The Post-buckling Analysis Of The Drill String In Vertical Well

The buckling of drill string is a key problem in the oil industry. Serious buckling of drill string will cause fuel pipe failure, drill string failure, and increase the friction during drilling. Due to the outer constraint of the circular cylinder, the buckled drill string 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 helical buckling state of gravitational tubular subjected to gravity and the effect of the torsion on the gravitational tubular were considered in this paper.The dissertation bases on the non-linear buckling differential equations of tubular subjected to the axial compressive force and torque, the post-buckling behavior of the gravitational tubular was analysed. The buckling equilibrium equations of gravitational tubular subjected to the axial compressive force and torque in cylinder are obtained using equilibrium method and energy method. The four-order nonlinear equation obtained was analyzed and solved. This analytic solution represented the practical buckling configuration. The results showed that the buckling configuration was helical curve for the gravitational tubular under the axial compressive force and torque. Herein, the natural boundary conditions, contact forces for the buckling differential equation were also derived, and as well the critical force for the gravitational tubular under only the axial load. Considering the condition of the minimal contact force was zero, the helical buckling state was certified as the possible stabilized state of equilibrium for gravitational tubular constrained by straight circular pipe.Otherwise, the impacts of the end-constrained boundary conditions namely fixed-end constraints on the helical buckling configurations were analyzed. This case is conventional engineering example. Herein, the tubular was divided into one spatial beam-column near the end and one buckling configured section...