Torsional vibrations of helically buckled drill-strings: Experiments and FE modelling

This paper presents investigations of a complex drill-string vibrations on a novel experimental rig, developed by the Centre for Applied Dynamics Research at the University of Aberdeen. The rig is capable of exhibiting of all major types of drill-string vibrations, including torsional, axial and lateral modes. The importance of this work lies in the fact, that the experimental rig utilizes real industrial drill-bits and rock samples, which after careful identification of Torque On Bit (TOB) speed curves, allows to use an equivalent friction model to accommodate for both frictional and cutting components of the bit-rock interactions. Moreover, the proposed Finite Element model, after a careful calibration, is capable of replicating experimental results, for the prebuckled configuration of the drill-string. This allows us to observe the effect of winding and unwinding of the helical deformation during stick-slip motion.