A New Upscaling Approach for Highly Heterogeneous Reservoirs
P. Zhang, Gillian Elizabeth Pickup, Michael Andrew Christie · 2005
Abstract Upscaling in highly heterogeneous reservoir models is a very challenging procedure, despite much research having been carried out over the past few decades.The fluid flow depends on the well locations, and crossflow may be significant. Traditional upscaling approaches such as the pressure solution method with locally applied boundary conditions, may be highly inaccurate. In two-phase systems,such as waterfloods, accurate reproduction of the flood front is also problematic.Two-phase upscaling is often impractical,but using only traditional single-phase upscaling may lead to large errors. In this paper we demonstrate how conventional upscaling approaches may produce erroneous results and suggest a simple alternative.The new method uses boundary conditions based on the actual well pressures and solves the single-phase pressure equation over the global fine scale geological model.Inter-block transmissibilities and upscaled well connection factors are then computed. By using the appropriate boundary conditions,single-phase flow is accurately reproduced,and therefore the accuracy of two-phase flow at the coarse-scale is greatly increased. We have verified that the new method may be applied to two-phase, highly heterogeneous reservoir models, including models with multiple relative permeability curves and significant gravity effects.We have also applied the method to the benchmark model of the SPE 10th Comparative Solution Project(1.1 million cells, unstable flood). The results show good agreement with the fine grid solution provided by Landmark using a parallel simulator. As models of tens of millions of grid cells are now solvable on a PC in an hour, this method is a feasible approach for achieving highly accurate upscaled models. This method is particularly appropriate for later stages of field development, when models are large and accurate flow simulation is required.