Study On Drill String Vibration And Vibration Reduction Mechanism Of Gas Drilling

Nowadays,in gas drilling engineering,drill string vibration has become the main cause of drill string failure,and the vibration types can be divided into three types.These include lateral vibration induced by drillstring reverse rotation motion,axial vibration caused by interaction between bit and wavy bottom hole,and torsional vibration caused by interaction between bit and accumulated cuttings.Considering the economic cost of drilling,it is very important to study the vibration and vibration reduction mechanism of drill string in gas drilling.In this paper,the drill string vibration of three kinds of gas drilling is studied by combining theoretical and numerical analysis.First of all,for the lateral vibration of gas drilling string,it is considered that the lateral vibration of gas drilling string is excited by reverse rotation motion and presented in the form of beat.Among them,the ring gap ratio has a great influence on the reverse rotation motion.Based on the establishment of the mechanical lateral vibration model of the drill string in gas drilling,the lateral vibration equation under axial tension load is derived,and the basic law of lateral vibration is obtained.The influence factors of the maximum bending deflection and the maximum bending stress are analyzed when the drill string vibrates laterally.Considering the drill string reversal,the corresponding lateral vibration reduction measures are given.Secondly,for the axial vibration of the drill string in gas drilling,the relationship between the drill bit and the wavy bottom hole is studied.The results show that the phenomenon of the drill bit jumping off the bottom hole exists,and it is considered that this is the main cause of the axial vibration.Using the mechanical model of axial vibration of drill string in gas drilling,the natural frequency equation of axial vibration with or without shock absorber is obtained.In order to protect the drill string and bit,a tuning relationship with undamped shock absorber is proposed for axial vibration.Finally,for the torsional vibration of gas drilling drill string,not only the mechanical model of torsional vibration of gas drilling drill string is established,but also the mechanical model of stick slip vibration of gas drilling drill string is established,and the natural frequency equations of torsional vibration and stick slip vibration are obtained.Among them,the influence factors of stick slip vibration natural frequency of drill string,maximum speed of drill bit and stick slip period are analyzed in detail.Based on the analysis of the numerical results of stick slip period and wellhead torque,it is considered that adjusting the rotation speed of the drill string by using the top feedback data is beneficial to weaken the damage degree of stick slip vibration to the drill string.Taking gas drilling in Xujiaweizi area as an example,ANSYS workbench is used to simulate the vibration of gas drilling string,the finite element model of gas drilling string is established,and the fluid solid coupling of gas drilling is completed.Through the modal analysis and static analysis of the drill string,the tenth order natural frequency and the response in the process of vibration,such as lateral displacement,axial displacement and torsional angle.