Study On Load Of Tubing String And Stress Of Connecting Thread In Pumping Well

The tubing string’s vibration during operation can cause fatigue,and this is a major factor in its failure.As the connecting element of the tubing,the threaded joint and the tubing string are exposed to intricate loads such as tension,compression,bending,internal pressure,external pressure and vibration for an extended period in the downhole.This paper studies the axial vibration and axial load of the tubing string in the directional well under the external load,and establishes the coordinate system through the axial vibration,and studies the transverse vibration,bending moment and shear force of the tubing string.Finite element analysis is employed to assess the connection strength of the threaded joint,ultimately.By taking into account the liquid pressure alteration in the sucker rod string,the concentrated load at the plunger end,the friction resistances and the Coulomb friction between the rod and the tube,a simulation model of the axial load of the sucker rod string is established based on the wave equation of its longitudinal vibration.Based on the axial load of sucker rod string,the calculation model of rod and pipe contact force is established,provides environmental load for simulation of axial vibration and lateral vibration of tubing string.Considering the fluid damping force on the tubing string and the Coulomb friction force between the rod and the pipe,the concentrated liquid load on the bottom of the tubing string,taken as the excitation of the axial vibration of the rod and pipe,establishes a simulation model of the axial vibration of the tubing string,thereby allowing for the simulation calculation of the axial load of the tubing string to be realized.Considering the excitation of alternating contact pressure and alternating axial load on the lateral vibration of the tubing string,and considering the impact constraint and excitation of the casing on the tubing,the simulation model of the lateral vibration of the tubing string is established,and the calculation of the bending moment and shear force on the tubing string is realized.The finite element analysis model of tubing connection thread stress is established,taking into account axial load,bending moment,shear force,internal and external pressure,and thread pre-tightening moment on the tubing string.Analysis results demonstrate that axial load and internal pressure are the primary determinants of the thread’s connection stress,with the latter intensifying the former.