Carbon dioxide (CO2) storage in geological formations: Overview of mechanisms, storage media, leakage risk, and monitoring techniques

The continuous rise in anthropogenic carbon dioxide (CO 2 ) emissions poses severe environmental challenges, including global warming and climate change. Geological CO 2 storage (GCS) has emerged as a reliable and large-scale mitigation strategy capable of securely immobilizing captured CO 2 within subsurface formations. This review provides a comprehensive assessment of CO 2 storage mechanisms, storage media, hydrate-based trapping, leakage detection, and the associated challenges. Four primary trapping mechanisms (structural, residual, solubility, and mineral) govern the immobilization of injected CO 2 under varying pressure, temperature, and geochemical conditions. Diverse geological media such as saline aquifers, depleted gas reservoirs, unmineable coal seams, basalts, and shale formations offer complementary storage advantages, with capacities ranging from hundreds to thousands of gigatonnes of CO 2 gas. The formation of CO 2 hydrates in marine and permafrost sediments provides an additional self-sealing, high-density storage pathway, supported by CO 2 -CH 4 replacement kinetics and experimental evidence from scaled and microfluidic studies. Ensuring storage integrity requires integrated multi-scale monitoring, where seismic methods image CO 2 plume evolution, electromagnetic techniques track resistivity changes associated with fluid substitution, geochemical monitoring detects variations in fluid composition and reaction products indicative of CO 2 migration or trapping, and interferometric synthetic aperture radar (InSAR) identifies surface deformation related to pressure-induced geomechanical responses. Despite its promise, GCS faces challenges including reservoir heterogeneity, caprock integrity, injectivity constraints, and socioeconomic barriers. However, technological advancements in real-time monitoring, microfluidics, and predictive modeling, alongside supportive regulatory frameworks, are progressively mitigating these risks. Collectively, this review emphasizes that integrating multidisciplinary insights and developing standardized monitoring protocols are critical for achieving safe, verifiable, and large-scale CO 2 storage, an essential step toward global carbon neutrality.