Permian (Wolfcampian) Admire "C": New exploratory potential in the northern Denver basin

Significant frontier exploratory potential exists in the lower Wolfcampian Admire "C" unit, a regionally continuous, porous dolomite interval occurrin g at depths of 7800-8500 ft (2379-2592 m) in western Nebraska, United State s. Based on core, mud-log, thin-section, and SEM (scanning electron microsc ope) image analysis, as well as both regional and detailed local mapping, t he Admire "C" has been found to be the most prospective of several. reservo ir zones in this region based on (1) consistency and occurrence of oil show s; (2) superior reservoir quality and distribution; and (3) established pat terns of production. Continuity of the reservoir directly reflects transgre ssive;regressive cycles responsible for carbonate deposition in a shallow, intermittently restricted basin (Alliance basin) affected by glacio-eustati c sea level changes. Highest reservoir quality is concentrated in higher en ergy packstones and rare grainstones that exhibit a combination of intercry stalline, moldic, and vuggy porosity. The Admire "C" unit has low-to-modera te permeabilities (0.5-30 md) that restrict short-term flow capacity. A num ber of wells, however, have shown recoveries in the 75,000-130,000 bbl rang e at low and decreasing rates of annual decline, suggesting that they are i n contact with a larger, more continuous reservoir than was previously thou ght. Source beds include black shales within the Pennsylvanian and Wolfcamp ian sections. Little free water exists in the Admire "C" zone, suggesting m obile water may have been displaced by hydrocarbon migration. A number of i ntriguing similarities between the Admire "C" and the Ordovician Red River "B" reservoir in the Williston basin imply that exploration strategies succ essful in the latter might be applied to the Admire.