Simulation and experimental study of deepwater subsea wellhead-shallow casing deflection considering system mass force

Abstract

Under the effects of offshore platform drifting and current and wave forces, risers exert a dynamic force on wellheads during drilling in deep water, inducing a bending moment on a deep water subsea wellhead-shallow casing (SW-SC) system. Additionally, the interaction between the casing string system and seabed soils below the mudline generates a force known as the foundation pressure. These two forces—particularly the mass force of the wellhead—lead to system instability. According to the Hamilton principle combined with functional analysis, the continuous virtual work done by the system mass force on the whole system during the deflection process is the major consideration because it increases the instability of the system. Therefore, a dynamic differential equation was established, followed by the finite-element discretisation of the casing system. Then, a dynamic equation was derived, and MATLAB was used to solve this equation. Furthermore, a dynamic performance simulation test of a shallow casing string was conducted by applying two types of seabed soils: two-layer soil and single-layer soil (homogeneous clay). The displacement, rotation angle, bending moment, and shear force of the SW-SC system were calculated and compared.