Japan says it has extracted gas from offshore deposits of methane hydrate - sometimes called "flammable ice" - a breakthrough that officials say could be a step towards tapping a promising but still little-understood energy source.
The gas, whose extraction from the undersea hydrate reservoir is thought to be a world first, could provide an alternative source of energy to known oil and gas reserves. That could be crucial for Japan, which is the world's biggest importer of liquefied natural gas and is engaged in a public debate about whether to resume its heavy reliance on nuclear power.
Experts estimate the carbon found in gas hydrates worldwide totals at least twice the amount of carbon in all of the earth's other fossil fuels, making it a potential game-changer for energy-poor countries such as Japan. Researchers had already extracted gas from onshore methane hydrate reservoirs but not from beneath the seabed.
Methane is a greenhouse gas, and the exact properties of undersea hydrates and how they might affect the environment are poorly understood. Japan has invested hundreds of millions of dollars to explore offshore methane hydrate reserves in the Pacific and the Sea of Japan. That task has become all the more pressing after the Fukushima nuclear crisis, which has all but halted Japan's nuclear energy program and caused a sharp increase in fossil fuel imports. Japan's rising energy bill has weighed heavily on its economy, helping to push it to a trade deficit and reducing the benefits of a weaker yen to Japanese exporters.
The Japanese Ministry of Economy, Trade and Industry said a team aboard the scientific drilling ship Chikyu had started a trial extraction of gas from a layer of methane hydrates about 300 metres below the seabed on Tuesday. The ship has been drilling since January in an area of the Pacific about 1000 metres deep, 80 kilometres south of the Atsumi Peninsula in central Japan.
The team drilled into and then lowered the pressure in the undersea methane hydrate reserve, causing the methane and ice to separate. It then piped the gas to the surface. Hours later, a flare on the ship's stern showed that gas was being produced.
"Japan could finally have an energy source to call its own," said Takami Kawamoto, a spokesman for the Japan Oil, Gas and Metals National Corp, or Jogmec, the state-run company leading the trial extraction.
The team will continue the trial extraction for about two weeks before analysing how much gas has been produced. Japan hopes to make the technology commercially viable in about five years.
It is unclear to what extent tapping methane hydrate would affect Japan's emissions or global warming. On one hand, natural gas would provide a cleaner alternative to coal, which still provides Japan with a fifth of its primary energy needs. But new energy sources could also cause Japan to slow its development of renewable energies or green technologies, hurting its emissions in the long run. Any accidental release of large amounts of methane during the extraction process would also be harmful.
Jogmec estimates that the surrounding area in the Nankai submarine trough holds at least 1.1 trillion cubic metres of methane hydrate, enough to meet 11 years' worth of gas imports to Japan.
A rough estimate by the National Institute of Advanced Industrial Science and Technology has put the total amount of methane hydrate in the waters surrounding Japan at more than 7 trillion cubic metres, or what researchers have long said is closer to 100 years' worth of Japan's gas needs.
Methane hydrate is a sherbet-like substance that can form when methane gas is trapped in ice below the seabed or underground. Although it looks like ice, it burns when it is heated. Experts say there are abundant deposits of gas hydrates in the seabed and in some Arctic regions. Japan, together with Canada, has already succeeded in extracting gas from methane hydrate trapped in permafrost soil. US researchers are carrying out similar tests in Alaska.
The difficulty had long been how to extract gas from the methane hydrate far below the seabed. In onshore tests, Japan explored using hot water to warm the methane hydrate and tried lowering pressure to free the methane molecules. Japan decided to use depressurisation, partly because pumping warm water under the seabed would itself require a lot of energy.