Reservoir stimulation’s effect on depletion-induced seismicity

Depletion-induced seismicity can pose a problem in some fluid-producing subsurface reservoirs, in some cases requiring production rate control in order to limit the seismicity. This study investigates the use of reservoir stimulation to reduce the depletion-induced seismicity rate. Depletion-induced stress and pore pressure changes are evaluated in a shale cap rock, sandstone reservoir, and shale underburden system, which contains a horizontal well, all modeled in plane strain conditions. The seismicity rate is then predicted based on an existing seismicity model and is found to be dependent on the direction the well is drilled in with respect to the principal stresses. The case where the reservoir has first been stimulated is compared to the case where stimulation has not been performed (using the same production rates) for normal, reverse, and strike-slip faulting stress regimes. Seismicity is reduced in the case of reservoir stimulation for both reverse and strike-slip faulting stress regimes. The seismicity rate is only slightly reduced for the normal faulting stress regime. Stimulation also increases the distance that changes in pore pressure dominate over poroelastic stress changes in the reservoir. Further, it is found that the optimal orientation of a horizontal well, in terms of induced seismicity, is parallel to the minimum principal stress in normal faulting stress regimes and parallel to the maximum principal stress in reverse faulting stress regimes. The orientation of a horizontal well determines where the seismicity is located in a strike-slip faulting stress regime.