Risk Based Marine Impact Assessment of NORM and Hg from Decommissioning Oil & Gas Infrastructure: Literature Review

Australia has a growing liability of non-producing oil and gas infrastructure in the marine environment, subject to decommissioning decisions. Complete removal is the base case for decommissioning, unless better outcomes can be achieved by alternative decommissioning options, such as leaving in place (i.e. in situ). The ecological benefit of leaving in place options are well established and related to the provision of hard substrate that allows the formation of epibenthic ecosystems. However, these benefits are challenged by the presence of mercury and Naturally Occurring Radioactive Materials (NORM) contaminants which may result in negative impact to surrounding ecosystems. This literature review is a comprehensive consolidation and critique of public and available grey
literature. It defines the current understanding of the risks that NORM and mercury pose in the marine environment from decommissioned oil and gas subsea pipeline infrastructure, when primarily left in situ. The key knowledge gaps and uncertainties are also established, along with a set of recommendations. The project’s aim is to enhance the understanding of the impacts and risks of NORM and mercury to the marine environment from decommissioned oil and gas infrastructure, to support science-based
decommissioning decision-making. The project is framed around three problem statements in which the Australian oil and gas industry are seeking to:
• Understand the threshold levels at which NORM in subsea production equipment and mercury in subsea gas transmission systems in the offshore environment become a concern during and after decommissioning, relative to the receiving environment, specifically: levels/dosage/concentration, form/chemical species and likely behaviour (how are they likely to leach over time and what are the likely pathways) if NORM and mercury is present in O&G
infrastructure.
• Understand the processes and exposure pathways whereby individual contaminants might (or might not) reach receptors after decommissioning.
• Improve its tools and procedures for measuring mercury and NORM associated with equipment/infrastructure in situ to inform decommissioning decisions and long-term monitoring objectives.
This literature review is structured by first defining the current understanding of Australia’s regulatory framework which defines the required environmental outcomes for decommissioning options. This section also reviews the behaviour of mercury and NORM in oil and gas systems, including the proposed mechanisms leading to the formation of contaminated products (products in oil and gas systems such as mineral scales, films, oxide layers, and so on that contain concentrations of NORM and mercury) and reviews measurement techniques for mercury and NORM. It steps through the components of an ecological risk assessment as they relate to mercury and NORM in marine
ecosystems including the ecosystem receptors they may impact, their behaviour, and key environmental transformations governing their exposure pathways, the impacts they may have on ecosystem receptors, and approaches to understanding and quantifying their risk as it relates to the legislative requirements. The current practice section compares industry practice with the understanding developed in earlier sections to identify potential gaps in assessing mercury and NORM impact and risk in the marine environment. This comparison will provide the context for the future drafting of a proposed risk
framework. The knowledge gaps and recommendations section identifies gaps and associated recommendations that can be addressed either in the next assessment (i.e. post literature review) or subsequent NDRI project phases.
The key knowledge gaps identified in this review include:
Understanding thresholds of NORM and mercury in the marine environment
1. How ecological risk assessments are applied to meet legislative requirements
2. Whether exclusion-type criteria (‘thresholds’) can be derived for mercury and NORM to inform subsea oil and gas pipeline decommissioning decisions
3. What is the inventory of contaminated products – including the contaminated products’ form, species, mass, and distribution in pipelines Understanding the fate of NORM and mercury 4. How the speciation and distribution of contaminated products in pipelines affects important environmental transformations controlling exposure pathways 5. How different environmental conditions affect contaminated products, their environmental transformations, and their resulting mobility and bioavailability Understanding of tools and procedures 6. What measurements are required for ecological risk assessments
7. What are the current and future technology options for measuring subsea in-situ mercury and NORM contamination which meet ecological risk assessment requirements The focus of the Research Team over the remainder of the current project will be to develop an ecological risk assessment framework that can be generalised to all contexts but provide the flexibility to tailor an assessment to local contexts. Steps to achieve this could include:
• Developing consensus on the management objectives required to meet legislative requirements of decommissioning and the assessment methodologies meeting these requirements. This can take the form of a NERA-issued report (or peer-reviewed journal article) and include input from all stakeholders.
• Identifying the most important factors controlling contaminant exposure pathways and hazard impacts. This will be used to inform the development of a tiered risk assessment framework and identify measurement methodology as well as measurement needs and can be achieved by consolidating reported parameters and their uncertainties used in risk assessments.
• Developing a tiered approach to mercury and radiological risk assessments that trades conservatism for data requirements at different levels.
• Identifying technology options for the in-situ measurement of mercury and NORM. This could be achieved by surveying operators and instrument providers to review technology options, and their readiness level.