To leave or not to leave: a tiered assessment of the impacts of scale residue from decommissioned offshore oil and gas infrastructure in Australia

There are a range of potential options for the decommissioning of offshore petroleum infrastructure, including: complete removal; removal of topside infrastructure with subsea infrastructure left in situ; or partial removal or modification of infrastructure. The current decommissioning liability in Australia is estimated to exceed US$40 billion over the next 50 years. This is founded on the base-case regulatory position of complete removal of all infrastructure, with over half the liability occurring in the next 10 years. In Australia, a recently updated decommissioning framework requires that the planning for decommissioning begins from the outset of the project, and plans are matured throughout the life of operations. Successful decommissioning of subsea oil and gas infrastructure requires an effective and safe approach for assessing and managing chemical and radiological residues. Naturally occurring radioactive materials (NORM) are ubiquitous in oil and gas reservoirs around the world and may form contamination products including scales and sludges in topside and subsea infrastructure. In situ decommissioning of infrastructure left in the marine environment has many ecological benefits including establishment of artificial reefs, economic benefits from associated fisheries, reduced costs and improved human safety outcomes. However, there may be ecological risks associated with leaving infrastructures in the marine environment that are not well understood. Following a scenario of in situ decommissioning of subsea petroleum infrastructure, marine organisms occupying the exteriors or interiors of production pipelines may have close contact with the scale (metal and radionuclide contaminants). Consequently, radio- and chemo-toxicological effects from the scale could occur respectively. This paper considers the current assessment process for NORM-contamination products in oil and gas systems, recent and emerging Australian research in marine radioecology. Here we demonstrate a tiered approach to assess the ecological impacts of pipeline scale related to decommissioning practices, and identifies key research priorities. This can further aid our understanding of the fate of NORM contaminates in subsea oil and gas systems and guide Australia-specific (expand to other petroleum operating countries) risk assessments for infrastructure decommissioning options. The creation of a tiered assessment will enable industry to optimise decommissioning solutions and allow regulators to set clearer expectations on the requirements for environmental protection.

Keywords

Residues, Petroleum residues, Offshore sites, Australia, Decommissioning, Regulatory guides, Ecosystems, Aquatic ecosystems, Reefs, Fishes, Contamination, Environmental protection

Citation

MacIntosh, A., Cresswell, T., Koppel, D., Hirth, G., Tinker, R., Dafforn, K., Chariton, A., Penrose, B., & Langendam. A. (2023). To leave or not to leave: a tiered assessment of the impacts of scale residue from decommissioned offshore oil and gas infrastructure in Australia. Poster presentation to the ICRP 2023 7th International Symposium of the System of Radionlogical Protection, Tokyo, Japan, 6-9 November 2023. Retrieved from: https://event.fourwaves.com/icrp2023/abstracts/6da3eabd-03d6-4fea-8d11-ddb21a5ffab1