Buckling and Lockup of Tubulars in Inclined Wellbores

This paper describes sinusoidal and helical buckling of tubulars in inclined wellbores and the ``lockup`` of tubulars due to buckling. The results show that tubular buckling starts from the tubular bottom in low-inclination wellbores, where axial compressive load is largest due to tubular weight. In high inclination wellbores it may start from the top portion of the tubular, where axial compressive load is largest due to frictional drag. This clarifies the confusion about whether or not tubulars buckle all at once, in the entire inclined wellbore. New sinusoidal and helical buckling load equations are presented to give better tubular buckling prediction in inclined wellbores (0--90 degrees). They show that the lower the wellbore inclination angle, the smaller the axial compressive load to initiate tubular buckling. But a certain non-zero axial compressive load is still needed to buckle the tubulars in vertical wellbores. When tubulars buckle helically, a large wall contact force will be generated. The `slack-off` weight at the surface will not be fully transmitted to the bottom of the tubulars due to the large resultant frictional drag. The ``lockup`` of tubulars, where the bottom load (bit weight) cannot be increased by slacking-off weight at the surface, usually is approachedmore » when a large portion of the tubular buckles helically in the wellbore.« less