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Ray Gerish, a floor hand for Raven Drilling, works on an oil rig drilling into the Bakken shale formation on July 28, 2013 outside Watford City, North Dakota. In April 2013, The United States Geological Survey released a new study estimating the Bakken formation and surrounding oil fields could yield up to 7.4 billion barrels of oil, doubling their estimate of 2008, which was stated at 3.65 billion barrels of oil.