Background Against the backdrop of achieving peak carbon dioxide emissions and carbon neutrality globally, renewable energy has developed rapidly and is gradually changing the world's energy mix. However, the intermittent and fluctuating nature of photovoltaic and wind power energy is prone to cause grid frequency fluctuations and reduced power supply reliability. Compressed air energy storage (CAES) technology has emerged as the key to the stable operation of the green power grid thanks to its large capacity and low cost.

Methods Based on a systematic review of domestic and international literature in recent years, this study organizes the current theoretical and technical state of the geological evaluation of underground gas storage (UGS) facilities for CAES. Furthermore, it compares and analyzes the applicability, performance characteristics, and key technical bottlenecks of three types of (UGS) facilities: soft rock caverns, porous medium, and hard rock caverns.

Advances and Prospects CAES in soft rock caverns (salt rocks or abandoned mines) features mature techniques but high cost. Accordingly, the evaluation of the soft rock caverns should focus on their stability and long-term sealing. CAES in porous medium (sandstones or abandoned hydrocarbon reservoirs) is characterized by large reserves but severe difficulties in gas control. This necessitates comprehensively considering trap conditions, reservoir physical properties, and fault sealing. CAES in hard rock caverns (basalts or granites) features strong stability but high construction cost. In this case, it is necessary to optimize fracture control and composite lining technology. Presently, the application research on CAES technology has achieved remarkable progress in the siting and evaluation of the UGS facilities for CAES, the evaluation of geological resource potential, and UGS modeling. However, the research is still facing following challenges: (1) Salt caverns are highly dependent, abandoned coal mines and hard rock caverns are subjected to limited economy, and the heterogeneity of porous medium affects the gas storage efficiency; (2) The evaluation of geological resource potential is limited by data accuracy and simplified assumptions; (3) The reservoir simulation does not involve the multi-field coupling effect. For future research, breakthroughs should be made in two aspects. It is necessary to intensify the fine-scale research on pore structure and caprock of porous reservoirs and construct high-precision geological models by integrating 3D seismic technology. Furthermore, it is advisable to develop heat-water-force multi-field coupling models and verify the reservoir behavior under dynamic conditions through experiments. The results of this study will provide a theoretical and technical reference for the large-scale applications of UGS facilities for CAES under varying geological conditions.