Abstract: CO₂ Geological storage is one of the key technologies to address global climate changes and reduce greenhouse gas emissions. Large-scale CO₂ injection into the formation is prone to inducing CO₂ leakage problem. In particular, the leakage problem of CO₂ through caprock includes capillary leakage, hydraulic fracture and leakage along pre-existing faults crossing caprock. Therefore, evaluation of caprock seal is crucial for prediction of long-term safety and stability of CO₂ geological storage. This paper provides an overview of the current status of research on sealing mechanisms, influencing factors, and damage modes affecting caprock seal of CO₂ geological storage. It is concluded that caprock seal mechanisms include capillary seal, hydraulic seal, and overpressure seal. The main influencing factors of caprock seal characteristics include caprock lithology, mudrock-sand ratio, caprock mechanical properties, and sequestration pressure. Then, the damage modes of caprock seal during CO₂ injection are illustrated, and some insight into the shortcoming of caprock seal is provided.

Key words: CO₂ geological sequestration, caprock sealing performance, breakthrough pressure, fracture pressure