Numerical and theoretical analysis of burst pressures for casings with eccentric wear

With the development of multilateral and extended-reach wells, trajectories of wellbores are becoming more complicated, and operating conditions are extending to higher temperatures and higher pressures. For safe down-hole operations, accurate predictions of casing burst strength are crucial. Based on the elastic-plastic theory for large deformations, we propose a three-dimensional finite element model (FEM) for predicting the burst pressure of a pipe having geometric eccentricity. Using the cross-sectional shape, we divide eccentric casings into two types: crescent-shaped and eccentric cylinder; then, we verify the accuracy and reliability of FEM results by comparing them to a series of full-scale experimental data. To estimate burst pressure, we derive a modified theoretical equation for eccentric pipes. Finally, we discuss how burst pressure is affected by wear radius and pipe eccentricity. Our results show that eccentricity has important effects on burst strength, whereas effects of wear radius are small. Our modified theoretical equation provides results that are consistent with experimental data published by others; moreover, the equation is more accurate and extends over a wider range of applications than previous equations. The FEM approach and the modified theoretical equation presented in this study are appropriate for predicting the burst pressures of pipes employed in the oil and gas industries.