Study On Fluid Solid Coupling Vibration And Eccentric Wear Of Tubing String

With the continuous development of high-temperature and high-pressure oil and gas well,higher requirements for wellbore integrity are put forward.During gas well production tubing string stress is relatively complex,tubing pressure bent and the borehole wall,the contact between the switch Wells or tubing buckling deformation intense vibration occurs when production fluctuation,reciprocating wear will be in contact with the casing,tubing eccentric wear problem.The high temperature and high pressure high-yielding gas Wells have higher performance requirements for the tubing,and the performance of the pipe wall is reduced,which will directly affect the service safety of the pipe column and pose a threat to the integrity of the wellbore.This paper is surrounding gas well tubing string of fluid-solid coupling vibration and eccentric wear problem,and researched the related literature at home and abroad,according to the linear coupling mechanism of pipeline and fluid,based on the coupled vibration model of pipeline,combining the compatibility condition of contact boundary to achieve vibration coupling,derived a fluid solid coupling vibration model of oil pipe column with gas transient flow.The coupling vibration equation is decoupled and solved by the means of MOC-transformation,characteristic relation,numerical finite integration and computational grid.Combined with the initial and boundary conditions of the tubing system during the process of gas well shut-in,the case well is selected to calculate the coupled vibration of tubing string,obtained the vibration response curve and vibration stroke displacement of the tubing string during the shut in process.The results show that,during the shut in process,the change of fluid pressure induces obvious poisson coupling effect between the tubing string and the inner gas.and the string axial stress remain the state of the pulsation of the unstable alternating stress,the axial do reciprocating vibration,caused the entire string and tubing string system vibration amplitude fluctuations under the influence of friction coupling effect gradually decay to the stable.Comparing the effect of gas well yield changes on the vibration response of tubing string in shut-in process,it is found that the larger the output,the more severe the coupling vibration response.Then the mechanism of eccentric wear of tubing is studied,and the characteristics and influencing factors of tubing eccentric wear are discussed.Then it carried out the wear experiments of tubing and oil casing,obtained the wear laws of the tubing under different contact force,different wear medium,different oil pipe material and different casing material.Based on the "wear efficiency" model,it established a prediction model of the vibration partial grinding of the tubing string based on the wear coefficient of the tubing vibration stroke and the eccentric wear experiment,and carried out the vibration and wear prediction of the case well.It is found that the middle and lower part of the well tubing string has a short vibration stroke,but the lateral force of the contact is larger,so there is uneven vibration and eccentric wear in the buckling contact part of tubing string.At the same time,it also analyzed the influence of output fluctuation on lateral contact force and tubing eccentric wear.Finally,the residual strength of tubing under different grinding depth is calculated by finite element method.The safety evaluation is carried out on the prediction of the tubing bias of the instance well,the residual strength calculation and safety coefficient are carried out,and the measures for the anti-wear and vibration reduction of the tubing are put forward.