The bit-bounce, or contact-instability, phenomenon which occurs in the drill string suspended from a floating vessel with an active drill string compensator to maintain a steady weight on the drill bit is investigated. This effect is sometimes ascribed to torsion effects when turning the drill bit, however, in this paper only the vertical effects induced by vessel heave are considered. A dynamic model is generated which is used for a set of simulations illustrating the contact-instability. An impedance approach for resolving this problem is described and included in the simulations which demonstrate that by modifying the impedance the bit-bounce is greatly reduced.
- Active heave compensation