Surface Casing Buckling Effect on the Wellhead Movement of a Subsea Well

In this work, the wellhead axial movement of a subsea well was predicted with a previously presented multi-string model modified to account for a possible buckling of the well’s surface casing. This model represented the structural casing with a nonlinear spring that considers the casing-soil interaction using t-z curves with hysteretic behavior. In addition, the surface casing was modeled with a nonlinear spring that incorporates buckling deformation when the effective force is compressive and may be assumed not fully cemented due to, e.g., its long length, formation characteristics, or limitations of the rig. Finally, the other casing strings were represented with linear springs. Two case studies were conducted to verify the proposed model. In the first, the wellhead movements during each step of a simplified well’s construction and production were compared with those obtained in an equivalent beam-based FE model. Both models yielded the same results, encouraging the analysis of a second case, which investigated an actual well. In this case, the surface casing buckling led to considerable wellhead movement variations, consequently affecting the surface casing stress, especially in scenarios in which the structural casing’s bearing capacity was surpassed, highlighting the need to account for this phenomenon in the design of subsea wells.