The Combined Bearing Mechanics And Fatigue Life Research Based On Wellbore Trajectory Control Tool

Wellbore trajectory control tool is a new kind of stepless adjustable point-the-bit rotary steering drilling tool,which can accurately and flexibly control the wellbore trajectory and have the ability to drill smooth and complete complex well.It has the advantages of high drilling speed,high displacement extension ability and so on.This tool excellent performance requires combined bearing of wellbore trajectory control tool to reliable operate in conditions of high temperature,high pressure,large deflection angle and heavy load.In order to control wellbore trajectory more accurately,combined bearing should have smaller radial displacement and better rotation accuracy.Therefore,to better meet the needs of precision guidance,the mechanical properties and fatigue life of the combined bearing of the borehole trajectory control tool need to be studied.Based on the prototype of the wellbore trajectory control tool,the working principle of the combined bearing are studied systematically and a set of analysis methods of bearing load,radial displacement and fatigue life are presented,which provides a theoretical basis for the design and analysis of the combined bearing and it has been well applied in the new wellbore trajectory control tool.The main contents are as follows:On the basis of considering the influence of tool shell stiffness,the working principle of tool spindle deflection supported by combined bearing,which are consist of selfaligning thrust roller bearings and self-aligning roller bearing,are analyzed.Outer spherical raceway of self-aligning thrust roller bearings and self-aligning roller bearing form a spherical space that allows the spindle to deflect.Associate with relationship between the deflection angle of the tool spindle and the eccentricity of the inner and outer rings,the static equilibrium equation of the combined bearing is established and the load distribution of the internal components of the combined bearing is solved by simultaneous the displacement compatibility condition of each bearing.Based on the static equilibrium equation of the combined bearing,the dynamic load of the centrifugal force and gyroscopic moment of the roller is taking into account as the static load,which related to wellbore trajectory control tool operating speed.The half space method is used to solve the problem of Hertz contact and sliding between the roller and the raceway in the static load setting and quasi-static equilibrium equation of combined bearing is established,which mainly includes four aspects,such as roller load,roller torque,raceway load and raceway resistance.A simplified finite element analysis model of combined bearing is established by considering the specific structure of the tool and the combined bearing as well as the bearing displacement compatibility condition.The effects of the radial load,axial preload,the deflection angle of the spindle,the rotating speed and the eccentricity of the inner and outer rings on the stress and radial displacement of the combined bearing are studied.The result shows that the maximum von Mises stress of the bearing is located between the contact surface of left self-aligning thrust roller bearing roller and raceway in the radial load direction,which is 362.86 MPa.Due to the high temperature of wellbore trajectory control tool working environment,this paper also studies the environmental temperature effect on bearing rollers and raceway solid-solid heat conduction and established thermo mechanical coupling analysis model.The distribution of the stress and temperature field of the combined bearing under the environment temperature conditions of 50?,100? and 150? are solved.The result shows that the highest temperature distribute in the contact surface between self-aligning roller bearing roller and raceway in the radial load direction,which is up to 152.7?.With the increase of ambient temperature,the maximum von Mises stress increase,which is respectively 415.05MPa(50?)?509.04MPa(100?),629.74MPa(150?).The radial displacement decreases with the increase of the ambient temperature,which is 5.16?m(50?)?5.04?m(100?),4.91?m(150?).Wellbore trajectory control tool and test control system as well as radial displacement measuring joint was used to test the radial displacement of combined bearing.The orthogonal experiment considering the influence of the rotational speed,deflection azimuth angle and the eccentricity of the inner and outer rings is designed and conducted.The 216 times of mixed level orthogonal test has been completed.The results show that the eccentricity of the inner and outer rings has the greatest influence on the radial displacement of the bearing and the trend is consistent with the finite element analysis results.Based on the single bearing Lundberg-Palamgren fatigue life theory and IoannidesHarris fatigue life theory,the combined bearing fatigue life emprical formula using multiplication theorem of probability as well as I-H fatigue life calculation method based on thermal mechanical coupling analysis and actual working conditions were respectively put forward.By comparing the results of two methods with the results of combined bearing life test,it is found that the calculation method of I-H fatigue life is more practical and can be used to calculate the fatigue life of various similar types of combined bearing.