Casing stress analysis under non-uniform in-situ stress in Ultra-deep horizontal wells

With the advancement of global oil and gas exploration and development, the proportion of deep and ultra-deep wells in oil fields is increasing. They face complex geological environment and extreme conditions, which often lead to casing deformation. In this study, a two-dimensional numerical model of casing-cement sheath-formation was established and solved by finite element method. Compared with the theoretical calculation, the maximum deviation of the inner and outer wall stress and the outer wall contact pressure of the casing is only 7.19 %, which verifies the reliability of the model. The simulation shows that the wellbore pressure and in-situ stress heterogeneity have a significant effect on the casing: 245 MPa detonation pressure makes the inner wall stress reach 749.8 MPa (580% higher than the static pressure); the increase of formation heterogeneity by 30% leads to an increase of stress by about 330%. The eccentricity of the cement sheath and the ovality of the casing have little effect. Compared with the normal conditions, the maximum increases are about 49% and 16.86%, respectively. This study provides guidance for casing design in ultra-deep wells.