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Tuesday, March 13, 2012
Methane hydrate energy solution?
Seabed deposits could rival natural gas but safety, cost issues loom
The launch of preparatory drilling for methane hydrate off Aichi Prefecture last month drew public attention amid hopes it will become an alternative to nuclear power at a time when Japan's self-sufficiency rate in energy is a meager 4 percent.
While the potential of methane hydrate is still unclear, the government aims to establish technical bases for commercial use in fiscal 2018. Here are some basic questions and answers about methane hydrate and Japan's efforts to develop it as an energy source.
What is methane hydrate?
The substance is a combination of methane and water molecules. The high-pressure, low-temperature environment under the seabed causes water molecules to encase methane, giving it a texture like sherbet.
Chunks of methane hydrate have been likened to fiery or burning ice cubes, which easily combust when exposed to flame.
Methane hydrate holds large amounts of combustible methane. When a cubic meter of methane hydrate decomposes, it releases about 160 cu. meters of gas that can be burned to generate power.
Where can it be found?
Methane hydrate can be only generated in a high-pressure, low-temperature environment. Since a temperature of about minus 80 is needed for it to form, it is generally only found in permafrost or deep below the seabed.
Is there an abundance in Japanese territory?
It is still unclear exactly how much methane hydrate lies in the seabed around Japan. But a recent study by Research Consortium for Methane Hydrate Resources in Japan, an industry-government-academia research body better known as MH21, estimated the Eastern Nankai Trough, which spans a stretch of seabed from Shizuoka to Wakayama prefectures, has about 1.2 trillion cu. meters of methane hydrate, or the equivalent of a large natural gas field that could provide Japan with 12 years' worth of such fuel.
How much R&D has been conducted and what are they trying?
The government has been looking into the potential of methane hydrate since the mid-1990s, so research and development are well under way.
The government formed MH21 in 2002 to carry out Phase 1 of the research until 2009. During that period, Japan was able to successfully collect methane from methane hydrate buried in permafrost in Canada.
R&D is now in Phase 2, which will continue until March 2016.
On Feb. 15, MH21 started preparatory drilling in the Eastern Nankai Trough, about 80 km south of Aichi's Atsumi Peninsula.
"We are now drilling and setting wells. But since this is the first attempt in the world, we are still not sure if the methane gas can be safely collected from the seabed," said Yoshihiro Nakatsuka, who leads an MH21 environmental team. "In that sense, we are just trying to make sure it can be collected," he said.
The approach MH21 is employing is called the decreasing-pressure method, in which a well on the seabed lowers the pressure of the layer with the methane hydrate by pumping water near it to initiate decomposition to release and collect the gas.
Will methane hydrate be economically viable?
That is unclear and will require more in-depth research.
Although MH21 has calculated it will cost between ¥46 and ¥174 to make 1 cu. meter of methane hydrate, more research is needed to ascertain whether harvesting it is economically viable, they said.
For example, Nakatsuka said nobody knows how much methane can be extracted from a single well. If the yield is low, many wells will be needed, hiking the cost.
Natural gas costs about ¥20 per cubic meter to produce, but that's likely to jump by March 2019, so it is uncertain at this point which will be more viable.
Are there any environmental risks associated with methane hydrate?
Raw methane released into the atmosphere produces a greenhouse effect 25 times more potent than carbon dioxide. So every effort must be made to ensure it doesn't leak during extraction.
MH21 says the decreasing-pressure method lessens the risk because the lower pressure in the wells allows gas released by methane hydrate under the seabed to flow up naturally, giving it little chance to escape.
It has also been noted, however, that when methane hydrate decomposes, it can trigger landslides as the decomposing layer disappears, warping the seafloor.
The impact of submarine landslides is still being studied, but they are known to occur on slopes. MH21 plans to drill only in flat layers until further studies shed more light on the risks.
More research is also needed on the potential impact that methane leaks from the seabed could have on ecosystems.
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