t o provide a d d i t i o n a l conduction t r a n s f e r across the c a r r y - o f f system. While the gas system can c a r r y a narrow gap. Debris removal techniques i n t h i s pene- considerable amount o f rock i n excess of t h e steady- t r a t o r system are completely analogous t o those em- s t a t e design, a severe surge can overload it. Suc- ployed i n t h e extended surface penetrator. cessful operation o f t h i s debris removal system has With tin 89-nnn-diam m e l t i n g body, a HARE pene- been demonstrated i n both v e r t i c a l and h o r i z o n t a l t r a t o r was operated i n t h e l a b o r a t o r y a t power l e v e l s orientations. I n a d d i t i o n t o operations i n hard of up t o 24 k and corresponding penetration r a t e s W rock, t h i s penetrator system has been tested i n po- i n b a s a l t rock up t o 0.28 mn/s (3.31 f t / h ) w i t h de- rous Bandelier t u f f w i t h encouraging r e s u l t s . The bris-handling and glass-forming systems f u n c t i o n i n g extrudate was e j e c t e d i n s h o r t rods which were e a s i l y c u l a t e d and experimentally measur- expelled from t h e system by t h e t r a n s p o r t gas flow, power r e l a t i o n s h i p s a r e i n excel- and there was evidence t h a t t h e penetration mode n a d d i t i o n t o hard rock, HARE has (i.e. , extrusiontor d e n s i t y consolidation) could be n compacted Hanford c o n t r o l l e d by varying t h e gas flow r a t e t o the ex- density o f 2.1 Mg/m3) and produc t r u s i o n nozzle and t h e heater power l e v e l . w a l l approximately h i c k using a longer tem- 3. High Advance Rate Extruder (HARE), The HARE pera ture-c:ontroll e former. E a r l i e r broblems design has a more conventional m e l t i n g body capable of i n producing a smooth glass borehole l i n i n g were woducing t h i c k e r glass l i n i n g s i n dense rock, a s i n - l a r g e l y a t t r i b u t e d t o t h e gases released from t h eu e annular resistance heater t h a t d e l i v e r s a higher rock during melting. A modification consisting o f leading edge heat f l u x , and m e l t removal e n t i r e l y a long extrudate tube-nozzle system has been employ- through t h e c e n t r a l e x t r u s i o n p o r t . The basic con- ed t o a l l e v i a t e t h i s problem by c o n t r o l l i n g t h e back- 9
  • pressure a t the glass-forming section thereby i n - Debris creasing the pressure i n the melt layer and sup- pressing gas bubble production. Figure 11-7 shows Remya HARE penetrator a f t e r testing i n basalt. 4. Melt Flow Augmented Extruder. An attempthas been made t o arrange the geometry of a pene-trator in such a manner that h o t molten rock i sforced t o flow past the leading edge and therebyprevent this region from cooling a t higher penetra-tion rates. A conceptual design is shown i n Fig.11-8 to i l l u s t r a t e this technique. A melt reservoiri s formed on the outside of the conical section andmaintained under pressure by the applied thrustload. The pressure differential resulting from thedebris removal causes the melt to flow forward pastthe leading edge. The hottest (and least viscous)rock flows most easily and carries a significant L R o c k Flow -Iamount of energy forward to prevent cooling of the Fig. 11-8. Conceptual design of a melt flow aug-leading edge and vanishing of the melt layer thick- mented penetrator.ness. A new penetrator design that augments leadingedge conduction heat transfer w i t h forced melt flowhas been developed and i n i t i a l l y tested i n an 86-m-diam version. Heater configuration and debris re-moval system operation are based on the HARE designwhich has demonstrated successful performance i n ex-tensive laboratory testing. The penetrator assemblyfor this melt flow augmented extruder i s illustratedi n Fig. 11-9 prior t o testing. The melt flow pass-age i s on the axis so that material melted near theperimeter of the hole must flow along the cone andover the leading edge i n order to reach the exit Fig. 11-9. Melt flow augmented extruding penetrator w i t h segmented molybdenum glass former. passage. A segmented molybdenum glass former is em- ployed. Tests showed t h a t t h i s penetrator can ac- cept higher power levels a t higher thrust loads w i t hFig. 11-7. HARE extruder a f t e r several tests i n an increase i n penetration rate without an increase basalt showing the molybdenum me1 ting i n melting body temperature. In the initial testing, body w i t h residual rock melt and the rates as high as 0.232 mn/s (2.74 f t / h ) were attained. graphite glass fomer.10
  • The maximum v e l o c i t y o f the rock m e l t as i t crosses Data from a l a r g e number o f laboratory andU h e leading edge i s approximately 200 times the pen- f i e l d t e s t s have confirmed the operating performance etration r a t e velocity. Despite t h i s very appre- maps and r e p e a t a b i l i t y o f the newer extruding pene- c i a b l e v e l o c i t y enhancement, absolute v e l o c i t i e s are t r a t o r systems. Typical of these data i s the r a t e vs s t i l l q u i t e low,and higher t h r u s t s are required t o power r e l a t i o n implied by laboratory t e s t data f o r provide t h i s hydrodynamic pumping. Preliminary lab- the extended surface penetrator melting i n b a s a l t as oratory t e s t data i n d i c a t e t h a t s i g n i f i c a n t l y higher indicated i n Fig. 11-10. me1t v e l o c i t i e s are required before any appreciable 0 Extruding penetrators have been used success- penetration r a t e increase can be r e a l i z e d as a r e - f u l l y t o nielt samples o f basalt, granite, porous vol- s u l t o f m e l t f l o w augmentation. Further t e s t s t o canic t u f f , and compacted alluvium. Typical labora- b e t t e r define the r o l e o f higher v e l o c i t y rock m e l t t o r y samples o f b a s a l t t h a t have been penetrated i n f l o w i n the leading edge region are planned. hardware development experiments are i l l u s t r a t e d i n 5. S i g n i f i c a n t Achievements. Fig. 11-11, which shows the r e s u l t i n g smooth-lined A1 1 three new extruding penetrator systems holes. A material p a r t i c u l a r l y d i f f i c u l t t o d r i l l have achieved penetration rates i n excess o f 0.2 mm/s. through by conventional techniques i s high quartz- The HARE design was operated i n the laboratory a t pow content g r a n i t e gneiss. Samples o f such a gneiss e r inputs o f up t o 24 k w i t h correspondina advance W were supp1,ied t o the program from a quarry s i t e i n r a t e s i n b a s a l t rock up t o 0.28 mn/s (3.3 f t / h ) . V i r g i n i a f o r melting experiments. Figure 11-12 shows Maximum penetration r a t e s a t t a i n e d exceed those o f a hole me1 ted i n t h i s g r a n i t e gneiss by an extruding the e a r l i e r 66-nnn-diam design by a f a c t o r o f 3 t o 4. penetrator and some o f the associated debris ejected E f f o r t s t o develop advanced penetration sys- i n the form o f short glass rods. Differences between tems capable o f s i g n i f i c a n t l y higher advance rates t y p i c a l b a s a l t debris and the gneiss extrudate are have reached the laboratory experiment stage. Ex- a t t r i b u t e d t o the l a r g e d i f f e r e n c e i n v i s c o s i t y be- periments r e l a t i n g t o d i r e c t m e l t heating and plasma tween the two glass melts and t o the s i g n i f i c a n t v o l - arc heating are i n progress (see Sec. 11. F. and ume f r a c t i o n o f quartz c r y s t a l s i n the gneiss. 11. H). Preliminary design o f a l a r g e r diameter (150- Production o f a 30-m-deep f i e l d hole i n ba- mm) penetrator based upon the HARE c o n f i g u r a t i o n i s s a l t has been completed w i t h the 84-rn-diam extended i n progress. The i n i t i a l m e l t i n g bodies w i l l be made surface penetrator operated from the experimental 0.251 I I I I I I f i e l d u n i t (see Sec. I V . C. 3). As a proof-of-concept experiment f o r a geo- I thermal energy prototype b i t , an extruding penetrator system was used t o m e l t a hole i n a block of Dresser b a s a l t preheated t o 650 K. The r e s u l t s o f t h i s t e s t were compared t o another s e t o f t e s t s conducted a t the same operating conditions w i t h the exception o f the b a s a l t block temperature, which was a t a normal ambient value o f 290 K. The l a r g e specimen o f Dress- e r b a s a l t was surrounded with m u l t i p l e e l e c t r i c a l resistance heaters and brought t o temperature over a 4-112-day heating period. Experimental data con- firmed t h a t the a n a l y t i c a l l y estimated 25% increase i n penetration r a t e i n t h e hot b a s a l t could be eas- I I I 1 I I2 14 1 6 18 20 i l y achieved. Results from t h i s "hot rock" t e s t Power (kW) have established t h a t operatton i n very hot rock i su f e a s i b l e , and t h a t enhanced penetration r a t e i s an Fig. 11-10. Rate vs power r e l a t i o n s h i p f o r 84-mm- diam extended surface penetrator from additional benefit. laboratory t e s t s i n basalt. 11
  • b u t i t i s not expected t o be a practical material for production penetrators. Information from laboratory and f i e l d t e s t s of extruding penetrator systems is being used to provide the basis for designs of larger diameter pen- etrator systems for high-pressure, deep-drilling geothermal energy applications. 6. Penetration Rate Paradox. Analytical cal- culations based on penetrator i n p u t power, calculat- ed thermal fluxes, and available published transport properties of viscous rock melts have indicated the potential for appreciably higher penetration rates than could be attained i n laboratory tests. While the basic agreement between the analytical calcula- tions and the laboratory established penetrator per- formance data has been very good, two particular areas where this agreement breaks down have been noted. The f i r s t area of concern was that calculat- ed penetrator thrust loads were considerably lowerFig. 11-11. E x t r u d i n g penetrator melted holes i n than those observed i n actual tests. The second typical laboratory samples of basalt. area o f concern was the inability of penetrator sys- tems t o consistently achieve rates i n excess of 0.25 mm/s with allowable body temperatures despite the fact t h a t the analyses indicate higher rates should be possible with acceptable temperatures. Resolu- t i o n of these discrepancies led t o the investiga- tion of molten rock thermal conductivities presented in detail i n the analysis section of this report. The conclusion arrived a t was that the thermal con- ductivity of molten rocks i s appreciably lower than some data in the literature indicates. The source of the problem stems from correctly removing the thermal radiation contribution from the measured effective conductivity to arrive a t the true thermal conductivity based only upon molecular conduction. Using a value of 0.25 W/m-K for the thermal con- ductivity of molten basalt i n the computer simula- t i o n program ( t h i s value i s appreciably lower than the ones used i n previous calculations), i t becomesFig. 11-12. Hole melted in h i g h quartz-content evident t h a t the penetration rate of an extruding granite gneiss with extruding pene- penetrator i s limited by the heat flux that can be trator, including associated debris i n the form of short glass rods. provided a t the leading edge or flow stagnation point. Based on allowable temperatures in the molyb-from Sic-coated graphite which can be fabricated a t denum body, the new calculations indicate that thea fraction of the cost of a refractory metal body. leading edge heat f l u x will r e s t r i c t penetrationLaboratory tests indicate t h a t this material will rates in basalt to approximately 0.25 mmjs. T h i shave a long enough lifetime for testing purposes, lower value of thermal conductivity also results i n a thinner melt layer a t the leading edge for the12
  • i same heat f l u x . A t h i n n e r m e l t l a y e r necessitates C. Coring Penetrator Development higher t h r u s t loads f o r penetration, and hence t h i s For a p p l i c a t i o n s such as geophysical prospect-Bjalso explains why t h e c a l c u l a t i o n s w i t h a higher ing, i t i s desirable t o e x t r a c t a r e l a t i v e l y undis- thermal c o n d u c t i v i t y always underestimated the ap- turbed core sample t o i d e n t i f y the rock l a y e r s and . 4 - p l i e d t h r u s t load. Away from t h e leading edge, how- f a u l t structures a t various depths. The Subterrene ever, the c o n i c a l shape o f t h e me1t i n g body provides concept o f rock penetration by progressive m e l t i n g a s i g n i f i c a n t geometrical enhancement and much has been expanded t o include a technique f o r obtain- higher penetration r a t e s are possible. This concept i n g g e o l o g i c a l l y i n t e r e s t i n g core samples from t h e was demonstrated i n a l a b o r a t o r y t e s t using a coni- material being penetrated. The c o r i n g concept u t i - c a l shaped penetrator m e l t i n g i n t o a b a s a l t sample l i z e s an annular m e l t i n g penetrator which leaves a t h a t was p r e d r i l l e d t o remove the rock t h a t would rock-glass encased core i n t h e i n t e r i o r . Although normally be melted by t h e leading edge region o f t h e the concept i s a p p l i c a b l e t o e i t h e r the e x t r u s i o n penetrator. With the penetrator body temperature o r d e n s i t y consolidation mode o f melt-handling, i n i - below the operating maximum, sustained r a t e s o f j u s t t i a l emphasis was placed on a consolidating-coring under 1 mm/s were attained. This represents a fac- penetratar. A 114-m-diam consolidating corer i n - t o r o f 4 t o 5 times t h e r a t e t h a t would have been tended f o r use i n porous a l l u v i a l s o i l s has been de- expected i f the leading edge heat f l u x were c o n t r o l - signed, constructed, and laboratory tzsted. The core l i n g the r a t e . This conical penetrator and a sec- diameter i s 64 mn and t h e m e l t i n g body, which i s t i o n o f t h e g l a s s - l i n e d hole i n b a s a l t t h a t i t pro- vacuum-arc-cast molybdenum, i s f a b r i c a t e d as a s i n g l e duced are i l l u s t r a t e d i n Fig. 11-13. Experimental s t r u c t u r a l component. The penetrator has a water confirmation of t h i s a n a l y t i c a l l y predicted r e s u l t c o o l i n g system which represents a departure from t h e l e d t o an i n t e n s i v e research program t o introduce conventional gas systems. Design power l e v e l i s 13 techniques f o r increasing the a v a i l a b l e leading edge kW, and i n i t i a l t e s t i n g was accomplished a t 9 k i n W heat f l u x . t u f f and alluvium w i t h low t h r u s t loads and penetr- t i o n r a t e s i n t h e range fo 0.05 t o 0.15 mn/s. rm During an i n i t i a l t e s t t h e penetrator assembly was allowed t o cool i n place a f t e r making a pene- t r a t i o n i n t o a volcanic t u f f sample i n t h e labora- tory A f t e r breaking away the rock sample and glass hole l i n e r , t h e m e l t i n g assembly i s shown i n place i n F g. 11-14. The end o f the core sample i s v i s i - b l e eaving the core removal tube and a p o r t i o n o f the t r u c t u r a l - g l a s s h o l e 1i n i n g can be seen behind t h e m e l t l n g assembly. A t y p i c a l segment o f t h i s ex- t e r n a l glass l i n i n g and a glass-encased core sample can be seen i n more d e t a i l i n Fig. 11-15. The ap- proximately 18-mm-thick glass hole 1i n i n g r e s u l t s from debris disposal by t h e combined mechanisms o f core removal and density consol i d a t i o n . Although t h e periphery o f the core sample w i l l be melted and an a d d i t i o n a l region w i l l be thermally a l t e r e d , t h e i n t e r i o r region can be preserved when the penetrator i s operating a t the c o r r e c t design conditions. This i s i l l u s t r a t e d i n Fig. 11-16,which i s a cross section o f a Subterrene-produced core i n Green River shale. The dark melted peripheral r e - Fig. 11-13. Conical penetrator and h o l e melted a t gion can be c l e a r l y distinguished from the s o f t high r a t e i n p r e d r i l l e d b a s a l t sample. shale remaining i n the i n t e r i o r . This unique a b i l i t y 13
  • Fig. 11-16. Cross section o f a Subterrene-produced core i n Green River shale showing glass l i n i n g and s o f t i n t e r i o r region. and d i r e c t i o n s f o r s i g n i f i c a n t performance improve- ments have been indicated. During the research pe-Fig. 11-14. M e l t i n g assembly o f c o r i n g penetrator r i o d covered by t h i s report, technical e f f o r t s were a t completion o f t e s t showing forma- t i o n of glass hole l i n i n g and emerging r e d i r e c t e d a t t h e request o f t h e program-sponsoring core sample. organization and f u r t h e r development o f t h e c o r i n g concept has n o t been pursued. D. Thermal Stress Rock F r a c t u r i n g Tool F r a c t u r i n g by developing thermal gradients i n a rock mass by r a p i d heating o r c o o l i n g o f i t s surface i s a well-known technique t h a t has been employed i n p r i m i t i v e forms o f mining and tunneling since ancient times. The modern excavation i n d u s t r y does n o t t y p i - c a l l y employ thermal s t r e s s f r a c t u r i n g , b u t research being conducted a t t h e U n i v e r s i t y o f Missouri i n d i - cates t h a t t h e technique can be e f f e c t i v e l y u t i l i z e d i n tunneling o f hard rock. Their experiments i n v o l v e d r i l l i n g an a r r a y o f holes i n rock face t o a prede- termined depth and i n s e r t i n g h i g h - i n t e n s i t y heat sources a t t h e hole bottoms. The r e s u l t i n g thermal stresses produce cracks normal t o the rock face and a l s o p a r a l l e l t o t h e rock face i n a plane containing t h e heat sources. Thus t h e heading i s advanced byFig. 11-15. External glass l i n i n g and glass-encased breaking an incremental depth o f the rock i n t o f a i r l y core sample produced by Subterrene c o r i n g penetrator i n volcanic t u f f . r e g u l a r blocks which are subsequently removed by me- chanical means. Requirements f o r the commercial ap-t o "package" a core sample i n a r i g i d glass casing p l i c a t i o n of t h i s technique demand the a v a i l a b i l i t yleads t o t h e p o t e n t i a l f o r obtaining oriented geo- of rugged, reusable, economical heat sources. De-l o g i c a l l y i n t e r e s t i n g samples i n f a u l t e d o r brokenground masses. Detailed a n a l y t i c a l analyses of t h i s vices developed f o r rock m e l t i n g as a p a r t o f t h e Subterrene program have these desired c h a r a c t e r i s t i c s . Li n i t i a l c o r i n g penetrator design have been developed They are capable o f sustained operation a t high14
  • blA.AloR wSEALASSEMW COMPOSITE HEATER MOCYBDENUM BODY ELECTRODE Fig. 11-17. Cross section of thermal stress rock fracturing tool. temperature in contact with molten rock; they are rugged and reusable, and i n production could be man- ufactured economically. The development of a spe- cial tool for rock fracturing based on rock-melting technology was therefore undertaken. The rock fracturing tool, shown in Fig. 11-17, i s 48 mm diam and 2 m long. The molybdenum heater - body operates a t 1700 K and i s hermetically sealed with helium for protection of the electrically pow- ered graphite composite heating element which oper- - ates a t 2100 K. Peripheral equipment required for operation of the fracturing tool consists of a power supply (40 V , 250 A) and an a i r compressor for cool- Fig. 11-18. Thermal stress fragmentation of a gran- i t e block produced by electrically ing gas (35 SCFM). A,typical power level of 5 kW heated molybdenum fracturing tool. i s required to produce fracturing. Rock fracturing tools have been successfully a gas-cooled graphite glass-forming section directly operated i n basalt, granite, limestone, and sand- behind the me1 ting penetrator, smooth-walled 1inings stone w i t h 3 t o 5 major fractures per hole occurr- were formed i n a wide variety of soft ground and po- ing w i t h i n 475 to 725 s a f t e r reaching operating rous rock mediums which permitted extraction of the temperature. The rock fragments typically range in penetrator assembly w i t h relative ease. Graphite size from 25 t o 140 kg. Figure 11-18 shows the i n i - was selected as the forming material because i t mini- t i a l fractures in a granite block produced by a sin- mized the tendency for the cooling glass to stick or gle rock fracturing tool and the fragmentation of adhere to i t s surface d u r i n g the solidification pro- this block after fracturing from both predrilled cess. The thick glass liners necessitated by density holes. Spacing of the predrilled holes i n the rock consol Ida tion penetrators readily accommodated the face has typically been 0.3 m. I t i s necessary t o presence of even large volumes of unmelted quartz develop fractures t o one or more free, unrestrained crystals without seriously affecting the integrity of surfaces to f a c i l i t a t e breaking out the rock frag- the liner. When experiments were performed with high- ments and to provide a surface t o which cracks can e r thrust loads, the glass walls of the resulting propagate. holes were of much better visual quality than noted E. Glass-Forming Technology previous1.y. I t appears logical t h a t the higher Early experiments w i t h density consol idation thrust loads and associated higher pressures i n the penetrators melting in Bandelier tuff and alluvium rock melt minimize gas-bubble evolution which canw d e m o n s t r a t e d the basic features of forming the mol- cause voids in the glass walls. ten rock into a competent glass hole l i n i n g . Using The use of extruding penetrators in hard compe- tent rock presents a different s e t of conditions for 15
  • liner optimization. The melting penetrator i s now tube t o significantly increase the pressure drop ofcontinuously extruding molten debris for removal and the entering rock melt. Operating w i t h this flowtransport t o the surface,and the glass liner require- restriction, melt pressure levels a t the glass-form-ments for a stabilized hole i n competent rock are i n g section are increased sufficiently t o suppressvery minimal. Penetrator development effort has gas bubble production while simultaneously minimizingbeen directed toward improving the ability of the the effects of surging a t the debris-forming nozzle.system to control conditions i n the molten rock to Tests with an 84-nim-diam extruder incorporating a re-influence the character and properties of the bore stricted extrudate passage, or surge suppressor, thatlining and the extruded debris. After completing increased the pressure i n the melt have produced re-the 30-m-deep field hole i n basalt, photographs of markably improved smooth glass borehole linings asthe hole wall were taken t o determine i t s surface illustrated i n F i g . 11-19.characteristics. The photographs indicated that two The problem of graphite glass-former wear wasdistinctly different wall conditions were evident. addressed by designing more rugged, abrasion-resis-These conditons were characterized by either (1 1 a t a n t assemblies employing refractory metal segmentsrelatively smooth glass liner of fused basalt w i t h i n place of the all-graphite segments. An i n i t i a la thickness estimated t o be of the order of 1 mn or design used a molybdenum forming r i n g followed by a( 2 ) a surface largely stripped of fused material graphite release r i n g to minimize rock glass stick-leaving behind only slightly glazed virgin basalt. i n g d u r i n g the critical cooling temperature range.Wall surfaces alternate between these two types In the cold condition, the graphite diameter isthroughout the depth of the hole due t o changes i n smaller than the molybdenum so that the abrasionpenetrator glass-former design and operating charac- from the hole wall i s born by the metal parts. Int e r i s t i c s d u r i n g penetration. Both o f these condi- laboratory t e s t s the new glass former produced ations had previously been observed i n laboratory cleanly stripped hole in basalt; i.e., the glass i stests. wiped from the wall by the p i s t o n effect of the form- Initial experiments w i t h extruding penetrators i n g section and the aspiration effect of the extrud-employed a segmented graphite glass-forming section ate nozzle. The seal between the forming section andbased on consolidating penetrator experience. Whilecapable of producing dense glass linings in hardrock, the early systems possessed two major short-comings. The relatively soft graphite was easilyscored by irregularities i n the liner d u r i n g extrac-tion, leading to frequent replacement of the formingsections. This limitation was considered t o be par-ticularly important i n view of the present programdirection toward the development of deep hole sys-tems for geothermal energy production. The secondproblem area concerns the dynamics of the moltenrock layer when melting through basalts which con-tain both carbonate inclusions and bound water, re-sulting i n appreciable gas generation d u r i n g melting.Rapid gas evolution in the melt can result i n voidsi n the glass lining and also surges of molten rockbeing forced i n t o the debris removal nozzle of thepenetrator. Extreme surging can overload the debrisremoval system resulting i n blockage of the debriscarry-off tube w i t h chilled rock debris. Fig. 11-19. Horizontal hole i n basalt. Note smooth This l a t t e r problem area resulted i n an extrud- glass l i n i n g produced by the penetratoring system modification employing a longer extrudate with extrudate tube restrictions.16
  • t h e rock w a l l i s enhanced by an annular r i n g o f TABLE 11-1s o l i d i f i e d rock t h a t has been observed t o form i n COMPARISON OF ELECTRICAL R E S I S T I V I T I E S OF ROCK, ROCK MELTS, AND GLASSESt h i s region. This mode o f operation i s considered Specificd e s i r a b l e i n competent rock which requires no l i n i n g Temperature Resistivitybecause i t minimizes t h e power requirement arld r e - Rock Type (K) (n-cm)duces t h e p r o b a b i l i t y o f d i f f i c u l t y w i t h e x t r a c t i o n Granite Sol i d * 300 1o8and i n s e r t i o n . A glass s t r i p p i n g section c u r r e n t l y Mol ten 1800 6 t o 15being tested has e n t i r e l y eliminated t h e use o fgraphite r i n g s , employing o n l y molybdenum segments Basaltf o r greater abrasion resistance. Sol i d * 300 1o1O Mol ten 1800 2 to 4 1. Introduction. The e l e c t r i c a l r e s i s t i v i t y Sandstone Sol i d * 300 1o1Oo f most minerals decreases w i t h increasing tempera- Mol t e n 2300 1o2t u r e i n both t h e s o l i d and l i q u i d phases. I n thel i q u i d phase t h e r e s i s t i v i t y i s t y p i c a l l y i n t h e Glass 300 1o1O t o Molten Na20-33% Si02 2020 0.5range o f 1 t o 1 0 n - c m which i s comparable t o the r e -s i s t i v i t y of m a t e r i a l s c u r r e n t l y used f o r penetrator Molten Mg0-33% Si02 2020 5.0heaters. The e l e c t r i c a l r e s i s t i v i t i e s o f moltenrocks are many orders o f magnitude lower than those * Typical o f conditions.f o r the parent s o l i d s as i l l u s t r a t e d i n Table 11-1.These factors make i t possible t o consider using t h e penetrator i n the melt-heating mode, t h e powerd i r e c t e l e c t r i c a l resistance heating i n t h e l i q u i d supplied t o t h e unprotected pyrographite wafer heat-melt layer. Successful development o f a rock-melt- e r i s f i r s t brought t o a l e v e l s u f f i c i e n t t o s t a r ti n g penetrator system which could u t i l i z e t h i s heat- formatior1 o f a m e l t pool on the surface o f t h e rocki n g concept would have s i g n i f i c a n t advantages over specimen. A f t e r t h e molten pool has been formed thethe present penetrator designs. The c u r r e n t pene- heater power i s increased substantially,which r e s u l t st r a t o r designs w i l l u l t i m a t e l y be l i m i t e d by t h e i n h i g h pyrographite heater temperatures, r a p i d dete-conduction o f heat from the i n t e r n a l e l e c t r i c a l r i o r a t i o n o f t h e wafer, and increasing heater r e s i s -heaters, through the penetrator s t r u c t u r e and the tance. A the same time the resistance o f t h e elec- tm e l t l a y e r t o the melt-to-rock interface. The pos- t r i c a l path through the molten pool i s decreasing sos i b i l i t y o f arranging t h e e l e c t r i c c i r c u i t o f a rock- t h a t a t r a n s f e r o f power deposition fo the heater rmm e l t i n g penetrator so t h a t c u r r e n t passes through a wafer t o t h e rock m e l t occurs. Normal mode opera-molten r e g i o n and deposits most of t h e m e l t i n g power t i o n o f the demonstrator would p r o t e c t the pyro-d i r e c t l y i n t h e m e l t l a y e r j u s t adjacent t o the graphite wafer from o x i d a t i o n and i t would remain asm e l t i n g i n t e r f a c e has been recognized f o r a long the resistance heating element as t h e tungsten r o dtime. This mode o f rock m e l t i n g has been i n v e s t i - heated up and t h e u n i t acted as a rock punch; i.e.,gated i n recent p r e l i m i n a r y l a b o r a t o r y experiments. no m e l t inemoval passages are included,and t h e hot 2. Melt-Heating Experiments. I n i t i a l experi- m e l t f l o w back i n the small annulus between t h ements were conducted w i t h t h e "desk top" rack-melt- hole w a l l and the tungsten rod. This s t a r t - u p andi n g demonstrator equipped w i t h a s u b s t a n t i a l l y t r a n s i t i o n phase i s i l l u s t r a t e d i n Fig. I I - 2 0 ( a ) andl a r g e r capacity power supply. The penetrator assem- I I - 2 0 ( b ) f o r the melt-heating concept. The experi-b l y of t h i s device c o n s i s t s o f a p a i r o f tungsten ments revealed t h a t once the c u r r e n t path throughelectrodes (a 12-mm-diam r o d s1 i t a x i a l l y ) connected the m e l t was established as shown i n Fig. II-20(c),a t one end by a t h i n wafer o f p y r o l y t i c g r a p h i t e the power supplied t o the tungsten r o d could be i n -which serves as t h e heating element i n t h e normal creased ( s i g n i f i c a n t l y , r e s u l t i n g I n a g r e a t l y enhancedpenetration mode. The electrodes are separated a t penetration r a t e . I n several experiments the powerthe upper end by a t h i n i n s u l a t i n g l a y e r and clamped was increased t o > 5 k . W Five k i l o w a t t s o f m e l t i n gi n massive brass electrode heat sinks. To operate power i s s u f f i c i e n t t o m e l t a 12-m hole i n b a s a l t a t a 17
  • . #Electric r e s i s t i v i t y data of the type depicted i n Fig. 11-21 are being incorporated i n t o one- and two-dimensional c a l c u l a t i o n a l techniques t o determine the e l e c t r i c a l energy deposition p r o f i l e s i n rock melts subjected t o both conduction and r a d i a t i o n energy transfer. Laboratory experiments using 60-Hz currents o f 50 t o 150 amps have achieved very hot, y e t remarkably sta- b l e melt pools.No tendency t o arc was observed a t Wafer oxidation applied voltages below approximately 30 V . High- temperature experiments i n molten Jemez b a s a l t show- ed a stable ohmic behavior o f the m e l t pool w i t h no change i n r e s i s t i v i t y noted f o r variable c u r r e n t den- s i t y o r frequency i n the 50-to5000-Hz range. Labo- r a t o r y t e s t s are c u r r e n t l y being conducted w i t h an annular melt-heating penetrator consisting o f two concentric cy1 inder power conducting electrodes sep-, arated by a high-temperature i n s u l a t o r . After es-! t a b l i s h i n g a rock m e l t pool, power i s conducted from the outer c y l i n d r i c a l electrode t o the inner one through the rock melt i n a manner analogous t o t h a t shown i n Fig. 11-20 b u t now i n an a x i a l l y symmetric (C 1 t o r o i d a l geometry. This c o n f i g u r a t i o n permits a Fig. II-2@(a). I n i t i a l heating i n pyrographite melt removal path through the center of the i n n e r wafer, w i t h s t a r t o f surface melting. electrode and has the p o t e n t i a l t o be incorporated (b). E l e c t r i c a l current path and heating t r a n s f e r t o melt w i t h oxidation o f i n t o more conventional melting penetrator designs as pyrographite wafer. a technique f o r overcoming the l i m i t a t i o n s of the (c). Heating e n t i r e l y i n melt, increased power and r a p i d penetration rate. leading edge stagnation p o i n t heat t r a n s f e r rates. Me1t i n g augmentation of t h i s type could improve ad- r a t e of about 11 mn/s (130 f t / h ) ! The highest pene- vance rates severalfold,and preliminary experimentsi t r a t o r v e l o c i t y a c t u a l l y observed was o f the order of 1 m/s, b u t the simple laboratory setup allowed l a r g e losses by conduction and r a d i a t i o n from the electrodes and by the escape o f very h o t gases. u3 9 230.63 1470 103.33 1564 b.9 37 These i n i t i a l experiments never achieved thermal mh 2.6 44 101 71 16.n equil ibrium,and the penetrator was not designed t o 1W u1 .1 remove melt. The melt-heating mode has been demonstrated i n a series o f experiments w i t h basalt, granite, and tuff. Although i n p r i n c i p l e the melt-heating mech- anism o n l y requires a conducting l i q u i d phase, there i s reason t o believe t h a t the actual mechanism a l s o involves the p a r t i a l e l e c t r i c a l breakdown o f vapors evolved from t r a c e elements i n rock. The success o f these preliminary experiments has i n i t i a t e d f u r - t h e r experimental and a n a l y t i c a l research t o define 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 l / l (K"x ) the d e t a i l s o f the heating mechanisms involved and the influence o f the t y p i c a l m e l t r e s i s t i v i t y vs Fig. 11-21. Temperature dependence o f e l e c t r i c a l temperature behavior on the process. Molten rock r e s i s t i v i t y f o r mol ten Dresser basalt. 18
  • i n d i c a t e t h a t e l e c t r i c current d i s t r i b u t i o n s are volume w i t h granulated s a l t o f s i m i l a r o r i g i n . When encouragingly s t a b l e and uniform. ResearCh the heating element approached operating temperature t i e s and l a b o r a t o r y experiments i n t h i s i n t r i g u i n g a molten pool formed a t the bottom o f the hole. This concept c u r r e n t l y have a high p r i o r i t y i n the cur- molten pool was maintained while the melting assembly r e n t program. was continuously withdrawn from the hole, a d d i t i o n a l G. S a l t Borehole Plugging by Melting granulated s a l t being added t o the hole as required. The disposal o f r a d i o a c t i v e wastes i n under- Mechaniml a g i t a t i o n o f the molten s a l t was found t o ground s a l t deposits depends on t h e long-term physi- improve the q u a l i t y o f the r e s u l t i n g borehole plug. cal i n t e g r i t y o f the selected s a l t formations. Pre- A cross *jection o f a borehole plug formed by t h i s e x i s t i n g boreholes, those formed f o r s i t e evaluation, technique i n a block o f l i v e s t o c k s a l t i s i l l u s t r a t e d v a u l t construction, and instrumentation monitors, i n Fig. 11-22. must be sealed t o r e s t o r e t h e i n t e g r i t y o f the s a l t Q u a n t i t a t i v e measurements o f the physical pro- formations proposed f o r r a d i o a c t i v e waste storage. p e r t i e s o f s i x borehole plugs formed i n s a l t samples The plugs used t o seal these holes must n o t repre- o r i g i n a t i n g from a mine located near Lyons, KS, were sent a t h r e a t t o the i n t e g r i t y o f the s a l t formation performed and compared w i t h the properties o f the during the hazardous l i f e t i m e o f the wastes. A v i r g i n s i i l t block. The v i r g i n samples had an aver- study o f the f e a s i b i l i t y o f forming borehole plugs age density o f 2.1 Mg/m3, average permeability o f by melting and r e s o l i d i f y i n g s a l t s i m i l a r t o t h a t 0.5 darcys, and average crush strength o f 28 MPa. found i n the formation was i n i t i a t e d on the basis The s i x laboratory-produced plugs yielded values of t h a t a plug w i t h physical and chemical properties 1.6 Mg/m3, 0.4 darcys, and 12 MPa, respectively for close t o those o f the formation could be formed by density, permeability, and crush strength,with both t h i s technique. Since melting and r e s o l i d i f i c a t i o n v i r g i n and laboratory-produced samples showing con- o f rock s a l t causes p r a c t i c a l l y no change i n the siderable i n d i v i d u a l variations. Although the melt- chemical properties , emphasis was directed toward ed borehole plugs contained s i g n i f i c a n t porosity, the r e s u l t i n g physical properties o f the plugs pre- the permeability data i n d i c a t e t h i s p o r o s i t y i s un- pared i n t h i s manner. The properties considered t o connectet1,and p o t e n t i a l l y e f f e c t i v e plugging can be be most important i n h u d e the physical structure, achieved by t h i s method. The plugs appear t o be w e l l f l u i d permeability, crush strength, and material bonding a b i l i t y o f the fused s a l t plug. Experimen- t a l l y formed plugs were evaluated on these terms r e - l a t i v e t o the rock s a l t i n t o which they were formed. The resistance heating element used i n these preliminary experiments was a m e t a l l i c s t r i p made o f Haynes 25, selected f o r i t s corrosion resistance i n the molten s a l t environment. Power was supplied t o the heater through a water-cooled copper electrode, and the m e l t i n g assembly was mounted on a piece o f d r i l l stem a c t i v a t e d by a hydraulic c y l i n d e r i n the rock laboratory t e s t frame. D i r e c t e l e c t r i c a l cur- r e n t was passed through the heater s t r i p t o provide the energy necessary t o m e l t the rock salt, and dur- i n g the experiments the heater temperature was main- tained close t o the melting temperature of the s a l t (1077 K) because there was l i t t l e thermal resistance between the heater element and the m e l t pool. Each experiment was i n i t i a t e d by i n s e r t i n g the m e l t i n gt assembly i n t o a 77-mm-diam p r e d r i l l e d hole i n ad Fig. 11-22. Cross section o f a borehole plug formed i n a s a l t block by melting and r e s o l i d i - s a l t block sample and then f i l l i n g the residual hole f i c a t i o n o f granulated s a l t . 19
  • bonded t o the hole w a l l as depicted i n Fig. 11-23, rock face. Plasma c e n t e r l i n e temperatures i n excesswhich i s a magnified view o f a t y p i c a l plug - parent o f 20 000 K are a reasonable expectation as theserock s a l t bond. The reduced plug density can be values are r o u t i n e l y attained w i t h commercial equip-a t t r i b u t e d t o the l a r g e volume reduction during the ment. Plasma arc t h r u s t e r s have demonstrated con-l i q u i d - s o l i d phase t r a n s i t i o n and the l a r g e amount tinuous run durations o f a month using r a d i a t i o n -o f thermal shrinkage which occurs when the plug cooled anodes operating a t 1800 K. References i ncools t o room temperature. Available data i n d i c a t e the l i t e r a t u r e also mention operations a t pressurest h a t modest pressurization o f the m e l t and the cool- above 10 MPa (1500 p s i ) . While the observation hasi n g plug would be extremely b e n e f i c i a l . Pressurita- been noted t h a t a plasma t o r c h r e a d i l y melts a rockt i o n would tend t o heal o r prevent gross defects i n sample, apparently no one has faced up t o the formi-the plug and i n the bond between the plug and the dable task o f providing a debris removal system f o rsurrounding formation. such a penetration device. Although the equipment used t o prepare the The Subterrene program has provided e x c e l l e n tborehole plugs i n t h i s study was q u i t e rudimentary, experience i n handling molten rock debris. Overi t was useful i n providing base-line operating expe- 500 kg o f molten b a s a l t were f l u i d i z e d and transport-rience from which design improvements can be made. ed t o the surface by a cooling gas from a s i n g l e holeDesirable features i n a prototype f i e l d device would produced i n the f i e l d by an extruding Subterreneinclude provisions f o r m e l t pressurizing, a g i t a t i o n penetrator. The technology being investigated i s theo f the molten pool f o r b e t t e r d i s t r i b u t i o n of the combination o f plasma arc heating w i t h a molten de-melted rock s a l t , and a system t o c o n t r o l the r a t e b r i s removal system t o produce a plasma-assistedo f a d d i t i o n o f rock s a l t t o the heated region. Subterrene penetrator. I n i t i a l experiments were con-H. Plasma Arc Experiments ducted w i t h the simple plasma arc device shown i n A technical approach being investigated for Fig. 11-24. A tungsten anode and cathode are employ-Subterrene penetrators i s the a p p l i c a t i o n o f plasma ed w i t h a high-temperature i n s u l a t o r fabricated fo rmarc heating t o increase penetration r a t e and handle boron n i t r i d e . The arc discharge nozzle i n the cath-the highest melting-point rocks. Conduction designs ode i s v i s i b l e i n Fig. 11-24. This u n i t has beennow employed are l i m i t e d by the temperature of the operated a t power l e v e l s up t o 15 k using nitrogen Wr e f r a c t o r y metal through which energy i s transferred f o r the plasma gas. Maximum arc temperatures, e s t i -t o the rock. External a p p l i c a t i o n o f energy permits mated from an energy balance, were i n excess ofsome cooling o f the penetrator body and the poten- 20 000 K. B r i e f a p p l i c a t i o n o f the arc discharge t ot i a l f o r applying much higher temperatures t o the a b a s a l t sample produced the r e s u l t s shown i n Fig. 11-25. Conceptual designs have been prepared f o r an integrated u n i t which combines t h i s high-temperature arc source w i t h a molten debris removal system. Successful a p p l i c a t i o n o f plasma heating i n a Sub- terrene penetrator has the p o t e n t i a l f o r providing a s i g n i f i c a n t l y higher penetration r a t e device through even the most r e f r a c t o r y rocks. I. Rock Laboratory Test F a c i l i t y The rock laboratory t e s t f a c i l i t y has been moved from i t s previous l o c a t i o n t o a three-story 2 high bay area providing 150 m o f f l o o r space. The f a c i l i t y consists o f two t e s t frames, a c o n t r o l room, an assembly and work area, and an equipment pad out- side o f the b u i l d i n g . One o f the t e s t frames was acquired fo a previous laboratory project; the rmFig. 11-23. Microstructure o f bond between melted other was moved from the o l d location. The small L i plug and Lyons, KS, rock s a l t . frame has a stroke o f 1 i and a load capacity of n20
  • W Fig. 11-26. Rock laboratory t e s t f a c i l i t y showing c o n t r o l room and two h y d r a u l i c a l l y Fig. 11-24. I n i t i a l plasma arc heating device show- thrusted t e s t frames. i n g tungsten cathode and arc discharge nozzle. the l a b o r a t o r y t e s t f a c i l i t y w i t h an extruding pene- 40 kN, w i t h a h y d r a u l i c c y l i n d e r mounted v e r t i c a l l y t r a t o r i n place i n t h e 1-m t e s t frame. The l a r g e r and t h r u s t i n g downward. Penetrator assemblies are t e s t fraine i s shown on t h e r i g h t side o f Fig. 11-26 mounted on t h e h y d r a u l i c ram and are thrusted i n t o and was only p a r t i a l l y completed a t the time t h e the s t a t i o n a r y rock samples. The l a r g e r frame has photograph was taken. The c o n t r o l room i s v i s i b l e a h y d r a u l i c c y l i n d e r mounted i n t h e f l o o r , w i t h a on t h e balcony above t h e t e s t frames and t o t h e l e f t 1-m-diam specimen p l a t f o r m t h a t moves up from t h e o f t h e room i s t h e c o o l i n g gas and water c o n t r o l f l o o r w i t h a 24-11 stroke. Penetrator assemblies are panel. mounted on the top o f t h e t e s t frame; rock specimens Figure 11-27 shows the i n s i d e o f the c o n t r o l are clamped t o t h e p l a t f o r m and move up i n t o t h e room. I n the foreground i s the calculator-based s t a t i o n a r y penetrator assembly. Figure 11-26 shows data a c q u i s i t i o n system w i t h t h e hydraulic and power c o n t r o l rack v i s i b l e i n the f a r corner. During an experiment, closed loop servo-systems provide options f o r maintaining constant power, current, voltage, applied load, o r penetration r a t e . Data a c q u i s i t i o n i s independent o f these c o n t r o l a c t i v i t i e s , b u t pro- vides processed data both during the experiment and i n storage f o r f u t u r e use. Sensor inputs t o the sys- tem include voltages, currents, thermocouple outputs, pressure and f l o w transducer outputs, as w e l l as load, rate,and p o s i t i o n transducer outputs. These i n p u t s are transformed i n t o desired engineering u n i t s and . p r i n t e d and p l o t t e d i n r e a l time as w e l l as stored on cassette tapes f o r f u r t h e r processing a t a l a t e r time. Most o f the p o s t t e s t data processing, manipu- l a t i o n , and p l o t t i n g can be performed w i t h t h e c a l -W Fig. 11-25. B a s a l t r o c k sample a f t e r b r i e f exposure c u l a t o r system, using i t s high-level BASIC language and 7904 word memory. A series o f programs has been t o plasma arc discharge. 21
  • ! developed for rapid routine data handling and stored in the form o f cassette tapes which are easily loaded into the calculator memory. Fig. 11-27. Laboratory control room with calculator- based data acquisition system. 22
  • 111. POWER SOURCE DESIGN AND DIRECTED R S A C EE R HLJ A. Electric Power Sources 1. Introduction. Electrical power has been used t o provide the rock-melting energy for a l l of the prototype Subterrene penetrators. Previous work has indicated t h a t production systems would be most effective w i t h electrical heating, a t least i n the range of diameters being considered for geothermal well applications. The heating technologies that have been studied f a l l into two general categories, one consisting of internal heat generation w i t h heat conduction through the metal penetrator wall t o the rock-melting interface, and the other consisting of energy deposition outside the penetrator surface. The l a t t e r category includes ohmic heating of the molten rock, dielectric heating of the heated s o l i d rock, and radiant heat transfer from a plasma arc F i q . 111-1. Cross section of a consolidating pene- source. trator with stacked pyrographite radiant heater and graphite radiation receptor. 2. Heater Development for Penetrator Research. a. Introduction. While many different heat- e r types have been tried, graphitic radiation ele- thermal conductivity i s normal t o the penetrator ments i n helium-filled cavities were selected for a l l axis and i n the direction of principal heat transfer. the penetrators constructed since the early stages 0 ,4 hollow heater cavity to allow control of of the program. The successful use of pyrolytic the re1 a t i ve heat generation a1 ong the penetrator graphite as a radiant heating element and the low length. thermal resistance of a polycrystalline-graphite ra- 0 Utilization of the exceptional combination diation receptor were combined t o produce a very of high compressive strength and low thermal con- stable heater assembly. Heaters typically consist ductivit.y of pyrolytic graphite for the insulator of a stack of oriented pyrolytic-graphite disks or between the heated penetrator body and the cooled annular rings held i n a graphite-lined cavity by a af terbody . spring-loaded electrode as illustrated i n Fig. 111-1 - Tailored Heaters. A series of heaters i n b. for a density consolidation penetrator. The advan- the form of either solid cylinders consisting of tages of t h i s system are based on the unique charac- stacked (disks or pellets (for the extended surface t e r i s t i c s of graphitic materials and the wide range extruders and density consol idation penetrators) or of mechanical , electrical and thermal properties ob- hollow c.ylinders consisting of stacked annular rings tainable in commercially available products. (for the high advance rate extruder and melt flow Features of this design which contribute t o ef- augmented extruder) was designed, tested, and in- ficiency and durability can be summarized as follows: corporated in operational penetrator systems. In 0 A heater cavity containing only graphite in each case, the desired power generation along the the hi gh-temperature region. length o f the heater was nonuniform and was tailored 0 The use of a specialty graphite for the re- to meet the melting demands of the penetrator a t a ceptor whose thermal expansion characteristics match given axial location. The energy requirements along those of molybdenum and whose absorptivity for radia- the penetrator length were calculated using the t i o n energy is near unity. analytical methods described i n Sec. i l . C of this 0 A nonisotropic pyrolytic-graphite heater report. The validity of these calculations was con- stack oriented so that the h i g h electrical resistiv- firmed in numerous laboratory experiments and by i t y i s parallel to the penetrator axis, and the high tailoring the output of the heater, localized over- 23
  • heating o f the penetrator body can be avoided. A Power demand from an operating heater i s n o t r a d i a lsystem o f a l t e r n a t i n g segments o f p y r o l y t i c graphite but a x i a l i n the region o f the leading edge of t h eand p o l y c r y s t a l l i n e graphite was o r i g i n a t e d t o ap- Penetrator. An i d e a l heater would c o n s i s t of a veryproximate t h e required power d i s t r i b u t i o n . Poly- short disk o r annular r i n g functioning as a heatingc r y s t a l l i n e graphite has a r e l a t i v e l y low r e s i s t i v i t y element i n contact w i t h the leading edge o f the pene-and was used where e s s e n t i a l l y no power generation t r a t o r followed by an extended heater assembly w i t hwas needed. P y r o l y t i c graphite has a high r e s i s t i v - much lower power generation per u n i t length. Thisi t y across the g r a i n and was used i n areas r e q u i r i n g configuration was evaluated and used i n a 51-nun-diama high thermal f l u x . A s p e c i a l t y graphite made from density consolidation penetrator, and the HARE ex-h i g h l y oriented pyrolytic-graphite f l o u r was used truder and was capable o f producing s u b s t a n t i a l l ywhen an intermediate r e s i s t i v i t y was required. An higher heat fluxes through the penetrator leadingexample o f a t a i l o r e d heater f o r the HARE extruder i s edge. An exploded view o f t h i s heater system f o ri l l u s t r a t e d i n Fig. 111-2. the HARE extruder i s i l l u s t r a t e d i n Fig. 111-3. c. Annular Heaters. Heaters i n the form o f d. Hermetically Sealed Heater Assembly.thin-wal l e d hollow cy1 inders were p a r t i c u l a r l y e f f e c - P r a c t i c a l penetrator assemblies f o r f i e l d hole pro-t i v e i n t h a t both i n s i d e and outside surfaces could duction would b e n e f i t from a hermetic sealing o f theradiate, thus increasing the heat t r a n s f e r area per heater c a v i t y . The design, f a b r i c a t i o n , and f i e l d -u n i t heater length. Again, a l t e r n a t i n g r i n g s o f t e s t i n g o f an improved e l e c t r i c heater f o r consolida-p y r o l y t i c graphite and polycrystal l i n e graphite were tion-mode penetrators ( i n which the penetrator body,used. A stepped j o i n t between the two graphites withdrawal structure, heater elements, and graphiteproved adequate f o r e l e c t r i c a l c o n t i n u i t y provided electrode are a hermetically sealed u n i t ) was com-the e n t i r e heater assembly was maintained under pleted. This design provided a small sealed reser-spring-loaded compression, and t h a t the j o i n t was v o i r o f helium. Laboratory and f i e l d t e s t s o f themachined t o close to1 erances. The polycrystal 1ine- system showed t h a t t h i s technique was successful i ngraphite member had t o be f r e e t o expand r a d i a l l y maintaining a clean helium atmosphere i n the heateraway from the p y r o l y t i c graphite, w i t h i t s much lower c a v i t y throughout the expected l i f e t i m e o f the pene-thermal expansion i n t h a t d i r e c t i o n . The highest t r a t o r assembly. This penetrator system w i t h the sealed heater assembly i s shown i n Fig. 111-4 a f t e r t e s t i n g . Included i n t h i s development program was the f a b r i c a t i o n o f a special heater-processing appa- ratus f o r f i l l i n g the penetrator w i t h helium and t e s t i n g the hermetic seal a t operating temperatures. e. Power Supplies. Previous work i n d i c a t - ed the d e s i r a b i l i t y o f operating the r a d i a n t heater system w i t h d i r e c t current power and w i t h the heat- i n g element p o s i t i v e w i t h respect t o the coolerFig. 111-2. HARE extruder t a i l o r e d heater assembly. Fig. 111-3. Exploded view o f HARE extruder heater Dark sections are p y r o l y t i c graphite; assembly. Note t h i n leading p y r o l y t i c l i g h t e r sections are polycrystal1 i n e graphite heater r i n g f o r maximum energy graphite. generation near penetrator leading edge.24
  • . . .... . . . . ,.... I ? . heater was designed for evaluation i n the heateru t e s t f a c i l i t y consisting of a BN mandrel, a poly- crystall ine-graphite tubular heater, a BN insulator, and a M outer cylinder simulating a penetrator o body. Small amounts of B4C formed in a 1-h t e s t a t 2473 K i n an argon atmosphere. Heater regions that .. . .. . did not exceed 2325 K d i d not appear t o react. Ex- Fig. 111-4. Consolidating penetrator w i t h hermeti- tended operation a t temperatures below 2300 K would cally sealed heater assembly. appear t o be feasible. This combination would be considerably less expensive to fabricate than cavity walls. Power supplies were developed that oxide insulator-metal wire or ribbon heater assem- provided a very stable regulated output. For exper blies. A similar t e s t using Be0 insulators and a ments both i n the laboratory and i n the field, op- R heater composed of a spiral wrap of four 0.5- e eration i n a regulated constant power mode was used mm-diam wires was also successful. Figure 111-5 w i t h current and voltage l i m i t i n g t o protect both shows t h i s assembly a f t e r testing w i t h parts of the the supplies and penetrator hardware from circuit outer M tube and Be0 insulating sleeve broken away o failures. An additional benefit from the h i g h sta- t o reveiil construction details. This configuration b i l i t y of these supplies was the a b i l i t y to measure should provide adequate flux for a l l b u t leading accurately the resistance of the heater system. The edge applications, a t wire temperatures low enough relationship between heater resistance and tempera- t o insui-e a long service l i f e . ture then permitted an estimation of average heater c. M1 t Heating. Power generation directly e temperature during operation. Overall heater volt- i n the melt film a t the leading surface of a pene- ages as h i g h as 100 V were employed successfully in trator can create higher film temperatures than i n the consolidator penetrator assemblies. the metiil wall, t h u s enhancing the penetration rate. 3. Alternatives t o Graphite Resistance Heating. The electrical resistivity of most minerals decreases a. Introduction. While the graphite radia- w i t h increasing temperature i n both the solid and tion heater configurations were adequate for the pro- l i q u i d phases. In the liquid phase the resistivity totype penetrators, future requirements necessitate i s typically in the range of 0.01 t o 0.1 n-m, which the investigation of different heat sources. Opera- i s comparable t o the resistivity of materials cur- tion a t the h i g h lithostatic pressures encountered rently used for penetrator heaters. In addition, a t depths o f 5 t o 10 km i n geothermal well production the electrical r e s i s t i v i t i e s o f molten rocks and preclude the internal penetrator cavities of radia- soils are many orders o f magnitude lower than those tion heater designs on the basis of required collapse for the parent solids. I n i t i a l experiments were strength. High-strength penetrator bodies devoid of designed t o demonstrate this principle i n a simple extended internal cavities must therefore be develop- ed. Penetration rates of penetrators relying only on heat conduction through a stagnant rock-melt film are a function of penetrator surface temperature. A practical limit seems t o be between 0.2 and 0.3 m ." ms a t reasonable metal wall temperatures. Research d i - rected a t higher penetration velocities must there- fore address the technical problems associated w i t h providing high-energy deposition rates i n the sol i d and molten rock ahead of the penetrator leading edge. b. Solid Heaters. The chemical systems C-BN-Mo and Re-BeO-Mo appeared t o possess the neces-k*! sary s t a b i l i t y t o be used for solid conduction heat- Fig. III-5. BeO-Re heater t e s t assembly broken open e r systems devoid of extended internal cavities. A after t e s t t o reveal internal details. 25
  • geometry,and l a t e r experiments concentrated on ex- basalt. A small amp1 itude perterbation analysisploring the power generation and electrical s t a b i l i t y (details in Sec. V. C of t h i s report) showed the pos-i n t h i n molten basalt films. Electrical resistivi- sible buildup of electrical instabilities i n a meltties of representative molten rock types were also heating penetrator geometry i n which the leadingdetermined under conditions approximating the freshly edge contained an annular electrical insulator be-melted rock to be expected a t the leading edge of an tween concentric electrodes. While the most directoperating penetrator. Significant technical achieve- way of determining the existence of these instabili-ments i n t h i s area include: ties would have been to construct and t e s t a series 0 Demonstration of h i g h penetration rates w i t h of prototype penetrators , time and funding restric-a simple two-electrode system. Operation of this tions led t o another approach. Figure 111-7 showsdevice i s described i n detail i n Sec. 11. F of this the l a s t i n a series of furnace experiments wherereport,and the desk-top demonstration u n i t and power preheated molten basalt was forced t o flow undersupply used i n the i n i t i a l melt heating experiments pressure i n confined passages. The object of thesei s shown i n Fig. 111-6. experiments was t o detect electrical current i n - 0 Demonstration of ohmic melt heating i n a s t a b i l i t i e s and temperature instabilities under con-penetrator configuration. Hardware from the 58-m- d i t i o n s simulating those a t the leading edge of adiam extruder experiments was modified t o produce me1 t heating penetrator. The arrangement i n Fig.a penetrator w i t h an annular melt flow passage. Al- 111-7 provided for a melt film thickness of 1 mm andternating current was passed through this gap and melt flow rates i n the range of 1 g-s-l, a t tempera-produced sufficient power t o penetrate a basalt sam- tures u p t o 2000 K , simulating penetrator conditions,ple. T o separate operational modes were identified. w b u t did not provide comparable heat sources and sinksInitially, current flows of u p to 10 A a t impressed or allow the formation of variable path cross sections.voltages of about 50 V could be sustained. The The results of these experiments were the productionglass melt layer apparently was behaving as an ohmic of stable currents u p to 3.8 A a t sustaining volt-heater i n the vitreous state. Increasing the voltage ages of 220 V a t 60 H through passage lengths of zbeyond this point caused a spontaneous reverting to 20 mm. No serious electrical or thermal instabili-another stable condition w i t h currents u p t o 200 A ties were detected.a t sustaining voltages of about 18 V. This condi- 0 Determination of electrical resistivity oftion was apparently one of controlled submerged freshly melted basalt and granite. Resistivity dataarcing. T h i s u n i t produced about 75-mn total pene- reported i n the 1 i terature for rock me1 t s generallytration depth i n basalt rock. appear to be obtained on material i n equilibrium 0 Direct electrical heating of t h i n molten ba- w i t h atmospheric oxygen. Since the molten films a l t films. A series of experiments was conducted A2%t o evaluate the behavior of t h i n films of flowing Ta MOLTEN BASALT THERMOCOUPLES (4) GRAPHITE FELT GRAPHITE CRUCIBLE BN MoF i g . 111-6. Desk-top demonstration u n i t used i n Fig. 111-7. Furnace experiment for direct electri- cid i n i t i a l melt heating experiments. cal heating of t h i n molten basalt films26
  • a t the leading edge o f a penetrator i s i n a confined determined as functions o f frequency and temperature.f r e s h l y melted condition, r e s i t i v i t i e s coyld be sub- These r e s u l t s , i l l u s t r a t e d i n Fig. 111-8, were com-s t a n t i a l l y d i f f e r e n t . The resistance of f r e s h l y bined w i t h the d i r e c t current r e s i s t i v i t y data t o es-me1ted b a s a l t and g r a n i t e were determined by me1t i n g timate the conditions needed f o r proper operation.under an atmosphere o f argon i n a molybdenum-lined I t appeared t h a t the frequency would need t o be abovecrucible. Uata f o r Jemez b a s a l t were s i m i l a r t o 1 MHt and t h a t the melt f i l m thickness would have t othose obtained by Corning Glass Company on a sample be very small f o r t h i s configuration t o produce hight h a t had been held a t 1760 K f o r 4 h, except t h a t t h e advance rates. One other aspect o f t h i s geometrypresent r e s u l t s showed a l e s s steep temperature de- has t o do w i t h the nature o f the melting interface.pendence and could be represented by a l i n e a r r e - Studies were made i n which an advancing melting rockl a t i o n between the l o g o f r e s i s t i v i t y and 1/T, while i n t e r f a c e was "quenched" and examined microscopically.the Corning data showed a d e f i n i t e nonlinear char- A region o f p a r t i a l l y melted c r y s t a l s i n a moltenacteristic. m a t r i x was present between the s o l i d rock and advanc- d. D i e l e c t r i c Heating. The r e s i s t i v i t y o f i n g molt.en pool. The e f f e c t o f the v e l o c i t y o f meltrock generally decreases w i t h temperature and also flowing past such an interface, and the e l e c t r i c a lw i t h increasing frequency o f the applied voltage. paths w i t h i n such a region, have n o t been adequatelyOne way t o o b t a i n higher advance r a t e s i s t o deposit eval i n the s o l i d rock ahead o f the penetrator. e. Plasma Arc. U t i l i z a t i o n o f plasma arcSuccess o f t h i s approach depends on the absolute technology f a r rock-melting penetrators requires avalue as well as the temperature dependence o f the stable arc source and adequate coupling t o the rock-rock r e s i s t i v i t y a t temperatures w i t h i n a few hun- melting i n t e r f a c e . Several design studies exploreddred degrees o f the lowest m e l t i n g p o i n t c o n s t i t u e n t ways i n which the melted rock could be removed fromo f the rock. The low thermal c o n d u c t i v i t y of rock the m e l t i n g i n t e r f a c e , thus maintaining high ratesr e s u l t s i n a very steep temperature gradient i n o f heat t r a n s f e r through the molten f i l m . A testf r o n t o f the advancing penetrator and a correspond- f i x t u r e using a tungsten radiation-cooled anode andi n g l y low cross sectional area o f heat-affected ma- cathode s t r u c t u r e and BN e l e c t r i c a l i n s u l a t o r s wasterial. An i d e a l combination o f s o l i d rock d i e l e c -t r i c properties ( a l t e r n a t i n g current r e s i s t i v elosses) and molten rock r e s i s t i v i t i e s would enablethe successful operation o f a simple penetrator con-f i g u r a t i o n . One such c o n f i g u r a t i o n might consist o f 6a9C ----Ian i n t e r n a l l y conduction-heated extended conical sur-face as used i n the consolidation penetrators. Theleading edge, however, would consist o f a c e n t r a l E -debris-removal passage j o i n e d t o the conical sur-face through an e l e c t r i c a l l y nonconducting r i n g .A l t e r n a t i n g voltage impressed between the conicalsurface and debris passage would cause a c u r r e n t t oflow through the melt f i l m between the rock and ad-vancing penetrator. As the frequency o f the impress-ed voltage i s increased, more c u r r e n t would f l o w i nthe rock ahead o f the f i l m u n t i l the desired balanceo f power deposition was achieved. A continuing sup-p l y o f f r e s h l y melted rock would f l o w i n t o t h i s re- 1gion from the conical surface, and a constant stream 1 10 ld ld 1 8 1 6 14 FREQUENCY (HZ1of melt would f l o w away fo the region o u t the de- rmbris-removal passage. Fig. 111-8. A l t e r n a t i n g current r e s i s t i v i t y o f D i e l e c t r i c properties o f l o c a l Jemez basalt were Jemez basal t .
  • tested in the laboratory. The desirability of higher the understanding that dynamic t e s t systems. would power operation led to construction of a water-cooled evolve as the program progressed. Both Mo and W and copper anode assembly. The f i r s t - u n i t accepted the alloy Mo-30W were studied i n various rock media powers up t o 18.5 k (66 V and 281 A) using a flow W including: tuff, basalt, andesite, granodiorite, of 9 x kg-s-’ nitrogen gas and a calculated amphibolite,and granite. In addition, the corro- plasma temperature of over 10 000 K. Another oper- sion effects within a series of basalts, e.g., Jemez, ating mode was explored i n which the arc was trans- Dresser, Hawaiian tholeiitic, and East Pacific Sub- ferred from the integral anode structure to an ex- oceanic Ridge, were determined. In this manner, the ternal water-cooled plate. I t i s possible that a degree of corrosion was correlated against a wide rock-melting penetrator could be designed in which range of rock chemical compositions. Significant the molten rock pool ahead of the penetrator would be technical results obtained from the laboratory a good enough electrical conductor t o permit i t to studies included the following: function as the external electrode. Some data are e Molybdenum and possibly some of i t s alloys available that indicate t h a t a plasma arc may be made have corrosion resistance superior t o t h a t of W i n to operate a t pressures encountered i n geothermal a l l tested rock types. The measurements of M and o hole completion tasks. W solubility show t h a t M i s less soluble, on the o average, by factors ranging from 4 to 20. B. Materials Science and Technology c A significant correlation was obtained a t 1. Introduction. A major and continuous effort constant temperature, time,and similar viscosity be- has been expended on the materials science aspects of tween metal solubility and the ferric-ferrous ratio, t h e Subterrene program. The very h i g h temperatures Fe+3/Fe+2, of the various basaltic compositions. originating within the penetrator and ultimately Corrosion was found t o vary with the basalt type, transmitted to the ambient rock environment have re- i.e., increasing with an increase i n Fe /Fe . +3 +2 quired the use of refractory materials for penetrator Thus, h i g h Fe+3 content basalts such as Dresser will construction. In t u r n , a wide spectrum of corrosion be more corrosive. studies has been generated including: ( a ) external a The more siliceous rock melts exhibited low- refractory alloy - molten s i l i c a t e (rock) interac- e r degrees of corrosion. T h i s i s due, i n p a r t , to tions; ( b ) internal power source material interac- the higher viscosity and lower metal diffusion rates. tions; and (c) miscellaneous corrosion effects on e Corrosion proceeds via a t least three general pipe stems and support systems. I n addition, quali- mechanisms as observed experimentally. These include tative compatibility and screening tests were per- oxidation and solution, alloying, and gas bubble ox- formed as p a r t of a general search for materials idation. The details of these corrosion mechanisms w i t h improved corrosion profiles i n various geo- have never been determined completely. Gross varia- chemical media. The rock-glass liners producedduring b i l i t y in chemical composition, viscosity, density, the melting operations were subjected to an intensive and flow rate differences w i t h their effects upon program of physical and mechanical strength measure- diffusion rates, solution thermodynamics, and vari- ments. Fabrication technologies for the refractory able rock oxygen potentials makes such determinations metals molybdenum (Mo) and tungsten (W) were investi- formidable tasks. The gross difference i n corrosion gated, resul t i n g in significant improvements. Advan- between M and W can be explained in part thermody- o ces in the preparation and use of new high-tempera- namically and kinetically on the basis that W has the ture brazes were also accomplished. As might be potential for faster reaction rates, for example, i n anticipated, the basic knowledge of the geosciences high-temperature steam and other oxidizing media. was used extensively throughout the program. a Based on geometric considerations and the 2. Refractory Alloy - Rock Melt Interactions. s t a t i c t e s t data, a model for the surface recession Corrosion studies were performed i n the laboratory Ii rate o f the outer surface of a cylindrical penetra- and when possible, during and after field tests. tor was derived. Combined w i t h engineering design Most laboratory investigations were done in s t a t i c data, i t was thus possible t o make estimates of t e s t systems i n order to derive base-line data w i t h penetrator lifetime based on chemical action alone. 28
  • Mechanical erosion effects were n o t considered al- chemical corrosion wear rates for molybdenum as com- though these add to the surface wear, particularly pared to tungsten. Exceptionally long lifetimes canW a t the penetrator t i p . The surface recession rate, be expected from molybdenum penetrators operating i n Art, i s given as either Bandelier tuff or granitic rocks. A a prac- s tical example, consider a cumulative surface reces- sion of 0.1 mm observed for a molybdenum penetrator i n Jemez basalt operating under the assumed para- meters o f Fig. 111-9. This value i s indicative of an where Dp = penetrator diameter, mm operating time of 2.8 x 103 ks (778 h ) . Typical Q , V = penetration velocity, mm/s penetrator designs would permit considerably larger f = 6/Dp surface recessions before a failure occurs, and hence the potential for long operating lifetimes under 6 = thickness of dissolved metal boun- these conditions i s excellent. dary layer i n the glass lining, mn 0 r l number of qualitative compatibility tests were made to identify useful penetrator materials H = penetrator length, mm other than M and W. Materials considered worthy of o P further Study included: M alloys containing rhenium o d = density of glass (d ) or penetrator (d ) (Re) , rhenium (pure Re provided reasonable fabrica- P tion techniques) , certain high-me1 ting-temperature a = solubility by weight of metal i n noble metal alloys containing rhodium and iridium P glass. for highly oxidizing environments such as exist i n Assigning certain engineering parameters and average carbonatle sedimentary rocks, and certain ceramics such as IHfC and ZrB2. Although these ceramics a l l 1900-K solubility values, the curves shown i n Fig. react t o some degree, they s t i l l may be useful pro- 111-9 were constructed. The value of 6 , 0.1 mm, was vided thle reaction follows parabolic-type kinetics. representative of observations i n the s t a t i c experi- Molybdenum disilicide, MoSi2, was found partially ments. Modifications could be made t o the model satisfactory, particularly a t temperatures below as additional data from dynamic t e s t s become avail- 1700 K. Both silicon carbide, Sic, and Sic- able. These lifetime estimates indicate lower conversion coated graphite resist attack (in basalt) t o some degree, generally below 1800 K. Quantitative corrosion data for the materials mentioned above were 1 Chemicol corrosion weor estimates for - - penetrator body metols-assumptions: not obtained with the exception o f some very limited - 8=0.1mm V.0.l m m h data for Re. The solubility of Re was a factor of 5 t o 10 less than that of Mo,which was encouraging. I t may also be possible to use the ductile alloy Mo-34 at.% ?e (E.10-50 w t % Re). l In view of the deep geothermal drilling ap- plication, i t was deemed prudent t o t e s t the penetra- t o r materials M and W i n types of basement rock o likely t o be encountered. Granodiorite and amphibo- l i t e samples, obtained from the LASL Geothermal Energy Project a t a depth of approximately 750 m, were used for these tests. Solubility of the metals i n this particular grade of granodiorite was similar Drilling Time (ks) t o t h a t i n surface tuff and granites. Amphibolite, however, proved t o have corrosion potential equalbj Fig. 111-9. Estimated lifetimes of M and W pene- o t o or worse than surface basalts. trators i n basalt and granitic rocks. 29
  • To a s s i s t i n the clarification of details of the i s 2(FeO)silicate melt + M = 2(Felalloy o +corrosion mechanisms , a subcontract was awarded toProfessor A. Muan of Pennsylvania State University. (Mo02)s1i ca te me1 t iThe objective of the work was to determine the de- for which the equilibrium constant may be writtengree of importance of the various corrosion mecha- aMo02 . aFenisms. The studies feature control of oxygen poten- K = 3t i a l (Po ) and the thermodynamic solution relation- aFeO 2ships i n the Mo-Fe and W-Fe systems. T h i s work wasspecifically directed a t the activity-composition where as an approximation aMo has been set equal t orelations i n Mo-Fe and WF alloys, and the charac- -e unity. (Identical equations may be written for thet e r i s t i c s of the oxide chemistry of tetravalent W-Fe-0 system.) Clearly, the strong positive devia-molybdenum, including the stability relations o f ticnfrom ideality i n the alloy system would meanphases formed between Moo2 and important rock-forming that the iron concentration i n the alloy phase i noxide components. equilibrium w i t h an iron-oxide-containing liquid Activity-composition relations i n Mo-Fe and W-Fe would be very small unless the iron and iron oxidealloys were determined i n the temperature range 1370- activities are very h i g h . I t is concluded that se-1770 K by equilibrating alloys w i t h i n this system vere corrosion of M (or w) penetrators should not ow i t h Fe-Cu alloys of known activity-composition rela- take place as a result of reactions between thetions. The method is based on the assumption that refractory metal and FO of the rock a t oxygen po- ethe solubility of Cu i n Mo-Fe alloys of low Fe con- tentials determined by the equilibrium expressed i ntents, and the solubility of M i n Cu-Fe alloys, are o the above equations. However, i t is likely thatsmall enough to have an insignificant effect on the these relations may be changed drastically i f theactivity-composition relations of the main constitu- penetrators are operated i n an atmosphere of higherents of the two alloys concerned. The compositions oxygen potentials, such as t o promote the formationof the alloys, following equilibration, were deter- of Mo- or W-oxides of higher valence status (Moo3 ormined by electron microprobe analysis. Both alloys, NO3).Mo-Fe and W-Fe, were found t o display large positive In addition to laboratory data, corrosion datadeviations from ideality. In the reaction between were also obtained from f i e l d t e s t operations suchM - or W-metal and iron oxide of various rock melts, o as the 30-m hole in Jemez basalt using 84-mm fluteda suspected mechanism of corrosion of the metal extrusion penetrators fabricated from M and Mo-30 W. oprobe i s the reduction of some of the iron oxide t o The observed corrosion i n that operation, as ex-form iron which i n t u r n may form a dilute alloy of pressed by surface recession rates and compared withiron i n the M or W. Hence, for an evaluation of the o the laboratory predictive model , was estimated t o beproblem of corrosion of Subterrene probes, the M - o greater by a factor of 15-20. A detailed analysisrich and W-rich regions of the Mo-Fe or W-Fe alloys revealed the following: e An oxidizing environment beyond that ex-are of primary interest. In order to make i n t e l l i -gent inferences regarding the behavior o f Moo2 d i s - pected i n normal Jemez basalt existed during majorsolved i n s i l i c a t e melts, and hence regarding the portions of the basalt operation. T h i s was attribu-interactions between M penetrators and s i l i c a t e o ted t o excess water and possibly some hydrated orphases,it i s necessary t o expand knowledge of the carbonated minerals. The predictive model had beencrystal -chemical and thermodynamic behavior of M4+ o generated from data obtained from "dry" basalt.i n oxide and s i l i c a t e phases. e Significant gas phase corrosion was In the application of no- o r W-probes as hot observed. 0 The complex geometry of the fluted penetra-penetrators i n basal t i c rocks, the main oxidation-reduction reaction likely to take place and have a tor would result i n a spectrum of surface velocitiesclose bearing on the rate of corrosion of the probe during the downward penetration. Forced convection I of a fluid is known t o increase corrosion rates on refractory materials.30
  • +3 +2 P Determination of a gross change in Fe /Fe after penetration corroborated laboratory work andLJ lent credence t o corrosion mechanisms involving the iron components of the basaltic melts. a Alloying was also identified as a corrosion mechanism, again corroborating 1aboratory experiments. Qualitative visual and metallurgical observa- tions were made on several field-tested 50-mn con- sol idation penetrators used i n tuff and alluvial soils. These penetrators were fabricated from Mo and, i n one case, thoriated W. Both solution and gas phase modes of corrosion were observed. Grain growth stabilization was observed both for the thoriated W unit as well as areas of the Mo units where carbon diffusion (from the internal heater) had occurred. Intergranular cracking, internal cavity Fig. 111-10. Tantalum carbide coated graphite re- ceptor used i n penetrator radiant blisters, and voids were also observed i n varying heater system. degrees of severity. 3. Power Source Materials. The radiant heater QJ 2300 aiid 2450 K; M body temperature of QJ 1800 K; o design w i t h an internal inert gas-filled cavity has i n p u t pouJer, 4-4.6 KW; heat f l u x a t the heater sur- been used successfully i n a l l penetrator development face of 1.2-1.4 MW/m2; and several thermal cycles models. Only for the advanced application of deep down to 300 K. The t e s t units appeared operableafter geothermal drilling and the associated high litho- shutdown. Analysis has demonstrated t h a t a coating s t a t i c pressures has i t been necessary t o consider as thin (3s 0.03 mm reduced the carbiding reaction by other designs, e.g., solid conduction heaters. a t least an order of magnitude. A number of small The basic chemical reactions for the r a d i a n t thermal stress cracks and some coating separation heater system concern those i n the Mo- or W-carbon were obslerved. systems. These have been studied extensively b o t h The very h i g h lithostatic pressures associated from thermodynamic and kinetic viewpoints. Their w i t h depth preclude the use of the radiant heater de- characteristics are reasonably well known and the s i g n for deep d r i l l i n g . Solid contact o r conduction lifetime of some of the internal components can now heaters (appear as a suitable alternative. Several be estimated. For example, using available Mo-C and high-strength systems were investigated thermodyna- W-C reaction rate data, the cylindrical receptor mical ly and experimentally. An early conceptual de- thickness required for a 1000-h (3.6-Ms) lifetime sign using M and boron nitride (BN) i s shown i n Fig. o was calculated a t selected internal operating temp- 111-11. A cylindrically symmetric M electrode is o eratures. Eventually, the metal carbiding that slgw- embedded in pyrolytic BN,which i s encased i n the Mo ly progresses provides a means for receptor failure. body. A t 300 K, BN is an electrical insulator with To reduce the scope of the carbiding reaction, a a resistivity of % 10l6 However, by QJ 1900 K, diffusion barrier was introduced and successfully the resistivity has dropped to QJ 105 R-cm across the tested. Preliminary calculations and testing in the grain ( Y direction) and to QJ 5 x 103 w i t h the materials laboratory identified stoichiometric tanta- g r a i n ("a" direction). However the Mo-BN system was l u m carbide, TaClS0, as an excellent barrier against shown t o be thermodynamically unstable (except per- carbon diffusion. Graphite receptors of the size haps under very high nitrogen gas pressure) a t oper- used in 50-m consolidation penetrators were coated ating temperatures of QJ 2300 K. with TaC (QJ 0.03 m thickness) by means of a chemical The use of systems such as Mo-ZrN or WHN was -f vapor deposition process (see Fig. 111-10) and sub- investigated, b u t again the decomposition probabi 1i tyb, jected t o two lifetime tests of duration 200 h (720 was h i g h . Further, the nitrides become excellent ks) and 278 h (QJ1 Ms), respectively. t e s t Par- electrical conductors a t high temperatures. Consid- ameters included: internal heater temperatures of eration (of other solid-state resistive heating 31
  • i 4. Structural Glass Liner Results. Density consolidation Subterrenes are used to form glass- lined stabilized bores in porous o r unconsolidated formation without any debris removal. A the hole s i s being melted, the rock melt i s consolidated into a glass lining forming a strong, relatively imper- meable boundary. To provide quantitative data on these formed-in-place rock glass linings, a contract was initiated w i t h Terra Tek t o characterize the lining formed in Bandelier tuff and compare its pro- perties to those of the parent material. W i t h know- ledge of the material properties, the engineering potential can be better evaluated. Sihce the forma- tion of rock-glass linings by a Subterrene penetra- tor i s a relatively new process, l i t t l e i s known of the properties of the solidified melt material form- I ing the lining. Fig. 111-11. Conceptual design of a contact heater To better characterize the lining material, melting body utilizing a pyrolytic boron nitride heating element. Terra Tek performed physical and mechanical tests i n a l l three principal directions whenever possible. systems suggested the use of stable oxides for the Figure 111-12 shows the orientation of t e s t samples electrical insulator part of the system. The severe with respect t o the original liner as supplied by thermal and electrical requirements eliminate the LASL. Bandelier tuff samples containing the glass majority of the known binary oxides and a consider- linings used in this study were supplied by LASL i n able number of ternary oxides as well. O those re- f the form o f hollow cylinders. The inner diameters maining, beryllia, (BeO), and thoria, ( T h o 2 ) , were were either 51 mn with a lining of the order of 20 mm considered the best. Magnesia, (MgO), might be used thick or 76 mm w i t h a 25mm lining, typically being provided i t s volatility can be reduced substantially 500 nm~ long. The lining material was observed to be and compatibility w i t h M and W established. Alumi- o generally competent except for the presence of radial na, (A1203), would also be useful provided operating fractures. Tuff samples n o t containing the fused temperatures are lowered. lining were also supplied for tests on the parent The compatibility of Be0 w i t h the metals Mo, W , tuff. Re,and graphite was investigated. Both BeO-Re and BeO-C appear t o be acceptable combinations. Although AXIAL SAMPLE the thermodynamic s t a b i l i t y of BeO-Mo and BOW i s e- also good, experimental studies have shown that elec- trical shorting eventually occurs on wire-wound heaters due t o conductive material deposition over the oxide surface. I n the case of Mo, the metal it- self has an appreciable vaporization rate a t operat- i n g temperature. A small t e s t unit comprised o f SAMPLE wire-wound Re about a Be0 core encased in M was runo for short periods and yielded some heat flux, power and temperature data. Maximum R wire temperature e recorded was 2376 K a t a flux o f % 1.23 MW/m . 2 Based on the results of this test, this configuration should provide adequate flux a t wire temperatures low enough Fig. 111-12. Cross section of glass lining showing t o insure long service l i f e . orientation of t e s t samples. 32
  • The dry and grain densities and wosity werew measured for both the parent tuff and glass liner; the results are presented i n Table 111-1. The debris disposal mechanism of density consolidation i s evi- I denced by the 50% increase i n dry density and greatly reduced porosity of the liner material compared to the original tuff. Even lower l i n e r porosities are probably achievable through the use of higher pene- trator thrusts resulting i n greater melt pressures. The density and porosity values obtained for the tuff are typical of other tuffs. Permeability as a function of effective stress (confining pressure) IO 20 30 40 5C was measured on several radial lining samples. The CONFINING PRESSURE (MPa) results of one of these t e s t s are shown in Fig. 111-13. A the confining stress was increased, the s Fig. 111-13. Effect of confining pressure on the permeability decreased from about 8 millidarcys a t permeability o f a typical radial glass very low confining pressure (sl MPa) to 200 micro- liner sample. darcys a t a confining pressure of 50 MPa. On un- loading, the permeability d i d n o t completely recover. contained the transition zone between the 1i n i n g ma- Changes of the order shown i n Fig. 111-13 are n o t terial amd the parent tuff. The radial samples al- common for typical rocks w i t h about the same inltial ways failed a t the "soft" end (outside end) suggest- permeability, suggesting the cause for the decrease i n g that. the strength of the lining i s a function of i s probably associated w i t h minor imperfections in the distance from the inside radius. This anisotropy the glass liner which are closed a t higher pressures. does not appear t o be associated w i t h a t h i n transi- These values compare t o a permeabilitity of approxi- tion layer alone, b u t rather i s inherent throughout mately 300 millidarcys for the parent tuff, indica- the material as a function of the radial coordinate. ting the sealing properties of the liner. The linings have a low tensile strength (0.8 t o 1.6 Compression and tension t e s t s were performed on MPa) that does n o t increase w i t h confining pressure both parent tuff and the glass linings a t confining and is lndependent of orientation. Such low tensile pressures ranging from 0 to 50 MPa. For the l i n i n g strength i s probably due t o local inhomogeneities and the axial and tangential samples were significantly flaws caused by the thermal stresses in the cooling s t i f f e r than the radial samples, and i n general, a l l melt. Neither mechanism would detract from the abil- samples were considerably s t i f f e r a t higher confining i t y of the glass l i n i n g t o carry compressive stresses pressures. Axial and tangential samples showed the b u t would influence i t s ability to support tensile same strength w i t h i n the experimental scatter; the or bending loads. radial samples , however, were weaker because they Tht! Terra Tek study represents a significant i n i t i a l step by characterizing one particular ma- t e r i a l (Bandelier t u f f ) and the rock-glass linings TABLE 111-1 formed from it. From the information obtained during t h i s study, the following conclusions can be drawn. COMPARISON OF DENSITIES AND POROSITY FOR PARENT TUFF AND FUSED GLASS LINER e The lining materials can be modeled as a cy1 indrical , transversely isotropic media w i t h the radial direction weaker and less s t i f f than the axial Dry Density Grain D s i t y Porosity e and tangential directions. Material ( M g h 3, (Mglm31 (%I e The l i n i n g has higher compressive strength (% 50 MPa) than the parent Bandolier t u f f :( 4 Wa). 1.50 2.54 41hd Parent Tuff Glass Lining 2.23 2.40 7 Strengtli increases w i t h confining pressure for both the glass l i n i n g and the parent tuff. 33
  • CD Both the glass lining and the parent tuff large e f f o r t was made to locate and use commercialmaterial possess tensile strengths of the order of fabrication sources and to develop appropriate fab-1 MPa. rication techniques t o accomnodate large stock size 0 The lining material has a permeability of requirements and design complexity. In addition,the order of 10 millidarcys a t low confining pres- requirements of high mechanical strength and moltensure (compared to approximately 300 mil 1idarcys for rock corrosion resistance a t various design j o i n t sthe parent t u f f ) b u t decreases rapidly as the con- necessitated expenditure of e f f o r t on a high-tem-fining pressure increases. perature braze program. Development of several use- 6 The results are very encouraging i n that the ful braze formulations was accomplished.enhanced material properties of the lining are f a r The objectives relative t o refractory metalsuperior t o the parent material and present the fabrication were: t o identify the s t a t e of the a r t ,possi bi 1i t y f o r many engineering appl ications. locate f a c i l i t i e s and associated skills, expand uponC. Refractory Alloy Fabrication the s t a t e of the a r t where required, and aid i n the 1. Introduction-General Fabrication Problems. development of the industrial sources for the pene-The h i g h temperatures a t which rocks melt and the t r a t o r hardware. An extensive nationwide survey wasrequisite higher internal operating temperatures of made i n support of these objectives. A l i s t of thoseSubterrene penetrators mandated the utilization of organizations hand1 i n g molybdenum (Mo) and tungstenrefractory alloys o r materials f o r construction. A ( W ) i s given i n Table 111-2. TABLE 111-2 FABRICATORS FOR T N S E AND MOLYBDENUM PARTS U GT N Work Has Been Performed A Follows. Sources Indentified, s B u t Not Yet Used, Are Marked W i t h An Asterisk.1. Vacuum-arc-cast, extruded molybdenum bar: 9. Si 1icide coating : C1 imax Molybdenum (Amax Specialty Metals) Vac-Hyd Processing, Torrance, CA. C eve1and , OH. 1 10. Machining:2. Powder-metallurgy, extruded molybdenum bar: Los Alamos Scientific Laboratory, Los Alamos,NM. Climax Molybdenum Northwest Industries, Albany, OR. General Electric, Cleveland, OH. Thermo Electron, Woburn, MA. Sylvania, Towanda, PA. 11. Medium-temperature brazing:3. Powder-metallurgy t u n g s t e n blanks: Los Alamos Scientific Laboratory, Los Alamos, NM. General Electric, Cleveland, OH Air Vac, Carrollton, TX. *Syl vani a , Towanda , PA. *Thenno Electron, Woburn, MA.4. Extruded tungsten bar: 12. High-temperature brazing: Canton Drop Forging and Mfg, Co., Canton, OH. Oak Ridge National Laboratory, Oak Ridge, TN. Nuclear Metals, W. Concord, MA. Thermo Electron, Woburn, MA.5. Upset forging -- molybdenum and tungsten: Advanced Technology, Pasadena, CA. Oak Ridge National Laboratory, Oak Ridge, TN. 13. Electron-beam welding: *Ladish Co., Cudahy, WI. Los Alamos Scientific Laboratory, Los Alamos, NM. *Northwest Industries, Albany, OR. Electrofusion, Menlo Park, CA.6. Molybdenum sheet spinning: Electron Beam Welding, Inc., Los Angeles, CA. Laeger Metal Spinning, East Linden, NJ. *Therm0 Electron, Woburn, MA.7. Chemical vapor deposition: 14. Alloy development (in conjunction w i t h L S : AL U tramet, Pacoima, CA. 1 *C1 imax Molybdenum, Cleveland, OH.8. Ring rolling: *Wah Chang, Albany, OR. *Ladish Co., Cudahy, WI. *Airco Viking, Verdi, NV.34
  • Vacuum-arc-cast low-carbon M has been the o The major phase addressed he problem of theprime t e s t material f o r penetrator development. develorment of other brazes for use t o sl900 K,Although W and some alloys such a s thoriated W have elimination of pore formation w i t h i n the brazecertain high-temperature metallurgical advantages joints, shear strengths of the braze joints, as well(small -scale tests have been performed), the s t a t e as conducting further compatibility tests. Con-of the a r t suggests t h a t a large fabrication de- clusions are best discussed i n terms of the indivi-velopment program would be necessary t o b r i n g W dual braze up t o a level comparable t o the sophisti- a Ti-65V. Kirkendall void formation was elim-cated quality standards and fabrication know-how of inated by heating the j o i n t a 0 K above the alloypresent-day Mo. An additional deterrent to large- flow temperature. The upper limit of compatibilityscale use of W has been the greater degree of cor- w i t h basalt was confirmed a t ~ 1 6 7 0 K. The h i g h -rosion observed i n molten rock experiments. tempera,ture strength was better than recrystallized The various penetrator designs including den- vacuum-.arc-cast Mo. Data f o r a l l brazes are showns i t y consolidators, fluted extruders, conventional i n Table 111-3. A typical shear t e s t specimen i sextruders, and si ngl e-piece me1 t i ng body corers shown in Fig. 111-14.resulted i n the need for both current and advancedfabrication techniques t o produce appropri ate1ysized stock b i l l e t s of material. Close cooperation TABLE 111-3was achieved w i t h the comnercial organizations i n SHEAF S R N T OF BRAZE JOINTS I M AT 1670 K TE GH N othis respect. In particular, the development oflarge-diameter M penetrator blanks was a signifi- o U timate 1cant achievement. Excellent b i l l e t s o f fully Braze 0.2% Yield Strength Shear Strengthwrought M (150 nnn diam) have been produced by o - ell - Materi (ksi ) (MPa) (ksi ) (MPa)forging and d i ffusion-bonding three shorter sintered T i -65V 2.6 5.1stock b i l l e t s together for a total length of 450 mm. 2.0 3.4 2. High-Temperature Braze Development. This 2.9 6.8program was conducted under a two-phase effort. The 2.2 3.6preliminary phase was largely on a screening level 2.5 5.8w i t h results a s follows: Average 2.4 2 0.3a 16 5 2 4.9 t 1 . 5 34 + 1 0 e The specific braze compositions Ti-lOCr, Pure V 1.6 4.7Ti-30V, Ti-65V, V , Cr, and N (for diffusion bond- i 2.6 6.0ing) were laboratory tested i n sample cups. The cups 1.4 4.7were used t o hold Jemez basalt f o r the molten rock 2.5 4.6compatibility t e s t portion of the program. O these f --- ---compositions, only V and Ti-65V were considered as Average 2.0 5 0.6 1 4 5 4 5.050.7 3455good vacuum furnace brazes. General applications b 50V- 50140 1.8for the Ti-65V alloy would be limited t o <1670 K 1.8and t o 4 9 6 0 K for V . Neither material could be 1.4expected to survive for any significant length of Averdge 1.7 f 0.2 12 2 1time i n contact w i t h mol ten basalt, and oxygen- 50MoB-50MoC 1.8 bcontaminated atmospheres are to be avoided. o Activated diffusion bonding o f Mo w i t h N i 2.3holds great promise. 3.2 e Pore formation from the Kirkendall effect Averdge 2.5 5 0.7 17 25became a problem when braze joints were overheated. J a + values are standard deviation o f the means. e Mo-Mo, W-W,and M- brazing were inter- oWchangeable. Joiiqt was substantially stronger than the base metal. 35
  • assisted by the various disciplines composing the geosciences. Many illustrations of Subterrene system - geoscience interaction have been encountered. Familiarization with basic physical and chemical property data of many rock types has been required f o r logical and orderly Subterrene development. A BRAZED JOINT large amount of literature data for solid and molten rocks as well as rock glasses was accumulated during the course of the program. Included were: chemical and mineralogical composition, thermodynamic func- tions, density, viscosity, melting ranges, thermal di ffusivi ty and conductivity , specific heat, coef-Fig. 111-14. Braze shear t e s t specimen, (a) as ficient of thermal expansion, permeability, elec- brazed blank, (b) finished specimen. trical resistivity, and dielectric constants. A number of these values were obtained as a function 50Mo-50V. Kirkendall voids were not ob- of temperature and pressure,and selected experi-served, probably due t o prealloying. Corrosion re- mental measurements were also made, adding t o thesistance was improved over that of pure v. Joints data base. For example, a precision gas comparisonwere substantially stronger than the base metal. pycnometer was obtained which was capable of measur- a 50MoB-50MoC. Although not an optimum mix- ing rock volumes t o 0.1 an 3 (out of a total of 50ture, i t was clear that the basic formulation was c 3 ). Coupled w i t h appropriate sample preparations mgood since the joints exhibited exceptional high- and a direct weight measurement, b u l k density, graintemperature strength, good corrosion resistance to density, and porosity could be determined.a t least 1670 K, and no void formation. This system 2. M1 ting Range Experiments. Melting range eshows excellent potential for joining Mo. measurements were accomplished routinely using 3 . Silicon Carbide Conversion Coatings. Parts either an induction heater optical or hot-stagefabricated from the refractory alloys for routine microscope technique (Lei t z 1750 model ). A though 1laboratory testing are reasonably expensive. To much data was available in the literature, the largereduce development costs, a preliminary evaluation variability in rock composition justified acquisitionhas been made of silicon carbide (Sic)-coated graph- of accurate information relative to the specifici t e for both glass-forming elements and developmental rocks used in the t e s t program. These measurementspenetrator bodies of various sizes. The coating i s were very important since the melting range en-produced by a surface conversion on premachined countered would affect a decision on (1) whether orgraphite parts. The finished unit i s relatively in- n o t a conventional Subterrene penetrator could beexpensive and offers the potential of improved me- used for that particular type of rock and ( 2 ) i f i tchanical wear and oxidation resistance. Compatibility could, which specific engineering design would betests i n basalt have demonstrated resistance to cor- appropriate. I t i s known that a number o f rockrosion t o %1800 K for periods of 4 h (14.4 ks). formations do not melt a t ambient pressure b u tCoating thickness should be of the order of 0.5 mn. rather decompose (for example, pure 1imestones).Careful dimensional design i s necessary to avoid un- In addition to measurements made on the localdue thermal stress cracking. While refractory metal rock formations, a number of rock types from otherpenetrator bodies would be required for field tests localities were checked. These included: sandstoneand lifetime studies, the Sic-coated graphite parts from Pecos National Monument, NM; basement graniteoffer a new dimension in flexibility for low-cost from the Fenton Lake region, NM; caliche soil fromlaboratory preliminary evaluation tests. Sandia Corporations t e s t grounds, NM; graniteD. Geosciences gneiss from F t . Belvoir, VA; various soils from the 1. Introduction. Engineering of Subterrene Hanford radiochemical tank storage farms, WA;systems for many applications has been materially36
  • Columbia river basalt from Bend, OR; and alluvial s o i l s from the Nevada Test Site, The National Park Service had also expressed an interest in using a Subterrene penetrator to melt holes for purposes of wall strengthening and water drainage in a number of archeological sites. As part of an independent program, melt tests were conducted on various rock formations from such South- west areas as Tuzigoot, Tumacacori , Casa Grande,and Montezuma Castle, a l l national monuments in Arizona, as well as F t . Bowie Historic Site, AZ. These t e s t s showed that although many of the rocks, soils, and adobe structural materials could be melted a t con- ventional Subterrene operating temperatures , certain others could not. Another use for the hot-stage microscope was the visual study of the melting kinetics of multi- component systems as well as individual minerals and crystals. For example, Bandelier tuff, when i n i t i a l l y melted, yields a highly fluid liquid which contains F,: 1. I 11-1 5. Temperature dependence of viscosity large crystals of quartz and cristobalite. T h i s for molten glasses and rock glasses. high fluidity permits easy penetration. As melting progresses, the l i q u i d begins t o dissolve the crys- - 4. Directed Research. Various rock types have t a l s with an attendant increase in viscosity. been usled i n experiments to determine the response 3. Molten Rock Property Studies. The Subter- of geological materials to Subterrene penetrators rene system i s capable of melting many types of rock, during the melting process. Careful analysis of the b u t penetration rates can be reduced because of high rock before and a f t e r passage o f the penetrator i s a viscosities exhibited by, for example, granites. In prerequisite to an understanding of the chemical and general, the melt should be no more viscous t h a n a mechanical interactions between the metallic comnercial glass, which i s normally worked below a viscosity of 103 Pa.s. A typical operating envelope IO,, - - , I I , , , I , I , I , I , , ,-I - - based upon this criterion and the practical tempera- - - - ture limitations of a M penetrator i s defined in o - lksD (K) Viae (Pa*#)- - Fig. 111-15. Corning Glass Works assisted the pro- - u93 UP 1%b m8 0 .0 UL6 7. lm . -0 xu 5.893 gram by obtaining molten rock viscosity data. A io2=_ 1mC 3. uo typical viscosity curve (for Dresser basalt) i s shown - 1W can* mu. VcQiu 1.W a. t i n Fig. 111-16. * - e To alleviate the penetration rate problem, the 3 - concept of pressurized flux injection was considered. The addition of a f l u x i n g or mineralizing agent under - - - - pressure just preceding the advancing penetrator - - should have beneficial results. A two-fold effect 3 occurs in that both the viscosity and the absolute values of the melting range are reduced. These are -5.4 1 5.6 5.8 6.0 62 . 6.4 6.6 6.0 7.0 7.2 well-documented phenomena and typical fluxing agents I/T (KxIO44) include water, boric oxide, borates, or alkali halideh/ salts. Fig. 111-17 illustrates the reduction in melting temperature w i t h a pressurized water system. F i g , 111-16. Viscosity o f molten Dresser basalt. 37
  • the boundaries between these zones are much narrower than the zones themselves. Partially fused rock samples exhibit an increase i n the amount and degree of homogeneity of glass toward the penetrator face. This observation i s con- sistent w i t h the fact t h a t highest temperatures are maintained for the longest times nearest the pene- trator face. Thus, textures of incipient fusion are preserved a t the outer edge of the fused zone, where- Tompmlure IK) as the most advanced stage of fusion i s present a t F i g . 111-17. The effect of pressure on the melting the inner edge. The mineral and glass mixtures i n curve (sol idus) of several rock-water the samples are the product of a complex interplay systems. of temperature gradients w i t h time of penetration. The rapidity of the Subterrene fusion and quenching penetrator and the molten rock. Many rock types process precludes attainment of chemical equilibriummust be studied i f a capability i s t o be developed i n the molten zone.for predicting the behavior of the Subterrene in Interpretation of the sequence of the fusionvarious geologic environments. A preliminary study process i s hindered by uncertainties i n (1) thewas performed t o i l l u s t r a t e the type of information effects of flow of the molten rock d u r i n g penetra-that can be obtained by petrographic and microchem- tion, ( 2 ) the geometry of migration of the rock-meltical analysis of rock-melt samples. Further work on interface d u r i n g heating, and ( 3 ) the nature anddetermining the degree of chemical inhomogeneity in duration of thermal gradients i n the rock duringthe glasses, the proportions of crystals to glass as penetration. The rocks record only the maximum ther-a function of distance from the penetrator, and the mal profiles effective over varying time intervals.identification of quench products will contribute Molten rock flow during Subterrene penetration i sgreatly to the understanding of the interactions indicated by the finely laminated texture of glassbetween the metallic penetrators and the complex near the penetrator face and the presence of streaksrock-glass mixtures. of melted mineral grains parallel to the hole wall. Petrographic modal analyses of numerous rock- The laminations are defined by variations in color,glass samples were made w i t h a Swift automatic p o i n t refractive index, and major element content (andcounter. Corresponding chemical analyses were made probably oxidation) , and they generally parallel thewith an Applied Research Laboratories Electron penetrator face, suggesting laminar flow d u r i n g f u -Microprobe. Subterrene samples show analogous tex- sion. In several specimens, laminae show complextures t o rocks which have undergone partial fusion swirling patterns suggesting t h a t the entire fusedin geological processes. Petrographic descriptions zone underwent mixing d u r i n g penetration. Such ac-were prepared for samples from the glass linings t i o n could mix crystals and l i q u i d i n the fused zoneformed i n various rock types. The thin sections and could transport partially molten crystals fromexamined were cut perpendicular t o the hole wall. the penetrator face throughout the fused zone, there-Each sample has three regions: (1) unaltered rock, by hindering the interpretation of the sequence ofunaffected because of i t s distance from the penetra- alteration and fusion.t o r face; (2) a transition zone, closer to the pene- Petrographic information derived from samplestrator face, i n which the rock shows alteration exposed t o Subterrene penetration may be used i n theeffects (such as darkening of the matrix o r certain Subterrene development program i n the following ways:minerals) or a small amount of partial melting, b u t 0 Petrographic analysis can provide data ondoes not appear t o have been converted t o a domi- the identity, volume percentage, and size distributionnantly glassy state; and (3) a fused zone, closest of r e l i c t unmelted crystals and quench products i nto the penetrator face, consisting of glass w i t h gas the fused zone of Subterrene samples. Estimates ofbubbles and <50% unmelted inclusions. In most cases,38
  • the degree of abrasion (mechanical and chemical) by 0 Petrographic techniques can be used to de- such crystals i n various rock types can then be made. termine the sequence i n which the minerals i n rocks The metallic penetrator t i p may be abradgd by the melt under the nonequilibrium conditions of the Sub-I m i x i n g action which brings angular r e l i c t crystals, terrene system. The early-melting fraction produces such as quartz and olivine,into contact w i t h the t i p . the liquid composition into which additional minerals Such abrasion m i g h t be lessened i f mixing were sup- will react and through which the Subterrene will pressed and i f a narrow zone o f completely fused penetrate a t a given temperature. The degree of material could be formed along the penetrator face, chemical corrosion of the penetrator may be depend- as i s present i n the Bandelier tuff samples. ent upon the chemical composition of the partially 0 Penetration rate i s inhibited by h i g h vis- melted rock which, i n turn, i s dependent upon the cosity, particularly i n highly siliceous melts. E f - temperature gradients i n the sample. fective viscosity measurements, coupled w i t h deter- Deep geothermal drilling requires knowledge of mination of temperature gradients i n the samples, the effects of both the lithostatic pressure and can be correlated with petrographic data t o inves- h i g h temperatures, alone and i n combination, upon tigate possible ways to reduce the viscosity of the penetrator materials. A though experimental 1 liquid-crystal mixtures i n the fused zone. high-pressure studies were not completed, a labora- 8 Fluid flow patterns, traced by the dark tory drilling experiment w i t h preheated (650 K) streaks of graphite and fused iron oxides i n the basalt was accomplished. The feasibility of Subter- glass walls of the holes, can be examined i n detail rene-type drilling i n hot rock was t h u s successfully by cutting series of oriented t h i n sections. Calcu- demonstrated. lations of the geometry of the glass flow can then be verified by careful observation of these patterns. 39
  • IV. FIELD TEST AND DEMONSTRATIONSA. Field-Demonstration Units 1. Introduction. The principal objectives offield-testing complete penetrator systems are theperformance evaluation of the system under actualfield conditions and the acquisition of realisticdata on system reliability and expected service life.Data and experience from field tests form an impor-tant input in the penetrator-system design-optimiza-tion process. The field-test program was establish-ed with the design, construction, and utilization ofa portable , modularized fiel d-demonstra ti on unit(FDU). This initial FDU provided a self-containedunit for demonstrating smal 1 -diameter rock-me1 tingpenetration system capabilities at locations awayfrom the immediate Los Alamos area. The major com-ponents of the FDU and their basic functions include Fig. IV-1. Mu1 tiple-exposure photograph taken in glass-lined bore produced by consolidat-dual hydraulic cylinders for thrusting the pene- ing Subterrene penetrator.trator assembly, a hydraulic power supply and con-trol console for operating the thruster, an electric used for a hard rock extrusion experiment in a pack-power supply and control console for providing the aged rock sample. This test was incompatible withpenetrator melting power, an air compressor to sup- the indoor rock laboratory test facility. Serviceply cooling air to the melting assembly, and the facilities for the FDU are being provided by theassociated Subterrene penetrator and required stem mobile experimental field unit which is described insections. detail i n Sec. IV. C o f this report. Field-demonstration units were initially used 2. Tunnel Lining Experiment. A significantwith density consolidation penetrators to form both advantage of a Subterrene-derived system for tunnel-vertical and horizontal glass-lined holes in porous ing or excavating in loosely compacted formations isand unconsolidated rocks. A sequence of exposures the glass lining produced in place around the pe-taken as a light source was moved along the bore of riphery of the melting penetrator. The structuralone o f these 15-m-long holes is shown in Fig. IV-1,depicting its smooth surface and straightness.Eight water drainage holes were melted with dn FDU atthe Rainbow House and Tyuonyi archeological ruins atBandelier National Monument, NM, in cooperation withthe National Park Service (NPS). A program to meltadditional water drainage holes at Tumacacori,Tuzigoot, and Casa Grande Ruins National Monumentsand Fort Bowie Historical Site in Arizona has beenunder development with the NPS. Rock and soil sam-ples from these areas have been received,and prelim-inary me1 ting-penetration experiments are in pro-gress. The versatility of the original FDUs has beenexpanded by adapting them for operation with hardrock extruding penetrator systems through the addi- Fig. IV-2. Field-demonstration unit in position fortion of a debris removal stem configuration. Fig- horizontal hard rock extrusion experi-ure IV-2 shows a field-demonstration unit being ment.40
  • i n t e g r i t y o f t h i s l i n i n g could be u t i l i z e d t o sup- the tunnel t o s t a b i l i z e the formation i n t h a t region.p o r t the r o o f o f a tunnel u n t i l a permanent l i n i n g A f t e r t h e holes were melted t o form the r o o f andcan be i n s t a l l e d . Use of the Subterrene-system w a l l s o f the tunnel, the i n t e r i o r volume was excavat-could p o t e n t i a l l y increase the safety and - e f f i c i e n c y ed by hand t b expose the glass l i n i n g . An FDU waso f tunneling i n formations which a r e n o t self-sup- e a s i l y adapted f o r the task by mounting the h y d r u a l i cp o r t i n g and might make possible the use o f tunneling, t h r u s t e r u n i t on an adjustable s c a f f o l d i n g as i l l u s -instead o f the d i s r u p t i v e c u t and cover method, f o r t r a t e d i n Fig. IV-4. Holes were p r e d r i l l e d i n thethe construction o f underground f a c i l i t i e s . The wooden r e t a i n i n g w a l l o f the bunker a t t h e properbasic f e a s i b i l i t y of t h i s tunneling concept has been l o c a t i o n s f o r i n s e r t i o n o f t h e Subterrene penetratordemonstrated by an excavation experiment conducted t o produce t h e continuous glass l i n i n g . The pene-i n a loose a l l u v i a l d i r t f i l l behind a wooden r e - t r a t o r assemblies employed a new design replaceablet a i n i n g w a l l which was formerly used as a b l a s t g r a p h i t e glass former which produced smooth glasss h i e l d bunker. The e x i s t i n g wooden w a l l made an l i n i n g s and showed r a d i a l wear o f l e s s than 0.005 mmi d e a l p o r t a l f o r t h e prototype tunnel opening (2 m per meter o f l i n i n g produced. Gaseous n i t r o g e n washigh, 2 m deep, and 1 m wide) which i s shown i n used t o c h i l l t h e m e l t and s o l i d i f y the glass, andFig. IV-3. t h e maximum penetrator power consumption was 4.5 kW. The r o o f and s i d e w a l l s o f the tunnel were 3 The excavated tunnel volume was 4 m and t h e volumeformed by me1 t i n g a series o f 50-mm-diam horizon- o f the glass l i n i n g which forms the w a l l was approxi-t a l holes approximately 2 m deep i n t h e loose s o i l mately 0.2 m 3 .This small t e s t tunnel demonstratesf i l l m a t e r i a l using e l e c t r i c a l l y heated d e n s i t y t h e concept o f supporting the overburden o f a tunnelc o n s o l i d a t i o n Subterrene penetrators t h a t a r e o r d i - w i t h a glass l i n i n g formed i n s i t u by a kerf-meltingn a r i l y used f o r l a b o r a t o r y and f i e l d development penetration system. The production o f tunnel l i n i n g st e s t s . The holes were placed s u f f i c i e n t l y c l o s e t o - by m u l t i p l e Subterrene penetrators operating simulta-gether f o r the glass l i n i n g s t o fuse and thus pro- neously i s a l o g i c a l extension o f t h i s t e s t .duce a double-walled l i n i n g r e i n f o r c e d by webs be- 6. Public Demonstrationstween t h e i n d i v i d u a l holes. Four v e r t i c a l holes 1. Washington, DC. The LASL Subterrene s t a f fwere melted from the surface a t t h e closed end o f staged a s e r i e s o f f i e l d demonstrations of consolidat- i n g and extruding rock-melting penetrator systems a t t h e U.S. Armys Engineering Proving Grounds quarryFig. IV-3. Subterrene-produced prototype tunnel Fig. IV-4. Field-demonstration u n i t m e l t i n g holes opening showing d e t a i l o f l e f t w a l l . f o r tunnel r o o f . 41
  • area at Fort Belvoir near Springfield, VA. Atten- to break through the end of the sample which enableddance averaged above 80 for the first three demon- the audience to watch as the molten earth was dis-strations and approximately 45 for the final pre- placed from the end of the shell and the hot, glow-sentation. Attendees at the sessions were primarily ing penetrator was visible. After each demonstra-from the following groups: tion the shell was removed and the observers were First Morning - Atomic Energy Commission, Congres- allowed to examine the glass casing formed by the sional Representatives, Military penetrator. This was followed by an extruder, oper- Personnel.First Afternoon - National Science Foundation, Con- ated in a vertical position, penetrating a hard rock gressional Representatives, Mili- sample and demonstrating the concept of molten debris tary Personnel. removal by the cooling gas stream. Second Morning - Industrial sector including rep- resentatives from tunneling, Subterrene staff members were available during horizontal hole boring, major oil the rock-me1 ting demonstrations to explain the se- companies, and manufacturers of quence of operations and answer questions on rock support equipment.Second Afternoon -Representatives from a1 1 areas. and soil melt handling, potential applications, and Each demonstration was initiated with a wel- the simplicity of the field-test equipment and oper-coming address and introduction by a representative ations. In addition to examining the penetrators,of either the AEC or NSF. A LASL scientist then associated equipment, and the melted holes at closepresented a brief historical and technical account range, the observers were invited to visit the dis-of the Subterrene program, the ways it differs from play trailer to obtain copies of Subterrene reports.conventional drilling methods, potential practical Additional background information was provided byapplications, and the characteristics of the melting the 20 specially prepared display posters located inpenetrators which the audience would observe during the trailer, as depicted in Fig. IV-6. This demon-the actual demonstrations. Part of the Subterrene stration series was sponsored by the Atomic Energyfield demonstration equipment is shown in Fig. IV-5 Commission and the National Science Foundation - RANNduring one of the Fort Belvoir demonstrations. Program with additional inspiration provided by the Each of the two portable Subterrene field units Interagency Comnittee on Excavation Technology (ICET).was then demonstrated, beginning with a horizontal 2. Denver, CO. As guests of the Bureau of Rec-consolidator penetrating a section of alluvium en- lamation, the LASL Subterrene staff staged a seriescased in a steel shell. The consolidator was allowed of field demonstrations of consolidating and extrud- ing rock-melting penetrator systems at the Denver Federal Center. Two demonstrations were given in theFig. IV-5. Subterrene rock-melting demonstration and briefing before audience in Fort Belvoir, VA. Fig. IV-6. Subterrene demonstration display trailer.42
  • morning, w i t h an average attendance o f 85, and one actual demonstration. V i s i t o r s were b r i e f e d on the i n the afternoon w i t h a phenomenal attendance o f techno1 og quipment w h i l e they observed theW over 400 v i s i t o r s . The program f o r t actual me peration a t close range. The f i n - t i o n s was s i m i l a r t o t h a t used a t F o r t Belvoir, VA, ished holes were smooth and stable and immediately w i t h a representative from the Bureau of Reclamation a v a i l a b l e f o r inspection upon withdrawal o f the pen- welcoming the group and introducing the LASL speak- e t r a t o r system. A f t e r cooling, segments o f the er. After a b r i e f h i s t o r i c a l and technical account glass l i n e r s were provided t o the spectators t o con- o f the Subterrene program, t h e two portable f i e l d clude the demonstration. The demonstrations and u n i t s were demonstrated. The observers then i n - equipment were viewed by a wide ranging audience of spected the penetration systems, melted qlass-lined engineering, c i t y management, and technology t r a n s f e r holes, and v i s i t e d the d i s p l a y t r a i l e r t o c o l l e c t oriented v i s i t o r s . technical reports and study the d i s p l a y posters on C. Mobile Experimental F i e l d U n i t the Subterrene program. 1. Introduction. The extension o f the fie-ld 3. Tacoma, WA. During t h e past three years, t e s t program t o l a r g e r diameter, deeper penetrations Tacoma has attempted t o create an environment i n i n t o hard rock formations has l e d t o the design, c i t y government f o r experimenting w i t h innovative f a b r i c a t i o n , and f i e l d u t i l i z a t i o n o f a specialized techniques and developing b e t t e r procedures and mobile Experimental F i e l d U n i t (EFU). This EFU i s hardware f o r improving c i t y operations through the designed t o operate w i t h consolidating, coring, and use o f new technology. A Technology Transfer Center extruding penetrator systems under f i e l d conditions has been created t o a i d i n the development and i m - and i n areas remote from the laboratory. For hard plementation o f proposed solutions t o departmental rock penetrations w i t h extruding systems, t h i s means problems i n the c i t y and t o e s t a b l i s h an i n t e r c i t y t h a t an appreciable t h r u s t load must be applied t o center for technology applications. As a p a r t o f the penetrator melting body i n order t o provide ex- t h i s program, Tacoma hosted a Technology Transfer t r u s i o n pressures i n the rock m e l t s u f f i c i e n t l y high F i e l d Day Program t o i l l u s t r a t e how i t i s attempting t o f o r c e the molten material t o f l o w through the t o mobilize i t s resources t o a i d p r o d u c t i v i t y i m - debris-removal passages i n the melting body. In provements throughout the c i t y . The F i e l d Days were nonstable formations such as caving o r squeezing held t o comnunicate information about progress i n s o i l s o r formations containing trapped ground waters, the a p p l i c a t i o n o f technology t o municipal opera- i t may be necessary t o produce m e l t pressures great- t i o n s d i r e c t l y fo the hardware developers and t o rm e r than the overburden stress t o s t a b i l i z e and sup- provide observers w i t h f i r s t - h a n d experience i n p o r t the hole and prevent blowout. Since the weight handling several types o f new hardware and t o view o f the c u r r e n t l y used gas-cooled stem i s i n s u f f i c i e n t operational improvements i n service d e l i v e r y systems. t o produce the required pressures, a l a r g e pull-down The 10s Alamos S c i e n t i f i c Laboratory was i n v f t e d t o c a p a b i l i t y has been provided. This hydraulic p u l l - p a r t i c i p a t e i n t h i s program by providing Subterrene down feature and the absence o f a r o t a r y t a b l e are rock-melting penetration system demonstrations aimed the c h a r a c t e r i s t i c s which d i s t i n g u i s h the EFU from a a t the p o t e n t i a l use o f t h i s technology f o r under- conventional, lightweight, work-over r i g . The Ex- perimental F i e l d , as received from the comer- f o r the demonstrations cia1 fabricator, l l u s t r a t e d i n Fig. IV-7. was loosely conSolidated l o c a l alluvium described as S i g n i f i c a n t design features o f the EFU a r e " p i t - r u n gravel" which consisted o f material varying b r i e f 1y summarized bel ow: from f i n e p a r t i c l e s t o 50-mn c h a r a c t e r i s t i c s i z e 0 The mast w i l l handle 300 m o f 114-mm- conglomerates. The sample was v i s i b l y wet and pack- (4.5-in.-) diam d pe i n 10-m lengths. ed i n a 1.2-x 1.5-x 2-m plywood sample container. I t i s r a i s e d and u l i c a l l y and i s de- A f t e r m e l t i n g a sample hole through the alluvium t o signed t o work wh r near v e r t i c a l . With t e s t the equipment and provide a f i n i s h e d hole f o r modifications i t can be operated a t greater i n c l i - the observers t o inspect, two a d d i t i o n a l holes were nations, even approaching horizontal penetrations. melted and s t a b i l i z e d w i t h glass l i n i n g s during the 43
  • Penetrating and h o i s t i n g speeds are continu- ously variable, fo 0 t o 5 mn/s (1 ft/min), and rm can be remotely c o n t r o l l e d w i t h an e l e c t r i c a l l y po- t s i t i o n e d spool valve i n the h y d r a u l i c supply l i n e . Manual c o n t r o l s produce higher speeds f o r t r i p p i n g o r other l i g h t - l o a d operations. The mast, pull-down and h o i s t i n g systems, hy- d r a u l i c pump and prime mover, and a h y d r a u l i c power- ed sandline are mounted on a tandem f l o a t . With the mast stored i n a h o r i z o n t a l position, the u n i t i s l e g a l t o m v e w i t h a c o m e r c i a l t r a c t o r without a special permit. Operation o f the system i s s t r a i g h t f o r w a r d and r e q u i r e s o n l y an operator and helper f o r r o u t i n eFig. IV-7. Mobile Experimental F i e l d U n i t as r e - penetration and t o o l t r i p p i n g . Automatic, closed- ceived from f a b r i c a t o r . loop servomechanism c o n t r o l i n several modes of pen- e t r a t i o n (constant load, constant rate,or p o s i t i o n The u n i t i s h y d r a u l i c a l l y powered and con- demand) i s provided, and monitor and alarm c i r c u i t strolled. Dual two-way h y d r a u l i c c y l i n d e r s attached warn the operator o f abnormal conditions. The pre- t o t h e f a s t l i n e s i d e o f t h e mast, Fig. IV-8, provide sent experimental nature of the operation d i c t a t e sthe force t o move the pipe i n o r o u t o f the hole and more complete instrumentation and recording of pene-t o p u l l down on t h e s t r i n g . Each c y l i n d e r s " d r i l l - t r a t o r performance than would be required i n r o u t i n ei n g " l i n e attaches t o i t s i n d i v i d u a l h y d r a u l i c a l l y h o l e forming.operated g r i p p i n g e l e v a t o r which can transmit a p u l l - 2. Stem Design and Performance. A 78-mm-diamdown o r e x t r a c t i o n f o r c e o f 89 kN (20 000 l b ) t o stem was designed, fabricated, and u t i l i z e d f o r f i e l dthe d r i l l stem. Both elevators can be used simulta- operations w i t h t h e EFU. This stem was designed f o rneously t o e x e r t a f o r c e o f 178 kN. e i t h e r c o n s o l i d a t i o n o r extruding Subterrene pene- t r a t o r s operating a t increased depths a t power l e v e l s up t o 30 kW. The concentric tube design o f the stem provides, i n a d d i t i o n t o s t r u c t u r a l support, e l e c t r i c power supply t o t h e penetrator, coolant and d e b r i s removal gas, debris removal c a r r y - o f f tube, i n e r t i n g gas (he1 ium) supply, and instrumentation c a p a b i l i t y . The o u t e r s h e l l i s t h e main s t r u c t u r a l member and i s f a b r i c a t e d from 6061 T-6 aluminum on t h e basis o f i t s low r e s i s t i v i t y , h i g h strength, atmospheric corrosion resistance, and low weight. Designed t o a l l o w 100-kN (22 500-lb) loading i n e i t h e r d i r e c t i o n , the s h e l l i s a l s o t h e negative l e a d f o r dc power transmission t o t h e penetrator. The i n n e r s t a i n l e s s s t e e l tube i s for d e b r i s removal w h i l e t h e annulus provides t h e space f o r the coolant gas flow, three i n s u l a t e d p a r a l - l e l copper power leads, helium gas l i n e , and i n s t r u - mentation leads. An end view o f a t y p i c a l stem sec- t i o n i s shown i n Fig. IV-9 i l l u s t r a t i n g these func- t i o n s a n d some a d d i t i o n a l p e r t i n e n t data on t h e stem Fig. IV-8. F a s t l i n e s i d e o f EFU showing hydraulic design i s presented i n Table I V - 1 . cylinders, d r i l l i n g l i n e s , and d i e s e l - hydraul i c power u n i t .44
  • depth goal of 30 m was selected as a compromise on the basis of demonstration of capability and field expense and does not represent any technological limitation of the penetrator or i t s support system. Deploymen8 o f equipment for the field operation with the EFU i s shown in Fig. IV-10. In addition to the diesel-powered EFU, the following auxiliary equip- ment was required. 0 Power conditioning and control equipment for the electrical power input to the penetrator. 220-V three-phase power supply to match the penetrator power conditioning requirements. 0 Cooling gas supply for hole forming assembly cooling requirements and debris removal. 0 Instrumentation for monitoring and control-Fig. IV-9. End view of 78m-diam stem section. l i n g the penetrator system operation. " The instrumentation control, recording, and power TABLE IV-1 conditioning equipment i s housed in the t r a i l e r to PERTINENT 78-MM-DIAMETER STEM DATA the l e f t of the EFU i n Fig. IV-10. The extruding penetrator selected for the ex-Section lengths 4.05 m periment was the 84mm-diam fluted molybdenumDebris carry-off tube i.d. 24.0 mm body design described i n more detail i n Sec. 11. BWeight per section 25.9 kg of this report. This extruder was designed speci-Resistance of copper electrodes 4.65 x n fically t o produce a deeper basalt penetration than per section had previously been made and to do so under fieldResistance of aluminum shell 1.13 n conditions. Preliminary laboratory testing, follow- per section a t 300 K ed by t e s t s employing rock specimens mounted on theMeasured dielectric s t r e n g t h 1200 V (minimum EFU preceded actual production of the 30-m hole. Production of the 30-m-deep basalt hole was completed, A structural coupling of Inconel 718 joins suc- and an aggregate- of 505 kg of debris was processedcessive sections and transmits tensile loads whilecompressive loads are absorbed by a mating shoulder . .on adjacent sections. This mechanical design coupled €w i t h simple "slip i n " power and flow connectors I .allows f a s t makeup of the d r i l l string. Under fieldconditions the contact resistance between adjacentaluminum stem sections was less t h a n 2 x natmoderate penetrator thrusts,indicating excellentelectrical performance. Field testing has confirmedthe validity of the stem design i n providing a l l nec-essary penetrator service functions and no difficul-t j e s were encountered i n the continuous gas transporto f the rock wool/scoria debris t o the surface forcol lection. 3. Proof-of-Concept Field Experiment. As aproof-of-concept experiment, the EFU was uti1 Ized toproduce a 30-m-deep hole i n a thick flow of Jemez Fig. IV-10. Deploymerlt of EFU i n basalt hole melt-basalt i n Ancho Canyon, southeast of 10s Alamos. The i n g field operation. 45 . . - 7. -..
  • i n the operation. The debris i s characterized as type of stoppage and occurs when very rapid penetra-approximately half rock wool and half scoria o r tion is made into a b u i l t - u p melt pool. T h i s causessolidified pellets. The cyclone separator and debris a large mass of molten rock t o be suddenly injectedstorage drums shown i n Fig. IV-IO were added t o col- into the carry-off tube substantially "overloading"l e c t the rock wool and scoria prior t o exhausting the transporting gas which allows the slowmovingthe coolant gas t o the atmosphere. The overall ex- mol ten rock t o contact the side wall. When the tubeperiment effected a sizable gain i n knowledge and wall temperature exceeds 600 K the molten rock debrisexperience i n field operations of Subterrene pene- can stick o r adhere t o the surface,and this buildupt r a t o r systems i n general and the 84-mn extruder i n can continue until a complete blockage is present.particular. All of the new f i e l d techniques required The solution of this problem was an internal designfor this novel method of hole production were success- modification which lowered the temperature of thefully developed over a relatively short time span. carry-off tube, t h u s preventing sticking and block-In this same interval the 84-mn system evolved by age. Subsequent deep hole penetrators may findmoderate changes frcm a 3/4-m-depth laboratory ex- water more effective f o r cooling of this regiontruder to a f i e l d device capable of sustained con- coupled w i t h d i s t i n c t advantages f o r debris trans-tinuous operation a t modest depths. I t i s noteworthy port. Plans f o r the EFU include f i e l d testing ofthat f i e l d testing brought out problem areas and so- advanced penetrator assemblies i n basalt and otherlution approaches that passed essentially undetected formations a t sites near Los Alamos. Other poten-i n the preliminary laboratory t e s t s . t i a l applications include utilization i n forming Hard rock buildup i n the lower portion of the test holes f o r heat flow measurements i n severaldebris carry-off tube was a primary cause of f i e l d geothermal resource areas , formation of drainageoperation stoppages a t the beginning of the experi- holes i n archeological ruins, and production of nearment. Surging i s a phenomenon associated w i t h this horizontal holes f o r u t i l i t y emplacement.46
  • V. SYSTEMS ANALYSIS AND APPLICATIONSA. Geothermal Well Technology available is not designed t o withstand the high 1 . Introduction. A t the request of the project- geothermal temperatures. sponsoring agency, increased emphasis was devoted to An additional desirable capability is t h a t of the application of the Subterrene concept t o the continuing d r i l l i n g past the anticipated production production of geothermal energy wells. Consistent zone towards the source of heat that drives thew i t h this task, the general status of the geother- reservoir. This could mean penetrating into hardmal industry and the technical problems being ex- igneous and metamorphic rocks a t very high tempera- perienced i n producing geothermal we1 1s were exten- tures. The objectives would be to gain a better sively reviewed and evaluated. An e a r l i e r L S AL understanding of the basic system and t o determine publication (LA-5689-MS) presented a summary status whether reinjection fluid, o r even additional fresh review of geothermal well technology, including water, might be added a t the lower hotter depths t od r i l l i n g and operational problems. Another objec- percolate upward into the production zone. Thetive of this study was t o begin the analysis and l a t t e r could greatly augment and a r t i f i c i a l l y stimu-evaluation of producing wells by means of the Sub- l a t e both the production and useful l i f e of theterrene rock-melting process. In addition t o the reservoir. A t the Geothermal Resources Researchuse of p u b l i s h e d l i t e r a t u r e and data, many personal Conference i n Seattle, i n September 1972, two rec- *discussions were h e l d w i t h people i n various fields ommendations were that h i g h priority be given t oof the d r i l l i n g and Geothermal Energy (GTE) indus- immediate improvement of exploration methods and t otries i n an e f f o r t t o arrive a t correct and objec- the development of cheaper d r i l l i n g methods i n high-t i v e conclusions. A l i s t of these contacts is temperature formations. These improvements wouldpresented l a t e r i n this section. result i n improved reservoir and economic models 2. Current Technolociical and Cost Status. which, the conference attendees concluded, were a. Exploration. Geothermal resource areas sorely needed. The average costs f o r shallow o i lof the vapor-domi nated o r hydrothermal types are and gas wells reported by the 1972 Joint Associationscattered throughout the world. Steam fumaroles or Survey are presented i n Table springs a r e indicators of such areas andas a result of o i l and gas d r i l l i n g a c t i v i t i e s , TABLE V-1other anomalous high heat flux areas have become AVERAGE DEPTH AND COST PER DEPTHknown. Data from these sources provide only rough TOTAL UNITED STATES IN 197Zaindications of geothermal energy resources because Type of Wells and Average Costba significant geothermal reservoir is a complex sys- per Meter ($/m) Averaqe Totaltem depending on location, nature of the heat source, Depth- Weightedrecharging characteristics , interrelation of perme- (km) Oil Gas Dry Averageable and nonpermeable s t r a t a , and on the total vol- 1.3 44.10 45.10 25.10 35.90ume of the system. Much more information i s needed (4300) (13.40) (13.80) (7.70) (11.00)before the f u l l extent and nature of the geothermal 1.9 52.95 53.80 34.80 45.20resource i s well understood. With the exploratory (6200) (16.10) (16.40) (10.60) (13.80)methods available, the presence of a significant GTE 2.6 68.00 82.90 54.40 65.00reservoir must s t i l l be proven by drilling. Explora- (8500) (20.70) (25.30) (16.60) (19.80)tory holes can be used for measurements of tempera- Numbers i n parentheses are f t and $/foot. Includes d r i l l i n g and casing.ture and pressure profiles, permeability, porosity,1i tho1 ogy, stratigraphy, f 1uid compositions , andproduction flow t e s t s . These uses of exploration *W. J. Hickel, "Geothermal Energy A National-holes are consistent w i t h todays capabilities f o r Proposal f o r Geothermal Resources Research ,"d r i l l i n g , downhole measurements, and logging except University of Alaska Conference held i nthat i n many cases the measurement equipment Seattle, WA (September 18-20, 1972). 47
  • wells would be worth r u n n i n g p i p e and completing Depth=LSkrn il 1972 Dollerr for extensive testing. The three unsuccessful wells would cost % $100 000 t o $200 000 each and the com- pleted wells - $150 000 t o $250 000. The net aver- I , age cost for each prospect worth completing and Y) 150 testing extensively is then $650 000. Perhaps one of four of the completed prospect wells would re- s u l t i n the discovery well of a reservoir large enough t o be commercially attractive. The r a t i o of total wells drilled t o each discovery well i s t h u s 16:l. Greider feels that t h i s i s a r e a l i s t i c r a t i o as the industry matures a f t e r the large easily located reservoirs are drilled. Greider’s defini- tion of a good discovery well is one defining a Fig. V-1. Typical well costs for 1.5-kmdeep wells. reservoir capable of 275 MW(e) power output. A sumnary of his cost model i s shown i n Table V-2. Cost data compiled a t LASL showed that average This simple calculation of exploratory drilling geothermal wells are considerably more expensive costs indicates that the costs are h i g h enough t o than indicated i n Table V-1 for o i l and gas wells. easily justify the cost of research leading t o low- These data are represented i n F i g . V-1 where i t can e r exploration drilling costs. The much higher be seen that t h e Imperial Valley hot-water wells costs associated with the production and reinjec- and The Geysers steam-dominated wells are two to tion wells will be discussed l a t e r . five times more expensive than the average o i l and b. Problems i n Completing Geothermal Wells. gas we1 1s . The methods used i n making geothermal wells are Greider* of Chevron O i l compiled cost data on essentially the same as those for o i l or gas wells. geothermal exploration wells. Wells t o depths of Indeed, t h i s very fact somewhat impedes GTE develop- 1.5 km (5000 f t ) i n most geothermal provinces i n ment because geothermal we1 1 d r i 1lers are forced t o sedimentary basins in the U. S . average 65 t o 100 use materials and equipment t h a t are not necessarily $/m (20 t o 30 $ / f t ) . In remote areas or i n those best for geothermal wells w i t h their higher temper- w l t h interbedded volcanic rocks, costs r u n from atures and corrosive conditions. Problem examples 100 t o 200 $/m (30 to 60$/ft). To run casing and are: ( 1 ) only oil-well tubular goods and b i t s are t o prepare for production i n these 1.5-km wells available, ( 2 ) muds and cements are not checked out costs 33 t o 50 $/m (10 to 15 $ / f t ) . Thus, costs of for high-temperature use because geothermal wells range from 100 to 250 $/m (30 t o 75 $ / f t ) or approximately two t o fike times higher TABLE V-2 than the average costs o f o i l or gas wells given i n COST TO PRODUCE A DISCOVERY WELL Table V-1. Greider presented other cost data: Sur- FOR A 275-MW(e) RESERVOIR face exploration costs run from $75 000 t o $90 000 % of per typical area of interest. Only one out of four Cost ($) Total o f these areas would probably justify an exploratory Land acquisition (nontechnical hole, resulting i n $300 000 t o $360 000 per d r i l l - leasing, bonus, rentals, etc.) 3 580 OOOa 45 able prospect. Only one of four of these prospect Drilling (12 unsuccessful + 4 completed holes) 2 600 000 32 Surface exploration (geology, geochemistry, geophysics) 1 840 000 23 *R. Greider, “Economic Considerations for Geothermal Total 8 020 000 100 Exploration i n the Western Uqited States,” presented a t the Symposium, Colorado Department o f Natural a Considering the h i g h bids made a t the Jan. 22, Resources , Denver , CO (December 6, 1973). 1974 KGRA competitions i n California, these costs are probably low..-.. 48 .- *
  • sui table high- temperature laboratory equipment i sn o t available, and (3) bit-bearing lubrication sys- terns are not designed t o withstand GTE tempera- - The Geysers vicinit!tures. This dependence is designated as an impor- hard rocktant consideration i n the NSF-sponsored study of Imperial Volley sieom-dominatedimpediments to geothermal development by Bechtel -dimentory (92 wells)Corp. for The Futures Group, Inc. In current geo- - hot-woter (33 we1 Is) Rthermal wells, drilling i s easy i n some sedimen-tary basins and i s very d i f f i c u l t i n hard, frac-tured rocks found, e.g., a t The Geysers. The l a t -t e r results i n high b i t wear and often in failures -of b i t bearings due t o a combination of temperature,stress, corrosion, and fatigue effects. To better understand the factors affecting I 1 2 3 4 5 0 I 2 3geothermal well drilling, the activity logs for (krn) (km)125 geothermal wells drilled i n California were u 0 3 6 9 1216 0 3 6 912studied.* The majority of the data were either (kft) (kft) Well Depthsfrom the general Geysers area or from ImperialValley, California, and are here designated Steam, Fig. V-2. Depths of geothermal wells drilled i nHard Rock (SHR); and Hot Water, Sedimentary (HWS); two geothermal regions.respectively. The data include 92 SHR and 33 H S Wtype wells. Their depths are indicated i n a fre- Valley geothermal costs are shown a s 160 $/m (50quency of occurrence-versus-depth plot i n Fig. V-2. $ / f t ) and 80 $/m (25 $ / f t ) , respectively. ForSelected depth intervals are 300 m. About 40% of depths of 15 km, costs could be % $20 000 000 tothe Imperial Valley wells ranged i n depth from $26 000000 per well. Clearly, GTE drilling w i t h1300 t o 1900 m (4300 t o 6200 f t ) . In The Geysers current techniques could be very costly (e.g., run-50% of the wells are i n the 1900- t o 2500-m (6200- ning into tens of billions of dollars) making i tto 8200-ft) range. A similar plot is shown in worthwhile and cost-effective to develop new,Fig. V-3 for overall average penetration rates cheaper techniques and equipment.where the average includes total time for spuddingi n to total depth. In the Imperial Valley thepenetration rates were 1.5 to 2.5 m/h (4.9 to 8.2ft/h) for 42% of the wells analyzed. In The 40 IGeysers, 52%of the wells were drilled a t 1 to 2m/h (3.3 to 6.6 f t / h ) , somewhat lower than therates in the Imperial Valley. The above discussions of cost centered pri-marily on wells i n conventional GTE areas wheremaximum depths may not exceed 3 km. For hot dryrock and geopressurized developments, the depthsand drilling costs could be considerably higher.Costs increase very rapidly w i t h depth, as illus-trated i n Fig. V-4. The average oil-and gas-well O W E Ok--+--hEcosts are shown shaded; typical Geysers and Imperial (fth) (fth)OvemlI Average Rnetmtion Rate* Petroleum Information Corporation, Denver, CO, Fig. V-3. Overall average penetration rates i n "Drilling Data File for Approximately 300 Geo- typical geothermal wells. thermal Wells," supplied to Los Alamos Scientific Laboratory for study purposes (March 1974). 49
  • 3. Conceptual Applications of Subterrene Devices I I I I 1 1 I t o Geothermal Wells. Nw Subterrene technology would e I969,ARPbfAEC Study- aOotol750 $/m open u p options for obtaining the most economically I lo 15km and technically suitable methods for any particular "t s e t of conditions and requirements. For example, i t could be most economical to use rotary d r i l l s for making holes rapidly i n known, easily penetrated formations. Then, in hot, hard zones, the tools and methods might change t o Subterrene technology t o complete the j o b . Listed below are current ro- tary drilling problems i n geothermal wells followed i n each case by a discussion of how the use of Sub- terrene devices could either help solve or eliminate the problem. 6 Problem: Hole stabilization in unstable formations. Subterrene: The optimum well hole produc- tion process minimizes excavation damage to the inherent structural integrity of the ground or rock and i s then followed by the continuous installation Depth (km) of a structural support and seal t o prevent the i n - flow of ground fluids. T h i s process may well beFig. V-4. Cost of wells permeter vs total depth. accomplished by a Subterrene system which makes the hole by melting and simultaneously forms a struc- I t has been amply demonstrated that naturally t u r a l rock-glass liner.occurring hot-water or vapor-dominated geothermal a Problem: Rock b i t wear and temperature-reservoirs can be penetrated by rotary drilling induced fai 1ures .methods t h a t have been developed for oil and gas Subterrene: A Subterrene depends uponwells. However, there are factors i n geothermal melting, not on cutting or mechanical fragmentation,fields such as h i g h temperature, corrosive fluids and therefore eliminates this problem. Also, h i g hand gases, unfavorable siting conditions, and, i n rock temperatures would enhance the performance ofmany cases, hard abrasive rocks, which combine to the Subterrene b i t because the b i t has to supplymake the average rotary-drilled geothermal wells less thermal energy to melt the rock.more expensive t h a n the average oil o r gas wells of a Problem: Cements a t h i g h temperature.comparable depth. High well costs could signifi- Subterrene: Steel casings may n o t be neces-cantly impede the expansion of geothermal energy sary i f good structural rock-glass hole linings cansources. There are many applications for geother- be made. If steel casings are used, the relativelymal temperatures less than 660 K, which i s about smooth surface inside the glass lining should fa-the upper limit measured a t well bottom t o date. c i l i t a t e the flow of the cement. Also, the require-To attain the higher temperatures desirable or re- ments that the cement be b o t h strong and impermeablequired for many heretofore unexploi ted GTE applica- should be lessened because of the presence of thetions, one has t o consider penetration into deep glass lining.h o t zones. Current drilling methods (especially m Problem: Production-zone hole completion.the use of muds and cemented casings for hole con- Subterrene: The Subterrene could penetratetrol and support) will t h u s be severely strained the production zone with a glass-lined hole. T h i stechnically and will probably make the wells ex- penetration would not kill or impair the zonescessively expensive. An evaluative summary of the production capability because drilling fluid, cut-various current drilling problems in geothermal tings, and lost-circulation material would not bewells is presented i n Table V-3.50
  • TABLE V-3 SUMMARY OF CURRENT GEOTHERMAL DRILLING PROBLEMS Type GTZ Field Sedimentary Hard, Igneous I tern Hot-Water Vapor-Dominated Symbols and Problem DescriptionsSurface locations 6: Difficult geological conditions typical of many GTE fields, including s i t e s , hard rocks, caving formations, etc.Drilling-rig design R: Rigs of h i g h mobility are needed, adequately equipped t o handle r a p i d changes i n hole conditions .Other surface X: Dependence on oil- and gas-industry materialsequi pmen t and equipnent, competition for supplies.Bits and d r i l l a b i l i t y T: Temperatures up to c, 660 K cause rubber, elastomer, metallurgical, mud, cement, and electronic problems.Mud-ci rcul ation C: Corrosion problems caused by ground fluidssys tems and gases.Hole support and E: High stem, casing, and surface-equipmentcontrol erosion by a i r + steam + rock cuttings.Cements D: Directional drilling equipment n o t available for hard rock a t high temperatures.Downhole measurements F: Hot saline waters contaminate drilling muds. Also, muds can reduce or kill well productivity or may hydrate clays.T u b u l a r goods 0: Lack of organized GTE wells drilling-data bank and ways t o use such data t o optimize d r i l l i n g programs.Optimized dri 11i n g 0 0 H: Costs are typically high because of inter- relating effects of items listed above.Costs of geothermal H Hwellspumped into the zone. Also, the sealing action of materials encountered i n the earth. However, Sub-the lining would f a c i l i t a t e stem and b i t changes, terrene-produced holes should be more effectivelyi f necessary. Several ways t o ultimately com- sealed from the corrosive materials. Also, stemplete the well and to allow the hot water or steam and b i t need n o t rotate so that protective coatingst o flow into the well are conceivable. One might should be easier t o to shatter the glass liner with a linear ex- e Problem: Formation evaluation and sampling.plosive; another, t o conventionally perforate the Subterrene: The Subterrene offers theliner w i t h shaped charges. possibility of extracting a continuous, oriented a Problem: High torque on long d r i l l stems glass-encased core. The glass hole lining eliminatesin deep wells. the problem of making logging measurements through a Subterrene: Subterrene bits are n o t rotated heavy steel casing or through variable depths of mudand therefore the torque requirements are invasion. Because the glass-lined hole interior i seliminated. better protected than the unlined hole, the possi- a Problem: Corrosive environment. b i l i t y o f developing continuous downhole logging Subterrene: The corrosion problem will may be enhanced.change because different materials will be used. a Problem: Directional drilling i n hot, hardAny drilling system must live with the corrosive rock. 51
  • Subterrene: Hot, hard rock does n o t bother 2. L. 0. Beaulaurier, Drilling Problems, Geo- thermal Technology Assessment Study for The Futuresthe Subterrene bit. Directional change is possible Group, Inc., Bechtel Corp., San Francisco, either mechanical means or by controlling the 3 . W. E. Boyd, Industrial and Business Trainingtemperatures circumferentially around the b i t . Bureau, Petroleum, Univ. of Texas, Austin, TX. In exploration and resource assessments , Sub- 4. M. Carasso, Project Mgr., Geothermal Technologyterrene devices m i g h t make small-diameter, shallow Assessment Study for The Futures Group, Inc., Bechtel Corp., San Francisco, CA.(e.g. , 50-m-diam by 150-m-deep) , self-cased holes 5. Tony Chasteen, Engineer, Union Oil o f Calif.,for thermal-gradient measurements. Many such holes Santa Rosa, CA.will be needed i n the near future. For production 6. Joe Cook, Rock B i t Production Mgr. , Administra-wells and systems, there are two specialized back-up tion Div. Hughes Tool Co., Houston, TX.or auxiliary devices that could be used in conjunc- 7. Glenn Damewood, Tech. V.P., Southwest Research Institute, San Antonio, TX.tion with conventional rotary dri 11ing systems. 8. John P. Finney, Project Engineer, Geysers,First, a hole-stabilization tool for use i n caving Pacific Gas and Electric Co., San Francisco, CA.formations, hydrating or swelling clays, or lost- 9. Jim French, GTE Data Bank, U. S. Geological Survey, Garden Grove, CA.circulation zones. This tool would be a thermal 10. Ed Gallo, Director of Research, Hughes Tooldevice producing either a rock-glass lining or i n - Co., Houston, TX.jecting structually stabilizing materials into the 1 1 . T. C. Gipson, Calvert Western Exploration Co.,borehole walls. Second, the tool would be used Tulsa, OK.for completing holes into production zones where 12. Bill Glass, V . P. and Operations Mgr., Big Chief Drilling Co., Oklahoma City, OK.h i g h s t a t i c temperatures and h o t fluids are en- 13. John Goode, Cement Lab., Halliburton Services,countered and where reservoir contamination i s n o t Duncan, OK.desirable. 14. R. Greider, Senior Geological Consultant, In certain water or steam reservoirs, or i n Chevron Oil, Minerals Staff, San Francisco, CA.magmas and lavas that are difficult t o penetrate 15. J . L. Kennedy, Editor, O i l and Gas Journal,with rotary d r i l l s , Subterrene systems could be Houston, TX.used t o produce entire production wells. Produc- 16. R. T. Littleton, Bureau of Reclamation, Boulder City, NV.t i o n fields would probably include waste-water re- 17. Jack Marsee, V. P. Engineering, Loffland Bros.injection wells and injection wells for production- Drilling Co., Tulsa, OK.augmentation purposes. These l a t t e r type we1 Is , of 18. John McNanee, Bureau of the Census, Waryland.smaller diameter than the production wells, could 19. R. W. McQueen, V. P . , Dresser Security Bits,have the same diameter as the exploration wells. Houston, TX.Note that one of the desirable requirements for 20. K. Mirk, P. Witherspoon,and H. Wollenberg, Lawrence Berkeley Lab., Univ. of Calif., Berkeley,small exploration boreholes i s t h a t the holes be CA.readily enlargeable, i f desired, to the size of a 21. Howard Morton, Technical Repr. , Rocky Mts., Baroid Div., N. L. Industries, Inc., Tulsa, OK.production well. With conventionally cased holes, 22. M. Newsom, R. Alvis and C. Morse, Sandia Corp.,such an enlargement i s very difficult and costly Albuquerque, NM.because the casing i s very securely cemented into 23. Dexter Polk, V . P., Dresser Oil Field Productsplace. In a glass-lined hole the l i n i n g might be Div. , Houston, TX.either reamed out w i t h a rotary b i t or i t could be 24. Henry J . Ramey, J r . , Dept. of Petroleum Engi-melted and the hole enlarged with a Subterrene b i t . neering, Stanford Univ., Stanford, CA. 4. Contacts Made t o Discuss Geothermal Well 25. W. Randall, Research, Amoco Production Co., Tulsa, OK.Drilling Problems. The following people were will- 26. R. W. Sartor, Dresser Industries, Dallas, TX.i n g t o discuss drilling problems and contribute . . 27. Calvin Saunders , Gen Mgr Research,data that were useful i n preparing report LA-56894, Hal 1i burton Services , Duncan , OK."Geothermal W1 1 Technology and Potential Appl ica- e 28. H. Snow and V. E. Suter, District Operations Mgr., Union Oil Co. of Calif., Santa Rosa, CA.tions o f Subterrene Devices - A Status Review. 1. A. L. Austin, Lawrence Livermore Lab., Univ. 29. Ken Tanner, Mgr. Tech. Services, Baroid Div., of California, Livermore, CA. N. L. Industries, Inc., Houston, TX.52
  • 30. Ted Welp, I n t e r n a l Revenue Service, U. S. 2. System Model Treasury Dept., Washington, DC. a. GEOWELL. A computer program c a l l e dW 31. Jim Youngblood, V. P., Houston, TX. Dresser Magcobar, GEOWELL was developed t o analyze the c r i t i c a l tech- n i c a l and economic aspects o f a Subterrene w e l l - B. Geothermal Well Systems and Cost Analysis production sjstem. System assumptions and the var- 1. Introduction. I n l i g h t of t h e f a c t t h a t a ious technical and cost elements t h a t make up the s i g n i f i c a n t p a r t o f t h e cost o f a geothermal energy model are presented i n the f o l l o w i n g discussions. e x t r a c t i o n f a c i l i t y i s associated w i t h w e l l costs, Because b o t h r o t a r y and rock-melting systems are improvements i n geothermal w e l l d r i l l i n g technology cost-optimized f o r producing d i f f e r e n t p a r t s of a would be p a r t i c u l a r l y b e n e f i c i a l , When the h o t d r y w e l l , the program contains both r o t a r y and rock- rock (HDR) and geopressurized e x t r a c t i o n systems m e l t i n g p r e d i c t i o n c a p a b i l i t i e s f o r deep geothermal are developed, geothermal energy could become very wells. For future studies and as more geothermal important as a n a t i o n a l energy source. According * w e l l data become available, t h e programs capa- t o estimates made by White and Williams, the geo- b i l i t i e s can be expanded t o include a complete thermal energy resource a v a i l a b l e t o H R and geo- D spectrum o f geothermal we1 1 types. pressurized systems i n t h e regional conductive en- b. Well Designs. Two e x p l o r a t o r y gas vironments (depths down t o 10 km, n o t i n c l u d i n g any w e l l s o f recent years, d r i l l e d under d i f f i c u l t Q, 33 500 000 methane c o n t r i b u t i o n ) i s x 10l8 J conditions and t o record depths, used some o f t h e (8 000 000 x 1 0 l 8 c a l = 31 800 x 10l8 Btu). This b e s t r o t a r y d r i l l i n g technology a v a i l a b l e today: i s 2600 times t h e estimated value f o r conventional (1) E. R. Baden No. 1 d r i l l e d t o 9158 m (30 050 ft) steam and h o t water geothermal energy resources and and (2) Bertha Rogers No. 1 d r i l l e d t o 9583 m 440 000 times the t o t a l U.S. energy consumption i n (31 441 f t ) i n t h e Anadarko Basin i n Western Okla- 1972 o f 75.9 x 1 0 l 8 J. homa by Lone S t a r Producing Co. o f Oklahoma City. Both HDR and geopressurized w e l l s can be d i f - A f t e r reviewing w e l l designs used i n many other f i c u l t t o produce. Hot d r y rock w e l l s are i n t e n - w e l l s both i n t h e U.S. and abroad, t h e designs o f t i o n a l l y made i n s o l i d and p r e f e r a b l y very h o t base- these two w e l l s were selected as guidelines f o r ment rock, hence t h e i r name, whereas geopressurized GEOWELL. Figure V-5 shows the w e l l design f o r a w e l l s are i n h i g h pressurized (approaching l i t h o - t o t a l depth o f 10 km d r i l l e d completely by r o t a r y s t a t i c ) and d i f f i c u l t - t o - d r i l l formations. A study b i t s . Moderate formation and f r a c t u r e pressures, was i n i t i a t e d on t h e a p p l i c a t i o n o f the Subterrene i.e., approximately hydrostatic, were assumed i n the concept t o t h e p r o d u c t f o n o f these d i f f i c u l t - t o - d r i l l upper 4300 m. High pressures, i.e., approaching wells. The basic study o b j e c t i v e s were t o : l i t h o s t a t i c , were assumed from 4300 t o 7000 m. e Study t h e a p p l i c a t i o n o f t h e Subterrene Thereafter, t o t o t a l depth, i t was assumed t h a t concept t o the production o f deep w e l l s such as pressures were moderate again. Figure V-6 shows may be used f o r h o t d r y rock o r geopressurized geo- the w e l l design when rock-melting b i t s are used thermal energy e x t r a c t i o n systems. below the 660-mm (26-in.) hole section. It was 0 Make technical and economic comparisons assumed t h a t the 914- and 660-mm holes would always w i t h r o t a r y d r i 11i ng techniques and sys tems. be made by r o t a r y d r i l l i n g . Below the bottom o f The r e s u l t s are published i n LASL r e p o r t t h e 660-mm hole, r o t a r y d r i l l s would continue t o LA-6555-MS, "Technical and Cost Analysis o f Rock be used u n t i l i t was desired t o s t a r t rock melting. M e l t i n g Systems f o r Producing Geothermal Wells" The s i z e of t h e hole a t t o t a l depth i n t h i s w e l l i s by J . H. Altseimer (October 1976) and a r e sum- i d e n t i c a l t o t h a t thown f o r t h e a l l - r o t a r y case. marized i n t h e f o l l o w i n g sections o f t h i s r e p o r t . However, note t h a t intermediate hole and casing sizes are smaller due t o t h e advantageous use o f the rock-glass l i n e r . c. Surface Equipment. Surface equipment *White, D. E. and Williams, D. L., Ed. "Assessment requirements f o r a combined rotary/rock-me1 ti ng o f Geothermal Resources o f t h e U.S. 1975," - U.S.G.S. C i r c u l a r 726 (1975). 53
  • 914 M (36 IN,) HOLE M (30 In.) E CASIWG, T 5 66-3m (26 IN.) !iOLE 19.0 M - [406 m (16 IN.) PILOT HOLE] 508 M (20 IN.) 6 5 CASING. T 16.1 m 406 M ( 6 IN.) HOLE 1 - OP OF ROCK ! L E HOLE i TD E 436 M (16 IN.) HOLE YITH LIGHT GLASS LINER u M (7 IN.) P l l O CASING, T 18.5 PLY 8 ?40 M tl3.37 IN.) PllO CASING, M (5 IN.) P u o M % T u.1 M I, 299 rn (U.8 IN.) HOLE WITH - HEAVY GLASS LINER NODERUE HOLE WIT!! LIGHT 200 ~y.l PRESSURES GLASS LINER 10 OM] M- 127 M T -(5 IN.) P l l O CASING, 12.1 MFig. V-5. Well design for the all-rotary drilled Fig. V-6, W1 1 design for rotary/rock-melted well. e we1 1.system are similar t o those now used for all-rotary The inner tube has a tight sliding f i t a t the j o i n tprojects. Also, the power levels required for rock for electric contact, b u t no axial forces can bemelting are compatible with those already required transmitted. Handling and operational character-on rotary deep-we1 1 rigs , e.g. , up to 3000 hp. In i s t i c s of t h i s pipe are very similar to those ofGEOWELL, the drilling contractors cost i s divided conventional d r i l l pipe. The i n i t i a l cost i s ap-into rig (CRIG) and drill-pipe (CPIPE) costs. For proximately three times higher b u t this disadvan-these estimates 1973 oil and gas data were compiled tage i s reduced by an enhanced operating lifetimefrom the open literature and then upgraded to 1975. for the Subterrene pipe due t o the fact t h a t Sub-Using EL as the total target depth in meters, the terrene pipe does n o t rotate and i s n o t exposed t oresultant curve-fit equations used i n the program the usual rotary pipe fatigue stresses and f r i c -are: t i onal wear.CRIG = 1453 -+ 0.2022 (EL) -+ 10.19 x (EL), $/d BONDED COAXIAL ALUMIMM DRILL PlPE FOR A TYPICAL IOOOOm TOTAL DEPTH WELLCPIPE = 106.8 - 0.0419 (EL) + 20.55 x 10-6(EL)*, $/de d. Drill Pipe. Design studies produced aSubterrene d r i l l pipe capable of carrying b o t helectric current and the downflow of drilling fluid.The pipe is shown i n Fig. V-7 and consists of twoconcentric 7075 aluminum tubes separated by a 2-mn-thick layer of material that,, structurally bonds thetubes together and acts as an electric insulator.A conventional tool j o i n t on the outer tube serves [Aluminum L S e a l 8 Eiaclrkal LElaclrkal. Thermalas the structural connection w i t h adjacent pipe. Condvclon Insulation inrulolionThe current i n the outer tube flows across thethread contact surfaces and the smooth metal con- F i g . V-7. Subterrene coaxial a1 umi num dri 11-pipe concept.t a c t and sealing surface a t the joint leading edge.54
  • A pipe with an 0.d. of 140 mn (5.51 i n . ) was equations give a range of ROP from 592 m/h a t found t o f i t well i n a l l sections of the boreholeBd being studied and was therefore selected as a spudding-in t o 1.2 m/h a t 10 000-m depth. Meterage ranges from 884 m i n i t i a l l y to 64 m a t 10 000-m standard. Thus, in the GEOWELL analysis the 0.d. depth. For rotary bits catalog data was used for i s maintained a t 140 mm, whereas the other dimen- carbide bits. The rock-melting b i t costs, PENC, sions are varied to meet current and load criteria. are based on Subterrene program experience and are Costs are calculated on the basis of these dimen- defined by the following equations, where DPEN is sions t o arrive a t a basic material and fabrica- penetrator diameter i n meters: tion cost. Other estimates are made as to deliv- PENC = 1286 + 20556 (DPEN) + 69053 (DPEN)2, 1975 $. ered pipe cost, pipe lifetime, drilling contrac- tors profit, etc., to finally arrive a t a Subter- f . Electric Power Generation and Trans- rene drill-pipe cost i n dollars per day. mission. For power transmission a1 ternating current e. Bits. The Subterrene b i t required for is the better choice over direct current for several producing deep wells is the me1 t-extruding type important reasons, the most important one being using either gas or liquid as the drilling fluid. corrosion. The presence of dc electric power flow- The assumed design-point b i t performances are a i n g i n a conductor immersed i n mud o r drilling fluid lifetime of 300 h and a rate of penetration (ROP) would enhance production of corrosion c e l l s due t o of 1 mm/s (11.8 ft/h) a t a rock temperature of the potential gradient along the conductor. Such 283 K. Note that rock temperature i s specified corrosion would be particularly detrimental around because ROP varies w i t h rock temperature. Attain- any conductor anomaly such as a threaded joint. B y i n g and demonstrating longer lifetime and higher its inability t o establish and support such corrosion ROP remain development problems for m e l t i n g b i t s . cells, ac has a distinct advantage. Direct-current Another problem is obtaining sufficient clearance equipment capable of a continuous voltage change between the glass former (located immediately be- over a wide range would be costly, bulky, and d i f - hind the melting face) and the hole so as t o facil- f i c u l t t o control. However, such voltage require- i t a t e b i t travel during trips. A clearance of ments could be met easily by the combination of an several millimeters on the radius i s desirable to ac power source and transformer or saturable reactor. prevent b i t damage or high-pressure drops across The use of ac also has some disadvantages such as the b i t d u r i n g f a s t trips. A t least five approaches inefficiencies due to hysteresis, dielectric losses, to solving this problem have been identified. and changing power factors. However, w i t h proper GEOWELL also includes rotary-bi t performance design, the small losses remaining in the trans- estimates. Field performances vary widely depend- mission circuit and other related equipment are ing on s i t e and operating conditions. An attempt acceptable. For power-cost estimates, GEOWELL i n - was made to simulate relatively easy rotary d r i l l - cludes calculations for the costs of diesel electric i n g i n the sedimentary upper formations and harder generators amortized over 10 yr as well as diesel drilling i n the deeper, more crystalline forma- fuel costs. tions. The equations defining performance vs 9. Drilling Fluids. The drilling fluid depth used i n the program are for rotary penetra- for a rock-melting system has to perform the follow- t i o n rate, RROP, a t any rotary depth, ROTEL, i n i n g functions: (a) form solid debris, (b) cool the meters : glass-former section, (c) control formation pres- sures and prevent caving, ,(d) carry out debris, RROP = 591.62 x (ROTEL)06739, m/h (e) hold solid additives in suspension under stag- and for b i t meterage: nant flow conditions, ( f ) reduce corrosion, and - ROTEL < 1440 m: BITM = 884.0 0.553 (ROTEL), m/bit (9) lubricate moving pipe o r casing. Based on - ROTEL > 1440 m: BITM = 97.0 0.0033 (ROTEL), m/bit. rotary drilling experience, drilling fluids like Some additional performance variations are included water, water-based muds, oil-based muds, etc. , could perform functions (c) through (9). I t is t o account for multiple operations like pilot holes estimated that functions (a) and ( b ) could also be followed by hole-opener operations. The above 55
  • handled even though t h i s c a p a b i l i t y has n o t y e t pressure, i s assumed w i t h m u l t i p l i e r s o f T.5, 30.0, been demonstrated experimentally. For t h e we1 1 and 0.77 on density, viscosity,and heat capacity,models s e t up f o r t h i s study i n which high forma- respectively .t i o n pressures are postulated, muds are deemed 0 The f l o w r a t e o f the d r i l l i n g f l u i d i sessential t o c a r r y o u t function ( c ) . based on upper annulus dimensions and i s calculated Open-literature data f o r mud costs i n o i l and t o be s u f f i c i e n t t o move the excavation debris gas w e l l s were used t o estimate the mud costs f o r (assumed as spherical p a r t i c l e s ) upward a t a veloc- the r o t a r y w e l l model. For normal geothermal i t y equal t o the terminal v e l o c i t y o f the p a r t i c l e s gradients, the t o t a l mud costs, CMUD, are: m u l t i p l i e d by 1.5. 0 Maximum p a r t i c l e diameter i s 10 mm w i t h a EL > 1354 m: CMUD = 21912 - 28.64 (EL) + 0.0108 (EL)2, 1975 $. density o f 2700 kg/m 3 . e F r i c t i o n f a c t o r s f o r the pipe and annulus For Subterrene mud costs, the b e n e f i c i a l e f f e c t s are based on absolute roughnesses o f 4.57 x o f the precise hole s i z e control w i t h rock melters and 3.05 x respectively. compared t o r o t a r y and also g l a s s - l i n i n g b e n e f i t s 0 T o o l - j o i n t pressure losses are zero i n s i d e i.e., i s o l a t i o n of mud from the formations, re- the d r i l l pipe because o f f l u s h design. Outer- s u l t e d i n an estimate t h a t Subterrene mud costs j o i n t losses are estimated.are Q, 0.75 times rotary. 0 Heat t r a n s f e r through the w a l l o f the co- h. Hole Support. The f o l l o w i n g glass- a x i a l aluminum pipe i s included. l i n e r c h a r a c t e r i s t i c s were assumed: (1) the s o l i d - e Heat t r a n s f e r t o o r from the surrounding i f i e d melt seals the hole e f f e c t i v e l y ; (2) the rock i s included, based on t r a n s i e n t heat conduction collapse strength o f the rock-glass l i n e d w a l l i s i n a s e m i - i n f i n i t e slab as a f u n c t i o n o f d r i l l i n g high; (3) l i n e r w a l l thicknesses are controllable; time. and (4) l i n e r t e n s i l e strengths are n e g l i g i b l e . 0 Heat a d d i t i o n t o the d r i l l i n g f l u i d from For the s t e e l casing used i n the modeled wells, the debris and cooling o f the glass l i n i n g i s i n - the conductor and surface casing are made o f low- cluded as a lump sum a t the penetration location.cost K-55 grade steel, whereas the remainder i s 0 Heat a d d i t i o n along the length o f the stemmade from a higher grade such as P-110. Casing due t o power-transmission losses i s included. costs were obtained from i n d u s t r i a l catalogs. 3. Study Results. The GEOWELL a n a l y t i c a l Cementing costs i n d o l l a r s per u n i t volume are r e s u l t s presented i n t h i s section are l i m i t e d t o mainly based on LASL h o t d r y rock geothermal the most severe technical conditions, i.e., a rock- d r i l l i n g experience. With the i n p u t dimensions, melting b i t advancing a t 1.0 mm/s a t the bottom o f the program calculates the weight of the casing a 10 000-in deep w e l l . Figure V-8 p l o t s the mass and the delivered-casing costs. For cement costs, flow r a t e required t o l i f t the debris i n the annulus the t o t a l volume o f delivered cement i s calculated as a function o f debris diameter f o r the w e l l de- f o r the w e l l model being considered, and t h i s sign i l l u s t r a t e d i n Fig. V-6. For the maximum volume i s m u l t i p l i e d by the appropriate cost i n p a r t i c l e s i z e o f 10 mm, the required mud f l o w r a t e d o l l a r s per cubic meter. i s 46.1 kg/s. Ifthe maximum p a r t i c l e s i z e (and i. Thermal and Hydraulic Conditions. hence flow r a t e ) i s reduced, then the corresponding Equations f o r the thermal and hydraulic conditions increase i n maximum mud temperature i s as shown i n i n rock-melted boreholes were s e t up t o f a c i l i t a t e Fig. V-9. Even i f the flow r a t e i s halved t o the evaluation o f rock melting. The f o l l o w i n g 23 kg/s, corresponding t o a p a r t i c l e s i z e o f 2.5 mm, assumptions are incorporated i n t o t h i s p a r t o f the the maximum mud temperature would s t i l l be a rea- program. sonable 336.5 K, even a t the high geothermal grad- 0 Geothermal temperatures increase l i n e a r l y i e n t w i t h a rock temperature o f 1033 K a t t o t a l w i t h depth. depth. Thus, the mud f l o w r a t e i s established by e A t y p i c a l d r i l l i n g mud, based on water the particle-removal c r i t e r i o n and n o t by the mud properties as a f u n c t i o n o f temperature and temperature.56
  • NOMINAL MELTING ROP : I m m / r NOMINAL MELTING ROP: Imm/s DATA APPLICABLE OVER 25 TO 7 5 K l k m - Y Gea gradlent*75 K/km QEOTHERMAL GRADIENT RANGE Bottom rock temprmlurr- IO33K (1399%) Ot I 0 0 2 4 6 8 IO Particle Diamater(mm1 I I I I I 0 2 4 8 8 ioFig. V-8. Typical mud f l o w r a t e vs debris p a r t i c l e Particle Diameter (mm) diameter f o r rotarylrock-me1 ted 10 000-mdeep we1 1 . For a p a r t i c l e diameter o f 10 mn t h e horse- Fig. V-9. Maximum t y p i c a l mud temperatures f o r rotary/rock-me1 t e d 10 000-m-deep w e l l .power required from the w e l l i n l e t t o t h e o u t l e t i sn, 720 hp. Taking i n t o account surface i n l e t pres- b e n e f i c i a l e f f e c t s o f higher rock temperatures onsure drops and motor i n e f f i c i e n c i e s , the actual the m e l t i n g process. These c a l c u l a t i o n s do n o tpump power might have t o be as h i g h as 900 hp, i n d i c a t e any p a r t i c u l a r power-transmission problemsw e l l w i t h i n the range o f power l e v e l s on c u r r e n t t o depths as g r e a t as 10 000 m f o r any o f the ex-d r i l l i n g r i g s . The t o t a l pressure drop between amples studied.the d r i l l pipe and the annulus f l o w channel i s 4. Cost Analyses18.04 MPa (2620 p s i ) , o f which 11.56 MPa (1680 a. Normal Geothermal Gradient Wells.p s i ) i s i n t h e d r i l l pipe and 6.48 MPa (940 p s i ) Figure V-10 shows both r o t a r y and Subterrene c o s ti s i n the annulus. I n c o n t r a s t t o t h e normally p r e d i c t i o n s vs t o t a l depth. The Subterrene w e l l shigh drops across r o t a r y b i t s , the drop across the use optimized r a t i o s o f r o t a r y t o Subterrene w e l lrock-melting b i t i s n e g l i g i b l e . Using the co- depth intervals,and the geothermal gradient i sa x i a l aluminum p i p e f o r a 10-km w e l l and i n c l u d i n g 25 Wkm. For these w e l l s the s t a t e - o f - t h e - a r tan allowance f o r a 650 000-N (146 000-lb) break- nominal m e l t i n g r a t e o f 0.2 mm/s i s n o t cost-away load, the maximum s t r e s s i n the aluminum pipe competitive with r o t a r y . The r a t e s r e q u i r e d f o ri s 364 000 kPa (52 700 p s i ) a t a y i e l d - t o - l o a d the melted w e l l s t o equal t h e r o t a r y - d r i l l e d w e l ls a f e t y f a c t o r o f 1.33. Under normal operating costs range from 0.24 t o 0.42 mm/s f o r 10 000- andconditions a t t h i s depth t h e maximum s t r e s s i s 5000-m deep wells, respectively. However, a t 0.6o n l y 170 900 kPa (24 800 p s i ) . Thus, no severe m/s the c o s t savings o f melted over r o t a r y w e l l sstress problems are indicated. range from 18 t o 8% f o r 10 000- and 5000-m deep The GEOWELL program c a l c u l a t e s the various wells, respectively, and a t the r a t e o f 1.0 mm/sdownhole losses, t o t a l required power, and t h e the corresponding savings are 23 t o 16%. Thesetransmission e f f i c i e n c y assuming t h a t t h e coaxi a1 savings are f o r w e l l s being made under r e l a t i v e l yaluminum d r i l l pipe i s used t o t r a n s m i t a l t e r n a t i n g cool, normal-gradient conditions.current. T o t a l power required ranges from 580 t o b. High Geothermal Gradient Wells. A hot740 k a t depths o f 5000 and 10 000 m, respec- W w e l l i s defined as one t h a t has a bottomhole tem-tively. The 10 000-m e f f i c i e n c y tends t o remain perature o f 673 K (752F). Very few s t a t i s t i c s a r ehigh compared t o t h e 5000-m values because o f the a v a i l a b l e f o r t h i s c l a s s o f w e l l s because (1) n o t 57
  • GEOTHERMAL GRADIENT:25 K/km 1 4 I I I I 1 1 (lo3 f t ) 1 6 20 24 28 32 IO I 1 I I 9- 8- - *7- z mns- - r- cn (n5- t;; s 4- -I -I 9 3- 2- I- 1 I I I I IFig. V-10. Well cost vs total depth i n cool wells with a geothermal gradient of 25 K/km.many very h o t geothermal we1 1s have been drilled Fig. V-11. Well costs vs total depth in hot wells w i t h various melting b i t performance.and (2) l i t t l e detailed data have been released Rock temperatures increase linearly toby the companies dri 11i n g the we1 1s. Nevertheless , 673 K (752F) a t total depth for a l l wells.estimates can be made to allow a comparison ofSubterrene and rotary systems. The procedure used c. Study Conclusions.i s t o apply correction factors to the appropriate e The GEOWELL computer program i s a good simu-cost equations in GEOWELL. The computed results lation of deep and d i f f i c u l t wells of the type de-for hot wells as defined above are shown i n fined, allowing the evaluation of major technicalFig. V-11. Because a l l bottomhole temperatures o r cost items. Other well models could be specifiedare assumed to be 673 K, the geothermal gradients and the program adjusted accordingly for furthervary with depth, b u t across the range of data studies.plotted a l l gradients are above normal. I t can e The Subterrene concept can be combined w i t hbe seen that w i t h the state-of-the-art nominal conventional drilling operations without major oper-melting rate of 0.2 m / s , the Subterrene well cost ational perturbations. However, for very hot bore-i s not much different from that for rotary d r i l l - holes, a change i n system design and operation isi n g . A t 0.6 mm/s, midway between current and indicated to develop the capability of maintainingprogram target rates, the cost savings are signifi- continuous , or nearly continuous, circulation whilecant (20 and 17%for 10 000-and 5000-m depths, working i n the hot p a r t of the borehole. Thisrespectively) , and are also greater than for applies t o both rotary and Subterrene systems.comparable depth normal-gradient wells. A t 1 mm/s e Subterrene performance of O.P-mm/s pene- Q,the Subterrene cost is indicated as being 30 and tration rate and 100-h b i t l i f e can, i n some cases,21% less t h a n rotary for 10 000-and 5000-m depths, provide marginal cost savings. However, i f therespectively .58
  • Subterrene system achieves the performance goal of The basic AYER code provides a time-dependent solu- 1 mm/s penetration rate and 300-h b i t l i f e , then tion to the nonlinear two-dimensional heat conduc-bl Subterrene-produced wells would be significantly t i o n equation in plane or cylindrically symnetric less expensive t h a n rotary. In h o t wells (673-K coordinates with temperature- and time-dependent bottom temperature) savings of 30 and 21% are material properties. This basic code incorporating predicted f o r depths of 10 000 and 5000 m penetrator material properties, in situ rock prop- respectively. Even i n cool , normal-gradient con- erties,and various treatments of the radiation has ditions, the savings are favorable, ranging from been used extensively. 23 to 16%for depths of 10 000 and 5000 m re- Two specific additions t o the basic code have spectively. extended the usefulness of AYER. One is the inclu- e Penetration rates of 0.4 t o 0.6 mm/s also sion of a hydrodynamics subroutine for the melt- result i n significant savings for deep geothermal layer flow. This treatment of the melt-layer hydro- wells. dynamics was developed for the VFQ code. I t s i n - e All other Subterrene design or operational corporation in AYER eliminates the necessity of problems t h a t were studied appear t o have viable separate set-ups and the transferring of data from solutions. one code t o the other. Since this routine calcu- e The most interesting feature of the d r i l l - lates the velocity flow field i n the melt and the ing by melting concept i s to form rock-glass liners hydrodynamic forces on the penetrator, i t gives the on the borehole wall. These liners offer oppor- imnediate interaction of the melt velocities and tunities t o solve well-production problems associ- temperatures with the internal temperature d i s t r i - ated with hole control , l o s t circulation, casing bution. The calculated forces on the penetrator, design, cementing,and highpressure packers. which are extremely sensitive to the surface tem- C. Mathematical Modeling and Analysis perature distribution, are automatically available 1. Introduction. The analysis effort has been for each change of penetrator configuration. A directed a t understanding and predicting Subterrene second addition was an energy deposition routine performance and in guiding new penetrator designs. for heating the melt layer a t the leading edge with The program has included the development and use an electrical current. The present form of t h i s of detailed computer programs adapted t o the spe- calculation has proved useful where the electric c i f i c geometries, physical phenomena, and material field could be assumed t o have a simple distribu- tion. I t gives the effect of the temperature-de- properties germane t o Subterrene performance. The development of analytical models has contributed pendent electrical resistivity of the melt on the power distribution and provides t h e interaction t o the basic understanding of specific relation- between the power deposition, heat flow,and hydro- ships such as the leading edge flux limitations and the thrust-veloci ty dependence. Also of major dynamics. An extension of this routine could i n - importance was the theoretical calculation of mate- clude a more complete solution of the Maxwell equa- rial properties when the experimental values were tions for the electric field configuration in the case of spatially dependent resistivity and dielec- not appropriate or available. The application of these models and techniques to specific designs t r i c constant. and the interpretation of t e s t results has received Other special -purpose codes have been written the largest portion o f the analysis program time. t o address the problems unique t o the Subterrene penetrators. For instance, VFQ i s a f i n i t e differ- a. Computer Program Development. The f i - ence program for computing steady-state thermal and nite element code AYER has been the single most hydrodynamic characteristics o f the melt flow to important analysis tool and has seen the most ap- determine such things as required thrust loads and plications to Subterrene problems because of the thickness profile of the melt layer. PLACID, a ease of operation and the versatility provided by finite-element program for stress analysis, has been the subroutine input. Any desired additional pro- used for the thermal and loading stress analysis of gramming can be included i n the five subroutines. the heated penetrator. 59
  • b. Analytical Models. A number of simpli- the thermal conductivity of liquid basalt was cal-fied analytical models have been used to examine culated with three different theories. For basaltspecific physical phenomena that affect the perform- these three methods give results from 0.10 to 0.34ance of Subterrene penetrator systems. In many cases W.m-’.k-’. A value of 0.25 W-m-l-k-’ was chosen forthese models have supplemented the more comprehensive the performance calculations. Thus f a r these methodscomputer programs and contribute to the overall have been applied only t o basalt b u t could be usedunderstanding by isolating specific effects. Some for any rock f o r which the sound speeds are knownhave been incorporated into the computer programs or for the solid and l i q u i d and f o r which the viscosityhave yielded specific results that were used i n the i s known as a function of analysis. These models have been used t o An analytical parameter study of the leadingcalculate material properties, the leading edge flux, edge flux was also developed which considers thethe thrust-velocity relationship, stem cooling, and effects of surface temperature, rock and melt thermalmelt-heating stability analyses. Some of these conductivities, and a f i n i t e radius of curvature formodels will be briefly reviewed here and the effects the leading edge. One significant result i s thaton the penetrator performance calculations will be the infinite radius of curvature or f l a t plate limitoutlined i n the next section. holds for the flux a t the leading edge for most Since the conditions a t the penetrator leading penetrators and operating conditions achieved thusedge are critical i n the determination of velocity far. This result i s valid for rocks w i t h a meltand thrust for a given penetrator surface temperature thermal conductivity less than that of the soliddistribution, i t i s necessary to calculate the radia- rock, advance rates of ~ 8 . 2mn.s-’,and radii oftive and conductive fluxes accurately. The data curvature >5.0 mm. Models that predict the force-available indicates that, above the melting temper- velocity relationship have been useful for scalingature, rocks and glasses are transparent t o radia- the penetrator thrust w i t h the velocity and materialtion over distances of several millimeters. This properties. In one case the total force requiredimplies that the t h i n melt layers (4.5 m ) are for a penetrator moving i n a medium w i t h continuousoptically t h i n . An optically thin approximation for properties i s developed. In another the leading edgeradiation crossing the melt layer was developed and - force’is derived with a model that recognizes ex-installed i n AYER. A maximum in total flux i s in- p l i c i t l y the discontinuous nature of the propertiesdicated when the optical thickness of the layer i s a t the melt-rock interface. Other analytical ap-one; that i s , when the melt can reradiate and i s proaches have examined the general effects of pene-s t i l l transparent. A t this maximum the total flux trator geometry on performance, stem cooling problems,is only ~ 2 0 % higher than the total flux occurring and the power-velocity relation.when the optically thin approximation i s applied. c. Status of the Calculations. Two phasesMainly because of the low emissivities of refractory of the analysis effort will be discussed: that d i -metal penetrators, radiation can contribute only a rected a t the production of specific penetrator de-small fraction of the required leading edge flux. signs and that directed a t predicting’penetrator I t i s the molecular contribution to the thermal performance as determined by the laboratory tests.conductivity of the melt that controls the leading AYER has been used to produce a number of meltingedge flux and the penetrator performance. The ther- body designs including the heater configurations andmal conductivity of basalt and many other rocks has refractory metal body geometry for consolidators andbeen measured to temperatures well above melting. extruders. These designs were accomplished with ex-However, the heat flux due t o the radiation cannot tensive parameter studies. The body geometries andbe separated from that due to molecular motion w i t h - heater configuration have been adjusted through manyout detailed knowledge of the temperature and fre- iterations to provide a good leading edge flux andquency -dependent absorption coef f i ci ents of each to insure that material temperature 1imitations wererock sample,and thus i t has been necessary to pro- met over a wide range of power and advance rates.duce theoretical calculations of the thermal conduc- The calculational procedure was generally for steady-tivity. An average molecule model was adopted,and state conditions and includes the melt layer and60
  • surrounding rock. The HARE extruder has been tested With the power and temperature d i s t r i b u t i o n sextensively as designed,and i t s performance i n ba- determined, the steady-state f o r c e on the penetrators a l t i s w e l l understood i n terms o f t h e analysis. by a well-developed m e l t l a y e r can be determined.The calculated temperature d i s t r i b u t i o n and power The hydrodynamic forces applicable t o t h e Subterrenelosses have been compared w i t h a c a l i b r a t i o n experi- geometries have been developed fo the Navier-Stokes rmment f o r the 114-mm c o r i n g penetrator i n an argon- equations and applied t o penetrators. The t h r u s tf i l l e d quartz container. I n an unusual application, values a r e a1 so extremely sensi t i v e t o the otherthe c a l c u l a t e d azimuthal temperature d i s t r i b u t i o n properties o f t h e m e l t layer: the v i s c o s i t y , t h ewas c o r r e l a t e d w i t h the c o r r o s i o n r a t e s f o r the thermal c o n d u c t i v i t y which determines the c r i t i c a lextended area penetrator. thickness a t t h e leading edge, the surface tempera- The l a b o r a t o r y t e s t i n g program generally pro- t u r e d i s t r i b u t i o n , and the m e l t v e l o c i t y f i e l d . Thevides data on instantaneous values o f heater power, i n c l u s i o n o f the hydrodynamics subroutine o f VFQ i nadvance r a t e , t o t a l t h r u s t , and temperature a t one AYER has provided the temperature d i s t r i b u t i o n andp o i n t i n the r e f r a c t o r y body during the course o f v e l o c i t y f i e l d i n the same c a l c u l a t i o n . Good ap-approximately 1-m t o t a l penetration. Because o f i n - proximations t o the r a d i a t i o n and molecular thermalhomogeneities i n t h e n a t u r a l rock samples, these c o n d u c t i v i t i e s are provided by t h e t h e o r e t i c a l c a l -q u a n t i t i e s vary considerably. However, averages culations. For t h e HARE penetrator i n basalt, t h i scan be taken over s h o r t periods during which steady canplete treatment has given reasonable t h r u s t valuess t a t e has been achieved between programmed changes on the assumption t h a t t h e HARE i s l i m i t e d by theo f t h r u s t , rate, o r power. These r e s u l t s can then f o r c e on the leading compared w i t h t h e r e s u l t s o f steady-state calcu- 2. The Thrust-Velocity Relationship f o r Ex-lations. This comparison i s most e a s i l y discussed t r u d i ng Penetrators .i n terms o f the power-velocity and the t h r u s t - a. Introduction. Calculations o f t h e t o t a lv e l o c i t y re1a t i o n s h i p. t h r u s t required t o maintain a given advance r a t e f o r For both consolidators and extruders the steady- Subterrene penetrators are d i f f i c u l t f o r variouss t a t e power as a f u n c t i o n o f v e l o c i t y depends on the reasons. For c o n s o l i d a t i n g penetrators, t h e f o r c elosses t o t h e unmelted rock, the m e l t l a y e r heat r e t a r d i n g the penetrator does n o t necessarily r e s u l tcapacity, and the stem c o o l i n g losses. For extruders from the pressure required t o move t h e viscous melt.the energy c a r r i e d o f f i n the debris must a l s o be I f the leading edge i s r e t a r d i n g the advance becauseincluded. The rock losses (energy conducted away o f i n s u f f i c i e n t heat f l u x , the concentration of t h efrom t h e penetrator beyond the me1t i n g isotherm) , f o r c e on a small area o f the s o i l o r rock can r e s u l tdepend i n t u r n on the heat capacity and thermal con- i n compaction and plowing o f t h e unmelted material,d u c t i v i t y o f t h e i n s i t u r o c k and the temperature and t h i s f u r t h e r complicates the t h r u s t - v e l o c i t ydistribution. The m e l t l a y e r and d e b r i s power are relation. I f t h e advance i s being retarded by t h edetermined by the heat o f fusion, m e l t heat capacity, consolidation requirement, t h i s c o n d i t i o n i s s a t i s -and c o r r e c t average d e b r i s and m e l t l a y e r tempera- f i e d by a d d i t i o n a l m e l t i n g o r by a combination oftures. The stem losses depend on penetrator geometry, m e l t i n g and compaction o f the c o l d o r heat-softenedc o o l i n g methods, and debris removal methods. E s t i - unmelted material. This l a t t e r e f f e c t has n o t beenmation o f t h e stem losses, which are u s u a l l y a small included i n the hydrodynamics codes used f o r thef r a c t i o n o f t h e t o t a l power, has n o t encountered any thrust calculations. However, t h e thermal analysiss i g n i f i c a n t problems. Since t h e c a l c u l a t e d and ex- o f e x i s t i n g penetrators i n d i c a t e s t h a t the consoli-perimental powers agree f a i r l y w e l l , i t can be as- d a t i o n c o n d i t i o n i s n o t always met a t t h e v e l o c i t i e ssumed t h a t the data f o r the important physical prop- achieved i n experiments. I f t h i s i s t h e case, forcese r t i e s ( i n p a r t i c u l a r the thermal c o n d u c t i v i t y of required f o r compaction could be t h e dominant c o n t r i -t h e s o l i d , the heat o f fusion, and t h e heat capaci- b u t i o n t o the thrust. The s i t u a t i o n f o r extruderst i e s ) are o f s u f f i c i e n t accuracy f o r t u f f and b a s a l t i n dense b a s a l t i s d i f f e r e n t w i t h no compaction oc-t h a t the AYER temperature d i s t r i b u t i o n s are c o r r e c t . c u r r i n g and no consolidation requirement. The f o r c e 61
  • on the penetrator results from the pressures re- The emissivity of the penetrator surface ( E ~ )isquired t o force the melt to the extruding ports. taken to be an average over wavelength for molyb- *Considerable data has been accumulated for the denum. The emissivity for the rock a t the meltthrust-velocity relationship for two extruders i n interface (€,,,)is n o t known; i f i t i s assumed t o bebasalt. However, the three-dimensional nature of near 1.0, then the effective emissivity i s 0.25.the melting surface of the extended area penetrator Experimental determinations of the thermal con-precludes any detailed analysis. The HARE extruder ductivity generally do not separate the radiative **has cylindrical symnetry throughout and i s amenable and conductive contributions. Because the meltt o computer analysis. Since the exterior of the layers a t the leading edge of most penetrators arebody i s parallel to the axis of symmetry, most of so t h i n , the contribution due t o molecular motionthe force i s on the f l a t annular leading edge. T h i s dominates and i t must be estimated separately.component of the force can be obtained approximately In Sec. C. 3,three theories are used to calcu-from a simple analytical model. Also, the two- l a t e the molecular thermal conductivity of an aver-dimensional geometry can be accomnodated by the AYER age rock ( S O 2 ) in the liquid phase. The phenomeno-heat conduction code. When used in conjunction with logical approach similar to t h a t of Bridgeman was useda subroutine based on the hydrodynamic analysis i n t o scale the conductivity from the solid to the liq-VFQ, this code will calculate a steady-state tempera- q u i d on the basis of the sound speed. The molecularture distribution, a melt velocity field, and a collision theory of Horrocks and McLaughlin was usedpressure distribution; and hence, determines a simul- with basalt viscosities determining the parameters intaneous power, advance rate, and thrust, In t h i s the molecular potential. The phonon transport modelreport, one steady-state analysis of the HARE pene- of Liebfried and Schlsmann for a perfect crystal wastrator i s discussed and compared w i t h time-averaged modified t o a form appropriate to a liquid. All threeoperating conditions for the laboratory model in models gave similar results and indicate an upperbasalt. limit of 0.34 W-m-l-k-1 for the conductivity i n the b. Material Properties. The properties o f temperature range of 1500 to 2000 K. A will be seen, sthe rock melt critical to the thrust calculations calculated values of the leading edge thrust can beare the specific heat, heat of fusion, density, and brought i n t o approximate agreement with the axperi-the thermal conductivities, both molecular and radi- mental values i f the radiation flux i s limited byative. Eq. (V-1) and i f a value of 0.25 W.m-.k- 1 i s used for The radiative contribution to the flux i s taken the thermal conductivity of the melt.t o be that given by the optically t h i n approximation. The viscosities of the equilibrium melts ofThis flux i s given by several basal ts have been measured. In particular, that of Jemez basalt was obtained a t Corning and the FR = E n 2 a(Ts 4 - Tm4 ) . uniform melts of t h o l e i i t i c basalts were also exam- *** ined during recrystallization by Shaw. These re- * s u l t s are plotted i n F i g . v-12. However, the be-The index of refraction i s n = 1.5 and CJ i s the havior of basalt as i t melts i s not known. For theStefan-Bo1 tzmann constant. The effective emissivity calculations considered here, i t i s assumed that i tis exhibits no significant liquid behavior below the melting temperature. In the melt layer a f i t t o the & s Em Corning data is used, and i n the analytical model E = E s + E m - E s E m x Touloukian, Y. S., and D. P. DeWitt, Thermal Radi- ative Properties, Vol. 7, (Plenum Publishing Corp. , Nw York 1970). e* ** Hess, H. H., and A. Poldervaart, Basalts, (John Murase, T., and A. R. McBirney, "Thermal Conduc-Wiley & Sons, Nw York, 1968). e t i v i t y of Lunar and Terrestrial Igneous Rocks in Their Melting Range," Science 170, 165-167 (1970). *** Shaw, H. R., "Rheology of Basalt i n Melting Range," J. Petrology lo (3), 510 (1969).62
  • W I F i g . V-13. Geometry o f HARE penetrator annular 1eadi ng edge. simple expression for the force-velocity relation- ship that explicitly recognizes the existence o f the I0 O melt-rock interface and the discontinuities of the I300 1500 I0 70 1900 TEMPERATURE ( K ) physical parameters a t the me1 ting temperature. Figure V-13 depicts a radial section through the melt Fig. V-12. Viscosity of basalt as a function o f layer for a penetrator with the HARE geometry. In temperature. this approximation the me1 t layer is characterized by a uniform thickness L and an average viscosity a value given by average melt temperature is used. -= ~(n determined by an average temperature. Con- * The density, specific heat,and heat of fusion sistent with these assumptions i s the assumption represent typical basal ts . that the velocity in the melt layer i s parabolic i n c. A Model for the Leading Edge Forces. A the radial direction number of analytical models g i v i n g the various com- ponents of force on a rock-melting penetrator have been produced. The treatment detailed here deter- mines the force resulting from t h e pressure gradient required t o force the melt from between the me1 t- where 6 = 6 ( x ) . Then u = a t L / 2 and u = 0 a t rock interface and the penetrator. I t assumes the y = 0 or L . An average velocity can be defined as existence of a melting isotherm a t which the mater- ial properties are discontinuous. The melt layer thickness and me1 t i n g temperature appear explicitly in the results, and above the melting temperature the me1 t i s represented by average uniform proper- ties. The shear rates a t the penetrator and melt surface If a penetrator i s operating in the correct are mode its advance rate (v*) will be limited by the leading edge force. In blunt extruders this force will dominate and i t will be convenient t o have a &I =4j=12u 0 L L * Clarke, B., e t a l . , "Rock Properties Related t obd - Rapid Excavation," University of Missouri Rolla, PB 184 767 (March 1969). 63
  • The continuity equation gives approximately, f o r an The melt layer thickness i s related to the meltannulus of effective radius R, properties and temperature by P c (2a Re) = uo (2r Re) + pi v* (2a Rx) , A - Tm) c= p V* (Cv 6T + H ) - FR ¶ (V-3which for pi = P gives which comes from the leading edge flux requirement. - = xv*+ u o u t , Fc t FR = AAT + FR = pV* (Cv 6T t H)where uo i s the average melt velocity a t the outsideedge (see Fig. V-13). The pressure gradient required Here 6T = Tm - Ta,where Ta i s the ambient tempera-t o move the melt a t a constant velocity i n the pres- ture and H i s the heat of fusion.ence o f a viscosity i i s i These equations are best suited for assessing the relative effects of penetrator t i p geometry, average material properties, and operating conditions. The value of force obtained depends on v * ~ , AT, and the third power of the material properties whichThe pressure i s taken to be a function of x only, makes the results sensitive to the choice of thesince the velocity i n the y direction i s small. appropriate average quantities. With the operating conditions of v* = 0.20 x rn-s-’ and Ts = 1900 K and material properties A = 0.25 W . m - l - f l , p = 2.7 x lo3 k g ~ m - ~ Cv = 1.25 x loe3 J-kg’l-K-’, H = 420 x , lo3 J-kg-’, and = u(T) = 5.0 N-s-m-2, w obtain for e the radiation flux, FR = 0.24 W’m- 2 , the melt layer thicknessThe resulting pressure is 24 F uo e= 0.10 n , p = x2 + - x , e2 e2 and the forcewhich gives r i s e t o a force on an annulus of width L F = 2.97 kN ,of, which i s i n essential agreement w i t h the 4 . 0 kN used F [= P dA 2 8a R V* - + 24a R L3 u uo 7 . L2 t o obtain t h i s velocity i n the laboratory. e3 e In a d d i t i o n to this simplified model, detailed steady-state computer analyses of the HARE penetratorIf uo = 0; that i s , i f no melt flows into the t h i n were carried out. The thrust calculations were im-annulus between the f l a t t i p and the unmelted rock, plemented with the addition of a hydrodynamics sub-then the force on the advancing face i s routine adapted from VFQ. During the iteration for the temperature solution, this subroutine uses the current melt temperatures to calculate the melt vis- cosities. From the conservation of mass and the Navier-Stokes equations, the velocity field in the melt i s calculated. The forces on the penetrator due64
  • t o the melt pressure and viscous drag are then de- and melting body powers. The points are the re- . termi ned sults of the simple model of Eq. (V-2). The points The procedure for one s e t of operating condi- @ and are the AYER results for a leading edge tions required the manual adjustment of the melt- temperature of % 1800 K. The dashed curve connects rock interface geometry between computer runs t o ob- . points scaled by v* 4 Unfortunately, these data tain internal consistency. T h i s was carried out for were obtained before thermocouples were installed in a velocity of v* = 0.15 mm-s-’ and a maximum molyb- the HARE melting body, and no correlations of cal- denum temperature of % 1900 K. A t the mid-point (in culations and experimental points with the same the radial direction) of the leading edge, the re- measured body temperatures can be made. However, a sulting surface temperature and melt layer thickness good agreement between me1 ting body power and advance were TS = 1800 K and L = 0.18 mn with an average rate has been obtained, Fig. V-15, and a temperature temperature of % 1600 K. The calculated leading distribution for a given velocity can be inferred edge force i s 1.09 kN with an additional axial force from the AYER calculations. I t should also be em- of 0.22 kN on the conical throat. For these condi- phasized that the reduction of the experimental data tions the model of Eq. (V-2) gives 0.76 kN, again in required a judgement a s t o whether or not steady f a i r agreement with the 2 to 3 kN needed to maintain state had been reached and includes an average over t h i s velocity in the laboratory. The situation i s an oscillating instantaneous velocity. illustrated in Fig. V-14 which i s a plot of force d. The Force on a Conical Section. The versus advance rate. The results of the calculations limiting effect of the leading edge flux has long discussed above are compared to some of the experi- been recognized and experimental verifications of mental results. The solid closed curves bracket the higher velocities for penetrator designs that can experimental data envelope for various basalt samples eliminate this difficulty have been carried out. A conical consolidator w i t h a diameter of 57 mn was HARE Penetrotor In Dense Basolt i c. a P K EXPERIMENTAL DATA EDGE ONLY - t @ AYER :LEADING @ EDGE ONLY AYER i TOTAL 1 Q Calculated Laboratory Data I I 102 1 I I I I 0.00 alo 0.20 0.2s VELOCITY (mrn s-’) 4 Power (kW)w Fig. V-14. Required thrust as a function of advance Fig. V-15. - Advance rate melting power and total power relationships for HARE extruding rate for the HARE extruding penetrator. penetrator operating in basalt. 65
  • used in basalt with a predrilled hole to remove the TABLE V-4rock that would normally be melted by the leading RESULTS OF CONICAL SECTION TESTS I BASALT Nedge region of the penetrator. The leading edge ad- W H PREDRILLED HOLE FOR LEADING EDGE I Tvances unrestricted and the hole i s melted to a larg- Average Body Measured Calculatede r diameter by the conical section with a length of Rate Temperature Thrust Thrust110 mm and half angle 0 = sin-’ 0.11. If the surface - (mn s-1) (K) (kN) (kN) Basalt 0.85 1770 4 6.5of the penetrator i s a t an angle of 0 t o the direc- Basalt 0.5 1690 4 6.9t i o n of advance, then the mass flux perpendicular t othe surface i s reduced by the factor sin 0. The melt conductivity of liquid basalt due to molecular motionlayer thickness i s then given by Eq. (V-3) with v* with that implied by the actual performance of Sub-replaced by v* sin 0. The expression for the force terrene penetrators. The force required to maintaini s further modified by the factor sin2 4. One factorof sin 4 i s for the effective velocity and one for a given penetrator velocity i s proportional t o the inverse cube of the thermal conductivity of the sur-the component of force parallel t o the penetrator rounding melt. Since most of this force i s accumu-axis. If two penetrator elements occupy the same lated i n the t h i n layer a t the leading edge whereannular area projected on a plane perpendicular to the conductive flux dominates, the calculated forcethe penetrator axis, then the force required t o ad- i s sensitive t o the value assumed for the liquid ther-vance each a t a given velocity will scale approxi- mal conductivity. The forces calculated by detailedmately as sin 20. Tab1 e V-4 1i s t s thrust calculated with this computer simulation of the penetrator and the viscous melt best match laboratory values i f 0.25 W/m-K i sapproximate model along w i t h some experimental re- used for the thermal conductivity. The data ofsults. The average advance rates are considerably *larger than the maximum (‘L0.25 mm-s-’) observed for Murase and McBirney for Columbia River basalt waspenetrators limited by the leading edge in basalt. used i n the simulations for temperatures below melt- i n g (1450 K ) . This data i s plotted i n F i g . V-16 asThe body temperature, taken to be the surface temper- the solid line labeled CRB. This basalt becomesature in the calculations, i s somewhat lower than transparent t o radiation near the melting temperaturethat usually achieved. For 2000-K temperatures, thevelocity could approach 1.0 mn-s-’ for t h i s conical and an abrupt r i s e in effective conductivity occurs.section. The calculational model includes many ap- The contribution due t o molecular motion i s masked by the radiation a t temperatures above 1450 K. Theproximations and does not include physical effects thermal conductivity of a liquid can be estimatedsuch as glass-former drag and the variations of phy- w i t h several theories, three of which are outlinedsical rock properties between samples; hence, only here. In the discussions which follow, thermal con-approximate agreement can be expected. ductivity represents only the molecular conduction 3. Liquid Basalt Thermal Conductivity Investi- and does not include any radiation contribution.gation. A number of circumstances combine to make The f i r s t i s a scaling based on the conductivitythe heat transfer due to molecular conduction domi- of the solid and the temperature dependence of thenate over radiation in the melt layer a t the leadingedge of Subterrene penetrators. These include the velocity of sound. The thermal conductivity can be written phenomenologically aslow emissivities of refractory metals, material tem-perature limitations, and the extreme thinness of theme1 t layer. Most high-temperature experimentalmeasurements of liquid rock thermal conductivity CM- wherebine the effects of conduction and radiation i n = an appropriate specific heat Cv -f a i r l y thick samples. Because the radiative proper- c/3 = velocity of sound averaged over threet i e s of liquid rocks are n o t well known, the radia- spatial directions.tion contribution to the flux cannot be accurately e = the mean free path.subtracted o u t . This situation has prompted a com- *parison of theoretical estimates of the thermal Murase, T., and A. R. McBirney, “Thermal Conductivity of Lunar and Terrestrial Igneous Rocks in Their Melt- ing Range,” Science 170, 165-167 (1970).66
  • where k = 1.38 x J*K- i s Boltzmanns constantW m = 20 x 1.66 x kg i s the atomic mass. This value i s close t o the measured value o f C = 3 P 1.1 x 10 f o r some basalts. Also, t h i s average l i q u i d has a distance between molecules o f d = 3.25 x 1 0 - l o m . 0 z s If = d i s used f o r the s o l i d , the thermal con- d u c t i v i t y given by Eq. (V-5) i s CALCULATED VALUES HM ---__ --0 AB (300 K) = 1.5 W-m- .K-l , I- FROM THREE MOOELS AND PENETRATDR DATA -PEN-- _________B O 1330 zoo0 m which i s close t o the measured value f o r CRB a t 500 la00 TEMPERATURE (K) 300 K. So the average mean f r e e path f o r the energy c a r r i e r s (phonons) consistent w i t h the measured t h e r - Fig. V-16. L i q u i d b a s a l t thermal c o n d u c t i v i t y r e - mal c o n d u c t i v i t y i s the dimension o f the space a v a i l - sul t s . able t o each molecule. Ifi t i s now assumed t h a t t h i s i s also t r u e f o r the l i q u i d , then from Eq. This can be separated f u r t h e r i n t o the contributions 0-5) o f longitudinal (L) and transverse ( t ) modes. AB (1500 K) = 0.38 W.m-lbK-l . Two o f the three l o n g i t u d i n a l modes c o n t r i b u t i n g t o X correspond t o i n t e r n a l modes o f the molecules, The sound v e l o c i t i e s i n basalt are given approximate- the remaining one t o the t r a n s l a t i o n o f the mole- l y i n Table V-5. L i q u i d b a s a l t w i l l be considered cules. I f i t i s f u r t h e r assumed t h a t i n t h e l i q u i d t o be composed o f average t r i a t o m i c molecules w i t h (but n o t i n the t i g h t l y bound s o l i d ) the i n t e r n a l molecular weight A = 60 and which contain atoms o f modes do n o t t r a n s f e r energy during a c o l l i s i o n , average weight A = 20. These values are f o r S i O z then a lower l i m i t t o A B i s obtained: and are close t o the average f o r basalt. The den- s i t y ( p ) o f l i q u i d b a s a l t i s 2.7 x lo3 k g - ~ n - ~ .The AB (1500 K) = 0.13 W*m-l-K-l . classica s p e c i f i c heat i s These values are i n d i c a t e d on Fig. V-16 by the dashed Cv = 3 = 1.25 x m lo3 J*kg-l-K-l , l i n e s labeled B. A second method i s the molecular c o l l i s i o n model * o f Horrocks and McLaughlin. This u t i l i z e s i n f o r - mation obtained from v i s c o s i t y data, which i s a v a i l - able f o r some basalts. Assumptions must be made con- TABLE V-5 cerning the type o f packing o f the molecules occur- SOUND VELOCITIES IN BASALT (mms-l) r i n g i n the l i q u i d and the type o f p o t e n t i a l between molecules. They o b t a i n f o r the thermal conductivity, S o l i d (300 K) Liquid 5.0 lo3 3.0 x 10 3 - c,e Tye, R. P, Thermal Conductivity (Academic Press Ct 3.7 lo3 0 Inc. , London, 1969). 67
  • 1/2 AHM = 0.34 W.m-.Kl , .(V-6) which i s indicated i n Fig. V-16 by the line labeledHere : HM . = 3k Another approach is t o modify the theory of * u3/v It v* = 1/2 Leibfried and Schlomann for a perfect crystal. They a = ( ~ v ) obtained for T > e v = volume per molecule E and u are the depth and zero crossing i n the LM potential : J where : h = 6.62 x J-S i s Plancks constant M = mean atomic mass r = molecular separation d = v1/3 M = molecular mass v = volume per atom z = coordination number of l a t t i c e 8 = Debye temperature L1 , M, are l a t t i c e sumnation constants. T = absolute temperatureThe l a t t i c e constants are taken t o be Z = 12, L1 = y = -3 (Ln e)/a (Ln v) i s the Grheisen an-22.11 and M1 = 10.56, corresponding t o a face-cen- harmonici ty parameter.tered cubic l a t t i c e . The estimation of u and 6 from The Debye temperature isv i scosi ty can be compl i cated, and the fol 1owingsimplified procedure i s used here. For the LM po- J htential e = T ; ~ L, 116 where vL i s the highest vibrational frequency of the u = R/2 , l a t t i c e . T h i s is obtained by integrating over thewhere R i s the separation a t minimum potential. Debye spectrumSince the molecules of a liquid are bound R % d =v1j3. The viscosity (TI) of liquids can be written g(v) = 4RV v2 (2 ct-3 + c i 3 ) . E - In the liquid there are only longitudinal modes w i t h kT n=noe Y N degrees of freedom; so on integrationwhere E is the depth of the potential seen by a 113molecule moving through the l a t t i c e and results from vL=(-) Yb i n d i n g t o n neighbors; E i s the depth of the po-tential for binary interactions. Let E be approxi- where V/N = v , the volume per atom. For liquid ba-mated by s a l t e 2 385 K; so the condition i s met on Eq. (V-8). The anharmonicity parameter can be written E = E/n . 0-7 1 Tye, R. P . , Thermal Conductivity (Academic PressFor basalt E = 41.5 x lo- J and for closely packed Inc. , London, 1969).spheres n = 12. Equation (V-7) then yields68
  • i melted by the leading edge region a the penetrator. With the penetrator body temperature below the oper- W ating maximum, sustained rates of j u s t under 1 mn/si were attained. This represents a factor of 4 to 5j times the rate that would have been expected i f the Y = Y1 + Yp leading edge heat flux were controlling the rate. Experimental confirmation of this analytically pre- The f i r s t term i s equal to 1/2; the second reduces dicted result led to a major research program to i n - to troduce techniques f o r increasing the available lead-! ing edge heat flux. 4. Stem Cooling w i t h Particle Transport. One of the analytical approaches to the general problem M of the effects of penetrator performance on stem where p = - i s the density. Data to evaluate y2 for V cooling has been the development o f an analytical a liquid basalt was not available. A rough estimate model and computer program to calculate stem cooling based on the solid data i s y2 % 3.75. The thermal characteristics with a centrally extruding penetrator. conductivity can now be estimated as This model includes the transport of, and heat trans- f e r from, highly idealized melt/solid particles i n = 1o3 0.67 x -W-m" .K-l the extrudate carry-off tube. A particular concern YLS T has been that the wall of the central extrudate tube gets hot enough to cause melt sticking near the "tip"1 and i s labeled LS in Fig. V-16. I t must be emphasized or penetrator end. A flow schematic of the system t h a t t h i s method in particular i s extremely sensitive modeled is shown in Fig. V-17. In this particular t o the longitudinal sound speed and i t s dependence on density. COOLING GAS All of the above methods involve gross assump- +I tions and would p r o f i t from more data for the funda- mental parameters (cl, E, 0 , etc.). However, they I 61 1 72 DEBRIS EXIT COOLING exhi b i t reasonable agreement with the thermal con- ductivity implied by the performance of Subterrene penetrators as indicated by the line labeled PEN i n Fig. V-16. Using a value of 0 2 W-m"-K- .5 for the thermal conductivity of molten basalt i n the computer simula- tion program, i t becomes evident that the penetration rate of an extruding penetrator is limited by the k a t f l u x that can be provided a t the leading edge (flow stagnation point). Based on allowable temperatures i n the molybdenum body, the calculations indicate that the leading edge heat flux will r e s t r i c t pene- tration rates i n basalt t o approximately 0.25 mm/s. Away from the leading edge, however, the conical ELTING shape of the melting body provides a significant PENE- geometrical enhancement,, and much higher penetration + RATOR VP rates are possible. T h i s concept was demonstrated i n the laboratory t e s t usSng a conical shaped pene- W trator melting into a basalt sample that was pre- drilled to remove the rock t h a t would normally be Fig. V-17. Flow schematic for stem model calcula- tions. 69
  • model, a short section of stem near the t i p end tip-end gas temperatures (or total stem lengths) for(0 z y - YZ) has a different flow geometry and wall < gas flow rates of 40 g/s (70.7 SCFM) and 100 g / smaterial t h a n the remainder of the stem. A t the (176.6 SCFM) f o r nominal conditions. These resultsstation y = YZ a heat load referred to as "tip con- indicate that as the net heat transfer t o the fluidduction" i s assumed to be added t o the total cooling i s reduced by conduction i n t o the rock, the tip-endgas flow coming down channel 1 (the "downcomer"). gas temperature quickly approaches a limit,and fur-This represents heat conducted from the melting ther increases i n stem length do not increase thispenetrator and from the hot rock in the region gas temperature. This tip-end temperature i s approx- < <0 - y - YZ. After the t i p conduction heat i s added, imately the maximum gas temperature, and the maximumthe flow i s s p l i t into two streams. One stream con- inner tube wall temperature closely follows this gastinues down a revised channel 1 and becomes the cen- temperature. This i s true even when a thermal re-tral "upcomer" flow i n channel 2 a t y = 0 where the sistance corresponding t o a relatively thick layerrock-melting debris i s introduced. The other be- of rock deposited on the tube wall i s included.comes the outer annulus "upcomer" flow in channel 3 Calculations for conditions different from thesea t y = YZ. The flow balance and downcomer pressure can be made quite easily for stem geometries of theare controlled by sonic restrictions a t y = 0 for general type of the 86-mn penetrator. Changes canflow into channel 2 and a t y = YZ for flow into be made t o the program f o r other geometry types,channel 3. Melt i s assumed t o be introduced already such as a single upcomer stem.formed in solid-like particles moving a t a low ve- 5. Melt-Heating Analysis.locity a t the t i p end, y = 0. These particles are a. Introduction. The concept of increasingassumed t o be rigid, spherical, and of uniform size the advance rate of rock-melting penetrators by theb o t h a t a given axial station and throughout the direct deposition of energy in the melting rock withlength of the stem. This i s obviously a simplifica- ohmic heating holds technical promise i f certaintion of the true particle characteristics, b u t by fundamental difficulties can be overcome. Highervarying the particle diameter parametrically i t can advance rates can be expected i f power i s depositedbe assumed that any significant effects of particle in the melt layer to mitigate the effect of the lowirregularity will be observed. melt thermal conductivity in isolating the h o t pene- A t any axial station the steady-state heat trator from the unmelted rock. In principle i t wouldbalance i s a result of convective heat transfer from be advantageous t o deposit the energy directly i n thethe particles (which are assumed to be a t a uniform unmelted rock; however, a l l penetrator electrode con-temperature), to the fluid in channel 2; combined figurations considered here result in deposition inradiative heat transfer from the particles and con- the higher temperature molten rock. This i s due t ovective heat transfer from the fluid i n channel 2 t o the highly nonlinear dependence o f the resistivitythe counterflowing fluid i n channel 1; and for y > of rock on temperature in the melting range. In t h i sYZ there i s heat transfer from channel 1 to channel report a simple model i s presented which estimates3 , and from channel 3 to ( o r from) the surrounding the velocity enhancement that can be expected withrock. In addition, as stated above, a lumped heat direct melt heating for a leading edge limited an-load i s added t o the total flow a t y = YZ. Equa- nular penetrator. Some of the problem areas are thetions for the heat balance and particle velocity are selection of a leading edge insulator, materials com-developed and are integrated numerically starting a t patibility, the s t a b i l i t y of the melt current d i s t r i -y = 0 with an assumed gas temperature a t the t i p end. bution, and the effects of natural inhomogeneities onIntegrations are terminated when the gas temperature the current distribution. Only the current d i s t r i -i n channel 1 (the downcomer) i s reduced t o the pre- bution will be considered here. Small amplitude per-scribed gas i n l e t temperature. The value of y a t turbation theory i s used to examine the conditionsthis point, then, i s the total stem length corres- under which the current distribution becomes unstableponding to the assumed tip-end gas temperature. in the t h i n annulus of rock melt a t the leading edge. Calculations were made of the 86-mm extruding b. Leading Edge Analysis. I t i s necessarypenetrator over a range of particle diameters and t o resort to the computer model to determine the70
  • temperature profile across the melt layer during temperature is plotted as a function of distancesteady-state advance and energy deposition. The from the penetrator surface a t the position labeledtemperature dependence of the electrical resistivity B i n Fig. V-18. Curves 2 through 5 i n Fig. V-19 areof the melt i s given by for the velocities indicated,and the melt power has been adjusted t o give a maximum temperature a t B of approximately Ts = 1950 K. The outside o f the melt layer i s a t Tm = 1450 K, the center o f the melting range of basalt. Curve 1 of F i g . V-19 i s for aVelocity effects make the one-dimensional model i n - velocity of 0.15 mm-s-’ w i t h no melt heating. Heretractable unless simplifying assumptions are made. the maximum molybdenum temperature (%1900 K ) occursAn energy deposition routine was installed in AYER a t the inside surface o f the metal body,and the tem-to deposit power i n the melt layer a t the leading perature is close t o linear w i t h position. To f a - c i l i t a t e a comparison of the two cases i t i s notededge of an insulated penetrator. The assumption i smade that the voltage gradients are parallel to the that w i t h melt heating the AYER temperature profilessurface of the insulated t i p . Then, w i t h the total can be f i t t e d closely with the parabolamelt current specified, the current density d i s t r i -b u t i o n across the melt layer and the local powerdensity, i 2 p , can be determined. The calculationsthen include the effects of the temperature-depend- which i s plotted as the dashed curves i n F i g . V-19.ent power deposition and melt velocity field on the Then, approximatelyheat transfer and hydrodynamic force solutions. Fordirect comparison with a conventional penetrator,the HARE geometry was used. An insulating nose i n -s e r t with the properties of boron nitride replacesthe conventional molybdenum leading edge. This and the conductive f l u x i s twice that of the almostgeometry i s illustrated in Fig. V-18 where item A linear, no melt-heating case a t the melt-rock inter-i s the boron nitride insert. face. The mass-averaged temperature is The case to be considered f i r s t i s that of anadiabatic leading edge. In these calculations theheater was adjusted to provide a zero temperature (V-lo)gradient a t the surface of the boron nitride. T h i scan be seen i n F i g . V-19 where the calculated - 1 I MOLY p +--r Il MOLY / II R II I200 90 PENETRATOR 0.I 0.2 y (mm) 0.3 0.4 0.5 SURFACE - - AXIS OF SYMMETRY - Fig. V-19. Calculated melt layer temperature pro-Fig. V-18. Penetrator geometry for me1 t-heating f i l e s as a function of penetration analysis. velocity with and without melt heating. 71
  • whereas, for the linear case i t i swhich i s somewhat lower. With the use of Eqs. (V-9), (V-lo), and (V-11) the expected reduction i n theleading edge force a t a given velocity can be ob-tained. For example, consider the curves 1 and 5 ofFig. V-19 for a penetrator velocity of v* = 0.15 , /-mn-s". From Eq. (V-10) w have for the melt heat ecase, T 1 1800; for curve 1, Eq. [V-11) gives T 11625. The effective viscosity for melt heating canbe a factor of 4 down from the conventional case.Also, Eq. (V-9) shows that f o r a given flux a t themelt-rock interface, and hence for a given velocity,the melt layer i s approximately twice as thick forthe melt-heating case. Since the force scales asL- 3 and as K, a given velocity with melt heating t too 0 01 . 0.2 03 . 0.4 05 0.6could require a thrust force as l i t t l e as 1/32 of VELOCITY ( m m * i )t h a t required w i t h o u t melt heating. I n fact, AYERand simple model calculations predict even lower Fig. V-20. Thrust force a s a function of penetrationthrusts. velocity w i t h and w i t h o u t melt heating. The situation i s illustrated i n Fig. V-20. whichi s a p l o t of force versus advance rate. The per- case the values of I! used i n Eq. (V-12) are takenformance map for the conventional HARE penetrator is from the AYER calculations. Because of the broadrepeated i n the upper l e f t corner. The closed curve maximum in the temperature curve, L i s n o t as sensi-brackets the experimental performance for various tive to the surface temperature as i n the linearbasalt samples and melting body powers. The points case. In practice, maintaining any given velocity are calculated with the simple model of Sec. requires an accurate control of thrust and internalC.2and include only the leading edge component of and melt powers, The upper dashed curve was obtainedthe force, given by by scaling the point (1850 K) w i t h F = v * ~ and represents a more conservative operating temperature. F = 8aR T ( k - . (V-12) If a uniform melt layer and power deposition can be maintained, i t should be possible t o obtain perfor- mance between the two curves without overheating theThe points and@ are the AYER results for the penetrator t i p .leading edge and total forces corresponding to the c. Instabilities in the Current Distribution.melt temperature profile of curve 1 in Fig. V-19. The temperature dependence of the resistivity givesFor most conditions the leading edge force i s pro- r i s e to a power density in the melt t h a t i s sensi-portional t o the fourth power of the velocity for a tive to the temperature. If the voltage gradient i sconstant leading edge temperature. The dashed lines constant, the power density increases w i t h increasingi n Fig. V-20 connect points scaled by F a v * ~ . The temperature. I f the current density i s constant,calculated performance of a HARE w i t h melt heating the power density ( p = i 2 p ) decreases with increas-i n basalt i s also plotted i n Fig. V-20 w i t h the same ing temperature. W are now concerned w i t h the ef- enomenclature as the conventional case. A second re- fects of this on the current and temperature d i s t r i -s u l t of AYER a t v* = 0.5 m . ~ - for a lower surface bution in a t h i n melt layer bounded by the insulatingtemperature (1850 K ) i s shown. For the melt heating penetrator leading edge, the rock-melt interface, and
  • Such a treatment applies only when the instabilities I’ begin b u t provides no information on the large ampli- tude limit. The conditions for growth will depend on the power deposition and the damping effects of the conduction and convection losses. The following assumptions are made: 1. Sinusoidal perturbations 2. Conduction losses from sides (z = 0, L) are neglected 3. Adiabatic condition a t melt-rock interface 4. Melt layer has no inhomogeneities. The conservation of energy gives, for the vol- ume element RL dxFig. V-21. Rectangular model used for current s t a b i l i t y analysis.the electrodes. W will consider a rectangular e /pC dV = 1 4 dV + /F-dA + JpC Tv-dAmodel which applies t o the annular penetrator w i t h dE = dQ + dPf + dPv . (V-13)R >> L. In Fig. V-21 the penetrator surface i s a ty = 0, the melting interface a t y = z, and the elec-trodes are a t z = 0 and z =L. For any such pair o f W assume the temperature i s of the form eelectrodes only the voltage V and the total currentI can be regulated. T = T + T~ eat sin wx = T+ (V-14) B an instability w mean a local change T in y e wheretemperature, whose magnitude increases with the time,from the value of the average melt layer tempera-ture required for a steady-state velocity of v*.- i s an average over the melt layerT The growth rate a can then be evaluated. From Eq. (V-14) f =m [ ’ Tdm ’ e t layer m1 1 aT a = -- T at *These instabilities can occur since a local increasei n temperature lowers the resistivity, which results Writing d i approximately asi n higher current density and power density, which int u r n continues the increase i n temperature. T h i scan cause an uncontrolled increase of temperaturethroughout the melt layer (thermal runaway) or theoccurrence of local high-current channels. A will s w obtain from Eq. (V-13) ebe seen, for voltage control both thermal runawayand channeling will be more likely than for current 1 + dPf + dPV) @ dV a = T ~ Cd (V-15)control. If the total current i s constant, thelocal current density can vary and produce channel- Each term on the r i g h t will consist of a steady-stateing ; however, thermal runaway i s prevented. To de- term and a contribution t o the growth rate: sotermine the quantitative conditions for the onsetof the growth o f instabilities for the condition of a = u +af+av q ,constant total current, w w i 11 use smal 1-amp1 i tude etemperature perturbation theory; that i s T << 7. 73
  • and the steady-state terms must cance T h i s i s the only term sensitive t o the shape of the instability. There is no steady-state contribution, (dj + dPf dPv and the growth rate, i n this case negative, i s dV dV)ss = O + WKeThe growth rates and the steady-state terms are de- u K =- - PC *termined by an expansion of each term of Eq. (V-15)i n a power series i n T. The zero-order terms rep- I t can also be shown that the inclusion of a radi-resent the steady s t a t e , and the remaining terms ation conductivity results i n no additional f i r s t -give the growth rates. For small-amplitude theory order terms,and the equilibrium value o f the radi-only the first-order terms i n T are retained. Gen- ation conductivity can be included i n Ke. Evenerally,a resulting from the power deposition will though the penetrator temperature i s maintained so 9be positive; af and av resulting from conduction that there i s no heat exchange w i t h the melt layerand convection losses will be negative. The pro- i n steady s t a t e , conduction from the instability t ocedure i s straightforward and will only be outlined the penetrator can provide some damping. The powerhere. density loss i s For the power deposition term the temperature-dependent r e s i s t i v i t y is expanded,and i t i s assumedthat the total current can be held constant by ex- dP F (T) J = P .ternal control. T h i s results i n a growth rate of dV e The flux F (T) depends on the y-dependence of T and (V-16) P on the properties of the penetrator t i p . However, the thermal resistance of the penetrator t i p willHere n = B/T, h = 2a/w i s the perturbation wave- dominate, and f o r an appropriately chosen conductionlength, v* i s the advance rate, L i s the melt layer length (A) f o r the insulator, the damping r a t ethickness, and C is the circumference of the annulus. becomesThe second term i n Eq. V-16 i s the damping provided Kby the constant-current condition. I t is not signi- p E -4K,A e ?mficant for perturbations small in extent compared t othe circumference of the penetrator. The melt layer The next significant term results from the mass flowthickness (e) can be determined by equating the con- ( i n the z-direction) across the layerductive flux to the mass-velocity flux a t the melt-rock interface. Then, f o r basalt w i t h Tm = 1450 K dPv = pC(vL TL - Vo To)Ldx . (V-17)and a penetrator surface temperature of Ts = 2000 K Considering f i r s t the HARE geometry, vo = 0, and as- - a - np~v*~ suming that the same perturbation applies t o TL as Ke t o T, w have ewhere Ke i s the thermal conductivity of the melt. The power density i n the element due to heat av . - 3LLV*2 - .flux can be separated into conductive and radiative Keparts and into x and y components. For the power To this point only temperature perturbationsloss by conduction t o the r e s t of the melt layer have been considered. However, since temperature(x-direction) , profiles can be established across the gap i n a time short compared to the risetime of temperature per- turbations, i t will be assumed that e and Ts retain the relationship74
  • dP $= -$(vLf-VoT0) - ? v L ~ .This r e s u l t s i n a p o s i t i v e c o n t r i b u t i o n t o a o f The a d d i t i o n a l term i n dPv/dV Iss necessitates an increase i n dQ/dV t o maintain the steady-state ve- l o c i t y v*. The corresponding increase i n a i s q - - v0 T - T owhich f o r basalt and v* i n mn-s-l i s A = a q n r T T . Further damping i s provided by the new term i n aV. The s i z e o f these terms i s determined by vo, whichThis i s the o n l y term r e s u l t i n g fo t h i s combined rm depends on the geometry and the advance rate. Formode; however, as seen i n the graph o f Fig. V-22, i t convenience m i s defined ascontributes s i g n i f i c a n t l y t o the onset of i n s t a -b i lit i e s . m = AR/h R L , I f the geometry of the penetrator i s such t h a tvo i n Eq. (V-17) i s n o t zero, two other e f f e c t s need -be considered. For a constant vo = vo the power where AR i s the area through which rock enters the1o s t per u n i t vol ume becomes r e s e r v o i r and 2s R L i s the approximate f r o n t a l area o f the leading edge. Then PERTURBATION WAVE LENGTH (mm) I 2 3 4 5 6 7 a v - - -’ - * (1 + m) z and If the m e l t enters the gap a t a high temperature, where To% T, then A q a % 0, and considerable damping i s provided by the new term i n av f o r geometries w i t h m>l. Another damping e f f e c t can occur because o f the temperature dependence o f the v i s c o s i t y .As the l o - c a l temperature r i s e s the decreased v i s c o s i t y w i l l r e s u l t i n an increase o f m e l t v e l o c i t y i f the pres- rop across the m e l t l a y e r i s constant. An upper l i m i t t o the s i z e o f t h i s e f f e c t can be ob- tained i f i t i s assumed t h a t the pressure i n the r e s e r v o i r i s constant. This can be t r u e i f the d i - mensions o f the r e s e r v o i r are l a r g e enough and the f l o w v e l o c i t i e s and v i s c o s i t y i n the r e s e r v o i r areFig. V-22. Small-amplitude i n s t a b i l i t y growth rates low enough. I n t h i s case the upper l i m i t t o the --HARE c o n f i g u r a t i o n i n b a s a l t . 75
  • damping r a t e contributed by the v i s c o s i t y i s , w i t h energy deposition i n a b a s a l t m e l t flowing throughs = 15 f o r basalt, an annular gap between two pieces o f boron n i t r i d e . The a p p l i c a t i o n o f the foregoing theory t o the sta- b i l i t y o f the c u r r e n t c o n f i g u r a t i o n i n such experi- ments requires t n a t c e r t a i n modifications be made. Since the m e l t l a y e r cannot grow i n thickness, wewhere have avl = 0. The o n l y p o s i t i v e c o n t r i b u t i o n t o the growth r a t e i s p = p e - ST o Tand s=a . However dQ/dV i s n o t determined by the melting power T r e l a t i o n b u t i s given byFor ?= 2000 K and since To 1~ Tm, (7 - To)/=i = 1/6. g = - (PCVL o ) T-T ,The sum o f the c o n t r i b u t i o n s t o the growth r a t e due dV Lt o v e l o c i t y would then be so t h a t = - e+( + Z 1 m - n m ) l m s 11 av z vL T - To (V-18) a q = n T - T . The s i z e o f the various growth r a t e s i n b a s a l t However, i n the temperature range applicable t oare compared i n the graph o f Fig. V-22. The s o l i d penetrators i n b a s a l t n 5 5, To > 1450 K and 7 %curves are the p o s i t i v e r a t e s t h a t lead t o i n s t a - 2000 K. Thenb i l i t y , and the dashed curves are the negative or vLdamping terms. The conduction damping term a K ( h ) aq 2 i-i s s i g n i f i c a n t o n l y f o r small wavelengths ( 1 ~ 1 .O mm).Only the v e l o c i t y damping f o r vo = 0 i s p l o t t e d and and, w i t h the v e l o c i t y damping termi s small compared t o the p o s i t i v e term f o r a l l v*.The damping a (v*, A ) due t o the c o n d u c t i v i t y o f the Ppenetrator t i p , here taken t o have the properties c t q + a vvL ~ vL i - = O ~ - .o f boron n i t r i d e , depends on the choice o f the con-duction length, A. I n Fig. V-22 A = 6 mn i s chosen Any o f the conduction terms ( a K < 0, a < 0) andas a reasonable thickness f o r the boron n i t r i d e , P a < 0 can insure s t a b i l i t y . Unless the m e l t i swhich connects the m e l t l a y e r t o the molybdenum pen- IJ heated t o high temperatures such t h a t T >> To, theetrator, which i s a t a uniform temperature because c u r r e n t c o n f i g u r a t i o n i n these experiments w i l l beo f the high thermal conductivity. For t h i s case the stable i n the small-amplitude approximation.sum o f the p o s i t i v e terms, aq(v*) and avl(v*), A second type o f experiment was an attempt t odominate the sum o f the negative terms f o r some range examine the me1t-heating process v i s u a l l y . Concen-o f A and f o r v* % 0.3 rnm-s-l. The second term i n t r i c graphite electrodes, separated by a boron n i -av as given by Eq. (V-18) can, i n p r i n c i p l e , provide t r i d e insulator, were heated by rf t o 1770 K and weres t a b i l i t y under most circumstances. However, t h i s brought i n contact w i t h a stack o f transparent Pyrexequation represents o n l y an upper l i m i t . disks. A 60-Hz voltage was impressed across the A number o f experiments have been performed electrodesand when c u r r e n t f l o w i n the m e l t was i n -which examine the c h a r a c t e r i s t i c s o f e l e c t r i c a l dicated, a slow penetration was started. The a c t i o n76
  • a t the electrodes was photograp..:d throug the Pyrex c o n f i g u r a t i o n the center conductor was replaced by disks. Since the r a t h e r slow (0.1 mn-s-’) forward a number o f copper cables. v e l o c i t i e s achieved were probably determined by the For each type o f stem, the d i r e c t - and alterna- 4 electrode temperatures and n o t the m e l t heating i n t i n g - c u r r e n t ( t o 10 Hz) transmission p r o p e r t i e s f r o n t o f t h e boron n i t r i d e , and since the m e l t l a y e r were determined. These analyses included the f o l - thickness was n o t determined, a q u a n t i t a t i v e a p p l i - lowing e f f e c t s : l c a t i o n o f the foregoing theory cannot be made. How- e Temperature-dependent e l e c t r i c a l p r o p e r t i e s ever, during some o f these experiments, b r i g h t , o f the conducting s t r u c t u r a l members (aluminum, r a d i a l , high-temperature filaments were observed coppen and s t e e l ). and photographed between the electrodes. I t i s pos- a E f f e c t s o f ground conduction i n p a r a l l e l w i t h s i b l e t h a t t h i s was a high-amplitude phase of an the outer r e t u r n conductor. unstable discharge i n t h e melt. Further experiments e Contact resistance a t the d r i l l stem j o i n t s . o f t h i s type are needed. e Properties o f possible i n s u l a t o r s and d r i l l - 6. Power Transmission Analysis o f Subterrene i n g f l u i d s and the e f f e c t s on the leakage conduct- - Stem. The properties o f the Subterrene d r i l l stem ance. t h a t a f f e c t the e l e c t r i c a l power transmission t o the These considerations r e s u l t e d i n an expected penetrator heater have been investigated. This con- range o f d i s t r i b u t e d parameters, c h a r a c t e r i s t i c i m - s i s t e d o f a consideration o f m a t e r i a l properties, pedances, and a t t e n u a t i o n constants. The e f f i c i e n c y the r e s u l t i n g e l e c t r i c a l p r o p e r t i e s o f two stem o f a number o f combinations o f d r i l l stems and melt- configurations, and sample c a l c u l a t i o n s o f t h e f r a c - i n g body heaters were c a l c u l a t e d as a f u n c t i o n o f t i o n o f transmitted power a v a i l a b l e t o heat t h e pene- hole depth. An example o f the e f f i c i e n c y versus trator. Because o f the generally high currents r e - depth f o r the c o n f i g u r a t i o n depicted i n Fig. V-23 i s s u l t i n g from t h e low resistances o f e x i s t i n g and shown i n Fig. V-24. Here t h e a l t e r n a t i n g - c u r r e n t proposed heaters, o n l y stem designs i n which t h e s t r u c t u r a l members are a l s o conductors were consid- ered. One such c o n f i g u r a t i o n i s i l l u s t r a t e d i n Fig. V-23. I t consists of concentric aluminum c y l i n d e r s i n s u l a t e d from one another and p r o v i d i n g downward and r e t u r n conduction paths. I n t h e other z 0.4 a R, = LOAD RESISTANCE R e 8 CHARACTERISTIC IMPEDANCE 0.1 Oa2 t 1 oC, 4 i ; i it 1 ; i2 1I I WELL DEPTH ( km 1W Fig. V-23. Cross section of proposed Subterrene Fig. V-24. Power transmission c h a r a c t e r i s t i c s o f a d r i l l stem u t i l i z i n g concentric aluminum conductors. , Subterrene stem as a f u n c t i o n o f depth and load resistance. 77
  • characteristics have been used,and good insulation costly and time-consuming procedure of inserting andand negligible contact resistance were assumed. If cementing metal casings typically associated w i t hthe characteristic impedance (Rc) and the load (Rs) wells drilled with rotary bits.are matched, perhaps through a downhole transformer, Studies made a t Los Alamos combined with a sur-negligible transmission losses result (curve A ) vey of potential users i n industry have revealed aeven a t depths of 12 km. For higher or lower loads large number of potential applications of the Subter-the efficiency lessens (curves B and C ) . A t heater rene. The systems inherent ability t o make holesresistances below 0.1 a, which i s typical of pre- of precise diameter could be utilized i n producingsent laboratory penetrators, the efficiency i s below holes for anchoring structures such as bridges, TV0.5 a t 10 km. The design direction for deep Sub- towers, and transmission line towers. Emplacementterrene systems would dictate the need for higher holes for anchoring pipeline supports could be read-resistance heating elements w i t h the prospects of i l y melted i n difficult materials such as Alaskanh i g h transmission efficiencies for load resistances permafrost. Loose gravel and other unconsolidatedabove 1 51. formations are d i f f i c u l t to d r i l l and stabilize withD. Applications and Technology Transfer conventional rotary equipment. The Subterrene, which The basic notion of developing an excavation would leave a glass-lined hole, provides a solutiontool based upon the melting of rocks and s o i l s was t o this difficulty. Conversely, hard, abrasive rocksgenerated by the need for very deep drilling as pro- can also be penetrated because the melting tempera-posed i n the original Mohole Project. The rock- ture, not the hardness or abrasiveness, determinesmelting idea recognized that very deep i n the earth the usefulness of the Subterrene.extremely high temperatures --approaching rock me1 t- Particular interest i n small -diameter, horizon-ing points --would be encountered. Therefore a tool tal , glass-lined holes motivated a separate study,that formed the borehole by me1 t i n g could uniquely which has been completed. These small horizontalsolve this problem. borings can be used as underground u t i l i t y conduits For the general field of drilling and excavation for the installation of telephone, gas, water, andtechnology, clearly del ineating some of the major television lines; as glass-lined holes for h i g h - problem areas was a straightforward task. To name explosive shot emplacement; and as drainage holes toonly a few, the following problems seemed significant: stabilize roadcuts and embankments. The study indi- High costs associated w i t h geothermal energy cates t h a t hole straightness requirements can be met .d r i 11i n g by adding deviation sensors and alignment-control 0 High costs associated w i t h drilling deep units t o the hole-forming assembly.wells, particularly as a result of trip time spent From the viewpoint of the energy research andmaking downhole equipment changes. development programs a t Los Alamos, two potential e Hole s t a b i l i t y problems in weak caving ground. uses are of special interest. The f i r s t involves 0 High cutter costs and low lifetime when melting holes i n h o t rocks for the extraction ofboring i n very hard abrasive rock. geothermal energy. Since the penetration of the Sub- 0 Maintaining a sustained advance rate when terrene depends on the melting of the rock, the h i g hboring in wet and variable loose ground. -- temperatures will be beneficial i n saving i n situ With the Subterrene concept the three major thermal energy and increasing the penetration rate.facets of excavation, namely, rock fracturing, debris The second i s related to the LASL program for develop-removal, and wall stabilization, are attacked i n a i n g underground superconducting transmission linessingle,integrated operation. In loose or porous for- for electrical power. A t present, such lines wouldmations the debris removal operation is eliminated have to be laid in trenches which could only be dugby density consolidation. Another unique advantage with considerable environmental disruption. W i t h aof the Subterrene system concept i s that the holes Subterrene, however, horizontal holes could be meltedare automatically lined with a hard glass-like w i t h a minimum disturbance of the ground surface.material. I t may thus be possible t o eliminate the The technology dissemination efforts expended by members of the Subterrene program a t Los Alamos have78
  • been extensive i n both scope and depth. Approxi- TABLE V-6 mately 60 technical papers and reports have been LASL INITIATIVES I TECHNOLOGY N written by the project staff on a l l phases of Sub- DISSEMINATION AND TRANSFER terrene activities for distribution and presentation Advisory a t various technical society meetings. These re- Documentation Briefings Panels Demonstrations ports continue t o be in demand and are forwarded t o LASL reports Technical Geosci- Rock melting society ences demonstrations a l l interested organizations and individuals. A presen- advisory for visitors substantial number of technical briefings have been ciety reports tations panel at L S AL presented to interested individuals and groups by Extensive mailing l i s t All inter- ested Indus- Washington, DC trial field demon- the Subterrene staff throughout the program. Inter- for reports visitors staff strations ested individuals and groups include members of the Applications t o LASL members Denver Federal United States Congress, representatives of major i n - survey l e t t e r s Visiting National Center field Journal covers lecture Science demonstrations dustrial concerns , representatives of the armed and a r t i c l e s tours Founda- tion Tacoma, WA forces, u t i l i t y and power distribution specialists, Subterrene Prospec- program Technology drilling and oil-field specialists, university pro- films tive managers Transfer Field Replies t o i n - funding agency Days fessors, professional engineers, and college stu- ERDA dustrial briefings program Drainage holes dents. For use a t meetings which cannot be attended a t Bandelier inquiries managers National Monu- by a member of the s t a f f , a short documentary color Internal ment film on the Subterrene concept has been produced LASL which utilizes technical animation t o i l l u s t r a t e the staff reviews basic operating concepts. Initial impact in the area of public demonstra- Displays exhi biting examples of Subterrene rock- tions has been achieved through the use of a mobile me1 ting penetrator systems, glass-lined holes, rock- Su bterrene f i el d-demonstration u n i t which performed me1 ted debris samples, and technical reports were successfully before several groups in Washington, prepared for the First Houston Technology Transfer DC. The demonstrations were held a t the U.S. Armys Conference i n Houston, TX, and the 1974 Annual Engineering Proving Grounds quarry area a t Fort Meeting of the Association of Engineering Geologists Belvoir, VA. Among the estimated 300 persons who in Denver, CO. Technical papers on Subterrene tech- attended one of the four scheduled demonstrations nology were presented a t each of these meetings. were representatives from Congress, U.S. Government Permanent display samples were prepared for the agencies, the news media, equipment manufacturers, American Museum of Atomic Energy in Oak Ridge, TN, and excavation firms. A similar demonstration was and Subterrene hardware and posters were included i n conducted shortly thereafter a t the Denver Federal the current ERDA traveling exhibit on geothermal Center in Denver, CO. A Subterrene field-demonstra- energy. tion unit was sent t o the c i t y of Tacoma, Wkto In conclusion i t appears that a l l of the pre- participate i n their Technology Transfer Field Days liminary steps in achieving the transfer of a new Demonstration a t their request. After performing technology have been accompl i shed by the Subterrene for the general public, the u n i t was viewed and s t a f f . The technical needs were identified i n depth, operated by personnel associated with underground the applicable technology was directed toward the uti 1 i ty emplacements. Such demonstrations , particu- development and testing of a new system, and a vast l a r l y when they involve the production of useful program i n techno1 ogy dissemination was implemented. holes by nonlaboratory work crews, are f e l t to be To complete this process, a large-scale commercial significant advances i n the technology transfer utilization of the technology i s required. arena. A brief sumnary of these activities i s pre- sented i n Table V-6.LJ 79
  • VI. TECHNICAL REPORTS AND PRESENTATIONS Copies o f the reports l i s t e d below can be obtained from: National Technical Information Service (NTIS) t U.S. Department o f C m e r c e 5285 P o r t Royal Road Springfield, VA 22151 ; the completed reports are i d e n t i f i e d by t h e i r LA-MS number by NTIS. Discussions of the technical reports can be directed t o i n d i v i d u a l authors at: University o f California Los Alamos S c l e n t i f l c Laboratory P. 0. Box 1663 Group P-DO, MS-570 Los Alamos, NM 87545 Telephone: (505) 667-6722 A. COMPLETED LASL TECHNICAL REPORTS LASL Report No. Title Author( s) LA-5354-MS Systems and Cost Analysis f o r a Nuclear Subterrene Tunneling J. H. Altseimer Machine - A Preliminary Study. (September 1973). LA-5422-MS A V e r s a t i l e Rock-Melting System f o r the Formation o f Small-Diameter D. L. Sims Horizontal Glass-Lined Holes (October 1973). LA-5423-MS Carbon Receptor Reactions i n Subterrene Penetrators (October 1973). W. A. Stark, J r . M. C. Krupka LA-5435-MS Rock Heat-Loss Shape Factors f o r Subterrene Penetrators (October G. E. Cort 1973). LA-5459-SR Rapid Excavation by Rock Melting -- LASL Subterrene Program -- R. J. Hanold December 31 , 1972 t o September 1 , 1973 (November 1973). LA-5211-MS Subterrene E l e c t r i c a l Heater Design and Morphology (February 1974). P. E. Armstrong LA-5502-MS Heat Transfer and Thermal Treatment Processes i n Subterrene-Produced A. C. Stanton G ass Hole Linings (February 1974). 1 LA-551 7-MS Conceptual Design o f a Coring Subterrene Geoprospector (February J. W. Neudecker1 1974). LA-5540-MS Selected Physiochemical Properties of Basaltic Rocks, Liquids and M. C. Krupka G asses (March 1974). 1 LA-5573-MS Development o f Mobile Rock-Melting Subterrene F i e l d U n i t f o r Uni- J. E. Griggs versal Extruding Penetrators ( A p r i l 1974). LA-5608-MS Numerical Solution o f Melt Flow and Thermal Energy Transfer f o r the R. D. McFarland Lithothermodynamics o f a Rock-Melting Penetrator (May 1974). LA-561 3-MS The AYER Heat Conduction Computer Program (May 1974). R. G. Lawton LA-5621 -MS PLACID: A General Finite-Element Computer Program f o r Stress R. G. Lawton Analysis o f Plane and Axisymmetric Solids (May 1974). LA-5689-MS Geothermal Well Technology and Potential Applications o f Subterrene J. H. Altseimer Devices -A Status Review (August 1974).! LA- 5826-MS Characterization o f Rock Melts and Glasses Formed by Earth-Me1 t i n g L. B. Lundberg Subterrenes (January 1975). 80
  • LASL Report No. ~~ Author(s) LA-5857-MS Chemical Corrosion o f Molybdenum and Tungsten i n L i q u i d Basalt, W. A. Stark, Jr. T u f f , and Granite w i t h A p p l i c a t i o n t o Subterrene Penetrators M. C. Krupka (February 1975). LA- 5838 Petrography and Chemistry o f Minerals and Glass i n Rocks P a r t i a l l y S. N. Ehrenberg Fused by Rock-Melting D r i l l s (September 1975). P r i s c i l l a Perkins M. C. Krupka LA-6038-MS Unique Refractory Techniques f o r Fabricating Subterrene Penetrators W. C. Turner (September 1975). LA-6135-MS Rock Property Measurements P e r t i n e n t t o t h e Construction o f Drain- 6. M. Pharr age Systems a t Archeological S i t e s i n Arizona by Subterrene Pene- t r a t o r s (November 1975). LA-6265-MS Development o f Coring, Consolidating, Subterrene Penetrators H. D. Murphy (March 1976). J. W. Neudecker G. E. Cort W. C. Turner R. D. McFarland J. E. Griggs LA- 6555-MS Technical and Cost Analysis of Rock M e l t i n g Systems f o r Producing J. H. Altseimer Geothermal We1 1s (November 1976). B. TECHNICAL PRESENTATIONS AND JOURNAL ARTICLES Conference on Research i n Tunneling and Excava- t i o n Technology (Abstract and Presentation) J. C. Rowley Rapid Excavation by Rock M e l t i n g NSF, Wayzata, MN, September 14- 15, 1973 1 5 t h Symposium on Rock Mechanics (Presentation and Paper) R. J. Hanold The Subterrene Concept and I t s Role i n Future U.S. National Comnittee on Rock Excavation Technology Mechanics , Custer, SD, September 17-19, 1973 26th P a c i f i c Coast Regional Meeting (Abstract and Presentation) M. C. Krupka Refractory M a t e r i a l and Glass Technology Problems American Ceramic Society, San Associated w i t h t h e Development o f a Rock M e l t i n g Francisco, CA, October 31: Drill. November 2, 1973 Tunnels & Tunnelling Magazine ( I n v i t e d A r t i c l e ) J. H. Altseimer Subterrene Rock Me1t i n g Devices B r i t i s h Tunnelling Society, January-February 1974 U n i v e r s i t y o f Wyoming ( I n v i t e d Presentation) J. C. Rowley Rock Me1t i n g and Geothermal Energy Laramie, WY, A p r i l 25, 1974 Geotechnical Eng. Group & Association o f Eng. Geologists J o i n t Meeting ( I n v i t e d Presentation) R. J. Hanold The LASL Subterrene Concept Los Angeles, CA, May 30, 1974U 81
  • Rapid Excavation & Tunneling Conference (Presentation and Paper)J. C. Rowley Rock Melting Subterrenes - Their Role i n Future American Inst. of MiningR. J. Hanold Excavation Techno1ogy Engineering, San Francisco, CA,C. A. Bankston June 24-27, 1974J. W. Neudecker Petroleum Enqineer (Journal Article)D. L. Sims Melting Glass-Lined Holes: Nw Drilling Technology e July 1974 Journal of Vacuum Science and Technoloqy (Article)W . A. Stark, J r . , Application o f Thick Film and Bulk Coating Tech- American Vacuum Society, Vol. 11,e t a1 nology to the Subterrene Program NO. 4, July-August 1974 3rd International Congress I R SM (Presentation and Paper)J. C. Rowley Rock Melting Applied t o Excavation and Tunneling International Society for Rock Mechanics, Denver, COY September 2-7, 1974 NATO Committee on Challenses of Modern Society (presentation)C. A. Bankston The Los Alamos Scientific Laboratory Subterrene NATO, Los Alamos, NM, September Project and I t s Applications t o Geothermal Energy 18, 1974 Conference on Research for Development of Geo- thermal Resources (Presentation and Paper)J. C. Rowley Rock-Me1 ting Technology and Geothermal Drilling NSF, JPL, CIT, Pasadena, CA, September 23-25, 1974 NASA - Houston Technoloqv Transfer Conference (Presentation-and Paper)R. J . Hanold The Initiatives of the Los Alamos Scientific Houston, TX, September 24-25,C. A. Bankston Laboratory i n the Transfer of a Nw Excavation e 1974J. C. Rowley TechnologyW. W. Long Earth & Planetarv Sciences Group-Johnson Space F i g h t Center (Presentation) 1R. J. Hanold The Los Alamos Subterrene Program and i t s Role i n NASA, Houston, TX, September Geothermal Energy Development- 26, 1974 17th Annual Meeting, Association of Engineering Geologists (Abstract and Presentation)C. A. Bankston The Rock Melting Subterrene and i t s Potential AEG, Denver, COY October 18, 1974J . H. Altseimer Role i n Geothermal Energy AIAA/SAE 10th Propulsion Conference (Presentation and Paper)J. H. Altseimer Nuclear Propulsion Technology Transfer to Energy AIAA/SAE, San Diego, CA, OctoberJ. D. Balcomb Systems 21-23, 1974W. E. KellerW. A. Ranken 1974 ASME Winter Annual Meeting (Presentation and Paper)R. D. McFarland Viscous Melt Flow and Thermal Energy Transfer for ASME, Nw York, NY, November 18- eR. J. Hanold a Rock-Me1 t i n g Penetrator 22, 1974 Tunnels & Tunnelling Hagazine (Article)R. E. Williams - Soil Melting A Practical Trial British Tunnelling Society, January-February 1975 1975 AM Winter Annual Meetins SE - (Presentation and Paper)H. N. Fisher Thermal Analysis o f Some Subterrene Penetrators ASME, Houston, TX, November 30- December 4, 1975 University of Colorado (Invited Presentation)J. H. Altseimer The Subterrene Program and Geothermal Energy Boulder, COY December 2, 197582
  • C. REPORTS RELATED T SUBTERRENE TECHNOLOGY PUBLISHED BY OTHER ORGANIZATIONS O C 1. Black,. D. L. , "Basic Understanding o f Earth Tunneling by Melting," Prepared f o r U.S. Department o f Transportation by Westinghouse Astronuclcar Laboratory, J u l y 1974. 2. Bledsoe, J . D., H i l l , J. E., and Coon, R. F., "Cost Comparison Between Subterrene and Current Tunneling Methods," Prepared f o r National Science Foundation by A. A. Mathews, Inc., May 1975. 3. Black, D. L., "A Study o f Borehole Plugging i n Bedded S a l t Domes by Earth Melting Technology," Westinghouse Astronuclear Laboratory, June 1975. 4. Nielsen, R. R., Abou-Sayed, A., and Jones, A. H., "Characterization o f Rock-Glass ~ Formed by the LASL Subterrene i n Bandelier Tuff," Terra Tek, November 1975. 5. Muan, A., "Silicate-Metal Reactions w i t h a Bearing on the Performance o f Subterrene Penetrators, The Pennsylvania State University, August 1976. . 6. S t . John, C. M., "Stresses and Displacements Around Deep Holes i n Hot Rocks," Univer- s i t y o f Minnesota, September 1976. * US. GOVERNMENT PRINTING OFFICE 1977-777410/14 83