State-run Korea National Oil Corp. has purchased a 23.67 percent stake in a U.S. oil field from Anadarko Petroleum Corp. for US$1.55 billion, the government said Monday.

   The shale oil field in the Maverick Basin region in Texas near the U.S.-Mexico border is estimated to hold 491 million barrels of oil equivalent, said the Ministry of Knowledge Economy, adding that KNOC will secure 116 million BOEs with the deal.

   Anadarko will continue to hold a 47.33 percent stake in the field that began commercial production in 2009 with other companies holding the remainder, the ministry said. 

   Shale oil refers to crude in organic-rich, fine-grained sedimentary rock, with global reserves estimated at 2.57 trillion barrels. It is considered an unconventional source of energy along with oil sand, tight gas and coal bed methane.

   "The investment marks the first time that KNOC has purchased stakes in an overseas unconventional fossil fuel field that is actually in production," the ministry said.

   In the past, both KNOC and Korea Gas Corp. bought stakes in oil sand, shale and tight gas deposits in Canada, but these were all exploratory fields.

   In addition to the Anadarko deal, the oil company has completed the take over of Kazakhstan's Altius Holdings Inc., which owns four operational and exploration fields in the Central Asian country.

The purchase was made on the Kazakhstan stock market.

The two purchases, meanwhile, will allow KNOC to increase the size of overseas crude oil fields it controls to 170 million barrels equal to 16,500 barrels of crude per day. This can raise the country's self-sufficiency in energy resources by 0.5 percentage point.

(Yonhap News)