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The AAPG/Datapages Combined Publications Database

Rocky Mountain Association of Geologists


The Mountain Geologist
Vol. 50 (2013), No. 1. (January), Pages 5-31

Review of Oil Families and Their Petroleum Systems of the Williston Basin

Paul G. Lillis


The petroleum system concept was first applied in 1974 (Dow/Williams) to identify three oil systems in the Williston Basin, and recent studies have expanded the number to at least nine. This paper reviews the petroleum geochemistry, oil-oil, and oil-source correlations of the oil systems of the Williston Basin, providing a new perspective and some new findings. Petroleum systems with a known source (documented oil-source correlation) include the Red River (Ordovician), Winnipegosis (Devonian), Bakken (Devonian-Mississippian), Madison (Mississippian), and Tyler (Pennsylvanian) systems. Petroleum systems with an identified source rock but no documented oil-source correlation are considered hypothetical and include the Winnipeg (Ordovician), Duperow (Devonian), and Birdbear (Devonian). The Deadwood (Cambrian-Ordovician) petroleum system is speculative because a good oil-prone source rock has not been identified. The stratigraphic distribution of the oil families from each system is generally limited to the same formation from which they were sourced due to efficient seals and a paucity of vertical migration pathways, but some notable exceptions do occur.

Oil bulk properties such as API gravity, sulfur content, and pour point are much underutilized in the recent geochemical literature and are found to be useful here in differentiating oil families. The Red River petroleum system has two oil families that can be differentiated based on pour point. The oils in the Madison petroleum system can be divided into two families based on API gravity-sulfur content relationships, with one family derived from Type II-S kerogen and the other family derived from Type II kerogen with medium sulfur content. The Tyler petroleum system of the Williston Basin may be distinguished from the Heath-Tyler petroleum system in central Montana based on differences in geology and petroleum geochemistry, with Tyler petroleum system oils having a higher pour point and lower sulfur content.

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