METHOD AND APPARATUS FOR ESTIMATING THE INSTANTANEOUS ROTATIONAL SPEED OF A BOTTOM HOLE ASSEMBLY

摘要

The present invention relates to a method of damping stick-slip oscillations in a drill string, to a method of drilling a borehole, to a drilling mechanism for use in drilling a borehole, to an electronic controller for use with a drilling mechanism, and to a method of upgrading a drilling mechanism on a drilling rig.
Aspects of the present invention are based on the insight that a PI or PID controller can in fact be used to obtain significant damping of stick-slip oscillations by the drilling mechanism. In particular it was found that a PI or PID controller can be tuned to ensure efficient damping torsional wave energy at and/or near the fundamental mode of stick-slip frequency. A further insight on which certain embodiments are based is that both the fundamental and one or more higher mode (e.g. second natural mode and greater) oscillation can also be damped by reducing the effective inertia of the drilling mechanism, which may be achieved in several different ways.