Summary.

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; at higher axial compression a helix is formed. Equations are given for computing the forces required to initiate these different buckling modes. Simple experimental laboratory results confirm the theory. Results presented in this paper apply to friction modeling of buckled tubulars to help predict when pipe can be forced to move along a long section of a horizontal well.

Introduction

Since 1950, many analyses have been performed on the mechanics of pipe in oil and gas wells. Lubinski et al. defined the helical buckling behavior of pipes in vertical wells. However, the postbuckling behavior of pipe in horizontal wells is different from that 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 to analyze these problems. Two modes of buckling can occur for tubulars in horizontal or steeply inclined wells: helical and sinusoidal (Fig. 1). The axial compressive force required to buckle the pipe into a sinusoidal configuration depends on pipe stiffness and weight and on hole size in a manner similar to a beam on an elastic foundation. As axial force is increased, the buckling mode changes from sinusoidal to helical. Model experiments confirm the results of the analyses.

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