updated 4/10/2008 8:28:18 PM ET 2008-04-11T00:28:18

The government estimated Thursday that up to 4.3 billion barrels of oil can be recovered from the Bakken shale formation in North Dakota and Montana, using current technology.

The U.S. Geological Survey called it the largest continuous oil accumulation it has ever assessed.

The Bakken Formation encompasses some 25,000 square miles in North Dakota, Montana, Saskatchewan and Manitoba. About two-thirds of the acreage is in western North Dakota, where the oil is trapped in a thin layer of dense rock nearly two miles beneath the surface. Companies use pressurized fluid and sand to break pores in the rock and prop them open to recover the oil.

North Dakota's entire oil production hit 137,000 barrels a day in January, the latest figures available. Industry officials believe the state's record production of 148,500 barrels a day, set in 1984, will be surpassed this year.

Donald Kessel, vice president of Houston-based Murex Petroleum Corp., said he believes the Geological Survey's assessment of how much oil can be recovered in the Bakken may be high.

"That's a lot of zeros," Kessel said Thursday.

Kessel said his company was the first to get a producing well in the Bakken in North Dakota three years ago. The company now has about 20 producing wells.

The report released Thursday by USGS was done at the request of Sen. Byron Dorgan, D-N.D., over the past 18 months.

A 1995 study by the USGS found 151 million barrels of oil could be recovered from the Bakken using technology at that time.

"This is great news," Dorgan said of the new report. "This is 25 times the amount of the previous assessment."

The assessment comes as U.S. crude production has fallen steadily over the past three decades, with rate of decline slowed — or offset — only slightly by production from the deepwater Gulf of Mexico. That has led to increased imports. But as oil prices surged over the past few months, calls are mounting for a reduction in import dependence.

"Many of the previous oil discoveries in the U.S. have produced for a long while and are producing at lower levels now," Dorgan said. "This report comes at a time when we are desperately trying to be less dependent on Saudi Arabia and other Middle Eastern countries."

Oilmen have known for more than 50 years that the Bakken holds vast oil reserves, Kessel said. But the price has never pushed demand high enough to develop technology to capture the oil, he said.

According to Jim Ehrets, a Denver-based geologist with Headington Oil Co., of Dallas, it costs about $5 million to drill a well tapping the middle Bakken, and companies need crude prices of at least $50 a barrel to make it economical.

Even with crude prices now double that, "there still is a ton of risk," he said.

Oil companies began sharing technology about two years ago on how to recover the oil. The technology involves drilling vertically to about 10,000 feet, then "kicking out" for as many feet horizontally, while fracturing the rock to release the oil trapped in microscopic pores in the area known as the "middle" Bakken.

Initially, companies had kept their technology secret, said Ehrets.

"Everybody was protecting their results while the lease play was still going on," he said. "Once it had been pretty well saturated and not much left to lease, there was cooperation in sharing information.

"I can't remember in my entire career that kind of cooperation," said Ehrets, an oil man for nearly 30 years.

Headington, which is based in Dallas, has about 150 wells working in the Bakken — about 100 of them in Montana — with plans to drill at least 100 more, Ehrets said.

The Geological Survey said about 105 million barrels of oil have been produced from the Bakken through last year. The Elm Coulee oil field in eastern Montana, near the North Dakota border, has produced about 65 million barrels of the total, said Rich Pollastro, a USGS geologist.

The Elm Coulee field was discovered in 2000, he said.

The study released Thursday by USGS does not estimate how much oil may be in the Bakken — only what the agency believes can be recovered using current technology.

Thursday's report did not cover the Canadian portion of the Bakken. Pollastro said a 2000 assessment found only about 15 million barrels of recoverable oil in that area using traditional vertical drilling.

Ron Ness, president of the North Dakota Petroleum Council, said the number of wells in the Bakken in North Dakota increased from about 300 in 2006 to 457 at the end of last year.

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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