Active Control of Distributed Subs With Anti-Slip Logic for Torsional Vibration Damping in Drilling

Previous publications showed that torsional vibrations of the drill pipe can be attenuated by subs equipped with sleeves in which the pipe rotates and is subjected to passive or actively controlled magnetic damping. The damping force depends on the relative velocity between the pipe and the sleeve and an adjustable damping coefficient, but is limited by the friction between the sleeve and borehole wall. If the commanded damping coefficient is too large, the sleeve will slip, potentially harming the borehole wall or casing, and itself. In this paper, we combine a previously designed on-off controller with anti-slip logic which learns the maximum available damping force and prevents the on-off controller from commanding a damping coefficient that leads to slippage. Occasional slippage is allowed, however, in order to learn the maximum damping force under changing down-hole conditions. Simulations demonstrate that both reduction in slippage and improved vibration damping are achieved by the modified controller.