Development of a Geologic Exploration Model for the
Permo-Pennsylvanian Petroleum System in South-Central Montana

The Permo-Pennsylvanian stratigraphic section in the Big Horn and Powder River basins is the most prolific oil-producing system in the central Rocky Mountain Region. This petroleum system has produced in excess of 2 billion barrels of oil (BBO) in the Big Horn Basin and in excess of 525 million barrels of oil (MMBO) in the Powder River Basin. Dramatic stratigraphic changes and thinning occur within this section between the Central Montana Trough and the Big Horn and Powder River Basins to the south. The erosional pinch-out of this system has been the focus of petroleum exploration Location map for the Tensleep-Minnelusa sectionin the past. Recent work in the northern part of the Big Horn Basin, by the co-investigator for this project, shows that petroleum accumulations are in fact controlled by more complicated stratigraphic changes that occur south of the erosional pinch-out of >this stratigraphic interval. This project will document the importance of these stratigraphic traps and will provide a new model for petroleum exploration within the Permo-Pennsylvanian system that is less dependent on Laramide tectonics and trapping along the erosional pinch-out of the stratigraphic system than previous models. In this proposal it is postulated that the true primary regional truncation trap will be found where truncation of the reservoir facies occurs within the system, and that Laramide tectonism and other influences have only modified this trapping mechanism.

The area of the proposed research includes the northernmost portions of the Big Horn and Powder River Basins. In this area the Pennsylvanian Tensleep Sandstone and Minnelusa Formation provide some of the most important petroleum reservoirs in the region. Reservoir facies were controlled by an eastward transition from marine to marginal marine to coastal depositional environments in combination with erosional wedging of the top of the sequence, which occurred in the Permian and Jurassic. The Tensleep-Minnelusa section pinches out completely in the area of the Central Montana Trough. In the past, petroleum exploration focused on this pinch-out.

The overall goals of this project are 1) Diagram of reservoir developmentto develop a new exploration model for the Permo-Pennsylvanian petroleum system, 2) to generate maps for industry showing an exploration fairway for oil accumulations in this system, 3) to reduce exploration costs by allowing focused exploration in the fairway that will be identified and by providing the background research from this project, and 4) to ultimately add petroleum reserves from new discoveries. This figure diagrammatically illustrates the hypothesis for reservoir development to be tested by the proposed project.

Project Publications 
Other Oil and Gas Publications

Poster (PDF file) presented at the AAPG convention in June 2006 on reservoir development in the Tensleep Sandstone, Pryor and Bighorn mountains, south-central Montana.

Funding for this project is provided by
DOE/NETL (National Energy Technology Laboratory) with matching funds from the Bureau and Ballard Petroleum Holdings, LLC. Steve VanDelinder of Ballard Petroleum Holdings is Co-Investigator. The Crow Tribe participated by granting access to tribal lands in the Pryor and Bighorn Mountains.