15 August 2012

Japan looks to methane under sea floor

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Large quantities of methane gas are stored as ice-like gas hydrates below the ocean floor and these could be used as an energy source, a Japanese geologist said.
Ice that burns

Ice that burns – Gas hydrates occur in large quantities in sediments below the ocean and researchers are developing techniques to make use of this untapped resource. Credit: J. Pinkston and L. Stern/US Geological Survey

BRISBANE: Large quantities of methane gas are stored as ice-like gas hydrates below the ocean floor and these could be used as an energy source, a Japanese geologist said.

Since the Fukushima nuclear disaster in March 2011, there has been a new focus in Japan on their research into using these gas hydrates as an alternative energy source to nuclear power. And the gas hydrates are found worldwide: they exist at almost all continental margins.

“One cubic metre of gas hydrate contains 164 cubic metres of methane,” said Ryo Matsumoto from the University of Tokyo, who presented his research at the 34th International Geological Congress in Brisbane, Australia. “Gas hydrates are very effective containers of methane.”

Methane trapped in water cages

Gas hydrates are ice-like solids made up of molecular water cages, in which methane molecules are trapped. They form naturally when methane comes into contact with water at low temperatures and under pressure. Ideal conditions exist in deep sea sediments and also within the permafrost in arctic regions.

Methane that forms the hydrates is constantly produced by the activity of anaerobic bacteria or through the decay of organic material at high temperatures deep in the sediments.

The total quantity of gas hydrates on Earth is not easy to estimate. “The gas hydrate exploration has not been completed yet,” said Matsumoto. But estimates suggest that the total amount of carbon contained in gas hydrates could match or even exceed that bound in fossil fuels.

Extraction tests next year

But most of the gas hydrates occur in small, dispersed deposits, adds Matsumoto. “These are not usable as a resource.”

As the world leader in gas hydrate research, Japan has launched an ambitious research program in 2001 with the aim of developing gas hydrates as a commercially viable energy source. The first stage of this program – the exploration and mapping of the resource – is now completed and identified zones of highly concentrated gas hydrates off Japan’s southeastern coast.

The second phase is a production test and scientists hope to be able to recover the first gas from gas hydrates as early as next year.

“A very simple way [to release the methane from the hydrates] is to inject steam into the hydrate reservoirs,” explained Matsumoto. But it is an energy-intensive process to pump hot steam down to 1,000 metres below the ocean and through hundreds of meters of sediments.

For this reason the Japanese scientist are testing a procedure that lowers the pressure in the hydrate-bearing sediments, causing the hydrates to dissociate into water and gaseous methane. But all extraction techniques are still in an experimental phase.

Can it cause an Earthquake?

It is also unclear whether the extraction of gas hydrates could pose an earthquake risk. “Depressurisation in sediments may trigger some tremors,” cautioned Matsumoto.

Not only methane but also carbon dioxide can be contained in gas hydrates. For this reason, scientists are also exploring the possibility to use carbon dioxide hydrates as a long term storage solution for atmospheric carbon dioxide. “That’s possible,” Matsumoto is enthusiastic. “It’s a great idea to exchange carbon dioxide and methane.”

But as with other extraction techniques, there are still lots of technological hurdles to be overcome until they become feasible at large scale. “It may still take 10 or 20 years,” he cautioned. “We are going towards that dream but it hasn’t come true yet. [Politicians pushing the idea] should be more patient.”

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