Floating Production Storage and Offloading (FPSO) floaters have the advantages of providing the required storage in the hull and direct offloading to tankers of opportunity in deep and ultra-deep water in areas lacking infra-structure.
Steel Catenary Risers (SCRs) are the preferred solution in wet-tree applications due to their simplicity, robustness and low Capital costs (CAPEX) and Operational costs (OPEX) compared to other riser options. However, due to its relatively high dynamic motions, FPSO is not a feasible host for SCRs in most environments and especially so in the North Sea very harsh environment. Also, for efficient production from rich reservoirs, large diameter and number of risers are typically required. This makes it more challenging to find a robust and commercially attractive riser solution.
In this paper a novel design for an FPSO with the ability to host SCRs in the North Sea very harsh environment is presented and evaluated. The novel design, namely, Low Motion FPSO (LM-FPSO), has a hull form with a generally rectangular cross-section. The platform is moored in-place using a conventional mooring system. The LM-FPSO performance is enhanced with the robust low-tech feature, namely, free-hanging solid ballast tank (SBT). The SBT is located certain distance below hull keel and connected to the hull through four groups of short tendons. All tendon components are the same as those used in conventional TLPs. Through the mass and added mass of the SBT, the LM-FPSO provides significantly improved heave, roll and pitch responses.
The paper presents detailed description of the novel North Sea LM-FPSO design and its in-service performance. The SCR’s feasibility is discussed. The identified risks and associated mitigations for the new design compared to the conventional FPSO are investigated and reported. The paper concludes with discussions on the project execution plan and cost benefit when developing fields using this novel design.