An overview of underground energy storage in porous media and development in China

Energy security is a global strategic issue that limits economic development and social stability. Improving the energy storage system is the key step and global solution for low-carbon energy transformation. Compared with above-surface energy storage, underground energy storage in geological spaces, especially in porous media, is significant and accounts for the largest proportion. This paper clarifies the framework of underground energy storage systems, including underground gas storage (UGS), underground oil storage (UOS), underground thermal storage (UTS) and compressed air energy storage (CAES), and the global development of underground energy storage systems in porous media is systematically reviewed. Then, the current state of art of underground energy storage engineering in porous media in China, including the construction status, policy environment, technical challenges and possible solutions, are comprehensively analyzed and discussed. In-depth theoretical research, novel methodology, comprehensive studies on site characterization and selection, sealing performance evolution, monitoring, etc., using integrated experiments, physical simulation experiments, and numerical simulations are the key to ensuring the safety, environmental friendliness, and economic efficiency of underground energy storage in porous media. In China, the development of both underground gas storage in depleted natural gas reservoirs and thermal energy storage in shallow aquifers is obvious and cost-effective. The UGS in depleted oil reservoirs and aquifers, UOS in porous media, UTS in deep aquifers, and CAES in porous media, however, are still at the stage of technological research and development, requiring strong policy support and government investment in the construction of demonstration projects before the future industrialization process.