For very viscous oils (>500cp), a stable polymer flood is not economical due to low processing rates. In such cases, a partially stable (mobility ratio >1) polymer flood must be designed. Depending on the magnitude of viscosity ratio, these displacements will be influenced by viscous fingering. Typically, viscous fingers cannot be accurately captured with the grid sizes used in full-field simulations. To optimize and design a partially-stable polymer or water flood, it is critical to correctly upscale the laboratory-generated relative permeability curves for reservoir simulation. In recent years, such models have been published in SPE literature. Unfortunately, most of these models require multiple fitting parameters (3+). In this work, we present a simplified technique that requires systematic change in only one parameter to generate upscaled relative permeability curve for a given viscosity ratio.
Using fine-grid simulations, we show that due to small-scale random heterogeneities, the flow at high viscosity ratio is channelized even in a core perceived to be homogeneous at laboratory scale. Upscaling averages these fine variations in heterogeneities, causing the grids to be over-swept, and thus the recovery is over-predicted. To compensate for this over-prediction, relative permeability curves need to be upscaled.