Petroleum reservoir simulation coupling fluid flow and geomechanics

This paper presents a discussion of the issues related to the interaction b etween rock deformation and multiphase fluid flow behavior in hydrocarbon r eservoirs. Pore-pressure and temperature changes resulting from production and fluid injection can induce rock deformations, which should be accounted for in reservoir modeling. Deformation can affect the permeability and por e compressibility of the reservoir rock. In turn, the pore pressures will v ary owing to changes in the pore volume. This paper presents the formulatio n of Slot's equations for multiphase fluid flow in deformable porous media. Based on this formulation, it is argued that rock deformation and multipha se fluid flow are fully coupled processes that should be accounted for simu ltaneously, and can only be decoupled for predefined simple loading conditi ons. In general, it is shown that reservoir simulators neglect or simplify important geomechanical aspects that can impact reservoir productivity. Thi s is attributed to the fact that the only rock mechanical parameter involve d in reservoir simulations is pore compressibility. This parameter is shown to be insufficient in representing aspects of rock behavior such as stress -path dependency and dilatancy, which require a full tensorial constitutive relation. Furthermore, the pore-pressure changes caused by the applied loa ds from nonpay rock and the influence of nonpay rock on reservoir deformabi lity cannot be accounted for simply by adjusting the pore compressibility.