An Approach To The Design And Selection Of A Cost-Effective Floating Production Storage And Offloading System
Authors: D&apos;Souza R.B. , Delepine Y.M. , Cordy A.R. 
Published: October 2008

Tanker Based Floating Production Storage and Offloading Systems (FPSOS) are an important component in developing marginal and remote offshore oil fields. This paper provides insight and guidance to operators and designers faced with the many complex issues and tradeoffs involved in selecting a cost-effective FPSO for particular field development conditions. A historical review is included that traces the evolution of the concept from the first installation in 1976 to the present. Useful statistical data on past, present and planned FPSOS is provided.

Design drivers, such as production data, service life, site conditions and statutory/regulatory requirements are discussed. Major selection issues, which include vessel size, type (newbuild or conversion) and mooring system type, and the factors that affect their selection are presented. A case study for a hypothetical field development illustrates a systematic approach to the selection and design of a cost-effective FPSO.

INTRODUCTION

FPSOS have traditionally been used in oil producing regions that lack an established pipeline network (China, Indonesia, West Africa). In the early years, FPSOS developed small fields (10-50 million barrels) and then only in regions with mild environments and shallow waters. Continuous improvements in mooring systems, swivel technology, and offloading systems have greatly increased the reliability of, and confidence in these systems. FPSO technology is now at the point where they are considered for both large and small field developments in harsh environments and deep water [1]. The recent decision by Statoil to use an FPSO on the Nome field in 1200 feet of water in the North Sea underscores the point.

When evaluating an FPSO as a field development option, an operator has to be fully aware of its capabilities and limitations relative to other fixed and floating systems.

The primary advantages are its low capital cost and short construction schedule (particularly a conversion), its ability to store and offload oil to shuttle tankers and its relocatabiiity. The latter features make it attractive for extended well testing, early production or for producing a series of small fields. Several contractors will now provide an FPSO on a lease or charter, which relieves an operator of some cost risk.

The principal limitation is the difficulty to drill or workover subsea wells. In weathetvaning systems, the current state of technology of the swivel, that directs the flow of fluid, hydraulics and electrical power to or from the fixed part (mooring system), to the rotating part (vessel), could be a constraint. The challenges of deepwater risers are common with other floating production systems.

Having established that an FPSO will be the primary production facility, an operator has to consider a host of interrelated, and often conflicting, factors that impact field economics and system reliability. This paper addresses the following three major questions:What size should the FPSO vessel be?Should it be converted from an existing tanker or be newbuilt? andHow should it be kept on station? To answer these questions, we first review past, present and planned FPSO systems to understand industry practice.

(Available in full paper)