Basement Faults and Their Influence on Marine Sandstone Depositional Patterns and

Hydrocarbon Entrapment, Greater Green River Basin

By

John C. Horne

Orion International Limited, Denver, CO

S. Parker Gay

Applied Geophysics Inc, Salt Lake City, UT

The trends of marine sandstone reservoir facies and hydrocarbon migration pathways in the Greater Green River basin are influenced strongly by basement faults. Many of the shoreline and marine sandstone depositional patterns and their associated reservoir-potential facies in this basin show a direct relationship to the juncture of basement structural highs with crosscutting regional linear features.

Northwest-oriented regional basement faults controlled the distribution and orientation of Muddy lowstand valley-fill deposits in the western Greater Green River basin, while orthogonal northeast faults controlled the orientation and distribution of reservoir facies in associated shoreline deposits. In the eastern Greater Green River basin, basement faults have affected the distribution of reservoir facies in the Upper Cretaceous Almond formation. The Almond formation accumulated as retrogradational shoreline deposits during a period of rising sea level. A north-south basement fault controlled the trend of the Echo Springs shoreline. Because of the transgressive nature of these deposits, much of the potential upper shoreface reservoir facies was stripped during the transgression. The thickest and best quality reservoir deposits accumulated as inlet fills associated with the retrogradational shorelines. The main reservoir facies at Echo Springs field is in inletfill deposits. A major northwest to southeast-oriented basement linear controls the southern limit of the inlet-fill reservoir facies in the Echo Springs field.

In the Greater Green River basin, production from marine sandstone reservoirs commonly ends abruptly or changes trend at basement linear discontinuities. Consequently, these faults are critical in controlling the productive limits of many marine sandstone stratigraphic entrapments.

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