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…