How The Pressure Of The Gas Storage When It Works Influences The Structure Integrity Of The Cement Sheath

The wellbore of the gas storage is influenced by the pressure and the alternating pressure,high pressure and frequency of alternating pressure could cause the integrity of wellbore failure,however,the researches about the cement sheath is relatively little,and the model is almost two-dimensional model.So this paper established a three-dimension wellbore model in the multi-stratum based on the elastic-plastic,the mechanical properties of a large number of rock and the material data of cement sheath.And through the ABAQUS,this paper analyze the cement sheath in the extreme pressure and in the alternating pressure,to ensure the cement sheath's stress condition in the ultimate pressure and the cement face and the fatigue of the cement sheath in the alternating pressure.Obtain the conclusions as below:In an ideal state,the gas storage should chose the cement which is low elastic modulus,high Poisson's ration of the cement system and pay no attention to increase the cement thickness.Because the cement sheath stress is grew with the increase of the elastic and the decrease of the Poisson's,however the thickness of the cement sheath play a minor role;the cement will not be destruction in the ideal state.In an imperfect state,the cement sheath is bigger than that of cement sheath under ideal condition.The cement sheath which in low ellipticity,low eccentricity and low cement sheath defect is close to the cement sheath in the ideal state,while it is far from the ideal state when the cement in high ellipicity,high eccentricity and high cement sheath defect.The heterogeneity of the cement become larger;the cement will have a destruction in the high ellipicity and the cement sheath defect which it happened near the high ellipicity and the cement sheath defect.In the ideal state,the profile map of casing stay close contact with different elastic',Poisson and thickness.In the imperfect condition,the profile map of casing also stay close in low ellipticity,low eccentricity and low cement sheath defect;no matter how the different the ellipicity is,there are no invalid in the cement sheath.however,the first bond of the cement begin separation when it is high eccentricity and high cement sheath defect,and the time of separation gradually advance.The second interface is always staying close.Therefore,under the condition of non ideal state,the high degree of eccentricity and the absence of cement ring may lead to the leakage of natural gas from one interface.Through the fatigue analysis,the number of the fatigue of the cement sheath is always greater than 50 times,it can meet the requirements of the gas storage.This paper thinks,that the cement slurry system with low elastic modulus and high Poisson's ration is more suitable for the gas storage,and at the same time,the gas storage could operation well with hole stability and Casing centering.