Dynamic characteristics of a drilling riser considering drill string–riser collision under internal solitary waves

Abstract

To address the large-deformation problem that may occur in a drill string–riser system under internal solitary waves (ISWs), a physical model is developed based on Hamilton’s principle, in which the coupled effects of ISWs, the drill string, drilling fluid, and the drilling riser are comprehensively considered. To accurately describe the post-collision displacement evolution of the drill string and the riser, an iterative collision-updating method is introduced for correction. The results indicate that the presence of the drill string can suppress the increase in riser displacement, but it increases the Von Mises stress. The collision loads are mainly concentrated in the upper section of the riser and shift with variations in environmental parameters. Parametric analysis shows that increasing the tension ratio can reduce displacement while increasing the equivalent stress, whereas changes in the weight on bit (WOB) do not significantly alter the motion trend of the drilling riser. The wave amplitude and the pycnocline depth are identified as key environmental factors. When η ₀ increases from 90 to 120 m, the maximum collision force increases from 814 to 1241 N. When d _u increases from 100 to 400 m, the maximum displacement increases from 5.684 to 12.525 m, while the maximum collision force decreases from 1487 to 1064 N.