National Geographic : 2014 Apr
or at any of the handful of other large storage sites around the world. Scientists consider the risk of a catastrophic leak to be extremely low. They worry more about smaller, chronic leaks that would defeat the purpose of the enterprise. Geophysicists Mark Zoback and Steven Gore- lick of Stanford University argue that at sites where the rock is brittle and faulted—most sites, in their view—the injection of carbon dioxide might trigger small earthquakes that, even if otherwise harmless, might crack the overlying shale and allow CO2 to leak. Zoback and Gore- lick consider carbon storage “an extremely ex- pensive and risky strategy.” But even they agree that carbon can be stored effectively at some sites—such as the Sleipner gas field in the North Sea, where for the past 17 years the Norwegian oil company Statoil has been injecting about a million tons of CO2 a year into a brine-saturated sandstone layer half a mile below the seabed. That formation has so much room that all that co2 emitted by fossil fuels, 2011 of global fossil fuel co2 comes from burning natural gas, mostly for heat and electricity. Venting co2 from a smokestack is usually free, like littering. capturing and storing co2 underground would cost up to a quarter of a power plant’s energy—and a lot of money. It won’t become the norm unless governments make it happen. carbon capture and storage (ccs) disposing of waste co2 ART: ÁlVARo VAlIño SoURceS: HoWARd HeRzog, MIT; U.S. eneRgy InFoRMATIon AdMInISTRATIon capture co2 is separated from other stack gases and com- pressed into a liquid-like state. This is the most costly step in ccS. the four steps of capturing and storing carbon dioxide transport Fluid co2 is moved to a storage reser- voir. Pipelines are the most efficient carrier, but trucks, trains, and ships can do the job. injection co2 is injected deep underground into a porous formation— an old oil field, say, or a saline aquifer— under a cap rock that deters leaks. Monitoring The reservoir must be watched in perpetuity for leaks. even slow ones could defeat the purpose of prevent- ing climate change. 21% Underground formations could hold 1,000 years’ worth of emissions.