Ekofisk DecommissioningAn Engineering Perspective

byPaul Shuttleworth

9th April 2015

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Introduction

• Today’s presentation – my involvement in the Ekofisk Decommissioning Project

• My position – engineer in the ConocoPhillips client team

• Based in ConocoPhillips office in Norway and Heerema’s office Leiden

• Based offshore on one of the heavy lift vessels each summer season for the platforms removed between 2009 and 2013

• Heerema Marine Contractors (HMC) was the main contractor

• Crane vessels used were Thialf, Hermod, Balder

• The Thialf and Balder worked on dynamic positioning (DP) and the Hermod on anchors

• AF Decom was the hook-down and disposal contractor using their VATS yard in Norway

• The disposal yard has sufficient quayside water depth to allow crane vessels to offload

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Ekofisk Platforms – General Data

• The platforms were installed in the mid 1970’s

• Jackets weigh up to about 8,000tonnes

• Jackets were launched as too heavy to lift at the time

• Jackets were piled through the legs and the annulus between piles and legs grouted

• Module Support Frame (MSF) installed on top of the jacket

• Topsides weigh up to approximately 11,000tonnes

• Topsides were installed as modules of about 1,000 to 1,500tonnes maximum lift weight

• Platforms were not designed with any provision for removal

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Platform Removal Summary

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Platform Removal SequencePre 2009• 2/4T topsides, satellite flares2009-2013• COD 7/11A• Albuskjell 1/6A• Albuskjell 2/4F• Vest Ekofisk 2/4D• 2/4R• 2/4P• Edda 2/7C• 2/4W• 36/22A• 37/4ANext phase starting 2015• 2/4A• 2/4B• 2/4H• 2/4Q • 2/4FTP• Tor 2/4E

Platforms Removed 2009 to 2013

2012-2013

2010-2011

2011-2012

2012-2013 2009-2010

2009

2009- 2010

2011-20122009-20102009-2010

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Next Phase Platforms to be Removed

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Topside Removal Status• Issues

• Tanks, pipes and vessels not emptied and steam cleaned

• Hazardous materials, asbestos, radioactivity, mercury, drilling mud remained

• Unsafe areas of rusted and missing walkways, grating, handrails, ladders, etc.

• Modifications during operation not fully documented

• Weights and centres of gravity unknown

• Structural strength degradation due to corrosion

• Removal method different to installation

Mitigation • Surveys to identify hazardous materials• Survey and sniff all pipes, tubes, vessels and equipment before cutting• Cold cut wherever possible, e.g. small pipes• Survey and prepare weight control reports• Check all available platform data including old installation records • Wall thickness, NDT and lamination checks on critical parts of structure• Perform detailed structural and marine analyses• Lift and transport analyses checked by Client, DNV and MWS

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Topside Removal Personnel and OperationsIssues

• Access, for example to cut seal welds

• Personnel transfer between platforms and vessels

• Control of crane vessel and supply vessels in vicinity of the platforms

• Impact of weather on marine operations, lifting and back loading

• Environment control, spills, etc.

• Fire from hot work due to residual hydrocarbons in pipes or legs

• Personnel hazards from burns, falling, dropped objects, fumes

• Failure of padeyes, slings, shackles, structure and structural components

• Mitigation

• All operations Risk Assessed, e.g. working at height

• Personnel to use PPE, harnesses and pressurised welding masks

• Restricted personnel access, controlled by T-card, barriers, etc.

• Crane vessels on anchors or DP3 - approved vessels only in 500m zone

• Weather monitored at all times , telescopic bridge disconnected and vessels move off

• Modules back-loaded to vessel deck not cargo barges

• Regular personnel to medical checks for exposure to hazards

• Follow UK Safety Case Regulations

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Topside Removal Illustrations (1 of 2)

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Topside Removal Illustrations (2 of 2)

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Jacket Characteristics and Preparations• All jackets had through-leg battered piles

• Some jackets had under-reamed piles with concrete bells or insert piles

• Drill cuttings contain heavy metals so generally left undisturbed - relocated where interfering

• Risers previously cleaned and purged

• Riser/pipeline exits at seabed cut

• Conductors removed prior to lift contractor arrival - except Albuskjell 1/6A

• Caissons pumps and loose piping removed prior to lift contractor arrival

• Marine growth largely removed

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Jacket Removal Principles

• Preferred – one-piece lift and place on HLV deck

• Larger jackets one-piece lift and transport on crane hooks

• Very large jackets subsea cut into two and transport each piece on crane hooks

• Jackets transported on hook clear of water surface to avoid waves

• Piles cut 2m below seabed – internally by water jet where possible otherwise externally by diamond wire

• Jackets transported by the lift vessel - on the deck if possible

• Lift at corner legs with pile lifting tools

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Jacket Removal Considerations

• Not designed to be lifted in this way – installed by launching

• Jacket may be weakened due to damage or corrosion

• Caissons, risers and J-tube supports may be damaged

• Pile/leg grouted connection may be incomplete or inadequate for loads

• As the jacket is cut it becomes progressively more unstable under wave loading

• Marine growth weight and wave load

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Jacket Removal Additional Considerations

• Delays due to weather

• Delays due to hazardous materials removal, e.g. residue in caissons

• Spills when cutting riser if not properly cleaned

• Loose internals inside piles can cause diamond cutting wire to break

• External cutting requires excavation which is lengthy and unpredictable

• Pile handling tools, slings or shackles may fail

• Vessel collision - crane vessel or other attendant vessels

• Safety provisions for personnel man overboard, dropped objects, etc.

• Adjacent live pipelines

• Vessel stability during transportation - jacket on crane hooks

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Jacket Removal Mitigation Measures• ROV visual surveys to check for damage, lost members, corrosion

• ROV flooded member detection

• Caissons, risers, J-tubes and supports secured as necessary

• Cut inspection holes to confirm grout presence - if in doubt install shear pins

• Remove marine growth where possible

• Avoid offshore lift onto barge - high weather dependency

• Jackets detailed analyses for lift, set down, transport (including jacket on crane hooks) and offload - set limiting weather criteria

• Perform cut jackets stability analyses - set limiting weather criteria

• Analyses and designs checked as appropriate by Client, DNV and Marine Warranty Surveyor

• Continuous weather forecasting and monitoring by offshore personnel

• MWS on board to check lifting procedures and equipment

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Offloading• Crane vessel moored at quayside

• Deep draught required – available at VATS

• Offloading by crane vessel

• Larger jackets toppled to give access for mechanical cutters

• Site moves by self propelled modular trailers (SPMTs)

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Deconstruction and Disposal• Larger jackets toppled to give access for mechanical cutters

• Remote demolition using mechanical cutters

• Hazardous materials removal - regulated

• Equipment and vessels removed - for re-use where possible, e.g. cranes

• Valuable materials separated, e.g. copper, stainless steel, titanium

• Steel cut up for recycling

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Offloading Deconstruction and Disposal IssuesIssues

• Hazardous materials

• Pollution – Norwegian fjords

• Environmental disturbance – noise, emissions, traffic, etc.

• Worker safety – site hazards, e.g. falling objects, fire, working at height

• Toppling operation hazardous

• Unstable structures during demolitionMitigation

• Ekofisk conformed with Norwegian hazardous material regulations

• Remote demolition/cutting rem

• Segregate personnel, barriers, permit to work, etc.

• Engineer all demolition and toppling

• Carry out risk assessments

• Bund work areas to catch spills, marine growth etc.

• UK – Construction Design and Management Regulations 2007 (CDM) –revision due 6th April 2015

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Decommissioning - Alternative MethodsPioneering Spirit (formerly Pieter Schelte)• Very large vessel 400,000tonnes, draft 10 to 25m• Length 382m (hull), 477m (max), Width 124m• Untried vessel - no operating experience• Access difficult in congested fields• Has to come close to the platform• Offloads cargo inshore onto a purpose built barge then

transferred from barge to yard at quayside• Offloading a large topsides/jacket requires many trailers• Demolishing while on barge presents difficult crane access• Working draft likely to exceed that available at potential UK

disposal yard quays

Typical UK Yard Water Depths:• Lerwick 12.5m – LPA, Fabricom• Hartlepool 15m - Able UK, Heerema• Tyneside 13m (ex McNulty)• Nigg Bay 10m – Global Energy Group

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http://hmc.heerema.com/content/news-media/multimedia-gallery/video-gallery/ekofisk-cessation-project/

Ekofisk DecommissioningAn Engineering Perspective

byPaul Shuttleworth

Thank you – any questions?

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