Analysis of the Hydrogeological Conditions Affecting Fault Response to Nearby Hydraulic Fracturing.

The response of critically stressed dormant faults to fluid perturbation, by oil and gas production, has been a major public concern because of its link to induced seismicity. In this paper, we study the hydrogeological factors that affect a nearby fault response, during and after hydraulic fracturing (HF) operations, evaluated by the change in Coulomb Failure Stress (CFS) and the rate of seismicity (R) through coupling solid deformation and fluid flow. Our results show that the pore pressure increases rapidly in a fault that is close (hydraulically connected) to HF operations, which might lead to its activation when the injection rate is high. When the fault is adjacent to HF but distant from it, its shallow region is subjected to a stabilizing deformation‐induced normal compressive stress and its deeper region is destabilized under extension. In this case, the fault orientation and damage zone size have a significant effect on the fault's stability and response. On the other hand, decreasing the rate of injection can either increase or decrease the CFS values depending on the fault location and the dominant stresses. Therefore, serious attention should be given to the fault position, its architecture, and the injection rate to help reduce the potential for induced seismicity from HF. Our findings are verified and confirmed using the case of the Duvernay formation in Alberta, Canada, where the reported seismic data correlate with high CFS and R values. Plain Language Summary: The main cause for the induced seismic events occurring during or after hydraulic fracturing (HF) operations can be attributed to fluid diffusion and/or stress changes along critically stressed dormant faults located near the operations. Different factors can affect the response of pre‐existing faults to HF operations including the distance between the fault and HF operations, fault orientation, size of its damage zone, and the injection rate of HF. Based on our simulations, we conclude that when the fault is far from the operations, its shallow region (i.e., closer to HF) is subjected to a stabilizing deformation‐induced compressive normal stress and its deeper region is destabilized under extension. However, for a close fault that is hydraulically connected to HF, the pore pressure increases rapidly which might lead to fault activation. Moreover, we found that decreasing the rate of injection can either increase or decrease the risk of induced seismicity depending on the fault location with respect to HF. Hence, besides avoiding fracturing rocks near faults, operators need to give serious attention to the location of faults relative to the operations, its architecture and the injection parameters to limit induce seismic events. Key Points: Faults can be destabilized by pressure diffusion if close to hydraulic fracturing and by increase in tensile and shear stresses if distantDamage zone size is important when normal and shear stresses dominate the fault response to hydraulic fractuirng (HF)Lowering injection rates does not necessarily reduce seismicity rates of faults that are stabilized by normal compressive stress during HF [ABSTRACT FROM AUTHOR]