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

摘要

A method of estimating the instantaneous rotational speed of a bottom hole assembly (16) at the lower end of a drill string (12) that is driven by a drilling mechanism (30) at the upper end of said drill string (12), and which drill string (12) is suspected of suffering stick-slip oscillations that have an estimated or observed fundamental frequency, which method comprises the steps of determining variations in a drive torque of said drilling mechanism (30), combining a known torsional compliance of said drill string (12) with said variations in a drive torque, and providing an output signal representing said instantaneous rotational speed.