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Underground salt caverns are used globally for large-scale energy storage. In the thinly bedded rock salt in China, two butted-well horizontal (TWH) caverns, as alternatives for energy storage, are regarded as having better suitability and economy than vertical caverns. However, understandings of the cavern shape development and control methods of TWH-caverns remain insufficient. To overcome these shortcomings with respect to TWH-caverns, we conducted physical simulations of TWH-cavern construction using a high strength steel mold and molded large rock salt specimens. We established a platform for physical simulation of TWH-cavern water-solution construction using the large molded rock salt specimens, so that the construction process is visible and easily observed. Six groups of physical simulations of TWH-cavern construction were designed and implemented. The variables which affect the cavern outline expansion were investigated and compared, including water injection rate, transferring of injection well, oil blanket, and retreating position of the water outlet. Finally the expansion rules of the cavern outline, and different effects when injecting from an inclined well vs. From a vertical well were explored, as well as an attempt of retreating water outlet. This study provides significant guidance for constructing horizontal caverns for energy storage in thinly bedded rock salt.

The maximum gas production rate from salt cavern gas storages is a key parameter affecting its operating safety and peak-shaving performance. However, there is no mature and reliable method for design in it. In this study, the components of a salt cavern gas storage were separated, and many factors affecting the gas production rate are studied in terms of the safety of cavern, tubing and wellhead. These include mechanical stability and volume shrinkage of the cavern, erosion and corrosion of the tubing, generation of hydrate and condensate at the wellhead. Methods are provided for determining the gas production rate to avoid adverse effects, and the thermodynamic parameters during production are modeled mathematically and solved. Finally, an evaluation system for selecting maximum gas production rate from a salt cavern gas storage is proposed and has been compiled into software UGS-GP-design. Applying it to Jintan T5-2 salt cavern gas storage, the feasibility of the proposed method was verified. The study is mostly applicable to natural gas storage, as well as offering theoretical basis and methodological support for salt cavern air and hydrogen storage.

Many insoluble sediments accumulate at cavern bottoms during the construction of salt caverns located in highly insoluble salt formations. Before using the void space for gas storage, knowing the porosity is essential for predicting void volume of insoluble sediments. However, most previous studies have focused on construction and operation of salt caverns, and insoluble sediments have been largely ignored. In this study, a series of laboratory tests, including screening and porosity tests, are conducted to obtain the particle size distribution and porosity of samples obtained by dissolving the nonsalt interlayers of target cavern. The results show that the porosity values of the samples decreases with increasing of fractal dimensions and have no relation to the maximum particle size when the fractal dimension is constant. Based on these results, a porosity prediction method is proposed to calculate the porosity of insoluble sediments combined with fractal and packing theories. In this method, the fractal dimension and the compaction index should be controlled within a reasonable range. The accuracy and reliability of this model was studied by calculating the porosity of insoluble sediments in an actual salt cavern. This study can provide a reference for evaluating the void volume in insoluble sediments.

Taking Jiangsu province of China as an example, large-scale underground hydrogen storage (UHS) in salt caverns is proposed to realize peak shaving for wind power. A bedded salt rock, Jintan salt mine in Jiangsu, is selected as the potential site for UHS. And the feasibility of UHS in bedded salt rocks is evaluated. Firstly, the regional geological conditions of Jintan salt mine are analyzed. It shows that this mine has good stratigraphic trapping and meets the site-selection requirements for UHS. Then, a numerical simulation model is established to analyze the stability and applicability of the proposed UHS caverns. The tightness of the UHS salt caverns is also investigated. It is indicated that gas tightness can be favorable once the permeability of interlayers is around 10−18 m2 or lower. Finally, it is estimated that the salt caverns for 36.9 TWh-scale UHS of Jiangsu can be mainly provided by salt mine enterprises, but more attention should be paid to the usability of caverns during extraction. This study provides a feasible and economical solution for fulfilling the large-scale UHS in the Jiangsu, as well as for the regions that are rich in both renewable energy and salt resources.