OTC 15311

New Build Generic Large FPSO A. Le Cotty, Single Buoy Moorings; M. Selhorst, Gusto Engineering

Copyright 2003, Offshore Technology Conference This paper was prepared for presentation at the 2003 Offshore Technology Conference held in Houston, Texas, U.S.A., 5–8 May 2003. This paper was selected for presentation by an OTC Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Offshore Technology Conference or officers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented.

Abstract The increasing demand for FPSOs and constant pressure for ever shorter delivery times has motivated SBM to design conversions and new-build hulls in a generic manner. SBM has been designing successfully generic FPSOs using converted VLCC hulls, based on a rationalized deck layout with integrated power generation and process equipment. Over a period of 3 years, this generic conversion design has been applied to a series of 7 FPSOs that will be briefly described in this paper. In order to meet the increasing world-wide demand for large new-build hulls, SBM has designed a generic hull with a storage capacity of 2mmbbls or 2.4mmbbls, capable of supporting large topsides with a high level of flexibility in the process layout and using a similar philosophy to that developed for the generic hull conversions. Typical machinery and accommodation blocks are proposed permitting future modifications to be tailored to specific requirement. This new-build hull design will permit fast track hull construction and FPSO delivery. Introduction FPSO designs, whether based on converted tanker or new-build hulls, are governed by a number of key technical factors:- typically the storage capacity, production capacity, export capacity, site environment and crew complement. However, a key non-technical factor affecting the entire project organization and major technical decisions is time schedule which is a significant challenge for designers. There is obviously a need for a fast track method for building or converting FPSOs. However, it is unreasonable to expect to simply squeeze indefinitely all project activities to achieve significantly reduced delivery times: this would result in

unacceptable risks during design and construction, with commensurate risks to the performance of the unit. Those conflicting requirements triggered an alternative approach to manage a fast track FPSO project, the so-called generic approach. At the end of 1999 SBM and Gusto invested time in screening all aspects of tanker conversion; defining a basis of design suitable for a wide range of applications and carried out an internal engineering study in preparation for expected future FPSO conversion projects. This investment proved to be very fruitful. The design was used in several projects including the FPSOs Falcon, Atlantic and Serpentina for ExxonMobil, FPSO Espadarte, Brasil and Marlim Sul for Petrobras and FPSO Mystras for Agip. The design is also currently proposed on many other projects. Despite the success of generic conversions, new-build hulls may be required for FPSO projects. This paper will first address FPSO conversion background and explain the main drivers for new build hulls. Then, the generic hull, including the basis of design, the structure, the hull systems and the interfaces with topsides plant, will be presented. Finally, construction phase and operational feed-back will be addressed briefly based on the experience gained as both prime contractor and leased vessel operator.

Conversion background In preparation for expected FPSO projects with capacities up to 130 mbd, a generic conversion study was carried out in 1999 and looked at lessons learned on all past projects, from initial proposal through design, procurement, construction, hook-up and commissioning, to normal operation, and analyzing project life cycles. This survey resulted in a generic design with standard tanker conversion documents, standard mooring system (either internal or external turret), and typical standard process modules. Subsequent projects have been executed on the basis of deviations from the standard specifications by reusing existing design wherever possible. The idea is to provide fit for purpose solutions using standard existing systems and modules. Turret systems and process modules are adapted to each specific project requirements but the fundamentals are already existing and known at a very early stage of the projects. This results in a cost and schedule reduction.

2 OTC 15311

Moreover, solid relationships with preferred equipment suppliers enable project efficiency to be improved. The generic design has proved suitable for all mooring systems: external & internal turrets, and spread mooring. In parallel with project execution, further concept development was, and continues to be, performed on specific systems and equipment where value can be added. Once concept improvements reach maturity implementation in subsequent projects is captured, providing a continuous design improvement cycle. The result is a delivery on site of 100 mbd oil production FPSOs in very short time duration – down to 15 months – with both external and internal turrets. Example of FPSO conversion:

Based on this experience where process topsides fabrication and integration has been optimized in terms of delivery time, a generic new-build FPSO suitable for large production capacity process plant has been designed. In a new build design, there are possibilities to increase the standardization level and to widen the generic concept to more systems than for a conversion. Limitations which exist in a conversion, such as existing tank or accommodation arrangements, do not exist for a new-build. Therefore, the generic new build design may address all systems that are strictly related to the hull and provide

flexibility to accommodate systems that are driven by specific project requirements such as the topsides plant. Need for new-built hulls Very Large Crude Carriers (VLCC) constructors were very active in the 1970s and in the 1990s, but far fewer new hulls were built in the 1980s. This is evident from the following graph.

0

10

20

30

40

50

Num

ber

1971 1975 1979 1983 1987 1991 1995 1999

Year

VLCC & ULCC delivery

FPSOs designed for a long operating life up to 25 years require high quality hulls which are becoming more and more rare among the 70’s tanker fleet. Recent tankers built in the 1990s remain rather expensive. Thus, it is anticipated that a shortage of existing tankers available for conversion at a competitive price will arise in the near future. The requirement of double-sided hulls in certain locations also leads to new build unit. Moreover, the need to accommodate large topsides plant and large storage/export capacities is also favorable for new-build hulls. High production capacities are increasingly required, with correspondingly heavier topsides plant. This increased weight in many conversion cases can, without additional buoyancy to the tanker, lead to a significant reduction in available storage capacity. Therefore, many VLCC tankers after conversion to FPSOs cannot accommodate any more 2mmbbls cargo storage capacity. If the project requirement is above 2mmbbls, a ULCC must be chosen for the conversion, however they are even more difficult to source.

System FPSO BrasilOil bpd 90,000Gas lift/export mmscfd 105Produced Water bpd 50,000Seawater lift bpd 360,000Water injection bpd 90,000Sulfate reduction bpd 90,000Cooling Medium MW 57Heating Medium MW 19

The situation is compounded by the need for additional power generation to feed the larger topsides plants, which is not available in existing tankers. Complete new power generation plants are easier to design and install in a new-build hull. New-built generic design basis The aim is to design a generic FPSO hull making best use of experience gained in the operation of several VLCC-hull based FPSOs and in the design, construction and integration of topsides plants. The aim is further to screen the possibility to build the hull in a wide range of shipyards under the supervision of an experienced management team to ensure the required quality level within the expected delivery time.

OTC 15311 3

The FPSO hull is intended for large deepwater field development, thus leading to:

• a large topsides plant, • a large production and storage capacity, • a long field life.

The FPSO hull shall have an oil storage capacity range suitable for most large FPSO developments. Therefore, the base case capacity is 2mmbbls and is extendible to 2.4mmbbls. A storage capacity of 2mmbbls is a typical size but a slightly higher capacity may enable to offload comfortably parcels of 1.5mmbbls to VLCC export tankers.

The FPSO hull shall be defined taking into account its interfaces with the topsides plant and be suitable to accommodate a wide range of process capacities with topsides weight up to 25,000mt for a long life operation – up to 25 years. The topsides plant itself is not addressed here, but typically the oil production rate is in the range of 200,000 to 250,000 BOPD, with associated gas compression, water injection and utility systems.

The water depth shall be up to 2000m and the hull will have a capacity to accommodate a large number of risers, up to 75/80 on side balconies. The environment criteria is specified as being the West Africa coasts, Brazil and South East Asia. The interfaces between the hull and topsides shall include the power generation, heating medium supply, cooling medium, and shall be flexible in terms of topsides supports. The interfaces issues are further developed below. The crew complement shall be 100 persons onboard (POB) with a peak to 130POB on a temporary basis. The generic hull design is presented below. After reviewing the general arrangement principles, we address the structural hull design, the cargo handling system, the accommodation block and the machinery room design. Explanations are then given on the design of the systems installed as a hull part but mainly driven by the topsides process plant: topsides supporting structure, power generation and water cooling system.

General arrangement The unit is designed as a box-like hull with a parallel midboby as long as possible - defined as the longitudinal hull part with constant transverse section - for ease of construction and cost effectiveness. The stern and bow sections are shaped to reduce impacts from the environment but still with concern for construction ease. The machinery room and accommodation are located at the aft ship with easy access to machinery stores spaces and adequate lifting facilities.

In the 2mmbbls storage capacity base case, the cargo area is divided transversally in 5 rows of 3 tanks of identical size. Double sides over the whole length ensure adequate ballast capacity. The longitudinal cargo area partition limits the eventual oil outflow in case of side damage. In the extrapolated case of 2.4mmbbls, one additional row of tanks is added longitudinally and the structure is up-graded accordingly to allow for increased longitudinal bending moment. The breadth of the ship has been fixed to allow dry-docking in sufficient shipyards around the world, either for construction, topsides integration or future maintenance or up-grade cases. The oil specific gravity is assumed at 0.9kg/m3. The main particulars are as follows:

Storage capacity 2mmbbls 2.4mmbbls Length overall 270m 310m Breadth 58m 58m Depth 32m 32m Draught 24.1m 24.1m

The general arrangement is presented in figure 1. Overall hull design Main focus in the design process was to merge design principles and technical solutions from previous projects to an optimum hull design. It is noted that margins are included to account for design growth and customer specific demands in further design phases.

Main focus in the overall hull design was the safety aspect of the vessel. Aft peak buffer area is included in the hull design to minimize engine room damage in case of collision with a shuttle tanker. There is no ballast capacity included in possible cargo space areas to minimize hull particulars and consequently vessel costs. The hull includes four dedicated inner shell ballast tanks at vessel ends to minimize heel and trim and to keep the vessel at a certain draft to minimize risk of bottom slamming.

4 OTC 15311

Implementation of typical FPSO structures The adopted philosophy in the structural design of the generic newbuilt FPSO is that it should provide flexibility to the topsides design. Detailed topsides information is not required for hull design upto the latest construction phase.

To enable sufficient flexibility in the supports, each module is placed on support stools (minimum four per module). Following this approach, interfaces between vessel and topsides structure are kept to a minimum.

In the vessel the flexibility is guarantied by a reinforced upper bulkhead strake so that support stools can be positioned at all webframe locations. The increased upper bulkhead strake has also a beneficial effect to the allowable bending moments. Mooring box integrations result in relatively small local vessel reinforcements, which will be fitted in the double shell. At the moment a standard mooring box design is adopted, which can be extended depending on field requirements. Benefits of flexible positioning philosophy are also investigated for flare tower and crane integrations. The flare tower height is typically about 100m above maindeck. It is concluded that the flare location should be determined in an early design and construction phase so that local integration can be provided. Should this not be feasible, support boxes executed on past projects will be adopted, enabling load spreading above maindeck and avoiding underdeck reinforcements. At the moment, the standard cranes for the FPSO fleet are in the range of 40t offshore cranes, mounted on box-type structures on maindeck level. The experience is that crane locations tempt to move during topsides design. Since integration forces are relatively small and cranes will in principle be mounted on top of the easily accessible double shell, no further precautions will be taken for crane integrations.

Hydrodynamic calculations The vessel will be commissioned at the yard and towed to site location. On its location, the vessel will be permanently moored for its field life. The motion analysis comprises the determination of the motion characteristics of the vessel using 3D-diffraction theory. The motion characteristics consist of the six basic motions, the 3 translations and the 3 rotations.

From the analysis, maximum expected motions of the FPSO in the West-African region are obtained and are indeed comparable with calculations results of other previous FPSO's projects. Calculated accelerations are used as input for topsides and flare tower design.

R o l l m o t io n R . A .O .F i g u r e 5 - 4 : L o a d i n g C o n d i t i o n 1 ( T = 9 . 4 [ m ] )

0 . 0 0

0 . 5 0

1 . 0 0

1 . 5 0

2 . 0 0

2 . 5 0

3 . 0 0

3 . 5 0

4 . 0 0

4 . 5 0

5 . 0 0

0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 1 . 4 1 . 6 1 . 8W a v e f r e q u e n c y [ r a d / s ]

0 d e g

2 2 . 5 d e g

4 5 d e g6 7 . 5 d e g

9 0 d e g

1 1 2 . 5 d e g1 3 5 d e g

1 5 7 . 5 d e g

1 8 0 d e g

3 6 0

9 0

0

2 7 0

1 8 0

Hydrostatic design As a consequense of the ballast minimization, special consideration is required for bending moments. For towing conditions when maximum wave bending moments are to be accounted for, still water bending moments are reduced using ballast water in cargo tanks.

Site specific conditions are considered to calculate wave bending moments. In the generic design, topsides and mooring / riser loads are modelled including margins to ensure that estimated hull girder loads will not be exceeded in later design phases. To establish hull girder bending moments, shear forces and minimum/maximum trim, all applicable hydrostatic calculations have been performed including analysis of maintenance cases to take all precautions to avoid downtime. Calculations prove that bending moments and shear forces fall within the allowable limits.

Structural Design To enable hull construction all over the world, it is decided to limit the amount of higher tensile steel in the hull structure to the upper and lower strake and to the integration of deck equipment into vessel structure (all high tensile steel H32). This approach also has a positive influence to fatigue build up. The vessel structural design was commenced in initial design phase with determination of optimum longitudinal tank configuration. It is concluded that the given three-tank layout is an optimum for (sloshing) strength and integration of support stools. The standard approach in initial design phase is to derive scantlings from estimated hull girder bending moments and shear forces based on as-build data from previous designs. In this phase, initial midship section scantlings are calculated using DnV Nauticus Hull software.

OTC 15311 5

In second phase hydrodynamical and hydrostatical calculations are more or less finalized. ABS Rules based sloshing loads and plate panel buckling checks are incorporated in the hull girder design and midship scantlings are thus optimized.

Parallel with the Rule scantlings in the second phase, a 3D FE analysis is performed. The analysis model consists of 2 tank lengths (1 tank in the middle and half tank length on each side). The model is created to verify longitudinal and transverse vessel structure for both Rules requirements for trading tankers and for the specific FPSO conditions (including support stools interface) where governing. From the analysis, it is concluded that stress levels and buckling usage factors remain within the allowable limits.

Fatigue design The FPSO is intended for uninterrupted service on site for 20 years. During design and construction phase precautions are to be taken to avoid corrosion or fatigue damage during this period. Based on experience with both newbuild and 25-year old tankers, special attention is paid to corrosion allowances, painting and fatigue design.

Full spectral fatigue assessment will be performed at the moment site specific data becomes available. In the generic phase, the vessel is optimized for fatigue using the FE model and paying extra attention to local details (e.g. connection of longitudinal stiffeners and webframes).

Mooring system and offloading system Since most of the current large FPSO units are intended for service offshore West Africa with a relatively mild environment and a large number of risers, the proposed mooring system for the base case is a spread mooring. However, the design can easily allow either an internal or external turret mooring system to be used, for projects in more demanding environments. Offloading is assumed to be achieved through a CALM export buoy connected to the FPSO in the base case, or by tandem offloading as an option. Cargo handling system The aim is to be able to provide a cargo handling system based either on a pump room arrangement or on deep well pumps mounted on deck. The pump room arrangement presents the advantage of simplifying the interfaces on main deck, in terms of pump dismantling and overhaul. The pump room arrangement is also known to be a proven and cost effective solution since it requires fewer pumps to be installed. This is typically true on large FPSO units having a large number of cargo tanks. The cargo handling system equipments themselves are less demanding in terms of maintenance, leading to additional operational cost reduction.

For the above reasons, the pump room arrangement has been selected as a base case. However, it is easy to remove the equipment and the space required for the pump room if deep well pumps are preferred by specific Clients. The pump room has been located aft of the cargo area in order to use the engine room for the pump drivers and avoid the need for a second engine room in the fore part of the FPSO. It is therefore assumed that the operation of the unit will be achieved with a trim by the aft to allow for an efficient pumping and an actual stripping of the tanks when needed. The pump room is equipped with 4 main cargo pumps, 2 stripping pumps and 2 stripping ejectors, as well as 1 main ballast pump and 1 ballast ejector. Each cargo pump has a capacity of 4,000m3/h enabling an offload rate of 8,000m3/h with two pumps running, or 12,000m3/h with 3 pumps. The cargo handling system consists of 2 transfer headers located in tank bottoms, and a loading header on main deck with drop lines leading directly to the cargo tanks. The offloading arrangement includes a connection on one side of the unit to a fiscal metering skid enabling offloading to an export buoy if the FPSO is spread moored.

6 OTC 15311

A crude Oil Washing (COW) system is fitted enabling washing of cargo tank walls and stiffeners including shadow areas. Accommodation block The accommodation block itself does not raise any specific difficulty as far as the basic design is concerned. This part of the FPSO is rather easy to design in a generic manner once the requirements in terms of rooms list and surfaces are defined. The following operator standard criterias have been taken into account in the design of an accommodation block.

• There should be a separation between the working spaces, recreation spaces and the dormitory areas in order to reduce noise in the living quarters.

• There should be a convenient watching of the topsides plant from the Central Control Room.

• There should be easy access to escape and muster zones and to the helicopter deck.

• There should be trunks enabling practical routing of ducts, pipes and cables and easy interfaces between the machinery room and the accommodation block.

• There should be an easy access route to the engine room hatch for handling of main pieces of equipment for maintenance purpose. The access route shall enable a handling from the location of the equipment up to a supply boat landing area.

Based on those fundamental principles, the accommodation layout is designed for a complement of 100 permanent people and 30 additional temporary crews. Regarding the construction, conversion experience is of great support: existing tanker accommodation are either partly or completely scrapped, and rebuilt with the constraint of the existing structural walls, which does not exist in a new build unit. Hull/Topsides interfaces There are a number of interfaces between the vessel hull and the topsides plant, the full list of which is actually depending on the design choices. On one hand, it may be better to install utilities on the main deck, and therefore use an offshore approach derived from platforms design, or on the other hand to install some utilities in the machinery room and so use more tanker conversion or traditional shipbuilding practice. The optimum level of integration may take into account such factors as production capacity and consequent utility demands, shipyard capabilities, severity of environment, crewing strategy, etc. Since the optimum choices regarding the utilities to be installed in the hull may depend on the project requirements, it has been decided to design a machinery room able to supply utilities to the topsides plant with special attention to reliability, availability and maintenance ease. The main choices are addressed below.

Topsides plant supporting structure The process plant supporting structure is one of the main

concerns among the hull and topsides interfaces. It is actually simplified in the case of a new build hull compared to a conversion since the hull design may incorporate supporting stools at the strongest points of the primary structure, as it has been described earlier. The stools may support large loads and therefore give more freedom in the topsides module design.

On conversion, deck loading is normally limited to a few hundred tons, whereas on new build design this can be increased up to a 1500t vertical load per stools.

Topsides modules fabrication

The modules design, fabrication and delivery to the shipyard has been performed on conversions according to schedules enabling fast track deliveries of FPSOs. This is the result of an adequate and balanced organization in the design, procurement and site supervision teams.

It is the intention to use this proven organization in the case of a new build FPSO with a large capacity topsides plant. The sizes of the modules are kept below a certain limit enabling the “pancake” construction whenever applicable. The “pancake” construction consisting in one main level module – and locally elevated small platforms – results therefore in a much reduced complexity in the design and construction work.

The limited size of the modules enables also an easy

handling and transportation with lifting means that are cost effective and widely spread on the market.

Moreover, smaller modules size reduces the risk to the design and construction process in case of slippage in equipment delivery.

Smaller modules also allow more flexibility in selection of potential fabrication yards. Power generation

On a converted FPSO, the proposed existing tanker is usually fitted with steam boilers and small turbo alternators feeding the machinery and accommodation consumers. The additional topsides consumers require the installation of a new large power generation system. Many options are possible to achieve this: gas turbine packages on the main deck, new

OTC 15311 7

turbo alternators on the main deck fed by vessel steam boilers, or new steam plant on the deck with boilers and turbo alternators. The choice for one option or another depends on the project requirements, the CAPEX and OPEX cost comparisons, taking into account the condition and characteristics of the tanker existing equipments (mainly boilers), quantity and quality of available gas, etc.

In a new build design, many of those criteria are still valid and the choice of the power generation system type needs careful analysis.

The steam plant is a traditional and reliable system used in the marine business and is widely used in FPSO operations since steam is available on many tankers and can therefore be envisaged for a new build vessel.

The steam plant is also cost effective. Operational costs are all reduced as maintenance on a steam plant can be achieved by the crew and does not require as much intervention from vendors as for gas turbines installations.

Therefore, the generic FPSO base case is designed with a steam plant. It has been decided to install this plant in the engine room in order to be able to choose marine equipment without the requirements and constraints of an installation on the main deck in a process area. Furthermore, equipment running or on stand-by in the engine room are in a relatively protected and mild environment, leading to higher availability and reliability.

As an alternative case, the whole steam plant may be removed from the engine room which can therefore be reduced in length and a packaged power generation plant is consequently installed on the process deck.

The steam plant shall be able to feed a large process plant requiring therefore a high power demand. Typically, a peak power requirement of 60MW has been calculated including water injection and gas compression power supply.

It is an absolute necessity to have redundancy on the system. The steam plant is consequently composed of 3x50% steam boilers and 3x50% turbo alternators of 30MW each.

In this case, the whole process power demand is produced in the form of electricity, assuming that water injection and gas compression equipment is driven by electric motors.

As an option, in case of Client preference, an alternative

solution using gas turbine driven generators on topsides has also been developed.

Cooling water supply

One of the main supplies to the topsides plant is the seawater used either for water injection or cooling purposes. Two options may be considered: supplying seawater from deep well pumps installed outboard on the side of the hull or in a ballast tank or void spaces, or supplying seawater from centrifugal pumps installed in the engine room. The engine room arrangement offers the advantages that pumps are easy to access and are running in a protected enclosed environment. Maintenance is rather easy, provided that the engine room lay-out has been properly designed. The centrifugal type pumps are also known to be cheaper than the deep well pumps particularly in case of high ship depth.

After having reviewed the generic hull, we now briefly introduce some aspects of the topsides plant, and then address

the issues of construction, operational feed-back and projects execution.

Engine room design philosophy Following the above explanations of the various equipment that have been located in the engine room as a base case, the design and lay-out of the machinery is essential for easy and convenient maintenance. The engine room shall enclose boilers for steam production, turbo alternators for the electricity production and utilities for power generation, accommodation block and deck consumers, including sea water cooling system. Among the key criteria retained in the design of the engine room are:

• The redundancy of the systems in order to provide a optimized uptime

• The ease of access and maintenance with room for dismantling pieces of equipment and routes to movethem in and out

• A rationalized design for an efficient construction time at the shipyard

The base case design of the engine room assumes that topsides process consumers are electrically driven. A preliminary load analysis shows that the overall electrical balance is in the vicinity of 60MW and that the corresponding steam demand is approximately 300t/hr. Considering those load levels, the required redundancy in the equipment availability leads to a 3x50% layout with 3 boilers of approximately 150t/hr each and 3 turbo alternators of 30MW each.

Depending on the FPSO heating requirements, the steam balance may be adjusted to supply a low pressure steam generator (LPSG) for process heating purpose.

The engine room is designed with: • Minimized length of piping between the boilers

outlets and the main turbines inlets • Minimized length of piping between the turbines

outlet and the condensers • Minimized length of piping between the condensers

and back to the boiler inlets

A typical machinery layout showing these principles is given in figure 2.

The other equipment is located in the engine room and grouped in a classical manner by systems. The main systems are:

• Inert gas system • Nitrogen generation • Service and control air system • Fresh water generation • Sea water cooling system • Marine growth prevention system • HVAC • Provision stores compressors • Fire-fighting system • Fuel oil system • Sewage system • Bilge system

8 OTC 15311

In order to optimize the construction, the intention is to build machinery modules: equipment located in an area and dedicated for a system is grouped together on a common support frame, thus making a module. The module is fabricated and assembled in a workshop. This leads to the following usual advantages of modularization:

• The time required to build indoor in a workshop compared to an onboard construction is reduced due to the ease of access around the module and the presence of permanent adequate lifting and handling means.

• The congestion of the engine room during the construction is reduced

• The level of completion of the machinery space prior to the installation of the module can be improved in terms of surface preparation and coating, since structural interfaces between equipment and structure are reduced.

• The construction of the machinery room is less on the critical path of the hull construction.

Those principles are obviously to be discussed and optimized with the construction yard taking into account the existing shipyard facilities. The main goal is to ease construction and therefore reduce the construction cost and schedule and increase the quality of the finished work. As far as schedule is concerned, the goal is to avoid having the engine room on the critical path of the hull part construction. Construction phase Construction slots and shipyard availability is often an issue on large FPSO project. Having a generic design offers various advantages:

• When the project schedule is uncertain and depending on oil field investigations or other field development procedures or approvals taking time to complete, it may be convenient to have a generic design available that can be discussed and reviewed as much as necessary.

• The readily available basic design can be adapted with little effort. The detailed engineering phase may then be kicked off whenever project green light is given and the hull construction can be ordered upfront prior to topsides design.

• Construction possibilities may be reviewed and revised whenever it is necessary during the basic design phase and when an accurate project schedule has been defined. Since the whole basic design is done independently from the construction yard, it offers more flexibility in the shipyard choice.

Another advantage is the possibility to build in a wider range of shipyards. If the shipyard does not have the necessary experience to design an FPSO, but has skilled manpower and good construction facilities, an FPSO contractor can bring the necessary complementary design and supervision skills to achieve a high quality construction. Using the generic design presented in this paper may then further increase opportunities for slots.

The topsides process integration may be done in the new build shipyard or in a separate integration yard depending on the availabilities and skills of the new-build yard. Operational feed-back Experience gained as a FPSO operator has been taken into account: design teams benefits from constant feedback from the operators allowing continuous improvement. This feedback allows execution of availability and reliability analysis of major equipment leading to constantly improved selection criteria for subsequent projects. The lease contracts give significant responsibility in the design and operation of the FPSO’s, and consequently the need for well-proven solutions is a major concern of the design team, resulting in a permanent search for reliability and operability. Design flexibility for the generic hull The design of the generic hull has been done with flexibility in mind to accommodate a wide range of requirements:

• The design of this generic hull provides flexibility for the cargo storage capacity, between 2 and 2.4 mmbbls.

• The mooring system depending from the site environment and field layout may be achieved using a wide range of existing proven designs and may be adapted easily to the generic FPSO hull.

• Power generation may be installed either in the engine room or on topsides, depending on final load balance and Client preference.

• The FPSO systems and utilities are designed taking into account extensive operating experience.

Conclusion A generic new-build FPSO hull has been developed to allow the cost and schedule saving techniques employed on FPSO conversions to be extrapolated into new build projects. At the same time, developing a generic design allows more choices in construction yards. The generic large FPSO hull presented offers the advantages of a simple box-like design with a long parallel midbody for optimization of construction costs. Its design also offers the flexibility of increasing the cargo storage capacity from 2mmbbls to 2.4mmbbls of oil. Maintenance and operational concerns have been considered at an early stage of the design using the experience gained on the operation of a large number of FPSO units. The interfaces and requirements of an FPSO topsides plant are also considered as a key part of the study and prior experience in the management and integration of process plant is widely utilized to design adequately the hull and its utilities.

Reference

1. Terpstra, T. et all, "FPSO design and conversion: a designer's approach, paper OTC 13210 presented at the 2001 OTC, Houston, TX, 30 April - 3 May.

2. Clarkson, The Tanker Register 2001

OTC 15311 9

Figures Figure 1 – General arrangement

10 OTC 15311

Figure 2 – Machinery Layout