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Turret Mooring Design Some Challenges and Solutions
FPSO Forum 2004 NUS, Singapore
Arun Duggal
FMC SOFEC Floating Systems
www.sofec.com31 March 2004
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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
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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 Basin
834m, 34 RisersSwivel Stack (Product/Lift/Controls)
Anchor Leg + Riser Pull-In Equipment
Manifolds + Pig Launching/Receiving
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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
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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
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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)
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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)
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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 transferInterfaces at Turret Support Structure
Parallel Design and Fabrication Effort
Easy / Quick Integration with Vessel
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Riser & Mooring Design in Shallow Water
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Mooring and Riser Design 2
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Integration of Turret & Vessel
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First Oil: November 2003
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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
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ChainTable
I-Tubes
Support Columns
Chain Supports
MainDeck
TorqueArm
Vertical Bearing
Radial
Bearing
Swivel Stack &Torque Tube
Piping /Manifolding
Riser Hang-Off
Pull-InDeck
Anchor Legs Risers & Bend Stiffeners
VLT: Deep Water, Large Capacity Internal Turret
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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 andreplacement
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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
ManifoldingSubsea 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.
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