Salt cavern solution mining is a complicated process of fluid dynamics and chemical dynamics, including salt boundary dissolution, cavern expansion, brine flow, and species transport. The reaction processes occur simultaneously and interact with each other. In this study, a multiphysical coupled model is established to evaluate the real time 3D salt cavern shape expansion, the velocity field, and the brine concentration distribution. Then, the predicted results are compared with the field data of a Jintan Gas Storage Well in China. The average relative deviations with the turbulent flow are 5.7% for outlet brine concentration and 4.0% for cavern volume. The results show that salt cavern can be divided into four regions, including the shock region, plume region, reflow region, and suction region. The results also indicate that the turbulent flow will stimulate the formation of the vortex, thus affecting the distribution of brine concentration. And, the brine concentration distribution primarily influences cavern corrosion. The results suggest that adjusting the inject velocity and the tube position can change the cavern construction rate and the cavern shape. Overall, these results have guiding significance for the design and engineering practice of salt cavern construction for energy storage.
In the current international situation, energy storage is an important means for countries to stabilize their energy supply, of which underground storage of natural gas is an important part. Depleted gas reservoir type underground gas storage (UGS) has become the key type of gas storage to be built by virtue of safety and environmental protection and low cost. The multi-cycle high injection and production rate of natural gas in the depleted gas reservoir type UGS will cause the in-situ stress disturbance. The slip risk of fault in the geological system increases greatly compared with that before the construction of the storage engineering, which becomes a great threat to the sealing of the gas storage. Reasonable injection and production strategy depend on the reliable assessment of the shear behavior of the fault belt, which can guarantee the sealing characteristics of the UGS geological system and the efficient operation of the UGS. Therefore, the shear behavior of the fault is studied by carrying out experiments, which can provide important parameters for the evaluation of fault stability. However, there is a large gap between the rock samples used in the previous experimental study and the natural faults, and it is difficult to reflect the shear failure characteristics of natural faults. In this paper, similar fault models based on high-precision three-dimensional scanners and engraving machines, filled with three types of fault gouge, are prepared for a batch of representative direct shear tests. The results show that the peak shear strength of the fault rocks with a shear surface is higher than that of the fault rocks with a tensile surface. Compared with the clay mineral content, the roughness of the fault surface is much more significant for the shear strength of the fault rock. For the fault rocks with similar fault surface morphology, the higher the clay content in the fault gouge, the greater the shear strength of the fault rocks. For the fault rocks with different fault surface morphology and the same fault gouge, the cohesion and internal friction angle of the tensile type is generally smaller than that of the shear type.
Salt cavern gas storage has become the key project of current and future underground gas storage (UGS) facilities construction due to their efficient peak-shaving and supply assurance capacities. The Sanshui Basin in Guangdong Province, China, is rich in salt resources and has high-purity salt rock, which is a potential area for the construction of salt cavern underground gas storage. To speed up the large-scale construction of underground gas storage in China and promote the sustainable development of the natural gas market, it is very necessary to analyze the geomechanics of the target salt layer and study the feasibility of gas storage construction. Based on comprehensive experiments of rock mechanics and thermodynamics, the strength, creep and temperature-sensitive mechanical properties of the target rock in Sanshui Basin were studied. Then, according to the geological conditions of Sanshui salt formation, a three-dimensional geological model was established to analyze the stability of salt cavern gas storage under the injection-production operation. The results show that the average tensile strength and uniaxial compressive strength of salt rock are 1.51 MPa and 26.04 MPa, respectively, showing lower strength. However, under triaxial compression, the compressive strength of salt rock increases significantly, and there is no obvious shear failure phenomenon observed. Moreover, after the peak strength, the salt rock still has a large bearing capacity. In addition, under the confining pressure of 30 MPa, the strength of salt rock decreases by 8.3% at a temperature of 60 °C compared with that at room temperature, indicating that the temperature has a low, modest effect on the mechanical properties of salt rock. The stability analysis shows that, under an injection-production operating pressure of 10–23 MPa, the displacement, plastic zone range and volume convergence rate of single cavity and cavity group are small, and the cavity shows good stability. Overall, the target salt formation in Sanshui Basin, Guangdong Province, presents a good geomechanical condition suitable for the construction of underground salt cavern gas storage. This study can provide a reference for the development and design of salt cavern UGS.
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