Effect of Soil-Conductor Gap Formation on the Fatigue of Subsea Wellheads

Resumo

The construction of offshore oil wells in deepwater typically involve the use of floating rigs. These rigs transmit their motion through the drilling riser to the wellhead and casings, which can result in fatigue damage. In our research, we verified a hypothesis suggesting that high loads (e.g., a storm or a rig drift-off) can cause plastic deformation in the soil, causing the opening of a gap between the conductor and soil. This would result in change of the dynamic behavior of system, and consequently on the cumulative damage. We modelled numerically the problem using Finite Element Method. Wave and current loads were simulated stochastically. Soil was implemented as nonlinear springs that obey a bounding surface plasticity model. The results compare displacements, bending moments and fatigue damage across several scenarios, as well as the likelihood of VIV onset.