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Spatial Distribution of Reservoir Quality in Deep-Water Wilcox Formation

Abstract

Over the last decade, the Paleogene Wilcox Formation in the deep-water Gulf of Mexico has emerged as a major hydrocarbon reservoir. Whilst large volumes of in place oil have been identified, the extraction of these poses significant challenges. The reservoirs are subsalt, relatively mud-rich, and highly compartmentalized. This contribution demonstrates that the drainage and producibility of these reservoirs are strongly impacted by facies distribution, and by the size and geometry of flow units. A conceptual model for channelized lobes designed to support both reservoir prediction and reservoir simulation is presented herein. The fundamental building blocks of deep-water fan systems are individual beds deposited from single sediment gravity flows. In the deep-water Wilcox the resultant beds range from relatively clean sandstones beds, to very dirty sand- and siltstone beds that contain a significant proportion of dispersed mud. These facies are attributed to sediment gravity flows transitional between laminar and turbulent, and display predictable vertical stacking patterns. Relatively closely spaced wells provide a unique opportunity to constrain the lateral distribution of these poorly-constrained facies. The subsurface data were coupled with outcrop and physical experimental data and used to develop a robust conceptual model for spatial distribution of facies in deep-water Wilcox. It is demonstrated that depositional reservoir quality in deep-water Wilcox channelized lobe settings is directly related to the spatial distribution of facies, with an upward increase and down-dip decrease in reservoir quality within separate flow units. Flow simulations were carried out on realistic facies scenarios and highlight the importance of accurate sedimentologically-based models to support management decisions about field development.