Impact of CO2 on well integrity

To de-risk the long-term geological storage of CO₂, understanding the potential for wellbore cements to degrade is essential. CO₂ dissolves in the formation water turning it acidic, which degrades the cement over time across a two-stage process: (i) cement carbonation occurs as various cement phases react with the CO₂-saturated brine to form calcium carbonate; (ii) the calcium carbonate dissolves into the formation water, potentially eroding the cement. For significant erosion to occur there would need to be a flow of water, under-saturated in calcium and carbonate ions, across the cement to remove dissolved calcium carbonate. We have developed a program of work to investigate cement degradation at the cement-formation interface using composite cement–sandstone core plugs. Core-flooding experiments at pressures and temperatures representative of storage conditions using CO₂ saturated pore fluid are undertaken to estimate the cement’s erosion rate.