Gas-Hydrate Deposits in Gulf of Mexico
U.S. scientists working on a research vessel in the Gulf of Mexico have made the most promising discovery so far of marine gas hydrate, a possible new energy source. Globally, gas hydrate--an icelike substance formed mainly of methane and water--is thought to be more abundant than oil, coal and conventional natural gas combined. However, it has proved difficult to find deposits that are concentrated enough to exploit, and none have yet been developed.
“We’ll now have a roadmap of what’s down there based on the borehole measurements,” said David Goldberg, director of the Lamont-Doherty Earth Observatory Borehole Research Group, which participated in the three-week study cruise this spring. Part of a project of the U.S. Department of Energy (DOE), the cruise also included scientists from the U.S. Geological Survey, U.S. Minerals Management Service, and a consortium of companies led by Chevron.
The researchers drilled into sand and found pockets of hydrate up to a hundred feet thick at two sites off Texas and Louisiana, known as Walker Ridge and Green Canyon. Hydrate saturations in the sand ranged from 50 to 90 percent. Lamont’s borehole group is currently analyzing measurements taken from the drill holes to estimate how much methane the two sites may hold. One early estimate was about 1 trillion cubic feet (tcf).
The USGS, which announced the discovery, estimates there is about 700,000 tcf of gas hydrate worldwide, most of it below the ocean floors, where hydrates form under high pressure and cold temperatures. The Minerals Management Service estimates that the Gulf may hold 6,700 tcf of methane hydrate in sand—enough to satisfy U.S. natural gas demand for about 290 years, if all of it could be removed economically.
Methane has the advantage over oil and coal of producing less carbon dioxide gas when burned. “Gas hydrates could be an interim fuel that can reduce our carbon footprint,” said Timothy Collett, a USGS hydrate expert who co-led the expedition. Japan, which imports nearly all of its energy from abroad, has set a goal for commercial production of methane from hydrate by 2017.
Geophysicist Ann Cook PhD. Student at Lamont-Doherty in the Gulf of Mexico.
Researchers said that one of the cruise’s main accomplishments was showing that scientists could predict where to drill. “When we hit it on the first hole, everyone was squealing,” said Ann Cook, a geophysicist finishing her PhD. at Lamont who was on the cruise.
Hydrate deposits have been found in waters off the Carolinas, and in the permafrost of Alaska’s North Slope, but researchers say the Gulf discovery is especially promising because it sits in thick reservoirs of permeable sand that make extraction with current oil production methods possible. Energy companies in the Gulf already have infrastructure in place to remove conventional fossil fuels.
“Not all hydrates are created equal,” said Ray Boswell, technology manager at the DOE’s National Energy Technology Laboratory who also co-led the expedition. “The ones in sand reservoirs will likely be the first to be developed.” However, engineers must first figure out how to safely extract it. Methane is a greenhouse gas 20 times more potent than carbon dioxide, and it is thought that some gas hydrate deposits could become unstable if disturbed.
U.S. researchers plan to return to the Gulf early next year to take more samples—the first of many steps toward possible commercial production.