A mechanism that couples longitudinal and torsional drillstring vibrations at the bit was studied. Torsional vibrations are associated with dynamic variations of the rotational bit speed. When a roller bit runs over a multilobed pattern, these speed variations have been shown to affect the input of longitudinal vibrations. The theory for this coupling mechanism is verified experimentally by high-rate data of near-bit accelerations and torque recorded in a 1000-m [3,280-ft] -deep well.

Keywords:
torque, bit speed, amplitude, nominal rotary speed, experiment, drillstring dynamics, spectrum, spe drilling engineering, vibration, upstream oil & gas
Subjects:
Drill pipe selection, Drillstring Design, Drillstring dynamics, Torque and drag analysis
Copyright 1988, Society of Petroleum Engineers
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