Assessment of the predicted seismic activity associated with a hypothetical industrial-scale geologic CO2 sequestration operation: effect of in-situ stress measurement uncertainties and friction law.

Carbon capture and storage (CCS) in geological formations has been recognized as a promising option for reducing CO2 emissions from large stationary sources. However, the pressure buildup inside the storage formation can potentially induce slip along preexisting faults, which could lead to felt seismic ground motion. To prevent this to happen geomechanical stability of faults have to be perform, but considerable uncertainties exist on the input parameters used for this simulation. In this study, we investigate how (i) uncertainties on the in-situ stress, as defined by the variation of stress measurements obtained within the study area and (ii) the distribution of the coefficient of friction and the frictional law used, could influence the assessment of the geomechanical stability of faults and the characteristics of potential injection-induced seismic events.Our modelling study is based on a hypothetical industrial-scale carbon sequestration project assumed to be located in the Southern San Joaquin Basin in California, USA. We assess the stability on the major (25 km long) fault that bounds the sequestration site and is subjected to significant reservoir pressure changes as a result of 50 years of CO2 injection. We present a series of geomechanical simulations in which the resolved stresses on the fault were varied over ranges of values corresponding to various stress measurements performed around the study area and the distribution of the coefficient of static and dynamic friction are changed to simulated a hardening and softening phase before and during rupture. The simulation results are analyzed by a statistical approach. Our main results are that the variations in resolved stresses had a negligible effect on the prediction of the seismic risk (maximum magnitude), but an important effect on the timing, the seismicity rate (number of seismic events) and the location of seismic activity. On the other hand, uncertainty related to the distribution of the coefficient of friction along the fault and to the friction law have a strong effect on the prediction of the seismic risk (maximum magnitude, number of seicmic events and a and b value).