Gullfaks Subsea Compression

Subsea Installation with monohull vessels - Pushing the limits

Amund Moen, 6 August 2015

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Introduction – Subsea 7

The Gullfaks Subsea Compression project

Working with existing subsea structures

Module installation

Marine operations

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A world leading seabed to surface partner

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Subsea 7 provide technical solutions to enable the delivery of complex projects

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The Gullfaks Compression project

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Increasing the recoverable reserves from Gullfaks...

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Why Subsea Processing?

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Existing field lay out

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• Project management, Engineering & Planning of the work– Installation engineering & interfaces

– development & modification of equipment/vessel to enable installation and future intervention

– Detailed design of layout, spools, covers

• Procurement/Subcontracting– Mattresses, big bags, dredging, cutting, etc

• Fabrication – Spools & covers

– Installation aids, spreader bars

• Installation/marine operations– Preparations (dredging, removal, modification), Wet Gas Compressor

(WGC), IPSU, spools, covers, tie- in, RFO, etc

Contract for Marine Operations was awarded 2012

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Contract for Marine Operations awarded 2012

• Company Provided Item’s– Hubs and tie in systems – FMC, OneSubsea & Subsea 7

– Wet Gas Compressor – OneSubsea

– Intergrated Power and Service Umbilical (IPSU) –Nexans

– Rock dumping

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Using the right tool for the right job

Seven Viking: WGC module installation

Skandi Acergy: Spools, covers and WGC hatches

Oleg Strashnov: Wet Gas Compression protection structure and compression station

Normand Oceanic: Integrated Power and Service Umbilical installation, incl UTA

Acergy Viking: preparation work, survey & dredging

Havila Subsea: Removal of existing structures, tie in & precommissioning

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Working with existing subsea structures

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Brown field challenges...

• Hub capacities and spool design– Little documentation available for existing

hub capacities

– Field layout consist of a very congested area where not much flexibility is allowed for spool size optimization

– Manifold manufacturer performed extensive documentation work for hub-capacities of existing templates

– Reduced hub capacities 60%, due to HISC

– Spools grew in size and all spare bends used to soften spools

– UTIS tool rebuilt to allow for stroke-bending mitigated spools

– Complex installation with tilting and airbags

Old layout

New layout

Old layout

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Brown field challenges...

• Requires new thinking on GRP covers design– GRP concept with grating and sand-filled

stiffening beams developed

– Cost effective solution which allows for fabrication of large covers that traditionally would not be feasible to install

– Due to the ventilation given by grating, thedesign allows for horizontal installation

– Installation possible in Hs>2.5m

– Reduced installation time due to reduction in amount of covers

– Dropped object tests was performed on cover (50kJ) with no delamination/deformation

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Testing of new cover design

• Conservative approach: – 1,5 tons

– 6 m height

– 12 m GRP beam

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• Removal of rock, schedule uncertainties– Rock size varies

– Drill cuttings

– Hardness of soil

– Height of different layers

– Handling of hoses, rock removed 50 m away...

Brown field challenges...

X-Subsea (Scanmachine)

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WGC Module installation

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Seven Viking - capacity

• Statoil IMR

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Seven Viking - capacity

• Module Handling System (MHS) data:– 70Te WLL winch (main winch)

– 20Te WLL winch (auxiliary winch)

– 3-off Guide Wires (WLL 5Te)

– Skidding Capacity of 78Te

– Moon pool hatch capacity of 80Te

– 7.2x7.2m Moon pool

– Lifting height in hangar ~10m

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OneSubea modules

• WGC Module– 4.7 x 2.9 x 8.5m, 65Te

• Cooler Module– 5.4 x 4.3 x 8.5m, 59Te

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Interface challenges between vessel and modules

Weight • Weight of module very close to max WLL

– Weight of Compressor module incl. installation tool plus cursor is

65Te + 5Te ~ 70Te

– MLW capacity of 70Te, DAF 1.7

• Available rigging height between installation tool and MLW was very limited due to large dimension on rigging

– New socket with swivel was designed

– 150Te Imenco ROV shackle was replaced with a purpose built plate shackle

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Interface challenges between vessel and modules

• Height of modules– Modules needs to be lifted above

skidding pallet

– Modules needs to be lifted high enough for moon pool hatches to be opened

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Interface challenges between vessel and modules

• New for supplier how module handling on a vessel is performed – Focus was on subsea interfaces

– Requirement for transport pallets on deck

– Deck logistic

– Sea fastening cases (operation and transit)

– Load picture when cursor frame is initiated

• Design and fabrication of the Module Handling System on Seven Viking was not completed when initiating interface towards Onesubsea -> Lack of available information

• ROV interface

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Interface challenges between vessel and modules

Guide Funnels and cursor Prongs not strong enough• Old prong design allow approx. 2 degree tilting of module before moment

force in cursor frame and module funnels occur

• New Prong design to avoid moment forces in Cursor Frame

New ball end design allows 6° tilt

New designOld design

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Operational criteria (sea state)

• The governing criteria is given when the module is hanging in the air

• The criteria was given by the module response relative to the vessel

• The module was allowed to move +/- 60cm transvers and +/-80 cm longitudinal

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Operational criteria (sea state)

• SIMO analysis showed that large pendulum movement in longitudinal direction would occur in waves with period of about 5 sec. due to resonance motions. Expected sea state around 1.5 m HS

• To increase the weather criteria two measures were put in place– Bumper acting on top cursor

– Vessel response forecast

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Operational criteria (sea state)

• Module movement forecast

Pitch:

Roll:

Heading:

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Experience from model testing at Marintek

• The hydrodynamic forces are limited for the UTA compared to the mass of the modules (DAF=1.3) compared to simplified approach in DNV-RP-H103

• The results were in accordance with logged data from offshore operations

• There seems to be no effect from the «bubble system»

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Vessel Integration Test

• Full scale test of WGC Module and Dummy Cooler Module

• Lessons learned:– Modified Skidding Pallets (interface towards modules)

– Clash check – verified

– Familiarisation of modules and equipment

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Offshore operations

• 2-off Cooler Module and 2-off WGC Module installed successfully

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1st time installation VS future intervention

• Main difference is the recovery phase where docking of the modulewill be carried out below the splash zone. Requirement for Cursor Camera.

• Procedures and concepts for recovery of modules, UTA and essential parts are established

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Marine Operations

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• SIMOPS

Busy installation season

The plan....

....and real life.

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Marine Operations

• Gullfaks Subsea Compression Installation work

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