DOE - Enhanced Geothermal Systems

Program Review

Experimental and Analytical Research on Fracture Processes 

in Rock

H...
Project Objectives
Addresses GTP areas of interest
No. 3: Fracture Formation and Growth
and
No. 4: Fracture Evaluation
thr...
EGS Problem

Importance:	 Fracture processes are central to much of geothermal energy
extraction
Technical issues: Propaga...
Project - Approach
Tasks
Task 1. Testing of different rock types and fracture geometries under different, mostly
biaxial s...
Experimental Work

s
flaw angle,b
Internal flaw tip
External flaw tip
flaw angle,b
2a=12.7mm
2a=12.7mm
ligament angle,a
li...
Experimental Work - Summary of Past Results

Type Schematic path of
Coalescence
Mode of
Coalescence
Type Schematic path of...
Experimental Work – Recent Results 

Single Flaw

gypsum
marble
Flaw Inclination = 45o
Experimental Work – Recent Results 

Double Flaws

Gypsum – Coplanar
Flaw Inclination = 75o
Gypsum – Stepped
Flaw Inclinat...
Experimental Work – Recent Results 

Double Flaws

Marble – Coplanar
Flaw Inclination = 30o
Marble – Stepped
Flaw Inclinat...
Analytical Work - Crack Initiation and Propagation Criterion

Core Region Propagation Criteria
Mathematical Formulation Fa...
Analytical Work - Comparison of Simulation and Experiment

Comparison between Numerical Prediction and Experiment for Copl...
Analytical Work - Comparison of Simulation and Experiment

Comparison between Numerical Prediction and Experiment for for ...
Experimental Schematic
Experimental Equipment
Experimental Equipment
Proposed Experimental Work

Parameters to be Varied
• Rock Type
• Flaw Length (12.7, 25.4, 6.35 mm
• Flaw Aperture (0.1 to...
Other Aspects of Proposed Research

•	 Measure Sonic Wave Velocity
•	 Analysis - New propagation/coalescence criteria?
•	 ...
flaw inclination angle 30o; positive bridging angles 30o,60o
PDWHULDO
R R
JSVXP FUDFN FUDFN
FUDFNV FUDFNV FUDFNV
PDUEOH
FU...
Expected Accomplishments of Proposed Research

•	 More complete picture of fracturing based on lab experiments including d...
Conclusions

- GTP related objectives - better knowledge of fracture formation and growth and fracture
evolution will be a...
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  1. 1. DOE - Enhanced Geothermal Systems Program Review Experimental and Analytical Research on Fracture Processes in Rock Herbert H. Einstein Massachusetts Institute of Technology Phone: 617-253-3598 Fax:617-253-6044 einstein@mit.edu
  2. 2. Project Objectives Addresses GTP areas of interest No. 3: Fracture Formation and Growth and No. 4: Fracture Evaluation through Laboratory experimental and analytical work to • Understand fracture propagation and interaction • Create basis for methods allowing one to indirectly infer fracture mechanisms in the field.
  3. 3. EGS Problem Importance: Fracture processes are central to much of geothermal energy extraction Technical issues: Propagation and coalescence of fractures are only partially understood, both under ambient temperature and under elevated (up to 150° C) temperature. Addresses EGS Technical Challenge: High-temperature rock usually is not extensively fractured. Effective geothermal energy extraction requires fractured rocks. The process of fracturing needs to be understood (effect of lithology, stress conditions, temperature, etc.)
  4. 4. Project - Approach Tasks Task 1. Testing of different rock types and fracture geometries under different, mostly biaxial stress fields under ambient temperatures. Task 2. Conducting experiments like Task 1 but at elevated temperatures. Task 3. Extension of crack (fracture) initiation-, propagation- and coalescence criterion and incorporation in numerical models. Task 4. Initial steps toward modelling larger/smaller scale fractures. Task 5. Reporting and suggestions for further research.
  5. 5. Experimental Work s flaw angle,b Internal flaw tip External flaw tip flaw angle,b 2a=12.7mm 2a=12.7mm ligament angle,a ligament length Internal flaw tip c s v 26 - 31 mm. 152.4 mm. Initial flaws s h s h External flaw tip 76.2 mm. s v (a) (b) Geometries of (Model) Rock Specimens. (a) Overall View. (b) Detail
  6. 6. Experimental Work - Summary of Past Results Type Schematic path of Coalescence Mode of Coalescence Type Schematic path of Coalescence Mode of Coalescence I Shearing V Shearing + tension II Shearing + tension VI Shearing + tension III Shearing + tension VII Shearing + tension IV Tension VIII Shearing Types of Coalescence Patterns in Uniaxial Compression Based on Past Work
  7. 7. Experimental Work – Recent Results Single Flaw gypsum marble Flaw Inclination = 45o
  8. 8. Experimental Work – Recent Results Double Flaws Gypsum – Coplanar Flaw Inclination = 75o Gypsum – Stepped Flaw Inclination = 30o Bridging Angle = 60o
  9. 9. Experimental Work – Recent Results Double Flaws Marble – Coplanar Flaw Inclination = 30o Marble – Stepped Flaw Inclination = 30o Bridging Angle = 60o
  10. 10. Analytical Work - Crack Initiation and Propagation Criterion Core Region Propagation Criteria Mathematical Formulation Failure Envelope
  11. 11. Analytical Work - Comparison of Simulation and Experiment Comparison between Numerical Prediction and Experiment for Coplaner-Open Flaw Geometry, Uniaxial Compression
  12. 12. Analytical Work - Comparison of Simulation and Experiment Comparison between Numerical Prediction and Experiment for for Stepped, Non-Overlapping Open Flaws Uniaxial Compression
  13. 13. Experimental Schematic
  14. 14. Experimental Equipment
  15. 15. Experimental Equipment
  16. 16. Proposed Experimental Work Parameters to be Varied • Rock Type • Flaw Length (12.7, 25.4, 6.35 mm • Flaw Aperture (0.1 to 1 mm) • Flaw Geometry Key b1 – flaw inclination angle b2 – bridging angle L – ligament length a – half flaw length • Stress States (Uniaxial, Biaxial, Different Magnitudes)
  17. 17. Other Aspects of Proposed Research • Measure Sonic Wave Velocity • Analysis - New propagation/coalescence criteria? • Details of Fracture Process • Scaling - Lab - Field - Seismic - Field - Rockbursts
  18. 18. flaw inclination angle 30o; positive bridging angles 30o,60o PDWHULDO R R JSVXP FUDFN FUDFN FUDFNV FUDFNV FUDFNV PDUEOH FUDFN FUDFN
  19. 19. Expected Accomplishments of Proposed Research • More complete picture of fracturing based on lab experiments including different scales • New analytical propagation/coalescence criteria if necessary • Some idea on relation to field
  20. 20. Conclusions - GTP related objectives - better knowledge of fracture formation and growth and fracture evolution will be achieved - Will provide analytical tools for modeling fracturing process. - Will provide ideas on how fractures in the field are created

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