Waterflood Performance Analysis for the South Cowden Grayburg Reservoir, Ector County, Texas

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A reservoir engineering study was conducted on waterflood performance in the South Cowden field, an Upper Permian Grayburg reservoir on the Central Basin Platform in West Texas. The study aimed to understand the historically poor waterflood performance, evaluate three techniques for incorporating petrophysical measurements and geological interpretation into heterogeneous reservoir models, and identify issues in heterogeneity modeling and fluid-flow scaleup that require further research. The approach included analysis of relative permeability data, analysis of injection and production data, heterogeneity modeling, and waterflood simulation. The poor waterflood recovery in South Cowden is partly due to the completion of wells only in the top half of the formation. Recompletion of wells through the entire formation is estimated to improve recovery by 6 percent of the original oil in place in some areas of the field over ten years. A direct three-dimensional stochastic approach to heterogeneity modeling yielded the best fit to waterflood performance and injectivity, but a more conventional model based on smooth mapping of layer-averaged properties was almost as good. The results reaffirm the importance of large-scale heterogeneities in waterflood modeling but demonstrate only a slight advantage for stochastic modeling at this scale. All flow simulations required a reduction to the measured whole-core kvl kh to explain waterflood behavior, suggesting the presence of barriers to vertical flow not explicitly accounted for in any of the heterogeneity models. They also required modifications to the measured steady-state relative permeabilities, suggesting the importance of small-scale heterogeneities and scaleup. Vertical flow barriers, small-scale heterogeneity modeling, and relative permeability scaleup require additional research for waterflood performance prediction in reservoirs like South Cowden.


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