Reaction mechanisms and evolution of pore structure and wettability in the CO2-shale system: A systematic review

The geochemical reactions involving CO₂-water-shale induce significant alterations in reservoir pore permeability characteristics and physical properties through mineral dissolution, clay swelling, and micropore structure evolution, exerting a crucial influence on CO₂-enhanced shale recovery and its geological storage. This review systematically summarizes the patterns and mechanisms of CO₂-water-shale geochemical reactions, examines the processes and recent advances in CO₂-shale geochemical interactions, and clarifies the impact of geochemical reactions on shale properties, including shale mineral dissolution, swelling, erosion, and precipitation triggered by CO₂ injection, and integrates the chemo-mechanical coupling mechanisms as well as multi-scale evolution mechanisms from the perspectives of mineral composition, microstructure, mechanical properties, and wettability. Studies indicate that the spatiotemporal coupling of geochemical reactions (e.g., dissolution and precipitation) and physical processes (e.g., swelling) fundamentally alters shale's pore structure, micro-morphology, and mechanical properties. Meanwhile, this process is jointly regulated by temperature, pressure, and the content and composition of minerals such as clay and carbonate. Furthermore, the review prospects challenges and future development trends concerning CO₂-shale interactions, providing a detailed theoretical foundation and scientific basis for research on injecting CO₂ into shale reservoirs for enhanced oil recovery.