Axial-Torsional Vibrations of Drill Strings with Crush-and-Shear Hybrid Bits at Constant Tension of Suspension Cables
V. A. Koronatov
Bratsk State University, Bratsk, 665709 Russia
Keywords: Drilling theory, rotary drilling, drill string, axial-torsional vibrations, head resistance force, crush-and-shear hybrid drill, stick-slip effects, deterministic chaos
Abstract
The article describes the rotary drilling modeling using the two-mass system of a drill string with a crush-and-shear hybrid drill bit. The head resistance of rocks on the bit is determined non-linearly: the penetration rate is added with the strength loss in the supporting medium under impact. The scope of the analysis embraces the continuous force generated by the rotating bit and the pulsed impacts by the drill strings at the end-points of the bit-bottomhole detachment. The initial conditions of the post-impact process, which define the initial penetration rate and the speed of the bit, are determined with regard to potential stick-slip effects. The numerical modeling proves that, as against the torsional vibrations, the axial-torsional vibrations of the drill string often result in the chaotic dynamics of drilling.
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