Operator Woodside Energy has been hit with compliance action by Australia’s offshore regulator to ensure the “safe and responsible decommissioning” of infrastructure left at its Enfield development, off the coast of Western Australia.

The National Offshore Petroleum Safety & Environmental Management Authority (Nopsema) has issued Woodside with enforcement action over the decommissioning of the Nganhurra riser turret mooring in the WA-28-L licence.


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Nopsema revealed on Friday that it had initiated the regulatory compliance action due to Woodside being unable to comply with an originally approved plan to remove the equipment for onshore disposal.

According to Nopsema, the equipment’s poor condition means that it is no longer feasible to comply with the original plan without “unacceptable risks to safety and the environment”.

Enforcement action

The inability to comply with the originally approved plan has seen Nopsema issue Woodside with enforcement action in the form of a general direction.

In the general direction, Nopsema states Woodside, and its partner Mitsui, had not taken adequate action to remove property pertaining to Nganhurra offshore operations since production activities ceased in 2018.

The direction lists property remaining in the WA-28-L licence area related to the Nganhurra operations as including six horizontal production wells and two deviated production wells, as well as eight water injection wells and two gas injection wells.

The remaining property also includes a flowline and riser system the riser turret mooring and anchor system, as well as subsea structures - such as manifold, rigid spools, electric and hydraulic jumper and other small structures.

The general direction requires all wells to be plugged or closed off, and property no longer in use to be removed “in a timely and proper manner”.

It also reinforces the legal requirements for property associated with offshore petroleum activities to be removed, with Nopsema noting that non-compliance carries significant civil and criminal penalties.

In addition, Nopsema said it was investigating possible breaches of the Offshore Petroleum and Greenhouse Gas Storage Act 2006, with the investigation particularly focused on possible breaches of the law relating to requirements to maintain property in good condition and repair.

In a report, Nopsema also stated it was considering a range of other enforcement and compliance options in relation to Woodside’s inability to remove the riser turret mooring from the marine environment for onshore disposal.

A Woodside spokesperson confirmed to Upstream that the company would co-operate with the regulator throughout its investigation and continue to provide Nopsema any relevant documents requested to complete its investigation.

Compartment failure sinks removal plan

According to Nopsema’s report, the original plan to remove the riser turret mooring could not be carried out due to the failure and subsequent flooding of internal compartment two within the riser turret mooring.

The compartment failure prevents the riser turret mooring from being successfully deballasted and rotated to a horizontal position to allow it to be towed for onshore disposal.

Nopsema has accepted a revised Nganhurra Cessation of Operations Environment Plan from Woodside, allowing for the removal of the riser turret mooring from the title area for placement on the seabed as part of an integrated artificial reef (IAR).

“Nopsma has concluded, after taking into consideration the information provided, that there is a low probability that the RTM could be successfully removed from the marine environment and disposed of onshore,” the regulator said in its report.

“Nopsema has concluded that the only practicable alternative is to dispose of the RTM at an offshore location. There are increased risks associated with deep-water disposal of the RTM and the proposed repurposing the RTM as part of an IAR is considered a practicable solution in the circumstances.”

Woodside’s decommissioning plan still requires a permit under sea dumping legislation administered by Australia’s Department of Agriculture, Water and the Environment, which is separate to Nopsema’s assessment of the environment plan.

Woodside intends to dispose of the riser turret mooring in an area within 1.7 to 4 kilometres from the Ningaloo World Heritage Area, with the final location to be determined through the permit approval process with the Department of Agriculture, Water and the Environment.

Plastics pose a problem

One area of concern with the riser turret mooring remaining in the water is the impact of residual plastics on the marine environment.

Woodside notes that the riser mooring turret includes about 5.9 million tonnes of polyurethane foam in compartment 13 of the turret, a small section of bend stiffener plastic at the end of each of the seven risers and an estimated 10 kilograms of residual plastics in components such as electrical cabling.

In order to reduce the impact of plastics and foam contaminants, Woodside intends to remove residual topside plastics in the riser turret mooring, remove risers and bend stiffeners, encapsulate the compressed foam in compartment 13 with grout, as well as encapsulate in grout any remaining bend stiffener that cannot be cut.

It will also develop a marine debris monitoring and management programme .

Woodside’s spokesperson told Upstream the company welcomed Nopsema’s acceptance of its revised Nganhurra Cessation of Operations Environment Plan.

“Since the cessation of production, we have executed substantial decommissioning work plus undertaken extensive studies and planning including seeking approvals for decommissioning of remaining Enfield infrastructure,” she said.

“General directions will be fulfilled based on existing work plans, noting that planning and engineering work to support these activities was already under way prior to receipt.”

Woodside’s Enfield project came on stream in July 2006 and production peaked two months later at 74,000 barrels per day of crude, which was below the rate Woodside had anticipated due to reservoir issues.

Operations ceased in 2018 and the Nganhurra floating production, storage and offloading vessel was disconnected and sailed away from the field on 5 December of the same year.