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 the removal of floating assets (FAR), as accepted in Revision 4, by NOPSEMA in March 2022. This revision now includes final seabed decommissioning activities on title, within WA-54-L, WA-26-L and WA-27-L to address sections s572 and s270 of the Offshore Petroleum and Greenhouse Gas Storage Act 2006 (OPGGS Act). The permit areas are within Commonwealth waters, approximately 160 km north of Dampier, in water depths ranging from 130 – 160m.

Cessation phase commenced when production ceased in 2018, flushing activities were completed and the FPSO departed the field. Floating asset removal of the DTM and MWA’s is planned to commence in Q4 2022 with removal planned to be completed by the end of 2022. Decommissioning is expected to commence in H2 2024 and will be completed by end 2025.
The reservoirs remain 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. Wells will be plug and abandoned under a separate EP.

The petroleum activities covered in this EP includes the following activities and will address inspection, monitoring, maintenance and repair (IMMR) activities on subsea equipment in the title area until removed, or decommissioned under this EP:
• removal of floating asset (DTM and MWAs) from the title area;
• removal of subsea equipment normally located on the seabed during production;
• decommissioning and abandonment in situ of select subsea equipment normally located on the seabed during production consisting of:
- two steel, epoxy coated gravity bases (approximately 19m x 6m x 3,1m high) complete with concrete ballast (approximately 6m x 1.4m x 2.35m high) weighing about 330t each set) and their associated tether chains (approximately 80m each); and
- Six deeply buried steel anchors and the six corresponding steel mooring chains of approximately 710 m / ~190t per mooring leg (each chain is partially buried).

Individual IMMR campaigns may take approximately 14 days with floating asset removal activities estimated to take up to 45 days in the operational area. Decommissioning of the seabed assets may take up to 12 months cumulative duration. However, unfavourable weather and operational delays this could extend the estimated project durations.
All activities could be undertaken at any time of the year, continuous over a 24-hour period and are expected to be conducted over multiple and concurrent campaigns during these time frames.

The activities may be supported by one, or a combination of the following ‘vessels’:
• tugs including Anchor Handling Tugs (AHT);
• barges;
• crew transfer vessel;
• Heavy Lift Vessel (HLV); and
• Dive Support Vessel (DSV) and rescue vessel

Helicopters and support vessel may be used to transfer crew and equipment to and from vessels and assist in emergency as required.