Storing carbon dioxide under NW seafloor proposed
Scientists say a partial solution to global warming may lie beneath the seafloor off the coasts of Washington and Oregon. Researchers envision a system where carbon-dioxide emissions from power plants would be captured, liquefied and pumped into porous basalt layers up to a half-mile below the ocean bottom. That would trap the greenhouse gas with virtually no chance of leaking, they say.
Seattle Times science reporter
Scientists say a partial solution to global warming may lie beneath the seafloor off the coasts of Washington and Oregon.
Deep volcanic rocks could serve as a kind of storage locker for carbon dioxide, trapping the greenhouse gas under great pressure with virtually no chance of leaking back into the atmosphere, says a study published today in the Proceedings of the National Academy of Sciences (PNAS).
Researchers envision a system where carbon-dioxide emissions from power plants would be captured, liquefied and pumped into porous basalt layers up to a half-mile below the ocean bottom. They estimate there's enough suitable rock off the Pacific Northwest to swallow up more than a century's worth of the nation's CO2 output.
"It's hard to deny the size of the prize," said David Goldberg, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory and lead author of the study.
The idea of pumping carbon dioxide underground isn't new. Oil companies have been doing it for years to force the last drops out of wells that are running dry. Scientists and some power companies are exploring ways to adapt the approach, also called sequestration, to create permanent underground storage areas to curb carbon-dioxide emissions and slow global warming. But most of that work has focused on the land, Goldberg said.
Undersea storage has been largely ignored, even though there's much more capacity and repositories would be much less prone to leak, said co-author Taro Takahashi, senior scholar at Lamont-Doherty.
"In principle, the type of reservoir we propose at the ocean floor is one of the safest — if not the safest — way of storing liquefied CO2 for a long, long time," he said.
But some experts fear the costs of collecting, piping and compressing the gas and drilling and servicing the wells could be astronomical.
"If it can't be done economically, it just won't happen," said Pete McGrail, of Pacific Northwest National Laboratory. McGrail is working on a sequestration pilot project in the basalt fields of Eastern Washington.
The proposal also raises questions about possible ecological impacts and seismic hazards. The location the scientists have singled out is on the Juan de Fuca plate, a geologic slab where molten rock oozes onto the seafloor at one margin. The other edge of the plate is being squashed under the continent, setting the stage for major earthquakes.
The scientists say they've mapped out a 30,000-square-mile area that avoids the seismically active regions of the plate. They also would avoid drilling near hydrothermal vents, where giant tube worms and other strange forms of sea life abound, said co-author Angela Slagle, a marine geologist. The wells would be more than 100 miles from the coast.
The Lamont-Doherty team is calling for a test well in the Pacific Northwest, to see if the technology could work.
"This is something that hasn't been done, so while we can make educated guesses about how these trapping mechanisms might work, we won't know until we are able to do some pilot studies," Slagle said.
Undersea basalts can trap and hold carbon dioxide in several different ways, providing multiple layers of protection against leaks, the researchers said.
Under the immense pressure and cold temperatures below the seafloor, carbon dioxide would form a very dense liquid — much heavier than sea water. Gravity would then prevent the liquefied gas from seeping upward, just as it prevents water in a well from flying into the air, said Kurt Zenz House, a Harvard researcher who was one of the first to propose undersea carbon storage.
One of the risks at the Juan de Fuca site is the possibility that magma or other seismic forces could heat the seafloor in some locations, lowering the density of the trapped carbon dioxide and allowing some of it to escape, said House, who was not involved in the PNAS paper.
"Since it's tectonically active, it's hard to know what it will look like a hundred years from now," he said. "It might warm up in spots."
If that happened, Takahashi said, any CO2 that leaked into the deep ocean would react with cold sea water to form an icy slush that wouldn't budge off the ocean floor. A third layer of protection is added by a chemical reaction that occurs between the carbon dioxide and the porous basalt: Over several hundred years, the liquefied gas will essentially solidify into calcium carbonate, the main ingredient in antacid tablets.
Carbon dioxide stored in land-based repositories tends to rise, because it isn't subject to the same cold and pressure found on the sea bottom. That increases the chance of leaks, Takahashi said.
Even though the so-called Cascadia subduction zone at the eastern edge of the Juan de Fuca plate has produced some of the world's most powerful earthquakes and tsunamis, Takahashi said violent shaking wouldn't dislodge carbon dioxide stored under the seafloor. Even if the rocks cracked, a thick covering of mud on the ocean bottom would provide an additional barrier, he said.
Some environmentalists are critical of carbon sequestration, saying it would simply delay the introduction of greener energy alternatives.
But most of those options are still years away, Takahashi said. In the meantime, power plants continue to spew greenhouse gases. More than 150 new power plants, mostly coal-fired, are on the drawing board in the United States alone; the number planned in China and India is much higher.
Undersea storage could provide a valuable stopgap — if it pencils out, Takahashi said.
"Right now we have the technology to drill the holes on the ocean floor and we can inject the CO2. But how much would it cost to do it on an industrial scale? ... That is the million-dollar question."
Sandi Doughton: 206-464-2491 or email@example.com
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