Analysis of finite element method solution of sinusoidal buckling behaviour of drill string in vertical, directional, and horizontal wellbores and comparison with analytical solutions

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2017
Cebeci, Mehmet
The buckling of drill string in oil, gas and geothermal wells is a critical problem that has been of interest to many researchers in the industry. Prevention of buckling of drill string is important since it may negatively affect the drilling operations. When buckling of drill string occurs, it may cause deviation control problems while drilling, inefficient load transfer to the bit, excessive torque values, even pipe failures due to fatigue. The first rigorous treatment of stability of drill strings for vertical wellbores was presented by Lubinski in 1950 and his equation is till most widely used in the industry. Since, he used power series to solve differential equation governing the stability problem, the terms of power series become very large for long drill strings, therefore, after a certain length, the calculations may lead to inaccurate results. Even if analytical solution for infinite-length drill string is used for deep vertical wells, the results are still under discussion. The subject studied in this thesis is of great importance in designing the bottom hole assemblies in deep and ultra-deep vertical wells to eliminate problems associated with instability of drill strings. The study includes Finite Element Method (FEM) solution of critical sinusoidal buckling force for 5 different pipes with 21 different lengths starting from 1000 ft. up to 25000 ft. The study shows effect of length on critical sinusoidal buckling force in vertical wells by FEM and to compare the results with the analytical solutions. To prepare finite element simulations, Integrated Dynamic Engineering Analysis Software (IDEASTM) is used. In summary, it is showed that critical buckling force decreases as the depth of the well increases according to FEM solutions, although, analytical solution gives only a fixed critical buckling force for a specific pipe independent from the length.

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Citation Formats
M. Cebeci, “Analysis of finite element method solution of sinusoidal buckling behaviour of drill string in vertical, directional, and horizontal wellbores and comparison with analytical solutions,” M.S. - Master of Science, Middle East Technical University, 2017.