Fire ice: Gas source is little understood

As unconventional sources of energy go, methane hydrate is one of the strangest. Known as “fire ice” for its resemblance to a burning lump of ice when ignited, it is a widespread but, until recently, little understood potential fuel source.

Methane hydrate comprises a lattice of water-ice, enclosing molecules of methane, the primary component of natural gas. It forms under pressure in the polar regions in sediments under the permafrost and under the seabed on the edge of the continental shelf.

When exposed to surface temperatures, the ice melts and the gas expands, with one cubic foot of solid methane hydrate releasing 164 cubic feet of gas.

Its concentrated nature helps to explain its appeal, but recovering it threatens to speed up climate change. Burnt as a fuel, methane is a clean source of energy but, if it escapes into the atmosphere during drilling or as a result of natural causes, it is a powerful greenhouse gas.

Releases of gas from methane hydrate deposits have been suggested as a factor in mass extinctions in the past and there are concerns drilling could destabilise undersea deposits, endangering drilling rigs and even triggering landslides that may cause tsunamis.

A 2006 UK government review of the threat of climate change warned that a possible release of gas from methane hydrates represented one of the “largest uncertainties” facing climate change researchers.

But the large volumes of hydrates in the earth’s crust and the rising prices of existing fuels have spurred a growing interest in exploiting this potential source of energy. A frequently quoted estimate of global methane hydrates, cited in a 2011 report by the US National Energy Technology Laboratory, is about 700,000 trillion cubic feet (Tcf), although “only a small portion of this enormous resource is likely to be harvested as an energy fuel”, the report warns.

Methane hydrates in the northern Gulf of Mexico alone have been estimated at more than 21,000Tcf, of which 6,700 Tcf was in high concentrations in sandy sediments – the sort of reservoir that could be most easily tapped. If only a third of these hydrates could be recovered the US would double its total natural gas resource, currently estimated at 2,074Tcf, the laboratory suggested.

Alaska’s North Slope, one of the other main focuses of research in the US, is estimated to contain about 85Tcf of recoverable gas and successful field trials have been completed, US energy secretary Steven Chu announced last month.

The US energy department is making $6.5m available this year for research and seeking an additional $5m for 2013. The goal is to make sustained production economically viable, the department says.

The Japan Agency for Marine-Earth Science and Technology began preparatory drilling in waters 1,000m deep off Aichi prefecture in February. Methane hydrate deposits off south-central Japan are estimated at 10 years’ worth of domestic consumption of natural gas.

But there is still some way to go before methane hydrate becomes a commercial proposition.

BP, another early participant in test drilling in Alaska, says it is not actively pursuing hydrates research. It described the tests as “a significant milestone” on the way to understanding the product’s potential. The company said: “But we have a conservative view. Hydrates as an energy source are unproven and will need lots of research and development.”

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