Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

8.6. SUMMARY
8.6 Summary
• I apply the workflow developed in Chapters 5 - 7 to the Weyburn reservoir.
• I develop a simple coupled fluid-flow/geomechanical model representing a typical pattern from
the field, including the stiff evaporite layers lying above and below the reservoir. This model
simulates the depletion during production through horizontal wells, and the subsequent injection
of CO 2 into the reservoir through a vertical wells.
• I use the inversion method developed in Chapter 6 to compute initial crack densities and aspect
ratios for the Weyburn rocks, enabling me to use the workflow developed in Chapter 7 to compute
changes in seismic observables.
• The first model I develop uses mechanical properties based on core sample measurements. The
regions where there is an increased likelihood of microseismic activity, and the stress-induced
anisotropy, do not provide a good match with the observations made in Chapters 2 and 3.
• I develop an alternative model with a reservoir unit that is softer than the overburden. The
motivation for doing so is that the presence of fractures and vugs in the reservoir, which are not
accounted for in core sample measurements, will make it considerably softer than rock physics
tests would suggest.
• This softer model does a much better job of matching both microseismic event patterns and shear
wave splitting predictions with the observations made in Chapters 2 and 3. This demonstrates
the importance of linking geomechanical models with observable indicators of deformation in
the field in order to groundtruth and calibrate the models.
• The geomechanical model demonstrates that the occurrence of microseismicity in the overburden
does not represent fluid migration through the caprock, but merely the transfer of stress.
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