Below the Bakken

BISMARCK More than 95 percent of the drilling in the North Dakota oil field targets the Bakken and Three Forks formations, state officials report.

That oil development going on in North Dakota is referred to by the term “The Bakken.”

But more specifically what is the Three Forks Formation, the formation below the Bakken Formation, and how does it differ from the Bakken Formation? In North Dakota the Three Forks Formation covers an area beyond the Bakken Formation.

Ed C. Murphy, state geologist and director of the North Dakota Geological Survey in Bismarck, a division of the North Dakota Department of Mineral Resources, and Stephan Nordeng, a geologist with the Survey, have provided information about the Three Forks Formation.

“The Bakken Formation and the Three Forks Formation are two separate formations. The Bakken Formation was named by J.W. Nordquist in 1953 for rocks found between the depths of 9,615 feet and 9,720 feet in the H.O. Bakken #1 in Williams County,” according to Murphy.

He said the name Three Forks was applied to rocks at the junction of the Three Forks and Missouri River in western Montana by A.C. Peale in 1893. “A paper by Sandberg and Hammond in 1958 identified the rocks at depths between 10,076 to 10,310 feet in the Mobil Birdbear #1 in Dunn County as the Three Forks Formation,” Murphy said.

He said the North Dakota Oil and Gas Division designates oil pools. “The Bakken Pool can include the base of the Lodgepole, the Bakken, and all or parts of the Three Forks and that is where the confusion can come in for the laymen,” Murphy said.

The Oil and Gas Division, a division of the North Dakota Department of Mineral Resources, regulates the drilling and production of oil and gas in North Dakota.

Distinct rock units

Murphy said the rocks of the Three Forks and the Bakken are quite different which is why geologists have split them into two distinct rock units.

“The Three Forks has four packages of rocks that create a specific pattern on electric logs that are called ‘benches’ that have been targeted for oil exploration. The uppermost one is called the ‘first bench’ because it is the first one they drill into, the next one is the ‘second bench’ etc.,” Murphy said.

Drilling in the Three Forks Formation is being done in several counties. Following is a list of the number of permits, by county, for the Three Forks, provided by Nordeng with information from the Oil and Gas Division.

– McKenzie, 914.

– Mountrail, 673.

– Dunn, 453.

– Divide, 411.

– Williams, 407.

– Stark, 196.

– Burke, 95.

– Golden Valley, 16.

“The number of permits that specify a Three Forks target has remained at about 40 percent of the total Bakken-Three Forks wells available since 2012,” said Nordeng. He said the data for 2014 is questionable at best because of confidentiality requirements.

The table below, provided by Nordeng, summarizes the available data.