Physics‐Based Evaluation of the Maximum Magnitude of Potential Earthquakes Induced by the Hutubi (China) Underground Gas Storage

The world's largest underground gas storage facility in Hutubi (HUGS), China, is a unique case where cyclic gas injection‐extraction induced both seismicity and ground deformation. To assess the potential for future induced seismicity, we develop a framework physically based on a well‐constrained hydro‐geomechanical model and on fully‐coupled poroelastic simulations. We first interpret the spatiotemporal distribution and focal mechanisms of induced earthquakes and take it as a key step and a premise to estimate the magnitude and location of the largest potential earthquake. The sharp increase in seismicity was controlled by poroelastic loading on secondary southwest‐dipping thrust faults with spatial scales too small to be resolved by 3D seismic surveys. Both operational and local geological factors affect the seismic productivity at the HUGS site, distinguishing it from most cases of seismicity induced by wastewater disposal and hydraulic fracturing. We then conduct slip tendency analyses for major faults imaged by the seismic data, including the largest reservoir‐bounding Hutubi fault hydraulically connected to injection wells. The reactivation potentials of these imaged faults are estimated to be extremely low. Accordingly, future seismicity would most likely occur on failure‐prone secondary faults in regions with positive stress perturbation due to poroelastic loading. The maximum magnitude likely depends on the spatial scales of the secondary faults. As the occurrence of detected earthquakes is spatially and temporally consistent with the simulated evolution of Coulomb stress perturbation, the location of the largest potential earthquake probably depends on the sizes of the poroelastic stressing regions. Across the world there are numerous underground gas storage (UGS) facilities that are either under construction or planned due to major demands for clean energy and major concerns over tackling issues related to global climate change. Induced seismicity at UGS facilities is a burgeoning topic, with few documented cases so far. In some cases UGS facilities are located in highly populated regions that could experience strong ground shaking due to local and shallow induced earthquakes. Under the typical scenario of earthquakes induced by pore pressure diffusion, the maximum magnitude is sometimes thought to be governed by fluid‐stimulated rock mass or the volume of injected fluids. However, in the case of earthquakes induced by poroelastic effects (rock deformation beyond the overpressure front), we know very little about the influence of additional critical parameters on the timing, location, and magnitude of induced earthquakes. The largest potential earthquake associated with the HUGS is a problem compounded by the effects from pressure and poroelastic perturbation. Our study helps to fill in the knowledge gap between pore pressure and poroelastic effects, and provides a reference to assess and mitigate the risk of seismicity related to UGS operations. Sharp increase of induced seismicity was primarily controlled by poroelastic loading on secondary southwest‐dipping thrust faultsSlip tendency analyses reveal low reactivation potential of the largest Hutubi fault hydraulically connected to injection wellsThe largest potential event would most likely occur on secondary faults in regions where poroelastic loading promotes frictional failure Sharp increase of induced seismicity was primarily controlled by poroelastic loading on secondary southwest‐dipping thrust faults Slip tendency analyses reveal low reactivation potential of the largest Hutubi fault hydraulically connected to injection wells The largest potential event would most likely occur on secondary faults in regions where poroelastic loading promotes frictional failure