fpsos are a mature & versatile fps technology

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Turret Mooring Design – Some Challenges and Solutions

FPSO Forum 2004 NUS, Singapore

Arun Duggal

FMC SOFEC Floating Systemswww.sofec.com

31 March 2004


FPSOs are a Mature & Versatile FPS Technology

• Over 100 units in operation worldwide

• FPSO total > than all other FPS combined

• Water depth range 20 m to > 1,400 meters

• 1 to 100+ risers

• 10,000 bbl – 250,000 bbls/day

• Up to 2,000,000+ bbls storage

• Benign (West Africa) to Extreme Environments (North Atlantic)

• Various flavors:

• Turret-moored

• Spread-moored

• Yoke-moored

• Hawser-moored


Typical Permanent Internal Turret System

Bearing (only upper in this case)

Turret Shaft / Riser Guide Tubes

Chain Table (Hawse Pipes/Chain Supports)

6 Anchor Legs + 34 Risers

Barracuda FPSO: Campos Basin834m, 34 Risers

Swivel Stack (Product/Lift/Controls)

Anchor Leg + Riser Pull-In Equipment

Manifolds + Pig Launching/Receiving


Design Considerations

Mooring System• Anchor Legs• Anchors• Risers• Thrusters & DP

Control

Environment• Water Depth• Waves• Wind• Current

Vessel Particulars• Storage / Tonnage• Topsides Layout• Vessel Motions

Turret Design• Configuration• Size• Location• Loads

Turret Mooring ofProduction Vessels

Fluid-Transfer Requirements• Well Heads• Subsea Manifolding• Risers• Turret Manifolding• Swivels• Offloading• Pigging


Some Current Turret Mooring Challenges

• More Complex Turret Systems

– Large number of risers

– Increased requirements for turret mounted equipment

– High pressures

• Riser Systems for very Shallow or Deep Water

• Project Schedule

– Short, fast-track schedules

– Project Design Basis not well defined

– Interfaces and Communication

• Installation in Deepwater

– Installation engineering, equipment, costs


Example 1: Fast-Track FPSO for Shallow Water

• Su Tu Den FPSO, Vietnam

• MODEC, Inc + FMC SOFEC + ConocoPhillips

• Newbuild FPSO (80,000 bbl oil/day)

• Schedule: Contact to First Oil – 19 months

– Turret Delivery Schedule – 12 months

• Shallow Water (48m water depth)

• Harsh Environment (100-yr wave of 8.1m Hs)

• Large Number of Risers (12)


Project Milestones• 2002 Mar. Contract Award (LOI)(2002/03/21)

• 2002 Apr. Order Long Lead Items – bearing, forgings, process

• 2002 Jun. Mooring Design Complete

• 2002 Aug. Turret Fabrication Begins (MSE)

• 2002 Oct. Hull Fabrication Begins (Samsung)

• 2002 Nov. Preliminary Riser Design Complete

• 2002 Dec. Topside Fabrication Begins

• 2003 Mar. Drydock – Block Assembly Begins

• 2003 Apr. Start Topside Module and Turret Installation

• 2003 May Launching

• 2003 Jul. Start Shipyard Commissioning

• 2003 Sep. Tow Out

• 2003 Oct. Offshore Installation

• 2003 Oct. 1st Oil (2003/10/29)


STD Turret Mooring Design & Fabrication

• Use Standard Components & Design

– SOFEC Large External Turret Design

• Bearing Capacity exceeds anticipated Design Loads

– Allows order of main components before final loads derived

• Design Riser Configuration Flexibility in Chain Table Design/Fabrication

• Clearly Define all Structural and Fluid transfer Interfaces at Turret Support Structure

• Parallel Design and Fabrication Effort

• Easy / Quick Integration with Vessel


Riser & Mooring Design in Shallow Water


Mooring and Riser Design 2


Integration of Turret & Vessel


First Oil: November 2003


• Application– FPSO weathervaning SPM– Large field (>100,000 bbld)– 50 to 100+ risers– Deep to ultra deep water– Worldwide

• Weathervaning advantages– Mooring tensions– Tandem offloading

• Simplified turret structure

– Allows for simple interface with vessel

• Robust bearing system

• Large Decks for Flowline Manifolding, and other Equipment

• Efficient Mooring & Riser Installation Equipment

Example 2: Very Large Turret


Chain

Table

I-Tubes

Support Columns

Chain Supports

Main Deck

TorqueArm

Vertical Bearing

RadialBearing

Swivel Stack & Torque Tube

Piping /Manifolding

Riser Hang-Off

Pull-InDeck

Anchor Legs Risers & Bend Stiffeners

VLT: Deep Water, Large Capacity Internal Turret


VLT Chain Table

• 3x3 mooring provides 3 riser corridors

• Riser quantity defines chain table (and turret) diameter

– 60 risers - 22 m dia



• 2 riser rows maximum

• No shadowing to allow inner row installation and replacement


VLT Main Deck

• Supports all loads, including:

– Riser hang-off loads

– Mooring loads through chain table and support columns

– Turret self weight

• Depth-to-diameter ratio is a key design parameter

– Flexibility to move with vessel

– Strength to support risers, mooring and turret weight loads

– 2.5 m depth / 32 m diameter for a 90 riser VLT


Conclusions

• Turret Moored FPSOs are a Very Mature Technology

– Design for Load Transfer is typically not an issue

– Current challenges mostly associated with Fluid Transfer

Large Number of Risers

High Pressure

Manifolding

Subsea Intervention & Control

• Project Parameters also Impact Turret Mooring Design

– Schedule

Fast-track: 18 – 22 months

Complex systems require more commissioning time

– Communication & Interfaces – among various contractors / client

– Knowledge of others scope of work, issues, etc.

fpsos are a mature & versatile fps technology

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