AAPG Article on The Three Forks Formation

Link here. Published April, 2011.

The article appears to be based on an interview with Steven Sonnenberg. Sonnenberg is professor of petroleum geology at the Colorado School of Mines in Golden, CO, and heads the school's Bakken Research Consortium, with 20 member companies and a grant from the National Energy Technology Laboratory.

Current thinking puts recoverable oil from the Bakken Shale at just over two billion barrels, and from the Three Forks Formation at just under two billion.

The U.S. Geological earlier estimated mean, technically recoverable, undiscovered volumes in the Bakken system of 3.65 billion barrels of oil, 1.85 trillion cubic feet of associated/dissolved natural gas and 148 million barrels of natural gas liquids.

Sonnenberg said the main source rock for the upper Three Forks is the lower Bakken Shale, although where the lower and middle Bakken thin in the southern Williston Basin, the upper Bakken is the main source.

The Three Forks underlies the Bakken, separated by the Sanish Formation.

The article, thus, clarifies the Sanish formation a bit more. 

(The term Sanish is used in several different contexts in North Dakota. Confusion over the name led one local geologist to declare, “The Sanish should vanish,” Sonnenberg said.)

I was happy to read that; I wasn't the only one confused by the "Sanish" term.