Microseismic Monitoring and Geomechanical Modelling of a CCS site, Weyburn, Canada

1. Microseismic Monitoring and Geomechanical Modelling of a CCS site, Weyburn, Canada • James P. Verdon • University of Bristol, U.K. • james.verdon@bris.ac.uk • BUMPS Sponsors Meeting • 28.02.2011

2. Recap: the Weyburn CCS Project • Located in Saskatchewan, Central Canada • Size = 70 miles2, 20-40m thick • Original Oil In Place = 1.4 billion barrels • Production began in 1955 • Oil recovered pre-CO2 EOR = 370 million barrels (26%) • Extra Oil Recovered by CO2 Injection = 130 million barrels (10%) • CO2 injection rate = 3 MT per year

3. Recap: the rocks at Weyburn • Reservoir found in Palaeozoic rocks. Upper dolostone and lower limestone zones. • Caprocks: an evaporite overlain by shale.

4. Recap: Monitoring at Weyburn • 4D reflection seismics used to monitor CO2 injection

5. Recap: Microseismics at Weyburn CO2 injection initiated in 2000. Microseismic monitoring initiated in 2003. 1 downhole array, 8 3-C geophones close to reservoir depth. CO2injection in a nearby vertical well initiated Jan 2004. Several producing wells are nearby.

6. Recap: Microseismics at Weyburn

7. Aside: Imaging event PDFs??

8. Recap: Microseismics at Weyburn

9. Recap: SWS at Weyburn

10. Recap: Geomechanical model of Weyburn

11. Recap: Fracture Potential Risk of fracturing is given by the fracture potential: FP = Q / (2 cocos(φ) + P sin(φ))

12. Recap: ModelledMicroseismics and SWS Reservoir: Overburden:

13. Today’s Presentation New microseismic activity at Weyburn Preliminary geomechanical model for new events AVOA measurements Future work

14. Acknowledgements AVOA: Don White, Alexander Duxbury (Natural Resources Canada) Microseismic Event Locations: ESG

15. Microseismic Activity in 2010

16. Microseismic Activity in 2010

17. Timeline of Activity, Sept-Oct 2010 • Sept. 19th: Injector at surface location 10-08 shut-in • Sept. 19th: drilling from surface location 10-08 spudded • Sept. 23rd: increase in noise triggers associated with deep drilling operations • Sept. 24th: 121/06-08 vertical injector is shut in. • Sept. 25th: noise triggers return to low levels • Sept. 26th: 52 microseismic events located; 7 unlocatable events • Sept. 27th: monitoring system down from 19:03 for the next 17 hours. • Sept. 28th: 1 locatable event; 5 unlocatable • Sept. 29th: 29 unlocatable events • Sept. 30th: 2 locatable events • Oct. 1st: 1 unlocatable event • Oct. 3rd: new hz well spudded at 04-08 surface position • Oct. 5th: 1 unlocatable event • Oct. 5th: cement job in abandoned well 121/06-08; ring buffer holds data in 10:30-15:00 window. • Oct. 6th: 1 unlocatable event • Oct. 12th: 2 locatable event • Oct. 13th: 4 locatable events, 4 unlocatable events • Oct. 14th: 3 locatable events, 1 unlocatable • Oct. 25th: 13:25 system is down for approx 24 hours • Nov. 12-18: 26 locatable events, 2 perf shots (in 111/06-08), 7 unlocatable events

18. Event locations

19. 2010 Events - Geomechanics Reservoir Production Injection Start injection End injection

20. 2010 Events - Geomechanics Overburden Production Injection Start injection End injection

21. Anisotropy and Geomechanics

22. Modelled Stress-Induced Anisotropy Above injectors – perpendicular to horizontal wells Above producers – parallel to horizontal wells

23. Anisotropy - AVOA AVOA – Amplitude variation with offset and azimuth. Essentially, AVO gradients vary with azimuthal orientation. Cause: layers above or below the reflector contain aligned vertical fractures, so velocities, and hence reflection coefficients, will vary with azimuth. AVOA analysis has been performed by Alexander Duxbury, NRCan, for the Phase 1A area – adjoining the microseismic monitoring area.

24. Anisotropy - AVOA

25. Anisotropy - AVOA

26. Future Work New microseismic events: address location uncertainties. shear wave splitting (provides a time-lapse from 2004 analysis). Geomechanics: More realistic model. History-matched flow simulation. Build model using geological surfaces. Linking geophys and geomech: Predictions about 4D seismic observables. Mapping stress changes into microseismic event probabilities.

27. Future Work Bruce Jones, PhD student, Rockfield Ltd. and Swansea University.

28. Future Work NERC Grant: NE/I021497/1. Still or sparkling: Microseismic monitoring of CO2 injection at In Salah.

29. Conclusions Shut-down of injection well has produced a burst of microseismic activity. Events are located around the shut-in well. Event locations are not inconsistent with our geomechanical analysis so far. AVOA observations match with our SWS observations. AVOA observations have extended our inferences about stress-induced anisotropy, confirming that the pattern of orthogonal fast directions above production and injection wells exists across the field. The new events, and the match between AVOA and geomechanical models, has provided scope for much further study, beginning with the construction of a new, more detailed geomechanical model.

30. J.P. Verdon, J-M. Kendall, D.J. White, D.A. Angus, 2011. Linking microseismic event observations with geomechanical models to minimise the risks of storing CO2 in geological formations: Earth and Planetary Science Letters, accepted.