Dynamic Analysis Of The Stick-slip Vibration Of Deep-well Drillstring

With the exploration and development of deep well and ultra deep well,widely exists in the process of drilling stick-slip vibration phenomenon.It not only causes mechanical drilling speed lowered and increases the drilling cost,but also accelerated the aging and failure of drilling tools,which seriously threaten the safety of drilling processes.Therefore,it is very significant to study the stick-slip vibration characteristics of deep well drillstring to improve the drilling efficiency and reduce the oil drilling cost.This dissertation focuses on the stick slip vibration of drilling system.Firstly a one degree of freedom lumped mass torsional vibrations model of drillstring system is established.The influence of the main control pararnctcrs on the stick-slip vibration of drillstring system arc analyzed in detail by MTLAB/Simulink program.Secondly,the axial-torsional coupling vibration model of the drill string system is established,The interaction model of drill bit and rock formation not only considers the friction contact but also considers the cutting process and the non-dimensional control equation is deduced.The stability of the axial-torsional coupling vibration of the drill string system is analyzed,and the system stability area under different influence parameters is obtained.Finally,the system response of the axial-torsional coupled vibration model of the drill string system is solved by MTLAB/Simulink programming,and the influence of the lumped parameters characterizing the bit geometry,rotation speed,weight-on-bit,damping coefficient,number of blades on the stick-slip vibration of drilling system arc analyzed in detail.The following conclusions are obtained:(1)Due to the Stribeck effect of the friction between the drill bit and the rock formation,the drill string system will occurs stick-slip vibration when the rotational speed of the rotary table is extremely low.(2)In the axial-torsional coupling model,due to the time-delay feedback caused by the cutting action,when the friction force is constant,the drill bit also exhibits stick-slip vibration.(3)When the geometrical characteristic parameter of the drill bit is greater than 1,the drill string system will not have the stick-slip vibration.Thus the inequality he geometrical characteristic parameter of the drill bit is smaller than 1 is a necessary but not sufficient condition for stick-slip to take placc.(4)For the dctermination of the drill string structure and system parameters,there is a critical value of stick-slip vibration.When increasing the rotary speed,reducing the drilling pressure and increasing the damping ratio to the critical value,the stick-slip vibration of the bit will disappear,and the number of blades will also be restrained by the stick-slip vibration.(5)When the viscous damping coefficient of the drill string system becomes larger,the critical value of the rotary speed will become smaller and the critical value of the weight-on-bit will become larger.When the number of bit blades increases,the critical value of the rotary speed will become smaller and the critical value of the weight-on-bit will be larger.