Development and Application of a New Technique for Upscaling Miscible Processes

Miscible gas injection offers both high local displacement efficiencies and a means for handling produced gas. As fine scale simulations of miscible processes can be very time-consuming, there is a clear need for an accurate and robust coarse scale miscible simulation capability. In this paper, we present a new upscaling technique for the accurate coarse scale simulation of first-contact miscible displacements. Our method contains two key components: Effective Flux Boundary Conditions (EFBCs) and the Extended Todd & Longstaff with Pseudo relative permeabilities (ETLP) formulation. EFBCs, which were applied previously within the context of immiscible displacements, account approximately for the effect of the global flow field on the local upscaling problems and as a result mitigate inaccuracies introduced by standard procedures. The ETLP formulation modifies the way effective fluid properties and upscaled relative permeabilities are computed in a limited compositional framework such that residual oil that is immobile and unavailable for mixing is efficiently represented. The accuracy of the new technique is demonstrated for several example problems. Using synthetic models with differing permeability correlation lengths, we show that the new method provides results superior to those obtained using existing upscaling procedures (standard upscaled relative permeabilities, upscaled absolute permeabilities only, and nonuniform coarsening) for partially layered cases. The breakthrough time, oil production curve and saturation profiles are predicted accurately. The method is also shown to perform well over a wide range of coarsening factors (4 – 2500) for several fields with different permeability heterogeneity structures. Finally, we apply the method to a real field case with encouraging results, indicating the practical applicability of the new technique.