An Analysis of Tubing and Casing Buckling in Horizontal Wells

Abstract

Abstract This paper describes new theoretical results for predicting the buckling behavior of pipe in horizontal holes. Pipe buckling in horizontal holes occurs initially in a sinusoidal mode along the low side of the hole and at higher axial compression a helix is formed. Equations are given for computing the forces required to initiate these different buckling modes. Simple laboratory experimental results are also used to confirm the theory. Results presented in this paper can have applications in friction modeling of buckled tubulars to help predict when pipe can be forced to move along a long section of a horizontal well. Introduction Many analyses have been performed on the mechanics of pipe in oil and gas wells since 1950. Lubinski, et al. [1] defined the helical buckling behavior of pipes in vertical wells. However, the postbuckling behavior of pipe is different for horizontal wells than in nearly vertical wells. Knowledge of the configuration of buckled tubulars is important to prevent costly failures and to predict whether a tool can be forced along a horizontal well. This paper provides methods for use in analyzing these problems. Two modes of buckling can occur for tubulars in horizontal or steeply inclined wells: a helical mode and a sinusoidal mode. The axial compressive force required to buckle the pipe into a sinusoidal configuration depends on stiffness and weight of the pipe and on hole size in a manner similar to a beam on elastic foundation. As the axial force is increased the buckling mode changes from sinusoidal to helical. Model experiments confirm the results of the analysis. (Equation available in full paper)