Project Description

Build a fully scalable decommissioning capability at a reduced cost

Find out how

North Sea, UK

Maersk Supply Service, a partner in the Maersk Decom joint venture, has project managed and executed the full scope of decommissioning for the Leadon subsea field.

By supplying and managing the entire marine requirement, it is possible to increase flexibility, optimise schedules and reduce risk throughout the project. The offshore work scope involved cutting the field’s pipe bundles, as well as recovering the mid-line structure and towheads. With more than 50 years of hands-on offshore experience, Maersk Supply Service can react safely to unpredictable environments and unforeseen events which can occur during decommissioning. With this capability, we ensures a safe and efficient project delivery.

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Project Details

CLIENT

Total E&P UK

WATER DEPTH

120 m

NO OF VESSELS USED

3

DURATION

2017 to 2019

OPERATIONS

Survey, subsea cutting, subsea infrastructure recovery

Full scope delivery

Project management, engineering and marine services

In addition to executing the offshore work scopes, Maersk Supply Service is delivering the project as an integrated solution including project management, engineering, subcontractor management, offshore planning, interface management, and management of the recycling and waste disposal of recovered infrastructure.

Advanced capabilities

Milestones achieved from newbuild vessel

The lift of the 26m-long South towhead, weighing 260 tonnes, represents the heaviest lift performed from a Maersk Supply Service vessel to date, and the first time such a structure has been lifted and recovered by a subsea construction vessel. With its 400-tonne active heave-compensated crane, the I-class vessels are an effective, cost efficient platform for subsea recovery.

Innovative method

Designing the recovery system

Having been installed with no conventional features for lifting, the Leadon towheads were secured to the vessel’s crane and recovery slings using remotely operated vehicles. The towheads were then lifted by Maersk Inventor’s 400-tonne crane, and a tagging winch system was used for rotating the structures.

Project Gallery

Recovering the South Towhead, 2018
Lifting the mid-line structure with Maersk Inventor's 400-tonne active heave-compensated crane
Recovering one of four subsea Christmas trees onto the 1,850m2 deck of Maersk Inventor
Transporting towhead to quayside on Maersk Inventor
Recovering the North Towhead, 2019

Work Scope

0
KM OF FLOWLINE RECOVERED ONTO AHTS WINCH
0
TONNE TOWHEAD LIFTED BY CONSTRUCTION SUPPORT VESSEL
0
X-MAS TREES TO BE RECOVERED
  • Multibeam echosounder survey by Maersk Achiever
  • Multibeam echosounder survey by Maersk Inventor
  • Flowline cutting by Maersk Master
  • 6x cuts of bundle pipe at 51″ in outer diameter by Maersk Inventor using diamond wire saw
  • Towhead structure preparatory work by Maersk Inventor included spool cutting using hydraulic shears and hole cutting using an abrasive water jet system
  • 6x riser bases and 1x concrete mattress recovered by Maersk Achiever
  • 6.1km of 139mm outer diameter gas import flowline recovered by Maersk Master, spooled in a complete section onto the vessel’s large winch drums
  • Mid-line structure, mid-line structure bouyancy pontoons, 26m-long South towhead weighing 260 tonnes, and 4x subsea X-mas trees recovered by Maersk Inventor
  • Debris clearance by Maersk Inventor
  • North towhead recovered at over 250 tonnes by Maersk Installer
  • 4x subsea X-mas trees to be recovered

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