WASHINGTON -- Frozen crystals packed with concentrated natural gas and buried 2,000 feet below the permafrost on Alaska's North Slope could become the next major domestic energy source, according to an assessment released Wednesday by the U.S. Geological Survey.

The study finds that in the North Slope, frozen methane-and-water crystals known as hydrates contain as much as 85.4 trillion cubic feet of recoverable natural gas. That's enough to heat 100 million homes for as long as 10 years, Interior Secretary Dirk Kempthorne said.

New research into how to extract those resources has moved the possibility of recovering the usable energy from the realm of ''science and speculation'' to that of the ''actual and useful,'' Kempthorne said Wednesday.

Globally, ''hydrates have more potential for energy than all other fossil fuels combined,'' he said. ``This can be a paradigm shift.''

Government research is beginning to show that it may be possible to extract hydrates using depressurization, a technique used to get at more conventional fuel sources. Simply boring into the ground may be enough to change the pressure to extract it, said Steve Rinehart, a spokesman for British Petroleum in Alaska. Or by pumping.

Gas hydrates exist all over the world, including offshore, but a combination of cold and pressure makes them especially prevalent in the Arctic, where there's also an existing oil and gas infrastructure to study them. The Department of Energy described them as ''ice-like solids that result from the trapping of methane molecules within a lattice-like cage of water molecules.'' Hydrates release gaseous methane -- the main component of natural gas -- when they melt.

Kempthorne on Wednesday demonstrated the flammability of the substance with laboratory-created hydrate made by government researchers. Real hydrates, which are 164 times more concentrated than natural gas, would be far too valuable to burn, in part because core samples are so rare.

Kempthorne lit a match to a fist-sized lab sample, sending up a small flare. He also passed out small, pebble-sized samples at his news conference. When he dropped a chunk of hydrate into a glass of water, it fizzed like Alka-Seltzer. As the human hand warms it, the hydrate snaps and crackles, releasing gas and water vapor.

Two of the biggest North Slope producers, ConocoPhillips and BP, have been involved in some of the government studies. BP and ConocoPhillips remain skeptical. There are tremendous conventional natural-gas deposits in Alaska to consider first, Rinehart said. ''We see the potential,'' Rinehart said, ``but our outlook is conservative at this point, because there really has not been a long-term production test.''

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