Effects of stratal architecture and diagenesis on reservoir development in the Grayburg formation: SSouth Cowden field, Ector County, Texas. Annual report, 1 October 1994--30 September 1995

This report presents the results of geological characterization studies in a typical Grayburg reservior in the Permian Basin. The work applies geological models developed in outcrop studies to better constrain the geological reservoir framework and heterogeneity in a typical Grayburg reservoir, The South Cowden Grayburg reservoir. This framework provides a strong basis for defining petrophysical and flow unit properties in the reservior and serves as a prototype model for other Grayburg reservoir characterization studies. The Grayburg Formation in the South Cowden field of eastern Ector County displays an internal stratal architecture that typifies Grayburg shallow-water platform successions throughout the Permian Basin. Study of core and wireline logs in South Cowden field documents three orders of cyclicity in the Grayburg. The entire Grayburg constitutes a single long-duration accommodation cycle that commenced with a major sea-level rise. Two major diagenetic events strongly affect reservoir character in some parts of the field. Recrystallized dolomite is developed along vertical burrows in highly cyclic mud-dominated packstones and wackestones of the HFS 4 Grayburg highstand succussion. Later alteration and removal of anhydrite are focused in structurally low sections along the eastern and southern margins of the field