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Like an ice that burns, methane hydrate is cold, white and would light up like a gas stove if held to a flame. And so much of the frozen fuel naturally blankets the seabeds off Japan and elsewhere that scientists say it could power the world for centuries.

Yet, as soon as researchers plumb the depths and pull the potentially revolutionary energy source to the surface, the frosty crystalized methane starts to fizz and bubble into oblivion as it warms up, gasifies and then dissolves into the ocean.

Most nations don’t even bother exploring offshore reserves for lack of harvesting technology. But in resource-poor Japan, plucking the deep-sea bounty off its shores is more than science fiction — it is a national initiative that the government hopes becomes reality in 15 years.

“Japan’s domestic resources are almost zero, so nonconventional sources are a top priority,” said Tetsuo Yonezawa of the methane hydrate research team at the government-backed Japan National Oil Corp.

“There is more than 100 years’ worth of Japanese natural gas consumption there,” he added.

Japan’s push heats up in January, when a drilling ship sets sail for the Pacific Ocean off central Japan to dig 10 to 20 wells in methane hydrate beds along the Nankai Trough, some 1,100 meters below the surface.

Japan hopes to determine by 2011 whether commercial methane hydrate mining is economically feasible and, if so, begin doing so four years later.

Methane hydrate is a crystal structure of methane gas surrounded by water molecules, held together by freezing temperature and crushing pressure. Separating the two yields the methane, or common natural gas.

Knowledge of the substance dates to the 1890s. But it never caught on as an energy source because it is found in hard-to-access Arctic permafrost and deep ocean sediments.

Worldwide resources, however, are massive. Current estimates run at 25 quadrillion cu. meters.

That amount would contain about twice the carbonized energy as the Earth’s coal, oil and gas resources combined.

Deposits around Japan are just a fraction of that, between 4 trillion and 20 trillion cu. meters.

But Japan believes it’s worth shelling out more than 14 billion yen next year alone on methane hydrate research to try to boost its energy self-sufficiency. The nation now imports about 97 percent of its natural gas and virtually all of its crude oil.

Japan is not alone in pursuing methane hydrate, but perhaps is the most desperate.

The U.S. Geological Survey has estimated the quantity of gas hydrates in the United States at 9.6 quadrillion cu. meters, 200 times conventional natural gas resources and reserves in that country.

The U.S. Congress has also appropriated millions of dollars for research, but projects are focused as much on academic as commercial applications — in part because methane hydrate on other planets is envisioned as a fuel source for future space travel.

In Russia, the entire Siberian tundra is laced with the frozen fuel. But Russia is so rich in crude oil and traditional natural gas, Moscow spends little time or money trying to perfect thorny methane hydrate mining techniques.

“A lot of scientists are involved in research,” said Vladimir Yakushev, a hydrate expert with Russia’s Institute of Natural Gases and Gas Technology. “But the most interested are the Japanese. They have no other resources, and hydrates are the last hope.”

Japan has already conducted experiments off its coast and at an international research site in the frozen Mackenzie River delta in northern Canada. The upcoming tests in the Pacific are aimed at finding a local “sweet spot” of hydrate deposits and learning how to regulate the temperature of the deposit during drilling.

Yonezawa, the government researcher, said temperature control is the hardest part — how to warm vast beds of icy substance and catch the released methane.

As soon as the temperature or pressure change, the methane typically gasifies and disappears.

Retrieval methods are largely hypothetical and mostly untried. One idea floated in Russia was to pump nuclear waste under the permafrost to thaw fields of hydrate.

Undersea, the richest methane deposits occur in densely frozen sediment. But there are also technical challenges with drilling so deep and keeping the drill bit lubricated.

It’s still too soon to tell whether the Japanese project will ever go commercial. And no matter what is achievable, Yonezawa said, it will be impossible to recover 100 percent of the methane hydrate deposits around Japan.

But even if a sliver can be harvested, it’s worth pursuing, he said.

“There are still a lot of uncertainties,” he said. “But the potential is too big to ignore.”