HEAVE COMPENSATED RESPONSE OF LONG MULTI-SEGMENT DRILL STRINGS

A model for estimating the dynamic behavior of a long drill string excited by the heaving motion of the drillship in a seaway, is presented. The drill string is modeled as an assembly of continuous rod segments of varying cross section and material properties, to which large package can be attached. A passive heave compensation model is derived which represents the system used for deep water scientific drilling activities. The drill string system response is characterized in terms of transfer functions representing displacement and stress at selected elevations along the drill string. The heave compensation for a variety of 20,000 ft (6,096 m) drill string systems is discussed. The numerical results illustrate the sensitivity of the dynamic response estimates in near-resonant conditions, and excitation of higher modes for very long drill string systems and the motion control available due to the introduction of passive heave compensation.