Numerical analysis of fault reactivation and stability in aquifer gas storage: a case of X oilfield

To clarify the damage evolution mechanism of fault reactivation and shear slip during multi-cycle gas injection and production in aquifer gas storage, a refined two-dimensional finite element fault model incorporating fluid-solid coupling effects was established. Based on the simulated operational scenarios, a fault stability evaluation method under alternating injection and production cycles was developed, systematically assessing the influence of injection-production pressure and in-situ stress state on fault damage behavior. The methodology was applied to evaluate fault stability in Block M, a proposed aquifer gas storage site. The results indicated the following findings. (1) Fault reactivation patterns were strongly affected by reservoir lateral connectivity. Faults intersecting highly connected reservoirs were more susceptible to shear slip and localized instability, whereas the aquifer-caprock interface exhibited secondary vulnerability to shear failure. (2) In laterally sealed reservoirs, low-permeability fault zones were prone to stress concentration, constituting primary risk areas for shear slip. (3) The pore pressure increment (ΔP) exhibited a strong positive correlation with stress redistribution, with fault activation occurring when the ΔP-induced reduction in effective stress caused the stress state to cross the Mohr–Coulomb failure envelope. (4) Numerical simulations of the target reservoir predicted a maximum induced shear displacement of 1.33 mm without tensile failure, thereby confirming the integrity of the aquifer-caprock interface. This study offers practical insights for optimizing injection and production strategies and ensuring the long-term operational safety of aquifer gas storage projects.