The multidirectional vibration and coupling dynamics of drill string and its influence on the wellbore trajectory

Abstract

For improving the accuracy of wellbore trajectory prediction in complex wellbore structures, especially in the kick-off section, a longitudinal, torsional and radial coupled drill string dynamics model is proposed. At the same time, the coupling dynamics model is solved based on the energy method, and the torque, weight on bit (WOB), the longitudinal displacement and velocity, the torsional angular displacement and angular velocity of the drill bit are obtained during the normal drilling and the stick-slip vibration phase. Combining the numerical example and experimental test, the differences between different models and actual drilling trajectories are compared and analyzed. The research results indicate that the torsional vibration and the longitudinal vibration have a great influence on each other in the coupling model, and the longitudinal vibration displacement increases, which can effectively reduce the torque variation range of the torsional vibration. The operation of the bit stagnation is weakened, maintaining a relatively stable wrotational angular velocity of rotation. The calculation results of the wellbore trajectory are more consistent with the experimental results, and can accurately reflect the real situation of the drilling process. The theoretical model has an important reference for predicting the new well structure, especially the judgment of wellbore trajectory of complex wellbore structures such as extended reach wells, horizontal wells, deep wells and high deep wells of coalbed methane, and the prediction of downhole dynamics results.