Chapter 13. An Improved Method of Establishing Extreme Metocean Conditions in the Gulf of Mexico
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Published:2022
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Metocean criteria at a Floating Production Unit (FPU) in the central Gulf Of Mexico (GoM) are being reassessed to support the facility’s Life Extension. Two key shortcomings of previous approaches to the development of hurricane ‘full population’ criteria have been addressed here. These include the extrapolation of correlated grid-point ‘pooled’ data and ‘non-peak’ storm data - both of which can lead to bias in extreme value estimates. These improvements have been achieved through the identification of a statistically homogenous set of hindcast grid-points. Each grid point exhibits variability in the tail region of the distribution, as a result of limited sampling of both storm track and intensity. By first, fitting a non stationary model of the marginal and joint extremes to the tails of storm peaks from each grid point and, then, merging the resulting distribution parameters from each, we establish a method of incorporating the spatial variability in both track and intensity - across a data sparse, homogenous hurricane region - into design estimates, without recourse to grid-point pooling or track-shifting and all their inherent issues. The new method also provides a set of statistically consistent hurricane storm trajectories, based on the extrapolated ensemble of tail distribution parameters. This is expected to provide significant reductions to the joint load cases, compared to standard practise.