A new energy frontier?
Posted: Thursday, August 20, 2009 6:46 PM by Alan Boyle
USGS |
Gas hydrates are
deposits of ice that
contain natural gas.
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Energy experts say vast undersea reserves of natural gas hydrates may be more accessible than previously thought, potentially offering an important stopgap in the coming energy transition.
But unless the transition is handled adroitly, gas hydrates could set off a vicious circle of global warming - and there are already signs that the situation is heating up.
The promise of gas hydrates is highlighted this week in the journal Science: Ray Boswell, a researcher at the National Energy Technology Laboratory, recaps a string of pilot projects aimed at assessing what it would take to harvest undersea gas hydrates.
Gas hydrate deposits are a big deal because they are so widespread, and yet so mysterious: These undersea deposits form from methane and water at low temperatures and moderate pressures. The methane molecules are trapped within lattices of water molecules, but they can be released by raising the temperature or lowering the pressure.
Boswell cites estimates suggesting that 20 quadrillion cubic meters of methane could be trapped within global deposits. If all that methane could be extracted, it would provide enough natural gas to supply the United States at current levels for more than 30,000 years.
That's an impossibly big "if," however. First of all, the vast majority of those deposits are either widely dispersed in mud or piled up in mounds on the deep-ocean floor. Getting at those deposits would be an expensive, ugly proposition with potentially catastrophic environmental consequences (more about that in just a bit).
Success in sand?
In recent years, gas hydrates have been found in more accessible settings, such as sandy deposits off the coast of Alaska and in the northern Gulf of Mexico. Sand reservoirs of gas hydrates also have been identified off the shores of southeastern Japan and Canada's Northwest Territories. Gas hydrate reserves have also been found in offshore clay sediments near India and Korea.
USGS via TAMU |
On the molecular level, gas hydrates consist of methane molecules (CH4, green and gray) embedded in lattices of water molecules (H2O, red and white).
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Drilling tests have suggested that extracting the methane from the sandy deposits could become commercially feasible, Boswell said. One method calls for reducing the pressure in the well bore, liberating the methane gas from the water. Another method involves injecting carbon dioxide to displace the methane from cavities in the deposits. The second method has the added benefit of locking up CO2, which could address climate change.
"Initial studies of these two approaches have been encouraging, but extended production tests of both methods are needed," Boswell wrote. "Such testing, currently in the planning stages for sites in Alaska, will be needed to help prepare for marine production tests, which are still several years away."
In a follow-up e-mail exchange, Boswell acknowledged that gas extraction wasn't a slam-dunk: "What can be done/accomplished, by when, is a function of many things: budgets, the continued interest of our industry collaborators, research findings going forward in the U.S. and internationally." He said the stated goal was to resolve the questions about commercial production from gas hydrates by 2015 for the Arctic, and by 2025 for the Gulf of Mexico.
A whiff of environmental worry
One of the big questions has to do with how harvesting gas hydrates would affect climate change. Methane is a far more potent greenhouse gas than carbon dioxide, and for a long time, researchers have wondered whether the release of undersea methane could kick off a runaway global-warming effect.
Here's how the scenario is set out: Warming oceans cause a thaw in gas hydrate deposits, which liberates methane, which adds to the greenhouse effect, which warms the oceans, which adds to the gas hydrate thaw, which ... well, you see where this is going.
The "methane apocalypse" often comes up in discussions of past extinctions or science-fiction tales (such as "The Mother of Storms," a past pick in the Cosmic Log Used Book Club). There's even a USGS Web page addressing concerns that gas hydrates are to blame for the Bermuda Triangle.
But you don't have to turn to science fiction or the fossil record to pick up on the concerns about gas hydrates. This month, Geophysical Research Letters published a study finding that an Arctic sea-temperature rise of 1.8 degrees Fahrenheit (1 degree Celsius) has coincided with heightened release of methane from the sea's depths.
"Our survey was designed to work out how much methane might be released by future ocean warming; we did not expect to discover such strong evidence that this process has already started," the University of Southampton's Tim Minshull said in a news release from Britain's National Oceanography Center.
And the world's oceans are continuing to warm, according to the latest statistics.
Joseph Romm, who has been following the gas hydrate issue at the ClimateProgress blog for the Center for American Progress, told me "there's no question that it is a potentially large resource - and it also is a potentially dangerous climate feedback."
This month's study highlighted a "very serious" concern, he said.
"Before any country were to engage in large-scale attempts to harness this, some scientific body should study the matter and render some advice," Romm said. In addition to the greenhouse-gas concern, "methane in the water is dangerous to sea life," he noted. (Unless you're talking about methane-eating bacteria, of course.)
Romm said the worst thing energy prospectors could do would be to mine gas hydrates using "some sort of bulldozer approach," without regard for the consequences.
I have a feeling Boswell would agree with that.
"Our goal is to provide another option for society to have available to help us deal with future energy demands," Boswell told me in our e-mail exchange. "We will as a nation need to weigh all sorts of issues in making these choices. Our program is designed to provide the relevant information so that those decisions are as informed as possible. This includes numerous projects we have to understand gas hydrates' role in the environment, in carbon cycling, in past climates, and in potential response to changing climates going forward."
What do you think? Will gas hydrates help us get by while we make the transition to alternative energy sources such as wind power, solar power and biofuels of all sorts (plus nuclear power)? Or does all this talk about a methane apocalypse scare you off? Feel free to weigh in with your comments below.
Update for 9:45 p.m. ET: Tim Collett, a researcher at the U.S. Geological Survey focusing on gas hydrate projects, told me that the Japanese are "by far the most motivated" to move forward with methane. They're planning to begin a test production project in the Nankai Trough in 2012, he said.
Collett stressed that the kinds of gas hydrate deposits currently under consideration are not the kinds that pose the greatest hazard for excess methane release. "The hydrates we think of for production issues are really deeply buried," he said.
Nevertheless, researchers are always mindful of methane's potential downside as well as the potential upside. "The hazard assessment with this type of hydrate occurrence is probably manageable, but the issues have to be considered in every case," Collett told me.
More on methane power:
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