CORVALLIS, Ore. – An international team of scientists looking for gas hydrates off the coast of India has discovered a pair of methane hydrate reservoirs buried in the sediment below the Bay of Bengal, and though the idea of a new energy source is tantalizing, researchers say the technology does not yet exist to make these reservoirs commercially feasible.
A similar field of gas hydrates was found off the coast of Oregon a few years ago, said Marta Torres, a marine geochemist at Oregon State University and an investigator on the India and Oregon expeditions.
“No one yet knows how to extract methane for energy from such sources,” said Torres, an associate professor in OSU’s College of Oceanic and Atmospheric Sciences. “We’re still learning how much gas hydrate is in the sediment and we need to learn more about how much energy is required to mine it, as well as look at environmental concerns and possible hazards associated with extracting gas from these deposits.”
Since that Oregon cruise, scientists have learned a lot about the processes that form such reservoirs, according to Anne Trehu, a professor of oceanography at OSU, who was the lead scientist on the Oregon expedition.
“We now have a good understanding of how methane is generated and how it moves from deep sediments to the shallow areas where massive hydrate is formed,” Trehu said.
The India research cruise aboard the vessel JOIDES Resolution, funded by the Indian government, began in May and continued for more nearly four months. Project coordinator Timothy Collett, from the U.S. Geological Survey, assembled a team of scientists from various institutions and agencies in the United States to provide the expertise and equipment for the project. OSU, which has been involved in gas hydrate research for nearly a decade, was joined by the U.S. Department of Energy, the Scripps Institute of Oceanography, the University of Rhode Island and the University of New Hampshire. Some 40 U.S. scientists worked with colleagues from India, Canada and England on the research.
Gas hydrates are crystalline substances that look like packed snow, or ice. They form when water and methane are combined at high pressure and low temperature. Commonly found along the continental margins, they are created from the natural gas that occurs after decomposition of organic material deep within ocean sediments.
Though scientists remain unsure about the overall abundance of methane hydrates in the world’s marine sediments, many believe it is a significant fossil fuel reservoir – perhaps the most abundant untapped fossil fuel. However, mining of methane hydrate has been problematic because of its instability.
“When you bring it up from deep water, it just melts,” Torres said. “As soon these methane chunks get warm, or the pressure eases, they disappear and the methane escapes into the ocean or atmosphere, unless it is trapped and confined.”
Working around the temperature and pressure problems is feasible, she added, because scientists can preserve small methane hydrate samples in liquid nitrogen or cooled pressure chambers. However, finding a way to bring vast amounts of methane hydrates to the surface profitably and safely has yet to be discovered.
There are also questions about the amount of methane stored in these hydrates, scientists say. Some of the early estimates about methane content are probably too high, Torres says, because remote sensing techniques had not been calibrated. One of the goals of gas hydrate research at OSU is to use a suite of tools, including thermal imaging and measurements of electrical resistance, to identify how much methane is contained in the sediments of hydrate reservoirs.
The 9-meter sediment cores they extracted from a site near the Andaman Islands at the southern edge of the Bay of Bengal were comprised predominately of clay, which typically included 1 to 3 percent hydrate. However, in the more permeable ash layers, it wasn’t unusual to find sediment samples that contained 30 to 60 percent hydrates – and samples reached as high as 87 percent.
“The technicians had to be extremely careful with the core samples so they didn’t explode,” Torres said.
In their research, the scientists first mapped large areas of the Arabian Sea and the Bay of Bengal. On the western side of India, they found little evidence of methane hydrate – in large part because there was very little organic matter. However, in the Krishna-Godawari Basin, where the margin is more fractured, they found a large area filled with hydrates that were relatively shallow. Here the methane is pushed closer to the surface through cracks and results in near-surface deposits similar to those found off the shore of Oregon and parts of Canada.
Later in the cruise, they found another site bear gas hydrate near the Andaman Islands in a volcanic arc, where layers of ash acted as a reservoir to trap the methane and form hydrates.
One of the intriguing things about methane hydrate as an energy source, Torres noted, is that in some situations it could be renewable at a much faster rate than other fossil fuels, although still in a time scale long enough to be formidable.
“The Oregon hydrate field is relatively young – about a thousand years – and produces some big chunks of methane hydrate,” Torres noted. “We’re just beginning the work on the data from India. But organic material is being buried at a fast rate, so the process of creating methane is continual.”