Research on a Model of Nonlinear Coupled-vibration of Directional Well Drill String

Abstract

Drill string vibrations are inevitable movement patterns during drilling process, the drill string vibrations form including longitudinal, lateral and torsional are recognized by most scholars. In the actual drilling process, the coupled vibration exhibits nonlinear features due to the impact of the eccentric rotation of the drill string and the influence of drilling fliud. Taking the whole drill string of directional well as the research object, a three-direction of longitudinal, transverse and torsional nonlinear coupled vibration model of drill string is established based on the nonlinear coupled deformations analysis in the longitudinal, transverse and torsional directions by using finite element analysis method. The nonlinear coupled vibration of drill string is studied by considering the effects of viscous forces of drilling fluid during the drilling process. The results show that the drill string resonance interval is relatively concentrated and the nonlinear coupled vibration frequency increase with the decrease of the length of the drill string.