Preliminary identification and evaluation of petroleum source beds within the Mississippian Madison Group: A step toward redefining the Madison petroleum system of the Williston Basin

The Mississippian Madison Group has been the most productive conventional oil play interval in the Williston Basin with more than 32,000 productive wells and 4.6 billion BOE of cumulative production to date. After 70+ years of exploration and development in the unit, the Madison could be considered a relatively “mature” hydrocarbon play interval. Initial geochemical fingerprinting studies beginning in the 1970’s linked Madison reservoir oils to the underlying Bakken shale source beds. However, numerous ensuing geochemical fingerprinting studies with improved technology and techniques have concluded that most Madison reservoir oils are distinct from Bakken oils and therefore were internally sourced by undefined Madison source rock(s). Previously undocumented carbonate source rock intervals are observed in core and wireline logs within the upper Lodgepole/lower Tilston and lower Bluell stratigraphic section of the Madison Group. Both source rock intervals contain present day TOC values of 1% to ≥5%, plot along Type I/II (oil prone) kerogen signatures using hydrogen versus oxygen index values, reach 40+ feet (12+ m) gross thickness, extend laterally in the subsurface for at least tens of miles (1-2 million acres), and appear to be within the peak oil generation window (436-456° Tmax). Understanding the stratigraphic positions, lateral extents, and hydrocarbon generation significance of petroleum source beds may be the key to unlocking one or more unconventional Madison resource plays within the Williston Basin.