Transition Of Post-buckling Configuration Of A Horizontal Pipe String In A Cylinder

In the past few decades,more and more horizontal wells have been used for exploration and development of oil and gas.However,with the extension of the horizontal well section,the buckling problem of the pipe string becomes very prominent.Buckling can cause difficulties in lowering the drill pipe,applying WOB and torque.As the axial load of the horizontal well increases,the string will experience sinusoidal buckling,eventually evolving into helical buckling,resulting in the string being locked and the axial load being unable to be transmitted.This article takes the horizontal well tubing in the oil and gas drilling and production industry as the engineering background,extracts the scientific problem of"transition of post-buckling configuration of a horizontal pipe string in a cylinder",and conducts finite element numerical simulation and experimental research.Based on the theory of sinusoidal and helical buckling of horizontal pipe string,the assumption of continuous contact is abandoned.The horizontal pipe string is discretized into beam elements,and the gap element method is introduced to establish a mechanical model for post-buckling analysis of a horizontal pipe string in a cylinder.To solve the problems of convergence difficulty caused by sudden changes in contact state and algorithm instability caused by the randomness of buckling modes,a dynamic relaxation method is proposed,which utilizes a virtual transient dynamic method to solve the nonlinear static buckling of horizontal pipe strings.The influencing factors in the post-buckling algorithm of horizontal pipe columns inside the cylinder were analyzed.Among them,damping only affects the response time,element size affects the buckling deformation,contact stiffness affects the calculation accuracy,and disturbance force does not affect the critical load of post-buckling.In various lengths of horizontal pipe strings from short to long,the relationship between axial compressive load and displacement exhibits rich non-linearity,and the evolution of post-buckling has many buckling modes.The sinusoidal buckling mode is one or more half sine waves,and when the dimensionless length of the pipe string is greater than or equal 3.73π,the dimensionless critical value tends to 1.Helical buckling mode is a deformation shape with one or more spirals.When the length of the dimensionless pipe string is greater than or equal to 6.21π,the dimensionless critical value tends to 1.414.A buckling experimental platform for horizontal pipe columns inside a cylinder was designed and constructed.The effects of loading speed,loading displacement,and column length on the sinusoidal and helical buckling of horizontal columns were studied.By comparing theoretical analysis,finite element results,and experimental data,it is found that the critical loadβ_h1for the first spiral buckling of a horizontal pipe string is in line with the sinusoidal buckling critical loadβ_s,in accordance with equation:1.414β_s≤β_h1≤2.828β_s.The research results of the paper have deepened the understanding of the evolution law of post-buckling of a horizontal pipe string in a cylinder.The obtained relationship between dimensionless length and critical load can be directly used for calculating the load after buckling of various lengths of horizontal pipe strings.It has certain guiding significance for the design,construction operation,and service application of horizontal pipe strings.