The effect of greenhouse gas CO2 on global warming has motivated numerous studies and projects around the world, which investigate new technology named Carbon Capture and Storage (CCS). Effective implementation of CCS technology will require containment of injected CO2 into subsurface geological formations over hundreds of years. The performance of structural seals overlying reservoirs targeted for CO2 storage will rely upon the integrity of well-bore cements in active and abandoned wells subjected to fluids rich in CO2. Micro fractures within the well-bore cement and micro-annulus at the casingcement and formation-cement may lead to seepage of CO2 to the surface and/or fresh water aquifers. Thus, understanding CO2- induced changes to the imperfections in the cement matrix is vital for safe and effective implementation of CCS and the impact such changes can have on the overall hydraulic conductivity of a wellbore system. This paper presents an experimental study that depicts changes of cement’s internal structure due to the interaction with acidic brine through a system of purposefully induced fractures within the cement matrix. The reported study is unique in that it employs advanced imaging analyses to quantify CO2- induced alteration of well-bore cements. Furthermore, a complementary high-resolution surface profilometry allowed quantification of changes of the roughness of fracture walls and their impact on the fracture aperture as a result of cement-acidic brine interaction over 100 days.
CCS projects require capturing carbon dioxide from large point sources such as fossil fuel power plants and other manufacturing processes that produce CO2 and storing it below the earth’s surface for hundreds of years. The long-term containment of injected gas is a critical component for effective CCS, requiring that potential pathways for leakage during early stages of injection be identified, investigated and risk assessment performed.
