Oil quality assessment and evolution process in insoluble sediment voids for underground salt cavern oil storage (SCOS): An experimental perspective

Underground salt cavern refined oil storage is a well-established method for large-scale of deep energy storage. Utilizing the salt cavern insoluble sediment void to store the refined oil in salt mines with plenty of insoluble interlayers and impurities can enhance the oil storage capacity. Assessing the refined oil quality in these salt cavern sediment voids is essential for efficient use. A suite of specialized testing equipment was developed to evaluate refined oil quality in salt cavern storage environments, including an oil storage environment simulation device, a water content tester, an oil demulsification time tester, a kinematic viscosity tester, and a sediment content tester. These integrated devices were developed based on a novel salt cavern sediment void oil storage conditions design to explore the oil quality evolution rule. The analysis focused on oil quality changes due to physical, chemical, and microbial factors and the evolution process of oil quality in salt cavern sediment voids. The 30 days of oil storage results indicate that refined oil quality remains generally stable in these salt cavern storage environments. Most refined oils, including diesel, gasoline, kerosene, and mineral oil, meet water content requirements, except for partially refined oil near the oil-brine interface. The oil's emulsification characteristics deteriorate over time, but significant emulsification zones do not form quickly in salt caverns. High-viscosity oils interact more with sediment than low-viscosity oils. The oil viscosity coefficient remains unchanged for about 30 days. High-viscosity oils exert greater extraction forces on sediment particles. These findings provide a foundation for optimizing storage design and operational strategies for SCOS.