Abstract:

The importance of geomechanics including the potential for reactivating faults associated with large-scale geologic carbon sequestration operations has recently become more widely recognized. However, not withstanding the potential for triggering notable (felt) seismic events, the potential for buoyancy-driven CO2 to reach potable groundwater and the ground surface is more important from safety and storage-efficiency perspectives. In this context, this work extends previous studies on the geomechanical modeling of fault responses during underground carbon dioxide injection, focusing on short-term integrity of the sealing caprock, and hence of potential leakage of either brine or CO2 to shallow groundwater aquifers during active injection. We account for a stress/strain-dependent permeability and study the leakage through a fault zone as its permeability changes during a reactivation, also causing seismicity. We analyze several scenarios related to the injected amount of CO2 (and hence as a function of the overpressure) both involving minor and major faults, and analyze the profile risks of leakage for different stress/strain-permeability coupling functions. We conclude that whereas it is very difficult to predict how much fault permeability could change upon reactivation, this process can have a significant impact on the leakage rate.

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