As an innovative energy technology that deeply integrates CO geological sequestration with compressed gas energy storage

compressed CO storage in saline aquifer achieves dual benefits by using CO as a circulating working fluid

simultaneously enabling large-scale carbon sequestration and grid-level energy storage. This technology aligns well with China's strategic development needs for energy transition and the “dual carbon” goals

offering broad application prospects. However

current research on compressed CO energy storage in saline aquifer primarily focuses on optimizing ground systems

with limited attention given to the underground factors that ultimately determine the success or failure of the entire project. Therefore

this paper reviews the key geomechanical issues related to compressed CO energy storage in saline aquifer. First

it summarizes state of the art in compressed gas energy storage technologies worldwide

and introduces the basic principles and operational characteristics of compressed CO energy storage in saline aquifer systems. Second

it summarizes the thermodynamic properties of CO

highlighting the advantages of CO as a working fluid compared to air. Third

it addresses key geomechanical challenges facing geological storage systems

detailing the multiphase coupling mechanisms between CO

brine

and rock during system construction and operation. It examines the potential stability and integrity issues arising from these interactions

including formation and surface deformation

sand production

caprock fatigue and fracturing

fault reactivation and induced seismicity

sealing mechanisms of caprock/faults

and leakage pathways. Finally

it summarizes the shortcomings and challenges in current research on compressed CO energy storage in saline aquifer and proposes several research recommendations.