Browsing by Subject "Grayburg Reservoir"
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Item Petrophysical Characterization of the South Cowden Grayburg Reservoir,Ector County, Texas(1996) Lucia, F. JerryReservoir performance of the South Cowden Grayburg field suggests that only 21 percent of the original oil in place has been recovered. The purpose of this study is to construct a realistic reservoir model to be used to predict the location of the remaining mobile oil. Construction of reservoir models for fluid-flow simulation of carbonate reservoirs is difficult because they typically have complicated and unpredictable permeability patterns. Much of the difficulty results from the degree to which diagenetic overprinting masks depositional textures and patterns. For example, the task of constructing a reservoir model of a limestone reservoir that has undergone only cementation and compaction is easier than constructing a model of a karsted reservoir that has undergone cavern formation and collapse as well as cementation and compaction. The Permian-age carbonate-ramp reservoirs in the Permian Basin, West Texas, and New Mexico, are typically anhydritic dolomitized limestone. Because the dolomitization occurred soon after deposition, depositional fabrics and patterns are often retained, and a reservoir model can be constructed using depositional concepts. Recent studies of the San Andres outcrop in the Guadalupe Mountains (Kerans and others, 1994; Grant and others, 1994) and the Seminole San Andres reservoir in the Permian Basin (Lucia and others, 1995) illustrate how depositional fabrics and patterns can be used to construct a reservoir model when depositional features are prominent. South Cowden field, Ector County, Texas, is a Grayburg (Permian age) anhydritic dolomite reservoir similar to many other Permian reservoirs in the Permian Basin. However, the diagenetic overprint has advanced so much that in some parts of the field, depositional patterns and fabrics no longer can be used to predict and model permeability. In this paper, we develop a reservoir model that includes areas where depositional patterns are useful and areas where they are not useful because diagenetic overprinting masks depositional patterns.Item Waterflood Performance Analysis for the South Cowden Grayburg Reservoir, Ector County, Texas(1996) Jennings, James W.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.