An investigation into CO₂-brine-cement-caprock interactions for wellbore integrity in CO₂ geological storage

Geological storage in saline aquifers and depleted oil and gas reservoirs can help mitigate CO₂ emissions. However, CO₂ leakage over a long period remains a major concern. Poorly cemented borehole and cement degradation after CO₂ injection can provide pathways for CO₂ leakage to groundwater and the atmosphere. Accordingly, it is critical to thoroughly understand the interactions between CO₂-brine and cement caprock/reservoir rock to assess the possible risk of CO₂ leakage. In this work, we performed a series of experiments simulating deep wellbore environments in order to investigate the alteration of chemical,
physical and mechanical properties of cement and rock. Here, we present the characterisation of composite cement-caprock core samples, including porosity, permeability and mechanical properties measured before and after exposure to CO₂-brine. Some of the composite samples were further analysed by micro CT, XRD and SEM-EDX. Moreover, the variation of ions concentration in brine at different time-scales was studied by performing ICP-OES analysis. It was observed that dissolution and precipitation of some minerals started from early stage of exposure and continued as time passed, and, as a result, cement and cement-caprock interface were affected.