volve subsea removal - subopsvolve subsea removal –wellheads cut and recovered to nsg deck....

Trond Hofseth

Subsea Operations ConferenceHaugesund 08.08.2018

Volve Subsea Removal

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Recovery and disposal of:

➢ STL loading buoy

➢ Mid-Water Arch (MWA)

➢ 9 off mooring lines

➢ Approximately 1.600m of exposed risers

and flowlines

➢ All subsea structures

➢ MWA gravity base structure (3 pieces)

➢ 3 off riser holdback anchors

➢ Drilling template

➢ SSIV

➢ 5 off GRP covers

➢ 10 off wellheads

Volve Subsea Removal – Overall scope of work

Removal of STL Loading Buoy

4Volve Subsea Removal - Cutting of riser and mooring line wire

Volve Subsea Removal – Simops - Recovery of STL loading buoy

Volve Subsea Removal - Towing and lifting the STL loading buoy

Volve Subsea Removal – Lessons learned - STL loading buoy

Lessons learned

➢ Successful vessel simops operation. The method

proved to be a well planned and well performed

operation

➢ During tow of STL the winch readings was approx. 41

tonnes with a velocity of 7.2 knots. This is a higher

speed than expected on this load (ref. tow analysis)

➢ Cutting procedures and subsea tooling worked well,

although the outer plastic layer on riser seems to clog

the diamond wire

➢ Successful use of dyneema sling with additional

protection for towing

➢ Towing calculations conservative with regards to towing

forces

Removal of the Mid-Water Arch (MWA)

Volve Subsea Removal – Mid Water Arch (MWA)

Volve Subsea Removal – Recovery of MWA

Volve Subsea Removal – Lessons Learned - Recovery of MWA

Lessons learned

➢ The vessel crew was well prepared, proactive, selfgoing

and extremely efficient

➢ Communication was excellent

➢ Cutting procedures and subsea tooling worked well

➢ Vessel A-frame with top roller proved to be perfect for the

handling of MWA. This A-frame made it possible to get the

whole MWA on deck instead of towing it to land

➢ Did allow vessel to use own procedures and routines

which improved the operations

Cutting and recovery of 9 off mooring lines

Page footer text | 13Volve Subsea Removal – Mooring line

Page footer text | 14Volve Subsea Removal – Cutting of mooring chain

Observation

➢ Highly trained personell on vessel, correct

equipment on vessel and good planning with input

from vessel crew made this to a very smooth

operation

Lessons Learned

➢ Back filling and loose sediments at the seabed

created bad visibility when Skandi Vega ROV tried

to connect rigging to the chain

➢ Testing and adjusting rotation speed on diamond

blade for cutting of chains is highly recommended

before mobilization

Volve Subsea Removal – Mooring line recovery

Cutting and recovery of flexible export lines

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➢ Did cut approx. 1.600m of exposed pipe

➢ 8 inch oil export line and 7.4 inch gas export

line

➢ Cut in 11m sections

➢ The cutter was upended on deck & deployed

vertically

➢ Very efficient, landed onto flexible vertically,

made the cut in 20 second

➢ The shear cutter was also used to lift the

flexible pieces into the subsea baskets

Volve Subsea Removal – Cutting of flexibles using shear cutter

Volve Subsea Removal – Relocation of cut flexibles pieces

Recovery of subsea structures

Volve Subsea Removal – Recovery of subsea structures

Volve Subsea Removal – Design vs actual lift-off weights

Cutting and recovery of wellheads

Volve Subsea Removal – Drilling template recovered to NSG deck

Volve Subsea Removal – Concrete removal at drilling template

Volve Subsea Removal – Concrete removal at drilling template

27Volve Subsea Removal – Cutting of wellheads

➢ Remove riser stumps (incl. tie-back connector)

➢ Drift clean wells internally and install internal cutting tool

➢ Cut through all casings and conductors below mudline

➢ Pull wellhead out of the cement / formation

➢ Recover wellhead to deck

➢ Cutting time approx. 5-6 hours

Volve Subsea Removal – Wellheads and upending frame

Volve Subsea Removal – Wellheads cut and recovered to NSG deck

Summary of vessel operations

VESSEL CAMPAIGN SCOPE DURATION WHEN

Wellservicer C0 Cut loose STL Buoy and MWA, SIMOPS. Cut all 9

chains at pile. Concrete removal at drilling template.

Dredge and relocate GRP covers. General prep work

29 days May/June

2017

Skandi Vega

(CPI)

C1 Tow STL Buoy and MWA to Vats. Recover all 9

mooring lines. Wires on winch and chains in locker

10 days May 2017

North Sea Giant C2 Cutting and recovery of exposed flexibles and risers 15 days Nov 2017

North Sea Giant C3 Release and recovery of 9 off tie-back connectors with

2m riser stumps on top. Cutting and recovery of 10 off

wellheads. Campaign aborted due to perforated

casings

14 days Oct 2017

North Sea Giant C4 Recovery of SSIV, 5 covers, 3 RHA, MWA GBS (3

lifts)

10 Nov 2017

North Sea Giant C3.1 Cutting and recovery of 10 off wellheads and 15 slot

drilling template

16 Dec 2017

Volve Subsea Removal – Summary of vessel operations

AF Decom - Disposal Yard

33Volve Subsea Removal – Disposal summary

CategoryDisposal method In tons

Energy Recovery

Landfill Recycled Reuse Technip Reuse AF Decom Sum

Hazardous waste 1,58 1,28 2,86

Low radioactive waste/Hazardous Waste

3,08 3,08

Metals 2231,83 4590,50 6822,33

Non-Metals 24,12 351,06 375,18

Items sent for inspection to Statoil

31,48 31,48

Saleable 55,16 55,16

Sum 25,70 4,36 2638,05 4590,50 31,48 7290,09

Summary

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➢ Decommissioning more complex than installation (lifting)

➢ Lack of As-Built information, especially from older fields

➢ Concrete removal takes a lot of time (double the time estimated)

➢ Good performance from all subcontractors

➢ Good performance from all three vessels

➢ 6% WOW October through December (North Sea Giant)

➢ Focus on planning as well as flexibility between campaigns and/or vessels required

➢ Great cooperation between Client and TechnipFMC teams

➢ No issues with NORM, but still important to measure

Volve Subsea Removal – Overall lessons learned

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Recovery and disposal of:

➢ STL loading buoy

➢ Mid-Water Arch (MWA)

➢ 9 off mooring lines

➢ Approximately 1.600m of exposed risers

and flowlines

➢ All subsea structures

➢ MWA gravity base structure (3 pieces)

➢ 3 off riser holdback anchors

➢ Drilling template

➢ SSIV

➢ 5 off GRP covers

➢ 10 off wellheads

Volve Subsea Removal – Overall scope of work

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