Research On Steering Principle And Dynamic Characteristics Of Full-Rotation Closed-Loop Pointing Steering Drill

Full rotation closed-loop directional drilling tool is the key tool for trajectory control of unconventional wells,such as multilateral wells,extended reach horizontal wells and highly difficult directional wells.The directional drilling tool is subject to a variety of complex loads in the downhole,which leads to the vibration of the directional drilling tool and affects its steering stability,accuracy and reliability,so as to improve the trajectory control and wellbore stability quality,etc.In this paper,aiming at the full rotation closed-loop directional drilling tool,firstly,the offset principle of the offset mechanism of the directional drilling tool is analyzed,the motion model of the offset mechanism is established,and a method of adjusting the offset angle and offset orientation of the steering shaft by controlling the rotation of the eccentric ring of the offset mechanism is proposed to realize the attitude control of the steering shaft.Based on the mathematical model of calculating the geometric build-up rate of the steerable drilling tool,the adjustment method of the build-up rate of the steerable drilling tool is proposed,and the relationship between the deflection angle and azimuth of the steerable axis of the steerable drilling tool and the deflection parameters of the wellbore trajectory is clarified.Secondly,the transient dynamic analysis of the spherical plain bearing of the offset mechanism of the steerable drilling tool under the combined action of radial load,downhole temperature and rotational speed is carried out,and the time history curves of the stress,radial displacement,radial velocity and radial acceleration of the spherical plain bearing are obtained.It is found that the radial displacement of the inner ring of the spherical plain bearing is unstable at the initial stage,and the peak value of the fluctuation is about 0.228 mm.The results show that there exists small vibration,which will affect the steering control precision of the fully rotating closed-loop directional drilling tool.Then,through the force analysis of the offset force,torque and lateral force on the guide shaft of the guide tool,the mechanical model is established.Based on dynamics theory and finite element method on the guide shaft vertical and horizontal two kinds of vibration modal analysis and dynamic response analysis,explores the direction axis offset Angle on its natural frequency,as well as the torque,bit pressure and offset angle effect on the guide shaft vibration characteristics,found the guide shaft and offset structure joint lateral amplitude is bigger,affect the position of steering axis offset.Finally,the finite element numerical model of bottom hole assembly(BHA)structure is established for four kinds of BHA structures with fully rotating closed-loop directional drilling tools,and the accuracy of the model is verified.The vibration index of BHA structure is calculated by numerical simulation,and the vibration characteristics of BHA are quantified.According to the vibration index,the cost function of optimizing stabilizer position is established Compared with the initial design,the vibration index of BHA structure is reduced.The research results provide a certain basis for improving the steering control accuracy and steering stability of the full rotation closed-loop directional drilling tool.