Study On The Characteristics Of Salt Rock Creep And The Longterm Stability Of Horizontal Salt Reservoirs

Salt rock formations are recognized internationally as the ideal medium for underground storage of oil,natural gas and other energy sources.As one of the most typical mechanical properties of salt rock,creep is closely related to the long-term stability of salt rock storage.Based on the results of the single-axis compression creep test of salt rock and the theory of misalignment,a fine view model of salt rock creep is established.And on this basis,according to the characteristics of salt rock deposits in China,the long-term stability of horizontal salt cavity reservoir is simulated by FLAC3 D software,and the relevant suggestions are given.The main research work and the research results obtained in this paper are as follows:(1)The single-axis compression creep test under different axial stress was carried out on the salt rock test.Based on the test results,the influence of the axial stress level on the instantaneous strain,creep rate,decaying creep strain and steady-state creep strain of salt rock is analyzed.The long-term strength of salt rock is determined by using the isochronous stress-strain curve turning point method,and the maximum decaying creep stress of salt rock varies with the axial stress.A method for determining the long-term strength of rock is proposed.(2)Based on the theory of crystal dislocation,the evolution law of micro variables such as dislocation density and dislocation velocity in salt rock crystal during the creep process is studied.The evolution law of micro variables and the macro creep behavior of salt rock are related by Orowan equation.A micro creep model with few parameters and reflecting the evolution law of micro structure is established,and the method to determine the parameters of the model is given.The sensitivity of model parameters is analyzed.(3)The results show that the theoretical curves of the model under different axial stress are in good agreement with the test results,which shows that the model can describe the macro creep response of salt rock well.On this basis,the creep mechanism of salt rock is further explained from the meso level by using the established creep model.(4)By using FLAC3 D software and numerical simulation method,the long-term stability of single cavity and double cavity horizontal salt cavern gas storage is simulated and analyzed.Based on the numerical simulation results,the variation laws of surrounding rock deformation,volume loss rate,surrounding rock stress and plastic area with operation time,diameter height ratio and pillar width are analyzed.The diameter of gas storage is given when the height is fixed Recommended values for height ratio and pillar width.