Methane hydrates are formed at high pressures and low temperatures, such as those found at the ocean bottom, where methane gas crystallises with water into lumps of ice. As methane freezes with ocean saltwater the salt crystallises out, leaving an icy mix of gas and pure water.
Mega-tons of gas hydrates are found at the bottom of the ocean – at least twice as much in tons as fossil fuels and releasing less carbon dioxide when burned.
The difficulty lies in accessing and transporting the hydrate, which melts and expands 164 times when brought to the sea surface. Hydrate instability in the reservoirs can also trigger submarine landslides, which can cause costly damage to pipelines and undersea cables.
“Many technological problems need to be resolved, and these need a coordinated international effort,” says Nick Langhorne, science officer at the Office of Naval Research. Nevertheless, deep sea methane offers an extension to the lifetime of fossil fuels.
“There’s another bonus in all this,” says Rick Coffin of the Naval Research Laboratory. “When methane combines with seawater in hydrates, fresh water is produced when the concentrated hydrates are melted. It’s a desalination process where the methane can be recycled to continue the process. For areas thirsty for water, this could be a real windfall. Perhaps I should have said, waterfall.”
A new US research centre will investigates the feasibility of extracting freshwater from gas hydrates (see related story).