Tightness evaluation and countermeasures for hydrogen storage salt cavern contains various lithological interlayers

Large-scale energy storage methods are required for shaving peak of renewable energy. Because of the good compactness of salt rock, it is proposed to store hydrogen in salt rock caverns to solve this problem. China has abundant salt rock resources, which provide good choices for large-scale hydrogen storage in salt formation. But the salt formations of China are mainly of bedded salt rock, which contain interlayers with various lithologies and different permeability and porosity. Therefore, the tightness of hydrogen storage in different bedded salt formations of China should be investigated. In order to demonstrate the tightness performance of salt cavern hydrogen storage and provide references for site selection and storage management, a series of lab-experiments, theoretical and numerical simulations, and discussions were conducted. Firstly, the porosity and permeability of interlayers with different lithologies were tested and analyzed. Then, a geological model was established, five cases of hydrogen leakage simulation are designed, these cases stand for the typical bedded salt formations of China. In each case, the interlayers have different lithologies, permeability and porosity. The COMSOL Multi physics software was used to simulate the hydrogen leakage of cavern under different cases, and the leakage range, pore pressure and leakage amount of hydrogen were analyzed. The results show that interlayers are the main positions of hydrogen leakage, and with the decrease of the interlayers' porosity and permeability, the tightness of cavern will be better. It is suggested that when hydrogen is stored in a single cavern, the permeability of interlayers should be less than 1E-17 m2, while when stored in a group of caverns, it should be less than 1E-18 m2. At the same time, a reflux zone is found in the surrounding rock of storage cavern, hydrogen in the reflux zone will flow back to cavern, which is not conducive to its operation. Leakage coefficient of the surrounding rock of cavern is defined as alpha, and it is proposed only when alpha & LE; 1.18E-20 m2, can the cavern meet the tightness requirements of hydrogen storage. Finally, some countermeasures are put forward for cavern utilization in bedded salt rock. This research provides guidance and basis for the site selection of hydrogen storage in salt caverns, and promotes the development of underground salt cavern energy storage in China.