Located in the Williston Basin in Montana and North Dakota and in the Canadian provinces of Saskatchewan and Manitoba, the Bakken Shale subsurface formation is mainly an oil play. Some figures put estimated oil reserves in the Bakken shale at 3.5 to 4.0 billion barrels of oil equivalent (boe), which would make it the largest oil find in US history outside the oil fields of Alaska.
Photo courtesy of Brigham Exploration.
The American Association of Petroleum Geologists (AAPG) says that the Bakken contains the largest continuous oil accumulation the organization has ever assessed. A continuous accumulation is one that is assumed to have hydrocarbons everywhere as opposed to a conventional, or discrete, accumulation with a distinctive hydrocarbon-water contact.
In the late 1980s and 1990s, the upper Bakken was the focus of considerable activity, but the wells were marginally economic and difficult to produce. Consequently, it usually was looked on as a bail-out zone rather than a target.
That changed dramatically beginning in 1995 when explorer Dick Findley of Prospector Oil determined there was good porosity and a likely oil zone in the fractured dolomitic middle section. This Eureka moment eventually led to the development of the giant Elm Coulee oil field in the Bakken in eastern Montana.
The huge assessment numbers the USGS released recently have raised more than a few eyebrows in the oil and gas community, but the consensus appears to be that there truly are hydrocarbons aplenty awaiting the drill bit.
"There's no question there's a tremendous amount of oil in place in general in the Bakken shale," said Bud Brigham, chairman, president, and CEO of Brigham Exploration.
He noted the company holds 240,000 acres total in the Bakken in Montana and North Dakota.
Houston-based EOG Resources is one of the pioneers in developing the play. In 2009, the company held a 21% share of total Bakken production. EOG has become a leader in horizontal drilling and well completions through innovative fracturing techniques it learned through its success in the Barnett.
EOG is also a successful operator in the Sanish-Three Forks play in the Williston Basin and in the Niobrara, Eagle Ford, Horn River, and Barnett shale plays.
Other large operators held large shares of Bakken production in 2009, including Continental Resources (10%), Whiting Petroleum (9%), XTO Energy (8%), and Enerplus Resources (7%). Others in the play are Hess Corp., Marathon Oil, SM Energy, Newfield Exploration, and ConocoPhillips — to name just a few.
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