Passive Compensator Load Variation for Deep-Water Drilling

This paper explores the dynamic behavior of a passive drill string compensator being used for deep-water drilling in moderate seas using a detailed dynamic simulation. Vessel heave, even moderate, gives rise to a disturbance; the purpose of the compensator is to mitigate this effect and to maintain a near-steady load on the drill bit; any variation is termed ldquoload variationrdquo; the compensator is imperfect with various friction elements and viscous losses affecting the compensator performance; the simulation set out in this paper illustrates the load variation in a manner consistent with that experienced during actual drilling. Significant load variation is demonstrated by the simulation, with the main contribution arising from the nonlinear friction in the compensator seals; in addition, significant contact instability occurs when drilling on a very hard bottom formation resulting in bit bounce; this effect is commonly observed.