Dynamic Buckling Characteristics of Drill String in Inclined Straight Well with Friction Effect

The buckling behaviors of drill string may cause serious down-hole problems, such as high friction during drilling, loss of weight on bit (WOB), and even drill string failure. This paper analyzes the dynamic buckling characteristics of drill string, considering the friction between drill string and wellbore. In the theoretical research, the key parameter expressions are determined, especially the contact behaviors of drill string and mathematical models are proposed, which include axial displacement, angular displacement and contact force. The numerical calculation results show that the influence of friction on the drill string buckling is mainly reflected in angular displacement. The influences of friction effect on the dynamic characteristics of drill string become greater with the increase of inclination angle, while become lower with the increase of drill string length. The friction effect appears to have insignificant influence on drill string condition with the accumulation of time. The comparison results indicate that the friction affects the action of axial load on drill string and delays the onset of buckling. On the other hand, the angular displacements decrease with drill string length increasing, while the axial displacements have an opposite effect. The research results provide theoretical references for studying dynamic buckling characteristics; furthermore, we can determine the methods and solutions to prevent drill string buckling based on this, and improve the safety of downhole drilling.