Geology and Assessment of Undiscovered Oil and Gas Resources in the Lodgepole Formation, Williston Basin, North Dakota and Montana

Gaswirth, Stephanie B.¹; Pollastro, Richard M.¹; Anna, Lawrence ¹; Lillis, Paul ¹; Roberts, Laura N.R. ^1
1 U.S. Geological Survey, Denver, CO.

The U.S. Geological Survey (USGS) recently completed an assessment of the technically recoverable undiscovered oil and gas resources of the U.S. portion of the Williston Basin. The assessment is based on geologic elements and processes within a petroleum system, which include detailed stratigraphic and structural framework studies and petroleum-system modeling, as well as on historical exploration data and production analyses that are applicable to resource estimation. Using this approach, the USGS defined ten total petroleum systems (TPS) in the Williston Basin that included thirteen conventional assessment units (AU) and six continuous (unconventional) AUs. Two of the TPSs include the Mississippian Madison Group: (1) the Bakken-Lodgepole TPS, which includes the Lodgepole Formation; and (2) the Madison TPS, which includes the Mission Canyon and Charles Formations. The Madison Group has been the largest producer of oil to date, with over 1 BBO produced from the Mission Canyon and Charles Formations and 50 MMBO from the Lodgepole Formation.

The Bakken-Lodgepole TPS is defined as the area in which oil generated from the upper and lower shales of the Bakken Formation has accumulated in reservoirs in the Bakken and Lodgepole Formations. The eastern extent of the TPS is defined by the limit of distribution of the upper Bakken shale, the southern extent is defined by extension of the 12-mi-wide buffer zone that has been established for mound production, and the western extent is marked by the province boundary. Two conventional AUs were identified in the Bakken-Lodgepole TPS, including one in the Bakken Formation and the second in the Waulsortian mound reservoirs of the lower part of the Lodgepole Formation. Lodgepole mound production has been historically restricted to a limited area in Stark County, North Dakota. Reservoirs are sealed by middle and upper Lodgepole tight argillaceous limestones. Other nonproductive mounds and mound-like structures have been identified in the Lodgepole Formation. This lack of productivity is strongly correlated with the defined oil window of the Bakken shales, and also indicates the likelihood of limited lateral migration of Bakken oil into Lodgepole reservoirs in North Dakota and Montana. Such considerations limited the estimated technically recoverable resources to a mean of 8 MMBO for the Lodgepole Formation conventional reservoirs in the U.S.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009