The MFB, a Deep Water FPSO with Surface Trees and Drilling Facilities
Authors: Valenchon C. , Rössig J.H. , Pouget G. , Biolley F. 
Published: October 2008

The Multi-Function Barge (MFB) concept has been developed for deep water, mild environment areas to combine, in one facility, the capabilities of an FPSO with the ability to drill and tie-in the field development wells and to perform all subsequent well workovers. The most significant innovation in the MFB concept is that only one facility is required for the economical development of a deep water oil field. Subsea wellheads or a separate wellhead platform are not required. Where the configuration of the oil reservoir or the use of directional drilling allow the centralization of the wells at a single location, the MFB permits the use of the more economical surface trees with rigid steel risers. Such an approach has the advantage of allowing reduced CAPEX thanks to more economical drilling and reduced subsea installation, as well as easy well intervention and lower OPEX during the whole life of the field, and is close for well access to the traditional exploitation methods from fixed platforms. Crude storage can be provided up to about 2 million bbl. Emphasis is made on riser design and dynamic analysis as well as on the methods used for analysis. The advantages of the maintenance-free buoyancy can tensioning system is discussed with respect to the more conventional hydropneumatic tensioners considered in previous related design work. The feasibility of the MFB concept is demonstrated also by the dynamic riser analysis results.

Introduction

Bouygues Offshore, the EPC Contractor for the NKOSSA Concrete Barge (ref. 1 & 2), has developed in association with Sedco-Forex and IFP, the Multi-Function Barge (MFB), a concrete monohull that combines the NKOSSA vessel functions (oil and gas treatment, utilities and living quarters) with crude oil storage and offloading, as on an FPSO. Most importantly, the MFB also incorporates drilling, tieback, completion and workover facilities with surface trees. From the unique experience of designing and building the NKOSSA concrete monohull and due to the particular advantages of concrete hulls, extrapolations towards other concepts using larger vessels have been developed (ref. 3). These concepts include concrete FPSOs for oil or LNG (ref. 4), and the "Multi-Function Barge" (MFB) (see table 2). The Multi-Function Barge concept is intended for deepwater developments in the Gulf of Guinea or in all offshore areas having a similar marine environment, with the aim of providing a cost effective alternative to the more conventional concepts of deepwater field developments.

Deep Water Fields Development

Currently, for deepwater field developments requiring site crude storage, two main approaches are considered :A first approach consists of using an FPSO for production and storage with submarine production trees linked to the FPSO by flowlines and risers. Today, this solution has been utilized for numerous developments in water depths from 100 m down to approximately 1,000 m and does not present major technical difficulties, but it involves high OPEX when subsea workover well intervention is frequently required. This development approach is particularly suited for deepwater fields where the configuration of the oil reservoir requires multiple dispersed well locations and does not allow surface trees to be centralized on a single wellhead platform.