A path to make well-informed decisions when considering the decommissioning of subsea pipelines

Abstract

Australia’s law mandates the removal of infrastructure once not in use unless the Titleholder can demonstrate an equal or superior safety and environmental outcome. Around 100 infield and export pipelines in Australian waters, with an approximate total length of 5000 km, are nearing their end-of-life period. Three common decommissioning options are considered for subsea pipelines: complete removal, partial removal, or in-situ abandonment. Decommissioning these pipelines will cost an estimated US$13 billion, ~33% of the cumulative Australian offshore decommissioning liability, should the full removal option be selected. When decommissioning subsea pipelines, it is essential to consider that they have been exposed to hazardous fluids and aggressive environments. Careful assessments should determine the recyclability of recovered materials, decontamination, and the environmental risks associated with each decommissioning option. A holistic approach is needed to identify and quantify contaminants in subsea pipelines. In the early stages of decommissioning, planning, sampling, and laboratory testing are necessary to identify plastic coating types, degradation mechanisms, constituents released to the environment, types and mechanisms related to mercury/naturally occurring radioactive materials, and chemical stability. This paper aims to identify and present effective methods for addressing the impact of pipeline constituents on the Marine Environment Assessment while assessing potential decommissioning options and explains how tools can support decision-making. In summary, decommissioning subsea pipelines requires careful assessment and planning to ensure environmental and safety compliance. The paper provides a guide to understanding the process, highlighting the importance of quality assurance, risk assessment, and the selection of appropriate decommissioning options.