Evaluating the Mechanical Durability of Well Cement and Geopolymer for Long-Term Integrity in CCS Wells

Abstract Ensuring wellbore integrity is crucial for the long-term success of carbon capture and storage (CCS) projects. Cement durability under various environmental conditions plays a pivotal role in maintaining the integrity of wells and acts as the main barrier to leakage. This study investigates the mechanical behaviour of different formulations of well cement, focusing on the effects of supercritical CO2 exposure on the cement's porosity, permeability and mechanical properties. The formulations tested in this study are neat Class H cement, neat Class C cement, a high porosity lightweight field blend, and a Class F Fly Ash Geopolymer. Cylindrical cement samples (7.5 cm x 3.81 cm) were cured at 60°C for 28 days and then exposed to supercritical CO2 for 28 days under 10.34 MPa and 60°C. Before and after treatment, porosity, permeability, and triaxial compression tests were conducted to assess mechanical properties at a confining pressure of 10.34 MPa. The study sought to determine changes in strength, elastic moduli, and overall integrity under these conditions. Post-treatment analysis revealed minimal changes in the porosity of cement samples. The permeability and mechanical properties of all the samples demonstrated significant changes. The highly porous cement showed reduced strength and elastic moduli compared to the low-porosity formulations, yet exposure to supercritical CO2 did not significantly alter these properties. The Geopolymers exhibited different results when compared to the other cement types. These findings suggest that, under the conditions tested, the structural integrity of well cement is maintained, which is critical for ensuring long-term wellbore stability in CCS applications. This study illustrates the robustness of several oilwell cements to supercritical CO2 exposure, highlighting their practical significance and appropriateness for long-term wellbore integrity in CCS projects.