A fully coupled multiphase flow and geomechanics solver for highly heterogeneous porous media

This paper introduces a fully coupled multiphase flow and geomechanics solver that can be applied to modeling highly heterogeneous porous media. Multiphase flow in deformable porous media is a multiphysics problem that considers the flow physics and rock physics simultaneously. To model this problem, the multiphase flow equations and geomechanical equilibrium equation must be tightly coupled. Conventional finite element modeling of coupled flow and geomechanics does not conserve mass locally since it uses continuous basis functions. Mixed finite element discretization that satisfies local mass conservation of the flow equation can be a good solution for this problem. In addition, the stabilized finite element method for discretizing the saturation equation minimizes numerical diffusion and provides better resolution of saturation solution. In this work, we developed a coupled multiphase flow and geomechanics solver that solves fully coupled governing equations, namely pressure, velocity, saturation, and geomechanical equilibrium equations. The solver can deal with full tensor permeability and elastic stiffness for modeling a highly heterogeneous reservoir system. The results of the numerical experiments are very encouraging. We used the solver to simulate a reservoir system that has very heterogeneous permeability and elastic stiffness fields and found that the numerical solution captures the complex multiphysics of the system. In addition, we obtained higher resolution of saturation solution than with the conventional finite volume discretization. This would help us make a better estimate of the numerical solution of complex multiphysics problems.