Eni Energy Bonaparte Pty Ltd is the titleholder of the Petrel gas field in the Bonaparte Basin in northern Western Australia. The Petrel field is located in permits NT/RL1 and WA-6-R. The closest wellhead to the shore is Petrel-3, which lies approximately 250km WSW of Darwin (NT) and 280km N from Wyndham, on the northern coast of WA, in water depths of approximately 95m.

Within the NT/RL1 permit, two wells (Petrel-3 and Petrel-4) have been identified as suspended since the 1980’s, with wellheads remaining in-situ. The wells were suspended in accordance with the regulations at the time with barriers across and above the reservoir including the testing of the barriers. The reservoir is isolated in both wells and will not flow in their current condition.

To ensure that the condition of the seabed equipment on the wells remains unchanged and to plan for the decommissioning campaign, Eni proposes the following activities as part of the Petrel-3 and Petrel-4 decommissioning strategy:
• Annual general visual inspections (GVI) as part of the in-force Well Operations Management Plan (WOMP) until Petrel-3 and Petrel-4 are permanently plugged and abandoned (P&A). The inspections will be performed within the five-year WOMP period using a suitable ROV deployed from contracted vessels. Marine growth removal may also be undertaken on the wellhead equipment to facilitate the inspection and prepare for the decommissioning campaign;
• Geophysical and Geotechnical survey campaigns;
• Pre-decommissioning vessel campaign to prepare the wells for decommissioning. High-pressure cleaning of the wellheads to allow detailed inspection and preparation for decommissioning. Removal of the corrosion caps, wellhead 3D scan by camera or laser to ensure integrity and corrosion cap replacement;
• Decommissioning campaign, to permanently seal and abandon the Petrel-3 and Petrel-4 wells pursuant to an accepted Petrel-3 and Petrel-4 WOMP. Partial, complete and leave in-situ removal options are included; and
• Post-decommissioning As-left survey, to ensure all infrastructure is removed as per scope.

Timing of these activities will potentially occur between 2025-2027 due to a number of factors, including wellhead integrity investigations, site specific surveys, vessel and rig feasibility checks, vessel and rig availability and scheduling, weather conditions and consideration of neap tides and seasonal metocean operability.