Your SlideShare is downloading. ×
  • Like
Geothermal well technology and potential applications of subterrene devices, 1974
Upcoming SlideShare
Loading in...5

Thanks for flagging this SlideShare!

Oops! An error has occurred.


Now you can save presentations on your phone or tablet

Available for both IPhone and Android

Text the download link to your phone

Standard text messaging rates apply

Geothermal well technology and potential applications of subterrene devices, 1974



Published in Technology , Business
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
No Downloads


Total Views
On SlideShare
From Embeds
Number of Embeds



Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

    No notes for slide


  • 1. @-93s- LA-5689-MS1y. Informal Report w Reporting Date: July1974 W Issued: August 1974 fr; *e 1 i 4 Geothermal Well Technology and Potential Applications o Subterrene f Devices - A Status Review by John H Altseimer . I D alamos scientific laboratory of the University of California LOS ALAMOS, NEW MEXICO 87544 UNITED STATES ATOMIC CNERGY COMMISSION . CONTRACT W-74 OS-E N G 36 OlSTRlBU v N OF THIS DOCUMENT I UNLIMITED S
  • 2. 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.
  • 3. DISCLAIMERPortions of this document may be illegible inelectronic image products. Images are producedfrom the best available original document.
  • 4. This report was prepared as an account of work sponsored by the UnitedStates Government. Neither the United States nor the United States AtomicEnergy Commission, nor any of their employees, nor any o their contrac- ftors, subcontractors, or their employees, makes any warranty, express or im-plied, o assumes any legal liability o responsibility for the accuracy, com- r rpleteness or usefulness of any information, apparatus, product o process dis- rclosed, or represents that its use would not infringe privately owned rights. In the interest of prompt distribution, this LAMS re- port was not edited by the Technical Informationstaff. Work partially supported by a grant from the National ScienceFoundation, Research Applied to National Needs (RANN). Printed i the United States of America. Available from n National Technical Information Service b U.S.Department of Commerce 5285 Port Royal Road Springfield, Virginia 22151 price: Printed Copy $4.00 Microfiche $1.45
  • 5. NOTICE This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any OF their contractors, subcontractors, of their employees, . makes any warranty, express or Implied, or assumes any legal UabUity or responsibility For the ICCUI~CY, com- pleteness or usefulness of any information, apparatus, product or process disclosed. or represents that its usebd would not infringe privately owned rights. CONTENTS I, INTRODUCTION 1 A. Objectives 1 B. History of Geothermal.Energy (GTE) Exploitation 1 C. General GTE Industry Status 2 1. Economic Incentives 2 2. Geothermal Resource Data 3 3. Environmental Pollution Awareness 3 4 Federal Support . 3 5. State Support 4 11. GEOTHERMAL WELLS: CURRENT TECHNOLOGICAL AND COST STATUS 4 A. Exploration 4 1. Extent an4 Nature of the Resource 4 2 Surface Prospecting Techniques . 5 3. Exploration and Discovery Wells 6 4 costs . 7 B. Problems in Completing Geothermal Wells 8 1. Dependence on Oil-and Gas-Drilling Equipment and 8 Methods 2 . Geological Factors 8 3 Surface Sites and Equipment . 9 4 Drilling . 9 5. Casing and Cements 12 6. Drilling Fluids and Muds 12 7. Downhole Measurements and Samples 13 8 . costs 13 9 Summary of Current Drilling Problems . 13 C. Production Operational Problems 14 1. Production Loss With Time; Reinjection; and 14 Augmentation 2. Large Surface Piping 14 3. Corrosion and Scaling 15 4 Desirability of Higher Electric Power Generating . 15 Efficiency 5 Summary of Current Operational Problems . 6 1 111. CONCEPTUAL APPLICATIONS OF SUBTERRENE DEVICES TO 16 GEOTHERMAL WELLS A. Subterrene Program History 16 B Basic Subterrene Technology . 19 1. Basic Types of Penetrators- 19 2. Other Coring Designs 21 3 Rock Glass Hole Linings . 22 C. Current Problems That Subterrenes Might Help Solve 23 or Eliminate iii DISTRIBUTION OF THIS DOCUMENT IS UNLl m
  • 6. D Potential Subterrene Applications in Geothermal Wells . 24 0 E Subterrene Program Accomplishrpents Still Required . 25 IV. CONCLUSIONS 26 REFERENCES 26 Appendix: Contacts Made to Discuss Geothermal Well Drilling 29 Problems 1I - ’ iv
  • 7. . GEOTHERMAL WELL TECHNOLOGY AND POTENTIAL APPLICATIONS - OF SUBTERRENE DEVICES A STATUS REVIEW by John H. Altseimer ABSTRACT The past, present, and some future aspects of the geothermal energy (GTE) industry have been reviewed with special attention given to geothermal well- drilling problems. Geothermal wells can be produced with present equipment and methods, mostly derived from the oil and gas industry, but costs are relatively high. Short-term improvements are needed in drilling rigs and auxiliary surface equipment, drill bits, bit-bearing lubrication systems, tubular goods, high-temperature muds and cements, logging and downhole sampling equipment, directional control equipment applicable to geothermal conditions,and in the use of a data bank for GTE wells to help optimize drilling programs. Two types of wells are needed: ( ) small-diameter wells 1 for exploration, reinjection, and disposal purposes, and (2) larger-diameter wells for production. To develop and greatly expand the use of GTE in the future, new methods and equipment are needed to penetrate hard abrasive rocks and to provide hole stabilization and support at the very high temperatures and other extreme conditions which can be encountered in GTE wells. New Los Alamos Scientific Laboratory concepts for penetrating rocks by use of rock- melting processes (called Subterrene concepts) offer potential solutions to sbme difficult GTE well-production problems. I. INTRODUCTION recalls Plato writing about ancient Atlantis in his A. Obj ectives Critias as follows: "Poseidon, as he was a god, A primary objective of this study is to present found no difficulty in making special arrangements a summary status review of geothermal well technol- for the center of this island, bringing two streams ogy, which includes drilling and operational prob- of water from under the earth, Which were caused to lems. A secondary objective is to begin the analy- astend as springs, one of hot water and the other of sis and evaluation of new concepts of making a hole cold". by means of melting processes (called Subterrene The first experimental attempts to produce concepts at the Los Altlmos Scientific Laboratory)to electric power from GTE began in 1904 at Larderello, improve the methods of producing geothermal wells. Italy, under the direction of Prince Piero Ginori Besides the use of published literature and data, Conti, general manager of the Larderello works. many personal discussions were held with people in These works had been developed by a Frenchman,c various fields of the drilling and GTE industries Francesco de Larderel, in 1818, primarily as a 1 in an effort to arrive at correct and objective con- source of boric acid. In a paper delivered ih 1924 clusions. A list of the contacts made is presented Prince Conti reported that in 1905 a 20-hp engine in an appendix. was run by the natural steam supply to generate B. History of Geothermal (GTk) Ernloitation plant lighting power. By 1912, the development of Man has made various uses of naturally occurr- a 250-kW steam turboalternator was initiated with 1 ing hot water for thousands of years. Indeed, Lieb subsequent success. Ir 1914, the erection of the t 1
  • 8. r e l l o Power S t a t i o n was begun, which housed GTE because o i l - d r i l l i n g technologies o f f e r a con- urboalternators of 2500 k each, two opera- a1 and one spare. W From these e a r l y beginnings venient way of entering i n t o these new e n t e r p r i s e s . Union O i l became a c t i v e a t The Geysers i n t h e 1960s c, r e l l o Power S t a t i o n has increased i t s out- while others l i k e Signal, Standard O i l of California, 4 MW i n 1969. With current technology, Sun, P h i l l i p s , Occidental, Gulf, and Getty a r e a l l u t may be near t h e maximum f o r t h a t loca- now a c t i v e i n t h e western United S t a t e s along with a growing group of small s p e c i a l t y companies. For r e l l o i s a vapor-dominated reservoir. A example, i n t h e KGRA bidding i n California, r e f e r r e d eservoir e x i s t s at The Geysers i n northern t o previously, 17 companies submitted as many a s 56 i a , I n 1960 The Geysers f i r s t became opera- bids. Various problems i n t h e p a s t had slowed t h e t 12.5 MW.3 Since the-several 110-MW com- growth of t h e GTE industry. Some problems a r e d i s - onsisting of two 5 - W subcornplexes, 5M appearing because of developments external t o t h e loped. A t t h e end of 1973, P a c i f i c industry and others a r e being taken c a r e of by accel- i c Co. reported a t o t a l capacity of erated e f f o r t s of t h e involved organizations o r r The geyser^,^ which became t h e l a r g e s t agencies. A discussion of t h e important f a c t o r s G E f i e l d i n t h e world. T More wells a r e a f f e c t i n g t h e industrys growth follows. i l l e d including one completed at 2898 m 1. Economic Incentives. The promise of genera- eepest producing steam well i n the t i n g low-cost e l e c t r i c power has probably kept t h eworld. Current estimates of t h e t o t a l power produc- GTE industry a l i v e , although t h e large-scale develop- a b i l i t y of The Geysers range from 1000 t o ment of f o s s i l - f u e l i n d u s t r i e s with easy and pre- e). An indication of t h e p r i v a t e s e c t o r s d i c t a b l e p r o f i t s has g r e a t l y overshadowed GTE. Also, a t i o n of t h a t areas p o t e n t i a l is given by t h e hydroelectric power p l a n t s were well understood and, 2 r e s u l t s of t h e January 22, 1974, bids f o r 202 km where water was a v a i l a b l e , such p l a n t s were b u i l t .(50,000 acres) of &own geothermal Resource Areas To f u r t h e r lessen t h e incentive t o build GTE power 2(KGRAsj in California. One 9.5-km (2340 acres) p l a n t s , large nuclear p l a n t s were advertised a s t h eKGRA brought a b i d of $3,200,000 or 337,000 $/km2 solution t o a l l power problems. I t i s , however, be-(1367 $/acre), and t h e average f o r 1 2 KGRAs was coming evident t h a t f o s s i l and nuclear power p l a n t s 4156,000 $/km2 (631 $/acre). have problems of c o s t , environmental pollution, and Encouraged primarily by Larderello successes, limited f u e l resources, which make other comple-GTE i n t e r e s t s sprang up a l l over t h e world. This menting energy sources, e.g., geothermal and s o l a r ,was t o be expected because GTE manifestations occur look increasingly a t t r a c t i v e . Finally, t h e poweri n many locations, being usually associated with industry, because of heavy f i n a n c i a l commitment re-volcanic a c t i v i t i e s and evidences of c r u s t a l p l a t e quirements, is an extremely conservative industryphenomena. Thus, G E a c t i v i t i e s occur from t h e T which measures changes i n decades r a t h e r than merelyAleutian Islands and southern Alaska down t h e west years.coasts of the North and South American continents, A b r i e f look a t t h e economics of GTE is worth-westward under t h e P a c i f i c through N w Zealand and e while. McMillan, who helped promote The GeysersOceania and up thrqugh Japan plus another volcan- development i n t h e 1950s presented comparative costi c a l l y a c t i v e zone extending through Hawaii. Mani- data i n a paper a t Pisa, Italy. While now severalf e s t a t i o n s a l s o appear through t h e mid-Atlantic years old t h e paper is valuable because it comparesOcean, including Iceland, i n t o the southern Atlan- c o s t s f o r d i f f e r e n t types of p l a n t s i n t h e same geo-t i c , up eastern Africa, and i n t o the Red Sea and graphic area. In 1968, i n California, The Geysers cMediterranean areas with sizeable extensions east- fuel and operating c o s t s were 2.75 mills/kWh, com-ward across Asia. A t l e a s t 19 ongoing GTE power pared with 5.78 m i l l s f o r t h e Humbolt Bay nucleardevelopment p r o j e c t s a r e presently s c a t t e r e d around plant and with 3.28 t o 10.32 m i l l s f o r a l l othert h e world i n t h e areas approximately outlined above. power p l a n t s i n t h e s t a t e , excluding hydroelectric. 7C. General GTE Industry S t a t u s Using s l i g h t l y d i f f e r e n t assumptions, Goldsmith Many o i l companies a r e becoming i n t e r e s t e d i n estimates a GTE e l e c t r i c i t y cost of 5.33 mills/kWh, bi2
  • 9. which compares favorably with McMillans data for for many years. One example is a detailed (3733 re-other power plants (average, 7 mills/kWh, excluding ferences) compilation by Waring et al.13 on the ther-hydroelectric). Included in a recent survey report mal springs of the United States and the world. How-by the State of Oregon Public Utility Commissioners ever, national geothermal resource estimates in theOffice, R. Bowen, State Economic Geologist, shows literature differ by orders of magnitude, becausethat GTE power costs are 46, 61, and 82% of nuclear, different assumptions are made as to what is or iscoal, and hydroelectric costs, respectively. For not economically feasible. The same phenomenondry-rock geothermal reservoirs being studied at the occurs in fossil-fuel resource estimates. Although 9Los Alamos Scientific Laboratory, Brown et al. show total resources remain the same, proven reserve es-in a preliminary study a power cost of 4.7 mills/ timates change when, for example, oil prices risekwh in 570 K rock in the New York area, compared and make formerly uneconomic and therefore unavail-with 11.8 and 13.3 mills for nuclear and coal, re- able resources suddenly economic and qualified asspectively. At Cerro Prieto in Mexico where a 7s-W proven reserves.plant with 15 supporting wells is operating by In GTE, confusion about resources and reservesflashing superheated water, the Mexican Department will continue until much more exploration and pro-of Geothermal Resources recently released cost data duction technology is established. The most ad-showing that the cost of the production installation vanced GTE power systems today are probably theamounted to 264 $/kW.l0 A previous release showed vapor-dominated types such as The Geysers. Yet, thean electricity cost of 8 mills/kWh. In Russia, exact nature of the thermal reservoir at The Geyserswhere enormous reservoirs of hot water are known, is not clear. The large energy resource in theKremnjov et a1.12 also conclude that, in many cases, Imperial Valley hot brine is still not being eco-GTE is competitive with other types of energy sys- nomically exploited because of technical diffi-tems. culties. Methods for using the geopressurized GTE Note that costs such as those quoted above are resources in the Gulf of Mexico are still quitefor small GTE installatiods and for very large coal speculative. Finally, the dry-rock concepts at theor nuclear power plants. Paver from these latter Los Alamos Scientific Laboratory which may make manytypes would be even more costly if generated in of the high GTE reserve predictions come true aresmall plants. Indeed, one advantage of GTE power still in an early stage of research.generation is the possibility of distributing many 3. Environmental Pollution Awareness. Hope-smaller plants over the country in lieu of fewer fully, the GTE inhustry will be able to maintain itsvery large installations with their attendant huge claim of being environmentally acceptable. Environ-cross-country power-transmission lines and right-of- mental awareness is a new phenomenon that could ben-way land-area consumption. Another economic attrac- efit the industry. However, H2S pollution insteadtion is the short construction time for a GTE power of SO pollution is not much of an improvement. 2 7 Also, thermal pollution becabse of the lower thermalplant. Goldsmith quotes Pacific Gas and ElectricCo. as estimating only 28 months needed to build a efficiency in GTE conversion to electric power (vis-110-MV system at The Geysers, from approval and 2-vis fossil-fueled thermal systems) is a disad-equipment purchase confirmation to commercial ser- vantage. Conversely, direct use of thermal energyvice. At Cerro Pyieto. Mexico, drilling was re- other than for electric-power generation could re-cently started for a new 7s-MW complex," which is duce the overall thermal pollution problem whilescheduled for power production in July 1976, or , making a significant cQntribution to efficient en-1ess)thanthree years from initiation. ergy utilization. 2. Geothermal Resource Data. A major factor in 4. Federal Support. Until recently, federalrestricting the growth of the industry has been the interest in GTE developmetit has not been great. Thelack of geothermal resource data, including detail- Geothermal Steam Act of 1 9 d 4 was passed to facili-ed understandings of how various types of reservoirs tate the issuance of leases on public lands for thebehave and can best be exploited. The United States purposes of GTE developments. However, three yearsGeological Survey has been gathering resource data elapsed before the final regulations were issued on 3
  • 10. cember 21, 1973.l’ While not a technical problem, Another preliminary i n d i c a t o r of GTE i s t h elack of d e f i n i t i v e f e d e r a l guidelines put t h e p r i - measurement of near-surface h e a t flow i n Heat Flowvate s e c t o r i n a p o s i t i o n where funding f o r G E pro- T 2 Units [HFU; one HFU being equal t o 1 pcal/cm as -j e c t s was i n h i b i t e d . Federal funding of technology 2 (0.0418 W/m ) ] . Knowing t h e average or normal valuedevelopment has also been low and fragmented among of h e a t flow f o r a region, one can then d e t e c t t h eten d i f f e r e n t government agencies. l6 Many problems abnormal a r e a s which may be s u i t a b l e f o r e x t r a c t i n gare assuming lesser importance as r e g u l a t i o n s aredefined, l e a s i n g competitions are held, and f e d e r a lgeothermal RED funds are increased and coordinated. heat. world i s - Very approximately, t h e average HFU f o r t h e value is -1.3, 1.5.18 I n t h e eastern United S t a t e s t h e whereas i n t h e western states it is 5. . S t a t e Support. A l l t h e western states are -2.0. Thus, HFU considerations would lead t o t h ee i t h e r accepting GTE as a v i a b l e energy source or conclusion t h a t t h e western United S t a t e s is a goodseem t o b e r a p i d l y becoming aware of its p o t e n t i a l s . place t o search f o r GTE. Again, heat flow is onlyActive p r o j e c t s or s t u d i e s are i n progress i n , a t one i n d i c a t o r i n a complex system. t , California, Oregon, Washington, Montana, Two United S t a t e s Geological Survey (USGS) sci-Idaho, Utah, Nevada, Arizona, New Mexico,and Colo- e n t i s t s , L. J. P. Muffler and D. E . White, have pub-rado. On t h e west c o a s t , where l a r g e power-load l i s h e d estimates of GTE resources. I n a 1965 paper,c e n t e r s e x i s t , i n t e r e s t i s high. Oregon and Wash-ington have both r e c e n t l y issued state-sponsoredstudies 8,17 o f energy resources, and both states de- White” t h e o u t e r 10 k o f t h e e a r t h t o be m - c a l c u l a t e d t h e amount of h e a t a v a i l a b l e i n c a l ) or several thousand times t h e heat re- 4 x lo2’ Jvoted a s i g n i f i c a n t p o r t i o n of t h e i r e f f o r t t o geo- presented by t o t a l world coal resources. In a 1972thermal energy. paper,20 Muffler and White estimated t h e t o t a l s t o r e d heat i n a l l geothermal r e s e r v o i r s t o a depth of 1011. GEOTHERMAL WELLS: CURRENT TECHNOLOGICAL AND km, including reservoirs of molten rock, abnormally * COST STATUS hot rocks of low permeability, and deep sedimentaryA. Exploration basins of near-normal conductive heat flow such as 1. ExtentandNature of t h e Resource. A s noted t h e U.S. Gulf Coast and Kazahkstan i n t h e U.S.S.R.e a r l i e r , GTE resource areas of t h e vapor-dominated They a r r i v e d a t a value o f a t least 4 x Jor hot-water types e x i s t throughout t h e world. c a l ) or about equal t o t h a t o f t h e world’s coal re- es or hot-water springs a r e i n d i c a t o r s source. B assuming an e f f i c i e n c y value f o r con- y and occur from t h e Rocky Mountain v e r t i n g t h e above GTE resource i n t o e l e c t r i c i t y ,S t a t e s westward t o t h e coast; hot s p o t s are known Muffler and White conclude t h a t G E is u n l i k e l y t o Tt o extend even out i n t o t h e Pacific Ocean basin. supply more than perhaps 10%o f domestic or worldAlaska has many hot-spring i n d i c a t i o n s of GTE. e l e c t r i c a l power. However, i n favorable areas suchH a w a i i , because of its inherent volcanic nature, power may be of major importance. They a l s o con-o f f e r s promise o f having l a r g e G E resources. T Yet, clude t h a t knowledge and extent of our geothermalWaring” points out t h a t Hawaii does not have many resources is s t i l l inadequate and new, and more ef-hot springs because t h e volcanic material is frag- f i c i e n t ways t o use t h i s resource are needed.mented and porous, leading t o a water t a b l e only a One o f t h e new approaches t o G E is t h a t of Tf e w feet above sea l e v e l . In t h e eastern United hydraulically f r a c t u r i n g hot d r y rock and then ex-S t a t e s , Waring lists numerous hot springs i n V i r - t r a c t i n g thermal energy with c i r c u l a t i n g water. i n i a and West Virginia, followed by Arkansas and This technique is i n t h e research s t a g e a t t h e LosGeorgia. The above d a t a are only rough i n d i c a t i o n s Alamos S c i e n t i f i c Laboratory (LASL) . Potter21 a to f G E resources because a s i g n i f i c a n t GTE reser- T C LASL estimated t h e t o t a l a v a i l a b l e United S t a t e s a Ev o i r i s a complex system depending on l o c a t i o n and resource using t h e hot-rock method t o b e 2 x J.n a t u r e of t h e h e a t source, on water supply and re- (For comparison, t h i s amount of h e a t is about 3000charging c h a r a c t e r i s t i c s , on i n t e r r e l a t i o n of per- times t h e 7 x J of t o t a l energy used i n t h e U.S.meable and nonpermeable s t r a t a , and on t o t a l volume i n 1970.)22 He f u r t h e r estimated t h a t 13 x J -7of t h e system. could be used d i r e c t l y as thermal energy and t h e W4
  • 11. remainder t o generate e l e c t r i c power equivalent t o TEMPERATURE FC) 488,000 GW-years. Using a gross averaging method,ti t h e l a t t e r i s equivalent t o a power output of 4,880,000 MW f o r an e f f e c t i v e G E lifetime of 100 T years. The average value of 4,880,000 MW compares favorably with t h e estimated t o t a l U.S. e l e c t r i c - power requirement o f 2,000,000 MW i n t h e year 2000. 23 Noteworthy is t h e fact t h a t t h e dry-rock method . could b e applied i n every state. In t h e vapor-dominated and hot-water r e s e r v o i r s now known, t h e maximum well depths are 3 km, and i n a good r e s e r v o i r t h e temperatures might be between 470 and 570 K. The highest temperatures, 660 K, have been measured i n t h e hot-water systems a t Cerro P r i e t o , Mexico. The Geysers, t h e downhole pressure is - I n t h e vapor-dominated system a t 3500 kPa (500 p s i ) and a t Cerro P r i e t o t h e pressures can be TEMPERATURE IT) as high as -12,000 kPa (1700 p s i ) . The temperature c h a r a c t e r i s t i c s i n a conventional water-based re- Fig. 1. Temperature p r o f i l e s controlled by conduc- 24 t i v e gradients within t h e "normal" range s e r v o i r have been explained by D. E. White. (A,B.C) and above "normal" (D), and by con- Figure 1 is reproduced from t h i s work and shows tem- v e c t i v e t r a n s f e r o f heat i n hot-water sys- tems of d i f f e r e n t subtypes, compared with perature-versus-depth changes f o r various conductive reference boiling-point curve F (see t e x t ) . and convective h e a t - t r a n s f e r conditions. Lines A, (Taken from White.)24 C, and B show d a t a f o r temperature gradients i n a purely conductive s i t u a t i o n of 8, 25, and 50 K/km, Yellowstone Park. These systems tend t o b e self- Areas r e s p e c t i v e l y , and might b e considered normal. s e a l i n g due t o mineral deposits forming near-surface are known with abnormal gradients such as 75 K/km r e s t r i c t i o n s t o t h e flow and can b u i l d up pressures ( l i n e D) which would r e s u l t i n 500 K a t 3 k depth. m and temperatures exceeding those o f Curve F. Curve The Reference Boiling-Point Curve F is a p l o t o f J i l l u s t r a t e s a steam-producing s i t u a t i o n where steam water b o i l i n g temperature a t t h e h y d r o s t a t i c pres- i s being generated i n a deep brine-water body which s u r e corresponding t o t h e depths shown and includes e x i s t s below 1400 m. Higher steam temperatures and a temperature c o r r e c t i o n f o r water density. Curve enthalpies may b e obtainable as t h e b r i n e becomes E i l l u s t r a t e s r a p i d upflow of water s t a r t i n g a t a more concentrated and b o i l i n g occurs a t g r e a t e r moderate temperature a t depth and b o i l i n g as it ap- i n i t i a l temperatures. proaches t h e o u t l e t and discharging a t 373 K. Curve 2. Surface Prospecting Techniques. To s t a r t a G starts a t a high temperature similar t o E but with GTE exploration one must determine an objective, f a low upflow rate. Thus, t h e heat has time t o con- e.g., is a low-grade o r a high-grade heat source re- ductively d i s s i p a t e and t h e water a r r i v e s a t a low quired? Some examples: (1) heating o f buildings, s u r f a c e temperature of 320 K. Curve H i l l u s t r a t e s greenhouses, mines, etc., can be done with 350 K. s a l i n e water i n t h e Salton Sea system. A t 550 K, (2) i n d u s t r i a l processing such as water d e s a l i n a t i o n Curve H crosses t h e reference b o i l i n g Curve F and could be done with 450 K, (3) e l e c t r i c power genera- then exceeds t h e reference temperature because of t i o n requires 450 K and preferably higher, and (4) s a l i n i t y effects on t h e b o i l i n g point. Because of a multitude o f new a p p l i c a t i o n s would open up i f t h e low-permeability sediments i n t h e Salton Sea temperatures > 670 Kwere t o becofie a v a i l a b l e by system t h e r e i s a s t r o n g conductive-gradient e f f e c t means of new heat-extraction techniques. The next on Curve H a t shallow depths. Curve I i l l u s t r a t e s s t e p s would usually be l i t e r a t u r e surveys and f i e l d a high-temperature system at depths similar to t h e surveys. Noteworthy, f o r G E l i t e r a t u r e , i s an ex- TW systems observed a t Wairakei, New Zealand, and a t t e n s i v e bibliography of worldwide G E r e p o r t s , T 5
  • 12. sponsored by the National Science Foundation and c Geophysical Methods. One of the most use- .published by the New Mexico Institute of Mining and ful geophysical tools is the measurement of deep-Technology, Socorro, New 1971. 25 Anothercurrent project, using all available well data, is to sounding electrical resistivity, which is primarily dependent on the effective porosity, temperature, 30 cmap subterrenean temperature conditions across the and salinity of the interstitial water at depth.North American continent. This is being done by This method is fast and convenient, and can be usedthe Amercian Association of Petroleum Geologists, to probe down to at least several kilometers, It hasTulsa, Oklahoma. Methods used for field tests are been demonstrated to be very effective in New Zealand.listed below. Meidav” reviewed the method at the U.N. 1970 meet- a Geochemical Analyses. The geochemical . ing in Pisa, Italy. Recent developments in electro-analyses of hydrothermal waters produce data on magnetic methods may become especially useful inwater condition at depth (steam or liquid), tempera- geothermal areas of low resistivity. At leastture at depth, source of the water, chemical compo- three different types of electromagnetic apparatussition at depth, and character of the water to be are being developed. Aeromagnetics have also beenhandled at the surface. D E White26 described . . used in attempts to locate hot plutons where watergeochemical methods at the U N Meeting in Pisa, . . can cause changes leading to reduced magneticItaly. Geochemical indicators of subsurface tem- proper tie^.^^ Gravimetric measurements are alsoperatures are sometimes called geothermometers, the normally made across an anomalous area.use of which are described by Fournier, White, and d Seismic. For the exploration of hot water .Tr~eSdell.~~ Fournier and Truesdell have also or vapor-dominated reservoirs, active seismic methodsstudied the problem of mixing hot and cold waters. 28 are only indirectly useful, active seismic data b Thermal Measurements. Aerial infrared sur- . being used primarily to define subsurface geologicveys of large areas have been used by the United structure and basement-rock depths and configura-Nations in Ethiopia and Kenya to delineate above- t i o n ~ . However, if future drilling capabilities ~~normal surface temperature^.^ The USGS has also allow exploitation of very hot intrusions or magmasdetected some warm areas by this method. This tech- then the active seismic methods could become muchnique has severe limitations, the signal-to-noise more interesting and applicable. Some success alongratio making it difficult to accurately detect heat- these lines is indicated by Furumoto.35flux anomalies less than about 100 to 150 times the Passive seismic methods are directly useful forn0-1;~’ however, the contrast needed may be much defining water or vapor reservoirs, one use being toless, depending on the terrain being surveyed. detect micro-earthquakes which seem to be prevalent Using boreholes, thermal gradients with depth in geothermal reservoirs. Alsathere is usually anare measured and heat flows calculated. Very shallow abundance of background noises caused by water or gas(-1-m-deep) holes are usually not worthwhile because movements. Exceptions to this statement are possi-of near-surface effects. Holes to 150 m have bccn ble, however--the most notable current example beingm r e successful although the data must always be eval- the high-heat-flow area being ktudied at Marysville,uated for effects of ground-water movement. Typical Montana, which is one of the most quiet spots known 18boreholes are drilled 100 mm ( i . in diameter 4 n) in the U S ..with a 20- or 25-mm (0.7-to 1-in.) pipe cemented 3 Exploration and Discovery Wells. With all .into the hole. The pipe is filled with water and the exploratory methods available, the presence of a viable GTE reservoir must still be proven bycapped, and after equilibrium is established atemperature traverse is made from the top down. 31 drilling. These exploratory holes should be used,CombsJo writes about gradient and flux-calculation according to Combs and Muffler,34 for measurements -results of 20 HFU average in a New Zealand field, of temperature and pressure profiles, permeability, porosity, lithology, stratigraphy, fluid composi-120 times normal near Steamboat Springs, Nevada,and of at least 67 HFU at Yellowstone’s Firehole tions, other geophysical logs, and production tests.Basin. They further state that these data, which can only be obtained from a borehole, are essential in: i6
  • 13. "1. Estimating the ability of the geothermal reser- TABLE IW voir to produce sufficient energy over B suffi- ciently long time to be economically attractive. AVERAGE DEPTH AND COST PER DEPTH TOTAL UNITED STATES IN 1972* 2. Distinguishing between different models of the Type of Wells E Average Cost** geothermal system, with the aim of accurately pre- per Meter, $/m dicting production characteristics under varying Average Total exploitation conditions. 3. Calibrating and Depth, Weighted refining geophysical and geochemical methods for ---km Oil Gas Dry Average 1.3 44.10 45.10 25.10 35.90 recognizing and delineating geothermal systems." (4300) (13.40) (13.80) (7.70) (11.00) The above described uses of exploration holes 1.9 52.95 53.80 34.80 45.20 are consistent with todays capabilities for drill- (6200) (16.10) (16.40) (10.60) (13.80) ing, downhole measurements, and lbgging. An addi- 2.6 6.0 80 82.90 54.40 65.00 tional desirable capability, not yet available, is (8500) (20.70) (25.30) ( 6 6 ) (19.80) 1.0 that of continuing drilling economically past the *Numbers in parentheses are ft and $/foot. anticipated production zone towards the source of **Includes drilling and casing. heat that drives the reservoir. This could mean penetrating into hard igneous and metamorphic rocks at very high temperatures. The objectives and to prepare for production in these 1.5-km wells, would be to gain a better understanding of the basic costs 33 to 50 $/m (10 to 15 $/ft). Thus, costs of system and to determine whether reinjection fluid, geothermal wells range from 100 to 250 $/m (30 to or even additional fresh water, might be added at 75 $/ft) or approximately two to five times higher the lower hotter depths to percolate upward into than the average costs of oil or gas wells given in the production zone. The latter could greatly aug- Table I. Greider presented other cost data: Sur- ment and artificially stimulate both the production face exploration costs run from $75,000 to $90,000 and useful life of the reservoir. At the Geothermal per typical area of interest. Only one out of four Resources Research Conference in Seattle, in Septem- of these areas would probably justify an exploratory ber 1972,36 two recommendations were that high pri- hole, resulting in $300,000 to $380,000 per drill- ority be given to immediate improvement of explora- able prospect. Only one of four of these prospect tion methods and to the development of cheaper wells would be worth running pipe and completing for drilling methods in high-temperature formations. These improvements would result in improved -- extensive testing. The three unsuccessful wells would cost $100,000 to $200,000 each and the com- pleted wells $150,000 to $250,000. The net aver- reservoir and economic models which, the conference attendees also concluded, were sorely needed. age cost for each prospect worth completing and 4. Costs. Let us start ,thisdiscussion on testing extensively is then $650,000. Perhaps one costs with a look at average costs for oil and gas of four of the completed prospect wells would re- wells as presented in the 1972 Joint Association sult in the discovery well of a reservoir large Survey Report on drilling costs37 and presented in enough to be commercially attractive. The ratio of Table I . total wells drilled to each discovery well is 16:l. For a number of reasons the costs of geothermal Creider feels that this is a realistic ratio as the wells are greater than those of averake oil and gas industry matures after the large easily located wells. Greider" of Chevron Oil compiled cost data reservoirs are drilled. AxtellS9 of Phillips Petro-? on geothermal exploration wells as follows: Wells leum Corp. agreed that 16:l is reasonable and cited to depths of 1.5 km (SO00 ft) in most geothermal historical data showing five discovery wells out of provinces in sedimentary basins in the U. S . average 75 exploration geothermal wells for a 15:l ratio. 65 to 100 $/m (20 to 30 $/ft). In remote areas or Greiders definition of a good discovery well is one in those with interbedded volcanic rocks, costs run defining a reservoir capable of 275 M ( ) power out- We from 100 to 200 $/m (30 to 60 $/ft). To run casing put. A summary of his cost model is shown in Table ItIs 7
  • 14. TABLE I1 given in Section I11 where rock-glass-lined holes I COST TO PRODUCE A DISCOVERY WELL are discussed. B. Problems in Completing Geothermal Wells FOR A 275-MW(e) RESERVOIR 1. Dependence on Oil-and Gas-Drilling Cost,$ % of Total Equipment and Methods. The.methods used in makingLand acquisition (nontech- nical leasing, bonus, geothermal wells are essentially the same as those rentals, etc.) 3,580,000* 45 for oil or gas wells. Indeed, this very fact some-Drilling (12 unsuccessful + what impedes GTE development because geothermal well 4 completed holes) 2,600,000 32 drillers are forced to use materials and equipmentSurface exploration (geol- ogy, geochemistry, geo- that are not necessarily best for geothermal wells physics) 1,840,000 23 with their higher temperatures and corrosive condi- tions. Problem examples are: (1) only oil-well Total 8,020,000 100 tubular goods and bits are available, (2) muds and*Considering the recent high bids made at the Jan. cements are not checked out for high-temperature 22, 1974 KGRA competitions in California. these costs are probably low. use because suitable high-temperature laboratoryIn Table 11, drilling amounts to 32% of the costs equipment is not available, and ( ) bit-bearing 3and is significant. Tabie I1 can also be used to lubrication systems are not designed to.withstandindicate the possible overall exploration drilling GTE temperatures. This dependence is designated ascosts to, e.g., the year 2000. Recalling Muffler an important consideration in the NSF-sponsored 40and Whites estimate that GTE might supply 10% of study of impediments to geothermal developmentthe nations electrical power (see Section 11, A 1 ) being done by Bechtel Corp. for The Futures Group,and the AEC predictionz3 of a total U.S. power ca- Inc. 2 . Geological Factors. The geological char-pacity of 2,000,000 MW(e) by the year 2000, onearrives at 200,000 M ( ) supplied by GTE in 2000. We acter of The Geysers, a vapor-dominated reservoir,This is low compared to the estimate36 of 395,000 is described by Cr~mling.~ The area is underlainMW(e) by 2000 made at the 1972 Seattle by the Jurassic-Cretaceous Franciscan formation --Geothermal Research Conference. However, using an eugeosynclinal sequence of graywacke, shale, ba-the 200,000-MW(e) estimate, 727 of Greiders salt, and serpentine. These Mesozoic rocks were275-MW(e) plants would be needed. Neglecting any uplifted and complexly faulted into a series ofeffects of capital costs and inflation, the total horsts and grabens and during Pleistocene time,costs for exploration drilling only for the 727 volcanic rocks were erupted onto the then erodedplants would be $2,600,000 x 727 = $1.89 x 109 . surface. The Geysers is at one end of a graben withThis simple calculation of exploratory drilling Franciscan graywacke overlain by basalt,which iscosts indicates that the costs are high enough to then overlain by serpentine. In some places theeasily justify the cost of research leading to low- basalt and serpentine have been downfaulted intoer exploration drilling costs. The much higher the underlying graywacke, the geometry of the faultscosts associated with the production and reinjection indicating that the thermal areas are located on thewells will be discussed later. fissures closest to the serpentine body. The Qua- A factor worth noting is that the hole size of ternary volcanic rocks indicate the presence ofan exploratory well is almost always the same as if young hot magma at depth. The rocks are hard andit were a production well, the reason being that a badly jointed. Not all geothermal areas have the charactersuccessful discovery well can then be easily con-verted to a production well. With current cemente& described above. For example, large sedimentary basins can provide hot water. In Hungary, Boldiz- .casing methods it is not feasible to drill a small-er, more economical well and later enlarge the well sar42 describes the Hungarian Basin of the Danubeto production size. A possible method for enlarg- River system as being filled with several kilometersing small exploratory holes to production size is of sand and clay sediments spreading over an area 2 of 92,000 km . No volcanic activity occurred in ,- ,8
  • 15. this area during the Cenozoic Era, but the heat flow equipped for rapid changes in drilling procedures is higher than normal-- between 0.084 and 0.142 as hole conditions change.45LJ W/m2 12.0 and 3.4 HFU (pcal/cm2 -s)] -- and thermal Another type of surface capability lacking in gradients are 50 to 70 K/km. Water free-flows at GTE work is the so-called Optimized Drilling "con- 357 K from wells of 1.8 km average depth and is cept". This concept has been developed in the oil used for heating buildings and greenhouses. The industry and is described by Lummis.46-48 The con- Imperial Valley, California, is a sedimentary cept envisions the establishment of a standardized basin with static water temperatures approaching data-acquisition system ultimately resulting in a 670 K. well-drilling data bank used to analyze and optimize The large sedimentary basins are usually the drilling of new wells. The data would cover the characterized by above-hydrostatic pressures.34 mud program, drilling hydraulics, bit types, bit Although these strata may be easier t o penetrate rotation, depths, formations, etc. Comparable data with rotary drills than The Geysers type rocks, are relayed to the data-bank location for analysis operations can be complicated by hot corrosive from an active drilling rig. Computer programs water at high pressures. would continuously analyze the data and optimize the Wunderlich4 described how present orogenic modes of operation to minimize total overall cost. activity may be an important factor in influencing Kennedy4 reports cost savings of 30 to 40% on a the heat-flow distribution of the earth and the 14-well program in Wyoming, using the Optimized location of GTE anomalies, in addition to volcanism, Drilling concept. Another example is a 25% savings highly permeable sedimentary basins, and rocks of on two North Sea wells linked by satellite with an high heat conductivity such as rock salt. He Dp-Drilling" headquarters in Tulsa, Oklahoma. states that "Some of the interesting zones of 4. Drilling. In current geothermal wells, abnormally high heat flow show a characteristic drilling is easy in some sedimentary basins and is position relative to young orogenic belts. Usually, very difficult in hard, fractured rocks found, e.g., orogenic fronts are combined with low heat flow at The Geysers. The latter results in high bit wear values in the foreland and high heat flow behind and often in failures of bit bearings due to a com- the front." Further development of Wunderlichs bination of temperature, stress, corrosion, and thesis may furnish guidance for locating new "hot fatigue effects. Cromling41 describes typical ac- spots" associated with young mountainous regions. tual penetration rates of 3 to 6 m/h, using mud, 3. Surface Sites and Equipment. Because geo- and of 3 to 11 m/h using air as the circulating flu- thermal anomalies are often located in volcanic and id for 310-mm (12-1/4 in.)-diam holes. In the final mountainous terrain, the drilling sites Can cause 222-mm (8-3/4 in.) hole into the production zone problems and abnormal expenses. Cr~mling~ldescribes (on air). rates of 7 to 23 m/h are attainable. Of his drilling-site problems at The Geysers very well. course, the overall effective penetration rate can He cites rugged, mountainous terrain; very small be considerably less than the actual drilling rate, drill sites; blasting required often; little top soil as illustrated by the detailed drilling data given and that little sloughing readily; steep roads re- by M a t s u ~ tand shown in Table 111. He states that ~~ quiring tractor towage; pits on various levels, etc. in Japanese steam fields, rock hardness, lost cir- His site costs run from $10,000 to a s much as culation, and other conditions unique to geothermal $40,000. The latter cost is corroborated by Hutchin- wells cause drilling of steam wells to be slower son of Standard Oil of Calif~rnia.~~ Cromling also than drilling for oil or gas at depths ranging from reports that at The Geysers the drill rig should be 500 to 1300 m and working at downhole temperatures overdesigned for the job so as to withstand the of about 370 to 510 K. excessive torque and shock loadings. To broaden our understanding of factors Of significant economic importance to the GTE affecting geothermal well drilling we have studied exploratory drilling industry is the lack of a the activity logss1 for 125 geothermal wells drill- modern, easily moved drilling rig capable of ed in California. The majority of the data were penetrating to depths of up to 4 km and adequately 9
  • 16. TABLE I11 AVERAGE DRILLING RATES FOR SIX GEOTHERMAL W L S I N JAPAN EL 50 (Data from Matsuo ) Average Penetration Average Total Rat e Overall Rate W11 e Twe Depth, When D r i l l i n g t o Total Depth Designation We1 1 - - m m/d - m/h m/d m/h Shikabe HGSR-1 Production 500 13.9 0.58 10.0 0.42 Matsukawa R-3 Production 210 17.3 0.72 11.4 0.48 Ohnuma R - 1 Production 850 25.0 1.04 12.8 0.53 Onikobe GO-10 Production 1350 18.2 0.76 10.9 0.45 Takinokami Survey 403 16.1 0.67 11.5 0.48 Takenoyu Survey 309 15.2 0.63 8.9 0.37e i t h e r from t h e general Geysers area or from Imperi- range. A s i m i l a r p l o t i s shown i n Fig. 3, buta l Valley, California, and a r e here designated Steam, for o v e r a l l average penetration rates where t h eHard Rock (SHR); and Hot Water, Sedimentary (HWS); average includes t o t a l time f r o m spudding-in t orespectively. The data include 92 S R and 33 HWS H t o t a l depth. In t h e Imperial Valley t h e penetra-type wells. Their depths a r e indicated i n a f r e - t i o n r a t e s peak a t about 1.5 t o 2.5 m/h (4.9 t oquency of occurrence-versus-depth p l o t i n Fig. 2. 8.2 f t / h ) for 42% of t h e wells analyzed. In TheSelected depth i n t e r v a l s a r e 300 m . About 40% of t h e Geysers, 52% of t h e r a t e s peaked a t 1 t o 2 m/h (3.3Imperial Valley wells ranged i n depth from 1300 t o t o 6.6 f t / h ) , somewhat lower than t h e peak r a t e s i n1900 m (4300 t o 6200 f t ) . In t h e Geysers 50% of t h e t h e Imperial Valley. Iwells a r e i n the 1900- t o 2500-m (6200- t o 8200-ft) The same data a r e shown i n Fig. 4 and 5 as 40 c The Geysers vicinity hard rock stem-dominated (92 wells) i - cn s3 0 40 The Geysers vicinity steam-dominated - 6 e c 0 0 020 e E IO 0 3 6 9 1216 - 0 0 3 1 6 2 3 9 1 2 4 0 0 u 0 4 8 1 1 2 2 (m/h) 3 4 2-0 0 Overall Average Renetmth Rate 1 (mlh) 2 (f trh) 3 4Fig. 2. Depths of geothermal wells d r i l l e d i n two Fig. 3. Overall average penetration r a t e s i n geothermal regions .So t y p i c a l geothermal wells.50 10
  • 17. penetration rates-versus-depths p l o t s . For t h eW I Imperial Valley, t h r e e widely s c a t t e r e d p o i n t s were discarded, and t h e remaining 91% o f t h e d a t a l i e i n -IO an area as shown. S i m i l a r l y , 99% o f t h e d a t a are enclosed i n Fig. 5 f o r t h e Geysers. The d a t a t r e n d s i n d i c a t e a decrease i n penetration rates with depth - -8 i n t h e Imperial Valley and a lesser decreasing t r e n d . r i n t h e Geysers. In t h e Imperial Valley t h e wells % ,-c* are d r i l l e d t o t o t a l depths with muds and a t higher temperatures and pressures than a t The Geysers where -4 t h e d r i l l e r s use air (which is simpler t o handle than hot muds) f o r much of t h e well i n more compe- -2 t e n t rock and a t lower temperatures. The d i f f e r e n c e i n d r i l l i n g techniques may account for t h e fact t h a t , I I I I I 1 I I 0 1 2 - 4 even though t h e strata a t t h e two l o c a t i o n s are (km) i ; v a s t l y d i f f e r e n t , t h e penetration performance is 1 0 I 2 4 I 6 8 0 I 12 h not. The Imperial Valley d a t a average 1570 m Total Well Depth(kft1 (5160 f t ) depth and 1.82 m/h (5.97 f t / h ) p e n e t r a t i o n Fig. 4 . Overall average penetration r a t e vs depth rate. Corresponding averages f o r The Geysers are f o r sedimentary h o t water wells.50 1890 m (6230 f t ) and 1.98 m/h (6.49 f t / h ) . However, 38 - well c o s t s at The Geysers, according t o Greider and C r ~ m l i n g ,are 1.5 t o 2.0 times higher, pro- ~~ bably because of higher c o s t s due t o d i f f i c u l t sit- ing conditions; erosion by high-velocity a i r and steam flow; and high b i t f a i l u r e rates i n h o t , hard, j o i n t e d rocks. I 12 1 The l o s t - c i r c u l a t i o n problem mentioned earlier is t y p i c a l o f The Geysers and o t h e r locations where low ground-fluid pressures e x i s t i n badly f r a c t u r e d o r highly permeable formations. Cromling41 and BuddS2 both v e r i f y t h i s problem a t The Geysers. A s i m i l a r problem occurred i n t h e Jemez Mountains at t h e Los Alamos S c i e n t i f i c Laboratorys second hot- dry-rock experimental well, GT-2, where excessive lost c i r c u l a t i o n i n t h e sedimentary s e c t i o n was en- countered i n t h e first 600 m. This problem is o f t e n solved by changing t h e d r i l l i n g f l u i d from mud t o air. The use of a i r i n a steam w e l l , however, re- s u l t s i n excessive erosion o f t h e d r i l l stem a n d o f a l l o t h e r metal p a r t s i n contact with t h e mixture of a i r , steam, and c u t t i n g s being blown out of t h e well. The flow r a t e o f t h e a i r is f i x e d by t h e bit-cooling and debris-removal requirements, b u t steam entering I I I I I 1 0 2 4 6 a 0 t h e well anywhere-above t h e b i t adds t o t h e t o t a l Total We1 I Depth (kft) volumetric flow rate t o create t h e excessive-veloc- i t y flow condition. The lack of adequate d i r e c t i o n a l c o n t r o l equip-W Fig. 5. Overall average penetration r a t e vs de t h f o r steam-dominated, hard-rock wells. 58 ment i n hard rocks i s a problem. states Cr~mling~~ 11
  • 18. that directional drilling at The Geysers is expen- need for cement squeezing, i.e., the special appli- cation of high pressure to force the cement back ofsive and adds as much as $100,000 to the cost of awell in difficult situations. MatsuoSo and Suter53 the casing, to recement channeled areas, or to iboth confirm the desire for good directional control correct cement-deficient zones. Cromling reportsand point out the difficulties of attaining it in requiring squeezing in about 50% of the wells athot hard-rock formations. For production wells, The Geysers. Dench listed four possible failure 54especially where the surface sites are expensive modes, which may result if the cementing operationand difficult to set up, directional control would leaves a length of casing not bonded to the hole:allow three or four wells to be drilled from one ( ) water in the annulus expands when the well 1central surface area. Currently available direc- goes into production causing high temperature/pres-tional downhole motors are inadequate in geothermal sure buildup and casing failure, (2) compressivewells because of high temperatures and also because failure of a joint due to heating, ( ) tensile 3water or mud is often used to drive the motors, failure of a joint due to cooling, and ( ) failure 4whereas the drilling fluid may usually be air. of the well-head connection. An example of the 5. Casing and Cements. The presence of hydro- first type of failure is the Matsukawa Well R-4 in 50gen sulfide is not new to the drilling industry and Japan where the casing collapsed at 35 m relatively common in GTE projects. Dench54 Matsuo reports that such repairs are very difficultreviewed the problems of casing design in the and expensive. Matsukawa Well R-3 also had a casinggeothermal fields of New Zealand and described the failure for some undefined reason when casing frag-problem of cold, damp hydrogen sulfide in contact ments began to be blown out of the well after sevenwith casing at high tensile stresses causing frac- months of production followed ten months later byturing in all grades of casing steels tested. In blowout of a large quantity of casing case, failure occurred at only 25% of the One possible reason for the latter type failurenormal ultimate strength. Due to thermal expansion andcasing disintegration is the fact that, typically,and contraction effects the casing joints can be a GTE steam well uses the stepped casing as the pro-loaded either in tension or in compression. Crom- duction-flow passage, which is constantly directlyling recommends buttress joints, which cause in- exposed to the high-velocity steam flow. In oilcreased casing costs, for wells at The Geysers. or gas wells, on the other hand, an inserted pro-Another temperature-caused problem is brought up duction tube of constant diameter is normally usedby Suter who states that casing wear occurs in The which is easily removed for maintenance, if neces-Geysers wells because rubber drill-pipe protectors, sary. A well-drilling system that would produce aused to centrally locate the drill pipe in the well, hole of constant diameter to total depth would fa-fail due to temperature and allow the drill pipe to cilitate the use of a production tube. Also, itrub against the casing. A problem of high operating would avoid sudden turbulent expansion conditionspressure requiring either new high-strength materials across a step that can cause precipitation of saltsor very heavy casing walls was noted by Bealaurier40 from the expanding fluid and their deposition onfor geopressurized wells under both static and the casing walls.dynamic flow conditions. 6 . Drilling Fluids and Muds. The use of air as In geothermal wells, one function of the casing the drilling fluid and the resultant erosion problemcement is to prevent the detrimental intrusion of have already been noted. Water is another readilycold water into the well. It was found early that available and easily handled drilling fluid, whichcommon cement at high temperatures suffered strong can be used if the downhole fluid pressure is notretrogression effects and became highly permeable, above hydrostatic and if lost circulation, should itas reported by Nakajima.” Special cement mixtures exist, can be compensated for by either having suffi-capable of setting up properly at higher temperatures cient makeup-water flow capacity or by pumping allhave been developed and will need further improve- the water and debris directly into the formation withment as temperatures in future GTE developments zero return to the surface. However, if the groundbecome higher. Nakajima Mentioned the frequent12
  • 19. fluid pressures are above hydrostatic then special of 25 reinjection wells would amount to $3,000.000LJ drilling muds must be composed, which are compatible with high temperatures and meet the following re- to $3,500,000. Thus,the total cost for production and reinjection wells would be -$10,750,000 per quirements: The mud must have the density needed complex. to hydrostatically balance the downhole pressures These costs, which average 94 $/m (29 $/ft), and to otherwise stabilize the hole; its surface are reasonable considering that only about one in tension must be adequate to transport the bit cut- twenty geothermal fields24 would be in a vapor-domi- tings out of the hole; it must serve as a good bit nant field like The Geysers, where drilling is most coolant; it must not dry out and bridge flow pas- expensive. Then, continuing the example started in sages during cementing (leading to casing failures); Section II,A,4, the total costs of production and and it Must not dry out or change chemically during injection wells to develop a complex with 200,000 time-consuming operations such as changing bits. MW(e) power output would be 727 x $10,750,000 = There are many references in the literature to the $7.28 x lo9. This, added to the previously derived high-temperature mud problems in geothermal wells. exploratory drilling cost of $1.88 x lo9, gives us Recently, GreiderS6 of Chevron Oil wholeheartedly the total drilling expenditures, $9.7 x lo9, just endorsed the development of high-temperature muds for finding and setting up the wells. Clearly, GTE and cements. Also, the Bechtel Corp. study4’ lists drilling with current techniques could be very 588 K as the current limit for muds. costly (e.g., running into tens of billions of 7 Downhole Measurements and Samples. The . dollars) making it quite worthwhile and cost-effect- early exploration and modeling phase of a GTE ive to develop new, cheaper techniques and equipment. reservoir requires taking many: downhole measure- Note, again, that the initial assumption of 200,000 ments and samples of the rock and general fluids. MW(e) may be low. Wither~poon,’~ is involved with studies of the who The above discussions of cost centered primar- national geothermal resources, feels that equipment ily on wells in conventional GTE areas where maximum and methods for obtaining the required downhole depths may not exceed 3 km. For hot dry rock and data leave much to be desired. Cores are used to perhaps geopressurized developments the depths and obtain data on the type of strata being encountered, drilling costs could be considerably higher. Costs on fracture orientation, and on other phenomena. increase very rapidly with depth, as illustrated in However, cores are taken in insufficient intervals Fig. 6. The average oil and gas-well costs are and the taking of many more core samples would be shown shaded; typical The Geysers and Imperial highly desirable. The alternative and perhaps ulti- Valley geothermal costs are shown as 160 $/m mate approach to this problem is to develop new (50 $/ft) and 80 $/m (25 $/ft), respectively; for downhole diagnostic techniques. Ground-water sam- depths of 15 km, costs could be - $ 2 0 , 0 0 0 , 0 0 0 to ples are also very important, if they can remain $26,000,000 per well. chemically undisturbed between the time of in situ 9. Summary of Current Drilling Problems. It sampling and the time of chemical analysis. In a has been amply demonstrated that naturally occur- water-based GTE reservoir assessment program the ring hot-water or vapor-dominated geothermal reser- data should, at a minimum, be sufficient to deter- voirs can be penetrated by rotary drilling methods mine downhole temperatpres and pressures, porosity, thdt have been developed for oil and gas wells. permeability, fluid chemistry, and GTE producibili- However, there are factors in geothermal fields tY. such as high temperature, corrosive fluids and 8. Costs. Cost data for a typical exploratory gases, unfavorable siting conditions, and, in many geothermal well have been presented in Section 11, cases, hard abrasive rocks, which combine to make A,4. According to Greider’s data for large-scale the average rotary-drilled geothermal wells more development of 275-MW(e) GTE complexes, the cost expensive than the average oil or gas wells of eom- of 50 production wells per complex would, with parable depth. High well costs could significantly careful planning, average $7,500,000; and the cost impede the expansion of geothermal energy sources 13
  • 20. s t i l l not c l e a r whether maximum output has been . reached. Also, complete monitoring of production performance a t Larderello has been i n i t i a t e d only recently. Indications a r e t h a t some Larderello areas have reached t h e maximum because steam y i e l d s per well have been d e ~ l i n i n g . ~ However, successful d r i l l i n g is being done a t t h e previous margins of t h e f i e l d , indicating t h a t t h e t o t a l heat resource is not completely understood. BuddS2 presented productivity data s t a r t i n g from 1967 a t The Geysers f o r wells feeding Genera- t i n g Unit 3. Two t y p i c a l wells showed a drop t o 50% of the o r i g i n a l production rate i n f i v e years. These wells a r e spaced a t 50 per km2 (one per 5 A a c r e s ) . KoenigS8 considers t h a t four or f i v e times fewer wells per area is more t y p i c a l . w,eil inter- ference was a l s o established,and a sharp production decrease was measured with more c l o s e l y spaced wells. Another e f f e c t of high production r a t e s w i t h - out r e i n j e c t i o n f o r sustained periods of time is surface subsidence, e s p e c i a l l y i n hot-water f i e l d s . The most notable data on subsidence a r e f o r Waira- k e i , Nw Zealand. a s reported by H a t t ~ n . ~ ’ A t t h i s eFig. 6. Cost of wells per meter vs depth. f i e l d , which has been monitored s i n c e 1956, the maximum subsidence r a t e was 0.4 m per annum (1.3 f tt o t h e level where they could contribute substan- per annum) and, a s of 1970, a t o t a l subsidence oft i a l l y t o our national energy supply. g r e a t e r than 3 m (10 f t ) i s indicated. In N w e There a r e many applications f o r geothermal tem- Zealand, t h e expended water was not i n i t i a l l y r e i n -peratures l e s s than 660 K, which is about t h e upper j e c t e d because disposal on t h e surface was permitted,l i m i t measured at well bottom t o date. To a t t a i n but now r e i n j e c t i o n i s being t e s t e d , a l s o .t h e higher temperatures d e s i r a b l e or required f o r Reinjection of spent f l u i d s has several objec-many heretofore unexploited GTE applications, one tives: F i r s t , t o dispose of t h e f l u i d e s p e c i a l l yhas t o consider penetration e i t h e r i n t o deep hot i n hot s a l i n e f i e l d s where salt disposal i s a l a r g ezones or close t o or d i r e c t l y i n t o magmas. Current problem; second, t o help prevent subsidence; t h i r d ,d r i l l i n g methods (especially t h e use of muds and ce- t o help recharge t h e r e s e r v o i r . However, becausemented casings f o r hole control and support) w i l l known r e s e r v o i r s are not completely understood, t h ethus be severely s t r a i n e d technically and w i l l p m - proper recharging procedures are not well estab-bably make t h e wells excessively expensive. lished. A evaluative summary of t h e various current n One concept envisions adding more than j u s td r i l l i n g problems i n geothermal wells i s shown i n spent waters back i n t o t h e r e s e r v o i r by i n j e c t i n gTable IV. additional water from some other convenient source.C. Production Operational Problems For example, it has been suggested t h a t i n some way 1. Production Loss with Time; Reinjection; water from t h e Gulf of California might be used t oand Augmentation. Only limited data a r e available recharge t h e Imperial Valley. Aon production l o s s with time. Even though Larder- 2. Large Surface Piping. Because each welle l l o has been producing power since 1912 it is might supply steam f o r only 5 t d 10 MW(e) of power14
  • 21. TABLE IVW SUMMARY OF CURRENT GEOTHERMAL DRILLING PROBLEMS Surface locations --- G G: Difficult geological conditions typical of many GTE fields, including sites, hard rocks, caving formations, etc. Drilling-rig design RsX R,GsX R: Rigs of high mobility are needed, adequately equipped to handle rapid changes in hole conditions. Other surface equip- T,C,X T,C,E,X X: Dependence on oil- and gas-industry materials ment and equipment, competition for supplies. Bits and drillability T,C,D,X G,T,C,D,X T: Temperatures up to -660 K cause rubber, elasto- mer, metallurgical, mud, cement, and electronic problems. Mud-circulation T,GsF,X T,G,F,X C: Corrosion problems caused by ground fluids and systems gases. Hole support and G,T,F G*T,F E: High stem, casing, and surface-equipment erosion control by air + steam + rock cuttings. Cements T3X D: Directional drilling equipment not available for hard rock at high temperatures. Downhole measurements T,X TsX F: Hot saline waters contaminate drilling muds. Also, muds can reduce or kill well productivity or may hydrate clays. Tubular goods T*C,X T,C,X 0 : Lack of organized GTE wells drilling-data bank and ways to use such data to optimize drilling programs. Optimized drilling 0 0 H: Costs are typically high because of interrelating effects of items listed above. Costs of geothermal H H wells production the collecting system of a power complex be designed to facilitate rework and maintenance. must clearly consist of a considerable array of Such rework might include cleanout of the scale and steam and hot-water lines. Budd described how the keeping the production zone clear to allow the lines at The Geysers vary from 300 mm (12 in.) to fluid to enter the well. A failed cemented steel 900 mm ( 6 i . in size in the surface installa- 3 n) casing cannot now be repaired easily or cheaply and tion. Directional drilling capability might be could result in abandonment of a well. useful to help minimize the problems of deploying 4 . Desirability of Higher Electric Power surface lines by concentrating several well heads Generating Efficiency. Due to the approximate in one area. temperatures of 470 to 620 K in conventional I X E 3. Corrosion and Scaling. In hot-brine fields reservoirs the thermal efficiency for generating the corrosion and scaling of surface equipment electric power is only about 14 to perhaps 25% com- are very severe problems. The problem also exists pared with approximately 33 to 40% for nuclear and for production wells, and wells should therefore fossil-fueled plants, respectively. If GTE wereW 15
  • 22. to become a large source of electric power thenthermal pollution could also become a significantproblem. The efficiency could conceivably be in-creased by the development of advanced.drills thatcan penetrate very hot GTE resources such as magmaor very deep, hot, dry rocks, increasing the power-plant operating-temperature levels. Such advanceddrilling devices are discussed in the next section. 5. Summary of Current Operational Problems. . 0 The decrease of well productivity with time has been observed in existing geothermal fields. This might be pre- vented with proper reinjection or aug- mentation techniques. Surface subsi- dence has also been observed and might be expected if widespread water withdrawals are made without replace- ment. Because each well has a steam produc- tion rate equivalent to only 5 to 10 Fig. 7. Cross section of hole melted in tuff. M() W e , a considerable number of wells are needed to generate, e.g., several hundred megawatts of power; hence, the surface array of piping becomes rather comp1ex. progressive melting with a non-rotating,hot bit 0 There are corrosion and scaling prob- rather than by chipping, abrading, or spalling.60 lems in geothermal wells, which require Rocks and soils melt at temperatures that are rela- that the installation be designed for long-term maintenance and replacement of components subjected to these - tively high: e.g., common igneous rock melts at 1500 K, almost the melting temperature of steel (1500 to 1800 K. Thus, the melting penetrators uti- ) problems. lize refractory metals such as molybdenum (Mo) and 0 The thermal efficiency of geothermal tungsten ( ) which melt at 2880 and 3650 K, respec- W, electric power plants is lower than tively, and which, in addition, have low creep rates that of nuclear or fossil-fueled at the rock-melting temperatures. plants. This is not an economic Excavation by rock- and soil-melting offers problem but relates to long-term ther- potentially new and novel solutions to the three mal pollution of the earth and needs major areas of the excavation process: to be addressed before geothermal Making the hole or breaking up the rock. electric power plants are developed on Providing structural support for the a large scale. borehole. 0 Removing or displacing the debris or111. CONCEPTUAL APPLICATIONS OF SUBTERRENE DEVICES cuttings. TO GEOTHERMAL WELLS The liquid form of the rock- and soil-melt produced A. Subterrene Program History by a heated penetrator introduces new solution con- Rock-melting penetrators (Subterrenes) are cepts into the latter two areas:under development at the Los Alamos Scientific 0 The liquid melt can be formed into a glassLaboratory (LASL) to produce self-supporting glass- lining to seal or support the walls of thelined holes in rock and soil (Fig. 7) by borehole, and16
  • 23. _. Any excess l i q u i d melt can be c h i l l e d andW formed i n t o g l s p e l l e t s , or rock wool (Figs. 8 and 9); or used t o form aglass-cased core t h a t can, f o r example, be removed by present w i r e - l i n e methods. The LASL development program i n rock- and soil-melt- ing techniques has already demonstrated i n laboratory and f i e l d tests an a t t r a c t i v e advancement i n p r a c t i - c a l excavaF>on technology f o r t h e production of s h o r t I h o r i z o n t a l , small-diameter holes. This experience has been p k i a l l y developed ,through t h e extensive Fig. 9. Debris from b a s a l t hole made by extruding t e s t i n g oftmelting-consolidating p e n e t r a t o r s p e n e t r a t o r showing rock wool and g l a s s - p e l l e t constituents. (MCPs) .61 h e t e s t s consisted o f : .* Melting 50-mm (2-in.)-diam, glass-lined dralin holes i n Indian ruins62 a t Bandelier Melting a 50-m (2-in.)-diam g l a s s - l i n e d National Monument (Fig. 10). horizontal hole i n Los Alamos volcanic t u f f Melting a 50-mm (2-in.)-diam g l a s s - l i n e d t o a length of 16 m (50 f t ) , Figs. 1 and 12. 1 ve&ical hole i n Los Alamos volcanic t u f f t o .* 63 a depth of 26 m (82 f t ) i n a s i n g l e run. Fig. 8 . Hole melted i n g r a n i t e specimen with an extruding penetrator. Note d e b r i s . 17
  • 24. cFig. 10. Modular Subterrene f i e l d demonstration u n i t melting d r a i n holes a t Bandelier National Monument. Fig. 1 2 . Stem and s e r v i c e head i n p o s i t i o n t o melt a 50-mm (2-in.)-diam horizontal hole. -/. I f # ( " I , Melting a sequence of 76-mm ( k i n , ) - d i a m glass-lined holes i n v o l c a n i c t u f f i n t h e laboratory (Fig. 13). Melting s t a b l e 50-mm-dim glass-cased holes i n s h a l e s , adobe, and allwiw (Fig. 14). In addition, t h e prototype test program has develop- ed a universal extruding penetrator (UEP) designed f o r hard, dense rock.64 Tests with t h i s u n i t have r e c e n t l y demonstrated t h e capability,:? penetrate b a s a l t a t a 620 K temperature with enhanced perfor- mance compared t o cold rocks. The modularized, mobile f i e l d - t e s t and demon- s t r a t i o n unit6 (Fig. 10) t h a t was a t Bandelier National Monument w i l l be used f o r a d d i t i o n a l f i e l d t e s t s and for demodtration of i m - proved consolidation and extruding penetrators. The most recent addition t o t h e f i e l d - t e s t equipment is shown i n Fig. 15 and is a trailer-mounted r i g for -Fig. 11. Consolidating Subterrene penetrator use i n t h e near f u t u r e t o make a 30-m-deep demon- * * "holing through" a 16-m (SO-ft)- s t r a t i o n hole i n b a s a l t . J I I long horizontal hole.18
  • 25. i Fig. 13. Consolidating penetrator after melting a 76-mm (3-in.)-diam hole in Los Alamos tuff. Fig. 15. Rig for vertical Subterrene hole production. In addition, LASL has conducted preliminary tests on a 114-mm (4.5-in.)-diam9 consolidating? coring penetrator designed to produce a 63-mm (2.5-in.)-diam glass-encased core. B. Basic Subterrene Technology 1. Basic Types of Penetrators. To illustrate basic technology, the design features of three devices that have been used in rock-penetration tests are described below. a. Melting Consolidating Penetrators (MCPs). Fig. 14. Exterior v i These penetrators utilize density consolidation for melt disposal, such consolidation relying uponW the porosity of the parent rock or soil. The process 19
  • 26. is illustrated in Fig. 16, which shows how therock melt is formed into a glass lining ?nd how thelarger hole diameter is melted to accommodate thelining. The need for debris removal is completelyeliminated. The ratio of outer-to-inner glass-lining radius can be related by conservation-of-massconsiderations to obtain: ooscoolont POSsogeS JT m= - 1 IP E*&ka! annecterwhere r is the outer radius of the glass lining, r m P w-is the radius of the penetrator or inner glass lin- Glass Farmering (hole radius), pR is the unmelted rock density, lnwlataand pL is the glass-lined density. Figure 17 is a Wb - yd Extmctordesign sketch of a MCP which has been tested success-fully at LASL. The various components are designated. Radiant Heater Graphite l h e d Receptor Penetrata Body Electrkal ctadt m I Unmclted porous rock -I Panatrator porosity. 44% Fig. 17. Design sketch of the Melting Consolidating Penetrator (MCP). b. Universal Extrusion Penetrators (UEPS). The UEP development was primarily directed to- ward melting holes in dense rock. However, because these devices can be used in most other rocks or soils, they are termed "universal". A sketch illus- trating the UEP concept is shown in Fig. 18. The mechanical design is similar to that of the MCP. The s .- molten rock confined by the unmelted rock and by the - F 0 a Penctmta melting surloce hot face of the penetrator is extruded continuously 0 through a hole (or holes) in the melting face. This 01 material is chilled and freezes shortly after the - - s u ?! Melting interface a t temperature. 1 , ) circulating cooling fluid impinges upon the extrudate a exiting from the extrusion region. If frozen quick- ly, the material will be in the form of frozen glass rods, pellets, or rock wool. The flowing coolant can then transport these small fragments up the stem to the exhaust section. Typical pellets and rock wool that were formed from frozen extrudate and were . k a d i u s removed by the cooling fluid during a basalt test were shown in Fig. 9.Fig. 16. Schematic of density consolidation in porous rock. c. Consolidating Coring Penetrators (CCPs) . The concepts incorporated in the MCP and UEP 20
  • 27. e Pyrolytic Graphite Thermal bulatwFig. 18. Design of the Universal Extruding Penetrator (UEP) . Fig. 19. Design concept of consolidating-coring penetrator.designs described above have been expanded to in-clude a technique for obtaining continuously re-trievable, oriented,and geologically interestingcore samples from the material being penetrated.The coring concept utilizes an annular meltingpenetrator which leaves an unmelted, but glass-encased, core in the interior that can be removedby conventional core-retrieval techniques. Al-though the concept is applicable to either theextrusion or consolidation mode of melt-handling,initial program emphasis has been placed on a con-solidating-coring penetrator as illustrated inFig. 19. A 114-mm-diam consolidating corer foralluvial soils has been tested in the laboratory.The core diameter is 64 mm. and the molybdenummelting body is fabricated as a single structuralcomponent as shown in Fig. 20. The water coolingsystem represented a departure from previous gassystems and performed successfully. Minor adapta-tions to commercially available core-extractiontools are visualized. 2. Other Coring Designs. To furtherillustrate the design of a Subterrene coringdevice, refer to Fig. 21, which shows theelements of the "Geoprospector". The Geo- Fig. 20. Photograph of 114-mm-diam consolidating-prospectorss purpose is to core and geologically coring penetrator. 21
  • 28. I-., Ml eW t Penetrator Glass Packer Flex Coolant Br Cae Retrieval " 7p-rl " " 7 Rock Heated core- Melt Cavity sensor Fig. 2K. Geoprospector conceptual design.explore horizontal tunnel routes,but its design is Figure 22 illustrates a liner deliberately keptillustrative of devices which may be used to pro- thinner by utilizing a UEP in porous tuff. Excessduce vertical wl es l! This design has been developed debris in the form of glass rods was removed, asin considerable detail at LASL. It requires 150 kW shown. A typical glass liner for hard dense rock,of electric power to melt a 300-mm-diam glass-lined formed by a UEP in granite, is shown in Fig. 8 . Fig-hole while removing a 200-mm-diam glass-encased ure 23 shows a liner formed in permafrost alluviumcore. The stable hole lining allows the use of apacker-thruster unit located in the hole-formingassembly. Provision is also made for an orientation-sensor package and for a guidance unit. A hollow,flexible stem contains the electric-power, coolant,and instrumentation lines and provides a passagefor debris removal. The core is removed through theflexible stem with conventional wire-line core-retrieval hardware. 3. Rock Glass Hole Linings. The Subterrenescapability to continuously form rock-glass linersprovides intriguing possibilities for a well-makingdevice. Figure 7 shows a 50-mm-diam hole madein tuff by a consolidating penetrator where theliner volume is slightly greater than the hole .itself. For larger sizes, liners would bemade only as thick as necessary to meet struc- Fig. 22. Hole in tuff melted by UEP. Note rods oftural, leakage, and advance-rate requirements. extrudate and thin glass hole lining. 22
  • 29. Subterrene: The optimum well hole produc- tion process minimizes excavation damage to the inherent structural integrity of the ground or rock and is then followed by the continuous installation of a structural support and seal to prevent the inflow of ground fluids. This process may well be accomplished by a Subterrene system which makes the hole by melting and simultaneously forms a structural rock-glass liner. Problem: Rock bit wear and temperature- induced failures. Subterrene: A Subterrene depends upon melt- ing, not on cutting or mechanical fragmen- tation, and therefore eliminates this prob- lem. Also, high rock temperatures would Fig. 23. Sample of glass-lined bore melted in enhance the performance of the Subterrene simulated arctic permafrost. bit because the bit has to supply less thermal energy to melt the rock. by a consolidating penetrator. The moisture close Problem: Muds at high temperatures. to the penetrator body was forced into the alluvium Subterrene: Subterrene cooling and debris- and away from the penetrator during liner formation. removal system can be isolated completely or The Subterrenes liner-forming capability might also almost completely from detrimental effects prove useful in preventing methane. which is perva- of the ground or rock. Therefore, the cool- sive in sediments, from leaking into the hole and ing and debris-removal fluid could be, e.g., becoming an explosive hazard during hole production. simply water or any other fluid that is C. Problems That Subterrenes Might Help Solve or easily made compatible with the static E1iminate temperature conditions. We do not intend to imply that rotary drilling Problem: Cements at high temperature. Subterrene: Steel casings may not be neces- methods in geothermal fields should be completely superseded by nonrotating, rock-melting devices. sary if good structural rock-glass hole lin- Rather, a new Subterrene technology would open up ings can be made. If steel casings are options for obtaining the most economically and used, the relatively smooth surface inside technically suitable methods for any particular set the glass lining should facilitate the flow of conditions and requirements. For example, it of the cement. Also, the requirements that could very well be most economical to use rotary the cement be both strong and impermeable drills for making holes rapidly in known, easily should be lessened because of the presence penetrated formations. Then, in hot, hard zones, of the glass lining. the tools and methods might change to Subterrene Problem: Abrasion and erosion due to steam- technology to complete the job. plus-air flow. Listed below are categories of current rotary Subterrene: This problem arises because the drilling problems in geothermal wells followed in amount of air is presently determined by bit- each case by a discussion of how.the use of Sub- cooling and cutting-removal requirements and terrene devices might either help solve or eliminate because steam leakage into the borehole isc the problems. unpredictable and uncontrollable. Subterrene Problem: Hole stabilization in unstable designs can isolate the bit working fluid from any steam inflow. Also, the glassoed formations. lining should minimize steam inflow. 23
  • 30. ~ e Problem: Production-zone hole completion. e Problem: High torque and shock loads on Subterrene: The Subterrene could penetrate long drill stems in deep wells. the production zone with a glass-lined hole. Subterrene: Subterrene bits are not rotated This penetration would not kill or impair and therefore the torque requirements are the zones production capability because eliminated. drilling fluid, cuttings, and lost-circula- e Problem: Difficult surface site conditions tion material would not be pumped into the in some GTE fields. zone. Also, the sealing action of the lining Subterrene: Since such large components would facilitate stem and bit changes, if such as mud ponds and rotary equipment are necessary. Several ways to ultimately com- not needed, the surface installation may be plete the well and to allow the hot water or simplified and more compatible with the steam to flow into the well are conceivable: terrain conditions. One might be to shatter the glass liner with D. Potential Subterrene Applications in Geothermal a linear explosive; another, to convention- - Wells ally perforate the liner with shaped charges; Potential applications of Subterrene devices and still another might be a system in which for making geothermal wells are summarized in Table liner porosity is controlled while the liner V. The four major types of geothermal fields are is formed. listed as hot-water or vapor-dominated, the LASL e Problem: Corrosive environment. hot-dry-rock type, magmas and lavas, and geopressur- Subterrene: The corrosion problems will ized reservoirs. Two basic well functions, explora- change because different materials will be tion and production, are indicated. used. Any drilling system must live with In exploration and currently urgent resource the corrosive materials encountered in the assessments Subterrene devices might make small- earth. However, Subterrene-produced holes diameter, shallow (e.g., 50-mm-diam by 150-m-deep), should be more effectively sealed from the self-cased holes for thermal-gradient measurements. corrosive materials. Also, stem and bit Many such holes will be needed in the near future. need not rotate so that protective coatings Subterrenes could also be useful for economical should be easier to maintain. exploration of deep heat and water reservoirs where 0 Problem: Formation evaluation and sampling. high static temperatures prevail. Subterrene: The Subterrene offers the possi- For production wells and systems there are two bility of extracting a continuous, oriented specialized backup or auxiliary devices that could glass-encased core. The glass hole lining be used in conjunction with conventional rotary eliminates the problem of making logging drilling systems: First, a hole-stabilization tool measurements through a heavy steel casing or for use in caving formations, hydrating or swelling through variable depths of mud invasion. clays, or lost-circulation zones. This tool would Because the glass-lined hole interior is be a thermal device producing either a rock-glass better protected than the unlined hole, the lining or injecting structurally stabilizing materi- possibility of developing continuous down- als into the bore-hole walls. Second, the tool hole logging may be enhanced. would be used for completing holes into production e Problem: Directional drilling in hot, hard zones where high static temperatures and hot fluids rock. are encountered and where reservoir contamination is Subterrene: Hot, hard rock does not bother not desirable. the Subterrene bit, Directional change is In certain water or steam reservoirs, or in possible by either mechanical means or by magmas and lavas that are difficult to penetrate controlling the temperatures circumferen- with rotary drills, Subterrene systems could be tially around the bit. used to produce entire production wells. Production24
  • 31. TABLE, V POTENTIAL SUBTERRENE GEOTHERMAL WELL APPLICATIONS Types of Geothermal Field Basic General Water or Vapor- GeopressurizedFunction Requirements Dominated Reservoir Hot-Dry-Rock Systems Magmas and Lavas Reservoirs e Small and e Thermal-gradient 0 Thermal-gradient e Thermal-gradient economical. holes. holes. holes. E e Directionally e Heat-anomaly probes. e Heat-anomaly probes. x . controllable. P L e Formation e Discovery wells. 0 evaluation R capability . A T e Holes enlarge- I able to pro- 0 duction size, N if desired. Large enough e Special hole- . e Special hole- e Special hole- e Special hole - to achieve stabilization tool, stabilization tool, stabilization tool, stabilization optimum pro- backup to rotary backup to rotary backup to rotary tool, backup to duction flow drills. drills. drills. rotary drills. rates. P R e Directionally e Production wells. e Hole-completion e Production wells e Hole completion 0 controllable. tool in very hot in very hot rocks. in very hot D rocks. rocks. U C e Hole made can e Reinjection disposal e Production wells T be reworked and holes. in molten rocks. I maintained. 0 e Production-augmen- N tation holes.fields would probably include waste-water reinjec- E. Subterrene Program Accomplishments Stilltion wells and injection wells for production- Requiredaugmentation purposes. These latter type wells, of Although the general feasibility of the Subter-smaller diameter than the production wells, could rene concept has been proven, the establishment ofhave the same diameter as the exploration wells. Subterrene devices as accepted hardware for commer- Note that one of the desirable requirements for cial use in the drilling industry has not yet beensmall exploration boreholes is that the holes be achieved. Extensions of work already underway in-readily enlargeable, if desired, to the size of a clude the development of higher penetration ratesproduction well. With conventionally cased holes, €or applications where this is economically advanta-such an enlargement is very difficult and costly geous, more testing and development of the compati-because the casing is very securely cemented into bility of hot bit materials with actual in situ en-place. In a glass-lined hole the lining might be vironments, refinement of penetrator designs toeither reamed out with a rotary bit or it could be maximize lifetimes, incorporation 6f more efficientmelted and the hole enlarged with a Subterrene bit. bit heating devices such as heat pipes, and elabora-Glass-lined holes, in general, might be readily re- tion of systems and cost studies for specific applica-worked or maintained with Subterrene melting tools. tions. New work is required on such technical aspects as the determination of rock-glass lining 25
  • 32. performance under downhole conditions, development obtaining undistuxbed fluid samples. Samplingof operating controls for producing linings meetingvariable -- requirements, and the development in situ methods that do not delay the drilling operation would be very desirable. tof power feed systems for deep holes. - An electronic network in communication with M S L has continuing program plans leading to drilling projects which would implement the conceptthe development of geothermal well devices such as of optimized drilling by means of centralizedthose indicated in Table V. In the immediate future computer programs and geothermal-well data banks.LASL efforts will concentrate on the production of 0 Two basic types of geothermal holes or wellsshallow holes (e.g., up to 300 m depths for measure- are needed:ments of exploratory data such as geothermal gra- - Small and economical: For shallow or deep -dients), and the development of the hole-stabiliza- exploratory probes into hot reservoirs; for wastetion tool. water disposal; or for reservoir production augmen-IV. CONCLUSIONS tation by injecting water into strategic reservoir The use of geothermal energy, although exploi- locations.ted on a small scale for millennia, has not yet - Large diameter (e.g., 300-mm-diam): Needed todeveloped into a mature industry. handle large hot-water and steam flow rates for 0 Geothermal wells can be produced with conven- many years of production operation.tional oil- and gas-well drilling techniques. How- Advanced drilling systems are needed for bothever, the unique combinations of GTE conditions of exploration and production, which cantemperature, pressure, hard fractured rock, and - Penetrate hard, abrasive rock formations.corrosion raise the cost of average geothermal - Be compatible with high rock temperatures up towells two to five times above the national average approximate magma temperatures, t 1300 K.for equally deep oil or gas wells. - Provide a hole stabilization and support system With current techniques, the drilling of explo- that is compatible with high geothermal temperaturesration, production, and reinjection wells needed and pressures. 0 The Subterrene concept, i.e., forming a hole byfor an electric-power capability of 200,000 MW(e)(10% of projected demand in the year 2000) would rock or soil ihelting, has the potential of greatlycost - $10 x 1 9 in current dollars. Thus, RED 0 . improving the art of making geothermal wells. For the near term, conceivable applications are heat--xpenditures for cheaper drilling equipment andmethods are justified. flow measurement holes, hole stabilization where Short-term improvements in current drilling conventional methods are inadequate, and completionequipment are needed as follows: of final production holes. Over the longer term. - A standardized drilling rig with 4-km depth applications may encompass the production of k t hcapacity, especially designed for mobility and exploratory and production holes, especially inequipped to adapt rapidly to changes in drilling very hot and hard rocks.plans. - Longer lifetimes for bit cutting edges and REFERENCESbearings. - Stem and casing materials that are more readily 1. H . N. Siegfried, "Geothermal Exploration in the First Quarter Century," arranged and edited byavailable than standard oil and gas tubular m o d s and D. N. Anderson and B. A. Hall, Geothermal Re- sources Council Special Report NO. 3 (1973).that can stand up better to GTE temperatures andcorrosive conditions. 2. G. Facca, "General Report on the Status of World - Muds and cements able to withstand high Geothermal Development," Rapporteurs Report, United Nations Symposium, Pisa, Italy (1970).temperatures. - Better methods to measure downhole temperature, 3. J . B. Koenig, Worldwide Status of Geothermal Resources Development," in Geothermal Energy, P. -pressure, porosity, permeability, fracture orienta- Kruger and C. Otte, Eds. (Stanford University - Press, Stanford, CA, 1973), Chap. 2.tion, and general lithology plus the means of26
  • 33. I 4. R. Curtin, Wnmnary of Activity at The Geysers, 19. D. E. White, "Geothermal Energy," U.S. Geologi- 1973," in Hot Line, Vol. 4, No. 1, published by cal Survey Circular 519 (1965).W the State of California Division of Oil and Gas (February 1974). 20. L. J. P. Muffler and D. E. White, "Geothermal Energy," in The Science Teacher, Vol. 39, No. 3 5. News Release, Denver Post (January 27, 1974). (March 1972). 6. D. A. McMillan, Jr., "Economics of The Geysers 21. R. M Potter, "Geothermal Resources Created by . Geothermal Field, California,"Geothermics. Hydraulic Fracturing in Hot Dry Rock." invited Special Issue 2, pp. 1705-1714, (1970). paper at Geothermal Research Conference, Battelle Seattle Research Center, sponsored by 7. M. Goldsmith, "Geothermal Resources in California. NSF, Seattle, WA (September 18-20, 1972). Potentials and Problems," California Institute of Technology, EQL Report No. 5, Pasadena, CA 22. National Energy Council, "U.S. Energy Outlook, (December 1971). An Initial Appraisal 1971-1985," Vol. 2 (November 1971). 8. R. Bowen, "Oregon Energy Study," Public Utility Commissioner of Oregon, Report LGR 72-15-23 23. "Nuclear Power 1973-2000," Forecasting Branch, (August 1973). Office of Planning and Analysis, U.S. Atomic Energy Commission, WASH-1139 (72) 9. D. W. Brown, M. C. Smith, R. M. Potter, "A New (December 1, 1972). Method for Extracting Energy From tDryt Geother- mal Reservoirs." Los Alamos Scientific Labora- 24. D. E. White, "Characteristics of Geothermal Re- tory internal report (September 20, 1972). sources," in Geothermal Energy, P. Kruger and C. Otte, Eds. (Stanford University Press, 10. M. J. Reed, "Cerro Prieto Cost Analysis," in Hot Stanford, CAB 1 7 ) Chap. 4. 93, - Vol. 4, No. 1, published by the State of Line, California Division of Oil & Gas (February 1974). 25. W. K. Summers, "Annotated and Indexed Bibliog- raphy of Geothermal Phenomena; New Mexico State 11. M. J. Reed, "Cerro Prieto Field Development," in Bureau of Mines and Mineral Resources, Socorro, Hot Line, Vol. 3, No. 7, published by the State NM (1971). of California Division of Oil & Gas (December 1973). 26. D. E. White, "Geochemistry Applied to the Dis- covery, Evaluation, and Exploitation of Geo- 12. 0 A. Kremnjov. V. J. Zhuravlenko. and A. V. . thermal Energy Resources, Rapporteurs Report, Shurtshkov, "Technical-Economic Estimation of United Nations Symposium on the Development and Geothermal Resources," Geothermics, Special Utilization of Geothermal Resources, Pisa, Italy Issue 2, pp. 1688-1696 (1970). (1970). 13. G. A. Waring, revised by R. R. Blankenship and 27. R. 0 Fournier, D. E. White, and A. H. Truesdell, . R Bentall, Thermal Springs of the United States . "Geochemical Indicators of Subsurface Tempera- and Other Countries of the World - A Summary," ture," Part I : Basic Assumptions" in press: U.S. Geological Survey Professional Paper 492 (1965). Geological Survey Journal of Research, Vol. 2, No. 3 (May 1 7 ) 94. 14. Geothermal Steam Act of 1970, P.L. 91-581, 84 Stat. 1566, 30 U.S.C. 1001-1025, signed into 28. R. 0 Fournier and A. H. Truesdell, "Geochemical . law December 24, 1970. Indicators of Subsurface Temperature, Part 11: Estimation of Temperature and Fraction of Hot 15. "Geothermal Resources, Leasing on Public, Acquir- Water Mixed with Cold Water," in press: U.S. ed, and Withdrawn Lands," Department of the Geological Survey Journal of Research, Vol. 2, Interior, Bureau of Land Management Geological No. 3 (May 1974). Survey, Federal Register, Washington, DC, Vol. 38, No. 245, Part 11. pp. 35968-35982 29. J. Barnea, "Geothermal Power." Scientific Ameri- (December 21, 1973). can, Vol. 226, No. 1 (January 1972). 16. T h e Potential for Energy Production from Geo- 30. J. Combs, "Review and Discussion of Geothermal thermal Resources," Report of the Subcommittee on Exploration Techniques, Compendium of First Day Water and Power Resources, Committee on Interior Papers Presented at the First Conference of the and Insular Affairs, U.S. Senate (December 1973). Geothermal Resources Council, El Centro, CA (1972). 17. Vaughn E. Livingston, Jr., State Geologist, "Energy Resources of Washington," Information 31. J. Combs, "Heat Flow Measurements and Shallow Circular No. 50, State of Washington, Department Hole Temperature Data Gathering Techniques," of Natural Resources (January 1 7 ) 94. Lecture at the Geothermal Exploration Short Course, Geothermal Resources Council, Sacramento, 18. D. D. Blackwell. "Case History of the Exploration CA (January 1974). of the Marysville Area in Montana," Lecture at the Geothermal Exploration Short Course, Geo- thermal Resources Council, Sacramento, CA (January 1974). 27
  • 34. 32. T. Meidav, "Application of Electrical Resistivi- 44. S. 0 Hutchinson, "Drillings Costs," paper pre- . ty and Gravimetry in Deep Geothermal Explora- sented at an Informal Seminar on the Develop- tion," United Nations Symposium on the Develop- ment and Utilization of Geothermal Resources, Pisa, Italy, 1970, Geothermics Special Issue 2, ment and Use of Geothermal Energy, United Nations, 8-10 January 1973 and reported in Geothermics, Vol. 2, No. 1 (March 1973). i Vol. 2, Pt. 1, pp.303-310 (1970). 45. T. c. Gipson, Calvert Western Exploration Co.,33. T. Meidav, "Introduction to Geophysical Explora- Tulsa, OK, personal communication (April tion." Lecture at the Goethermal Exploration 1974). Short Course, Geothermal Resources Council, Sacramento, CA (January 1974). 46. J. L Lummis, Wrilling Optimization," J. Pet. .34. J. Combs and L J. P. Muffler, "Exploration for . Geothermal Resources,* Chapter 5 in Geothermal Tech. (November 1970). 47. J. L. Lummis, "Acquisition and Analysis of Data . Energy, Resources, Production, Stimulation. ed. for Optimized Drilling," J. Pet. Tech. P. Kruger and Care1 Otte, Stanford University (November 1971). Press (1973). - 48. J. L. Lummis, "Drilling in the Seventies Part35. A. S. Furumoto, "Geophysical Exploration on the I, Drilling Assistance Program Key Link in Structure of Volcanos: Two Case Histories," Technology Chain," Petroleum Engineer (September Hawaii Institute of Geophysics, University of 1973). Hawaii at Manoa. Paper presented at the U.S. - Japan Cooperative Science Seminar on Utilization 49. J. L Kennedy, Wp Drilling Passes Satellite . of Volcqno Energy, Hilo, Hawaii (4-8 February Test, Gears For Expansion," Oil and Gas Journal 1974). (August 28, 1972).36. W. J. Hickel, "Geothermal Energy - A National 50. K. Matsuo, "Present State of Drilling and Re- Proposal for Geothermal Resources Research." pairing of Geothermal Wells in Japan," Geother- University of Alaska Conference held in mics, Special Issue 2, Vol. 2, pt. 2, pp.1467- Seattle, WA (September 18-20, 1972). 1479 (1970).37. 1972 Joint Association Survey of the U.S. Oil 51. Petroleum Information Corporation, Denver, CO, and Gas Producing Industry, Section I, Drilling "Drilling Data File for Approximately 300 Costs, Section 11, Expenditures for Exploration, Geothermal Wells,"supplied to Los Alamos Scien- Development and Production (November 1 7 ) 93. tific Laboratory for study purposes (March 1974).38. R. Greider, "Economic Considerations for Geo- 52. C. F. Budd, Jr., "Steam Production at The thermal Exploration in the Western United Geysers Geothermal Field," in Geothermal Energy, States," presented at the Symposium, Colorado Resources, Production, Stimulation, P. Kruger Department of Natural Resources, Denver, CO and C. Otte, Eds (Stanford University Press, (December 6, 1973). Stanford, CA, 1973), Chap. 6. L.iJ. H. Axtell, "Economics of Exploration," Lec- 53. V. E. Suter, District Operations Manager, Union ture at the Geothermal Exploration Short Course, Oil Co., Santa Rosa, CA, personal communication Geothermal Resources Council, Sacramento, CA (March 1974). (January 1974). 54. N. D. Dench, "Casing String Design for Geother-40. L. 0 Beaulaurier, Power Technology Group, . mal Wells," Geothermics, Special.Issue 2, Bechtel Corp., San Francisco, CAD "Technical pp. 1485-1496 (1970). Assessment Study of Geothermal Energy Resources: National Science Foundation funded study through 55. Y. Nakajima, "Geothermal Drilling in the Matsu- The Futures Group, Inc., personal communication kawa Area," Geothermic Special Issue 2, (March 1974). p . 1480-1484 (1970). p41. J. Cromling, "Geothermal Drilling in Califor- 56. R. Greider. Senior Geological Consultant, Chev- nia," Paper SPE 4177 presented at the 43rd ron Oil, Minerals Staff, San Francisco, CAD Annual California Regional Meeting of the personal communication (March 1974). Society of Petroleum Engineers of AIME, Bakers- field, CA, November 8-10, 1972 and published in 57. P. Witherspoon, Dept. of Geological Engineering, J. Pet. Tech. (September 1973). University of California, Lawrence Berkeley Laboratory, Berkeley, CA, personal communication42. T Boldizsar, "Geothermal Energy Production from . (March 1974). Porous Sediments in Hungary," Geothermics. Special Issue 2, Vol. 2 pt. 1, pp.99-109 (1970). . 58. J. B. Koenig, "Decision Making in Geothermal Exploration, Including Geologic Techniques,"43. H. G. Wunderlich, "Geothermal Resources and Lecture at the Geothermal Exploration Short Present Orogenic Activity," Geothermic Special Course, Geothermal Resources Council, Issue 2, Vol. 2, pt. 2, pp.1226-1230 ( 9 0 . 17) Sacramento, CA (January 1974).28
  • 35. 59. J. W. Hatton, t*Ground Subsidence of a Geothermal 63. R. G. Gido, tlDescription Field Tests for ofW Field During Exploitation," Geothermics, Special Issue 2, pp. 1294-1296 (1970). Rock-Melting Penetration," L s Alamos Scien- o tific Laboratory report LA-5213-MS (February 1973). 60. E. S. Robinson, R. M. Potter, B B. McInteer, . J. C. Rowley, P. E. Armstrong, R. L. Mills; 64. J. W. Neudecker, A. J. Giger, and p. E. Arm- M. C. Smith, Ed, "A Preliminary Study of the strong, "Design and Development of Prototype Nuclear Subterrene," Los Alamos Scientific Universal Extruding Subterrene Penetrators." Laboratory report LA-4547 (April 1972). Los Alamos Scientific Laboratory report LA-5205-MS (March 1973), 61. J. W. Neudecker, "Design Description of Melting-, Consolidating Prototype Subterrene Penetrators," 65. R. E. Williams, "Development of a Modularized Los Alamos Scientific Laboratory report Mobile Rock-Melting Subterrene Demonstration LA-5212-MS (February 1973). Unit," Los Alamos Scientific Laboratory report LA-5209-MS (March 1973). 62. R. E. Williams and J. E. Griggs, "Use of the Rock-Melting Subterrene for Formation of Drain- 66. J. W. Neudecker, "Conceptual Design of a Coring age Holes in Archeological Sites." Los Alamos Subterrene Geoprospector," Los Alamos Scien- Scientific Laboratory report LA-5370-MS (August tific Laboratory report, LA-5517-MS (February 1973). 1974). APPENDIX CONTACTS MADE TO DISCUSS GEOTHERMAL WELL DRILLING PROBLEMS The following people were willing to discuss 13. John Goode, Cement Lab, Halliburton Services, drilling problems and contribute data that were Duncan, OK. useful in assembling this report, for which the 14. R. Greider, Senior Geological Consultant, author is appreciative: Chevron Oil, Minerals Staff, San Francisco, CA. 1. A L. Austin, Lawrence Livermore Lab., Univ. . 15. J. L. Kennedy, Editor, Oil and Gas Journal of Calif., Livermore, CA. Journal, Houston, TX. 2 L 0 Beaulaurier, Drilling Problems, Geother- . . . 16. R. T. Littleton, Bureau of Reclamation, mal Technology Assessment Study for The Futures Boulder City, NV. Group, Inc., Bechtel Corp., San Francisco. CA. 17. Jack Marsee, V. P. Engineering, Loffland Bros. 3. W. E Boyd, Industrial and Business Training . Drilling Co. Tulsa, OK, Bureau, Petroleum, Univ. of Texas, Austin, TX. 18. John McNanee, Bureau of the Census, Maryland. 4 M. Carasso, Project Mgr. Geothermal Technology . 19. R . W. McQueen, V. P.. Dresser Security Bits, Assessment Study for The Futures Group, Inc., Bech- Houston, TX. tel Corp., San Francisco, CA. 20. K. Mirk, P. Witherspoon E H. Wollenberg, 5. Tony Chasteen, Engineer, Union Oil of Calif. Lawrence Berkeley Lab., Univ. of Calif. Berkeley, Santa Rosa, CA. CA . 6 Joe Cook, Rock Bit Production Mgr. Adminis- . 21. Howard Morton, Technical Repr., Rocky Mts., tration Div. Hughes Tool Co., Houston, TX. Baroid Div.,N.L. Industries, Inc., Tulsa, OK. 7. Glenn Damewood, Tech. V.P., Southwest Research 22. M. Newson, R. Alvis and C. Morse, Sandia Corp., Institute, San Antonio, TX. Albuquerque, N. M. 8 John P. Finney, Project Engineer, Geysers, . 23. Dexter Polk, V.P., Dresser Oil Field Products Pacific Gas and Electric Co., San Francisco, CA. Div., Houston, TX. 9. Jim French, GTE Data Bank, U. S. Geological 24. Henry J . Ramey, Jr., Dept. of Petroleum En- Survey, Garden Grove, CA. gineering, Stanford, Univ., Stanford, CA. 1 . Ed Galle, Director of Research, Hughes Tool 0 25. W. Randall, Research, Amaco Production Co., Co., Houston, TX. Tulsa, OK. 11. T. C. Gipson, Calvert Western Exploration Co., 26. R. W. Sartor, Dresser Industries, Dallas, TX. Tulsa, OK. 27. Calvin Saunders, Gen. Mgr. Research, Hallibur- 12. Bill Glass, V.P. and Operations Mgr., Big ton Services, Duncan, OK. Chief Drilling Co., Oklahoma City, OK. 29
  • 36. 28. H. Snow and V. E . Suter, District Operations 30. Ted Welp, Internal Revenue Service, U. S .Mgr., Union O i l Co. of C a l i f . Santa Rosa, CA. Treasury Dept., Washington, D.C. 29. Ken Tanner, Mgr. Tech. Services, Baroid Div., 31. Jim Youngblood, V . P . , Dresser Magcobar,N. L. Industries, Inc., Houston, TX. Houston, TX.hK: 717(510)30