Post-Buckling Behaviors Of Tubulars Within Circular Cylinders

The buckling of tubulars is a key problem in the oil industry. Serious buckling of tubulars will cause casing failure, drillstring failure, increase in drillstring drag and torque. Furthermore, it limits coil tubing applications and extended reach drilling. Due to the outer constraint of the circular cylinder, the buckled tubulars would undergo sinusoidal configuration, transition from sinusoidal to helical configuration and helical configuration, eventually it will be lock-up, so the post-buckling behavior is very complicated. The dissertation will give comprehensive analysis for buckling and post-buckling of the tubulars based on energy method and equilibrium method.1. The dissertation studies comprehensively the post-buckling behavior of two typical tubulars subjected to axial and torsional load in cylinders, and relative non-linear differential equations. (1) The buckling differential equations with its boundary conditions and the equations of the contact force between the buckled tubulars and confining cylinder are obtained. (2) The analytical solutions of sinusoidal and helical configurations of the buckled tubulars and corresponding contact force are obtained, and the solutions are in good coincidence with the numerical results for the corresponding fourth order strongly nonlinear ordinary differential buckling equations. (3) The stability of the sinusoidal and helical equilibrium states of buckled tubulars is analyzed by energy stability criterion. Based on the current continuous contact assumption, the results show that identical loads correspond to two stable equilibrium states of sinusoidal and helical configuration. However, according to the condition that the contact force is not less than zero, the two solutions of sinusoidal and helical configuration are not physical simultaneously. Therefore, the sinusoidal and helical buckling behavior of tubular could be determined analytically. (4) The effects of pinned and fixed...