Strength Analysis And Structural Parameter Optimization Of Connection Thread Of Petroleum Coring Drilling Tool

As the human demand for oil increases year by year,people pay more and more attention to the efficiency of oil exploitation.As one of the indispensable tools for petroleum exploration,the drilling efficiency of coring tools directly affects the oil production.At present,the technical problem of petroleum coring drilling tools is the failure of connecting threads between drill pipes.Increasing the strength and service life of the connecting thread is a research hotspot of petroleum core drilling tools.In this paper,the integral connecting thread of the drill pipe of the oil coring drilling tool-the upper centralizer part is taken as the research object.Firstly,according to the four different working conditions of drilling tools,the strength analysis is carried out by finite element software to determine the stress and displacement of connection threads under the four working conditions.Then,the modal analysis of the part and fatigue analysis of connection threads are carried out.Finally,on the basis of the above analysis,the structural parameters of the connecting thread are optimized for the most dangerous working conditions to improve the service life of the connecting thread.The main contents of this paper are as follows:(1)Strength analysis.Aiming at the four different working conditions of the drilling tool in the actual working process: When the drill tool is tightened by pretightening torque,and when the drill tool touches the ground after pre-tightening,it works normally and reaches the maximum speed.,the finite element software Hyper Works is used to carry out the finite element analysis and calculation,and the corresponding stress and displacement under the four working conditions are obtained.The results show that the maximum equivalent stress of the connection threads under the four working conditions is less than the allowable stress and meets the strength conditions.(2)Modal analysis.This part takes the whole handover part of the oil coring drilling tool-the upper centralizer part as the modal research object.The first 15 modes are analyzed in detail,Then the frequency values of the lowest mode are compared with the external excitation frequencies under the four different working conditions,the dynamic characteristics of the thread under different working conditions are analyzed.The results show that under the four typical working conditions,the natural mode and excitation of the structure are not coupled,but the natural frequency is close to the excitation frequency under the maximum speed condition,and it should be optimized to avoid resonance.(3)Fatigue analysis.In view of the most dangerous condition,i.e.the working condition of the pre-tightening of the drill tool under the action of the upper buckling torque of 3500 N M,the stress fatigue analysis method of n Code Design Life is used to predict the fatigue life of the connecting thread.The results show that the minimum life of the connecting thread is 216100 times,and the area where the first fatigue failure occurs is the end of the first thread of the external thread and the meshing surface of the last thread of the internal thread,which is consistent with the strength analysis results.(4)Structural parameter optimization.In view of the most dangerous working conditions,Hyper Study is used to optimize the structural parameters of connecting threads from three aspects: pitch,tooth profile angle and tooth height.Then the fatigue life of the optimized connection thread model is predicted by the stress fatigue analysis method.The results show that the number of fatigue life of the optimized connection thread is 1147 000 times,which is higher than that of the original model,and the rationality of the optimization scheme is verified.