Taiwan Chelungpu-Fault Drilling Project Meeting Mark Zoback Stanford University October 21, 2003

1. In Situ Stress Measurements, Wellbore Stability and Fault Mechanics Taiwan Chelungpu-Fault Drilling Project Meeting Mark Zoback Stanford University October 21, 2003

2. z 0 ( ) S z = ò r g dz v 0 0 Obtaining a Comprehensive Geomechanical Model Parameter Data Vertical stress Least principal stress Shmin LOT, XLOT, minifrac Max. Horizontal Stress SHmax magnitude  modeling wellbore failures Stress Orientation Orientation of Wellbore failures Pore pressure Pp Measure, sonic, seismic Rock Strength Logs, Modeling Wellbore failure, Lab Faults/Bedding Planes Wellbore Imaging

3. Will There be Problems Drilling through Dipping Shales? (Shale Reaction with Mud/Stress State and Weak Bedding Planes)

4. What is the stress state before/after Chi Chi Earthquake?

5. What can we learn from the stress state after the earthquake? Kaj Johnson

6. z 0 ( ) S z = ò r g dz v 0 0 Obtaining a Comprehensive Geomechanical Model Parameter Data Vertical stress Least principal stress Shmin LOT, XLOT, minifrac Max. Horizontal Stress SHmax magnitude  modeling wellbore failures Stress Orientation Orientation of Wellbore failures Pore pressure Pp Measure, sonic, seismic Rock Strength Logs, Modeling Wellbore failure, Lab Faults/Bedding Planes Wellbore Imaging

7. Hydraulic Fractures Propagate Perpendicular to the Least Principal Stress

8. Extended Leak-Off Test

9. Visund Field

10. z 0 ( ) S z = ò r g dz v 0 0 Obtaining a Comprehensive Geomechanical Model Parameter Data Vertical stress Least principal stress Shmin LOT, XLOT, minifrac Max. Horizontal Stress SHmax magnitude  modeling wellbore failures Stress Orientation Orientation of Wellbore failures Pore pressure Pp Measure, sonic, seismic Rock Strength Logs, Modeling Wellbore failure, Lab Faults/Bedding Planes Wellbore Imaging

11. Stress Concentration Around a Vertical Well

12. Stress-Induced Wellbore Failures UBI Well A FMI Well B

13. Stress Orientations in North America

15. Drilling Induced Tensile Wall Fractures FMI FMS

16. Visund Stress Field Orientations

17. z 0 ( ) S z = ò r g dz v 0 0 Obtaining a Comprehensive Geomechanical Model Parameter Data Vertical stress Least principal stress Shmin LOT, XLOT, minifrac Max. Horizontal Stress SHmax magnitude  modeling wellbore failures Stress Orientation Orientation of Wellbore failures Pore pressure Pp Measure, sonic, seismic Rock Strength Logs, Modeling Wellbore failure, Lab Faults/Bedding Planes Wellbore Imaging

18. UCS Models for Shale

19. 0 0 0.25 1000 0.5 2000 0.75 3000 1.0 4000 1.25 5000 psi Unconfined Compressive Strength Horsrud (F) - #18 Coefficient of internal friction

20. z 0 ( ) S z = ò r g dz v 0 0 Obtaining a Comprehensive Geomechanical Model Parameter Data Vertical stress Least principal stress Shmin LOT, XLOT, minifrac Max. Horizontal Stress SHmax magnitude  modeling wellbore failures Stress Orientation Orientation of Wellbore failures Pore pressure Pp Measure, sonic, seismic Rock Strength Logs, Modeling Wellbore failure, Lab Faults/Bedding Planes Wellbore Imaging

21. Image Logs from the SAFOD Pilot Hole UBI FMI

22. z 0 ( ) S z = ò r g dz v 0 0 Obtaining a Comprehensive Geomechanical Model Parameter Data Vertical stress Least principal stress Shmin LOT, XLOT, minifrac Max. Horizontal Stress SHmax magnitude  modeling wellbore failures Stress Orientation Orientation of Wellbore failures Pore pressure Pp Measure, sonic, seismic Rock Strength Logs, Modeling Wellbore failure, Lab Faults/Bedding Planes Wellbore Imaging

23. KTB Stress Profile Zoback and Harjes (1997)

24. Visund Magnitudes - Strike-Slip (Almost Reverse)

25. Central Australia Reverse/Strike Slip SHmax>>Shmin~Sv Well-27 (HDT) Well-30 (HDT) Well-54 (FMS)

26. Will There be Problems Drilling through Dipping Shales? (Shale Reaction with Mud/Stress State and Weak Bedding Planes)

27. Stable Wellbores Depend on Controlling the Width of Breakouts

28. Well design usually means mud window and casing

29. if Weak bedding introduces strength anisotropy Rock mechanics test on rocks with weak planes

30. Weak Bedding Planes Can be a Source of Wellbore Instability

31. Weak Bedding Planes Causing Enlarged Breakouts in Shale

33. Side Track abandoned PG-2 Successful GIG-3 • Result • Company successfully drilled well • GIG-3 through the FB Shale • by limiting deviation to 27° and • mud weights to 10.5 ppg – 11 ppg • Company avoided costly stability • problems by following GMI’s • recommendations for this well

34. Modeling anisotropic breakouts in the FB shale with the given in situ stress state Anisotropic failure Anisotropic failure • Bedding plane properties: • dip = 8° (from core data) • Azi = 23° (from core data) • S0 = 4.8 MPa (from lab data) • ms = 0.21 (from lab data) Result: The in situ stress tensor derived in this study and the bedding plane properties measured in the lab can account for the anisotropic breakouts seen in the FB shale MW = 10.5 ppg MW = 12 ppg Observed Isotropic failure

35. What is the stress state before/after Chi Chi Earthquake?

36. Can We Use Wellbore Observations to Identify Presence of Active Faults? • Anomalous stress orientations • Anomalous stress magnitudes

37. Drilling-Induced Slip and Breakout Perturbation

38. Anomalous Breakout Orientations

39. Wellbore Breakout Rotations Due to Fault Slip

40. Drilling-Induced Tensile FracturesRotated Near Fault at 3100 meters

41. Modeling Fault-Induced Stress Perturbations at the Wellbore Wall

42. KTB Stress Orientation Profile

43. Co-Seismic Slip Model of Chi-Chi Earthquake (GPS) Johnson and Segall (in press)

44. What can we learn from measuring the stress state after the earthquake? Kaj Johnson

45. Summary • Obtaining a Comprehensive Geomechanical Model can provide insight and help in addressing wellbore stability problems as drilling is underway and can make important contributions to the fundamental scientific objectives of the project • Engineering – Must build the model as you go – “real time” analysis with careful mud logging (cuttings analysis) • Science – Obtain critical data as project is being carried out - can’t go back and get missing data

46. Recommendations • Obtain logs after each phase of drilling • A complete suite of geophysical logs • Wellbore image logs are essential (both ultrasonic and electrical, if possible) • Carry out an Extended Leak Off Test (hydrofrac) each time casing is set • Carry out additional hydrofracs (if possible) – only to measure S3 • Carry out careful mud logging as drilling is underway. Laboratory tests on core samples will be important primarily for science • Make data available to science team as rapidly as possible

47. Most Importantly GOOD LUCK To us all!