Impact of soil-conductor p-y curves on fatigue life assessment of offshore drilling systems

Guevara, M., Doherty, J., Watson, P., Gomes, V., Mootz, A. and White, D. (2023) Impact of soil-conductor p-y curves on fatigue life assessment of offshore drilling systems. In Offshore Site Investigation Geotechnics 9th International Conference Proceeding. Society for Underwater Technology. pp. 1312-1320 . (doi:10.3723/OZKU3988).

Abstract

During subsea drilling campaigns, the conductor is the outermost pipe of the well in contact with the soil near the seabed. It is used to prevent the walls of the borehole from collapsing and to provide axial support to the structure. While drilling, the wellhead system is connected to the drilling riser system, which links the seabed components to the drilling floating rig. Environmental loads acting on the entire system produce cycles of bending stress in the well that could lead to fatigue at critical locations, referred to as hot-spots. Estimating the fatigue life of hot-spots in the system is critical and the soil-conductor stiffness plays an important role. The forthcoming ISO 19901-4 recommendations (expected to be published shortly) provide two alternatives for deriving p-y curves for fatigue analysis of conductors: a “spring-only” and a “spring-dashpot” method. This paper provides a review of the p-y curves derived with the “spring-only” method, for which care must be taken when interpreting results due to large variability in fatigue life predictions between different load cases. This conclusion is drawn by comparing the results of Finite Element (FE) modelling of a subsea system for two different loading scenarios and using three sets of p-y curves, including the ISO recommended method.

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Contributors

Author: D. White

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