All-systems-go for Woodside to embark on subsea infrastructure decom ops off Australia

Australian energy giant Woodside has received a stamp of approval from the country’s offshore regulator for an environment plan (EP), covering decommissioning and dismantling activities at a field off the coast of Australia.

FPSO Griffin Venture; Source: BHP

The National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) accepted Woodside’s environment plan on November 21, 2023, proposing to undertake closure of the Griffin field facilities, located in production license WA-10-L off Western Australia, 65 km northwest of Onslow and 94 km northeast of Exmouth, in a water depth of approximately 130 m.

The field comprises 12 former subsea oil production wells, permanently plugged in 2017, and associated subsea infrastructure, which has been flushed of hydrocarbons. A gas export pipeline (GEP) extends from the field through Commonwealth – pipeline license WA-3-PL – and state waters – pipeline license TPL/10 – to the former onshore Griffin gas export facility, south of Onslow.

Furthermore, the decommissioning of the Griffin field is planned to be undertaken in stages under relevant Commonwealth and state government approvals, with the first stage including the removal of flowlines, wellheads, and subsea ancillary equipment from WA-10-L. This revised EP will also cover the removal of the wellhead of an exploration well in the neighboring license, WA-12-L, along with ongoing field management activities on the subsea infrastructure and the GEP in Commonwealth waters, as required until permission is granted to relinquish the licenses.

Therefore, the scope of the EP includes the removal of thirteen wellheads and guide bases, twelve Xmas trees, the full removal of the riser turret mooring (RTM), six RTM mooring lines, nine flexible production risers, around 47 km of flexible production flowlines, about 12 km of rigid production spools and flow lines, twelve electrohydraulic umbilicals and flying leads, pipeline end manifold, six mooring chains, four distribution skids and assorted mud mat structures: heat exchanger, 3 x Umbilical termination assemblies and electrical distribution units, choke skid, 17 x pyramid anode skids.

According to Woodside, the removal activities will start no sooner than 3Q 2023, pending regulatory approvals, support vessel availability, and weather constraints. The activities covered in the EP may occur at any time of year, with completion by the end of calendar year 2024. The GEP and remaining field equipment – such as piles, anchors, and concrete gravity bases – will be subject to separate future environmental approvals.

While in production, the Griffin field comprised the FPSO Griffin Venture with 12 production wells from the Griffin, Scindian, and Chinook reservoirs routed to the riser turret mooring via flexible and rigid flowlines. Oil products were stabilized and stored for offloading via tanker, while gas products were transported to the shore via the Griffin gas export pipeline (GEP) for domestic sale. The field ceased production in 2009.

In a bid to put its decommissioning plans into action, the Australian giant handed out a batch of decommissioning deals to multiple players – Transocean, TechnipFMC, Heerema, McDermott, Fugro, DOF, and McMahon – for the removal and disposal of subsea infrastructure at several oil and gas fields offshore Western Australia, including Griffin.