The petroleum activity is defined as non-production and decommissioning operations within VIC/RL17, involving removal of the West Seahorse-3 wellhead and Wardie-1 conductor (located only 2.8 meters apart) in water depths of approximately 40m.

The wells have been designated plugged and abandoned, and there are no other petroleum activities associated with the wells other than the cutting (approximately 2 meters below the mudline) and retrieval of the well head and section of conductor pipe, along with associated activities and monitoring. There are no credible hydrocarbon spill scenarios from the wells and the extent of the Petroleum Safety Zone (PSZ) covering a 300 m-radius area around the wells has been used to define the operational area.

To determine the extent of the environment that may be impacted by the activity, the unlikely event of a marine diesel oil (MDO) spill due to a vessel collision within the operational area was considered as the worst-case spill scenario. A vessel spill would be restricted to less than 150m3 of MDO, however previous Oil Spill Trajectory Modelling (OSTM) undertaken for a 200m3 MDO vessel spill incident at the West Seahorse location was utilised for this activity. This approach is conservative and mitigating strategies (such as tank lightening) would further limit potential spill volumes.

The decommissioning activities will be completed as part of a vessel-based program lasting 7 to 14 days conducted in 2025-2026, subject to vessel availability and weather constraints.