Governors' Wind Energy Coalition

Michael Szulczewski, Juanes Research Group, M.I.T.M.I.T. researchers estimated the total potential storage capacity of deep saline aquifers in the United States by analyzing how liquefied carbon dioxide would spread from deep injection wells.

Michael Szulczewski, Juanes Research Group, M.I.T.M.I.T. researchers estimated the total potential storage capacity of deep saline aquifers in the United States by analyzing how liquefied carbon dioxide would spread from deep injection wells.

In a perfect world, greenhouse gas emissions would be on the decline in the near future, with fossil fuels replaced by clean sources of energy like wind and solar. But current emissions are so daunting that the chances of the planet cleaning up its act in a timely manner are slim.

“It’s such a big number that it’s sort of hard to grasp what it means,” said Ruben Juanes, a geoscientist at the Massachusetts Institute of Technology. “With emissions as enormous as they are right now, even if we try to deploy alternate energy technologies as quickly as possible, there’s still going to be a huge source of emissions from fossil fuels that we’d better address.”

So Dr. Juanes proposes a bridge solution — a quick fix for the time being — in the form of carbon capture and storage, or C.C.S. This technology captures carbon dioxide from sources like power plants, converts it into a dense liquid form and then disposes of it deep underground in saline aquifers.

Take a look at a few numbers and you’ll begin to grasp the gravity of the situation. In the United States alone, around 6.5 billion metric tons of carbon dioxide are emitted per year. Of that, maybe a third could be captured from large stationary sources like power plants; let’s round that off to 2 billion metric tons. If converted to liquid, those 2 billion metric tons would amount to 80 million barrels of compressed carbon dioxide produced per day.

To put that figure into perspective, the United States consumes about 20 million barrels of oil per day. And remember, that’s only a third of our daily emissions.

Dr. Juanes and his colleagues are not the first to think of storing emissions underground, but they have cleared up some major unknowns. Past studies varied wildly in their estimates for how long the aquifers could function, from just five years to 20,000 years. “We felt that there was such a big disparity in numbers out there that C.C.S. deserved a closer look,” Dr. Juanes said.

Michael Szulczewski, Juanes Research Group, M.I.T.Using glass beads, researchers simulated the way liquified carbon dioxide would spread through water in the pores of deep rock formations.

The M.I.T. researchers created what they believe to be the first model that takes into account the two major impediments to accurately calculating storage capacity: estimating the aquifer’s volume and the fracturing pressure that may result from injecting carbon dioxide into an aquifer too quickly. The researchers modeled how the carbon dioxide would percolate through the rock and included the rate of injection and details of porous rock absorption characteristics down to the micron scale in their calculations.

“We think that by bringing some more physics into the estimates, we can reduce uncertainty by quite a bit,” Dr. Juanes said.

Their results, published in the Proceedings of the National Academy of Sciences, indicate that if the current emissions trend continues, the United States should be able to store about a century’s worth of carbon dioxide from the nation’s coal-fired power plants. Their model includes more than 20 parameters but is simple enough to assess the storage capacity of a large number of saline aquifers around the country.

The study’s authors say that similar conditions exist around the world, meaning that C.C.S. could be a viable quick fix for the 40 percent of global carbon emissions that come from coal-burning power plants. Countries like Norway and Algeria have already used the technique, and more pilot projects are on the way around the world.

One concern with C.C.S. is whether the buried carbon dioxide would eventually escape to the surface. When liquefied carbon dioxide is dissolved in water, the resulting solution is denser than either of its constituents, so it naturally sinks. The risk of a leak also decreases over time as the liquid carbon dioxide is trapped and dissolved by capillary forces. The researchers say that understanding the geology of an area is crucial to ensuring that the buried carbon dioxide never again reaches the surface, although there is no way to completely avoid this risk at the moment.

Saline aquifers provide ample storage space for liquefied carbon dioxide, but a number of regulatory and policy questions would have to be worked out before the technique was used. The costs of maintaining the system could also be significant, and past analyses indicated C.C.S. could add 15 to 30 percent to the cost of coal-generated electricity.

Dr. Juanes said he believed that undertaking such storage would be in humanity’s best interest, but that the benefits might not be completely realized for hundreds of years. “We all live in four-year cycles, so politically and as a society I’m not sure we’re up to the challenge to really put in place what is needed,” he said.

But he added: “We don’t need all countries to agree. We only need two, China and the U.S., which account for over 50 percent of global emissions.”

Here’s a video in which Dr. Juanes explains his research effort.