New Concepts for Helical Buckling

Summary An approximate analytic solution for the helical buckling of tubing with weight has been determined. This solution has good accuracy except near the neutral point. The solution used by Lubinski to solve the helical-buckling problem is shown to be a special case of this new analytic solution. It is generally accepted that Lubinski's solution is a good approximate solution, but the range of applicability has been unknown because the approximations used in its derivation were not well understood. In this new solution, the approximations are explicit and an accuracy criterion is established. Initial conditions at the packer are investigated and their effects on the solution are described. Finally, the effect of this solution on tapered strings is described, and a new approximate buckled solution for tapered strings is presented. This analysis puts the Lubinski solution in a technical context that allows such further developments as inclined wellbores and friction.