In the last several decades, hundreds of projects have successfully transported the CO2 into the reservoir underground. After the injection underground, the CO2 gas is potentially move upward or sideways due to the unbalanced pressure in the subsurface. CO2 may leak from the interface of different materials, such as the interface of steel casing and cement, the interface between steel casing and cement plug, the voids inside the cement, the crack of steel casing, the crack of cement, and the interface of rock and cement. This dissertation presents different methodologies to analyze the potential reasons of leakages and further find a solution on how to repair the leakages. Due to the harsh underground environment, especially high concentration of CO2 and chloride, distressing and fracturing occurs in the hardened cement which could cause the severe cracks and further leading to the leakages of storage CO2 . The chloride-induced corrosion and carbonation effect are the two main effects to deteriorate the mechanical properties of the oil well cement. The modeling works are adopted for simulating the chloride-induced corrosion and carbonation effect. After the reason analysis, the experimental program is conducted to inject nanoparticles into the oil well cement. Several beneficial nanoparticles can be injected into the cement not only to repair wellbore leakages but also to extract harmful ions for the cement simultaneously. Injection is done using the electro-migration method. In the last step, a simulation work is presented for the effectiveness of nanoparticles injected into the cementitious material. The general framework of numerical modeling is developed to describe the proposed electrochemical injection technology. A model for nanoparticle injection is developed first, in which an externally applied current on the system is characterized. Based on this general framework, the chloride removal is included, which means this process can not only repair the leakage and cracks, but also remove the harmful ions from the well cement.</p
