1. 1 Microseismic Monitoring of CO 2 Storage at Weyburn James Verdon University of Bristol, U.K. james.verdon@bris.ac.uk 26.05.2010 Microseismic Monitoring of CO 2 Storage at Weyburn

2. Acknowledgements NR-Can: Don White Bristol: Kendall, Wustefeld, Wookey Leeds: Angus, Fisher, IPEGG £££££: UKERC, PTRC 2 Microseismic Monitoring of CO 2 Storage at Weyburn

3. Motivation for CCS 3 Microseismic Monitoring of CO 2 Storage at Weyburn

4. Motivation for CCS 4 Microseismic Monitoring of CO 2 Storage at Weyburn

5. Geological CCS Issues Likely leakage pathways: Wells. Abandoned and not...... Loss of caprock integrity: Geochemical dissolution. Geomechanical deformation. Monitoring methods: Geochemical: Detecting CO 2 at the surface Detecting CO 2 breakthrough at wells Fluid-rock reactions. Satellite: Ground surface deformation due to pressure increases Seismics: Controlled source 4-D – detect spatial extent of CO 2 Microseismic – detect fracturing and geomechanical deformation 5 Microseismic Monitoring of CO 2 Storage at Weyburn

6. The Weyburn CCS Project Located in Saskatchewan, Central Canada 6 Microseismic Monitoring of CO 2 Storage at Weyburn

7. By the numbers CO 2 provided by a coal gasification plant in Beulah, North Dakota. CO 2 is pumped via pipeline over 200km. Storage rate is now ~3 Mtonnes of CO 2 per year. Equivalent to the emissions from 1/2 Million (American, gas-guzzling) cars per year. 7 Microseismic Monitoring of CO 2 Storage at Weyburn

8. The Weyburn Reservoir 8 Reservoir found in Paleozoic rocks. Upper dolostone and lower limestone zones. 30-40m thick in total. Caprocks: Evaporite overlain by shale. Microseismic Monitoring of CO 2 Storage at Weyburn

9. Enhanced Oil Recovery 9 Producing since the 1950s. 20% of OOIP retreived by conventional measures. CS/EOR will significantly prolong the life of the field, retrieving an additional 10% of the OOIP Microseismic Monitoring of CO 2 Storage at Weyburn

10. The Caprock(s) 10 Microseismic Monitoring of CO 2 Storage at Weyburn

11. 4-D Seismics 4-D seismics have dominated the monitoring strategy. BUT, What saturation is yellow??? Attempts to match with fluid-flow modelling (c) 11 Microseismic Monitoring of CO 2 Storage at Weyburn

12. Microseismics at Weyburn 12 CO2 injection initiated in 2000. Microseismic monitoring initiated in 2003. 1 downhole array, 8 3-C geophones close to reservoir depth. CO2 injection in a nearby vertical well initiated Jan 2004. Several producing wells are nearby. Microseismic Monitoring of CO 2 Storage at Weyburn

13. Microseismics at Weyburn 13 Microseismic Monitoring of CO 2 Storage at Weyburn

14. Questions raised…. Why do events occur near the producing wells, not the injection well? What do the events above the reservoir signify? Fluid migration into the overburden or just stress transfer? 14 Microseismic Monitoring of CO 2 Storage at Weyburn

15. SWS Results from Weyburn Splitting finds a dominant NW striking fracture set, with a weaker NE striking set. Match with core sample work, except cores suggest NE set should be dominant. 15 Microseismic Monitoring of CO 2 Storage at Weyburn

16. Microseismics and geomechanics 16 Geomechanical modelling allows us to predict where to expect failure. There is a key link between interpretation of microseismic events and geomechanical modelling. Shear wave splitting will also be sensitive to stress changes. We have constructed a simple geomechanical model to represent the Weyburn reservoir. Microseismic Monitoring of CO 2 Storage at Weyburn

17. Geomechanical Modelling Strategy Geomechanical model ELFEN CamClay (capped) model: Confining stress Shear stress Elastic behaviour Shear failure Pore collapse Pore pressure Porosity, permeability Fluid flow simulator e.g., MORE ECLIPSE VIP Model the reservoir only Pore pressure, fluid properties 17 Microseismic Monitoring of CO 2 Storage at Weyburn

18. Geomechanical Model Simple, representative model: 18 Microseismic Monitoring of CO 2 Storage at Weyburn

19. Geomechanical Model Gas saturation after injection 19 Microseismic Monitoring of CO 2 Storage at Weyburn

20. Geomechanical Model Pore pressure changes after injection 20 Microseismic Monitoring of CO 2 Storage at Weyburn

21. Fracturing 21 Risk of fracturing is given by the fracture potential: F P = Q / (2 c o cos( ) + P sin( )) Microseismic Monitoring of CO 2 Storage at Weyburn

22. Fracturing 22 Reservoir Overburden Fracture potential decreases at the injection wells. Little stress evolution in the overburden. Microseismic Monitoring of CO 2 Storage at Weyburn

23. Shear-wave splitting 23 Microseismic Monitoring of CO 2 Storage at Weyburn

24. A softer reservoir? Core samples can miss the effects of large scale fractures on rock stiffness 24 Microseismic Monitoring of CO 2 Storage at Weyburn

25. Fracturing 25 Reservoir Overburden Fracture potential increases in the overburden above the production wells. Microseismic Monitoring of CO 2 Storage at Weyburn

26. Shear-wave splitting 26 Microseismic Monitoring of CO 2 Storage at Weyburn

27. Discussion The minimum conditions for site closure and transfer of responsibility includes the conformity of the actual behaviour of the injected CO2 with the modelled behaviour. Directive 2009/31/EC of the European Parliament on the geological storage of carbon dioxide. This work has demonstrated the need to compare models with observed behaviour in order to calibrate them properly. Geomechanical models can be compared with: downhole pressures, stress measurements, surface deformation, and, induced seismicity. The seismicity in the overburden is caused by stress transfer as the reservoir is softer than expected - it does NOT represent the migration of fluids in the overburden. 27 Microseismic Monitoring of CO 2 Storage at Weyburn

28. Feasibility of Microseismics and CCS 28 Most CCS projects will aim to minimise geomechanical deformation - if so why bother to monitor? If there is little seismicity occurring, how useful can this technique be? Microseismics as an early warning? Like soil gas flux and shallow aquifer chemistry (will regulators require it?). The need to link with geomechanical modelling to interpret events…. Microseismic Monitoring of CO 2 Storage at Weyburn

29. Feasibility of Microseismics and CCS 29 Microseismic Monitoring of CO 2 Storage at Weyburn

30. Conclusions In most CCS projects, low rates of microseismicity will be desired. This is what is observed at Weyburn. Events are located near to the production wells, in the reservoir and overburden. Shear wave splitting measurements imaged two fracture sets that match fracture sets noted from core work. Geomechanical models have been developed to improve our interpretation of the induced seismicity. However, the initial model did not match observations. The initial model did not account for the softening effects of fractures in the reservoir. With a softer reservoir, the model provides a good match with both event locations and shear-wave splitting measurements. This highlights the need to match model predictions with observation before they are used to assess the security of storage. 30 Microseismic Monitoring of CO 2 Storage at Weyburn

31. Future Work Improved (full field) geomechanical models. Improved methods of microseismic prediction. Geochemical effects on mechanical properties. Links with other indicators of deformation (e.g., surface deformation). In Salah…… 31 Microseismic Monitoring of CO 2 Storage at Weyburn

32. Any Questions? 32 james.verdon@bris.ac.uk http://eis.bris.ac.uk/~gljpv/JPV.html J.P. Verdon, J-M. Kendall, D.J. White, D.A. Angus, Q.J. Fisher & T. Urbancic, 2010. Passive seismic monitoring of carbon dioxide storage at Weyburn: The Leading Edge, 29(2), 200-206. Microseismic Monitoring of CO 2 Storage at Weyburn