The Buckling Analysis of Drill String in Inclined Wellbore with a Concave Curved Geometric Defect

Abstract

Some inclined boreholes have to be drilled in directional wells, but the track of inclined borehole is impossible to be a ideal straight line, there are always some geometric defects such as bending, thus the drilling string in it is bound to have initial bending due to the constraints of borehole, hence the drilling string in inclined borehole is usually a curved compressed rod. Its buckling nature is quite different from straight compressed rod, it is necessary to analyze it specially. In this paper the buckling problem of drill string in inclined borehole with a concave curved geometric defect is studied by energy method, the computing formula of buckling load for it was obtained. And the influence of initial concave bending on buckling load was discussed. The research indicates that when drilling string in inclined well bore has a initial concave bending, the greater the degree of initial bending of drill string, the greater its buckling load.