3D compositional reservoir simulation using unstructured grids in homogeneous reservoirs

Abstract

This paper presents a 3D implementation of an element-based finite-volume method (EbFVM) using hexahedron, tetrahedron, prism and pyramid elements in conjunction with a compositional reservoir simulator. The EbFVM approach combines the conservative advantage of the finite volume method and adds flexibility to handle irregular geometries. The EbFVM is implemented into the UTCOMP simulator considering a full permeability tensor formulation for the advection terms. The UTCOMP simulator was developed at the Center for Petroleum and Geosystems Engineering at The University of Texas at Austin for the simulation of enhanced recovery processes. UTCOMP is a compositional multiphase/multi-component, Implicit Pressure Explicit Composition simulator (IMPEC), which can handle the simulation of miscible gas flooding processes. Only permeability and porosity are stored into the cells, and all other properties are evaluated in the grid vertex, and therefore the balance equations are performed in a cell-vertex approach. The balance equations are locally evaluated into the elements and each piece of the elements, called sub-control volume, are assembled to form the control volumes around each vertices. The results of several cases studies are presented in terms of volumetric rates of oil and gas, and saturation fields. The results of the original formulation of the UTCOMP simulator using Cartesian meshes are also presented.