November 14, 1998 The Ice that Burns
Can methane hydrates fuel the 21st century?
By RICHARD MONASTERSKY
In October of next year, the Japan National Oil Corp. will send a ship to a spot about 60 kilometers off a cape called Omae zaki, not far from Mount Fuji. Its crew will lower a drill through 950 meters of water and then start cutting a circular hole the width of a dinner plate into the seafloor. At first, the bit will slice through fine silt as soft as birthday cake. Then, at a depth not yet known, the diamond-tipped drill will breach a hard icelike layer and, in the process, reach into the postpetroleum future.
The frozen substance is called methane hydrate, a name that has been increasingly echoing off the walls of Congress, university research offices, and oil company conference rooms around the world. Found under the ocean floor and polar permafrost, methane hydrates are a crystalline combination of natural gas and water, locked together into a substance that looks remarkably like ice but burns if ignited. Until recently, the natural gas industry considered it only a nuisance, something that occasionally plugs up pipelines. Now, some scientists view methane hydrates as the resource that may power the 21st century, and governments are scrambling to explore its promise.
"Methane hydrates are a potentially enormous natural gas resource," declared a U.S. presidential commission last year in its report on future energy research. "It may be that [natural] gas can be produced economically from the methane hydrates on the continental shelf, and this may prove to be a very large new source globally, particularly for some developing countries such as India as well as for the United States," concludes the report.
With some geologists predicting that oil supplies will tighten in the next 15 years (SN: 10/31/98, p. 278), the prospect of vast new fossil fuel deposits has fired the imagination of energy experts. According to some estimates, the energy locked within methane hydrates amounts to more than twice the global reserves of all conventional gas, oil, and coal deposits combined (SN: 11/9/96, p. 298). The U.S. Geological Survey (USGS) estimates that the methane hydrates hidden beneath U.S. waters alone hold some 200 trillion cubic feet of natural gas, enough to supply all the nations energy needs for more than 2,000 years at current rates of use.
Lured by such a vast resource, Congress is currently considering a bill that would establish a national methane hydrates research program. At the same time, the U.S. Department of Energy is proposing a plan aimed at making it possible to extract methane commercially from hydrates in less than 20 years. Canada, India, Korea, and Norway have all joined Japan by initiating their own hydrates research programs.
Such hopes may be little more than drill-pipe dreams, though. At this point, no company or government has demonstrated how to pull natural gas out of methane hydrates deposits without pouring a tremendous amount of money down the borehole.
"The bottom line is there is a lot of gas hydrate. Theres probably more gas hydrate than all other resources. But because we have no sense of how much gas hydrate is actually recoverable, we have to be careful," says Timothy S. Collett, a geologist who studies methane hydrates at the USGS in Denver. "It may be totally irrelevant to any resource issue," he says.
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Japan has taken the lead on methane hydrates exploration because its geologic heritage has left it with few options. "We dont have many energy resources near Japan, so we mainly import oil and gas from foreign countries," explains Arata Nakamura, assistant project director at the Japan National Oil Corp. (JNOC), a quasi-governmental company headquartered in Tokyo. "JNOC is very interested in conducting research to develop methane hydrates," he says.
Just how deep that interest runs is a matter of some secrecy. Like other oil and gas companies, JNOC considers many exploration issues proprietary. In 1994, Japans Ministry of International Trade and Industry established a 5-year methane hydrates research plan, culminating in the offshore-drilling project slated for next year. Nakamura declined to specify exactly how much the plan will cost but said it will total more than $60 million.
In a preview of next years program, JNOC funded a drilling operation in February and March of this year at an inland site in the Mackenzie Delta of northwest Canada. Working with the Geological Survey of Canada, a Japanese team bored a well 1,150 m deep into the Arctic permafrost, where methane hydrates are common.
Using a hollow drill, they pulled up cores of sandy sediment that formed the ocean bottom many millennia ago. This once-soft sand was as solid as concrete. In places, methane hydrates filled almost all the space between the sand grains, cementing the sediment into frozen layers located between 900 m and 1,100 m below the surface.
The main purpose in drilling the well, called Mallik 2L-38, was to measure how much hydrates hide in the sediments, says Scott Dallimore of the Geological Survey of Canada in Ottawa, who coordinated the scientific research at Mallik. "Methane hydrates occur in very high concentrations in the Mallik well, much higher [concentrations] than have been observed anywhere else," he says.
In sand, explains Dallimore, the grains occupy only about 65 percent of the total space, leaving a network of pores that take up the rest of the volume, much like the gaps between the nuts in a jar of cashews. At Mallik, methane hydrates fill 55 percent of the pore space surrounding the sand grains. So, roughly 20 percent of each coreful of the cemented sand was methane hydrates. That percentage exceeds the concentration found even in the richest known deposits under the seafloor, says Dallimore.
The Japanese team chose to drill onshore at Mallik because it is easier to work on land than under the ocean. When it comes to searching for domestic methane hydrates, however, JNOC must move underwater. Japan has no permafrost of its own.
The lair of most methane hydrates lies far from shore and deep below the waves. There, in water depths of at least 600 to 800 m, low temperatures and extreme pressures in the sediments combine to squeeze methane and water into a crystalline structure. Each molecule of methane gets trapped within a cagelike lattice of frozen water molecules, an arrangement that greatly concentrates a large amount of methane into a small space. Hydrates also go by the name of clathrates, a term derived from the Latin word for lattice.
The methane in most hydrate deposits originally comes from bacteria living beneath the seafloor. As they consume bits of plant and animal remains in the sediment, the bacteria excrete methane, a process still going on today. "Its the same thing as swamp gas or sewer gas," says Roy D. Hyndman of the Geological Survey of Canada in Sidney, British Columbia. When conditions are cold and the pressure is high, the bacterial gas gets locked up into hydrates.
In some deposits, the source of the gas lies much deeper, in sediments warmed by Earths internal heat. Several kilometers below the seafloor, the temperature in the sediment rises so high that it cooks the buried organic debris. This slow simmer produces petroleum and hydrocarbon gases, which leak upward toward the seafloor. As the gases reach cooler sediments, they can form hydrates containing a mixture of hydrocarbons.
Or so the theory goes. Methane hydrates lie so deep beneath Earths surface that geologists are uncertain about even the most basic details concerning the deposits. "We have to understand where they occur and why they occur," says Collett. The Energy Department, in its plan for a 10-year research program, puts the top priority on resource characterizationin other words, determining how much is out there and how to locate the richest deposits.
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The same methane locked up in hydrates also comes out of the rear ends of cows and sheep, but the gas industry is not bursting down barn doors to collect the flatus of farm animals. Each animal produces only a little methane, and companies would go bankrupt trying to collect sizable quantities of gas. Likewise, most methane hydrate deposits are probably uneconomical because the gas is not concentrated in large-enough amounts, says Arthur H. Johnson, a geologist with Chevron USA Production Co. in New Orleans.
"While the published estimates of methane hydrate abundance are enormous, it is likely that most of the hydrate occurs in low concentrations and has no commercial potential. Our goal is to be able to find locations where the methane hydrates are sufficiently concentrated to warrant commercial production," Johnson testified at a hearing of the House Energy and Environment Subcommittee in September.
To spot underwater hydrate deposits, geologists rely principally on a technique routinely used by companies searching for petroleum. Blasts set off near the ocean surface send out sound waves that reflect off deep geologic structures and then return to the ocean surface, where they are recorded.
This process, called seismic reflection profiling, sometimes picks up a distinct band in the sediments that parallels the contour of the seafloor. Geologists call these "bottom simulating reflectors." The band marks the bottom of a hydrate deposit, where bubbles of methane gas in the sediment have become trapped below the impermeable frozen layer.
A related technique spots hydrates by estimating the speed of the sound waves as they penetrate the seafloor. In places where hydrates have stiffened up the otherwise soft sediment, sound travels much faster, says Hyndman. He and his colleagues at the Geological Survey of Canada recently used these techniques to pinpoint the potential locations of hydrate deposits off the coast of India.
People in both India and Japan pay three to four times as much for natural gas as do consumers in the United States. The steep price provides an incentive for these countries to pursue methane hydrates, whereas countries with domestic sources of hydrocarbons currently find hydrates far too expensive to seek.
In next years drilling, Japan plans primarily to extract cores of methane hydrate, which will help in assessing the richness of the deposit, according to Nakamura. The company says it does not intend to "produce" the hydrate, a term engineers use to mean pulling commercial quantities out of the ground.
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Nonetheless, U.S. geologists believe that Japan is taking steps toward that goal. At a meeting last year in England, a JNOC official said that after next years drilling, the company hopes to take the commercially significant
step of classifying some of the hydrate resource as energy reserves, says Michael D. Max, a geologist with the Naval Research Laboratory in Washington, D.C. "What that means is [the resource] changes from a possibility to a certainty. That means they would be able to put some recovery numbers on it, and they can start looking at the commerciality and the costs," says Max.
Right now, the costs of producing methane hydrates remain a big question mark because nobody has tried to extract this resource, with the possible exception of the operators of a controversial well in Siberia. Solid hydrates wont come out of the ground as easily as oil and so-called conventional gas, which can flow through rock pores and then up through the drill pipe.
One way to pry hydrates loose would be to release some pressure on the deposit, which would cause the methane and water to split apart, or dissociate. The advantage of this technique is that it would be relatively cheap, says Collett. To relieve pressure, a drill crew could tap the methane gas that often accumulates underneath and pushes up on the deposit. Unfortunately, this process might work too slowly, he says. As hydrates dissociate, they cool down, which stabilizes them and prevents more hydrate from melting.
To speed up the process, crews could drill far below the methane hydrates and pump hot water upward into the deposit, thereby melting the hydrates. Or, they could inject antifreeze from the surface to spur dissociation. "But when you look at the total balance sheet of the issue," says Collett, "the minute you start looking at enhanced techniques, youre putting energy and money into the project, and gas is not a real expensive commodity. So, you end up with the problem that youre putting more money in than youre going to get out in the form of gas."
Even though hydrates remain uneconomical at present, U.S. policy makers see other reasons for researching these deposits. Oil-drilling operations in the Gulf of Mexico are now moving into water more than 1,000 m deep and are starting to drill through methane hydrate layers more frequently, raising safety concerns. A drill spinning through the hydrate can cause it to dissociate, and each liter of melted hydrate releases 160 liters of gas, says Robert S. Kripowicz, acting assistant secretary for fossil energy at the U.S. Department of Energy.
The freed gas can explode out of the hole, causing the drilling crews to lose control of the well, a costly problem to solve.
"Offshore operators are increasingly reporting problems of drilling through hydrates," Kripowicz told the House energy subcommittee.
Engineers are exploring whether unstable hydrate layers could give way beneath oil platforms or even play a role in triggering tsunamis (SN: 10/3/98, p. 221). Climate researchers have also grown concerned about hydrates because global warming could melt some shallow methane deposits, releasing millions of tons of this potent greenhouse gas into the air.
With so little known about methane hydrates, energy experts say that it is hard to predict whether society will ever tap into these deposits as a fuel source. Still, the Japanese initiative has spurred other oil companies to take an active interest. At a meeting last month in Chiba City, Japan, a group from Shell International Exploration and Production, B.V., discussed its analysis of exploiting methane hydrates. "Our consensus is there are no show stoppers. There is nothing that we cannot handle technically. If we encountered a good accumulation of natural gas hydrates, we could develop it with the existing technology," says Wim J. A. Swinkels, a member of Shells gas hydrate team. The only issue standing in the way right now, he says, is economics.
Yet, the days of plentiful oil and gas are numbered, and countries will require new energy sources to keep the wheels of progress spinning. "Were enjoying a wonderful economy right now, largely because of the very low cost of energy," said Rep. Vernon J. Ehlers (R-Mich.) at the recent hearing on methane hydrates. "Im very worried about whats going to happen when the cheap oil is gone, and were not paying enough attention to it."
From Science News, Vol. 154, No. 20, November 14, 1998, p. 312. Copyright Ó 1998 by Science Service.
The Department of Energy proposal for a methane hydrate research program is available at http://www.fe.doe.gov.
Monastersky, R. 1998. Geologists anticipate an oil crisis soon. Science News 154(Oct. 31):278.
______. 1998. Waves of death. Science News 154(Oct. 3):221.
______. 1996. The mother lode of natural gas. Science News 150(Nov. 9):298.
Information on drilling in the Mackenzie Delta is available at http://sts.gsc.nrcan.gc.ca/page1/hydrat/content.html.
The Natural Gas Supply Association has a Web site devoted to methane hydrates at www.hydrates.org.
Timothy S. Collett
Denver Federal Center
Box 25046, Mailstop Code 939
Denver, CO 80225-0046
Geological Survey of Canada
401 Lebreton Street
ttawa, Ontario K1A 0E8
copyright 1998 ScienceService