June Evening Technical Meeting

Presentations include:

A Student Perspective on Subsea Decommissioning: A Comparative Framework for the Northern Carnarvon Basin ExitEmma Winton, UWA

This presentation outlines a framework developed by the UWA design class for assessing in-situ pipeline decommissioning. The framework evaluates contaminant risks, including plastics and mercury and integrates a Net Environmental Benefit Analysis (NEBA) covering ecological, habitat and species considerations. The methodology integrates stakeholder engagement and is intended as a replicable tool for future decommissioning assessments but also highlights the challenges with data availability and valid modelling of environmental benefit.

Assessing alternatives to full removal of subsea pipelinesEmilien Rulence, Atteris

In Australia, complete removal of subsea infrastructure is the base strategy for offshore decommissioning. While this approach is generally appropriate for small discrete structures, it can present significant challenges for larger components such as long submarine pipelines. This presentation explores some of these challenges and discusses why alternatives to full removal may sometimes deserve consideration.

The presentation does not advocate for abandonment. Instead, it demonstrates how selecting a decommissioning strategy can be best supported by a multi-criteria comparative assessment that balances factors extending beyond simple removability. Such an approach enables better-informed decisions and helps identify opportunities to improve the overall outcome.

The case study of a long export pipeline tied back to an onshore facility is used to illustrate the key factors and trade-offs associated with different decommissioning strategies.

Plastics, NORMs and Mercury in offshore decommissioning: From hidden liabilities to environmental riskSander Scheffers, Hydrobiology

Offshore decommissioning is more than an engineering or waste management exercise. It is a complex environmental risk assessment challenge. As subsea infrastructure is removed, partly removed, or left in situ, plastics and other non-metallic materials, naturally occurring radioactive materials (NORMs), and mercury require explicit consideration. These materials behave differently, create different uncertainties, and carry different regulatory implications. Plastics persist, fragment and create long-term microplastic and leachate pathways. NORMs may occur in scales, sludges and contaminated infrastructure, while mercury risks depend on speciation, mobility and bioavailability.

This presentation examines how these issues should be integrated into decommissioning ERAs, Environment Plans and option assessments, with emphasis on source terms, exposure pathways, sampling, analytical uncertainty, ALARP decision-making and long-term marine environmental protection.

Reef or Recover: Comparing Insights from Offshore Reefing of Seven Jackets in the Gulf of Thailand with Onshore Decommissioning of Similar Structures in Later