• Energy Research

This paper provides a systematic visualization of the development, current status and challenges of salt cavern hydrogen storage technology based on the relevant literature from the past five years in the Web of Science Core Collection database. Using VOSviewer (version 1.6.20) and CiteSpace software (advanced version 6.3.R3), this study analyzes the field from a knowledge mapping perspective. The findings reveal that global research hotspots are primarily focused on multi-energy collaboration, integration of renewable energy systems and exploration of commercialization, highlighting the essential role of salt cavern hydrogen storage in driving the energy transition and promoting sustainable development. In China, research mainly concentrates on theoretical innovations and technological optimizations to address complex geological conditions. Despite the rapid growth in the number of Chinese publications, unresolved challenges remain, such as the complexity of layered salt rock, and thermodynamic coupling effects during high-frequency injection and extraction, as well as issues concerning permeability and microbial activity. Moving forward, China’s salt cavern hydrogen storage technology should focus on strengthening engineering practices suited to local geological conditions and enhancing the application of intelligent technologies, thereby facilitating the translation of theoretical research into practical applications.

The utilization of sediment voids for natural gas storage represents the future direction of salt cavern underground gas storage (UGS) in China. In this study, we first analyzed the way in which the sediment interacts with the salt caverns and the equilibrium state of the process. Subsequently, a novel approach employing the Discrete Element Method (DEM) for simulating sediment-filled salt cavern UGS was introduced, successfully modeling the operational process of sediment-filled salt cavern UGS. Moreover, deformation, plastic zone behavior, effective volume shrinkage rate, equivalent strain, and safety factor were employed to assess the impact of sediment on salt cavern stability. The findings indicate a positive influence of sediment on salt cavern stability, particularly in regions directly contacting the sediment. Deformation and effective volume shrinkage of the cavern were effectively mitigated, significantly improving the stress state of rock salt. This effect is more pronounced at lower internal gas pressures. In summary, sediment enhances the stability of salt caverns, providing a long-term and stable environment for natural gas storage within sediment voids.

Salt cavern flow batteries (SCFBs) are an energy storage technology that utilize salt caverns to store electrolytes of flow batteries with a saturated NaCl solution as the supporting electrolyte. However, the geological characteristics of salt caverns differ significantly from above-ground storage tanks, leading to complex issues in storing electrolytes within salt caverns. Therefore, investigating and summarizing these issues is crucial for the advancement of SCFB technology. This paper’s innovation lies in its comprehensive review of the current state and development trends in SCFBs both domestically and internationally. First, the current development status of SCFB energy storage technology both domestically and internationally is summarized. Then, eight main issues are proposed from the perspectives of salt cavern geological characteristics (tightness, conductivity, ions, and temperature) and electrolyte properties (selection, permeability, corrosion, and concentration). Finally, a novel SCFB system is proposed to address the most critical issue, which is the low concentration and uneven distribution of active materials in the current SCFB system. The review in this paper not only comprehensively summarizes the development status of SCFBs both domestically and internationally, but also points out the direction for the future research focussing on SCFBs.

Salt rock, renowned for its remarkable energy storage capabilities, exists in deep underground environments characterized by high temperature and pressure. It possesses advantageous properties such as high deformability, low permeability, and self-healing from damage. When establishing a cluster of salt cavern gas storage facilities, the careful selection of ore column widths between these reservoirs is crucial for minimizing the risk of structural failure, optimizing salt rock resource utilization, and enhancing the construction and operation of gas storage reservoirs. In current practices, square triangular arrangements are commonly used in designing well layouts for reservoir groups to balance stability and economic considerations. This study, conducted in the context of the Jintan salt cavern gas storage project in Jiangsu Province, employed FLAC3D to create a finite element model for proposed gas storage configurations. A comprehensive analysis of the long-term operational safety of salt cavern gas storage with triangular well layouts was carried out. Various indices were examined, covering aspects such as cavern wall displacement, characteristics of the plastic zone, volume shrinkage, safety coefficients, seepage range, pore pressure fluctuations, and seepage volume. The study also considered the mechanical behavior of hexagonal columns within the surrounding rock during extended storage operations, leading to the optimization of allowable widths for these columns. The results indicate that, at operating pressures ranging from 6.5 to 17 MPa, the permissible column width should exceed 1.67 times the maximum cavern diameter to ensure compliance with criteria for long-term stability and containment within a square triangular layout. These findings provide valuable insights into determining the optimal allowable widths of salt cavern columns for positive triangular layouts.

To address the inherent intermittency and instability of renewable energy, the construction of large-scale energy storage facilities is imperative. Salt caverns are internationally recognized as excellent sites for large-scale energy storage. They have been widely used to store substances such as natural gas, oil, air, and hydrogen. With the global transition in energy structures and the increasing demand for renewable energy load balancing, there is broad market potential for the development of salt cavern energy storage technologies. There are three types of energy storage in salt caverns that can be coupled with renewable energy sources, namely, salt cavern compressed air energy storage (SCCAES), salt cavern hydrogen storage (SCHS), and salt cavern flow battery (SCFB). The innovation of this paper is to comprehensively review the current status and future development trends of these three energy storage methods. Firstly, the development status of these three energy storage methods, both domestically and internationally, is reviewed. Secondly, according to the characteristics of these three types of energy storage methods, some key technical challenges are proposed to be focused on. The key technical challenge for SCCAES is the need to further reduce the cost of the ground equipment; the key technical challenge for SCHS is to prevent the risk of hydrogen leakage; and the key technical challenge for SCFB is the need to further increase the concentration of the active substance in the huge salt cavern. Finally, some potential solutions are proposed based on these key technical challenges. This work is of great significance in accelerating the development of salt cavern energy storage technologies in coupled renewable energy.