The National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) has accepted a revised Nganhurra Cessation of Operations Environment Plan by Woodside, for the decommissioning of the Nganhurra riser turret mooring from title area WA-28-L, which is located approximately 40 kilometres offshore of the north-west of Australia’s North West Cape.
Woodside operates the Enfield field within Production Licence Area WA-28-L. In 2018, the Nganhurra floating production, storage and offtake facility (FPSO) was utilised to flush, isolate and preserve the riser turret mooring (RTM) and the subsea infrastructure, before the FPSO was disconnected and removed from the Enfield field.
According to NOPSEMA, the Nganhurra Operations Cessation Environment Plan (EP) was revised and resubmitted by Woodside on 20 December 2019 (Revision 3) to address alternatives for removal of the RTM from the field for onshore disposal.
Following further stakeholder consultation, the company elected to withdraw the EP and submit a new revision (Revision 6). The revised EP involves a more comprehensive evaluation of the impacts and risks associated with repurposing the RTM into an Integrated Artificial Reef, as well as further consideration of the practicability of onshore disposal.
Activities which form the scope of this revised Environment Plan are as follows:
- The implementation of an inspection regime during preservation period until all wells are abandoned and subsea infrastructure is decommissioned (which will be subject to a future, separate EP);
- Inspection, monitoring, maintenance and repair (IMMR) activities to ensure integrity of subsea infrastructure;
- Well intervention, if required;
- IMMR of the RTM while it remains on station;
- Disconnection of mooring lines from RTM and lay on seabed (accepted as part of Revision 2);
- Removal of RTM from the title area;
- Towing the RTM to the proposed integrated artificial reef (IAR) site;
- Placing the RTM on the seabed and undertaking stabilisation and modification (removal of risers and grouting foam, etc.) activities for it to become part of an IAR; and
- Augmenting the RTM by installing additional purpose-built reef modules to complete the IAR.
The RTM removal is planned to be completed between March and April 2021 and is estimated to take 30 days (with potential for a cumulative 90 days when accounting for potential IMMR activities and limiting operations to periods of suitable weather conditions i.e. within cyclone season).
Through accepting the environment plan, NOPSEMA has required the company to implement a range of measures to prevent and mitigate impacts to whale sharks, turtles, and seabirds.
Australia’s offshore energy regulator has also initiated regulatory compliance action due to Woodside being unable to comply with an originally approved plan to remove the equipment for onshore disposal. Due to the equipment’s poor condition and repair, NOPSEMA said this is no longer feasible without unacceptable risks to safety and the environment.
Woodside has been issued with enforcement action in the form of a General Direction requiring wells be plugged or closed off, and property no longer in use to be removed in a timely and proper manner.
The General Direction reinforces legal requirements regarding the removal of property associated with offshore petroleum activities, and carries significant civil and criminal penalties for non-compliance.
Further, as Woodside is unable to decommission the riser turret mooring as originally approved, NOPSEMA is investigating possible breaches of the Offshore Petroleum and Greenhouse Gas Storage Act 2006.
The investigation will examine possible breaches of the law relating to requirements to maintain property in good condition and repair.
Decommissioning of the riser turret mooring can now be through removal from the title area for placement on the seabed as part of an integrated artificial reef.
Decommissioning in this way requires a permit under sea dumping legislation administered by the Department of Agriculture, Water and the Environment. This regulatory process is in addition to NOPSEMA’s assessment of Woodside’s environment plan.
NOPSEMA has issued a report addressing the key matters that arose through the assessment of the environment plan, including concerns around the degradation of the riser turret mooring. The Key Matters Report and Woodside’s accepted environment plan are available here.
The General Direction (no. 812) and previously issued Improvement Notice (no. 775) are available here.
In December 2020, NOPSEMA launched an industry-wide compliance plan to reinforce legal requirements regarding the removal of property associated with offshore petroleum activities. Compliance actions include the issuance of Directions to some titleholders specific to decommissioning and end-of-life requirements.
