Torsional Buckling And Vibration Control Of Flexible Drill String

In drilling engineering,the drill string with a large aspect ratio bears the role of transmitting torque.It has great flexibility and may experience torsional buckling behavior when encountering stuck drilling conditions.Twisted and buckled drill pipes may lead to drill string failure accidents,making it impossible to continue underground work.Therefore,this article mainly conducts finite element analysis and experimental research on dynamic torsional buckling of simulated flexible drill pipes,and designs a dynamic torsional buckling experimental platform,as well as a stick-slip vibration control system with the same objective as torsional buckling control.This article establishes a finite element model to simulate the dynamic torsional buckling of rods,adopts transient dynamic methods to study the configuration evolution of drill string torsional buckling,and got a dynamic critical torsion angle determination method based on torque peak.Based on this method,this article discusses the influence of rotational speed on the dynamic critical torsion angle,as well as the effects of elastic modulus,density,and aspect ratio on the dynamic critical torsion angle.Subsequently,based on the experimental platform of dynamic torsional buckling,this paper studied the feasibility of simulating rods made of ABS and polyurethane materials in dynamic torsional buckling experiments,and analyzed the effects of rotational speed and aspect ratio on the dynamic torsional buckling of rods.The results indicate that the configuration evolution of dynamic torsional buckling can be summarized as a straight rod state,subcritical instability state,and spiral buckling state;The higher the rotational speed,the greater the dynamic critical torque angle;The higher the elastic modulus and density,the greater the dynamic critical torsion angle;The larger the aspect ratio,the greater the dynamic critical torsion angle;The finite element analysis is consistent with the experimental results.To suppress the torsional buckling behavior of the drill string,it is necessary to control the angle difference between the drill bit and the rotary table of the drill string system.Considering that the goals of torsional buckling control and stick-slip vibration control are consistent,this paper establishes a dual centralized mass spring damping system for the drill string.The effects of top drive speed,top drive torque,and bottom hole drilling pressure on stick-slip vibration were studied.Subsequently,this article studied the control effects of various controllers on stick-slip vibration.Research has shown that the model free adaptive controller has a lower peak output torque and a smoother torque output curve,making it suitable for working conditions with lower rated torque of top drive motors;The torque feedforward sliding mode controller can make the system work at lower expected speed;The sliding mode controller can significantly improve the performance of model free adaptive controller.