An experimental and theoretical study of coupled boundary conditions for vibrations in drillstrings

The boundary condition at the bit for longitudinal vibrations in a drillstring has been studied. A theory for torsional vibrational response on the longitudinal response on the longitudinal excitation is presented. Experiments in a 1000m deep vertical well have been performed. High data rate measurements of near bit accelerations, weight on bit and torque have been used to verify the theoretical predictions in drilling situations.