ABSTRACT: A parametric study has been done using a fully coupled single-phase geomechanics-fluid flow simulator to determine the effect of coupling deformation and fluid flow on reservoir response during production. We have compared these results to standard reservoir simulation and reservoir geomechanical models to see the effects of coupling and under what conditions coupling is important. . Standard reservoir simulation and geomechanical modeling approaches miss the dynamic, implicit coupling between fluid pressure and rock deformation, between reservoir deformation and overburden/sideburden deformation, and between stress and permeability.
For example, standard reservoir simulation predicts that a low compressibility in a highly compressible reservoir will yield the same drawdown and production history as a highly compressible fluid in a low compressibility reservoir provided the total compressibility of the two systems is the same. Fully coupled modeling shows that the two systems can have vastly different drawdown and production histories due to the coupled response of the fluid-reservoir-overburden system. Our modeling also shows that geomechanical models of the reservoir can often be misleading because they utilize an "uncoupled" fluid pressure distribution to calculate reservoir and overburden deformations. In addition, fully coupled modeling shows that in many reservoirs, Geertsma's approximations of uniaxial strain do not apply. Modeling shows that reservoir stress paths during drawdown arc strongly affected by ratios of over-burden and reservoir moduli and by the ratio of reservoir thickness to lateral extent. Also, coupled modeling shows that lateral fluid pressure variations in the reservoir can lead to near wellbore stress paths approaching isotropic stress conditions in many reservoirs
