Estimating Design Currents During Joint Eddy-TRWs and Joint Eddy-Hurricanes

摘要

While the Industry has been aware of TRWs (Topographic Rossby Waves) for several years, they have been assumed to occur solely on their own. Recent observations summarized in this paper suggest that in fact a warm-core eddy or associated features often affects a site at the same time as a strong TRW. It remains uncertain whether this is a cause-and-effect or a random occurrence. When the profile from an eddy and a TRW are combined, the result is an onerous case for riser design in an important new production region of the Gulf. While there is insufficient data to support a published design profile, our paper does offer some thought-provoking evidence that TRWs and eddies should be considered to occur jointly. As for the joint eddy-hurricane event, the Industry has typically treated it by either arguing that the event was too rare to be considered or by linearly superimposing the eddy-only and hurricane-only currents from moderate events. As the Industry has moved into the ultra-deep waters of the Gulf where eddies are more persistent, our analysis suggests joint events occur every few years. In addition, recent research shows there is a strong nonlinear enhancement of the subsurface currents during the joint event. Both these factors mean that the previous approaches to estimating the eddy-hurricane event can be unconservative. We suggest a method for calculating the joint event and show that at a site in the deepwater west-central Gulf, the joint eddy-hurricane condition is quite strong.