Cementing technologies for CO₂ and hydrogen wells: A critical review of degradation mechanisms, advanced materials, and long-term well integrity

The integrity of wellbore cementing systems is central to the long-term success of carbon capture and storage (CCS) and underground hydrogen storage (UHS), both of which are critical pillars for global decarbonization and energy transition goals. This review provides a comprehensive analysis of cement performance in CO₂ and hydrogen wells, identifying degradation mechanisms, environmental challenges, and operational stressors, with a dual focus on challenges and emerging solutions. In CCS applications, cement deterioration is dominated by carbonation, leaching, and chemical transformation, whereas hydrogen wells face risks related to diffusion, cyclic mechanical fatigue, and interface debonding. Traditional Portland cement systems often fall short under these conditions. To address these limitations, advanced alternatives have been developed, including CO₂-resistant pozzolanic blends, MgO-based systems, geopolymers, nanomaterial-enhanced binders, and self-healing cements. These novel systems demonstrate improved chemical durability, enhanced crack resistance, and the potential to reduce costly remediation, thereby strengthening long-term well integrity. The review synthesizes laboratory studies, field monitoring data, modeling approaches, and regulatory developments, while highlighting performance benchmarks and testing limitations. By also outlining unresolved research gaps in degradation modeling, smart cement systems, and lifecycle assessment, the work demonstrates how next-generation cements can directly contribute to secure CCS and UHS operations. These advances not only improve well reliability but also accelerate the large-scale deployment of subsurface storage, supporting international decarbonization pathways.