TitleUnlocking the Potential of 'Flammable Ice'
BodySAPPORO, Japan — The road to Japan’s energy future runs through a cluster of low buildings in this city, the largest on the northern island of Hokkaido. Here, working on their own and in collaboration with American scientists, researchers are studying sediment cores containing methane hydrates, icy constructs of water molecules with the explosive gas methane trapped within. Hydrate-containing sediments are found in large amounts around the world, both under the sea and to a lesser extent in permafrost. If they can be tapped safely and economically, they could be an abundant source of fuel, especially for countries like Japan that have few energy reserves of their own. The Japanese researchers’ work has already borne fruit: in March, the government announced that it had successfully produced methane from hydrates in sediments under the Pacific Ocean. The effort, conducted from a drilling ship in the Nankai Trough about 100 miles east of Osaka, was the world’s first hydrate production test in deep water. But scientists say there is still much that is unknown about the unusual compounds, sometimes referred to as “flammable ice,” and that the commercial production of gas from them is still far-off. “We need to know more about the physical properties of hydrates themselves, and of the sediments as well,” said Hideo Narita, the director of the research laboratory, part of the National Institute of Advanced Industrial Science and Technology, which is financed largely by the government. Further research, here and at labs around the world, will help scientists better understand the environmental impact of hydrate production, including the possible release of methane, a potent greenhouse gas, into the sea or atmosphere. There is also the potential for subsea landforms to become unstable when hydrates are removed. Timothy S. Collett, a research geologist with the United States Geological Survey, said that despite all the talk about their potential as an energy resource, “hydrates are largely still a scientific issue.” The research poses special challenges because hydrates form under high pressure, caused by the weight of all the seawater or rock above them, and that pressure must be maintained when the sediment cores are analyzed. If it is not, the hydrates within quickly dissociate into water and gas, and the sediments “look like chocolate mousse,” said Carlos Santamarina, a professor at Georgia Tech. In the mid-2000s, Dr. Santamarina designed the first instruments “that could determine the properties of the sediments without destroying them in the process,” he said. He and other American researchers traveled to Japan this year for tests using his instruments and others in the Sapporo lab. Methane hydrates have bedeviled petroleum engineers for decades, as they can form in subsea pipelines and obstruct flows. They played a small but unwelcome role during efforts to stop the Gulf of Mexico oil spill in 2010, quickly clogging a huge steel box designed to funnel the oil safely to the surface. Running into hydrates while drilling can also complicate exploitation of conventional oil and gas reserves. But for years, scientists have considered that hydrates might be an energy source in themselves. Hydrates can sometimes appear as clumps of ice on the seafloor. However, for energy production, researchers are most interested in those that form in sediments. They are created when methane — which is produced by microbes, or heat and pressure, acting on organic matter — migrates upward in the sediments and mixes with water under specific conditions of temperature and pressure. The icy substance forms in the microscopic spaces between the sediment grains, often in substantial amounts. “You have a lot of methane, you have a lot of water, and guess what, they’re going to form hydrates,” said Carolyn Ruppel, the chief of the geological survey’s hydrate research project, which focuses on the potential impact on climate and seafloor stability, as well as energy. Sandy sediments, with bigger grains, are preferred over clay. “They’re very permeable, so it’s easy to get the hydrates out,” Dr. Ruppel said. Permeability is one of the important characteristics measured at the Sapporo lab, which has a series of interconnected rooms at its heart. In the middle is a smaller storage space, with about 20 heavy steel cylinders standing upright. These hold the cores — the most recent ones were drilled two years ago in the Nankai Trough — which are about 2 inches in diameter and 12 inches or more long. The cores are kept at a pressure about 200 times higher than atmospheric pressure through water lines connected to a pump. As needed, cylinders can be wheeled into various rooms for testing. The instruments are equally rugged and connect with the core cylinders through valves so there is no loss of pressure. In addition to permeability, instruments can measure sediments’ thermal conductivity — how quickly heat will flow through them — and mechanical qualities like strength and stiffness, both with hydrates and after the hydrates dissociate and the gas and water are removed. Other instruments analyze the size of the sediment grains and the pores between them. And a specialized version of a scanning electron microscope, which keeps the samples at low enough temperatures so that the hydrates do not dissociate, even in a near-vacuum, provides detailed images of the grain-hydrate structure. The measurements allow researchers to refine production techniques, both for longer tests and for eventual commercial production. For now, hydrate production calls for using conventional methods in which a well is drilled into sediments, lined with steel tubing called casing and kept filled with water. The water would be pumped out, lowering the pressure enough so the hydrates dissociate. Because water is produced along with the gas, the pumping would have to be continuous. But the dissociation of hydrates is endothermic — it uses, rather than releases, energy — so when methane gas is produced, the sediments begin to cool. That can slow or stop dissociation, so production will probably have to involve the introduction of heat as well as pumping. Conventional techniques would not work well in clays, which contain the vast majority of known hydrate reserves, because the pore sizes are much smaller, Dr. Santamarina said. Outside-the-box thinking will be required to come up with ways to extract methane from them. “Much of the current paradigm for production in methane hydrates is anchored around oil production,” he said. “And probably with that paradigm we may not go very far.” “We’ll have to come up with smart solutions,” he added. “It will take good engineering to figure it out.”
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