Unveiling complexity of drill-string vibrations: Experiments and modelling

We investigate complex drill-string dynamics on a novel experimental rig [1], capable of reproducing all major types of drill-string vibrations. One of the most important features of this versatile experimental rig is the fact that commercial drill-bits and rock-samples are used. The rig allows for different configurations, which enables the experimental study of various phenomena, such as stick-slip oscillations, whirling, drill-bit bounce and helical buckling of the drill-string. Special attention is given to the estimation of the physical parameters of the flexible shaft, which is the element used to mimic the characteristics of the drill-string and plays a crucial role in the creation of undesired vibrations. Furthermore, a low-dimensional model of the drilling assembly based on a torsional pendulum is developed and calibrated by means of the experimental measurements. In addition, a detail high-dimensional model of the drilling rig is developed using a Finite Elements Analysis approach. The experimental and numerical results demonstrate the predictive capabilities of our mathematical models, in particular when stick-slip oscillations occur. (C) 2015 Elsevier Ltd. All rights reserved.