Study On Salt Rock Damage And Capacity Expansion And Method For Determining Minimum Operating Pressure Of Gas Storage

Salt rock is an excellent medium for underground energy storage as its good creep property,low permeability,damage self-healing ability and chemical stability.It is of great theoretical and practical value to study the damage development and dilatation law of salt rock media.Salt cavern gas storage is deeply buried underground.How to determine the minimum operating pressure of gas storage is the core problem to be solved in the construction of gas storage.In this thesis,the characteristics of the salt rock damage are analyzed from macro and meso perspectives by laboratory triaxial test and acoustic emission monitoring.The damage expansion constitutive model of salt rock is constructed,and the method of determining the minimum operating pressure of salt cavern gas storage is proposed based on the proposed constitutive model.The longterm stability of salt cavern gas storage is evaluated.The research results of this thesis are as follows:(1)Based on the triaxial compression test,the damage dilatation characteristics of salt rock at the stage of compaction,elastic deformation,damage stable development,damage unstable development and plastic deformation are studied.The sample of salt rock shows obvious "drum shape" during dilatation failure.The confining pressure has obvious influence on the stress-strain relationship and the change of bulk strain of salt rock.With the increase of confining pressure,the deviatoric stress and bulk strain at the initial dilatation point of salt rock increase obviously.(2)The acoustic emission activity of salt rock under confining pressure of 5 MPa,10 MPa and 15 MPa are studied.The amplitude of acoustic emission signal and ringing count show the same characteristics.At the beginning of the experiment,the activity of acoustic emission signal is intense.At the middle stage of the experiment,the acoustic emission activity is at a low level.At the late stage of the experiment,the acoustic emission signal kept a steady trend of continuous growth.(3)Based on the strain softening constitutive model,the plastic shear straindilatation Angle change criterion is introduced to construct the damage dilatation constitutive model of salt rock which can better reflect the plastic mechanical behavior of salt rock.Through the secondary development of the constitutive model,the program of the constitutive model is realized,and the constitutive model is embedded in the numerical simulation software.The correctness of the constitutive model is verified by laboratory test results.(4)The constitutive model obtained from secondary development is used to simulate the actual working conditions of the gas storage under different operating pressures.The minimum operating pressure of the gas storage is determined as 6MPa based on whether the junction of the top of the gas storage cavity and the interlayer around the cavity enters the relative expansion zone.(5)Through the improved analytic hierarchy process,the stability of gas storage is evaluated.According to the engineering practice and related research results,the evaluation index of gas storage stability is determined,and the stability evaluation model is constructed.Through the improved analytic hierarchy process,the long-term stability of the gas storage is evaluated,and the state of the gas storage is confirmed to be stable.