The Role of MgO as Swelling Cements Admixtures under CO₂ Attack on API Class-G Cement

API Class-G Portland cement commonly put in as zonal isolation material in oil and/or gas well. Corrosion against the well zonal isolation material could lead to potential leakage of formation fluid such oil, gas, or water. It is widely known that ordinary Portland cement is thermodinamically unstable in CO₂ rich environment, which can be found in the CO₂ geological sequestration. CO₂ attack on API Class-G cement had been observed through experiments that simulate the down hole condition of Geological Sequestration of CO₂. Some of the experiment reveal the detrimental effect of CO₂ such as increase of porosity and permeability of cement sheath corroded by CO₂ attack. The degradation of API Class-G cement by CO₂ involves emergence and crystallization of CaCO₃ from Ca(OH)₂ which is formed during hydration of cement. In this experiment, we examine the role of addition of MgO swelling cement by weight fraction to mitigate the corrosion caused by CO₂ against downhole hardened API Class-G cement thus inhibits the occurrence of leakage path of CO₂. Observation for characterization and analysis by XRD, optical microscope, and cement paste uniaxial volumetric expansion presented in this paper. The conclusion will provide insights into design of carbonation resistant cement slurries using swelling cements admixtures.