Huerta, N.J., S.L. Bryant, B.R. Strazisar and et al., “Dynamic Alteration along a Fractured Cement/Cement Interface: Implications for Long-Term Leakage Risk along a Well with an Annulus Defect”, Energy Procedia, Vol. 4, pp. 5398-5405, 2011.
The long term fate of wells proximal to CO2 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 CO2 along a defect in a wellbore, the leakage rate would decrease over time.
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