We investigate experimentally and numerically suppression of drill-string torsional vibration while drilling by using a sliding mode control. The experiments are conducted on the novel experimental drill-string dynamics rig developed at the University of Aberdeen (Wiercigroch, M., 2010, Modelling and Analysis of BHA and Drill-string Vibrations) and using commercial Polycrystalline Diamond Compact (PDC) drill-bits and rock-samples. A mathematical model of the experimental setup, which takes into account the dynamics of the drill-string and the driving motor, is constructed. Physical parameters of the experimental rig are identified in order to calibrate the mathematical model and consequently to ensure robust predictions and a close agreement between experimental and numerical results for stick–slip vibration is shown. Then, a sliding mode control method is employed to suppress stick–slip vibration. A special attention is paid to prove the Lyapunov stability of the controller in presence of model parameter uncertainties by defining a robust Lyapunov function. Again experimental and numerical results for the control cases are in a close agreement. Stick–slip vibration is eliminated and a significant reduction in vibration amplitude has been observed when using the sliding controller.
In this work we investigate forward and backward whirls of a drill-string using a novel experimental drilling rig [1] capable of reproducing major types of drill-string vibration, including stick-slip, bit-bounce and whirling. We focus our attention on whirling motion of the Bottom Hole Assembly (BHA) with a particular attention to the coexistence of forward and backward whirls. We present experimental results, showing for the first time co-existing whirling solutions and characterizing the parameter space in which different whirls can be observed. Those results are then used to calibrate a simple mathematical model, which can be used for further studies of whirling phenomena.
Large Rates of Penetration (ROPs) with a good borehole stability in hard rock formations is still one of the major challenges in downhole drilling. In this regard, the Resonance Enhanced Drilling (RED), a new downhole drilling technology being developed by the University of Aberdeen, could offer a radically new way of drilling for oil and gas wells at a reduced cost and a lower environmental footprint. Market research estimated that the RED technology could result in an annual savings of $1.05 billion for operators [1].
The RED technology applies a controllable high frequency dynamic stress on the drilled formation, which is induced by axial oscillations of a drill-bit at the resonance conditions. The resonance conditions between the drill-bit and the formation are maintained for varying drilling conditions by adjusting the frequency and amplitude of the dynamic load to produce a steadily propagating fracture zone. The RED technology is particularly well suited for hard rocks.
Through an extensive physical and mathematical modelling, and experimental studies on the developed full scale experimental rigs, it has been proved that RED can significantly reduce wellbore creation time and deliver the capability to drill with one bit through in various rock formations and drilling conditions. RED also allows to drill efficiently even with a smaller Weight-On-Bit (WOB).
The University of Aberdeen is just about to complete a large multi-million pounds research and development programme funded by the Scottish Enterprise aimed to scale up the laboratory findings and bring the RED technology closer to the commercial world. The paper introduces this technology and discusses its potential impact on the industry.
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