Effects Of Drillstring Length On Snake Buckling Loads

Flexible drillstrings have been frequently used in extended reach wells,and their stability is one of the key factors to be success in drilling engineering.It is required to understand the detailed buckling behavior of them 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 drillstring buckling analysis in wellbors.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 drillstring buckling in wellbores.Based on the the actual working conditions of the drillstring in wellbore and to ensure the consistency of the minimum of an energy functional with its corresponding equilibrium equation eigenvalue,the boundary conditions are given.Then,using the differential quadrature(DQ) element method,a stiffness equation for analysing the snake buckling of the drillstrins subjected to radial constraints are deduced. Besides,the explicit form for the element stiffness and incremental stiffness matrices is also given.After that,FORTRAN programs were written for snake buckling analyses of drillstrings in inclined wellbores.Various numerical examples are studied.The mechanism about the snake buckling of drillstrings in the inclined wellbores is explained via numerical analysis method.The effects of oblique angles of wellbores,constraint conditions of ends and drillstring length on the buckling loads are investigated,and the rationality of the proposed model and mothod is confirmed by being compared with the theoretical solution and experimental results in literature., Some results for engineering reference are given.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.