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Icy substance called gas hydrate might be source of clean-burning fuel
Monday, December 13, 1999 By Byron Spice, Science Editor, Post-Gazette
Flammable ice sounds like a bad oxymoron, something that belongs on a list with "tight slacks," "fresh frozen," "simply confusing," "Microsoft Works" and the ever popular "military intelligence."
But flammable ice is a fair description of the planet's most abundant, if least recognized, form of fossil energy.
Called methane hydrate, or gas hydrate, it's an ice-like substance composed of methane -- the main constituent of natural gas -- trapped inside cages of water molecules. It forms under pressure, with deposits found underneath permafrost in Arctic regions and beneath deep ocean floors.
When extracted and placed in normal atmospheric pressure, chunks of the stuff pop and fizzle as highly concentrated methane escapes. It can even be set aflame.
Gas hydrate ceased to be this Mr. Wizard-ish curiosity in 1995, when the U.S. Geological Survey assessed U.S. gas hydrate resources. The study concluded that hydrate deposits entrapped between 112,000 trillion cubic feet and 676,000 trillion cubic feet of methane. The estimate was refined in 1997 to a more conservative 200,000 trillion cubic feet, but it still dwarfed the 1,400 trillion cubic feet in the nation's conventional gas reserves.
Worldwide, the figures are even more staggering -- 400 million trillion cubic feet, compared with 5,000 trillion feet in known gas reserves. Even oil and coal reserves are no match.
"There's more energy in the form of methane hydrate than in all the other forms of fossil fuels combined," said Gerald Holder, dean of engineering at the University of Pittsburgh and a pioneering hydrate researcher.
The methane stores are so vast that two questions loom large for researchers: Can gas hydrates be safely and economically tapped as a long-term source of clean-burning fuel? And could an event such as ocean warming cause the sudden release of methane, a greenhouse gas, into the atmosphere, spurring global warming?
Japan, looking to end its dependence on imported oil, last month began drilling in the Nankai Trough east of its main island to see if hydrates could be harvested, part of a five-year, $60 million research program, India is beginning a five-year, $50 million effort. In October, Germany launched a major research program and Australia and France recently announced their interest in hydrate deposits discovered by the Australian Geological Survey.
The U.S. Department of Energy spent $8.5 million studying gas hydrates in the 1980s, but phased out the program in 1992 because conventional gas resources seemed adequate to meet foreseeable demands for methane. DOE expects to re-launch its hydrate program soon at the National Energy Technology Laboratory, which leads the department's natural gas and ultraclean fuels efforts. Formerly known as the Federal Energy Technology Center, based in Morgantown, W.Va., with a branch in South Park, it was redesignated last Friday as DOE's newest national laboratory.
A bill sponsored by Rep. Mike Doyle, D-Swissvale, would authorize $47.5 million for DOE hydrate research over the next five years. The House passed the bill in October and the Senate approved a slightly amended version last month; the House will vote on the amended version when it reconvenes next month.
"It's kind of an area that's mushrooming," said Hugh Guthrie, senior technical advisor at Morgantown, who oversaw the DOE gas hydrate program in the 1980s. Oil companies have yet to spend much money on it, he added, "but they're watching it very carefully."
Last summer, about 250 people -- including oil company representatives -- coughed up $1,300 apiece to attend an international meeting on hydrate research in Salt Lake City. Pitt's Holder, who chaired the meeting, recalls the days when only a few scientists did hydrate research.
"We'd have international meetings with 10 or 12 people. We'd sit in a room and present our papers to each other," he said. "Now we've gone from maybe five to 500 scientists.
"When I first started working on gas hydrates" as a graduate student in the early 1970s, "I think most of the people in the oil industry felt most of the problems were already solved," Holder said. Indeed, when they were first recognized 70 years ago, gas hydrates were an industry nuisance, an icy sludge that fouled natural gas pipelines.
That gas hydrates were first noticed in gas pipelines was no mere happenstance; pressurized lines contaminated with water happen to be a perfect environment for making the icy stuff.
Gas hydrates form when methane and water are together under pressure. The combination of pressure and the stabilizing effect of methane on water molecules allows the icy substance to form at temperatures above the normal freezing point of water. The water freezes into a crystal lattice that absorbs, concentrates and traps the methane.
"It works just like a sponge," Holder said. "The only difference is the lattice wouldn't exist without the methane."
Gas companies eliminated their gas line problems by making sure they kept water out or by adding antifreeze.
It wasn't until 1964 that drilling crews in a Siberian gas field encountered gas hydrates underground, confirming that hydrates were not just a byproduct of pressurized pipelines, but occurred naturally. In the early 1970s, geologists began finding gas hydrates in ocean sediments that are at least 500 meters deep -- where pressures and temperatures combine to trap methane produced by decaying organisms or that is seeping up through the Earth's crust.
Just how methane can be economically extracted from gas hydrate deposits isn't clear.
The simplest way, Holder suggested, might be to drill a conventional well into a natural gas reservoir that is underneath a cap of hydrate. As natural gas is removed from the reservoir, the pressure within the reservoir would drop, which would cause some of the overlying gas hydrate to dissociate, or melt, releasing more methane into the reservoir which can then be pumped out of the well.
That's exactly what some say occurred years ago in the Messoyakha gas field of Western Siberia. Usually, pressures in the gas formation decrease after a gas well has been in production for a while, but the pressure in this field remained steady throughout production. The sustained pressure may have been due to breakdown of gas hydrates, Guthrie said, though not all researchers agree.
Holder said it might also be possible to produce methane directly from a gas hydrate deposit by drilling into it; the resulting depressurization would cause dissociation of the hydrates and release methane. An alternative might be to use two well bores -- one to deliver steam, warm water or antifreeze to melt the hydrates, another to extract gas. It might also be possible to dredge up hydrates, pumping them as a slurry to the surface.
None of this will be cheap. Production facilities will require drilling either in deep water or in Arctic regions, such as northern Alaska and Siberia. The collapse of gas hydrate layers can destabilize the ocean floor, triggering submarine landslides. And production and distribution provides opportunities for methane to escape into the atmosphere, where it serves as a potent greenhouse gas.
Many of these issues demand immediate attention because they already are plaguing oil and gas drillers, said William Dillon, the geologist who heads the U.S. Geological Survey's gas hydrates program at Woods Hole, Mass. Though oil companies might not be trying to tap gas hydrates, wells in northern Alaska and Canada often are drilled through hydrate layers.
"The process of drilling itself can cause dissociation," Dillon said, and has been blamed for rig fires and blowouts. Likewise, oil production in the Gulf of Mexico and North Atlantic has moved into deeper waters where gas hydrates are found. Those ocean rigs have problems with seafloor stability in addition to blowouts.
Another pressing question is what effect the warming oceans -- temperatures have risen more than a degree in the past century -- might have on global climate. As temperatures rise, more gas hydrates will melt, releasing methane into the atmosphere, where it serves as a highly effective greenhouse gas.
That in turn could cause even greater global warming, even warmer oceans, and the release of still more methane.
Some scientists, such as Gerald Dickens of Australia's James Cook University, believe this mechanism might have contributed to climatic changes in Earth's history, such as a period of abrupt global warming that occurred 55 million years ago.
Scientists at the Carnegie Museum of Natural History have argued that this warming period enabled the first mammals to migrate from China to North America.
Last month, Dickens and colleagues reported in the journal Science that they had found evidence from core samples and soundings off the coast of Florida that this warming period coincided with the release of methane from the ocean floor.
But Dillon said further research is necessary to fully understand this mechanism. It's possible, he noted, that gas hydrates may actually serve to moderate climate changes. Warmer waters might release methane, boosting global temperatures. But increased melting of the polar ice caps would raise sea levels, increasing ocean floor pressures and prompting formation of more gas hydrates.
Conversely, the growth of the ice caps during cool periods would lower sea levels, reducing ocean floor pressures and releasing more methane.
One basic question still to be determined is the rate at which methane is normally released from hydrate deposits, Dillon said.
It's possible the methane is constantly released from the top of these deposits, even as additional methane that is seeping up is absorbed at the base of the deposit.
"Are we looking at something that is an active process?" Dillon said. "We don't know the answer. But if methane is cycling through the hydrate, then we may be looking at a renewable resource."
Dillon said he expects that methane recovery from hydrates eventually will be economically feasible, if for no other reason than the hydrocarbons from declining petroleum reserves will be too precious to burn and will be diverted exclusively for use in producing plastics and other polymers.
"Realistically," Guthrie said, "we will know by 2015 if it's economical to produce methane from hydrates. We'll either have wells by then or it won't be economically feasible."
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