--> A Parallel Black Oil and Compositional Multiphase Flow Simulator for Unstructured 3-D Finite Element Grids

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A Parallel Black Oil and Compositional Multiphase Flow Simulator for Unstructured 3-D Finite Element Grids

Abstract

We present a massively parallelized reservoir simulator for both black oil and fully compositional three-phase flow. The simulator is built on higher-order finite element methods that are well suited to parallelization and provide maximum flexibility in conforming the computational grid to any geological formation geometry. We consider gas, oil, and water phases. Phase compositions and fluid properties can be described by either a black oil model (for greater computational efficiency) or a fully compositional equation-of-state model (for more challenging problems, such as enhanced oil recovery by CO2 injection). We adopt an implicit-pressure-explicit-saturation/composition scheme. Mass conservation equations are solved explicitly by a local discontinuous Galerkin (DG) method, which allows a higher-order approximation of phase compositions within each element. The DG method is locally mass conserving and readily parallelizable. Phase-split calculations are computationally expensive, but strictly local and also trivially parallelized. Finally, we use a mixed hybrid finite element (MHFE) method to simultaneously solve for globally continuous pressure and velocity fields. The MHFE pressure update is implicit and results in a non-trivial parallelization problem involving domain decomposition. This is particularly challenging for fully unstructured grids, such as tetrahedralizations. We present a number of complex large-scale simulation results that demonstrate the robustness, accuracy, and scalability of our parallel finite element reservoir simulation model.