A hybrid finite element model for non-isothermal two-phase flow in deformable porous media

This paper presents a numerical method to model the coupled thermo-hydro-mechanical (THM) processes in porous media saturated with two immiscible fluids. The basic equations of the system have been derived based on the averaging theory, considering skeleton deformation, two-phase fluid flow, and heat transport. As applying the standard Galerkin finite element method (GFEM) to solve this system of partial differential equations may lead to oscillatory results for saturation and temperature profiles, a hybrid numerical solution is proposed. In this frame, the GFEM is combined with a control volume based finite element (CVFE) approach, and a streamline upwind control volume finite element (SUCVFE) scheme, respectively for the mechanical, hydraulic and thermal part of the system. The CVFEM has been adopted to provide a smooth saturation profile by ensuring local mass conservation, while the streamline upwind scheme has been applied to remove the spurious temperature oscillation by adding stabilizing terms to the thermal part of the system. The CVFE and SUCVFE formulations have been derived using a similar approach as the standard FE practice in the context of weighted residual technique, but using different weighting functions. This will significantly facilitate the implementation of the proposed model in existing FE codes. Accuracy and efficiency of the proposed method have been justified using several numerical examples and comparing the results with available analytical or numerical solutions.