As the decommissioning work at the Enfield oil field off North West Cape in Western Australia, Heerema’s heavy lift behemoth Aegir has been called into action. The vessel recently lifted the Nganhurra Riser Turret Mooring (RTM) weighing 2,500 tonnes onto a 120-metre barge. 

Once secured onto the barge, the RTM headed to the Australian Marine Complex (AMC) near Perth where it will be cleaned and deconstructed in preparation for recycling and reuse. This operation carried out by Aegir was a world first, according to Woodside Energy.

According to the Australian energy giant, the removal of the RTM is a significant milestone and further demonstrates its ability to manage activities in the sensitive marine environments where it operates.

The Nganhurra RTM is about 83 meters long and brought subsea production lines from the Enfield oil field to a Floating Production Storage and Offloading facility. Enfield ceased production in November 2018 and the RTM is being removed as part of decommissioning activities at the field, which also includes the permanent plugging and abandonment of 18 former production wells.

The decommissioning concept for the Nganhurra RTM was matured over more than two years of careful planning and detailed engineering, undertaken in conjunction with a range of specialist contractors. In-field preparatory activities included Remote Operated Vehicle inspections, removal of redundant equipment and installation of a purpose-built lifting point.

Following an assessment of the forecast weather and sea-state, the remaining mooring lines were cut, and the RTM was towed to a sheltered location to ensure the lifting operation could be executed safely. After the RTM is unloaded at AMC, it will be cleaned of marine growth and deconstructed for recycling and reuse opportunities, supporting local employment and contracting opportunities. More than 95 per cent of the Nganhurra RTM will be recycled or re-used.