Leakage of CO₂ through abandoned wells: Role of corrosion of cement

The potential leakage of CO₂ from a geological storage site through existing wells represents a major concern. An analysis of well distribution in the Viking Formation in the Alberta basin, a mature sedimentary basin representative for North American basins, shows that a CO₂ plume and/or acidified brine may encounter up to several hundred wells. If carbon dioxide is geologically stored in regions, such as this, that have experienced intensive exploration for petroleum products, the acidified brine will come into contact with numerous abandoned wells. Corrosion of the cement that seals the well could lead to rapid leakage, so it is essential to determine the duration and intensity of exposure to the acid. Detailed numerical simulations with Dynaflow, incorporating a flash calculation to find the phase distribution and speciation in the brine, indicate that the carbonated brine may spend years in contact with the cement in abandoned wells. Preliminary results from an ongoing experimental study of cement corrosion indicate that the rate of attack is rapid, when the pH of the solution is low, so the risk of leakage will be high if the acidic brine can flow through an annulus and bring fresh acid into contact with the cement.