Study On Stability Of Layered Salt Rock Gas Storage Under Injection-production Action

Due to its excellent creep properties,damage and self-recovery properties after damage,salt rock is an ideal natural gas storage site.My country’s salt mines are rich in resources,but generally layered,which makes the safety and security issues of my country’s salt rock underground gas storage in the process of construction and operation more complicated and important,the catastrophic accidents of salt rock underground storage often occur due to improper internal pressure control during the operation of the gas storage,therefore,in order to ensure the safety and stability of the long-term injection-production process of the interlayer-containing salt rock gas storage,this paper mainly studies the stability of the layered salt rock gas storage under injection and production by numerical simulation calculation method.On this basis,the reliability method is applied to the instability risk of the stability of the salt rock underground gas storage.Optimize the design and operating parameters of the gas storage to improve its efficiency and safety.The specific research work and conclusions are as follows:(1)A mechanical model of the incompatibility of the deformation of the layered salt rock mass system is established,the model regards the interlayer and its salt cavity surrounding rock as a complete mechanical system,reveals the failure process law of the layered salt rock mass:after the strength failure of the salt cavity surrounding rock,when the strength and stiffness of the interlayer and the salt cavity surrounding rock are greatly different,the layered salt rock mass system is prone to unstable failure.(2)The influence law of interlayer occurrence characteristic parameters,such as interlayer thickness、interlayer number and interlayer location,on the deformation、stress and instability risk of surrounding rock during the operation stage of the salt rock gas storage is studied.The results show that with the increase of the thickness and number of interlayers,the overall shrinkage deformation of the salt cavity decreases;the compressive stress、volume shrinkage rate、plastic zone volume and instability risk of gas storage in the salt cavity surrounding rock all increase.As the distance from the interlayer to the top plate of the cavity decreases,the overall shrinkage and deformation of the salt cavity increases;the compressive stress of the surrounding rock in the salt cavity first decreases and then increases;the volume shrinkage of the salt cavity shows a decreasing trend.(3)The influence of injection-production parameters such as operating pressure interval、minimum operating pressure、minimum operating pressure residence time、injection-production cycle on the stability and instability risk of surrounding rock during the operation phase of the layered salt gas storage is analyzed.The research results show that with the upward movement of the operating pressure range and the increase of the minimum operating pressure,the overall shrinkage deformation of the salt cavity is significantly reduced;the compressive stress 、expansion coefficient and plastic zone volume of the surrounding rock of the salt cavity all increase;the volume shrinkage rate of the salt cavity and the instability risk of the gas storage are reduced.With the increase of the minimum operating pressure residence time and the injection-production cycle,the overall shrinkage and deformation of the salt cavity increases;the expansion coefficient of the surrounding rock in the salt cavity decreases;the volume shrinkage rate of the salt cavity and the instability risk of the gas storage increase.(4)The sensitivity analysis method was used to compare the sensitivity of the stability and availability of the salt cavity to the occurrence characteristics of the interlayer and the parameters of injection and production.The sensitivity coefficients of the characteristic parameters of each interlayer are ranked as follows: interlayer thickness、interlayer number、interlayer position;The sensitivity coefficients of each injection-production parameter are ranked as follows: operating pressure interval、minimum operating pressure、minimum operating pressure residence time、injection-production operation period.(5)It is suggested that the gas storage should be built at the position of the salt layer with thin interlayer and a small number of salt layers,the interlayer should be avoided near the roof during the design of the gas storage.On the premise of meeting the design requirements,the operating pressure range and the minimum operating pressure of the gas storage should be appropriately increased,the proportion of the minimum operating pressure and the injection-production period should be reduced.There are 77 figures,18 tables,and 121 references.