Coiled Tubing Mechanics Analysis

For more then 40 years of continuing study and improvement, the quality of Coiled tubing(CT) now has largely increased, its technology and application has became more and more mature,which makes CT more adeptable to work at harsh environments and complex operations. Now CT is widely used in well workover, well completion, well logging, stimulation treatment, well drilling and transportation pipeline, the so-called Universal Operating Equipment. But its downhole buckling behavior makes downhole operation tougher and even worse can lead to some unexpected accidents, so it's necessary to conduct the study of CT's downhole buckling behavior.In this thesis, fistly, a spline model of 3D well trajectory was created based on the basic inclinometer data of well trajectory, which can calculate deviation angle, azimuth angle, deviation rate, azimuth rate, curvature and torsion of well trajectory at any depth. Secondly, the buckling equation of the CT that constrained by wellbore was established based on the geometrical relationship of downhole CT and well trajectory, equation of static equilibrium, physical equation. This buckling equation was under the consideration of axial force,CT weight, internal pressure, external pressure, anti-force of well wall, coulomb friction and viscous force. Then this buckling equation was once again derivation by energy method, which had proved the rationality of the buckling equation. At last by combining the static method and the energy method, the buckling equation was solved and the critical sinusoidal and helical buckling force were obtained, the analytic solutions which presents the CT post buckling configuration was also obtained. Finally, axial force, anti-force of well wall and flexural moment of the whole downhole CT were obtained according to the given boundary conditions and using finite element method, then the analysis of stress and transfiguration are presented, you can also predict whether the CT can safely put down to the required depth by comparing the safety factor, if not, the maxinum depth will be presented.A software was developed by VB language according to the above theory and calculation method. In the preprocessor part of this software you can input the basic inclinometer data of well trajectory and CT parameter and working condition. In the post processor part, the result can be viewed both by graphics and basic data. Such as the horizontal projection and vertical projection and 3D coordinate graph of well trajectory. The hook load and force and stress and transfiguration and safety factors chart based on the variation of the depth can also be output as well as their specific data.