Mitigating Injection-Induced Seismicity Along Basement Faults by Extraction: Application to 2016-2018 Pohang Earthquakes

The risk of induced earthquake is considered as the major obstacle for sustainable subsurface energy activities. As a mitigation approach, mechanistic risk assessment can be essential to minimize the potential of seismic hazard. Coupled hydro-mechanical modeling approach is integrated with geomechanical analysis to better assess the occurrence of seismicity induced by injection and/or extraction, which will provide a basis to update operational conditions (e.g., number and location of mitigating wells, rate and duration of operations) for mitigating earthquake nucleation. The Coulomb stability analysis and seismicity rate estimates from this generic study indicate that simultaneous extraction can relieve injection-induced pore-pressure buildup, but also transfer and accumulate elastic energy along the faults. Field-scale simulation with variation in well design for the Pohang EGS site, South Korea, show that multiple wells aligned across a preexisting fault form gradients of pressure and stress fields normal to the fault, which can enhance the direct impact of diffusion process and poroelastic stressing on the fault stability perturbation. Our mechanistic study suggests multiphysics-oriented mitigation strategies that consider (1) possible mechanical deformation, caused by hydro-mechanical coupling effects, and (2) proper configuration of well operations based on site-specific geological characteristics.