Geomechanics of Reservoir Depletion–Induced Fault Reactivation in Nonhomogeneous Subsurface Rock Layers

Fault reactivation may occur during reservoir depletion, leading to geomechanical hazards such as seismicity. Understanding and predicting the depletion–induced stress variations within subsurface layers and on the fault plane are crucial for mitigating the risk of induced seismicity. For this purpose, an analytical approach is proposed to assess these stress variations and the associated sliding potential of a fault in the general vicinity of a depleted rock layer confined between two mechanically different formations. The depletion–induced nonuniform distribution of in situ stress changes within each rock layer is first derived from constitutive equations of poroelasticity and Navier’s equations of static equilibrium while considering continuity of stress and deformation across rock layers. The solution is then utilized to compute the stress state on the fault plane through a series of coordinate transformations and Cauchy’s law. Subsequently, the fault sliding potential is evaluated to assess the stability of a fault in the vicinity of the reservoir after depletion. Findings highlight the significant influence of nonhomogeneity of subsurface layers on the sliding potential of normal faults, particularly for those located inside the depleted reservoir. Moreover, the results of this study demonstrate the substantial errors of uniaxial strain models in estimating the sliding potential of faults in the vicinity of depleted reservoirs.