Three Forks Group Explained

Three Forks Group
Type:Geologic group
Prilithology:Dolomite, mudstone, shale
Namedfor:Three Forks, Montana
Namedby:A.C. Peale, 1893
Region:Western Canadian Sedimentary Basin, Williston Basin
Country: Canada
United States
Subunits:Bakken Formation, Lyleton Formation, Big Valley Formation, Torquay Formation
Underlies:Madison Group
Overlies:Saskatchewan Group
Thickness:35m (115feet) to 80m (260feet)

The Three Forks Group is a stratigraphical unit of Famennian age in the Williston Basin.

It takes the name from the city of Three Forks, Montana, and was first described in outcrop near the city by A.C. Peale in 1893 (for the Three Forks Shale).[1]

Lithology

The Three Forks Group is composed of dolomite, mudstone and bituminous shale.[2]

Hydrocarbon production

In the subsurface of the Williston Basin, the Three Forks is referred to as the Three Forks Formation, which lies between the Birdbear Formation below, and the Bakken Formation above.[3]

Oil produced from the Three Forks Formation in the Williston Basin of North Dakota and south-eastern Saskatchewan is often included in production statistics with the overlying Bakken Formation. For instance, the Three Forks and Bakken were combined in estimates of potential production released by the United States Geological Survey on April 30, 2013. The estimate by the USGS projects that 7.4 billion barrels of oil can be recovered from the Bakken and Three Forks formations and 6.7 trillion cubic feet of natural gas and 530 million barrels of natural gas liquids using current technology.[4] [5] [6]

Distribution

The Three Forks Group reaches a maximum thickness of 80m (260feet), but can be as thin as 35m (115feet).[2]

Subdivisions

Lithology Max.
Thickness 		Reference
40-1NaN-1[7]
Lyleton Formation 40-1NaN-1[8]
Big Valley Formation 40-1NaN-1[9]
Torquay Formation 65-1NaN-1[10]

Relationship to other units

The Three Forks Group conformably overlies the Saskatchewan Group and is disconformably overlain by the Madison Group.[2]

It is equivalent to the sum of the Wabamun Group and Exshaw Formation in Alberta.

Notes and References

  1. Peale, A.C., 1893. The Paleozoic section in the vicinity of Three Forks, Montana. U.S G.S., Bull. 110, p. 9-56.
  2. Web site: Three Forks Group . . 2010-01-01 . dead . https://web.archive.org/web/20090416121153/http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl . 2009-04-16.
  3. US Geological Survey, Three Forks, accessed 6 Jan. 2013.
  4. Web site: North Dakota Oil Boom Getting Bigger - Valley News Live - KVLY/KXJB - Fargo/Grand Forks . 2013-05-01 . dead . https://web.archive.org/web/20131029190609/http://www.valleynewslive.com/story/22118577/north-dakota-oil-boom-getting-bigger . 2013-10-29 .
  5. News: Northern plains site has twice as much oil as previously thought, Interior says. May 1, 2013. The Washington Post. April 30, 2013. Lenny Bernstein. The doubling of the estimate resulted largely because of the first look at the Three Forks Formation in North Dakota, which the Geological Survey said contains 3.73 billion barrels of oil. Its reassessment of the Bakken Formation, which lies above Three Forks, showed 3.65 billion barrels, only a little more than a 2008 USGS estimate. The agency’s conclusion that the formations contain 6.7 trillion cubic feet of natural gas and 530 million barrels of natural gas liquids represented a tripling of previous estimates..
  6. Web site: National Assessment of Oil and Gas Fact Sheet Assessment of Undiscovered Oil Resources in the Bakken and Three Forks Formations, Williston Basin Province, Montana, North Dakota, and South Dakota, 2013. Fact Sheet 2013–3013. United States Geological Survey. May 1, 2013. Stephanie B. Gaswirth . Kristen R. Marra . Troy A. Cook . Ronald R. Charpentier . Donald L. Gautier . Debra K. Higley . Timothy R. Klett . Michael D. Lewan . Paul G. Lillis . Christopher J. Schenk . Marilyn E. Tennyson . Katherine J. Whidden . Using a geology-based assessment methodology, the U.S. Geological Survey estimated mean undiscovered volumes of 7.4 billion barrels of oil, 6.7 trillion cubic feet of associated/dissolved natural gas, and 0.53 billion barrels of natural gas liquids in the Bakken and Three Forks Formations in the Williston Basin Province of Montana, North Dakota, and South Dakota..
  7. Web site: Bakken Formation. . 2010-01-03.
  8. Web site: Lyleton Formation. . 2010-01-03.
  9. Web site: Big Valley Formation. . 2010-01-03.
  10. Web site: Torquay Formation. . 2010-01-03.

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