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 are usually very long1 . The first stability criterion which considered the stabilizing effect of weight on long pipes in inclined wellbores was developed by Paslay and Dawson2 .

The post-buckled configuration tells us about tubing movement, bending stresses, contact forces, and axial load distributions. The original buckling analysis by Lubinski and Woods3  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, three dimensional 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 three decades since the original papers were published. 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.

Keywords:
trajectory design, drill pipe selection, Exhibition, lateral, pipe, boundary condition, well planning, friction, helically buckled pipe, helix
Subjects:
Well Planning, Drillstring Design, Drilling Operations, Trajectory design, Drill pipe selection, Torque and drag analysis, Directional drilling
Copyright 2006, Society of Petroleum Engineers
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