Nonlinear vibrations of composite drill strings considering drill string–wellbore contact and bit–rock interaction

Vibration and dynamic behavior of drill strings are of significant concern to oil and gas industries. In recent years, composite drill strings are under development to overcome numerous restrictions of drilling operations. This research aimed to investigate the fully coupled nonlinear vibrations of composite drill strings, using the full-order nonlinear equations, which are derived by the finite element method. Drill string–wellbore contact and bit–rock interaction considering the initial deformations are taken into account. In addition, the gyroscopic effect, the major nonlinear terms and especially the geometric stiffening effect are taken into consideration. The capability of various configurations of composite drill strings to track and transmit the fully coupled nonlinear vibrations is investigated. The effects of initial deformation on dynamic behavior and the capability of different fiber orientations and stacking sequences to reduce nonlinear vibrations of composite drill strings in the different drilling conditions, especially different weight on bit, are examined.