In 'ocean floor' lab at Brookhaven scientists create, study methane hydrates

Data may help in developing strategies for mining natural gas locked up in seafloor sediments

Devinder Mahajan (left) and Michael Eaton Click here for a high resolution photograph.

Scientists at BNL have recreated the high-pressure, lowtemperature conditions of the sea floor in a tabletop apparatus for the study of methanehydrates, an abundant but currently out-of-reach source of natural gas trapped within sediments below the ocean floor. This research, which was initially funded by BNL’s Laboratory Directed Research & Development program, is now funded by DOE’s Office of Fossil Energy.

Michael Eaton, a Stony Brook University (SBU) graduate student working for BNL’s Devinder Mahajan of the Energy Sciences & Technology Department, presented a talk outlining the use of the apparatus for the creation and study of methane hydrates during a special March 13 and 14 symposium co-organized by Mahajan at the 229th National Meeting of the American Chemical Society in San Diego, California.

The symposium, which was on Gas Hydrates and Clathrates, was co-sponsored by the Petroleum and Fuel Divisions of the American Chemical Society. The symposium proceedings will be published later this year in a special issue of the Journal of Petroleum Science & Engineering for which Mahajan is guest editor.

“The amount of natural gas that is tied up in methane hydrates beneath the seafloor and in permafrost on Earth is several orders of magnitude higher than all other known conventional sources of natural gas — enough to meet our energy needs for several decades,” Mahajan says. But extracting this resource poses several challenges.

For one thing, methane hydrates — which are ice-like cages made of water molecules surrounding individual methane molecules — are only stable at the very low temperatures and high pressures present at the ocean floor. “If you try to bring them up, these things fizzle and decompose, releasing the trapped methane,” Mahajan says.

So a multi-agency team led by DOE — as part of its mission to secure America’s future energy needs — is trying to learn about the conditions necessary for keeping hydrates locked up so they can be extracted safely and tapped for fuel.

At BNL, Keith Jones and Huan Feng of the Lab’s Environmental Sciences Department, Stanmire Tomov of the Information Technology Division, William Winters of the U.S. Geological Survey, and Roger Flood and Miriam Rafailovich of SBU, are all among the researchers working with Mahajan. The group has built a vessel that mimics the seafloor temperature and pressure conditions, where they can study the kinetics of methane hydrate formation and decomposition.

Unlike other high-pressure research vessels, the BNL apparatus allows scientists to interchange vessels of different volumes, study even fine sediments, and visualize and record the entire hydrate-forming event through a 12-inch window along the vessel. In addition, massbalance instrumentation allows the BNL group to collect reproducible data in the bench-top unit. Even better, Mahajan says, they can study the kinetics in actual samples of sediment that once contained hydrates — as close to the natural conditions as you can get in a lab.

“You fill the vessel with water and sediment, put in methane gas, and cool it down under high pressure. After a few hours, the hydrates form. You can actually see it. They look like ice, but they are not. They are stable at 4 degrees Celsius,” he explains.