Carbon dioxide injection has been used for years in the oil and natural gas industry to enhance the amount of fuel extracted from underground deposits. Field testing of deep injection as a means of sequestering excess carbon dioxide created when burning fossil fuels, however, is a more recent undertaking, with many projects cropping up only in the last 10 years or so. Regardless of the intended goal, the process is easily understood. The gas is captured, highly pressurized, piped to a site, and then injected deep into the ground or ocean.

An aqueous solution of carbon dioxide at the interface with calcium carbonate. Hydrogen bonds are not visible in this representation.

If injected into porous, isolated rock, the carbon dioxide interacts with whatever minerals are present and may not have a negative environmental impact. If that porous rock happens to be an oil reservoir, the carbon dioxide helps move the oil out the well. When injected into the water of an aquifer or the ocean, the carbon dioxide may simply dissolve into a solution with the water. If the pressure is high enough, the carbon dioxide will take on a "supercritical" liquidlike state, remain separate from the water, and not interact much at all.

"One of carbon dioxide's main sinks is the ocean, anyway—most of it ends up dissolved there as a part of the natural carbon cycle. In a way, sequestration just speeds up that process," says Kirkpatrick. And, according to a 1997 study by the Center for Energy and Environmental Studies at Princeton University, thousands of years of excess carbon dioxide produced by the burning of fossil fuels at the current rate could be managed using aquifer and ocean sequestration.

Clusters of sodium and carbonate ions in aqueous solution.

The overall impact is still uncertain, though.

"Nobody knows these [products of sequestration] and their environments well enough to know which of these approaches might be best," says Kalinichev, a visiting researcher at the U of I and head of the Physical Research Laboratory at the Institute of Experimental Mineralogy in Chernogolovka, Russia.