Nonlinear Vibration of a Time-Space Coupled Drill String System Based on the Surface Morphology of Rock

A B S T R A C T In this paper, the nonlinear vibration of a time-space coupled axial and torsional drill string system is investigated. Considering the surface morphology of rock, top drive system and mud, the drill string system is discretized by finite element method. The dynamic equations of the fully discrete drill string system based on rock surface morphology (SM) is established. Based on the surface morphology and strength of rock, the concept of rock surface state matrix is proposed. The stability and time domain response of the system are obtained by numerical simulation and compared with the multiple regeneration (MR) model. The results show that stick slip vibration and bit reversal are more likely to occur when drilling system cuts unhomogeneous rock, and stick slip vibration is the main reason to cause the drill bit impact rock. The stable driving torsional speed is lower than that of calculated by conventional models. In the calculation process, the volume conservation accuracy of the SM model is higher than that of the MR model. Moreover, the numerical convergence and efficiency of SM model are higher than that of MR model. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This paper investigates the nonlinear vibration of a time-space coupled axial and torsional drill string system, introducing the concept of a rock surface state matrix based on the surface morphology and strength of rock. The results show that stick slip vibration and bit reversal are more likely to occur when cutting unhomogeneous rock, highlighting the importance of surface morphology in drilling dynamics.