More energy is trapped under the sea as frozen natural gas than is stored in all the world’s oil reserves — and researchers this week took a step toward tapping it.

Vast reserves of methane hydrates — a form of natural gas — could power the world for decades to come. But mining the deep, frozen deposits presents an enormous technical challenge.

An estimated 200,000 trillion cubic feet of methane hydrates exists under the sea, and the Department of Energy has a major research program under way that could result in commercial production starting by 2015.

This week, researchers announced completion of a table-top research apparatus that re-creates the high-pressure, low-temperature conditions found on the sea floor, allowing scientists to study ways of bringing the volatile frozen gas to the surface.

For millions of years, microbes have munched away on organic matter in ocean sediments, releasing methane as a byproduct. In cold, high-pressure environments at depths of 1,000 feet and more, individual methane molecules get trapped in ice-like cages of frozen water — methane hydrates.

When they are brought up from the sea floor, the ice cages fizzle and decompose, releasing the trapped methane. Put a match to the decomposing ice and voilà: Ice that literally burns.

Devinder Mahajan (.pdf), a chemist at Brookhaven National Laboratory, has been able to “cook up” hydrates in the new apparatus with this simple recipe: “You fill the vessel with water and sediment, put in methane gas, and cool it down under high pressure (1,500 pounds per square inch). After a few hours, the hydrates form. They are stable at 4 degrees Celsius,” he said.

Such data about hydrate formation in natural sediment samples is scarce. By studying different samples and learning what combinations of pressure and temperature keep the methane locked up, practical ways may be found to bring hydrates to the surface with minimal loss of methane.

More here.