Abstract: “Complicated behavior of oilwell drill string with both torsional and lateral whirl vibrations are explored numerically and experimentally within this paper. A modified Jeffcott rotor model with attention to drill string and outer shell interactions is developed. Drill mud drag forces within a thin annular film surrounding the vibrating rotor are considered. With respect to the rotation speed drill mud damping effect on drill string behavior is studied. Numerical efforts are compared to experimental studies conducted with laboratory scale drilling system. The results obtained suggest that the drill mud dynamics are highly related to the drive speed and rotor deflection. The findings of this work are relevant to the understanding of hydrodynamic mass of drill muds on drill string dynamics and schemes for controlling them.”

Keywords: drill string dynamics, drilling mud, modified Jeffcott rotor, lateral whirl.