Bakken Formation


Bakken Formation

Infobox Rockunit
name = Bakken Formation


caption = Map of Williston Basin oil fields with reservoirs in Bakken Formation (Saskatchewan is north border). Most oil comes from Elm Coulee Oil Field
type = Geological formation
prilithology = Shale, Dolomite
otherlithology =
namedfor =
namedby = J.W. Nordquist, 1953
region = Williston Basin of
central North America
country =
coordinates =
unitof =
subunits =
thickness =
extent =
area = convert|200000|sqmi|km2
age = Late Devonian to Early Mississippian

The Bakken Formation, initially described by geologist J.W. Nordquist in 1953, [ "Mississippian stratigraphy of northern Montana", Nordquist, J.W., Billings Geological Society, 4th Annual Field Conference Guidebook, p. 68–82, 1953] is a rock unit from the Late Devonian to Early Mississippian age occupying about convert|200000|sqmi|km2 of the subsurface of the Williston Basin, covering parts of Montana, North Dakota, and Saskatchewan.

It is estimated that there are significant reservoirs of oil spread beneath the Bakken's shale. As the oil is beneath the shale rather than in it, these reservoirs are not considered oil shale. Oil was first discovered there 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, with a mean of 3.65 billion. [cite web
url= http://www.usgs.gov/newsroom/article.asp?ID=1911
title= 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
date= April 10, 2008 |work= |publisher= U.S. Geological Survey
accessdate= 2008-04-11
] The state of North Dakota also released a report that month which estimated that there are 2.1 billion barrels of technically recoverable oil in the Bakken. [ [http://money.netscape.cnn.com/story.jsp?floc=FF-APO-1333&idq=/ff/story/0001%2F20080428%2F1512753592.htm&sc=1333 ND study: 167 billion barrels of oil in Bakken] ]

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. [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.] However, the presence of horizontal fractures makes the Bakken an excellent candidate for horizontal drilling techniques in which a well drills along the extent of the rock layer, rather than punching a hole vertically through it. In this way, many thousands of feet of oil reservoir rock can be penetrated in a unit that reaches a maximum thickness of only about convert|140|ft|m|-1. [ Donald Barrs, Devonian System, "in" Geologic Atlas of the Rocky Mountain Region, Rocky Mountain Association of Geologists, Denver, CO, 1972: p. 98.] Production is also enhanced by artificially fracturing the rock, [cite web |url=http://www.canada.com/calgaryherald/news/calgarybusiness/story.html?id=5e2f44e4-c351-4871-8b8d-ab4783de3fca&p=2 |title=Using horizontal drilling techniques in Canada |author=Yedlin, Deborah |publisher= "The Calgary Herald" |date=2008-01-16 |accessdate=2008-01-23] to allow oil to seep through for centralized collection.

History of Bakken Oil Generation Estimates

A landmark paper by Dow and a companion paper by Williams (1974) recognized the Bakken as atremendous source for the oil produced in the Williston Basin. These papers suggested that the Bakkenwas capable of generating 10 billion barrels of oil (BBbls). Webster (1982, 1984) as part of a Master’sThesis at the University of North Dakota further sampled and analyzed the Bakken and calculatedhydrocarbon 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 andMontana. 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, with a mean of 413 billion barrels. [ [http://www.undeerc.org/Price/ "Origins and Characteristics of the Basin-Centered Continuous Reservoir Unconventional Oil-Resource Base of the Bakken Source System, Williston Basin"] .] 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. Unfortunately, Price passed away 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." [ [http://www.nd.gov/ndic/ic-press/bakken-form-06.pdf Bakken Formation Reserve Estimates] , which is a [http://www.nd.gov/ndic/ic-new.html July, 2006 Press Release from the North Dakota Industrial Commission] which is [http://www.nd.gov/ndic/ic-about.htm part of the North Dakota State Government] thus in the Public Domain] . 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 of oil [ [http://money.netscape.cnn.com/story.jsp?floc=FF-APO-1333&idq=/ff/story/0001%2F20080428%2F1512753592.htm&sc=1333 ND study: 167 billion barrels of oil in Bakken] ] .

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. [ [https://www.dmr.nd.gov/ndgs/bakken/newpostings/07272006_BakkenReserveEstimates.pdf State of North Dakota Bakken Formation Reserve Estimates] (PDF).] 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, with a mean of 3.65 billion. [cite web
url= http://www.usgs.gov/newsroom/article.asp?ID=1911
title= 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
date= April 10, 2008 |work= |publisher= U.S. Geological Survey
accessdate= 2008-04-11
] Later that month, the state of North Dakota's report [ [http://money.netscape.cnn.com/story.jsp?floc=FF-APO-1333&idq=/ff/story/0001%2F20080428%2F1512753592.htm&sc=1333 ND study: 167 billion barrels of oil in Bakken] ] estimated that of the 167 billion barrels of oil in-place in the North Dakota portion of the Bakken, 2.1 billion barrels were technically recoverable with current technology.

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 — more than the entire state of Montana a few years earlier. [ [http://www.searchanddiscovery.com/documents/2006/06131walker/index.htm Elm Coulee Field] .]

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 of oil [ [http://bakkenoil.com/faq/ Bakken Oil FAQ] ] . This, combined with other factors, including an oil-drilling tax break enacted by the state of North Dakota in 2007, [ [http://www.bismarcktribune.com/articles/2007/04/04/news/state/131390.txt Measure offers oil tax rate cut] .] shifted attention in the Bakken from Montana to the North Dakota side. The number of wells drilling the North Dakota Bakken jumped from 300 in 2006 [ [https://www.dmr.nd.gov/oilgas/stats/2006Formation.pdf 2006 North Dakota Oil Production by Formation] (PDF).] to 457 in 2007. [ [https://www.dmr.nd.gov/oilgas/stats/2007Formation.pdf 2007 North Dakota Oil Production by Formation] (PDF).] Those same sources show oil production in the North Dakota Bakken increasing 229%, from 2.2 million barrels in 2006 to 7.4 million barrels in 2007.

References


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