Simulation and analysis of dynamic characteristics of drilling string in extra-deep well

Drilling string dynamic simulation and analysis can provide support for safe, high-quality and efficient drilling. With the increase of drilling depth, the mechanical problems involved in drill string dynamics become more complicated. How to simulate drill string dynamics is very challenging. In order to explore the dynamic characteristics of drill string in extra-deep borehole, the Newmark method is used to discrete the time, and the SOR node iteration method is used to solve the whole configuration of drill string at each time step. The dynamic simulation of drill string with vertical depth of over 9000m is realized. The whirl trajectory, whirl velocity and lateral acceleration, et al, of drill string at three typical positions are given. The whirl and stick-slip characteristics of drill string are analyzed. The results show that the whirl and stick-slip phenomena in the upper part of drill string are not obvious. As the position moves down, irregular whirl and insufficient stick-slip phenomena appear, and the drill string near the bit may experience violent whirling and stick-slip vibration. The drill string near the neutral point has the most violent whirls and serious friction, which may bring potential safety risks to the drill string and require special attention.