Japan says it has successfully tapped a potential new source of energy from the ocean bottom -- the slushy, frozen chemical called methane hydrate - but there’s one tiny problem. Any accidental releases of seafloor methane could boost the amount of heat-trapping greenhouse gases in the atmosphere.

Oil companies have been trying for decades to figure out how to turn frozen methane hydrates into natural gas. Methane hydrate, also known as clathrate, is a compound of methane that exists under pressure at depths below 1,000 feet and under certain conditions in the Arctic.

Japan’s Ministry of Economy, Industry and Trade said this week that an oil exploration ship drilled into and then lowered the pressure in an undersea methane hydrate reserve. That caused the methane and ice to separate. It then piped the natural gas to the surface.

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Japan is an energy-poor nation that has no reserves of gas or oil, and has been at odds over whether to restart its massive nuclear power program two years after the Fukushima disaster. The ministry said that it hopes to have commercial production of methane seafloor gas in five years. But one expert is skeptical. John Carroll, a process engineer at Canada’s Gas Liquids Engineering, said that methane hydrates tend to be found in the soft seafloor sediments. It’s very difficult to both capture and depressurize it.

“For now, it’s kind of a pie-in-the-sky science project,” said Carroll. “I still see some problems getting it to the surface and getting it to a condition to sell.”

Even though methane is cleaner to burn than coal or oil, there is the risk of releasing methane from the seafloor to the atmosphere, he said.

“If they are melting it, it will be just released into the ocean and then the atmosphere,” Carroll said from Alberta. “Methane is a terrible greenhouse gas, much worse than carbon dioxide."

Japan has also been a leader in developing green technologies. A big new source of cheap natural gas could slow those efforts.

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Japan and the United States have been working together to figure out how to safely exploit hydrates. Last year, a team that included researchers from the Department of Energy successfully drilled for hydrates locked under the permafrost of Alaska’s North Slope.

The team was able to produce methane gas for 30 days, a record.

“This is an area we are greatly interested in,” said Chris Smith, acting assistant secretary for fossil energy and previously the head of the DOE office oversees the methane hydrate research. “There’s a lot we have to learn about how the (undersea) formations will react to being depressurized. We’ve got a good theoretical understanding. We don’t really know until we’ve done the field research.”

The joint DOE-Japan drilling project will be continuing in the Gulf of Mexico with several oil companies, Smith said. He compared the science of hydrate drilling to where shale gas technology was several decades ago.

Whatever technology that ends up chosen, any hydrate drilling project has to be careful to capture all the methane gas from the seabed sediments, said Ian MacDonald, professor of biological oceanography at Florida State University.

“In terms of climate, there’s a big concern about methane releases in the Arctic,” said MacDonald, who monitored environmental risks from the Deepwater Horizon spill in the Gulf of Mexico in 2010. “If they lost an entire (undersea) reserve that would discharge gas for an unknown amount of time.”