Major Challenges for Reservoir Upscaling

Abstract In the past two decades, many upscaling procedures have been proposed. The major methods are power-law average, renormalization technique, pressure-solver method, tenser method, and pseudo-function technique. The common problem of conventional upscaling methods is that they tend to smear out the spatially continuous extremes, such as shale barriers and open fractures. However, experience and previous simulation work in heterogeneous reservoirs have shown that oil recovery (especially water breakthrough oil recovery) mainly depends on the spatial connectivity of the extreme permeability values. CitationLasseter et al. (1986) proposed that scale-up of properties should be done from the scale of a representative elementary volume (REV), a volume for which the measured property does not change with an increase in scale over a given limit of scale. The notion of REV is physical-model oriented and proposed a criterion for upscaling technique. However, the decisive factor in upscaling is the grid system rather than individual physical point. This article concludes that how to obtain REV for real system, how to evaluate the upscaling results quantitatively, how to treat extremes of permeability, as well as how to perform upscaling for naturally fractured reservoirs and carbonate reservoirs are the remained major challenging problems in this area. It is concluded that a great effort should be made on how to obtain the REV grid, which could best describe the heterogeneity of given reservoir at a given scale. Secondly how to perform the upscaling of all properties based on the REV grid is also a critical aspect and should be considered according to the different extent and pattern of heterogeneity of the original geological model respectively. Keywords: reservoir upscalingREVREV Gridupgriddingupscaling extent