Dynamics of a Buckled Drillstring Rotating in a Curved Oil Wellbore

Abstract

Drillstring failures caused by unstable rotation of the drilling assembly are continually ranked as one of the most frequent and costly problems in the oil industry. Although many other methods of oilwell drilling have been tried historically, rotary drilling technique dominates the industry. The drillstring components, i.e. drillpipes, are typically 5” in outside diameter and 4.275” in inside diameter. Depthwise the assemblies can extend up to 8 km or more downhole, i.e. drillstring is a very flexible slender rod. Directional drilling toward the desired target, which is very popular now, complicates the problem as wells are drilled with substantial curvatures and threedimensional characteristics. In order to provide pressure for forcing the drillbit into formation, especially in case of horizontal drilling, the drillstring is axially compressed, i.e. it is buckled in its static configuration and rotates in a curved well. The objective of the presentation is to analyse the stability of the drillstring rotation.