FPSO With Turret Based Drilling System (FPDSO): An Approach to a Cost-Effective Deepwater Field Development
Authors: Wanvik Leiv , Poldervaart Leen , Mong Henning 
Published: October 2008

Abstract
The paper presents a description of a Floating Production, Drilling, Storage and Offloading vessel (FPDSO) concept developed jointly by Kvaemer Oil and Gas (KOGAS) and Single Buoy Moorings Inc., in cooperation with Statoil which has provided input to the functional requirements and operational aspects for the FPDSO concept. The vessel is designed as a monohull which supports a combination of drilling, production, storage and offloading functions. With a subsea completion system placed directly below the vessel the FPDSO allows a full field development and operation from one single unit. Oil export normally will be by shuttle tanker. The drilling arrangement is based on a novel solution developed for drilling through the center of a geostationary large diameter turret. It offers a unique and highly efficient riser and drillpipe storage and handling system, allowing automated vertical racking of 1500 m of 21" risers with floatation, including 338 stands drillpipe racking capacity, supported from 20 m below drillfloor elevation. Surface handling and service of BOP and subsea equipment handling takes place at the vessel main deck elevation as the proposed turret solution offer direct access into the turret center from the deck level. This allows a moderate substructure/derrick stacking height in the drilling area, and the arrangement resembles the one used on modem large semisubmersibles. Thanks to the vessel's high topside deck payload and consumable supplies capacity and its favorable motions characteristics, it is particularly well suited for deep water operations m remote areas.
A key element in the developed design is the fluid transfer system which allows a +/- 270 degrees rotation of the vessel at the same time as it offers access from the main deck into the center moonpool. The vessel is kept on station by a turret mooring system which is designed to be "passive" under normal sea states, but will be assisted by a number of thrusters in order to maintain proper operative heading and position control in bad weather. The FPDSO concept is one of the most promising solutions for areas like the West of Shetlands or the Voering Plateau in the Northern North Sea. Several FPDSO versions have been investigated, all of them specifically designed for harsh environment and deep water (800 to 1500m water depth). However, like most of the floating concepts, the FPDSO is relatively in-sensitive to water depth variations, and may easily be adjusted to suit significantly shallower water depths. Without doubt the FPDSO concept could compete efficiently on fields currently being developed with traditional FPSO systems.

INTRODUCTION
The FPDSO concept has been developed through a cooperation development study undertaken by KVAERNER and SBM for the Northern North Sea area conditions. The main particulars of the FPDSO were based on and developed for one particular location on the Voering Plateau. The location represents several prospects in the area with water depth ranging from 800 to 1500 m. Distance to shore is approximately 200 km, and the area is located about 150 - 200 km North West of the Haltenbanken area (Nome / Aasgard field). Exploration drilling is currently ongoing on several of the prospects, and the demanding water depth and weather conditions requires the use of ultra large deepwater DP semi submersible units.