BUCKLING OF DRILL STRING UNDER THE ACTION OF GRAVITY AND AXIAL THRUST

A number of different equilibrium helical buckling configurations for a tubing or drill string confined within a cylindrical casing or hole of larger radius and buckled under static compressive forces are determined. Our work is more general and informative than earlier work since the solutions relating the buckling load and the postbuckling configuration are given explicitly for the string of weight and at any inclined positions. A consideration of the state of transient string buckling when the string undergoes sudden change in the helix radius and might lose contact with the hole wall is also proposed.