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.

Abundance of Corals on Offshore Oil and Gas Platforms in the Gulf of Mexico.

Scleractinian, octocoral, and antipatharian corals have colonized many of the offshore oil and gas platforms in the northern Gulf of Mexico. We surveyed 25 offshore oil and gas platforms for these cnidarians. Few to no corals were detected on inshore, shallow-water structures at <25 m depth; however, the abundance of corals increased, ranging from 14 to 194/m2, on platforms in waters deeper ≥25 m. The most common coral encountered were Tubastraea coccinea (Scleractinia) and Telesto spp. (Octocorallia). The data suggest that the offshore platforms located in waters of >25-30 m in the study area are often colonized by these corals. We recommend that structures located in deeper waters should be surveyed for coral and, if the populations are substantial, consider alternate uses for the retired platforms, and leaving them in place, when feasible.

Using environmental DNA to better inform decision making around decommissioning alternatives for offshore oil and gas infrastructure.

Artificial reefs are being utilised globally to aid in natural resource management, conservation, restoration or the creation of unique marine habitats. There is discussion around the optimal construction materials and designs for artificial reefs, the influences these have on biological communities, and the resulting ecological and social benefits. This discussion also includes the ecological value of repurposed marine infrastructure, such as decommissioned oil and gas platforms. Platforms often have an operational life spanning multiple decades, over which time they can develop extensive and unique community assemblages. The creation of artificial reefs by repurposing oil and gas platforms can have ecological, economic and sociological merit. However, with >12,000 platforms requiring decommissioning globally, there is the need for holistic assessment of biological communities associated with these platforms to inform the potential outcomes of different decommissioning options. We use environmental DNA metabarcoding (eDNA) of water, bio-foul and sediment samples to census broad eukaryotic diversity at eight platforms in the Gulf of Thailand (GoT) and five nearby soft sediment habitat locations. We sampled three target depths at sites (shallow, mid, deep) and detected 430 taxa at platforms, with higher diversity in shallow (near-surface) samples (313 taxa), compared to mid (30 m collection depth; 261 taxa) and deep (50 m; 273 taxa). Three percent of taxa were shared among all depths at platforms with distinct assembles at each depth. Introduced species are an ongoing risk for platforms, however the eDNA detected no known introduced species. While the eDNA data provide broad taxon coverage and significant assemblage patterns, ongoing sampling innovation, assay design and local reference material still require development to obtain the maximum benefit of the technique. This study highlights the versatility and scalability of eDNA metabarcoding to holistically census marine infrastructure and inform the management and potential conservation of extant communities.

Evidence of fish following towed oil and gas platforms to a reefing site and rapid colonisation.

We investigated the composition and abundance of fish assemblages associated with seven offshore oil and gas platform jackets in the Gulf of Thailand before (pre-lift and pre-tow), and immediately after relocation (post-tow and reefed). Jackets were cut, lifted until partly out of the water, and attached to the rear of a heavy lift vessel. They were towed at speeds of 2.7 - 3.3 knots for between 133.9 and 205.4 km before being placed on the seafloor at an artificial reef site. Sixteen species of fish were observed both before and after jacket towing. We believe these species have sought refuge in the complex structures out of the current and have remained with the jackets. Ten species of fish were observed before towing, but not after. A further seven species of fish were only observed after the jackets were relocated onto the seafloor and were assumed to be early colonisers to the structures. The paper provides empirical evidence of a much-discussed paradigm that fish can swim great distances following moved structures, and further evidence of the ability of fish to rapidly colonise reefed structures.

Small suspension-feeding amphipods play a pivotal role in carbon dynamics around offshore man-made structures.

The establishment of artificial hard substrates (i.e. offshore wind farms and oil and gas platforms) on marine soft sediments increases the available habitat for invertebrate communities that would otherwise be restricted to natural hard bottoms. Suspension feeding invertebrates clear a significant amount of particles from the water column and release organic matter in the form of feces, influencing the basis of marine food webs and affecting surrounding environments. Artificial structures in the southern North Sea are dominated by a suspension-feeding crustacean in terms of abundance and sometimes even biomass: the amphipod Jassa herdmani. Animal densities of this tiny biofouler are known to exceed 1 million individuals per m2. Despite their small body sizes and their simple filter apparatus, we hypothesized that J. herdmani is a highly effective suspension feeder with a significant impact on neighboring communities due to its high abundances. In a feeding experiment, individuals of J. herdmani were provided with either an algal or an animal diet under two different temperature regimes. Clearance rates and fecal-pellet carbon (FPC) were measured. The results revealed high clearance rates and subsequent FPC, which were more pronounced at the higher temperature. Furthermore, clearance rates and FPC varied insignificantly with different food items. We further used the current findings for upscaling calculations to the total number of offshore windfarms and oil and gas platforms in the southern North Sea. Our calculations indicated that J. herdmani alone clears 0.33-4.71 km3 water per year in the southern North Sea. At the same time, these amphipods release 255-547 tons of carbon per year by means of defecation, thus enriching the surrounding soft sediments with organic matter. Our study highlights that tiny amphipods can mediate indirect effects of man-made structures in the North Sea, which could have a profound impact on pelagic and benthic habitats.

Medical evacuations in the oil and gas industry: a retrospective review with implications for future evacuation and preventative strategies.

Background: Businesses increasingly conduct operations in remote areas where medical evacuation [Medevac(s)] carries more risk. Royal Dutch Shell developed a remote healthcare strategy whereby enhanced remote healthcare is made available to the patient through use of telemedicine and telemetry. To evaluate that strategy, a review of Medevacs of Shell International employees [i.e. expatriate employees (EEs) and frequent business travellers (FBTs)] was undertaken. Method: A retrospective review of Medevac data (period 2008-12) that were similar in operational constraints and population profile was conducted. Employee records and Human Resource data were used as a denominator for the population. Analogous Medevac data from specific locations were used to compare patterns of diagnoses. Results: A total of 130 Medevacs were conducted during the study period, resulting in a Medevac rate of 4 per 1000 of population with 16 per 1000 for females and 3 per 1000 for males, respectively. The youngest and oldest age-groups required Medevacs in larger proportions. The evacuation rates were highest for countries classified as 'high' or 'extreme risk'. The most frequent diagnostic categories for Medevac were: trauma, digestive, musculoskeletal, cardiac and neurological. In 9% of the total, a strong to moderate link could be made between the pre-existing medical condition and diagnosis leading to Medevac. Conclusion: This study uniquely provides a benchmark Medevac rate (4 per 1000) for EEs and FBTs and demonstrates that Medevac rates are highest from countries identified as 'high risk'; there is an age and gender bias, and pre-existing medical conditions are of notable relevance. It confirms a change in the trend from injury to illness as a reason for Medevac in the oil and gas industry and demonstrates that diagnoses of a digestive and traumatic nature are the most frequent. A holistic approach to health (as opposed to a predominant focus on fitness to work), more attention to female travellers, and the application of modern technology and communication will reduce the need for Medevacs.

Considerations in evaluating potential socioeconomic impacts of offshore platform decommissioning in California.

The 27 oil and gas platforms offshore southern California will eventually reach the end of their useful lifetimes (estimated between 2015 and 2030) and will be decommissioned. Current state and federal laws and regulations allow for alternative uses in lieu of the complete removal required in existing leases. Any decommissioning pathway will create a complex mix of costs, benefits, opportunities, and constraints for multiple user groups. To assist the California Natural Resources Agency in understanding these issues, we evaluated the potential socioeconomic impacts of the 2 most likely options: complete removal and partial removal of the structure to 85 feet below the waterline with the remaining structure left in place as an artificial reef-generally defined as a manmade structure with some properties that mimic a natural reef. We estimated impacts on commercial fishing, commercial shipping, recreational fishing, nonconsumptive boating, and nonconsumptive SCUBA diving. Available data supported quantitative estimates for some impacts, semiquantitative estimates for others, and only qualitative approximations of the direction of impact for still others. Even qualitative estimates of the direction of impacts and of user groups' likely preferred options have been useful to the public and decision makers and provided valuable input to the project's integrative decision model. Uncertainty surrounds even qualitative estimates of the likely direction of impact where interactions between multiple impacts could occur or where user groups include subsets that would experience the same option differently. In addition, we were unable to quantify effects on ecosystem value and on the larger regional ecosystem, because of data gaps on the population sizes and dynamics of key species and the uncertainty surrounding the contribution of platforms to available hard substrate and related natural populations offshore southern California.

Decision framework for platform decommissioning in California.

This article describes the overall decision framework for eventual decisions about decommissioning the 27 operating oil and gas platforms offshore southern California. These platforms will eventually reach the end of their useful lifetimes (estimated between 2015 and 2030, although specific dates have not been determined). Current law and regulations allow for alternative uses in lieu of the complete removal required in existing leases. To prepare for eventual decommissioning, the California Natural Resources Agency initiated an in-depth process to identify and investigate issues surrounding possible decommissioning alternatives. The detailed evaluation of alternatives focused on 2-complete removal and artificial reefing that included partial removal to 85 feet below the waterline. These were selected after a comparison of the technical and economic feasibility of several potential alternatives, availability of a legal framework for implementation, degree of interest from proponents, and relative acceptance by state and federal decision makers. Despite California's history of offshore oil and gas production, only 7 decommissioning projects have been completed and these were all relatively small and close to shore. In contrast, nearly 30% of the California platforms are in water depths (as much as 1200 feet) that exceed any decommissioning project anywhere in the world. Most earlier projects considered an artificial reefing alternative but none were implemented and all platforms were completely removed. Future decisions about decommissioning must grapple with a more complex decision context involving greater technological and logistical challenges and cost, a wider range of viable options, tradeoffs among environmental impacts and benefits, and an intricate maze of laws, regulations, and authorities. The specific engineering differences between complete and partial removal provide an explicit basis for a thorough evaluation of their respective impacts.

Evaluating alternatives for decommissioning California's offshore oil and gas platforms.

This paper introduces a series of 6 additional papers in this issue that describe an in-depth analysis of options for decommissioning oil and gas platforms offshore southern California. Although current leases require lessees in both state and federal waters to completely remove all production facilities and restore the seafloor to its pre-platform condition, other options have emerged since these leases were signed. Laws and regulations in other jurisdictions (particularly in federal waters) have evolved to allow a number of other uses such as aquaculture, alternative energy production, and artificial reefing. In response, the California Natural Resources Agency initiated an effort to investigate the issues associated with these and other decommissioning alternatives. The papers in this series are the result of the second phase in this process, a broad investigation of the engineering, economic, and environmental costs and benefits of the most feasible and likely options. In addition to the project's final report, the authors produced an interactive mathematical decision model, PLATFORM, that enables users to explore the implications of different decommissioning projects and options, as well as the effects of different approaches to valuing the associated costs and benefits.

A multi-attribute decision analysis for decommissioning offshore oil and gas platforms.

The 27 oil and gas platforms off the coast of southern California are reaching the end of their economic lives. Because their decommissioning involves large costs and potential environmental impacts, this became an issue of public controversy. As part of a larger policy analysis conducted for the State of California, we implemented a decision analysis as a software tool (PLATFORM) to clarify and evaluate decision strategies against a comprehensive set of objectives. Key options selected for in-depth analysis are complete platform removal and partial removal to 85 feet below the water line, with the remaining structure converted in place to an artificial reef to preserve the rich ecosystems supported by the platform's support structure. PLATFORM was instrumental in structuring and performing key analyses of the impacts of each option (e.g., on costs, fishery production, air emissions) and dramatically improved the team's productivity. Sensitivity analysis found that disagreement about preferences, especially about the relative importance of strict compliance with lease agreements, has much greater effects on the preferred option than does uncertainty about specific outcomes, such as decommissioning costs. It found a near-consensus of stakeholders in support of partial removal and "rigs-to-reefs" program. The project's results played a role in the decision to pass legislation enabling an expanded California "rigs-to-reefs" program that includes a mechanism for sharing cost savings between operators and the state.