Summary This paper aims to present a buckling analysis of the surface casing under vertical loads in subsea wells, considering cases in which the surface casing is partially cemented. The study employs the Lubinski model for vertical columns and incorporates the effects of variable and continuous wear, assuming that buckling occurs in a helical mode. In this study, the effect of variable wear on the casing is taken into account. Since wear alters the internal diameters of the column, the problem is addressed by modeling an increase in the internal diameter characterized by continuous wear, along with the application of a mathematical model used to adjust the geometric properties of the cross-section. The governing equations include the influence of axial forces, bending moments, and internal and external pressures. The buckling condition is defined by the occurrence of negative effective forces along the column, and the impact of variable wear on the Lubinski formulation is systematically evaluated. The results indicate that the uncemented portion of the surface casing has a significant influence on the movement of the wellhead system, especially in wells where continuous wear is considered. However, the wear values adopted in the two methodologies should not be treated as equivalent for analysis purposes, due to the integral increase in internal diameter in the continuous wear approach. As wear increases, the resulting changes in internal diameter lead to variations in stiffness and buckling resistance, ultimately causing greater displacement of the wellhead under vertical load. Additionally, in the analysis with variable wear, the emergence of bending moments due to eccentricity was observed. Finite element simulations and comparative analyses show that incorporating wear effects into the Lubinski model yields a more accurate prediction of the buckling behavior of vertical casings. Neglecting these effects may result in underestimating the structural response, which can compromise the safety and integrity of subsea well installations. The study confirms that accounting for variable wear is essential for a realistic evaluation of wellhead movement, providing engineers with greater reliability in design assessments. This formulation provides a key advantage by enabling the evaluation of combined loading effects due to buckling while incorporating the influence of variable wear a factor absent in the original Lubinski model. This novel approach enhances prediction accuracy and supports safer, more reliable design of offshore wells.
Santos et al. (Tue,) studied this question.