Hydrate-containing sediments seen as a potential energy source

Scientists at a Japanese laboratory are studying sediment cores containing methane gas - if tapped safely, it could be the future of energy

PUBLISHED : Wednesday, 18 September, 2013, 12:00am
UPDATED : Wednesday, 18 September, 2013, 3:45am

The road to Japan's energy future runs through a group of low buildings in Sapporo, the largest city on the northern island of Hokkaido.

Researchers there are studying sediment cores containing methane hydrates, icy constructs of water molecules with the explosive gas methane trapped within. The unusual compounds are sometimes referred to as "flammable ice".

Hydrate-containing sediments are found in large amounts around the world, both under the sea and to a lesser extent in permafrost. If they can be tapped safely and economically, they could be an abundant source of fuel, especially for countries like Japan that have few energy reserves of their own.

The Japanese researchers' work has already borne fruit. In March, the government said it had successfully produced methane from hydrates in sediments under the Pacific Ocean. The effort, from a drilling ship in the Nankai Trough about 160 kilometres east of Osaka, was the world's first hydrate production test in deep water.

But scientists say there is still much that is unknown about the substances, and that the commercial production of gas from them is still far off. "We need to know more about the physical properties of hydrates themselves, and of the sediments as well," said Hideo Narita, the director of the research laboratory, part of the National Institute of Advanced Industrial Science and Technology, financed largely by the government.

Further research, there and at labs around the world, will help scientists better understand the environmental impact of hydrate production, including the possible release of methane, a potent greenhouse gas, into the sea or atmosphere. There is also the potential for subsea landforms to become unstable when hydrates are removed.

Timothy Collett, a research geologist with the United States Geological Survey, said that despite all the talk about their potential as an energy resource, "hydrates are largely still a scientific issue".

The research poses special challenges because hydrates form under high pressure, caused by the weight of all the seawater or rock above them, and that pressure must be maintained when the sediment cores are analysed. If it is not, the hydrates within quickly dissociate into water and gas, and the sediments "look like chocolate mousse", said Professor Carlos Santamarina of Georgia Institute of Technology.

In the mid-2000s, Santamarina designed the first instruments "that could determine the properties of the sediments without destroying them in the process", he said. He and other US scientists travelled to Japan this year for tests using his instruments and others in the Sapporo lab.

Methane hydrates have bedeviled petroleum engineers for decades, as they can form in subsea pipelines and obstruct flows. They played a small but unwelcome role during efforts to stop the Gulf of Mexico oil spill in 2010, quickly clogging a huge steel box designed to funnel the oil safely to the surface.

Permeability is one of the important characteristics measured at the Sapporo lab, which has a series of interconnected rooms at its heart. In the middle is a smaller storage space, with about 20 heavy steel cylinders standing upright. These hold the cores - the most recent ones were drilled two years ago in the Nankai Trough - which are about 5cm in diameter and 30cm or more long.

The cores are kept at a pressure about 200 times higher than atmospheric pressure through water lines connected to a pump.

Outside-the-box thinking will be required to come up with ways to extract methane from hydrate reserves.

"Much of the current paradigm for production in methane hydrates is anchored around oil production," Santamarina said. "And probably with that paradigm we may not go very far."

"We'll have to come up with smart solutions," he added. "It will take good engineering to figure it out."