• Australia
  • Oceania
  • Asia-Pacific
Case Study

Tui

Tui – an extensive decommisioning and retrieval of subsea infrastracture of tui oil and gas field

The New Zealand Government awarded Shelf Subsea to perform the decommissioning of Subsea Assets in the Tui Oil and Gas Field in New Zealand. The scope of work involved the removal of the entirety of the Tui Field subsea infrastructure (except production wells) encompassing the management, design, engineering, procurement and fabrication required to complete the scope.

In addition, time allowing, SHELF is tasked cut the casing strings of wells Tui SW-2, Tieke-1 and Amokura-1 at a minimum of 3m below seabed, and recover and remove the wellheads and casing stubs of these three exploration wells, as well as the net-guard located over Amokura-1.

Services provided during the project

The work was performed over 3 months in Taranaki Bay on the Saturation Diving Vessel the Southern Star, with two installed WROVs and integrated Survey and positioning systems and extensive project equipment. Project activities included:

  • As found and as left Survey
  • Removal of various (27 items) Flowlines, umbilical’s , risers, jumpers, gas coil tubing totalling 38,660m form Tui, Amokura and Pateke subsea production systems and deliver to port either on Reel (reverse lay) or cut and sectioned (on deck)
  • Midwater Arch and Gravity Base Removal
  • Well head cutting and removal
  • PLEM removal
  • Anode skid removal

This was achieved with the mobilised equipment

  • DSV – Southern Star
  • Saturation Diving and tooling
  • ROV and tooling  (2 WROVs Quasars)
  • Reels, Spooler and under rollers
  • Rigging and decommissioning aids
  • HP water jetting
  • 150t winch for MWA removal
  • Subsea Diamond wire cutting
  • Flexible reverse lay and sectioning.

 

Project outcome

Over 110 days operational activities, Shelf performed 36 Saturation Bell runs, 136 ROV dives with 30 marine and 35-61 project crew. During this time 38,660m of flexible product of all types was retrieved to deck, flushed, sectioned, racked and returned to shore for disposal. Two PLEMS were retrieved, cleaned and returned to shore for disposal, along with 8 Anode skids. One Mid-Water Arch was XXm x XXm and weighing XX tonnes was disconnected and brought to surface in a controlled retrieval, cleaned and also returned to shore, along with the gravity base.  XX Wellheads were cut, retrieved for disposal.

The Southern Star performed excellently as a work platform in sometimes challenging conditions in the Southern Ocean.

At the time the project was one the most extensive decommissioning programmes undertaken by Shelf Subsea requiring the full engagement of  our ‘Integrated Services’ from Vessel, Diving, ROV and Survey, Project Management and Engineering resources.  Additional third party specialist equipment and resources were involved and managed by Shelf Subsea to round out a ‘one stop’ solution for the scope of work. Of particular note was the removal of a Subsea Mid Water arch requiring careful engineering and lift management.