Microseismic Monitoring of CO 2 injection

1. Microseismic Monitoring of CO2 injection • James Verdon • James.Verdon@bristol.ac.uk • International CCS Workshop, Austin, TX • 02.12.2011

2. School of Earth Sciences, University of Bristol Natural Environment Research Council (NERC): Early Career Research Fellow PhD (2010): Microseismic Monitoring and Geomechanical Modelling of CO2Storage http://www1.gly.bris.ac.uk/BUMPS/ 7 Industry sponsors 2 x staff, 4 xpostdoc Shale gas, CCS, geothermal, mining, nuclear waste storage, volcanic tremor, depletion of mature reservoirs Bristol

3. Acknowldegments Geological Survey of Canada: Don White University of Leeds: Quentin Fisher, Doug Angus Rockfield Software: Martin Dutko, Jose Segura Pinnacle: Shawn Maxwell (now at Schlumberger)

4. Geomechanics and CCS Hooke’s Law: Terzaghi: Any pore pressure change will generate changes in effective stress, and thereforeproduce strain, or deformation. When strain exceeds a certain threshold, deformation cannot be accommodated elastically – at this point, microseismic events can be produced.

5. Geomechanics and CCS $ $ ? ?

6. What is a Microseismic Event? Microseismic events are analogous to earthquakes – slip on joints or fractures P and S wave energy is released. Typical Magnitudes: MW = -3 to 0 (cf. earthquakes >3) M0 = 1011 to 1016 D.cm(cf. 1020) Typical rupture: A = 0.001m2 – 0.5m2 (cf. 100m2)

7. What is a Microseismic Event?

8. Microseismic Monitoring Methods Surface Arrays: A dense array of 100s – 1000s of 1C geophones placed on the ground surface. Larger events detected directly, smaller events located with migration algorithms. t1 tn t1 tn x000m

9. Microseismic Monitoring Methods Surface Arrays: t1 tn t1 tn

10. Microseismic Monitoring Methods DownHole Arrays: A string of 6 – 20 3C geophones is installed in a borehole near to the injection site. Differential P-S arrival times, and P wave particle motions, are used to locate the events. 500m

11. Microseismic Monitoring Methods DownHole Arrays:

12. Microseismic Monitoring Methods DownHole Arrays: Accurate depth location. Good detectability. Limited lateral extent. Poorer X-Y locations. Surface Arrays: Poor depth location. Limited to larger magnitudes. Good lateral extent. Good X-Y location. Computational expense

13. Case Examples • Hydraulic Fracturing with CO2: A Worst Case Scenario • In this example, CO2 has been injected at high pressure to create fractures. This can be considered a worst case scenario for a CCS site.

14. Case Examples • Hydraulic Fracturing with CO2: A Worst Case Scenario • In this example, CO2 has been injected at high pressure to create fractures. This can be considered a worst case scenario for a CCS site.

15. Case Examples • Hydraulic Fracturing with CO2: A Worst Case Scenario • Events track formation of fractures. Through time, events move to shallower depths. Upward migration of CO2?

16. Case Examples

17. Case Examples • Microseismic Monitoring at Weyburn: • A single downhole array has been installed to monitor injection in one pattern

18. Case Examples • Microseismic Monitoring at Weyburn: • Events located in the reservoir and in overburden. Many events are located near the production wells, not the injection point

19. Microseismic Monitoring and Geomechanics • Geomechanical models can aid interpretation of event locations: • Fluid flow computes pressure changes, loading a mechanical model. Flow Simulation: Geomechanical Simulation:

20. Microseismic Monitoring and Geomechanics • Geomechanical models can aid interpretation of event locations: • Changes in stress can be used as a proxy for microseismic event likelihood.

21. Microseismic Monitoring and Geomechanics • Geomechanical models can aid interpretation of event locations: • Changes in stress can be used as a proxy for microseismic event likelihood.

22. Case Examples • Geomechanical Deformation at In Salah • InSAR images show uplift above the injection points at In Salah. • The double-lobe footprint has been interpreted as evidence for a fault.

23. Case Examples • Geomechanical Deformation at In Salah • A MS monitoring array has now been installed. Shallow array with 6 3C geophones. Increase shallow array planned 2011-2012. • Several events identified but not located.

24. ‘Beyond the dots in the box’ • Focal Mechanisms/Source Tensors: • Image the failure mechanism. Invert fot stress. Tensile vs shear. • Shear-Wave Splitting: • Image seismic anisotropy produced by aligned fracture sets. • Seismic ‘B’ values • Statistical distribution of magnitudes – can distinguish tensilevsshear failure.

25. Future Issues for Microseismic Monitoring DownHolevs Surface Arrays: Do we want a general sense of ongoing seismicity, or to target a specific point (or full coverage with lots of downhole arrays)? This may depend on the number of injectors. Hypothesis Testing:General monitoring vs identification of a specific concern? Risk Assessment: What seismic observations would mean injection should stop? (Bowland shale traffic light example?).

26. http://www1.gly.bris.ac.uk/~JamesVerdon/ http://www1.gly.bris.ac.uk/BCOG/ http://www1.gly.bris.ac.uk/BUMPS/