Williston Basin Petroleum Systems Part #1: Ordovician (Winnipeg Group & Red River Formation)

Approximately two dozen geologic formations have compositely produced more than 10 billion barrels of oil and 14 TCF of gas within the Williston Basin over the past 75+ years. The basin’s production ranges from deep thermogenic gas within the Cambrian-Ordovician sandstones, intraformational (self-sourced) oil within Late Ordovician to Early Pennsylvanian reservoirs (variable migration)), migrated and stratigraphically trapped oil in Triassic-Jurassic reservoirs, and biogenic gas within the shallow Cretaceous strata. The most prominent producing stratigraphic horizons in the basin (in descending order) include: the Devonian-Mississippian Bakken and Three Forks Formations, Mississippian Madison Group, and the Ordovician Red River Formation.

Early studies of Williston Basin petroleum studies published in the 1970’s identified three prospective horizons with thermally mature petroleum source rocks: Ordovician Icebox Formation (Winnipeg Group), Devonian-Mississippian Bakken Formation, and the Pennsylvanian Tyler Formation. During this period, substantial vertical hydrocarbon migration between formations, on the order of 100’s of meters, was thought to have occurred across the basin in order to source hydrocarbons from the Icebox shale to the Red River reservoirs and the Bakken shales to the Madison reservoirs.

However, during the past few decades, several additional petroleum source rock horizons have been identified and characterized, most notably the Ordovician Red River (Yeoman) Formation and Mississippian Madison Group. As additional petroleum source rock horizons have been identified and characterized, vertical hydrocarbon migration between formations appears to be much less pronounced than originally thought.

Understanding the vertical and lateral distributions of petroleum source rocks provides a foundational cornerstone for delineating the extent of petroleum systems within the Williston Basin, and a step further for continued exploration efforts.