A floating platform in deep water East Canada is required to withstand iceberg loads and/or be disconnected and towed away in the event of very large approaching icebergs, leaving the mooring lines and risers in-place, support large topsides and in most cases, provide large quantities of oil storage in the hull. Concepts considered for deep water application in the area include ship shaped self-propelled disconnectable FPSO and disconnectable and permanently connected deep draft floaters. This paper presents the details of Concrete Spar platforms that have been configured to satisfy all the above requirements. Several variations in the functionality and configurations of the platforms were studied to understand the impact on the overall cost and risks. The case variations primarily included:
• Disconnectable options for hull, mooring and risers
• Non-disconnectable option able to handle the full iceberg load
• With and without crude oil storage in hull
• Sacrificial or non-sacrificial mooring or risers
• Steel riser configurations (freely hanging catenary, SCR vs. lazy wave, SLWR)
• Hull with and without riser support Buoy
• Location of mooring fairleads (on Upper hull or Buoy)
• Riser support configuration (Pull Tubes or Flex Joints)
The iceberg loads experienced by the hull depended on the disconnection philosophy. The Concrete Spar hull is a 6-cell structure with the risers located inside the open centerwell. The paper describes several key features of the hull, mooring and riser systems for each case that are specifically designed to withstand iceberg loads and other environment loads while maintaining the characteristic low motion response for all the options considered. Additionally, the system has been designed to minimize the disconnection and reconnection time for the disconnectable cases.
The platform dimensions and weights have been compared for the various options considered. The cases without oil storage in the hull have significantly smaller and lighter hull relative to similar cases with oil storage. The cases without hull disconnection option had similar hull dimensions but marginally higher concrete weight relative to the hull disconnection option. However, the cost of Buoy, required for the disconnection option, compensates for the concrete cost difference. The SCRs work for the inplace extreme environment and iceberg load cases. Depending on the hull offset required to avoid icebergs for the non-disconnection cases or the risers lowering depth for disconnection cases, SLWR may be needed.
Recommendations are made for the preferred option for field development.