Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: SUNDAY, March 26, 1995 TAG: 9503250010
SECTION: HORIZON PAGE: G-1 EDITION: METRO
SOURCE: RICK WEISS THE WASHINGTON POST
DATELINE: LENGTH: Medium
Chunks of the frozen fuel, called gas hydrate, have occasionally been brought to the Earth's surface by researchers drilling into ocean sediments. The nuggets of ice, which are saturated with gas, hiss and bubble when exposed to air, and when touched with a match they burst into flames.
Scientists are approaching the unusual resource cautiously, in part because they are worried that attempts to tap the gas reserve might release into the atmosphere tons of methane, a ``greenhouse gas'' that can contribute to global warming. Indeed, recent research suggests that natural emissions of methane from gas hydrate deposits beneath the ocean floor may be one of the untallied contributors to long-term climate change. Sudden eruptions of methane from undersea gas hydrate may occasionally roil upward in huge, fizzy oceanic burps, events that some scientists half seriously suggest could explain a few sudden sinkings of ships.
Scientists are only now starting to figure out how they might safely harvest the gas in gas hydrate. But one thing seems certain: The material will prove difficult to study. Samples brought to the surface melt or evaporate quickly, releasing their gaseous cargo into the atmosphere.
``You have about 20 or 30 minutes to work on it,'' said Keith Kvenvolden, an organic geochemist with the U.S. Geological Survey in Menlo Park, Calif., speaking last month at the annual meeting of the American Association for the Advancement of Science. ``Then all that's left is a few drops of water and a few bubbles of methane.''
Although it looks and feels like everyday ice, gas hydrate is weird. It is a type of crystalline water that forms only in the presence of gas and high pressures. A single microscopic ``cell'' of the material consists of a handful of water molecules whose atoms are interlinked not in the usual hexagonal configuration found in snowflakes and glaciers but rather in an elegant crystalline cage. The most common form, if visible to the naked eye, would look something like a soccer ball made of 12 pentagonal faces, with the edges representing bonds between neighboring hydrogen atoms. Because of the unusual configuration of the water molecules, it melts and freezes at higher temperatures than ordinary ice.
Inside each icy cage is a ``guest molecule'' of gas that can vibrate and rotate freely but is too big to slip through its jailhouse bars. Countless such ice units can build upon each other into immense condo complexes of crystallized water and trapped gas. These formations can stretch for hundreds of miles beneath continental shelves, arctic ice packs and Siberian wastelands at depths ranging from 1,000 to 5,000 feet below the Earth's surface. (Methane, a common waste product of bacterial metabolism, is often abundant in seemingly lifeless environments and is the most common prisoner in naturally occurring gas hydrate.)
Scientists first created gas hydrate around the year 1800 in high-pressure laboratory experiments. For more than a century, it was considered no more than a curiosity - ice that could burn. Only in the 1930s, when natural gas drillers found icy accretions of gas hydrate gradually blocking their pipelines, did scientists learn that the material could form spontaneously in nature and pose an industrial nuisance. In the 1960s, gas hydrate began to generate interest as a potential source of abundant, clean-burning fuel.
Estimates of the world's gas hydrate reserves vary widely. But information gleaned from undersea sediment samples and sonar studies of the sea bottom suggest there are about 10,000 gigatons of carbon stored in gas hydrates, or about twice the amount of carbon believed to exist in all other fossil fuel deposits in the world combined. (A gigaton weighs the same as 200,000,000,000 10-pound bags of charcoal briquettes.)
Some scientists have suggested that gas hydrate mining could prove hazardous to the Earth's health. Undersea images indicate that some continental slope sediments covering gas hydrates are unstable, and mining-induced underwater landslides could expose veins of the material. Such an event, resembling a break in a gas main, could release quantities of methane into the water and air. That's a concern because methane is a potent greenhouse gas, reflecting heat back to the Earth about 10 times more efficiently than carbon dioxide - and the amount of methane stored in gas hydrate is believed to be 3,000 times greater than all the methane in the atmosphere.
Even if gas hydrate is not mined soon, research into its odd molecular structure could pay off in other ways. Some scientists say the atomic ice cages could act as unique chemical sieves for separating large molecules from small ones. Others believe they may offer a new way to desalinate sea water, since salt is naturally excluded from the soccer ball structures.
by CNB