Rub-impact rule between drill string and deep-water riser string in “tube-in-tube” coupling system

During deep water drilling, the drill string rotates and cuts rocks under the driving of top drive. The riser string will vibrate under the influence of marine environment, and the contact relationship between the riser string and the drill string is very complex. It is difficult to study the vibration characteristics of riser and drill string in the deep water drilling, for the understanding of complex contact relationship between riser and drill string is challenging. To address this issue, this paper proposes a model of “tube-in-tube” coupled system that encompasses both the riser in ultra-deep water and the drill string in ultra-deep well, taking the contact and collision into account. This model is used to simulate the coupled vibration of the riser in ultra-deep water and the drill string during deep water drilling. The simulation results show that the vibration characteristics of riser and drill string obtained by considering the coupling effect. Notably, the marine environmental parameters have a significant impact on the drill string's dynamics: under high ocean current velocity, the riser string in ultra-deep water experiences significant bending, which affects the movement of the drill string. Additionally, the rotation speed of drill string has minimal influence on the whirling characteristics near wellhead. However, increasing the rotational speed leads to rub-impact between the drill string and the inner wall of the riser string, increasing the failure risk of drill string and riser string.