Effects of anisotropic poroelasticity on stress and pore pressure changes around subsurface reservoirs and storage sites

Stresses and pore pressures change around depleting hydrocarbon reservoirs or fluid injection sites as result of reservoir pore pressure change. Such changes influence the stability of new wells drilled and may lead to fault activation, resulting in induced seismicity and possibly to casing damage in existing wells. Forecasting requires reliable geomechanical modeling of the reservoir and its surroundings. Classical analytical solutions are too simple, so numerical models are required. The rocks surrounding reservoirs are often anisotropic (like overburden shale), but their anisotropic elasticity is normally neglected, either because of model limitations, or in lack of input data. Here, however, the impact of anisotropy along with the elastic contrast between undrained surroundings and drained (isotropic) reservoir rock is addressed through a series of numerical scenarios. It is shown that isotropic models are unable to reproduce the stress changes predicted by the anisotropic models. Pore pressure changes may be underestimated by neglecting the anisotropic nature of the poroelastic Skempton parameters.