Stratigraphic Entrapment of Hydrocarbons in the Upper Cretaceous Lewis Shale and

Lower Fox Hills Sandstone, Eastern Green River Basin, Wyoming

By

David S. Muller and Fabian T. Wirnkar

BP America, Houston, TX

Commercial hydrocarbons are entrapped within sands of the Lewis Shale and Fox Hills Sandstone in the eastern Green River Basin. Stratigraphic traps within the Lewis and Fox Hills of the Red Desert Basin occur in sands deposited within basin floor fans, slope fans, lowstand wedge deposits, and in nearshore marine environments associated with the final major regression of the Western Interior Cretaceous Seaway. Lewis gas and condensate are generally produced as part of a co-mingled production stream together with gas from the underlying Almond Fm. of the Mesaverde Group. Production logs and stand-alone Lewis producers demonstrate that the Lewis is locally an important part of the hydrocarbon production stream within the Red Desert Basin.

Entrapment in Lewis Shale within the Red Desert Basin occurs at the now updip, distal edges of sand packages that were deposited from a northerly provenance (“Red Desert Delta” or “Sheridan Delta”) within and near the margins of the Lewis seaway during the Maastrichtian. Geometries, log character, seismic data, and other characteristics of the sands within the Lewis shale for a number of differerent traps at several stratigraphic levels are compared and contrasted.

AAPG Search and Discovery Article #90004©2002 AAPG Rocky Mountain Section, Laramie, Wyoming