A decoupling model for fatigue life assessment of double wellhead system with subsea suction anchor

The double wellhead system equipped with a suction anchor is subject to alternating loads, such as shear forces and bending moments, which can lead to fatigue failure. Considering the impact of the suction anchor on the subsea wellhead, an equivalent theory has been derived, and a refined equivalent model established to determine the fatigue hot spot moment-stress transfer function. To address the challenges of high computational complexity and convergence difficulties in the dynamic analysis of the refined equivalent model, a simplified theory of global coupling analysis has been derived, and a corresponding simplified subsea wellhead model established. Utilizing the environmental conditions of X gas field in China south sea, the fatigue life of the double wellhead system with suction anchor is evaluated. The results were compared with those of a conventional subsea wellhead, demonstrating that the double wellhead system with suction anchor can significantly improve fatigue life of the subsea wellhead. The fatigue life of high and low pressure welds in conventional subsea wellheads under drilling conditions has been extended from 17.77 years to 1.20 years-186.16 years and 25.62 years, respectively.