Buckling behavior of pipes in directional and horizontal wells

Abstract

A comprehensive study of buckling behavior of pipes in directional and horizontal wells has been conducted. The study includes a new theoretical analysis on sinusoidal buckling of pipes, a modified theoretical analysis on helical buckling of pipes, and an experimental study of pipe buckling in directional and horizontal wellbores (including curved wellbores). A fundamental review of the classical buckling of columns and an introduction to the special features of buckling of pipes in wellbores are discussed. A review of the current literature on the buckling of pipes in oil wells is also presented. The new theoretical analysis on sinusoidal buckling of pipes in directional and horizontal wellbores employs a new energy analysis that greatly simplified the analysis. The results, including the explicit expressions of sinusoidal buckling loads, resolve the problems and clarify the questions that exist in the current literature concerning sinusoidal buckling of pipes. The modified theoretical analysis on helical buckling of pipes in directional and horizontal wellbores employs a modified energy analysis on helical buckling of pipes, which takes into consideration of the gradual increase in axial load during the helical buckling process from the critical buckling status to the fully buckled helix. This approach results in higher helical buckling loads and resolves the inconsistency between the assumptions and the results present in the current literature where an assumption of constant axial load during the helical buckling process is made. Small scale laboratory experiments were conducted using simulated wellbore and pipe to measure the buckling loads and axial load increase during the helical buckling process. The experimental results verify the theoretical analyses on pipe buckling in oil wellbores, and assist in the establishment of the new helical buckling analysis. The effect of wellbore fluids on the buckling of pipes in oil wellbores is also investigated. An "equivalent axial load" concept and an "effective axial load" are introduced to account for the effect of the fluid.