Carbon dioxide's great underground escape in doubt

LOCKING carbon dioxide underground sounds like a neat way of getting rid of it - but not if it eventually leaks out again.
In October 2004 experimental CO2 injection began at the Frio formation, an old brine-filled oil reservoir on the Texas Gulf Coast. Yousif Kharaka from the US Geological Survey in Menlo Park, California, and colleagues collected fluid and gas samples before injection began, and at regular intervals afterwards. More recent samples suggest that minerals in the rock walls, including carbonate, are being dissolved by the mixture of CO2 and saltwater in the reservoir.
If enough carbonate is dissolved this could create tunnels in the rock through which the CO2 gas may seep out into the atmosphere again (Geology, vol 34, p 577).
While this hasn't happened yet at Frio, Kharaka says that it could be a problem at other sites, particularly where existing cracks in the rocks are filled with carbonate-rich minerals. If organic compounds and trace metals dissolved in the brine also leak out, they could contaminate groundwater, Kharaka says.
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From issue 2560 of New Scientist magazine, 18 July 2006, page 19