Local mechanical model of down-hole tubular strings constrained in curved wellbores

Kinds of tubular strings are widely applied to the development of oil and gas fields. Most of these tubular strings constrained in straight or curved wellbores can be taken as homogeneous thin elastic rods constrained in straight cylinders or tori. Recent studies have shown that connectors on the tubular strings play an important role on the tubular string deflection problem. On the basis of previous studies, this paper provides a new model to describe the deflection behaviors of a tubular string with connectors constrained in a curved wellbore. The axial force on the ends of the tubular string is divided into axial tension and axial compression. The deflection state is divided into no contact, point contact and wrap contact according to the radial displacement of the tubular string or divided into initial configuration, sinusoidal buckling and helical buckling configurations according to the angular displacement of the tubular string. The critical conditions between no contact and point contact, between point contact and wrap contact in the initial configuration are studied. The deflection curves under the three contact cases in the initial configuration are obtained. These results show that the deflections curves and critical conditions are closely related to the tubular string weight and wellbore curvature. The effects of tubular string weight, wellbore curvature, connectors and axial force on bending moment and contact force are also analyzed at last.