Yibal Seismicity

1. Yibal Seismicity M. N. Toksöz, D. R. Burns and S. Sarkar, S. Kuleli, H. Zhang November, 2007

2. Summary • Surface subsidence, deformation and earthquakes are induced by gas and oil production. • Subsidence is monitored by leveling, GPS and InSAR. • Shallow and deep seismic networks have recorded thousands of earthquakes. • Locating earthquakes poses a challenge due to strong velocity contrasts in the strata. • Earthquakes occur on preexisting faults and are caused by gas production and associated reservoir compaction. • Earthquakes can be used for determining the stress regime, anisotropy and reservoir properties.

3. SEISMICITYOutline • Review of Seismicity • Seismic Networks • Shallow, Deep stations • Earthquake Locations • Epicenters, Focal depth • Correlations • New Approaches and Validations • Synthetic Seismograms • Time Reversed Acoustics Refocusing • Double Difference/Tomography • Suggestions for New Network • Felt Events and Earthquake Hazard • Conclusions

4. Overall Seismicity in the Region

5. Earthquake Distribution in Yibal: Epicenters (Map View)

6. Earthquake Distribution in Yibal: Depths (Cross-section)

7. Seismic Monitoring Network Shallow Network 10/99 Present ~ 150 m below surface

8. Seismic Monitoring Network Shallow Network 10/99 Present ~ 150 m below surface Deep Network 08/03 02/02 ~ 750 – 1300 m below surface

9. Deep-borehole Network MSL Gas Top Oil Top

10. Earthquake Data, Phase Picks: Shallow Network

11. Earthquake Data, Phase Picks: Deep Network P S

12. Map View – All Events (Deep and Shallow)

13. Earthquake Locations – Plan ViewDeep Network, 10/02 – 08/03 Events from 800-900 m depth

14. Earthquake Locations – Plan ViewDeep Network, 10/02 – 08/03 Events from 900-1100 m depth

15. Analyzing IndividualClusters of events B A’ • Looking at seismic locations in 3D helps identification and mapping of faults and fractures. A B’ A A’ B B’

16. Velocity Models MSL

17. Depth Distribution of Events from Shallow Network using a “Smooth” Velocity Model MSL

18. Depth Distribution of Events from Shallow Network using our Improved Velocity Model MSL

19. Depth Distribution – All Events(Deep and Shallow) MSL

20. # OF EVENTS GAS PRODUCTION OIL PROD / WATER INJ Seismicity vs. Gas Production/Water Injection (11/99 – 06/01)

21. Seismicity vs. Gas Production (12/02 – 05/06)

22. Nov 99 – Jun 01 Dec 02 – May 06 Cross-correlation: Gas Production and Seismicity

23. Earthquake Source Mechanism

24. Big Small Regional Tremors of July 19, 2006

25. Regional Big (Yibal) Seismograms of Two Tremors

26. Location of the Regional Event

27. Location of the Two Tremors in Yibal

28. Comparing Observed with Modeled Seismogram

29. Comparing Observed with Modeled Seismogram

30. Conclusions • Seismicity in Yibal is primarily induced by depletion/compaction of the gas reservoir • Earthquakes occur on preexisting faults, reactivated by compaction • Earthquakes create operational and safety issues • Microearthquakes provide data (P and S-waves) for reservoir characterization and time-lapse monitoring • Continuation of earthqauke monitoring in Yibal requires upgrade of network operations.

31. THANK YOU

32. Event Locations: Past Two Years and Earlier Events located with only P -picks Events located with both P & S -picks

33. Fast S-Wave Direction and Location Distribution of Induced Earthquakes

34. Depth Distribution of Events from Deep Network

35. SOULTZ Early Experimental Phase In The Upper Reservoir 1987 - 1997 Exploration of the Deep Reservoir 1988 - 2000 Downhole seismic network

36. Hydraulic Experiment Soultz,1993 JHD Collapsing

37. Rutledge J. and Phillips S., 2002 – Upper Cotton Valley, TX

38. Comparing Observed with Modeled Seismogram

39. Comparing Observed with Modeled Seismogram