Study on Directional Drilling Coupling Dynamics Based on Drill String Rotary Controller

Abstract

In the process of long horizontal well in directional drilling, serious contact between drill string and wellbore leads to weight on bit loss. Therefore, this paper proposes a drill string rotary controller (DSC) for directional well, and its function test is completed through the experimental platform. Connected DSC working mechanism, a drill string coupling dynamic model is established under conditions of horizontal well in directional drilling. In the case study, the coupling dynamic characteristics of different units, including drill pipes and bottom-of-hole modules in axial and torsional directions, are studied. The results show that the effective value of drilling rate increases while the axial vibration velocity and amplitude of drill bit decreases. Moreover, in torsional direction, when drill string system is stable state, the rotating angular velocity of different drill pipes, rotary table, and collar is 31.16 rad/s, and the angular velocity of drill bit is 43.19 rad/s, respectively. It indicates the DSC working performance, which enhances the drilling system balance capacity. Overall, different from the sliding friction between wellbore and drill string, the addition of DSC realizes the separation and meshing of drill string and bottom hole modules, which can significantly increase the transition efficiency of weight on bit and torque value. Theoretical and experimental researches prove that the tool can effectively solve the problem of serious weight on bit loss in directional drilling process, and provides a new reference and idea for developing directional drilling technology when facing new challenges.