Contact Mechanics Analysis Of Steerable Ribs Of Directional Drilling Tool Of Raise Boring Machine And Hole Wall

The rotary steerable system is a cutting-edge directional drilling equipment that has been widely used in large-scale engineering projects.The push-the-bit steering principle makes the rotary steerable drilling tool highly dependent on the formation,which can cause poor directional control when drilling in weak formations due to the plastic deformation of the borehole wall,leading to borehole deviation.This paper focuses on the directional control problem of small-sized steerable rib in reverse circulation drilling machines and conducts research on the mechanical characteristics of the contact between the steerable rib and the borehole wall through theoretical analysis,numerical simulation,and experimental verification.The steerable rib structure is also optimized.The main research work and achievements are as follows:(1)Based on Hertz theory and bilinear hardening model,the contact theory model between the steerable rib and the borehole wall is established,and the factors influencing the contact stress of the borehole wall are investigated.The study shows that the contact stress is related to five factors: the size of the reverse circulation drilling machine’s borehole,the curvature radius of the steerable rib working surface,the mechanical parameters of the steerable rib material,the mechanical parameters of the borehole wall,and the push-the-bit force of the steerable rib.(2)Finite element analysis software is used to supplement the dynamic factors based on the static analysis,simulate and analyze the factors influencing the indirect contact stress between the winged blade and the borehole wall during the drilling process,and analyze the impact levels of various factors using the orthogonal experimental method.The study shows that the push-the-bit force and the elastic modulus of the borehole wall have a significant impact on the contact stress,the front chamfer of the winged blade also has a noticeable effect,while the friction coefficient between the steerable rib and the borehole wall and the drilling pressure have a negligible influence.(3)According to the theoretical model,a bidirectional loading experimental device for the steerable rib is designed to verify the effect of the push-the-bit force and the elastic modulus of the borehole wall on the contact stress,as well as the application effect of the optimized front chamfer of the steerable rib.The results show that the experimentally obtained contact stress is consistent with the numerical simulation results,with a maximum deviation of no more than 15%.In directional correction in weak formations(compressive strength ≤ 30 MPa),the maximum pushthe-bit force of the steerable rib should be controlled within 25 kN to reduce the disturbance to the borehole wall.The application effect of the combined chamfer structure is better than that of the single chamfer structure.The research results provide a reference for the application of the rotary steerable drilling tool in weak formations in reverse circulation drilling machines.