Climate Feedback

Time to unleash seabed methane?

methanehydrate.jpgA new reservoir of fossil fuel could be ready to tap much sooner than previously thought. R&Ders have been talking up natural gas extraction from methane hydrates – a solid form of the greenhouse gas, found tucked away beneath the sea floor where low temperature and high pressure keep it stable.

Following an enthusiastic Congressional testimony, Ray Boswell of the US Department of Energy’s National Energy Technology Laboratory (NETL) has a commentary in Science on hydrates’ potential as an energy source. But methane hydrates are also making headlines this week as a worrying harbinger of climate change. Some scientists have warned that ocean warming could destabilize hydrates and send methane gas bubbling into the ocean. Now a team led by Graham Westbrook of the University of Birmingham has spotted over 250 such gas plumes near Svalbard, Norway – echoing a similar observation from a group in Siberia earlier this year.

Much of the released gas dissolves in the water column, but any portion that reaches the air could amplify warming.

By drilling for hydrates, could we wake a sleeping giant? Boswell doesn’t tackle this question head on, but he offers some relevant points.

First off, hydrates in the Arctic – where gas plumes have been seen – are hard to get at. Before they go messing with the permafrost lid that protects the vast northern stores of methane, prospectors will find more enticing targets, says Boswell. Specifically, it’s hydrates found in sandy deposits in the Gulf of Mexico that are raising hopes at NETL.

Hydrate-bearing sands were first spotted off Japan in 1999. By recent estimates the Gulf of Mexico holds 190 trillion cubic meters of natural gas in such sands – over 300 times the amount of gas the US burns annually. An April expedition to probe the Gulf’s deposits found promising pockets of highly saturated hydrates. There are technical and economic hurdles to extracting this gas, says Boswell, but many could be overcome with existing technology. That’s a big difference from the hydrates known a decade ago, which were dispersed across muddy fields or packed into solid mounds.

Methane from sandy hydrates may also be easier to control. Boswell writes:

These resevoirs are commonly buried many hundreds of meters below the sea floor and enclosed in a matrix of impermeable sediments that help to prevent the escape of released methane. The most prospective gas hydrate deposits are also those that are most effectively buffered from environmental change.

In other words, drillers are keen to avoid the escape of methane – they want to get it to customers who’ll burn it.

Speaking of which, does the world need another fossil fuel reservoir? Not if you’re hoping our supplies will run out in time to save the climate. But with the world facing dwindling oil reserves and a sluggish start on renewables, Boswell implies the gas could fill an important gap: “hydrates may offer an important ‘bridging’ fuel that will help ease the transition to the sustainable energy supplies of the future.”

Anna Barnett

Image: Methane actively dissociating from a hydrate mound / National Energy Technology Lab


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