Mechanical Stability Analysis Of Multi Interbedded Salt Cavern Gas Storage In The Process Of Injection And Production

Based on the "west to east gas pipeline project" in our country and the needof natural gas peak shaving engineering, a large number of underground naturalgas storage would be built in the eastern part of our country, Jiangsu Jintan saltcavern gas storage became China’s first salt cavern gas storage which had putinto production in2010. Because of the rock salt has larger plastic andrheological property, the gas storage cavern would occur a certain number ofrheological deformation in the long operation process. In addition, China’sunderground rock salt formation occurrence characteristic is that single-layerthickness is thin with many mudstone interlayer, therefore, the mechanicalproperties of layered salt rocks would be relatively special. For this paper, thebasic mechanical properties of layered salt rocks and its mechanical propertiesunder the condition of periodic cyclic loading were studied, as well asunderground salt cavern gas storage containing intercalation had carried on thefinite element numerical calculation.(1) Through the uniaxial compressive strength and creep experimentalstudy of Jiangsu jintan layered salt rocks, it is concluded that the strength of salt rock is about17MPa which is belonging to the category of soft rock, with theincrease of content of mudstone interlayer, the strength of the layered salt rockswill be improved; NaCl salt rocks deformation ability is mainly characterized byits creep, steady creep rate of mudstone was obviously less than salt rock, andthe existence of interlayer for salt rock creep has a certain inhibitory effect.(2) Through the cyclic loading and unloading test of the salt rockspecimens, it is found that the halite strength does not change obviously, thesurrounding rock strength could be effectively guaranteed in the process ofinjection-production; In the different loading strain rate (2.0×10-5/s,2.0×10-4/s,2.0×10-3/s) conditions, the impact of the halite strength is not very big. Thecavity surrounding rock strain rate controlled in between10-5~10-3/s couldguarantee the safety and stability of the gas storage cavity in the process of thegas storage operation.(3) By using the transient analysis methods the finite element numericalanalysis software ANSYS, built a ideal calculation model of optimal shape forthe gas storage to calculate the long term rheological deformation of theunderground salt cavity gas storage in20years’ injection-production cyclicloading. The settlement at the top of the cavity and the cavity volume shrinkagedeformation will increase gradually, while the speed is becoming slower, and thelate settlement becomes nearly3.6m and the cavity volume shrinkage rate isabout17.07%; By changing the gas recovery rate in the injection-productionprocess, it was found that the settlement at the top of the cavity and the volume shrinkage could be effectively controlled, thus the long-term stability of theunderground salt cavern gas storage could be improved.