Assessing the Feasibility of Using Coastal Salt Caverns for Strategic Energy Storage from Safety and Economic Perspectives

To support the strategy of building a strong maritime nation, oil and gas resources need to be shifted from inland to coastal areas, and large-scale strategic reserves must be established to meet national security and energy security requirements. Currently, the primary method for offshore gas storage involves onshore steel tanks, which suffer from high costs and limited capacity. The offshore sediment-type salt cavern gas storage is a high-quality alternative solution; however, its long-term stability and economic viability remain to be studied. The feasibility of gas storage in an abandoned cavern of a coastal, low-grade salt mine was simulated using ANSYS Parametric Design Language (APDL) and FLAC3D 7.0, and the cost–benefit comparisons were conducted among abandoned salt caverns, newly constructed single- and double-well salt caverns, and onshore storage tanks. The results show that, without utilizing the sediment storage space, the gas storage capacity is reduced and surrounding rock deformation is increased. On the other hand, the sediment’s supporting effect can mitigate creep deformation and enhance cavern stability. In addition, increasing the operating cycle frequency can significantly reduce volume shrinkage, roof subsidence, and the extent of the plastic zone. Economic analysis shows that the estimated construction cost for repurposing coastal sediment-type salt caverns is approximately 82 million CNY, which is significantly lower than the 450 million CNY required for onshore storage tanks. Compared with newly constructed single- and double-well salt caverns, it offers advantages in cycle time, cost, and revenue. Accordingly, this research can provide theoretical guidance for evaluating abandoned cavern reserves and conducting feasibility studies. Furthermore, it offers technical support for the large-scale, sustainable storage of carbon dioxide, hydrogen, compressed air, and other renew-able energy carriers in abandoned salt caverns.