Assessment of Undiscovered Technically Recoverable Oil and Gas Resources of the Bakken Formation, Williston Basin, Montana and North Dakota, 2008

Richard M. Pollastro, Laura L. Roberts, Troy A. Cook, and Michael D. Lewan
Energy Resources Team, U.S. Geological Survey, Denver, CO

Advances in drilling technology combined with new concepts and models in exploration for oil from fractured shale in the Upper Devonian-Lower Mississippian Bakken Formation, Williston basin, resulted in improved recoveries and new discoveries in areas such as Parshall field, Montrail County, North Dakota. These factors have led to renewed exploration and increased the geographic area of potential success for commercial Bakken production.

The U.S. Geological Survey (USGS) is assessing undiscovered oil and gas potential of the Bakken Formation in the Williston basin, which includes parts of Montana and North Dakota. The assessment, based on geologic elements of a total petroleum system (TPS), is for the Bakken-Lodgepole TPS, where oil sourced from upper and lower shale members of the Bakken Formation is reservoired in a primary continuous-type reservoir and two conventional reservoirs. A composite continuous fractured Bakken reservoir is defined as the entire Bakken Formation including, where present, the “Sanish Sand” of the underlying Three Forks Formation. Conventional reservoirs include Waulsortian carbonate mounds of the overlying Lodgepole Formation and sandstone units of the middle member of the Bakken Formation where Bakken oils have migrated beyond the Bakken “oil window”.

Five continuous-type assessment units (AU) and one conventional AU are defined by the USGS for the Bakken Formation within the Bakken-Lodgepole TPS. The five continuous AUs are: 1) Elm Coulee-Billings Nose AU, 2) Central Basin-Poplar Dome AU, 3) Nesson-Little Knife Structural AU, 4) Eastern Expulsion Threshold AU, and 5) Northwest Expulsion Threshold AU. A conventional Middle Member Sandstone AU was also assessed.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado