Tubing Buckling—The State of the Art

Abstract

Summary Almost unique in engineering analysis is the problem of tubing buckling in wellbores. In general, structures loaded above their critical load fail catastrophically. Yet, both tubing and drillstrings are commonly operated above the critical load. These tubing strings do not fail because the wellbore provides the necessary support for "post-buckling" equilibrium. The two fundamental questions about tubing buckling are What is the critical load? What is the post-buckled configuration? The critical load tells us if the tubing will buckle. Euler solved the problem for "short" columns, but these results rarely have application in a wellbore because the pipes in a wellbore are usually very long (Timoshenko and Gere 1961). The first stability criterion that considered the stabilizing effect of weight on long pipes in inclined wellbores was developed by Dawson and Paslay (1984). The post-buckled configuration tells us about tubing movement, bending stresses, contact forces, and axial-load distributions. The original buckling analysis by Lubinski et al. (1962) proposed a helical configuration in a vertical wellbore and used the method of virtual work to determine a specific constant pitch for that helix as a function of the axial force and bending stiffness. These two works set the following themes for further analysis of tubing buckling: What is the critical buckling load in curved, 3D wellbores? How does torque affect the critical buckling load? How do tapered strings affect the critical buckling load? What is the buckling configuration in inclined wellbores? How do the boundary conditions affect the configuration? How do tapered strings buckle? How does torque affect the buckling configuration? What effect does friction play in tubing buckling? Many of these questions have been, at least, partly answered in the past three decades. This paper will examine the technical fundamentals of the tubing-buckling problem; summarize the most useful, new results from these papers, and discuss the remaining challenges in tubing-buckling analysis.