Pragmatic Fatigue Assessment of Subsea Wellhead and Conductor System: Key Parameter, Soil Model and Mitigation Strategy

Fatigue in subsea wellhead and conductor system is a governing integrity concern for offshore drilling, driven by cyclic environmental loads from waves and currents. Two mechanisms dominate: wave induced first-order fatigue (FOF), generally critical in shallow water, and vortex-induced vibration (VIV), which governs deeper water. While design codes provide frameworks for fatigue assessment, they often oversimplify key parameters, particularly soil–structure interaction, leading to results that may be either overly conservative or non-conservative. A pragmatic approach to fatigue assessment and mitigation, emphasizing realistic parameter representation and actionable strategies rather than prescriptive workflows is proposed. Key factors discussed include conductor sizing and wall thickness, weld quality, connector placement and stress concentration factors (SCFs), riser tension management, soil model selection, and the use of external structural support such as BOP tethering. The benefits of VIV suppression devices, continuous monitoring, and seasonal/operational planning are also explored. A case study from a shallow-water well offshore South America demonstrates how soil model choice redistributes fatigue damage above and below the mudline, altering hot spot locations and system margins. Additional examples illustrate how mitigation measures such as riser tension adjustment and BOP tethering can improve fatigue life by orders of magnitude. By combining targeted parameter control with robust mitigation strategies, operators can achieve fatigue assessments that better reflect field behaviour, enabling safe, cost-effective, and operable drilling campaigns even in fatigue-critical environments.