Route Selection – Laverda Development Project

Background

Atteris was engaged to perform and manage the Concept Select phase of the Ragnar flowline (1100m WD) and Laverda trunkline engineering. The scope included route development for the 30 km flowline and 113 km gas trunkline from the Laverda FPSO (830 m WD) to the Turbridgi Gas Plant or the Macedon Gas Plant, both of which required a shore crossing, river crossing and up to 15 km of onshore pipeline.

Work Performed by Atteris

Interfacing with SURF and flow assurance teams, Atteris split the scope of the Trunkline routing up into 4 areas: deepwater, shallow water, nearshore and shore crossing, and onshore sections.

Deepwater: A number of routing challenges where presented including approach to the FPSO, rough / steep seabed bathymetry, and existing assets. To ensure route length was kept to a minimum, Atteris explored a number of alternatives, each with varying risk profiles.

Shallow Water: Using our knowledge and experience from the Macedon Project, Preliminary routing through the shallow water was achieved with minimal bathymetry data and considered secondary stabilisation design constraints.

Nearshore: This routing was challenged by sand waves, routing close to existing operating pipelines, islands and reefs, together with meeting two shore crossing locations.

Shore crossing: The proposed landfall area is challenged in a number of ways but principally constrained by environmental and heritage requirements. A number of locations were identified to facilitate onshore pipeline routing option optimisation which were dependent upon the termination point, length of pipeline and complexity of the routes.

Onshore pipeline: Routing had to navigate around areas prone to water inundation and consider rights of way and access constraints. Local knowledge of the area was paramount for success. Pipeline routes to the Macedon Gas Plant also had to consider a river crossing.

Benefits

  • A concept pipeline route with alternatives was developed using limited bathymetry data without the need for costly data acquisition.
  • Cost premise of no allowance for secondary stabilisation was assured.
  • A significantly reduced survey scope for detailed geophysical and geotechnical data in preparation for the following phase of the project was identified.