Decommissioning

Heerema vessel removes riser turret mooring from Enfield offshore Australia

Oct. 23, 2023

Heerema Marine Contractors has lifted the Nganhurra riser turret mooring onto a barge offshore North West Cape in Western Australia for operator Woodside Energy.

Offshore staff

PERTH, Australia — Heerema Marine Contractors has lifted the Nganhurra riser turret mooring (RTM) onto a barge offshore North West Cape in Western Australia for operator Woodside Energy.

The system is now heading to the Australian Marine Complex near Perth where it will undergo cleaning of marine growth and deconstruction, with a target to recycling and reuse 95% of the structure.

According to Woodside, the removal operation was a world first. The heavy-lift vessel Heerema Aegir, with three supporting tugs, lifted the 83-m long, 2,500-metric tons RTM onto the 120-m barge where it was secured for its onward journey.

The system connected subsea production lines from the Enfield oil field to an FPSO. Production at Enfield ceased in November 2018, and the RTM removal is the latest phase of the decommissioning program at the field, which includes permanent P&A of 18 production wells.

Devising the decommissioning concept for the RTM involved over two years of planning and detailed engineering, in cooperation with various specialist contractors. Preparatory activities included ROV inspections, removal of redundant equipment and the installation of a purpose-built lifting point.

Once conditions offshore were acceptable for the final operation, the remaining mooring lines were cut, and the RTM was towed to a sheltered location to ensure the lift could be executed safely.