by Stephen Leahy

17-03-05

More energy is trapped under the sea as frozen natural gas than is stored in all the world's oil reserves -- and researchers 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 tcf 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. 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 by-product. 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 viola: Ice that literally burns.
Devinder Mahajan, 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 psi). 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.
The Brookhaven simulator is just a first step. Before any major extraction efforts can go forward, more-reliable means of identifying the location and composition of methane hydrates are needed. Seismic probes that find oil and gas deposits don't work well with hydrates, Mahajan said -- they're prone to too many false signals.

Mahajan and others involved in the Department of Energy's National Methane Hydrate Program are trying to fine-tune seismic probes to eliminate the false signals. They'd also like to find out whether methane hydrate deposits vary in composition, concentration and behaviour with depth.
The voyage of the Uncle John later may provide some of the answers. A semi-submersible drilling vessel, the Uncle John will spend 35 days in the Gulf of Mexico collecting the first-ever sediment samples from methane hydrate deposits at 4,300 feet beneath the gulf's surface.

"We're going to pull up 3-1/2-inch diameter cylinders of sediments and keep them under same conditions they were at the bottom," said Ray Boswell, a technology manager for methane hydrates at the DOE's National Energy Technology Laboratory in Morgantown, West Virginia. The expedition is just one part of a $ 23 mm, four-year effort funded by the DOE and ChevronTexaco to get samples from the ocean and analyse them. Mahajan and others will study the samples to determine the nature of the methane hydrate in the sea floor and develop methods to estimate reserves.
"In the labs we can raise and lower the temperatures in test chambers to find out what it will take to get the methane to flow," said Boswell.

Source: Wired News