Dynamics of an offshore drilling tube system based on a riser-drill string-drilling fluid coupling model

Accurate prediction of dynamic characteristics of an offshore drilling tube system under marine environmental loads is significant to secure the safety of offshore drilling operations. Based on previous works for coupling riser with drill string to form a pipe-in-pipe structure, in this present work, the influence of drilling fluid is taken into consideration to develop a riser-drill string-drilling fluid coupling model; and the corresponding verifications are conducted via comparison with the experimental results. The collisions between riser and drill string are demonstrated to restrict the lateral drifting of the riser, which, however, can be intensified by the upward flow of drilling fluid. In addition, as increasing the offset of the drilling platform, the lateral drifting of the riser also increases; moreover, the position for the maximal drifting moves upwards to the sea surface. When the part of the drill string below the mudline is taken into consideration, the increasing angle of well inclination is illustrated to restrict the lateral drifting of the riser above the mudline.