Poroelastic Stressing and Pressure Diffusion Along Faults Induced by Geological Carbon Dioxide Storage

Injecting CO₂ into a deep geological formation (i.e., geological carbon storage, GCS) can induce earthquakes along preexisting faults in the earth’s upper crust. Seismic survey and regional geo-structure analysis are typically employed to map the faults prone to earthquakes prior to injection. However, earthquakes induced by fluid injection from other subsurface energy storage and recovery activities show that systematic evaluation of the potential of induced seismicity associated with GCS is necessary. This study mechanistically investigates how multiphysical interaction among injected CO₂, preexisting pore fluids and rock matrix alters stress states on faults and which physical mechanisms can nucleate earthquakes along the faults. Increased injection pressure is needed to overcome capillary entry pressure of the fault zone, driven by the contrast of fluids’ wetting characteristics. Accumulated CO₂ within the reservoir delays post shut-in reduction in pressure and stress fields along the fault that may enhance the potential for earthquake nucleation after terminating injection operations. Elastic energy generated by coupled processes transfers to low-permeability or hydraulically isolated basement faults, which can initiate slip of the faults. Our findings from generic studies suggest that geomechanical simulations integrated with multiphase flow system are essential to detect deformation-driven signals and mitigate potential seismic hazards associated with CO₂ injection.

Previous field demonstration projects revealed that detected seismicity is low magnitude and relatively small numbers [White & Foxall (2016)], suggesting that geological CO₂ storage is unlikely to pose a seismic hazard. However, the amounts of injected CO₂ have typically been small (less pressurization expected), and the lack of subsurface monitoring tools also limits the detection of seismic activities in spatial extent and/or temporal coverage [Nicol et. al. (2013)]. The successful storage of carbon dioxide (CO₂) at commercial–scale, thus, requires evaluating potentials of the seismic hazard and its impacts on mechanical stability of the target formation [Verdon et al. (2013), Rinaldi et al. (2014), Dempsey et al. (2014)].