Study On Mechanical Stability Of Single Cavity Of THM Three-field Coupled Salt Rock Gas Storage

Due to the good sealing and strong peak shaving ability,salt rock gas storage has been widely used as an effective measure for energy storage such as natural gas.The underground gas storage is in a complex stratigraphic environment for a long time,and it will be affected by a variety of physical fields during operation,so the study on the long-term operation stability of salt gas storage under multi-field coupling is the key to ensure the safe operation and prolong the service life of gas storage.In this paper,taking account of the domestic underground salt rock gas storage（Jintan salt rock gas storage）as the research background,the following research work is carried out on the mechanical characteristics,creep behavior of salt rock and the key problems of the gas storage during operation.Firstly,on the basis of the research on the strength characteristics,creep characteristics and creep constitutive relationship of salt rock,using the heat-fluid-solid coupling theory,a THM three-field coupling mathematical model is constructed,and the Norton Power constitutive model is used in the model to calculate the creep of salt rock.The effective tensile stress criterion and the salt rock creep dilatancy damage criterion are used as the judgment criteria for analyzing the stability of the salt rock gas storage,and the model is numerically solved based on the finite element program LOCAS.Secondly,based on the results of the sonar cavity measurement,a three-dimensional calculation model was established by Gmsh finite element meshing software.The size of the model was optimized.The optimal mesh size for numerical simulation calculation was determined to be 40m.The time cost of numerical calculation is shortened.Finally,the stability analysis of salt rock gas storage is carried out.In this paper,a new numerical simulation software LOCAS^3D is used to carry out numerical simulation calculation in terms of volume shrinkage rate,cavity wall deformation,distribution of dilatation area around the cavity,and stress concentration of salt cavity and surrounding rock.First,through the long-term stability analysis of the gas storage under different constant pressure conditions,it is obtained that the operating pressure range of the gas storage is 8～15MPa.Second,through the research on the creep behavior of gas storages with different cavity shapes in the long-term operation,under the premise of ensuring the economy of storage space,the approximate ellipsoid with greater regularity should be considered as much as possible in the design of the gas storage cavity.The dissolution cavity can effectively control the volume contraction of the salt cavity of the gas storage.Third,based on the numerical calculation of cyclic injection and production conditions,the creep law of the salt rock gas storage under this cyclic pressure is studied,and the high incidence area of gas storage failure is determined during the long-term operation of salt gas storage.It is suggested to strengthen the on-site management and safety prevention and control of this area in the actual operation.