Dynamic Responses of the Cylindrical Floating Drilling Production Storage and Offloading System with Annular Anti-Motion Structures under the Survival Sea Scenario

At present, dry wellheads are usually adopted on small-storage TLP and SPAR platforms to develop offshore oil and gas because of the robust hydrodynamic performance under severe-wind seas. On the other hand, FPSO and FDPSO platforms that have a larger storage capacity can hardly use this cost-saving facility due to their relatively poor vertical motion performance. Cylindrical FPSOs are proposed to improve the heave performance of ship-type FPSOs, but their behaviors are still too large to adopt the dry wellheads. In the present work, a cylindrical FDPSO platform is proposed based on the FWPSO platform, adding an extension cylinder and a new damping structure at the bottom. Their hydrodynamic performances are calculated by the potential theory and compared in the frequency domain. Taking two particular mooring systems, including both catenary and 'chain-polyester-chain' types, and the survival sea scenario in the South China Sea into account, a time-domain coupling analysis was adopted to simulate the dynamic performance of the platform-mooring system. The feasibility of dry wellhead adoption on the FDPSO is discussed by investigating the platform motion and the mooring tension. The results show that the FCDS platform with the 'chain-polyester-chain'-type mooring system can meet the motion response requirements, and the mooring system can also meet the requirements of the specification.