The Bakken Formation was first formally described in 1953 by geologist J.W. Nordquist. He used samples from a well in Williams County, the H.O. Bakken #1 well, named for the surface owner, Henry Bakken.
Today, Henry Bakken’s name is synonymous with one of the country’s biggest oil reserves. While the history of oil production in this formation goes back over 60 years, it’s only recently that new technologies have allowed us to tap in to the incredible oil reserves that lay deep under the surface.
The Bakken/Three Forks is the largest oil field (in square miles) in the world. It underlies approximately 18,000 square miles of North Dakota and is about the size of the State of West Virginia. The formation has been known about by geologists for decades, but it wasn’t until 2009 when the use of horizontal drilling combined with hydraulically fracturing in stages that the Bakken was considered to be an economic play.
The Bakken/Three Forks formations produce crude oil and associated natural gas. Oil is the primary energy resource contained in Bakken/Three Forks wells and is the principal economic driver for energy producing companies.
The Bakken shale lies in the Williston Basin in western North Dakota and eastern Montana. According to a 2013 survey, the U.S. Geological Survey (USGS) had estimated that the Bakken/Three Forks Shale contains between 4.42 and 11.43 billion barrels of technically recoverable oil, along with 6.7 trillion cubic feet of undiscovered, technically recoverable natural gas and 0.53 billion barrels of undiscovered, technically recoverable natural gas liquids.
Throughout most of the Williston Basin, the Bakken Formation consists of three layers, or “members.” The upper member is a layer of black marine shale approximately 23 feet thick. The middle member is composed of sandstone, limestone, siltstone and dolomite about 85 feet thick, and the lower member is black marine shale about 50 feet thick.
The shale members have high levels of organic material that converts to oil and natural gas under the proper conditions. The three members of the Bakken formation are sandwiched between thick rock layers hundreds of feet deep. As the Williston Basin subsided, the increased pressure and temperature converted the organic materials into petroleum. Sealed by low-permeability rock layers above and below, the shale members and middle members of the Bakken began to fracture.
The result is the unique geology of the Bakken that we see today. In areas where it’s “thermally mature,” the heat and pressure have caused the organic material to convert to petroleum. These areas are capable of the highest production rates. Some areas of the Bakken are not yet thermally mature.
Early efforts at extracting oil from the Bakken focused on the shale members, with limited success. The technology depended on vertical wellbores and recovery of the oil through existing natural fractures, but the recovery process often damaged both the wellbore and the natural fracture.
Today, science and technology have provided the keys to unlocking the oil stored in the Bakken Formation. Current efforts focus on the middle member, which is more porous and permeable, and serves as a “reservoir rock” for the petroleum. Horizontal drilling provides access to the rock, while hydraulic fracturing creates fissures that allow the oil to be recovered.