Abstract: Understanding the Geologic Controls on Shale Oil Play: Lessons Learned from the Bakken Formation, Williston Basin, Elm Coulee Field, Montana

Houston Geological Society Bulletin 15 The Bakken Formation in the Williston basin is divided into three informal members: upper, middle and lower. The upper and lower Bakken consist of dark grey to black pyritic and finely laminated mudstones. The middle member of the Bakken is composed of various lithologies including siltstones, sandstones, limestones and dolostones. Total thickness of the Bakken Formation in the Williston basin ranges from 0 to 110 ft, with the upper member ranging from 0 to 30 ft, the middle ranging from 0 to 92 ft, and the lower ranging from 0 to 46 ft. The upper and lower mudstones are world-class petroleum source rocks with TOC ranging from 8% to 36% wt., with an average of 25% to 28% wt. across large areas of the basin. They can easily be identified by their high radioact ive s ignatures (GR > 200 API). The Bakken was estimated to have generated 200 – 400 billion barrels of low sulfur (< 0.1%), 40 – 45° API gravity oil in place.