Effect of wellhead tension on buckling load of tubular strings in vertical wells

The geometrical and contact nonlinearities in tubular buckling problem lead to convergence difficulty in calculation. To solve this problem, we present a slow dynamic method and its solution strategies for the nonlinear static buckling analysis based on the implicit finite element method. For different length and boundary conditions, we calculate the length of each section of the helical buckling configuration. To measure the pitch of helical buckling, we introduce two methods. The first method is to use the spiral angle between the bottom and top contact points to measure the pitch, and the second method is to use the spiral angle of the continuous contact section to measure the pitch. For the first method, the string has three types of buckling configurations for different boundary conditions without the tensile section. With the tensile section, the helical buckling configuration is composed of the bottom compressed section, the middle helically buckled section, the top compressed section and the tensile section for the hinged or clamped boundary at both ends. For the second method, the buckling configuration consists of four non-contact sections, one continuous contact section without the tensile section. A tension section is added to the buckling configuration for the influence of the tension section. The critical load decreases gradually and tends to the minimum with the effect of the tension section. Since the critical load of the second methods is greater than the value of the first one, it is recommended that the former method be adopted in engineering applications.