A Comparison Study of Improved SCR Response for HVS Semisubmersible

A new deep draft semisubmersible HVS (Heave and VIM Suppressed) has been developed at Technip as another wet-tree floating platform option, which achieves significantly improved heave motion and Vortex-Induced-Motion (VIM) performance as compared to conventional semisubmersible concepts. This paper presents results from a study that compares the strength and fatigue performance of a gas export (20 inch) SCR that is supported by either the HVS semi or a comparable conventional semi in 4000 ft or 6000 ft of water depth. Both floaters are designed for the central Gulf of Mexico, and have comparable hull principal dimensions and mooring configurations. For the HVS semisubmersible in an extreme sea state (100-yr hurricane), the reduced heave motion significantly improves SCR strength performance at the Touch Down Zone (TDZ) and effectively eliminates the compression load at the sag bend region. The assessment of SCR fatigue responses indicates that most damage near the TDZ results from wave induced motion fatigue and hull VIM fatigue. The suppressed VIM response of the HVS semisubmersible due to the unique blisters attached to the four hull columns significantly enhances the SCR fatigue life near the critical TDZ. The results from this study confirm HVS as a SCR-friendly wet tree host concept for the deep waters in GoM.