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In order to explore the influence of initial strain on the photo-oxidation aging process of HDPE sheath, the actual strain value of HDPE sheath was calculated based on the design method and the production process of parallel steel wire suspender. The initial strain of HDPE specimen was applied by fixture, and xenon arc lamp accelerated aging test of HDPE were carried out. The results show that after 5000 h xenon arc lamp accelerated aging, the tensile strength, yield strength and secant modulus of the elastic stage of the specimen decrease by 11.19%, 9.15% and 40% respectively. During the aging process, there is no obvious increase or decrease in the elongation at break.There is a critical time in the aging process, when the aging time exceeds the critical time, the yield elongation of HDPE specimen will increase sharply; When the aging time is less than the critical time, the tensile properties of the specimens are basically unchanged with the increase of the initial strain; When the aging time is greater than the critical time, with the increase of initial strain, the tensile strength of the specimen decreases gradually, while the yield strength and secant modulus increase gradually. The critical time increases with the increase of initial strain. In addition, based on the experimental results, the prediction model of HDPE strength and secant modulus is established. The results of this paper lay a foundation for the prediction of the remaining service life of HDPE sheath, which can provide a theoretical basis for the durability design of suspension bridge cable system. • The tensile properties of HDPE sheath for parallel wire suspender after photo-oxidative aging is explored. • The characteristics of elastic stage, strain softening stage, necking stage and orientation hardening stage are analyzed. • With the increase of aging time, the tensile and yield strength and secant modulus in the elastic stage decrease. • When the aging time exceeds a critical time, the yield elongation of the specimen suddenly rises. [ABSTRACT FROM AUTHOR]

Casing deformation occurs frequently in shale gas wells, resulting in the failure of some fracturing stages to complete normal operations, which seriously affects shale gas production. This paper firstly analyzes the casing deformation mechanism of shale gas wells and determines that the casing shear deformation caused by formation slip is the main factor of casing deformation. In order to solve the problem of casing shear deformation, a finite element numerical model including the formation, cement ring, and the casing is established. The casing shear deformation caused by formation slip is simulated, and the deformation results obtained are consistent with those measured in the actual wellbore. Based on the numerical model, a casing deformation governance method is proposed to optimize the wellbore trajectory and adjust the cement ring properties. It is calculated that reducing the dip angle á of the formation and casing vertical direction and reducing the formation slip is beneficial to reducing casing deformation. The use of low elastic modulus cement and uncementing operations can provide a buffer space for formation slip, effectively reduce casing deformation, and provide an effective treatment method for shear deformation of shale gas wells. [ABSTRACT FROM AUTHOR]