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Monday, July 8 • 16:30 - 16:50
CAMPBELL DIAGRAM AND MASS UNBALANCE RESPONSE OF A DRILLSTRING

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The rotary drilling is performed with a long drillstring composed of an assembly of 9-10 m pipes screwed together and driven by a motor located at the surface. In the lower part, the drill-collar ensures the transmission of the rotation and the weight on the cutting tool. The mud is pumped down the pipes to the bit, back up into the annular drillstring-well space loaded with cutting debris, calories. Moreover, it provides the drillstring-well lubrication. During the drilling, the mass unbalances distributed along the drillstring, the mud pulsations, the Weight-on-Bit and Torque-on-Bit generated by the shapes of the rotating bit (RC, PDC, etc.) induce the drillstring vibrations combining axial, torsional, and bending motions corresponding with bit bouncing, stick-slip, forward-backward whirls. This set of vibratory phenomena may cause pipes wear, unscrewing, fatigue-cracking-rupture, etc. Consequently, the rate of penetration is slowed down and the mean time between failures reduced. Understanding, predicting and controlling drilling dynamic, a complicated rotordynamics problem, are required to ameliorate the drilling performance. The proposed beam element model predicts the drilling dynamics by taking into account the slender, rotating and pre-loaded drillstring immersed and deflected inside a 3D well. Consequently, this specific rotordynamics model combines in particular nonlinearities, couplings and parametric loads. The carried out numerical simulation concerns a 200 m drillstring in a 3D field borehole. First, its quasi-static equilibrium position is computed. Then, the Campbell diagram is considered for the modal analysis. Finally, the nonlinear mass unbalance response is studied. The conducted parametric analysis focuses on the interest of a Campbell diagram on the response prediction. This research is conducted by Drillab, a joint laboratory of DrillScan and LaMCoS, grant Labcom-SME program ANR 15-LCV4-0010-01. The authors are indebted to the Agence Nationale de la Recherche (ANR) for its financial support.


Monday July 8, 2019 16:30 - 16:50 EDT
Outremont 7
  T07 Struct. dyn. & nonlin. vib., RS04 Rotordynamics