Nonlinear Analysis Of Tubular Buckling In Straight And Curved Wells

Flexible tubular has been frequently used in extended reach wells, and the stability of the tubular is one of the key factors to be success in drilling engineering. It is required for us to understand the detailed buckling behavior of tubular in order to optimize the design of drilling assembles and to reduce the cost. Nowadays, theories and methods are, however, far more perfect for the analysis of tubular buckling in both straight and curved wells. Therefore, there is an urgent need for more comprehensive researches in this field.Firstly, a literature study is performed. The research contents are determined based on the current status of the buckling of tubing in well-bores. Based on the general theory of the bending and twisting rod in space, the governing differential equilibrium equations of tubular subjected to radial constrains in 3D well-bore are obtained by introducing of the constraints of the well's wall. Then, the equilibrium equations of tubular subjected to radial constraints in perpendicular plane-curved and straight wells are deduced.After that, a differential quadrature element (DQE) incremental iteration method, based on the differential quadrature element method and Newton-Raphson iteration method, is proposed for obtaining solutions of the nonlinear buckling problem of tubular subjected to radial constrains. Straight and curved differential quadrature beam elements are established. The method for obtaining the structural differential quadrature equation is also given. A method for selecting initial iteration values, differing from the existing one, is proposed herein. It is shown that the proposed method reduces the computation effort and improves the computational efficiency. The proposed DQE-based computational tactics and algorithm extend the application range of the differential quadrature element method in engineering practice.FORTRAN programs were written for linear and nonlinear buckling analyses of tubing within straight and curved wells. Various numerical examples are investigated. To verify the proposed method and solution procedures, numerical results are compared with existing finite element data and experimental results. The influence of tubing length, gravity, deviation angle of the well-bore, curvature, and axial frictions is investigated, and some results for engineering reference are given. The definition of lateral buckling and helical buckling of tubular in wells is presented based on the computational results and the test data, and the corresponding solution methods are given. The sinusoidal buckling load of tubing in well-bore, the lowest eigenvalue, can be obtained by solving an eigenvalue problem. The helical buckling load of tubing in well-bore can be obtained by directly solving the non-linear differential equations. The load is applied incrementally. When a negative constraint force appears which means that a small portion of the tube is no longer contact with the well wall, then, the load corresponding to the previous step is defined the helical buckling load.Finally, the dissertation is ended by a summary. The research work is summarized. Some innovative research results are pointed out. And a few topics for further study are given for reference.