Study on Corrosion Rate of Cement Monomineralic C₂S in CO₂ Geological Sequestration Environment

In geological sequestration and application of CO₂, the cement used in well cementing is easy to react with CO₂, an acidic gas produced downhole, causing the set cement for well cementing to be corroded and the mechanical properties of the set cement decline remarkably. Presently, the corrosion rate of the set cement monomineralic C₂S in CO₂ geological sequestration and application environment is still not clearly understood. In this study, several measuring methods, such as SEM, XRD and TG etc., are used to quantitatively analyze the changes of the corrosion products of C₂S. The yield coefficient α of the corrosion product CaCO₃ can be obtained by fitting the molar yield rate of the corrosion product CaCO₃ with the non-steady state diffusion permeation model. The SEM experimental results show that after the corrosion reaction, the surfaces of the C₂S cement monomineralic particles have undergone great changes, producing part of the corrosion product CaCO₃; The XRD experimental results show that crystal forms of the corrosion product CaCO₃ of the monomineralic C₂S are mainly calcite and aragonite. The TG experimental results show that the amount of the corrosion products increases with the corrosion time of the C₂S cement monomineral. The fitting results indicate that the yield rate of the corrosion products of C₂S increases with temperature, at 90 ℃ the yield rate of the corrosion product CaCO₃ has a maximum yield coefficient α of 54.90.