A Comparative Study of Geometrical Upscaling Methods for Inclusion of Fault Zone Structure into Upscaled Reservoir Simulation Models

Abstract

Most petroleum reservoirs contain faults, and a key methodological challenge in full-field reservoir modeling is to include the effects of 3D sub-seismic fault zone structure within the 2D fault surfaces represented in commercially available simulators. To address this shortcoming, connectivity-based geometrical upscaling (GU) is introduced to include these fault zones implicitly in the upscaled reservoir model, and in this study, a comparison is made of the accuracy and flexibility of two different GU methods. The existing template-based geometrical upscaling (TBGU) method is compared to a newly developed flow-based geometrical upscaling (FBGU) method. In both methods, the faults and their associated single-phase fault rock properties are represented in the upscaled reservoir simulation model implicitly as neighbor and non-neighbor cell-to-cell connection transmissibilities, which are determined from 3D fault zone structures, but these transmissibilities are calculated in very different ways. Both approaches require a high-resolution reservoir model (i.e., truth model), containing 3D fault zone structure explicitly within the model geometry, which is then upscaled using the two methods to take into account the influences of the fault zone structure. The accuracy of both the upscaling methods is examined by comparing the flow behavior of the truth model with that of model versions upscaled using two different ways. The results of the two versions of upscaled models revealed significant differences and indicate that the FBGU technique is a much more accurate and flexible means of including structurally complex fault zone into low-resolution upscaled reservoir simulation models.