Regional Stratigraphic Analysis of the Pronghorn Member of the Bakken Formation, Williston Basin, USA

The Pronghorn Member of the Bakken Formation is a silty and fine-grained sandstone interval above the Upper Three Forks and below the Lower Bakken Shale. It has previously been informally referred to as the Sanish Sandstone. This interval has been an important tight oil resource play in a large basin center oil accumulation of the Williston Basin.

The lithology of the Pronghorn member varies greatly and is present as a burrowed dolomitic siltstone, bioturbated sandstone, or a gray to green shale.

The Pronghorn has low porosity and permeability, but has produced hydrocarbons sourced form the Bakken shales and has allowed fluid migration to the underlying reservoirs of the Three Forks.

Paleostructural elements such as the Bottineau, Nesson, Cedar Creek, and Poplar anticlines influence Pronghorn depositional patterns and lateral extent.

The contact of the Pronghorn with the underlying Three Forks Formation maybe conformable in the deeper parts of the Williston Basin and is unconformable on the basin flanks. The same relationships exist for the overlying Lower Bakken Shale.

An understanding of regional thickness variations and facies changes will be key for future drilling in this important basin center system.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California