Bakken Formation

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Bakken Formation
Type Geological formation
Age Late Devonian to Early Mississippian
Underlies Madison Limestone
Overlies Wabamun Formation, Big Valley Formation, Torquay Formation or Three Forks Formation
Area 200,000 square miles (520,000 km2)
Thickness up to 40 metres (130 ft)[1]
Lithology
Primary Shale, Dolomite
Other Sandstone, Siltstone
Location
Named for Bakken, Williams County, North Dakota
Named by J.W. Nordquist, 1953


Region Williston Basin of
central North America
Country  United States,  Canada
Map of Bakken Formation reservoirs in the US portion of the Williston Basin (Saskatchewan is north border). Most oil comes from Elm Coulee Oil Field
Map of Bakken Formation reservoirs in the US portion of the Williston Basin (Saskatchewan is north border). Most oil comes from Elm Coulee Oil Field

The Bakken Formation, initially described by geologist J.W. Nordquist in 1953,[2] is a rock unit from the Late Devonian to Early Mississippian age occupying about 200,000 square miles (520,000 km2) of the subsurface of the Williston Basin, covering parts of Montana, North Dakota, and Saskatchewan.

There are significant reservoirs of oil in the Bakken shale.[3] Oil was first discovered in the Bakken in 1951, but efforts to extract it have historically met with difficulties. An April 2008 USGS report estimated the amount of technically recoverable oil in the Bakken Formation at 3.0 to 4.3 billion barrels (680,000,000 m3), with a mean of 3.65 billion.[4] The state of North Dakota also released a report that month which estimated that there are 2.1 billion barrels (330,000,000 m3) of technically recoverable oil in the Bakken.[5]

Contents

[edit] Geology

The rock formation consists of three members: lower shale, middle dolomite, and upper shale. The shales were deposited in relatively deep marine conditions, and the dolomite was deposited as a coastal carbonate bank during a time of shallower water. The middle dolomite member is the principal oil reservoir, roughly two miles (3.2 km) below the surface. Both the upper and lower shale members are organic-rich marine shale.

Porosities in the Bakken average about 5%, and permeabilities are very low, averaging 0.04 millidarcies—much lower than typical oil reservoirs.[6] However, the presence of horizontal fractures makes the Bakken an excellent candidate for horizontal drilling techniques in which a well drills horizontally along the bedding, rather than vertically through it. In this way, a borehole can contact many thousands of feet of oil reservoir rock in a unit with a maximum thickness of only about 140 feet (40 m).[7] Production is also enhanced by artificially fracturing the rock,[8] to allow oil to seep to the oil well.

[edit] History of Bakken oil generation estimates

A landmark paper by Dow and a companion paper by Williams (1974) recognized the Bakken formation as a tremendous source for the oil produced in the Williston Basin. These papers suggested that the Bakken was capable of generating 10 billion barrels (1.6×109 m3) of oil (BBbls). Webster (1982, 1984) as part of a Master’s thesis at the University of North Dakota further sampled and analyzed the Bakken and calculated hydrocarbon generation capacities to be about 92 BBbls. These data were updated by Schmoker and Hester (1983) who estimated that the Bakken was capable of generating 132 BBbls of oil in North Dakota and Montana. A research paper by USGS geochemist Leigh Price in 1999 estimated the total amount of oil contained in the Bakken shale ranged from 271 billion to 503 billion barrels (8.00×1010 m3), with a mean of 413 billion barrels (6.57×1010 m3).[9] While others before him had begun to realize that the oil generated by the Bakken shales had remained within the Bakken, it was Price, who had spent much of his career studying the Bakken, who particularly stressed this point. If he was right, the large amounts of oil remaining in this formation would make it a prime oil exploration target. However, Price died in 2000 before his research could be peer-reviewed and published. Nevertheless, the drilling and production successes in much of the Bakken beginning with the Elm Coulee Oil Field discovery in 2000 have proven correct his claim that the oil generated by the Bakken shale was still there. New estimates of the amount of hydrocarbons generated by the Bakken were presented by Meissner and Banks (2000) and by Flannery and Kraus (2006). The first of these papers tested a newly developed computer model with existing Bakken data to estimate generated oil of 32 BBbls. The second paper used a more sophisticated computer program with extensive data input supplied by the ND Geological Survey and Oil and Gas Division. Early numbers generated from this information placed the value at 200 BBbls later revised to 300 BBbls when the paper was presented in 2006."[10]. In April 2008, a report issued by the state of North Dakota Department of Mineral Resources estimated that the North Dakota portion of the Bakken contained 167 billion barrels (2.66×1010 m3) of oil[5].

While these numbers would appear to indicate a massive reserve, the percentage of this oil which might be extracted using current technology is another matter. Estimates of the Bakken's technically recoverable oil have ranged from as low as 1% — because the Bakken shale has generally low porosity and low permeability, making the oil difficult to extract — to Leigh Price's estimate of 50% recoverable.[11] Reports issued by both the USGS and the state of North Dakota in April 2008 seem to indicate the lower range of recoverable estimates are more realistic with current technology.

The flurry of drilling activity in the Bakken, coupled with the wide range of estimates of in-place and recoverable oil, led North Dakota senator Byron Dorgan to ask the USGS to conduct a study of the Bakken's potentially recoverable oil. In April 2008 the USGS released this report, which estimated the amount of technically recoverable, undiscovered oil in the Bakken Formation at 3.0 to 4.3 billion barrels (680,000,000 m3), with a mean of 3.65 billion.[4] Later that month, the state of North Dakota's report [5] estimated that of the 167 billion barrels (2.66×1010 m3) of oil in-place in the North Dakota portion of the Bakken, 2.1 billion barrels (330,000,000 m3) were technically recoverable with current technology.

[edit] Oil production estimates

The greatest Bakken oil production comes from Elm Coulee Oil Field, Richland County, Montana, where production began in 2000 and is expected to ultimately total 270 million barrels. In 2007, production from Elm Coulee averaged 53,000 barrels per day (8,400 m3/d) — more than the entire state of Montana a few years earlier.[12]

New interest developed in 2007 when EOG Resources out of Houston, Texas reported that a single well it had drilled into an oil-rich layer of shale below Parshall, North Dakota was anticipated to produce 700,000 barrels (111,000 m3) of oil.[citation needed] This, combined with other factors, including an oil-drilling tax break enacted by the state of North Dakota in 2007,[13] shifted attention in the Bakken from Montana to the North Dakota side.[citation needed] The number of wells drilled in the North Dakota Bakken jumped from 300 in 2006[14] to 457 in 2007.[15] Those same sources show oil production in the North Dakota Bakken increasing 229%, from 2.2 million barrels (350,000 m3) in 2006 to 7.4 million barrels (1,180,000 m3) in 2007.

[edit] References

  1. ^ Lexicon of Canadian Geological Units. "Bakken Formation". http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:000705. Retrieved 2009-03-26. 
  2. ^ "Mississippian stratigraphy of northern Montana", Nordquist, J.W., Billings Geological Society, 4th Annual Field Conference Guidebook, p. 68–82, 1953
  3. ^ US Energy Information Administration, November 2008, Technology-based oil and natural gas plays: Shale shock! Could there be billions in the Bakken?, PDF file, retrieved 16 January 2009.
  4. ^ a b "3 to 4.3 Billion Barrels of Technically Recoverable Oil Assessed in North Dakota and Montana’s Bakken Formation—25 Times More Than 1995 Estimate". U.S. Geological Survey. April 10, 2008. http://www.usgs.gov/newsroom/article.asp?ID=1911. Retrieved 2008-04-11. 
  5. ^ a b c ND study: 167 billion barrels of oil in Bakken
  6. ^ Diagenesis and Fracture Development in the Bakken Formation, Williston Basin: Implications for Reservoir Quality in the Middle Member, by Janet K. Pitman, Leigh C. Price, and Julie A. LeFever, U.S. Geological Survey Professional Paper 1653, 2001.
  7. ^ Donald Barrs, Devonian System, in Geologic Atlas of the Rocky Mountain Region, Rocky Mountain Association of Geologists, Denver, CO, 1972: p. 98.
  8. ^ Yedlin, Deborah (2008-01-16). "Using horizontal drilling techniques in Canada". The Calgary Herald. http://www.canada.com/calgaryherald/news/calgarybusiness/story.html?id=5e2f44e4-c351-4871-8b8d-ab4783de3fca&p=2. Retrieved 2008-01-23. 
  9. ^ Price, Leigh. "Origins and Characteristics of the Basin-Centered Continuous Reservoir Unconventional Oil-Resource Base of the Bakken Source System, Williston Basin" (unpublished paper). http://www.undeerc.org/Price/. 
  10. ^ Bakken Formation Reserve Estimates, which is a July, 2006 Press Release from the North Dakota Industrial Commission which is part of the North Dakota State Government thus in the Public Domain
  11. ^ State of North Dakota Bakken Formation Reserve Estimates (PDF).
  12. ^ Elm Coulee Field.
  13. ^ Measure offers oil tax rate cut.
  14. ^ 2006 North Dakota Oil Production by Formation (PDF).
  15. ^ 2007 North Dakota Oil Production by Formation (PDF).

[edit] External links

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