Do we know enough to make future-proofed decisions about contaminants when decommissioning offshore oil and gas infrastructure?

Offshore oil and gas infrastructure must be decommissioned at the end of its operational life. The base case approach for decommissioning under Australia’s regulatory framework is the complete removal of all infrastructure. However, alternative decommissioning approaches, such as leaving some infrastructure in situ, may deliver better environmental, economic, and health and safety outcomes. Derogation from complete removal requirements is possible if alternative approaches have acceptable environment impacts and deliver equal or better environmental outcomes. Potential environmental contaminants are present in all offshore infrastructure and if decommissioned in situ could pose unacceptable risks to marine ecosystems. Contaminants may accumulate in infrastructure as a result of oil and gas production, such as scales of mercury and naturally occurring radioactive materials, or arise from the degradation of infrastructure itself, such as plastics and steel corrosion products. The unique behaviour and interactions of contaminants with local ecosystems makes assessing their potential impacts challenging. This presentation reports on the contaminants likely to be present in offshore oil and gas infrastructure proposed to be decommissioned in situ. The expected behaviour of these contaminants in the marine environment is discussed to give context to measures of their potential hazards (i.e. guideline values). This paper is intended to start a conversation and serve as a useful guide for titleholders and regulators about some data needs to assess potential contaminant impacts from in-situ decommissioning.