The long term fate of wells proximal to CO 2 sequestration operations remains poorly understood. To date, experiments have shown that total degradation of well cement is unlikely and that severe, uniform degradation of a conductive pathway can lead to self-healing of a fracture. However these experiments did not carry out the degradation reactions while the (fractured) cement was under mechanical load comparable to subsurface conditions. A new experiment procedure that couples reactive flow through a fracture in cement with confining pressure has shown reaction along well defined flow channels along the fracture face. Injection of acidic (2<pH<3) aqueous solutions yielded effluent pH histories with a characteristic spike of rapid neutralization followed by a slow approach toward inlet pH. In all experiments, the effective hydraulic aperture after acid injection was smaller than the initial hydraulic aperture. This indicates that in a system with a slow leak of brine saturated with CO 2 along a defect in a wellbore, the leakage rate would decrease over time.