Corrosion Evolution of a Concrete/Casing Steel in Simulated Formation Water under Different CO2 Partial Pressures

The corrosion behavior, mechanical properties, and microstructural evolution of a concrete/P110 casing steel system were studied in a simulated, CO2-saturated formation water under different CO2 partial pressures. It has been found that the corrosion and mechanical properties of the cement and the cement/casing interface were affected by both cement hydration and CO2 corrosion, making the performance of the cement matrix and the interfacial transition zone improve initially and then deteriorate with time. The corrosion resistance of the casing steel reduced with increasing the immersion time and CO2 pressure. The degradation of cement and cement/casing interface was aggravated under the high CO2 pressure, which assisted the formation of a defected corrosion product layer (predominantly FexCa1-xCO3) and led to severer corrosion on the casing steel surface.