Vorticity-based coarse grid generation for upscaling two-phase displacements in porous media

Abstract

Coarse grid generation from finely gridded geological model is a main step in reservoir simulation. Coarse grid generation algorithms aim at optimizing size, number and location of the grid blocks by identifying the important geological and flow features which control flow in porous media. By optimizing coarse grid structure we can improve accuracy of the coarse scale simulation results to reproduce fine grid behavior. A number of techniques have been proposed in the literature. We present a novel coarse grid generation procedure based on vorticity preservation between fine and coarse grids. In the procedure, the coarse grid mesh tries to capture variations in both permeability and fluid velocity using a single physical quantity — “vorticity” which is extracted from single-phase flow simulation. One essential element in the procedure is that the improved coarse grid (ICG) has minimum single-phase vorticity error with respect to the fine grid vorticity. Our numerical investigations on modeling two-phase flow demonstrate that the ICG represents fine grid flow behavior very closely. In addition, our analyses show that the use of single-phase vorticity has only a minor impact on the ICG generation, and its performance is not affected by two-phase flow parameters such as mobility ratio.