Shore Approach Design and Shore Crossing Design – Wheatstone Project

Background

The 44-inch diameter Wheatstone Gas Export Trunkline System traverses challenging seabed areas, with multiple pipeline and umbilical crossings and a shallow water shore approach.

Work Performed by Atteris

The shore approach design for the trunkline system included developing engineering solutions to deal with:

  • Rough seabeds with exposed limestone rock formations
  • Erodible calcareous seabed sections comprising silts, sands and clays
  • The crossing of a major shipping route
  • A long shoreline crossing with a very high environmental value, comprising complex geology, and a tidal lagoon

The engineering work included detailed numerical analyses and physical model testing, in combination with cost, schedule and risk studies, and constructability assessments. In order to reduce cost, schedule and risk, Atteris’ focus was to reduce as much as possible the use of quarry rock as a secondary stabilisation method. This was successfully achieved in favour of pre-trenching in combination with trench backfill with locally sourced sand, which is much more cost-effective.

Atteris completed a concept and technical feasibility assessment for a micro-tunnel option for the shoreline crossing, and also to support future Chevron projects. A micro-tunnel solution offers an advantage for shore crossings of this nature, and can allow flexibility in usage even after tunnel construction has concluded. The preceding engineering study undertaken by Atteris for Chevron Australia, which included a cost, schedule and risk assessment, looked at all options, including conventional open cut trenching and horizontal directional drilling (HDD). It was concluded that micro-tunnelling was the clear winner. Atteris was able to leverage their expertise with open cut trenching, HDD and micro-tunnelled shore crossings to deliver a cost-effective and practical solution.

Atteris assembled an experienced pipeline engineering team, including in-house specialist micro-tunnel and HDD experts, and perform comparative cost, risk and schedule reviews to develop a technically feasible solution for this project and for potentially a range of future assets.

Benefit

Atteris delivered value to Chevron through:

  • Demonstrating technical feasibility of an alternate solution that provides operational flexibility for staging future projects
  • Prepared comparative cost, risk and schedule reviews with subject matter experts for the available alternatives
  • Demonstrated that the recommended solution met all technical, environmental and safety limitations posed by the shoreline crossing location.