Post-buckling Configuration of Drill Strings Constrained in Curvilinear Wellbores

Nowadays, with the advent of new techniques of drilling deep and curvilinear boreholes, understanding the buckling behavior of a drill string in a wellbore is crucial for the success of a drilling operation. Unlike the classical Euler buckling mode of a rod, redistribution of drag, gravity and contact forces acting on the drill string confined in a wellbore make the drill string buckling behavior more complex. This phenomenon has been studied comprehensively for straight holes (vertical, inclined and horizontal), but it is still perceived incompletely when the drill string operates in a curvilinear hole. In this study, the nonlinear differential equations related the equilibrium state of the drill string confined in the wellbore of a curvilinear hole were presented. A generalized differential quadrature rule was employed to discretize governing equations and the resultant set of nonlinear algebra equations is then solved with Newton-Raphson iterative method. The post-buckling configuration development of the drill string obtained from the method was found to be in a good agreement with field observations and available results taken from the literature. It is demonstrated that the well path can considerably influence the post-buckling configuration of the drill string. The prone to buckling is the straight segment, the inclined section is followed and the curved section is hard to buckling. The capability of the proposed model in predicting accurately both common buckling configurations (sinusoidal and helical), making it a powerful tool not only at the design stage but also for real-time analysis.

Keywords:

buckling , drill string , curvilinear wellbore , generalized differential quadrature