Study On Safety And Stability Of Salt Cavern Underground Gas Storage Under Earthquake Loading

As one of the main ways of energy reserve,the underground salt cavern gas storage has the characteristics of large single voluae,large difference of buried depth and complex geological conditions.The wall may fall off and the top span collapses during the earthquake.Moreover,the gas stored in the salt cavern has the characteristics of high pressure,flammability and explosiveness.Once the salt cavern is destroyed in the earthquake,the gas will leak,which will cause serious secondary disasters such as fire and exptosion.Therefore,it is of great necessity and engineering value to analyze the dynamic response and safety evaluation of salt cavern gas storage under seismic loads.Based on the summary of the physical and mechanical properties of salt rock,the rheological damage characteristics and the feilure criterion that salt rock should meet,the Mohr-Coulomb failure criterion applicable to multi-interlayer salt rock is selected.Secondly,the effects of single-cavity seismic wave incident angle,seismic intensity,seismic wave type,internal cavity pressure and cavity height-diameter ratio on the safety and stability of gas storage are studied,and corresponding control measures are proposed.Thirdly,the effects of seismic intensity,earthquake time,seismic wave type,the internal pressure of the cavity,cavity height to diameter ratio and safety pillar width on safety and stability of gas storage group are studied,and corresponding control measures are proposed.Finally,the stress of the casing string of the gas storage tank under the action of seismic load is analyzed.This paper mainly completed the following four aspects of research work:(1)The physico-mechanical properties,rheological damage characteristics of salt rock and the feilure criterion of salt rock are sorted out.The Mohr-Coulomb criterion applicable to multi-interlayer salt rock is modified.The salt rock experimental data are used to obtain the corresponding egressions of salt rock fadure criterion under axial compression and tensile stress,and compared with the calculation results of Ratigan criterion and Hunsche criterion.(2)Based on the 3D numerical simulation model established in FLAC 3D software,the effects of seismic wave incident angle,seismic intensity,seismic wave type,operating pressure,salt cave height-diameter ratio on the stress and deformation of surrounding rock of rock cavern under seismic loading are studied.The results show that the salt cavern gas storage is at the most unsafe condition when the incident angle of the seismic wave is perpendicular to the ground plane.With the increase of the earthquake intensity,the safety is reduced,and the reduction of the upper structure of the salt cavern is smaller than that of the lower salt cavern.The maximum acceleration of seismic waves and the duration of earthquakes have the greatest impact on the safety of rock caverns.It is advantageous to increase the internal pressure appropriately.When the height-to-diameter ratio is about 1.8,the safety of the salt eavern gas storage under the action of seismic toads is better.(3)Taking a salt cavern underground gas storage in China as an example,based on the study of a single cavity,two adjacent salt caverns were selected as the research object,and the time-history analysis nethod was used to simulate the rock caverns in the earthquake disaster.The effects of seismic intensity,seismic wave type,seismic moment,operating pressure,salt cavern height-diameter ratio on the stress,deformation and plastic zone volume and safety faector of the surrounding rock of salt cavern under seismic loading are studied,and the corresponding control measures are proposed.(4)The force of the casing string of the gas storage tank under the action of seismic load is studied.The G-N-M algorithm in the back analysis calculation method of the casing extrusion toad in the creep formation is improved.The direct derivative method in random finite element method is used instead of the difference method in the traditional G-N-M nethod to solve the partial derivative,and the casing extrusion load in a salt rock formation is solved.The improved G-N-M algorithm has higher calculation accuracy,greatly reduces the number of iterative calculations and improves the calculation efficiency.By establishing the 2D and 3D numerical models of the casing string of a multi-interlayer salt rock gas storage in China,the variation law of the casing extrusion load is anatlyzed,and the collapse mechanism of the casing column in the salt rock formation is revealed.The effects of interlayer dip angle,friction coefficient of interlayer and salt rock layer and interlayer thickness on the stress and deformation of casing string in multi-sand rock salt formation are studied.The study believes that the presence of the cement ring is beneficial to the safety of the casing string in the salt rock formation and to optimize the stress state of the casing string.