Abstract

Wells Field in Dawson County, Texas has produced over 7.5 million barrels of oil since 1955 from Silurian carbonates. Wells Field is an extremely complex system of structured and stratigraphic Fusselman and Wristen reservoirs that are not easily characterized by traditional subsurface mapping techniques. The Fusselman here, as elsewhere in the region, appears to vary in thickness independently of the thickness of the overlying Wristen section, which is the result of karst topography at the top of the Fusselman. This topography influenced deposition and reservoir development in the overlying Wristen, all of which was further imprinted by structural and erosional events prior to deposition of the Woodford Shale.

Detailed lithologic analyses of well cuttings from 29 wells in and around this field were conducted in order to evaluate reservoir zonation and potentials for either new field development wells, or recompletions from existing well bores. These analyses have shown that paleotopographic highs on the Fusselman unconformity across the field created optimum sites for Fusselman dolomite reservoir development, and collateral development of Wristen reservoirs. A certain amount of structure and facies-induced reservoir separation has been documented. The results of this study have been used to identify several areas of the field where each of the three reservoirs could be exploited for underdeveloped reserves, and to provide a model for exploring for and exploiting other such reservoirs in the northern Midland Basin.