Ensuring long-term caprock integrity in carbon capture, utilisation and storage: a comprehensive review of geo-mechanical and monitoring approaches

Caprock integrity is essential for the successful implementation of carbon capture utilisation and storage (CCUS) technologies, which are pivotal for reducing atmospheric carbon dioxide (CO 2 ) levels and mitigating climate change.The present study examines the role of caprock in preventing CO 2 leakage, methods for assessing and ensuring its integrity and the techniques for monitoring its long-term stability.Caprock, typically composed of low-permeability materials such as shale and/or anhydrite, acts as a barrier to prevent the upward migration of CO 2 from the underlying storage reservoirs.The effectiveness of caprock in preventing the leakage is determined by its physical and mechanical properties, including high porosity, low permeability, high mechanical strength and geochemical stability.Case studies from projects like Sleipner and In Salah demonstrate that effective caprock can secure CO 2 for extended periods without significant leakage.Different methods are employed to ensure caprock integrity.They include laboratory testing, field experiments and geo-mechanical modelling.Core sampling and laboratory tests provide the data on caprock properties, whereas in situ stress tests and hydraulic fracturing experiments offer insights into the stress distribution and mechanical behaviour of the caprock formations.Numerical models coupled with fluid flow and mechanical deformation simulations predict the impact of CO 2 injection on caprock stability.Risk assessment and mitigation strategies, such as optimising injection pressures and using chemical sealants, are essential for reinforcing the caprock integrity.The long-term stability of caprock is critical to the sustainability of CCUS projects.Geochemical models simulate CO 2 -brine-rock interactions, assessing the impact of geochemical reactions on caprock properties.Advanced monitoring technologies, including seismic surveys, interferometric synthetic aperture radar (InSAR) and fibre optic sensors, provide realtime data on the mechanical and chemical behaviour of caprock.Integrated monitoring programmes from projects like Weyburn-Midale and Otway highlight the importance of comprehensive monitoring and adaptive management strategies.Future research should prioritise the development of advanced models that incorporate complex geo-mechanical and geochemical interactions and enhance real-time monitoring technologies.Policy development should emphasise comprehensive risk assessments, continuous monitoring and international collaboration to ensure the safety and effectiveness of CCUS projects globally.