Innovative Technologies, Creative Solutions
Turret Mooring Design – Some Challenges and Solutions
FPSO Forum 2004 NUS, Singapore
Arun Duggal
FMC SOFEC Floating Systemswww.sofec.com
31 March 2004
Innovative Technologies, Creative Solutions
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
Innovative Technologies, Creative Solutions
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
Innovative Technologies, Creative Solutions
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
Innovative Technologies, Creative Solutions
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
Innovative Technologies, Creative Solutions
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)
Innovative Technologies, Creative Solutions
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)
Innovative Technologies, Creative Solutions
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
Innovative Technologies, Creative Solutions
Riser & Mooring Design in Shallow Water
Innovative Technologies, Creative Solutions
Mooring and Riser Design 2
Innovative Technologies, Creative Solutions
Integration of Turret & Vessel
Innovative Technologies, Creative Solutions
First Oil: November 2003
Innovative Technologies, Creative Solutions
• 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
Innovative Technologies, Creative Solutions
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
Innovative Technologies, Creative Solutions
VLT Chain Table
• 3x3 mooring provides 3 riser corridors
• Riser quantity defines chain table (and turret) diameter
– 60 risers - 22 m dia
– 90 risers - 31 m dia
– 120 risers - 40 m dia
• 2 riser rows maximum
• No shadowing to allow inner row installation and replacement
Innovative Technologies, Creative Solutions
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
Innovative Technologies, Creative Solutions
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.