Experimentally-tuned mathematical model for drillstring vibrations

Field experience manifests that drillstring vibration is one of the major causes for a deteriorated drilling performance. It is crucial to understand the complex vibrational mechanisms experienced by a drilling system in order to better control its functional operation and improve its performance. Experimental studies of drillstring dynamics are essential to complement the theoretical studies, and to alleviate the complexity of such dynamic models. This paper presents an experimental investigation using a specially designed drilling test rig. The test rig can simulate the drillstring vibrational response due to various excitation mechanisms, which include stick-slip, well-borehole contact, and drilling fluid interaction. The test rig is driven by a variable speed motor which allows for testing different drilling speeds, while a magnetic tension brake is used to simulated stick-slip. In addition, a shaker is employed to excite the drillstring axially in order to simulate the weight-on-bit (WOB). The drillstring is instrumented for vibration measurements. The experimentally identified parameters are used to refine the finite element multibody model of the drillstring, which was derived earlier by the investigators [1]. Comparisons with published data demonstrate the reliability of the developed scheme for prediction of drillstring vibrations.