Research status of self-sealing mechanisms of caprocks and fractures during CO₂ geological storage

Through a systematic review of the existing literature, the current research on the dynamic effects of material re-equilibration on caprock and fracture self-sealing patterns during CO₂ geological storage is summarized. Laboratory experiments, field monitoring at well sites, and numerical simulation studies generally show that CO₂ injection will not breach relatively thick caprocks in the short term, and even if the directly overlying caprock is breached, CO₂ will be secondarily trapped and sealed by multi-layered caprock systems. The mechanisms of caprock self-sealing mainly include self-sealing due to injection of supercritical-phase CO₂ into confined spaces, mechanical self-sealing resulting from rock pore structure compression or particle migration, and self-sealing induced by chemical reactions. Under the fluid and rock interaction mechanisms after CO₂ injection, fractured or faulted systems tend to progressively develop self-sealing over time. Low CO₂ flow rates and small fracture apertures are identified as the main factors in the formation of fracture/ fault self-sealing. However, the dynamic quantitative effects of CO₂ physical diffusion and chemical reactions on caprocks and fractures under time-scale effects still require further detailed investigation. Currently, research on this dynamic process at home and abroad is gradually evolving toward a systematic approach that integrates multi-spatiotemporal scale coordination, multiple research methods, and multi-factor coupling, and it is increasingly becoming a hot topic in research on CO₂ geological storage.