The Asquith Marker and Other Lewis Shale Strata as an Oil and Gas Source Rock, Greater Green River Basin, Wyoming, United States

Abstract

Abstract

Large volumes of gas and some oil have been produced from the Cretaceous Lewis Shale, and it is often considered a regional source of gas in the Greater Green River Basin of the Western U.S. However, the Lewis Shale has never been studied as a potential oil prone source or reservoir rock despite the fact that there is a small Lewis oil field on the western part of the Wamsutter arch named the Stage Stop field.

The Asquith Marker, in the lower Lewis Shale, is a relatively organic rich shale easily recognizable on the GR log as an anomalously high API. It is a third order condensed section that has a maximum thickness of 100 ft. and covers a large area of the Greater Green River Basin.

Core data obtained from the Champlin 276 Amoco D well indicate the Asquith marker has a “high potential” to generate hydrocarbons from Type II kerogen. Based upon limited subsurface data, we have evaluated samples from one cored well that penetrated the Asquith as well as samples from six other Lewis Shale cores above the Asquith Marker, for a total of 5 well cuttings and 8 outcrop samples. Analyses included Rock-Eval, vitrinite reflectance, XRD, and biomarker geochemistry, from which the composition, maturity, oil potential and kerogen type were determined. Structure and stratigraphic maps were also compiled and used to identify the areas where the Asquith Marker is thickest and structurally deep enough to have generated oil.

The general sparseness of data has hindered a more robust analysis, but several indicators suggest the Asquith Marker may be an oil-prone unconventional resource shale, and is worthy of further investigation.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016