A Study on the Stress Field Around an Elliptical Wellbore with an Eccentric Casing in Deep Wells

Casing stress distribution is one of the most relevant topics in the study of the wellbore stress field. Due to factors such as uneven geostress, the wellbore is often elliptical, and the casing may not necessarily be in the center of the wellbore. This article adopts the theory of elasticity and uses the finite element method for calculation. The main research focuses on the effects of ovality and eccentricity on the overall stress distribution of the casing and the stress distribution at the interface between the casing and cement sheath (i.e., the outer wall of the casing). The research results indicated that when the casing is centered, higher ellipticity is beneficial for improving the casing’s response to non-uniform stress. However, when the casing is eccentric, higher ellipticity significantly increases the non-uniformity of the stress distribution and the risk of stress concentration in the casing. The risk of casing failure increases with increasing non-uniform stress. Additionally, a lower elastic modulus and higher Poisson ratio of the cement can improve the casing’s response to stress. This research result has a certain reference value for implementing high-quality cementing construction and ensuring the normal production of oil and gas wells.