For the NPR-A, US Geological Survey scientists now think that there may be anywhere from 1.7 billion barrels to 21.8 billion barrels of undiscovered technically recoverable oil, with a mean estimate of 8.8 billion barrels. The corresponding figures for natural gas are 5.5 trillion cubic feet to 112.9 trillion cubic feet, with a mean of 28.2 trillion cubic feet.

The last assessment, published in 2010, did not take the Nanushuk and Torok into account and indicated a mean oil resource of 896 million barrels and a mean gas resource of around 53 trillion cubic feet. The fall in the estimated gas volume appears to result primarily from the dropping of some Brookian plays that were in that earlier assessment - the Nanushuk and Torok are in the Brookian rock sequence.

The new assessment for the Beaufort Sea, prepared by the Bureau of Ocean Energy Management and involving a re-assessment of the western part of the region, suggests 4.4 billion to 15.4 billion barrels of undiscovered, technically recoverable oil, with a mean of 8.9 billion barrels. Estimated natural gas resources range from 14.3 trillion cubic feet to 42.2 trillion cubic feet, with a mean of 27.7 trillion cubic feet. The estimated mean volume of oil in the Nanushuk play has increased from 475 million barrels to 1.2 billion barrels.

"Earlier this year I visited the North Slope to talk with Alaska Natives and elected officials about what responsible energy development means for the communities and the state. The response was overwhelmingly positive and the message was clear: the path to American Energy Dominance starts in Alaska," said Interior Secretary Zinke when announcing the new assessments. "Today's updated assessment is a big step toward that goal. Thanks to the incredible work of scientists at the USGS and BOEM, we know what's available and what our potential is."

-Alan Bailey

See story in Dec. 31 issue, available online Friday, Dec. 29, at www.PetroleumNews.com