Research On The Shaft Deflection Performance Based On The Wellbore Trajectory Control Tool

The wellbore trajectory control tool,set of information,intelligence and automation as a whole,is a new kind of steerable drilling system that can accurately and flexibly control complex well trajectory.It represents the development trend of advanced drilling tools,gradually be applied in ultra-deep and difficult directional wells,cluster wells,horizontal wells,large displacement wells,multilateral wells and the special process wells.The drilling accuracy and the quality of well trajectory as well as the drilling speed and efficiency depend on the mechanical behavior and the deflection performance of the shaft.Therefore,based on the wellbore trajectory control tool prototype and the dynamic simulation test bench studied in "11th Five-Year" and "12th Five-Year",the theoretical research,numerical simulation and experimental verification of the tool shaft performance are carried out.According to the specific structure of the wellbore trajectory control tool,the tool shaft is simplified as a statically indeterminate beam which supported by cantilever and hinge in both end.The static model of the shaft under bending condition is established and the relationship between the deformation of the tool case,the eccentricity and the deflection of the shaft and the deflection angle is established.The relationship between the force and eccentricity of the eccentric mechanism,the load of the housing and the bearing distance between the upper and lower bearings are also established,and get the critical drilling pressure of the shaft.Based on the main structure parameters of the shaft,the static model of the shaft is solved,and the critical parameters such as the bending force,the deflection angle and the critical drilling pressure are obtained.According to the three motion states of the eccentric mechanism,the inner ring rotation,the outer ring rotation and the simultaneously rotation of inner and outer ring,the motion rule of the center of the shaft section under the bending condition has been studied.The assembly relationship between the inner and outer ring drive and the hole of the inner ring is analyzed.Based on the motion vector synthesis of the inner and outer eccentric rings,the kinematic model of the eccentricity of the inner and outer rings,the rotation angle and the eccentricity vector of the shaft is established.The relationship between the deflection of the inner and outer rings and the offset of the shaft at the measuring point is obtained and completed the kinematics analysis of the tool shaft.Founded on basic theory of rotor dynamics and Hamilton theory and energy method,the steady state dynamic model of the shaft is established considering drilling pressure,torque and rotational speed.Based on the finite element analysis model,the dynamic model of the shaft is solved,which lays the foundation for the study of the dynamic characteristics and the performance of the shaft.According to the static and kinematic model of the tool shaft,the numerical simulation of the mechanical behavior of the tool shaft is completed.The influence of the housing stiffness and load on the mechanical behavior and the deflection of the shaft is obtained.That is,the eccentric force,the maximum bending moment and the deflection angle increase with the increase of the housing stiffness and decrease with the increase of the load.The influence of eccentric mounting position and shaft stiffness on the mechanical behavior and the deflection of the shaft is simulated,the optimum design of tool shaft is proposed.That is,to keep the shaft cross-sectional area unchanged and change the cross section size to reduce the stiffness of the shaft,which can reduce the force of the eccentric structure and the maximum bending moment of the shaft,and almost does not affect the deflection angle and the deflection of the shaft;The ratio of stiffness and stiffness of the housing is 25;Casing load will reduce the shaft deflecting performance,should be reduced as much as possible;The eccentric mechanism shall be installed at the 9/12 of the length of the cantilever bearing at the upper end.Based on the established shaft dynamics model,the influence laws of rotational speed and eccentricity on the dynamic characteristics and the deflection performance of the shaft are simulated.It is concluded that the dynamic characteristics and the deflection performance of the shaft show the corresponding small fluctuation with the excitation of the fluctuating WOB.With the increase of the rotational speed,the respective mean values of the eccentric mechanism force,the combined bearing support reaction force and the shaft deflection angle are unchanged while their fluctuation periods decrease,their frequency increase and their amplitudes are constant.With the increase of eccentricity,above three mean values increase while their fluctuation periods and frequency are constant and their amplitudes increase.The variation law of mean values of the shaft deviation at the measuring point is simulated with eccentricity change from 1mm to 6mm in the 60 rpm speed.The results show that mean values of the shaft deviation increase while their fluctuation period and frequency are constant and amplitudes increase with the increase of eccentricity.The variation law of mean values of the shaft deviation at the measuring point is simulated under different fluctuation WOB.The results show that the two sets of data are basically the same,indicating that changes of WOB have little impact on the shaft deflection performance,so small WOB can be used to drill to ensure higher drilling safety with the wellbore trajectory control tool.On the dynamic simulation test bench of the wellbore trajectory control tool,the indoor experiment of the deflection function and the deflection performance of the tool shaft are carried out.The indoor tests of the shaft deviation without WOB and with WOB are made.A total of 13740 sets of experimental data of the shaft deviation at the measuring point are collected and analyzed with the Pauta criterion.The results show that the calculation results of the statics model,the kinematics model and the dynamics model are in good match with the experimental results,and the maximum error is 4.7%,which verifies the deflection performance of the shaft.Based on the analysis of the contact form between the tool shaft and the inner eccentric ring,the variation law of the contact stress between the inner ring and the spindle of the eccentric mechanism is analyzed.The influence law of eccentricity of the inner and outer rings,the inner ring width,the inner ring structure fillet and the outer diameter of the shaft on the contact stress are obtained.The cumulative damage calculation formula of the shaft is established by using the theory of linear fatigue cumulative damage and the fatigue life experiment of the shaft material.The fatigue life of the shaft is obtained and the results show that the deflecting reliability of the shaft can be guaranteed.