Update, 12 March 2013: In a world first, Japan has successfully begun extracting commercial quantities of natural gas from icy clathrates beneath the sea bed. , according to the Japan Oil, Gas and Metals National Corporation.
Original article, published 7 March 2013
IN THE search for new sources of energy, Japan is digging deep. Just off its south-west coast, 1300 metres below the surface, a huge cache of slushy, combustible ice lies buried in the ocean floor. This month, Japan is carrying out the first offshore attempt to produce methane gas from these frozen methane hydrates. If successful, this could be the next great energy source.
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Methane hydrates consist of methane molecules trapped in a cage-like structure of water called a clathrate. Cold temperatures and high pressures keep them solid, and their compressed structure gives them 164 times the energy potential of an equivalent volume of natural gas.
They are abundant in ocean floors around the world and under Arctic permafrost. Some estimate that the planet holds three orders of magnitude more gas in hydrates than in traditional gas seams, and that their total energy is greater than all other energy sources combined. The US, India, South Korea and Russia all have programmes to explore the potential of hydrates, but the on-going natural gas boom makes it a low priority for now.
“The total energy stored in methane hydrates is greater than in all other energy sources combined”
Japan is the exception. It has invested hundreds of millions of dollars in hydrate research, especially in the Nankai trough off its Pacific coast. The area may hold enough gas to meet the country’s energy needs for a century. Japan is the world’s largest importer of natural gas, and the hydrate project was expedited after the Fukushima nuclear plant disaster in 2011.
This month, a team led by the Japan Oil, Gas and Metals National Corporation will drill 300 metres below the seabed, and place a pipe to carry methane to the surface. The goal is to produce tens of thousands of cubic metres of gas over about two weeks. Commercial production could start in 2018.
First, the team must solve a number of environmental and technical challenges. Chief among these is how to turn the solid hydrates into gas. The plan is to pump out seawater from inside the gas pipe. This will lower the pressure in the pipe and break up the hydrates into water and methane gas, which will rise up the outer pipe (see “graphic”). If that doesn’t work, other solutions include pouring in an antifreeze.
Even the authors of the project’s environmental impact statement admit they know little about the problems large-scale extraction could cause. Landslides are the biggest known risk. Hydrates are often key structures in the sea floor. Before oil and gas companies became interested in exploiting them, hydrates were considered a risk because they collapse beneath heavy oil rigs. Deliberately drilling through them or mining them could disturb the seabed stability.
Ancient history offers evidence to support this, says Euan Nisbet of Royal Holloway, University of London. A landslide off Norway 8000 years ago triggered a 4-metre-high tsunami that swamped Scotland. Geological data suggests it was accompanied by a massive methane release, possibly because warmer temperatures melted sea-floor hydrates (Nature, ).
The current test at Nankai is unlikely to pose such a risk, says Nisbet, but large-scale hydrate mining could. In shallower waters or on steeper slopes, anything you do could cause a landslide, says Arthur Johnson of the Hydrate Energy International consultancy.
It’s not clear whether the natural processes that led to the Scottish tsunami 8000 years ago are a good model of what will happen with human interference, says Ray Boswell of the US Department of Energy (DoE). “Nature slowly nudges a big area over a long time.” The Japanese team will monitor sea floor movement during their test. They hope this will help them calculate how much gas can safely be extracted over a larger area, and how fast.
Richard Charter, who sits on the DoE’s hydrate advisory committee, worries that large-scale mining could cause greater unforeseen impacts, like small earthquakes or an uncontrollable gas release that would escape into the atmosphere or acidify the waters around the borehole. “You’re basically punching a hole into a zone we don’t know about,” he says.
In some respects, deep-sea hydrates may be less risky than conventional gas seams. Uncontrolled leaks are a risk for any gas rig and for the climate, as methane is a powerful greenhouse gas. But Tetsuya Fujii of the Japan Oil, Gas and Metals National Corporation says deep-sea hydrates have a built-in fail-safe: if the pipeline breaks, the water pressure would make the hydrates recrystallise, helping to stem the leak. Any gas that did escape would dissolve in the water column or be eaten by bacteria.
Would-be hydrate miners should tread more carefully in shallower waters or the Arctic permafrost, where hydrate mining projects have also been proposed, says Nisbet. “Every gram of methane in the air is a disaster.”
So it may come as a surprise that hydrates could one day become a carbon-neutral energy source. Carbon dioxide can also form clathrates. Researchers are looking for ways to pull the gas out of the atmosphere and substitute it for methane hydrates. That would have the added advantage of leaving the sea-floor structure unchanged.
The technology for this is still embryonic. In April last year, a US team performed the first large-scale test by pouring liquefied CO2 down a borehole at Conoco-Phillips’ oil field on Alaska’s North Slope. The clathrates traded some of their methane for CO2, and released the gas back up the pipe. The project ran for about 30 days, says Boswell. It will be some time until such technology is deployed, says Nisbet. “Still, it’s a very good idea.”
