Capturing greenhouse gases with sandstone, water

Capturing carbon dioxide as it comes out of smokestacks is easy, say scientists. The tough part is sequestering the gas underground so it won't leak out. A big burp could wipe out people living nearby (through suffocation) while a slow leak would put the gas back up in the atmosphere where it would contribute to global warming.

Researchers at MIT have come up with a novel idea that would effectively take advantage of the nearly ubiquitous presence of salt water under the earth's surface.

Under the proposal, CO2 would be captured, compressed and then injected underground into porous rock like sandstone or limestone. The gases would permeate the porous rock and be chased by underground salt water. The salt water and CO2 would then juggle for position in the rock's crevasses. Salt water adheres to rock, which would constrict the pores in the rock.

Eventually, the CO2 would be diffused into tiny blobs or bubbles, which would remain trapped in the pores. Details of the concept are featured in a paper published in a recent issue of Water -Resources Research by MIT Professor Ruben Juanes.

Some have proposed sticking the gas in depleted oil wells surrounded by sensors. In the event of a leak, the sensors would sound an alarm so that residents could evacuate. The danger of a quick release of gases, or an earthquake, is problems with this concept.

Research has also begun to see if CO2 can somehow be liquefied or turned into a solid and stored underground. The problem there is how do you turn the gas into a liquid or solid without consuming energy and thus producing more CO2 in the process.