Santos Ltd (Santos) proposes a revision to its inforce Mutineer Exeter Cessation of Production (CoP) Environment Plan, to enable the continued operation of the Mutineer, Exeter, Fletcher and Finucane (MEFF) facilities in cessation phase, and to allow for a new stage of activity for floating asset removal (FAR), within WA-54-L, WA-26-L and WA-27-L. The permit areas are within Commonwealth waters, approximately 160 km north of Dampier, in water depths ranging from 130 – 160m.
The facility has been in cessation phase since the MV-11 FPSO which sailed away in July 2018, leaving the disconnectable turret mooring (DTM) system in place at approximately 30 m below sea level and remaining connected to six mooring chains. The mid-water arches (MWAs) also remain in place at approximately 82 m below sea level.
The reservoirs are isolated from the subsea production system at the Xmas trees (XTs), although the subsea production system remains connected to the DTM via risers. All well valves will remain isolated unless they are required to be operated to allow decommissioning activities. Ongoing integrity management of the facilities is as per a Risk Based Inspection (RBI) regime to ensure that these floating assets can be removed from title.
Typical subsea inspection and intervention activities carried out may include:
• DTM inspections, such as inspecting the spider buoy and mooring lines;
• riser, flowline, umbilical and MWA inspections;
• subsea production centre inspections, such as inspecting the XTs, manifolds, spools, umbilical termination assemblies (UTAs), production umbilical distribution units (PUDUs), jumpers, etc;
• cathodic potential measurements;
• maintenance and repair, such as replacing anodes or installing anode skids;
• recovery of dropped objects;
• clearing debris (e.g. calcareous marine growth) using high pressure water jetter and/or flapper tool;
• Close Visual Inspection (CVI) and measurements of critical components; and
• seabed burial and environmental survey
o multi-beam echo sounder (MBES)
o side scan sonar (SSS)
o sub bottom profiling (SBP)
o seabed grab sampling
o Autonomous Underwater Vehicle (AUV)towed camera for identification of debris or raise seabed features.
Floating asset removal is planned to commence in Q4 2022 with removal of buoyant infrastructure planned to be completed by the end of 2022.
It is envisaged that the total duration of the floating asset removal activities covered by this environment plan will be up to 45 days in the operational area. However, with potential for unfavourable weather and operational delays this could extend the project duration for floating asset removal activities to a period of 90 days in the operational area. Individual general inspection and maintenance campaigns are expected to take approximately 14 days. Activities could be undertaken at any time of the year. Activities would be continuous over a 24-hour period and are expected to be conducted over multiple and concurrent campaigns during these time frames.
The activity may be supported by one, or a combination of the following marine ‘vessels’:
• Tugs including Anchor Handling Tugs (AHT);
• Barges;
• Crew transfer vessel;
• Heavy Lift Vessel (HLV); and
• Dive Support Vessel (DSV) and rescue vessel
Inspection and maintenance activities are expected to be conducted with one vessel with minimum one ROV.
Helicopters and support vessel may be used to transfer crew and equipment to and from vessels and assist in emergency as required.
