Simulation of two-phase fluid flow through compactible reservoirs

Fluid-flow simulators used in the oil industry model the movement of fluids through a porous reservoir rock. These simulators either ignore coupling between the flow and concurring deformation of the solid rock frame or take it into account approximately, in the so-called loose or staggered-in-time mode. In contrast to existing simulators, the one we describe here fully couples two-phase (oil and water) flow to subsurface deformation and simultaneously accounts for all relevant physical phenomena. As such, our flow simulator inherently links time-dependent fluid pressures, saturations, permeabilities and flow velocities to stresses in the whole subsurface. These stresses relate to strains through the non-linear theory of elasticity, allowing us to model time-lapse changes in seismic velocities and anisotropy. The velocity variations manifest themselves in time shifts and reflection amplitudes that are conventionally measured from 4D seismic data. Changes in anisotropy produce time-dependent shear-wave splitting that can be used for monitoring the horizontal stresses.