Upscaling and Gridding of Geologically Complex Systems for Reservoir Flow Simulation

Wednesday, March 13, 2002 - 9:30am - 10:30am
Keller 3-180
Louis Durlofsky (Stanford University)
Geostatistical reservoir descriptions are generally much too detailed for direct use in reservoir flow simulations. Upscaling procedures are required to coarsen these detailed reservoir descriptions to scales more suitable for flow calculations. In this talk, several upscaling procedures, appropriate for both moderate and high degrees of upscaling, will be described and applied. A technique for the improved calculation of coarse scale equivalent permeability tensors, which entails the use of a border region of fine grid cells around the target coarse block, will be described. This technique is then combined with a flow-based grid generation procedure that is able to provide flexible, structured grids for geometrically complex, generally anisotropic systems. The permeability upscaling and gridding techniques will each be shown to lead to improvements in the accuracy of coarse scale reservoir descriptions relative to reference fine grid results. When used in combination, the overall methodology provides significantly enhanced coarse models.

To achieve higher levels of upscaling, subgrid models of transport are required. A methodology for representing subgrid effects in the saturation (water transport) equation, based on the use of volume averaging and the approximate modeling of higher moments, will be presented. The technique couples local fine scale fluctuations with global coarse scale information to provide a subgrid model that is driven by large scale flow behavior. For a series of model problems, it will be shown that this technique provides much more accurate results than coarsened models that do not contain a subgrid treatment.