The U.S. Geological Survey (USGS) estimates the Bakken and Three Forks formations in North Dakota, South Dakota and Montana to contain a mean of 7.4 billion barrels of undiscovered, technically recoverable oil.
The Bakken has an estimated mean oil resource of 3.65 billion barrels of oil and the Three Forks formation contains an estimated mean resource of 3.73 billion barrels of oil, according to the USGS assessment released Tuesday. The two formations are also estimated to contain an average of 6.7 trillion cubic feet (Tcf) of undiscovered technically recoverable natural gas and .53 billion barrels of undiscovered, technically recoverable natural gas liquids.
The assessment of both formations represents a significant increase over the estimated mean resource of 3.65 billion barrels of undiscovered oil in the Bakken formation that was estimated in 2008. The estimate in gas and gas liquids represents an almost threefold increase in mean natural gas and a nearly threefold increase in mean natural gas liquids resources from the 2008 assessment.
The assessment marks USGS' first update of Bakken resources since 2008. The USGS in 2008 estimated the Bakken formation to contain estimated mean undiscovered volumes of 3.65 billion barrels of oil, 1.85 trillion cubic feet of associated/dissolved natural gas.
The primary difference between the new assessment and 2008 assessment is the inclusion of information for the Three Forks formation, said USGS officials in a conference call with reporters Tuesday. The size of the overall increase in oil, natural gas and natural gas liquids resources is largely due to the inclusion of the Three Forks formation.
While the estimates for Bakken oil resources would appear to be the same for 2008 and 2013, the size of the Bakken estimate increased as well, a USGS spokesperson told Rigzone in an email statement.
"It's deceptive, because although our current estimate of 3.65 billion barrels of oil for the Bakken is numerically the same as the 2008 assessment for the Bakken, you have to remember that oil companies have been producing millions of barrels of oil since the 2008 assessment, gradually transforming the undiscovered resources to the proven reserves then production barrels," the spokesperson commented. "Because our assessments do not include proven reserves or produced barrels of oil, the 3.65 billion does represent an increase."
The assessment was conducted as part of a nationwide project to assess U.S. petroleum basins using standardized methodology and protocol. More than 4,000 wells have been drilled in the Williston Basin since the 2008 USGS assessment, providing updated subsurface geologic data on both the Bakken and the Three Forks formations.
Approximately 450 million barrels of oil have been produced from the Bakken and Three Forks formations since the 2008 Bakken formation assessment.
Little data had previously existed on the Three Forks formation, which was generally thought to be unproductive. However, new drilling has brought to light new understanding of the reservoir and its resource potential.
Secretary of the Interior Sally Jewell called the assessment "another piece in the puzzle to reduce U.S. dependence on foreign oil".
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