Carbon dioxide stored in underground reservoirs can, due to interaction with host rocks, find multiple ways of escaping, according to research conducted by scientists at Penn State University. Researchers studied the interaction between carbon dioxide-saturated brine and sandstone or limestone. The researchers also considered how the mixture reacted with cement. “If this plume of carbon dioxide-saturated brine reaches an abandoned well, it will react with the cement,” Zuleima Karpyn, associate professor of petroleum and natural gas engineering, said in a press release. “This may open up cracks in the cement depending on the conditions, which would increase the likelihood of carbon dioxide escaping.”
The researchers found that the CO2 brine ate away at limestone, slowly dissolving the rock. However, as the mixture dissolved the limestone, it became less acidic and did little to the cement. The opposite was found true with the sandstone, which stayed more intact but led to greater degradation of the cement. “”In the limestone interactions, the rock itself becomes the dominant medium for the dissolution reaction while the cement was the secondary reactant,” Karpyn said. “This means that wellbores are more likely to stay intact if you have limestone. But dissolving the limestone can create leakage pathways, for example, by forming finger-like channels of dissolved rock.”
The study has been published in the February edition of the International Journal of Greenhouse Gas Control.
