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USGS: Alaskan North Slope May Hold 85.4 Tcf From Hydrates

An estimated 85.4 Tcf of undiscovered, technically recoverable gas from natural gas hydrates may be available on the Alaskan North Slope, according to a U.S. Geological Survey (USGS) assessment released last Wednesday.

"The assessment points to a truly significant potential for natural gas hydrates to contribute to the energy mix of the United States and the world," Interior Secretary Dirk Kempthorne said during a press conference in Washington, DC. "This study also brings us closer to realizing the potential of this clean-burning natural gas resource."

The USGS assessment is the first resource estimate of technically recoverable natural gas hydrates -- ice-like solids in which water molecules trap natural gas molecules in a structure known as a clathrate -- and further research, including long-term production tests, is still needed to demonstrate that gas hydrates are an economically producible resource, Kempthorne said.

The area assessed extends west from the National Petroleum Reserve to the Arctic National Wildlife Refuge, and north from the Brooks Range to the state-federal offshore boundary, located three miles north of the Alaska coastline. Of the estimated 85.4 Tcf of gas within hydrates on the North Slope, approximately 56% occurs on federally managed lands, 39% on lands and offshore waters managed by the State of Alaska, and 4% on Native Alaskan lands, according to the assessment.

A 1995 USGS assessment estimated 590 Tcf of all volumes of gas within the hydrates of northern Alaska. The new assessment resulted in a much lower estimate because it includes only technically recoverable gas and does not include offshore federal waters, which were covered in the earlier assessment.

Gas hydrate in the North Slope has been known for decades, but producers have traditionally focused their interest on the conventional crude oil and gas reserves. Producers also have been awaiting technology to separate the natural gas from the solid gas-water-ice clathrate. Among the various techniques for production of natural gas from gas hydrates, the USGS said depressurization appears to be the most promising method. Depressurization, which involves changing the pressure of the hydrate accumulation, was the only production technique assessed in the USGS estimate.

Last year BP Exploration (Alaska) Inc. partnered with U.S. officials to drill an exploratory well into a natural gas hydrate-bearing core on the North Slope (see NGI, Feb. 26, 2007). The test well was part of an ongoing research partnership between BP and the Department of Energy's (DOE) National Energy Technology Laboratory, which began in 2002. Gas hydrate is an ongoing DOE research target (see NGI, Nov. 14, 2005).

Conventional undiscovered, technically recoverable gas resources on the North Slope are estimated at 119.15 Tcf, the USGS said. Previous USGS assessments have estimated that the Wyoming Basin holds 85 Tcf of technically recoverable natural gas resources; the National Petroleum Reserve in Alaska, 73 Tcf; the Western Gulf Basin in Texas, 71 Tcf; and the San Juan Basin in New Mexico and Colorado, 50 Tcf.

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