Study On The Buckling Of Coiled Tubing Based On Theoretical And Experimental

In recent years,the coiled tubing has been used for downhole operation in the field of oil and gas engineering.The downhole operation string is related to the stability of the key of construction operations.The coiled tubing unit is used widely in oil and gas field exploration and development in the process of washing,completion,logging and workover and other fields.However,the theory and method of studying the buckling of underground tubular string are not perfect.Therefore,it is very important to study the buckling problem of the downhole system under radial confinement.In this paper,the following research work are carried out.First,the buckling behavior of the coiled tubing is studied on the basis of analyzing and summarizing the previous research results.In this paper,the buckling analysis model of coiled tubing in an inclined wellbore is established by considering the influence of column friction,well deviation angle and boundary condition.The differential equations for buckling control of underground tubular string are derived by the principle of variational and the minimum energy method.The perturbation method is used to obtain the tube column angular displacement under sinusoidal buckling and helical buckling.Second,the sinusoidal buckling and helical buckling critical loads of the obtained string are obtained by the perturbation method.In this paper,the influence of the inclination angle and the friction of the well on the sinusoidal buckling and the critical load of the helical buckling are analyzed.In this paper,the effects of three different boundary conditions on the critical buckling load of the tubular string are studied,which are fixed end constraint at one end,fixed end constraint at the one end and hinge constraint at the other end.This paper deduces the expression of the axial force under the condition of cylindrical sinusoidal buckling and helical buckling.According to the analytical solution of the column axial force and the buckling critical load of the pipe string,the induced position of the sinusoidal buckling and the helical buckling of the tubular string are analyzed.Third,based on the principle of minimum potential energy and variational principle,a buckling analysis model of tubular string in well is established.By solving the buckling equations,the critical load of the sinusoidal buckling and helical buckling are obtained.The influence of borehole diameter and radius of curvature on the critical load of sinusoidal buckling of tubular string in curved wells is analyzed.It is found that the critical loads of sinusoidal buckling and helical buckling are higher than that of the critical buckling load of tubular string in curved wells.Fourth,the critical load of sinusoidal buckling and helical buckling in vertical wells are studied through experiments.In the experiment,the friction loss under different friction coefficient was measured.In this paper,the friction loss calculated theoretically is compared with the experimental data.The relationship between column displacement and axial load is studied through experiment.The axial displacement of the pipe with different diameters and friction coefficients were analyzedIn short,the buckling of underground tubular string is carried out under the premise of considering the important influence factors of friction.In this paper,the sinusoidal buckling and helical buckling critical load of underground tubular string are obtained,and the expression of the axial force under these buckling modes are obtained.Compared with the influence of friction factors,the results of this study improve the accuracy of calculation,which is very important to grasp the force of downhole string.