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Rôle du processus de forabilité des roches dans les vibrations de torsion des systèmes de forage pétrolier

Abstract : PDC drillbits can experience intense rotary speed fluctuations which hamper drilling operations. This phenomenon, known as stick-slip, is self-sustained and occurs in many common drilling contexts. It is generally assumed that stick-slip instabilities result from the decrease of the torque-on-bit with the drillbit rotary speed. Many solutions have been introduced to mitigate stick-slip, but neither the root cause of the torque decrease, nor the effective role of the drillbit have been clearly identified yet. This thesis aims at studying the influence of the rotary speed on the mechanical response of the PDC drillbit, both experimentally and theoretically. An extensive program of drilling tests has shown that forces acting on PDC drillbits, as well as on their individual cutters, strongly depend on the cutting velocity. This rate-effect has been attributed to the dynamic shearing of a dense layer of crushed rock trapped at the tip of the cutter. A new semi-empirical rate-dependent bit-rock interaction model has been calibrated on these experiments to predict the dynamic response of real PDC drillbits. It is in good agreement with drilling tests performed with full scale PDC drillbits. The model has been coupled with a drillstring torsional dynamics software to compute the corresponding risk of stick-slip. The dynamic bit-rock interaction model explains why the torque decreases with the rotary speed and shows that the risk of stick-slip can be significantly reduced by selecting the appropriate PDC drillbit design.
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Submitted on : Monday, February 7, 2011 - 1:56:14 PM
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  • HAL Id : pastel-00563835, version 1


Gilles Pelfrene. Rôle du processus de forabilité des roches dans les vibrations de torsion des systèmes de forage pétrolier. Géologie appliquée. École Nationale Supérieure des Mines de Paris, 2010. Français. ⟨NNT : 2010ENMP0062⟩. ⟨pastel-00563835⟩



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