Abstract

The upper Tannehill (Frye) Sandstone of northeastern Stonewall County, Texas, is part of an elongate, east-west oriented fluvio-deltaic complex of Wolfcampian age located on the Eastern Shelf of the Permian Basin. Assessment of regional and local conditions (including a core of the upper Tannehill Sandstone) indicates a depositional setting transitional between a delta distributary channel and a meandering channel/point bar. The Polk and Patton Oil Company Fast Break Field (upper Tannehill) occupies a mid-channel rather than point bar position, and is approximately twice the productive area of nearby point bar upper Tannehill fields; with respect to at least one nearby field, cumulative production in the Fast Break Field is larger by an order of magnitude.

Petrophysical assessment of the core indicates a reservoir rock dominated by quartzose detrital mineralogy. Although early-diagenesis compaction of detrital micas and lithic sedimentary fragments and formation of secondary calcite cement has (in places) contributed to porosity reduction, late-diagenesis dissolution of plagioclase feldspar and lithic sedimentary fragments has enhanced original depositional porosity.