A New Method for Accurate and Practical Upscaling in Highly Heterogeneous Reservoir Models

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractGeologists often generate highly heterogeneous descriptions of reservoirs, containing complex structures which are likely to give rise to very tortuous flow paths. However, these models contain too many grid cells for multiphase flow simulation and the number of cells must be reduced by upscaling for reservoir simulation. Conventional upscaling methods often have difficulty in the representation of tortuous flow paths, mainly due to the inappropriate assumptions concerning the boundary conditions. An accurate and practical upscaling method, which is able to preserve the flow behaviour caused by highly heterogeneous fine scale geological features, is therefore required.In this paper, the problems encountered in routinely used upscaling approaches are outlined, and a more accurate and practical way of performing upscaling is proposed. The new upscaling method, Well Drive Upscaling (WDU), employs the actual reservoir boundary conditions. The main advantage of this method is that the dominant flow paths can be preserved, and thus the geological knowledge can be assimilated appropriately. The new method has firstly been applied to a synthetic model with a tortuous channel, and is shown to have significant improvement over the traditional approach. The sensitivity study on the scale up factor using a bench mark model shows the advantage of the method with various scale up factors. The method was then applied to a model of a field in the central North Sea, which involves three phase flow. In the cases studied, the WDU method produced a comparable result to the dynamic Pore Volume Weighted approach which involves running the fine grid simulation and computing appropriate relative permeabilities and inter-block transmissibilities. The new method makes the upscaling process both practical and accurate and ensures that field predictions can be made more confidently with greater geological realism.

Rate Dependency in Steady-State Upscaling

“…Global methods, see, e.g. Kyte and Berry (1975) and Zhang et al (2006), require solutions to the full fine-scale model, while local methods only consider the fine-scale region corresponding to the target coarse cell. Noting that this is a simplified view, there are also combinations of the two.…”