Influence of Local Missing Cement Sheath on the External Load of Casing in Deep Gas Wells
Poor cementing quality in the long cementing section of deep gas wells can easily lead to local missing of cement sheath,resulting in a decrease in the service life of the casing.This article analyzes the effects of mechanical parameters,missing angle,missing thickness,and internal pressure of the cement sheath on the mechanical integrity of the casing by establishing a finite element model.The results show that under the current engineering parameter conditions,the maximum equivalent stress of the casing occurs on the inner wall of the casing after the cement sheath is missing,and the maximum equivalent stress of the casing decreases with the increase of the elastic modulus of the cement sheath.When the elastic modulus of the cement sheath is less than a certain value,the maximum equivalent stress on the inner wall of the casing where the cement sheath is missing exceeds the design safety stress of the casing.The variation law of casing stress with Pois-son's ratio is opposite to that of elastic modulus,but the influence is relatively small.As the angle of missing cement sheath increases,the stress on the inner and outer walls of the casing first increases and then decreases.When the angle of missing cement sheath is 45°,the stress on the inner wall of the casing is the highest.If the angle exceeds 45°,the stress on the casing decreases slightly,but it is easy to cause later eccentricity.The maximum stress of the casing increases with the increase of the missing thickness.As the pressure inside the wellbore increases,the stress on the inner and outer walls of the casing at the missing cement sheath decreases first and then increases.Af-ter the internal pressure exceeds a certain value,the maximum equivalent stress on the casing shifts from the inner wall to the outer wall.The conclusions obtained can provide useful references for the long cementing section of deep gas wells.
missing cement sheathcasing stressmissing anglemissing thicknessfinite element analysis
万方数据
维普
