Australian energy giant Woodside has received a blessing for its environmental plan (EP) from the country’s offshore regulator to carry out permanent plug and abandonment (P&A) of multiple subsea exploration wells off the coast of Australia.

The National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) gave Woodside the green light on April 17, 2025, to move forward with activities proposed in its submitted environment plan, entailing the permanent plug and abandonment of subsea exploration wells in the Julimar-Brunello licence WA-49-L.

The company intends to undertake P&A of three subsea wells associated with the Julimar-Brunello field using a mobile offshore drilling unit (MODU) with combined dynamic positioning (DP) and mooring capability. These wells are Julimar East-1, Brunello-1 ST1, and Brulimar-1.

In addition, Woodside proposes an additional contingent activity to remediate/remove and/or isolate non-water-based mud (NWBM) in the annulus of one additional well, Balnaves Deep-1. This activity will be attempted using a vessel-based strategy under the accepted North West Shelf (NWS) and Julimar Exploration Wellhead Decommissioning EP.

If completed using a vessel-based strategy, no further activity will be performed under this EP. On the other hand, if the vessel-based strategy is not feasible or unsuccessful, the activity will be undertaken by a MODU-based strategy. The operator explained that all four wells were drilled as exploration or appraisal wells between 2007 and 2011.

The three wells scheduled for P&A were suspended following exploration activities; however, the temporary abandonment methodology conducted does not align with current legislative requirements, regulatory expectations, and best practice for permanent abandonment, driving the need for further P&A activities.

Due to the cement-based temporary abandonment plugs already present in these three wells, Woodside believes it is unlikely that a flow path exists between the wellbore and the reservoir(s), and the most likely fluid contained in the wellbore is suspension fluid rather than reservoir hydrocarbons.

The reservoir interval in the Balnaves Deep-1 exploration well has already been accepted as permanently abandoned. NWBM was left in one of the annuli in the well, with the annulus being exposed to the marine environment upon wellhead removal.

As all wells are located in Commonwealth waters of the Barrow Sub-Basin around Woodside’s existing production facilities, the petroleum activity is located in this area. The wells are in permit area WA-49-L, approximately 185 kilometers WNW of Karratha in around 135 to 171 meters of water depth.

The P&A and well intervention will be undertaken using a moored or hybrid semi-submersible MODU with up to three MODU support vessels and an inspection, maintenance, and repair (IMR) vessel. The MODU will undertake plug and abandonment activities, wellhead cutting, and may be used to remove wellheads.

The company underlines that wellheads may be cut by the MODU and temporarily wet parked, or left in their existing position for later removal under the accepted NWS and Julimar exploration wellhead decommissioning environment plan. NWBM remediation, removal, or isolation activities, if required, will also be undertaken by a MODU.

According to Woodside, support vessels will undertake preparatory activities, such as inspection, maintenance, and repair, pre-laying and recovery of moorings and/ or tether clump weights, and anchor hold testing.

The MODU and support vessels are expected to operate within the operational area for approximately three to seven months, including mobilization, demobilization, and contingency activities, which will be done 24 hours per day, seven days per week.

The operator elaborates that timing and duration of the P&A activities are subject to change due to project schedule requirements, metocean conditions, vessel availability, unforeseen circumstances, and weather. As a result, this is prepared as a three-year EP.

This environment plan is not intended to be the final decommissioning EP for Woodside’s property in WA-49-L and WA-34-L. Operated by Chevron on behalf of the Wheatstone joint venture, Wheatstone LNG processes gas from the offshore Wheatstone, Iago, Julimar, and Brunello gas fields in Western Australia.

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