Peridotite rocks show new promise for storing CO2
10.1021/es803498g
2009 American Chemical Society
Published on Web 01/07/2009
rock’s permeability will evolvesjust the kinds of issues that are in this [new] paper, such as clogging,” Kelemen says. Most CO2 storage research is focused on shallower geological reservoirs such as sedimentary deposits or saline aquifers. These approaches rely mainly on dissolving CO2 in liquid or in pore space. “The problem with those systems is that if any CO2 leaks, it can go back into the atmosphere,” Andreani says. Turning the gas into a solid prevents leakage. A single power plant can generate millions of tons of CO2 per year, so the geological capacity needed to offset emissions globally could be in the billions of tons. According to the U.S. Department of Energy, the U.S. has the capacity to to store all of the CO2 generated by its own coal-burning power plants for more than 1000 years at current production rates, not counting peridotite formations. However, storage capacity is not evenly distributed globally. Storing CO2 in peridotite “is less well understood right now than carbon storage in abandoned oil fields or saline aquifers,” says Sarah Forbes, an expert on carbon storage at the World Resources Institute, a nonprofit research group. “It’s easy to poke holes at new ideas, but we need to explore even the niche opportunities in order to ultimately solve the climate problem,” she says. Next, Andreani’s team plans to run their experiment for several months to see how much carbon they can store. —ERIKA ENGELHAUPT MURIEL ANDREANI
ate formation after 8 hours and said, There’s a new rock star on the cli‘Wow, what will happen after a mate scene. Scientists recently promonth?’” posed locking away massive The key to preventing clogs is to amounts of CO2 in peridotite, the find the right injection conditions, most common rock in the earth’s Andreani says. The team found that mantle. The idea has been garnering small variations and branching patattention, and now experimental reterns in the rock’s structure allowed sults published in ES&T (DOI 10.1021/es8018429) support the notion that it could actually work. Geologists have long known that peridotite reacts with CO2 to form solid carbonates such as limestone. But harnessing peridotite’s CO2-trapping power has been an elusive goal, because the rocks are usually found more than 12 miles deep. The new research suggests that CO2 could be successfully injected directly into rock formations under the right conditions, says the study’s lead author, geologist Peridotite rocks may be valuable CO2 trappers, thanks Muriel Andreani of Univertheir ability to turn the gas into solid carbonate. site´ Montpellier 2, now at Universite´ Claude Bernard CO2 to continue flowing through Lyon 1 (both in France). Previously, scientists have studied some parts of the rock while still fillthe possibility of mining peridotite ing in crevices with carbonates. and grinding it into a powder that However, the flow rate must be could be used as a CO2 sponge, but finely calibratedsnot too fast and not too slowsto keep the process that would create big transportation, going. waste, and energy problems, AnAs much as 4 billion tons of CO2 dreani says. More recently, researchers suggested that CO2 could be could be permanently stored in pericaptured from power plants and dotite formations that cover half of other sources and then pumped the country of Oman, located on the down boreholes into peridotite forArabian Peninsula, and that occur in mations. But they feared that as carother scattered locations worldwide, bonates form, the tiny pore spaces in according to recent estimates by Cothe rock might clog and shut down lumbia University researchers who the process, a common problem published their findings in the Prowith this type of injection system. ceedings of the National Academy of Andreani’s team created a smallSciences U.S.A. (2008, 105, 17,295scale experimental injection system 17,300). to pump CO2 and water into a That study, by Peter Kelemen and colleagues, estimated the storage cachunk of peridotite and then used pacity of peridotite on the basis of its electron microscopes to look at geological extent and the age of where carbonate formed. “We were natural carbonate veins. However, very surprised to see that the reac“an important caveat in our paper tion is quite fast,” Andreani says. was that we don’t know how the “We realized we already had carbon-
February 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 973
