Offshore decommissioning horizon scan: Research priorities to support decision-making activities for oil and gas infrastructure

Assessing fish assemblages on oil jackets off the Angolan coast: Implications for decommissioning decisions

West Africa plays a significant role in global oil production. Much of the offshore infrastructure in this region is due for decommissioning. An understanding of the marine communities associated with the infrastructure is essential to predict the outcome of different decommissioning alternatives, such as leave-in-place or full removal. Using ROV inspection footage, we sampled nine jackets off Angola (Cabinda Province) to quantify the abundance and species composition of fish. Sixty-five species of fish were observed among jackets, including several taxa that are commercially important to the region, such as sardine (Sardinella spp.) and mackerel species (Trachurus spp.). We also observed taxa that are commonly targeted in small-scale (artisanal) fisheries in Angola, such as groupers (Epinephelidae) and snappers (Lutjanidae). Distinct fish assemblages were observed at each jacket, and attributed to differences in jacket location, depth, and infrastructure design. Time of day also affected the assemblage detected across jackets, although similar dominant families were present across day and night at a specific depth zone when pooled. Unlike patterns observed in other regions, there was not a clear depth zonation pattern at individual jackets, and only a weak depth zonation pattern was evident when all jackets were combined. Six species had not previously been recorded off Angola, suggesting that the jackets may either facilitate range extensions or highlight a paucity of fish studies in the region. Our results have important implications for evaluating decommissioning options, including addressing questions on jacket removal or reefing and implications for species of importance to fisheries.

Increased fish abundance, biodiversity, and body size near a North Sea oil and gas platform

In the North Sea, offshore oil and gas (O&G) platforms must be totally removed through decommissioning at the end of their productive life. However, the role of O&G platforms in marine ecosystems, especially for fish assemblages, is not well enough defined yet. Here, we document the association between an O&G platform in the North Sea and the fish assemblages along a distance gradient of 1-600 m from the platform. Scientific angling provided data on fish biodiversity, abundance, and body size. In addition, acoustic data on fish density and target strength were collected to explore spatial and diel fish distributions. The angling data comprised 1217 fish from 11 species, with the highest fish abundance, and all species occurring, within 20 m from the platform. Platform proximity was positively associated with fish biodiversity, and total fish abundance, as well as the specific abundances of Atlantic cod Gadus morhua, dab Limanda limanda, whiting Merlangius merlangus, and mackerel Scomber scombrus. Body sizes of Atlantic cod, whiting, and mackerel were also positively associated with the platform. Absent non-native or invasive species provided no support for stepping stone scenarios. This study highlights the attraction of a variety of fish species towards O&G platforms in the North Sea. Potential local loss of marine biodiversity following full platform removal should be considered in future discussions on platform decommissioning policies.

Global potential for seaweed aquaculture on existing offshore infrastructure

Seaweed aquaculture is growing 8.9 % annually to a forecast US$ 22.13 billion in 2024 and has several environmental, economic and social co-benefits. A proposed approach to expanding seaweed aquaculture is to develop offshore aquaculture. However, the costs of the infrastructure remain a key barrier. Reducing costs by growing seaweed on obsolete oil and gas infrastructure and offshore wind farms may make offshore seaweed cultivation economically viable, but the scale of opportunity needs to be clarified. We estimate an area of 53,387-106,774 ha is currently available to cultivate seaweed on offshore wind farms, which could yield 736,831-4,441,116 tonnes of dry seaweed annually. Existing offshore oil and gas infrastructure could create 1,357,530-5,430,120 ha for growing seaweed. Using 2019 seaweed prices, seaweed production on offshore wind farms and oil and gas infrastructure could return USD $3356 - $50,320 Million, sequester 687,784-8,616,449 tonnes of CO₂, and subsequent low carbon seaweed products could displace 987,642-33,221,364 tonnes of CO₂ emissions. While the scale of opportunity is significant, we caution that the regulatory and engineering costs of 'keeping the lights on' for decommissioned oil and gas infrastructure may make costs prohibitively high for seaweed cultivation. Even with existing infrastructure, the cost of cultivating seaweed offshore remains the largest barrier to implementation. A significant increase in market value for seaweed products is required to make offshore infrastructure economically viable. Similarly, many ecological and regulatory risks to offshore seaweed cultivation need to be further understood and minimised.

Investigating how H2S can alter the interactions between Hg0 and corroded steel surfaces to guide future decommissioning projects

Many oil and gas developments will soon be decommissioned and, knowledge on the accumulation of mercury (Hg), throughout offshore infrastructure is limited. Any release of Hg could have a detrimental impact on marine ecosystems. To bridge this knowledge gap, a fractionation approach was taken on steel samples exposed to Hg0 and H2S, separating Hg compounds removed from the surface into polar, non-polar and insoluble fractions. Hg0 reacted on corroded surfaces to form several compounds, over 50 % of which were removed by seawater. This suggests that pipelines on the seabed could release a dramatic amount of Hg into the sea if they are left in place. Furthermore, a Cu-Hg amalgam, was identified to be a dominant species, by a combination of XFM, XANES and LA-ICP-TOFMS. Seawater-soluble and amalgam-bound Hg were present regardless of co-exposure to H2S. When H2S was present Hg nanoparticles accounted for up to 1 % of the total Hg on the steel. This investigation has shown that the Hg speciation on the surfaces of pipelines is complex and future decommissioning strategies should consider a range of Hg species beyond only Hg0 and metacinnabar (β-HgS), all of which could interact with biota and impact Hg biomagnification through the marine the food web.

The re-use of offshore platforms as ecological observatories

The high number of offshore platforms at the end of their productive phase offers the opportunity of their re-use and the development of effective management solutions, such as the possibility of utilizing them as ecological observatories for monitoring marine ecosystems and their biological resources. Here, through a multiparametric observatory deployed at an unproductive offshore platform, located in the Central Adriatic Sea (Mediterranean Sea), we collected data for 13 months on benthopelagic fish assemblage and habitat conditions. A total of 155.5 h of high-frequency (30 min) video-monitoring, recorded higher fish abundances during spring-summer periods during daytime, while fish diversity was highest in autumn. Some environmental variables contributed significantly to explain the overall community variance. Our results suggest that offshore platforms can be re-converted into ecological observatories, to collect relevant amounts of information that can be difficulty obtained with alternative approaches, contributing to our understanding of changes occurring in open water ecosystems.

Multi-Criteria Decision Analysis for Sustainable Oil and Gas Infrastructure Decommissioning: A Systematic Review of Criteria Involved in the Process

The decommissioning of oil and gas (O&G, hereafter) facilities presents complex challenges when addressing the diverse needs of stakeholders. By synthesizing information from previous Multi-Criteria Decision Analysis (MCDA, hereafter) studies on decommissioning projects, this study aims to do the following: (a) formulate a structured set of criteria adaptable to MCDA for both offshore and onshore O&G decommissioning, (b) identify and analyze the evolving trends and regional disparities in MCDA for decommissioning, and (c) explore current O&G onshore decommissioning procedures and map specific criteria to these processes. Following a systematic literature review approach, this study analyzed 63 references across four stages from 2006 to 2024 and identified 158 criteria. These criteria were consolidated into a framework of 22 factors across dimensions comprising technical, environmental, societal, financial, health and safety considerations, and additional concerns from stakeholders. This study observed a significant focus shift from technical aspects to environmental considerations in decommissioning practices from 2011 onwards, reflecting growing awareness of sustainability. It also revealed regional differences, such as the technical emphasis in the North Sea and environmental concerns in Australia. Furthermore, this study refined O&G onshore decommissioning procedures and identified criteria gaps for further research, particularly in societal impact regarding public resource availability, recreational opportunities, and operating company reputation. The study provides a robust foundation for the development of future MCDA frameworks tailored to O&G infrastructure decommissioning projects, thus supporting long-term environmental and social sustainability.

Offshore oil and gas infrastructure plays a minor role in marine metapopulation dynamics

Decommissioning consequences of offshore oil and gas infrastructure removal on marine population dynamics, including connectivity, are not well understood. We modelled the connectivity and metapopulation dynamics of three fish and two benthic invertebrate species inhabiting the natural rocky reefs and offshore oil and gas infrastructure located in the Bass Strait, south-east Australia. Using a network approach, we found that platforms are not major sources, destinations, or stepping-stones for most species, yet act as modest sources for connectivity of Corynactis australis (jewel anemone). In contrast, sections of subsea pipelines appear to act as stepping-stones, source and destination habitats of varying strengths for all study species, except for Centrostephanus rodgersii (long-spined sea urchin). Natural reefs were the main stepping-stones, local source, and destination habitats for all study species. These reefs were largely responsible for the overall metapopulation growth of all study species (average of 96 % contribution across all species), with infrastructure acting as a minor contributor (<2 % average contribution). Full or partial decommissioning of platforms should have a very low or negligible impact on the overall metapopulation dynamics of the species explored, except C. australis, while full removal of pipelines could have a low impact on the metapopulation dynamics of benthic invertebrate species and a moderate impact on fish species (up to 34.1 % reduction in the metapopulation growth). We recommend that the decision to remove offshore infrastructure, either in full or in-part, be made on a platform-by-platform basis and consider contributions of pipelines to connectivity and metapopulation dynamics.

Response of Microbial Communities to Naturally Occurring Radioactive Material-Contaminated Sediments: A Microcosm-Based Study

There is a growing need to understand the potential ecological impacts of contaminants in offshore oil and gas infrastructure, especially if that infrastructure is to be left in situ as a decommissioning option. Naturally occurring radioactive material (NORM) is one type of contaminant found in solid deposits on internal surfaces of infrastructure that poses potential ecological harm if released into the marine environment. Microbes are important components of marine sediment ecosystems because they provide ecosystem services, yet the impacts of NORM contamination to these communities are not well understood. The present study aimed to investigate the response of benthic microbial communities to NORM-contaminated scale, collected from an offshore oil and gas system, via controlled laboratory microcosm studies. Changes to microbial communities in natural sediment and sediments spiked with NORM at radium-226 activity concentrations ranging from 9.5 to 59.8 Bq/kg (in partial equilibria with progeny) over 7 and 28 days were investigated using high-throughput sequencing of environmental DNA extracted from experimental sediments. There were no significant differences in microbial community composition between control and scale-spiked sediments over 7 and 28 days. However, we observed a greater presence of Firmicutes in the scale-mixed treatment and Chloroflexi in the scale-surface treatments after 28 days. This could suggest selection for species with contaminant tolerance or potential resilience to radiation and metal toxicity. Further research is needed to explore microbial tolerance mechanisms and their potential as indicators of effects of radionuclide-contaminated sediments. The present study demonstrated that microcosm studies can provide valuable insights about the potential impacts of contamination from oil and gas infrastructure to sediment microbial communities. Environ Toxicol Chem 2024;43:1648-1661. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Naturally occurring radioactive materials in offshore infrastructure: Understanding formation and characteristics of baryte scale during decommissioning planning

Contaminants, including naturally occurring radioactive material (NORM) of the 238-uranium and 232-thorium decay series, have been recognized as a global research priority to inform offshore petroleum infrastructure decommissioning decisions. This study aimed to characterize pipeline scale retrieved from a decommissioned subsea well tubular pipe through high-resolution elemental mapping and isotopic analysis. This was achieved by utilizing transmission electron microscopy, Synchrotron x-ray fluorescence, photostimulated luminescence autoradiography and Isotope Ratio Mass Spectrometry. The scale was identified as baryte (BaSO4) forming a dense crystalline matrix, with heterogenous texture and elongated crystals. The changing chemical and physical microenvironment within the pipe influenced the gradual growth rate of baryte over the production life of this infrastructure. A distinct compositional banding of baryte and celestine (SrSO4) bands was observed. Radioactivity attributed by the presence of radionuclides (226Ra, 228Ra) throughout the scale was strongly correlated with baryte. From the detailed scale characterization, we can infer the baryte scale gradually formed within the internals of the tubular well pipe along the duration of production (i.e., 17 years). This new knowledge and insight into the characteristics and formation of petroleum waste products will assist with decommissioning planning to mitigate potential radiological risks to marine ecosystems.

Developing expert scientific consensus on the environmental and societal effects of marine artificial structures prior to decommissioning

Thousands of artificial ('human-made') structures are present in the marine environment, many at or approaching end-of-life and requiring urgent decisions regarding their decommissioning. No consensus has been reached on which decommissioning option(s) result in optimal environmental and societal outcomes, in part, owing to a paucity of evidence from real-world decommissioning case studies. To address this significant challenge, we asked a worldwide panel of scientists to provide their expert opinion. They were asked to identify and characterise the ecosystem effects of artificial structures in the sea, their causes and consequences, and to identify which, if any, should be retained following decommissioning. Experts considered that most of the pressures driving ecological and societal effects from marine artificial structures (MAS) were of medium severity, occur frequently, and are dependent on spatial scale with local-scale effects of greater magnitude than regional effects. The duration of many effects following decommissioning were considered to be relatively short, in the order of days. Overall, environmental effects of structures were considered marginally undesirable, while societal effects marginally desirable. Experts therefore indicated that any decision to leave MAS in place at end-of-life to be more beneficial to society than the natural environment. However, some individual environmental effects were considered desirable and worthy of retention, especially in certain geographic locations, where structures can support improved trophic linkages, increases in tourism, habitat provision, and population size, and provide stability in population dynamics. The expert analysis consensus that the effects of MAS are both negative and positive for the environment and society, gives no strong support for policy change whether removal or retention is favoured until further empirical evidence is available to justify change to the status quo. The combination of desirable and undesirable effects associated with MAS present a significant challenge for policy- and decision-makers in their justification to implement decommissioning options. Decisions may need to be decided on a case-by-case basis accounting for the trade-off in costs and benefits at a local level.

To what extent can decommissioning options for marine artificial structures move us toward environmental targets?

Switching from fossil fuels to renewable energy is key to international energy transition efforts and the move toward net zero. For many nations, this requires decommissioning of hundreds of oil and gas infrastructure in the marine environment. Current international, regional and national legislation largely dictates that structures must be completely removed at end-of-life although, increasingly, alternative decommissioning options are being promoted and implemented. Yet, a paucity of real-world case studies describing the impacts of decommissioning on the environment make decision-making with respect to which option(s) might be optimal for meeting international and regional strategic environmental targets challenging. To address this gap, we draw together international expertise and judgment from marine environmental scientists on marine artificial structures as an alternative source of evidence that explores how different decommissioning options might ameliorate pressures that drive environmental status toward (or away) from environmental objectives. Synthesis reveals that for 37 United Nations and Oslo-Paris Commissions (OSPAR) global and regional environmental targets, experts consider repurposing or abandoning individual structures, or abandoning multiple structures across a region, as the options that would most strongly contribute toward targets. This collective view suggests complete removal may not be best for the environment or society. However, different decommissioning options act in different ways and make variable contributions toward environmental targets, such that policy makers and managers would likely need to prioritise some targets over others considering political, social, economic, and ecological contexts. Current policy may not result in optimal outcomes for the environment or society.