AN IMPROVED GLOBAL UPSCALING APPROACH FOR RESERVOIR SIMULATION

Abstract

Realistic upscaling of fine-scale reservoir models is a great challenge for reservoir engineers. The common problem of conventional upscaling methods is that they may smear out the spatially continuous permeability extremes, such as shale barriers and open fractures. Recent studies have shown that such smearing effect has a significant impact on recovery in heterogeneous reservoirs, especially the breakthrough oil recovery. The conventional methods are considered as local upscaling which concentrate on only local areas and ignore geologically important structural information. A recent global upscaling approach attempts to solve this problem, but the resulting grid system may be over-irregular and becomes impractical for field applications. This paper presents an improved global upscaling approach based on the representative elemental volume (REV) theory and the stepwise idea from renormalization. The new method focuses on the use of a new concept of REVGS (REV Grid System) for constructing coarse blocks, which taking into account the spatial connectivity of a global permeability field. Mathematically, the variance of permeability in the coarse blocks is the smallest within the blocks, and the largest between the blocks. The resulting system can be readily used in flow simulators. The proposed method is applied to two case studies. Compared to the conventional methods, the coarse grid system derived from our improved global method successfully retains the permeability extremes observed in the fine-scale models. The flow simulation results show that the consistency of the reservoir behavior before and after upscaling is excellent.