Study On The Integrity Evaluation Of Cement Sheath In Gas Storage

In underground salt beds,holes are formed by dissolving salts in water to store natural gas,which is called salt cavern gas storage.The salt cavern gas storage has been widely used for efficient gas storage and gas recovery,providing natural gas peak shaving.However,the failure of wellbore seal integrity seriously affects the safety and development of gas storage.Therefore,it is important to evaluate the integrity of the cement sheath.It is of great significance to study the effect of different conditions on the integrity of the cement sheath sheathring.This paper focuses on the integrity evaluation of the cement sheath sheathseal in the salt cavern gas storage,Firstly,this paper studies the mechanical integrity of cement sheath,establishes the casing-cement sheath-formation model,analyzes the stress of the cement sheath sheathand the deformation characteristics of the material.The results show that the inner wall of the cement sheath sheathis easy to accumulate and damage easily under different stress conditions.It was analyzed on cement sheath sheathstress influence rule by different casing pressure,size of ground stress,formation characteristics,cement sheath sheaththickness and young's modulus of cement sheath sheathring,cement sheath sheathring poisson's ratio,casing wall thickness,the failure mode of cement sheath sheathseal integrity is analyzed and the failure criterion is given.In order to avoid the failure of cement sheath sheathseal integrity in the gas storage,the cement sheath sheathcharacteristics and the thickness of cement sheath sheathring are optimized that the cement sheath sheathring does not produce plastic strain.Secondly,for the gas storage gas relief phase,the relationship between the contact force of the cement sheath sheathring and the pressure of the casing,the elastic modulus of the cement sheath sheathring and the elastic modulus of the formation is analyzed.The results show that the interface of cement sheath sheath is easy to produce microannulus.Therefore,the generation of the micro-ring gap in the cement sheath sheathis considered as the criterion.The effect of pressure relief velocity on wellbore integrity is analyzed by different sizes of casing wellbore,the reasonable relief value is selected to ensure the sealing integrity of wellbore.Finally,series of experiments were made on the cement sheath,an experimental method is established to study the integrity of cement sheath sheathring seal.The failure mode and failure mechanism of cement sheath sheathring seal integrity under two working conditions are verified.