Offshore Drilling Riser VIV Suppression Devices: What’s Available to Operators?

Abstract

VIV suppression and drag reduction are key issues for improved operation in offshore drilling. Properly designed helical strakes are effective in the mitigation of VIV fatigue damage for many riser applications. However such strakes tend not to be applicable to offshore drilling riser applications. This is due to increases in drag force due to increased apparent diameter as well as workability problems for drilling operations. For these reasons, effective devices are sought that would mitigate VIV and reduce, or at least not increase, drag for drilling applications. Along with yielding good hydrodynamic performance, a drilling riser VIV suppression device must be compact and robust enough to be used in a drilling-rig environment. It needs to be deployable and recoverable in declared operational sea states. It must also be easy to store and assemble. Finally, and most importantly, it must be efficient to deploy and recover during normal riser operations. This last point is vital to drilling operations in deepwater in hurricane-prone areas. Weather conditions can change quickly and even a non-faired deepwater riser takes 2 to 3 days for a full retrieval. BP continues to research and document suppression device types and to assess their practical performance. A supply choice in the market place is important so that the correct device can be used for particular situations. To this end, we have recently worked with cooperative partners to demonstrate the hydrodynamic performance of a handful of the most promising devices. This paper is a tailored synopsis of previous suppression concepts and the philosophical pathway toward what is available on the market today. At its core are recent circumstances which precipitated a need to quantify and qualify for operational acceptance the performance of two commercially available short aspect ratio fairing devices. (i.e. a dual-fin splitter and an airfoil-shaped fairing). This paper discusses the results of the large-scale model acceptance tests over prototype Reynolds number for these devices. In addition to rigid devices, a relatively newer suppression product that “inflates” in the direction of the relative flow was also assessed by BP for expected hydrodynamic performance. This device shows particular promise for the mitigation of VIV during drilling operations surprises in high currents along with appearing potentially commercially viable.