Located in Browse Basin about 220 kilometres offshore Western Australia, Ichthys represents the largest discovery of hydrocarbon liquids in Australia in 40 years. The Ichthys LNG Project is currently under construction and is ranked among the most significant oil and gas projects in the world. The Ichthys LNG Project is effectively three mega-projects rolled into one, involving some of the largest offshore facilities in the industry, a state-of-the-art onshore processing facility and an 889km pipeline uniting them for an operational life of at least 40 years.
The Ichthys Riser Support Structure (RSS) is a fully submerged, jacket-like offshore structure supported on a shallow skirted foundation. The RSS will be a physical, fixed support for flexible risers and dynamic umbilical’s that connect subsea gathering systems to the project’s semi-submersible central processing facility. It is required to maintain 25 risers in a fixed-S configuration.
Arup independently verified the RSS foundation design during the EPCI phase. This included assessing the foundation performance in terms of stability and deformation, under storm, soliton and seismic events, as well as assessment of the foundation installation. The verification provided confidence in the design, particularly with the removal of conservatisms adopted and the identification of potential risks for the execution phase.
A dynamic soil-structure interaction analysis undertaken by Arup provided a realistic representation of RSS behaviour during seismic events. In addition, a comprehensive set of failure mechanisms were considered for installation of the foundation using suction.
The Ichthys Riser Support Structure is the largest subsea structure ever laid on the seabed and the installation of the 6,500 tonne structure was safely completed in November 2014. When the RSS arch is placed, the structure will stand 110 metres off the seabed.