Dynamic Buckling and Snaking Motion of Rotating Drilling Pipe in a Horizontal Well

Abstract

Summary This paper is a focused theoretical and experimental study on the dynamic buckling and snaking motions of rotating pipe in a horizontal well. First, a comprehensive dynamic buckling model is presented. As part of this model, a group of fourth-order nonlinear partial-differential equations is derived and discussed. Then, a perturbation solution of the model is obtained that represents the snaking motion of the rotating pipe. On the basis of the perturbation solution, critical dynamic buckling load and dynamic behavior of rotating pipe are analyzed. It has been found that there are two different kinds of snaking motion. In one type, the pipe moves up and down around its static buckling configuration. In the other type, the pipe moves from one side of the wellbore to the other side. The authors also conducted an experimental study with a small- scale experimental facility. Depending on axial compressive load and rotating speed, different motion patterns of drilling pipe are observed. Measurements of axial load at both ends and axial displacement at the loaded end are recorded. These observations and measurements provide us with very important information about the dynamic behavior of rotating pipe in a horizontal well. Observations also show that the pipe may take two different patterns of snaking motions. Both critical static buckling load and dynamic buckling load were measured with this facility. Both theoretical and experimental results show that pipe rotation does not affect the critical load of dynamic buckling. Experiments also show that there exist two different kinds of snaking motions, which support the analytical solution of the dynamic model presented in this paper. The results are useful for practical design applications related to calculation of buckling loads and selection of bottomhole-assembly (BHA) elements and pipe rotational speeds.