Burying carbon dioxide might be the best way to keep it out of the atmosphere.
Thu, Apr 16, 2009 at 03:20 PM
In the Illinois basin, an oil field is nearly dry. For more than 65 years companies have drilled there for black gold. Harvesting the last remnants requires more work and money for a smaller reward, and in mid-March drillers went after the last drops, using the time-tested method of forcing carbon dioxide into the ground to remove the remaining oil.
But there was something unusual about this effort. For one, it was conducted by scientists from the Department of Energy, not oil industry workers. And while one of the goals was to get oil, the project’s primary aim was to test a possible way to get rid of carbon dioxide: by storing it underground indefinitely.
Injecting compressed carbon dioxide, which is a liquid, into depleted oil reservoirs is nothing new; the oil industry has been doing it for over 30 years to increase production. But as greenhouse gas levels rise, some environmentalists hope that instead of releasing sequestered carbon back into the atmosphere, we’ll be able to keep it underground—for good.
“If we don’t do these injections,” says George Peridas, a scientist at the National Resources Defense Council, “we think that what these emissions will do to the climate [will be] much greater.”
The Illinois basin project is administered by the Midwest Geological Sequestration Consortium, one of seven regional partnerships overseen by the Energy Department across the United States. Right now, the Midwest region’s 126 coal-fired power plants contribute 296 million metric tons of carbon dioxide to the atmosphere annually.
The field tests in Illinois used the “huff-n-puff” approach: researchers injected—or huffed—45 tons of compressed CO2 through porous rock into the oil reservoir. Kept underground by an overlying impermeable rock, the CO2 dissolved into the oil, which becomes less sticky and easier to sweep out of the ground. When they started up the pumps again, about a week later, the group measured the amount of oil forced out—or puffed. Researchers are analyzing the results now, but early results showed that oil production increased by as much as four times.
When it comes to the viability carbon sequestration in depleted oil reservoirs, scientists are still in the early stages of testing the process. For now, they’re focused on measuring exactly how much CO2 ground can hold, which some estimate is about 40 percent of what is injected.
“We’re doing this to verify that the CO2 is going to do what we’re thinking it’s going to do,” says Dawn Deel, project manager in the carbon sequestration program for the Energy Department. Oil recovery could also help offset the costs of the carbon dioxide and sequestration.
But depleted oil reserves are not the only place to bury CO2, and they might not be the best. Today, the US contributes 3.2 billion metric tons, or gigatons, of carbon dioxide to the atmosphere each year, according to the Energy Information Association. Depleted oil and gas reservoirs nationwide might hold as much as 80 gigatons of carbon dioxide, whereas saline formations, or deep saltwater pools that are widespread throughout most of the country, might be able to sequester 3,200 gigatons of carbon dioxide, according to Sean Plasynski of the Energy Department.
“I think that we can identify enough good sites were CO2 will stay underground and it will do what we expect it to do, which is to basically be permanently sequestered,” says Sallie Benson, the executive director of the Global Climate and Energy Project at Stanford University. “I think we can find enough sites so that it’s definitely worth getting started and it’s much better than just continuing to put CO2 in the atmosphere.”
The Midwest Consortium plans to conduct additional field tests in the coming years, including some on saline formations, says Sallie Greenberg, a spokesperson for the Midwest Geological Sequestration Consortium.
Until then, the regional partnerships will keep crunching numbers to analyze the sequestration potential of various geological formations below the surface, says Deel: “Right now our research is focused on making sure that the carbon dioxide stays in the ground.”
As scientists continue to test sequestration technologies, some power plants may be able to capture and bury their carbon dioxide emissions sooner rather than later. Today, energy companies in the US don’t have an incentive to incorporate those technologies into their operations, but regulations might force them to in the future. “They are becoming concerned about things that might come down the line,” says Plasynski.
Story by Susan Cosier. This article originally appeared in Plenty in May 2007.