During drilling operations, the wellhead system and top hole casings shall be designed to support dynamic loads from the connected riser through the BOP stack/LMRP. As dynamic motions are associated to stress variations, fatigue becomes a major concern for designers. The accumulation of damage at the wellhead and close regions is dependent on several aspects, such as the riser components, the interactions soil-conductor and conductor-surface casing, and of course the environmental conditions. Consequently, fatigue analysis involves complex numerical models and requires the simulation of a huge number of loading cases. The present paper aims to estimate the fatigue damage at critical components of the top hole casings and at the wellhead. Two different approaches were investigated. In the first, a global model is analyzed in the time domain (TD), and the Rainflow cycle counting method is used to calculate fatigue damage. The global model includes the drilling riser, wellhead, casings, and interactions between components and with soil. In the second, the same model is analyzed in the frequency domain (FD), and the Dirlik method is used to calculate fatigue damage. Additionally, to allow a better evaluation of stresses at complex geometry regions, forces and moments obtained using the TD methodology were combined with load-to-stress transfer functions, defined by means of a local model and symbolic regression (SR) analysis. The local model includes a detailed 3D model of the pressure housings, and soil-to-casing interaction. The obtained results indicate that the pressure housings are not sensitive to fatigue, and also that the analyses performed are feasible, contributing to reduce computational costs in wellhead fatigue assessments.

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This article presents a numerical-based study on the vertical holding capacity of a typical finless torpedo anchor embedded in a pure cohesive isotropic sol considering setup effects. A strategy based on two axisymmetric nonlinear finite elements (FE) models is proposed. In these models, the soil is represented with continuous solid elements with both plane translational and pore pressure degrees of freedom, which allow the modeling of the soil's strength regain after the installation of the anchor, i. e., the soil setup. The anchor is also modeled with solid elements, and its interaction with the soil is addressed with contact elements. Several analyses are conducted to evaluate setup effects, and, additionally, a parametric study on different soil undrained shear strengths and permeability coefficients is performed. The results obtained show that the permeability of the soil and its undrained shear strength have an important role in the setup process, and an inverse relationship between consolidation time and the permeability coefficient of the soil is observed. Finally, an analytical approach is calibrated with a reasonable agreement to the numerical results

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