Coupled VIV and Heat Transfer Analyses: Design of VIV Suppression Configuration for the Independence Hub SCRs

Independence Hub (IH), a semisubmersible production platform in the deepwater Gulf of Mexico is currently under construction and will produce gas and condensate from multiple subsea developments. The platform, installed in some 8000 feet of water, is located in a region of the Gulf that is well known for its severe environment, particularly persistent loop currents that could last several months out of a year. The current profiles are such that there is a significant risk of fatigue failure of the risers due to Vortex Induced Vibration (VIV) and adequate mitigation through installation of VIV suppression devices, such as strakes and fairings, are required. An additional challenge that impacts the topsides facility and flex joint design is the low arrival temperature of the produced gas due to Joule-Thomson (JT) cooling. In the case of a bare riser (one without any VIV suppression), the heat transferred from the ambient seawater to the produced gas is sufficient to exceed the target arrival temperature. However, installing VIV suppression devices along the span of the riser may insulate it, which in turn has the potential to decrease the arrival temperature significantly. This paper will discuss coupled VIV and heat transfer analyses carried out to assess the risk of both VIV and low arrival temperatures for the IH production risers. The heat transfer analyses were carried out rigorously using 3D Computational Fluid Dynamics (CFD) simulations of the riser with and without VIV suppression devices. Helical strakes and short fairings were analyzed and optimum suppression configurations for two production risers that meet both the VIV and thermal requirements are presented. The optimum configuration was also subject to the requirement that the suppressed risers be S-layable. A hybrid suppression design based on both strakes and fairings are presented that meets the fatigue and arrival temperature requirements while minimizing installation risks using the S-lay method.