Research On Torsional Vibration Characteristics Of Drill String And Optimization Of Drilling Parameters

With the increasing human demand for oil and gas resources and the rapid development of the petroleum industry,oil drilling has gradually developed into deeper formations.In the drilling process of deep wells and ultra-deep wells,the drill string often produces torsional vibrations,severely damaging the drilling tools,reducing drilling efficiency,and increasing drilling costs.Therefore,it is very important to study the torsional vibration characteristics of the drill string,complete the optimization of drilling parameters,and increase the mechanical drilling speed when the torsional vibration is relatively stable.This is of great significance for protecting drilling tools,improving the efficiency of oil and gas drilling,and reducing oil drilling costs.In this paper,the torsional vibration model of the drill string is first established on the basis of the friction torque at the drill bit,the characteristics of the torsional vibration of the drill string are studied,the mechanism of stick-slip vibration of the drill string is explored,and the influence of drilling parameters on the torsional vibration is analyzed.Secondly,the near-bit drilling comprehensive parameter measurement tool was used to measure the vibration data in the field,and the measured data was analyzed in time domain and frequency domain to reveal the characteristics of the drill string torsional vibration.Finally,based on the vibration model,combined with the actual measured data,a torsional vibration model of the drill string was established,and the drilling parameter optimization was completed in conjunction with the mechanical drilling speed equation to form a preferred range of drilling parameters suitable for different formations.The results of theoretical analysis of the drill string torsional vibration model show that the turntable torque during the critical rotation of the drill bit is less than the maximum static friction torque of the drill bit;there will be four situations such as micro stick slip,typical stick slip,stable with stick slip,and no stick slip when the drill bit rotates;when the maximum static friction coefficient and dynamic friction coefficient of the drill bit both exist and satisfy a certain relationship,the drill string will produce stick-slip behavior;the angular velocity of the drill bit increases with the increase of the torque or speed of the turntable,and the drill string develops toward the direction of non-stick slip stability,and the influence law of the weight on the bit is opposite.The results of on-site data analysis show that when the drill string undergoes torsional vibration,the measured data will show periodic changes that occur repeatedly with severe and weak fluctuations.The results of drilling parameter optimization show that selecting reasonable weight and torque can effectively eliminate the torsional vibration of the drill string and improve the mechanical drilling speed;when the drill string produces stick-slip behavior,the harder the formation being drilled,the greater the turntable torque required,and the more effective it is to reduce the weight-on-bit to eliminate stick-slip behavior.