DYNAMIC MODELING OF ROTATING DRILLSTRINGS WITH BOREHOLE INTERACTIONS

A dynamic model for the axial and transverse vibrations of a rotating drillstring is presented. The governing non-linear equations, which ar e obtained by using a Lagrangian approach, are fully coupled with time varying coefficients. They include the effects of gyroscopic moments, contact with the borehole wall, axial excitation due to bit/formation interactions, and hydrodynamic damping due to the presence of drillin g mud outside the drillstring. Simulation results show that parametric resonance and whirling may occur simultaneously within the range of o perating conditions of drilling. The dynamic behavior is quite complic ated and may become non-periodic, suggesting a chaotic behavior. (C) 1 997 Academic Press Limited.