Geologic reservoir characterization of the Shannon sandstone southwestern Powder River Basin, Wyoming

Abstract

The Upper Cretaceous (early Campanian) Shannon Sandstone Member of the Cody Shale is an unconventional stratigraphic play in the southwestern part of the Powder River Basin in Wyoming, USA. Despite decades of petroleum exploration and analysis, varying interpretations of the Shannon Sandstone depositional environment remain. These include a shelf sand ridge complex, prograding shoreface, or incised valley fill. The Shannon Sandstone near Pine Tree Field is less well studied than the nearby Hartzog Draw and Jepson-Holler Draw Fields. To address these issues, this study includes detailed analysis of nine cored wells and 27 wells with core associated reservoir property data across these fields in Johnson and Campbell Counties and subsurface analysis across the area. Key outcomes of this detailed geologic reservoir characterization include evidence that the Shannon is a heterolithic shelf current dominated marine sandstone deposited under tidal and wave influences, identification of the highest quality reservoir facies where fluid flow is mappable at a field level, and insight into the potential for future development in the area. A core to field scale study facilitates the understanding of lateral changes within the Shannon. This increased understanding of the depositional environment has broad implications for the geologic evolution of the basin as a whole.