RATIONALITY OF END CONSTRAINT EQUATIONS FOR BUCKLING ANALYSIS ON A DRILLSTRING IN A WELLBORE

The rationality of end constraint equations on buckling loads of a drillstring in an inclined wellbore is investigated. The lower end of the drillstring is supported by hinge while the upper end can move freely in the circumferential direction of the wellbore. The drillstring buckles under the action of its self-weight and a compressive force applied at its upper end. Buckling loads of the drillstring are calculated by using the Ritz method. It is found that buckling loads corresponding to the different boundary constraint equations are quite different. To ensure the consistency of the minimum of energy functional with its corresponding equilibrium equation eigenvalue, some essential boundary conditions have to be included. A set of more reasonable end constraint equations are given for buckling analysis of drillstrings, based on the actual working conditions and the existing experimental results.