Upper Three Forks Shoreline Facies and Potential Reservoirs in the U. S. Williston Basin

Hendricks, Michael¹ (1) Hendricks and Associates, Inc, Centennsial, Algeria

The upper Three Forks is a complex assemblage of shoreline and subtidal sediments that were part of a regional base level rise near the end of the Devonian. Reservoir development within these strata is problematic. The most notable production occurs in Antelope Field, North Dakota, where extensive fractures are present. Matrix porosity is limited in this area, and the fractured Three Forks reservoir probably extends vertically into the overlying Bakken Formation.

Along the southern and eastern edges of the Three Forks- Bakken basin, shoreline sediments are ripple laminated, very fine to fine-grained sandstone and sandy dolomite beds with gray-green shale drapes and gray-green and brown shale beds. Basinward, the upper Three Forks beds are burrowed, shallow subtidal sediments that locally contain small crinoid ossicles and other open marine fauna.

Potential petroleum reservoirs occur in shoreline sediments where dolomitization and subsequent removal of carbonate cement produced effective porosity. Lateral facies changes in these peritidal sediments are one of several challenges associated with Upper Three Forks horizontal drilling.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana