Offshore Industry Thematic Assessment

The implementation of OSPAR measures has resulted in a measurable decrease in discharges and associated impacts

Oil and gas exploration and exploitation can lead to a range of impacts in the marine environment. The reported data and results of the environmental monitoring studies (Report on impacts of discharges of oil and chemicals in produced water on the marine environment and Assessment of the disturbance of drill cuttings during decommissioning) show that the implementation of OSPAR measures has resulted in a measurable decrease in discharges and associated impacts. This section presents an overview of studies of water column, sediments, physical impact, cuttings piles, decommissioning and light and noise effects.

Table S.1: Trends in impacts from oil and gas activities

*Reported data for region IV is very limited, and the trends are therefore uncertain

Discharges and associated impacts in the water column

Water column impacts from discharges of produced water

Water column monitoring (WCM) has been carried out in the OSPAR area to determine the possible effects of discharges of produced water. The monitoring of toxic effects in the water column focuses on biomarkers in fish (especially cod and haddock) and blue mussels and aims to identify sensitive endpoints that can be linked to the exposure to produced water.

Norwegian WCM has found significantly higher concentrations of PAH and NPD (naphthalene, phenanthrene and dibenzothiophene) in caged mussels located 500 m from an offshore installation as compared to reference areas, and histopathological analyses have indicated a minor stress condition in caged mussels located 500 m and 1000 m from the platform. Thus, the worst-case exposure (500 m from the discharge point) has mainly confirmed the exposure through observation of a minor stress condition in the mussels. Increased levels of PAHs, alkyl phenols and measured biological responses also suggest exposure of wild fish. The combined exposure to the constituents in produced water may lead to a toxic effect on organisms in the sea. This is reflected in OSPAR Agreement 2012-7 on Guidelines in support of Recommendation 2012/5 for a Risk-based Approach to the Management of Produced Water Discharges from Offshore Installations which allows for risk to be estimated by either the whole effluent toxicity or by the (summed) toxicity of each substance.

Controlled laboratory experiments have shown that exposure of salmon and herring fry to low PAH levels (ng to µg per L) induces cardiac defects which impact the fish fry in several critical ways, including through reduced swimming performance and in prey capture and prey avoidance, with repercussions on survival and a possible impact on population level. Haddock has been observed to be more sensitive than cod when egg/embryo surface (chorion) is exposed to oil droplets.

Generally, however, the results obtained from field-realistic concentrations indicate that impacts are expected to be modest. The overall risk of produced water discharges exerting an adverse impact on populations of wild fish and other pelagic organisms is therefore expected to be low.

It is generally accepted that produced water effects are limited to areas where the produced water is diluted less than 1 000 times, roughly corresponding to distances less than 1 000 m from the discharge point, depending on the discharge rate, water depth, local currents, and other environmental factors. Based on laboratory results where the test organisms are exposed to constant concentrations over several days as well as studies with caged animals placed in the produced water plume, acute toxicity effects can be expected at such concentrations.

The monitoring of toxic effects in the water column focuses on biomarkers in fish (especially cod and haddock) and blue mussels (Mytilus edulis) and aims to identify sensitive endpoints that can be linked to exposure to produced water. The Research Council of Norway concluded in 2012 that toxic effects such as cell death, genetic change, DNA damage, a change in fatty acid composition and interference with reproduction is detected at concentrations of produced water at 0,1-1% or higher, i.e., when the produced water has been diluted less than 100-1 000 times. Moreover, the focus of the testing of produced water effects has recently shifted towards the possible effects of chronic, low-concentration exposures to sensitive endpoints and to life stages of marine species such as early life and sexual maturation.

However, a constant exposure scenario is improbable, because an organism is unlikely to be exposed for days to static concentrations. Drifting plankton (including fish eggs) passing the discharge point may be exposed to high produced water concentrations, but because of dispersion and dilution the exposure duration is short. For adult fish, the effect or accumulation of produced water constituents have not been demonstrated in wild animals caught in produced water-influenced areas, perhaps because they can avoid polluted areas. This does not mean that laboratory results should be disregarded, especially when the exposure concentrations correspond to dilutions of 1 000 times or more. While effects at these low concentrations are observed after weeks of continuous exposure, this is unlikely under dynamic environmental conditions. Also, sessile organisms are expected to experience constantly high pollution levels only rarely, as the direction of a pollution plume changes with the tide, currents, and wind.

Despite the large volumes of produced water released, the effects of the constituents appear to be low and mainly seen at biomarker level. However, the causality between biomarkers and toxic effects and impact at the organism and population levels remains to be proven. Other anthropogenic factors are difficult to exclude when assessing the impact of produced water in marine ecosystems. While the conclusions from OSPAR’s Quality Status Report 2010 are still valid, it should be emphasised that this does not imply that no causal relationships exist between impacts at organism level and impacts at population or ecosystem level. It should only be seen as an indication that there is a lack of evidence and that further investigations are needed to establish whether such relationships exist.

Discharges of produced water can occasionally lead to the formation of oil sheens at the sea surface, especially in calm weather conditions. Investigations of produced water discharges to date have not included possible effects of such oil sheens. Assessing the extent and possible effects of oil sheens originating from discharges of produced water has been identified as a task that needs to be addressed in the coming years.

Water column impacts from contaminants released from cuttings piles

Monitoring undertaken near cuttings piles historically contaminated with organic-phase fluids indicates that the concentration and spatial extent of the contamination have been reduced and leaching rates diminished since the initial discharge.

Based on the case studies reviewed (OIC 2014) the majority of impacts from cuttings piles have been noted within 100 m of the centre of the pile; generally, beyond 500 m there is little discernible impact. When cuttings piles are disturbed, the pile is aerated, allowing some additional degradation to take place. However, this disturbance results in additional, albeit generally short-term and localised, impacts on the water column, and in some (not all) cases could cause contamination of the seabed outside the areas impacted by the original cuttings discharge.

Fishing may be able to resume over cuttings piles previously contained in a 500 m safety zone where fishing activities would have been excluded. Where cuttings are left in situ or relocated on the seabed there is the potential for trawling activities to disturb the cuttings pile, resulting in the contaminants contained within the cutting pile being released into the water column, as well as the potential for the nets and catch to be contaminated.

Water column impacts from accidental spills

Accidental spills of oil and chemicals may have an impact on the marine life in the upper water column, including mammals and seabirds. The level of impact arising from an oil spill is dependent on the location and size of the spill and when it occurs. Assessment of the environmental effects following the 2012 Elgin platform incident in the United Kingdom which resulted in the release of gas / condensate have shown that dispersion and evaporation of the gas/condensate occurred within hours of its release, with the sheen never travelling further than 60 km from the platform’s location. Environmental surveys following the incident have found no evidence of significant effects on the water column, fish or seabed from the condensate or water-based mud (WBM). There was also no evidence of significant mortality among either birds or marine mammals during or after the incident, and the hydrocarbons did not beach. There is no evidence that accidental spills of chemicals significantly impact the water column.

Impact of discharges on sediments

Impacts of discharges of drilling fluids and contaminants released from historic cuttings piles

As a result of contamination by organic-phase fluids and the settlement of suspended fine cuttings, benthic fauna become stressed. This results in lower diversity and the dominance of tolerant opportunistic species in several square kilometres around the well location. Since the ban on the use of diesel oil-based drilling fluids and the prohibition on the discharge of untreated cuttings contaminated with organic-phase drilling fluids, and after the substitution of most of the hazardous chemicals with less hazardous substances, the impact has significantly reduced. Studies have shown that at the peak of discharge of oil-contaminated cuttings, fauna disturbance could be found at more than 5 km from some platforms, but it is now seldom detected beyond 500 m.

Although it is more than 20 years since the discharge of cuttings contaminated with organic-phase fluids was prohibited, historical cuttings piles are still present beneath some installations. Monitoring undertaken near cuttings piles historically contaminated with organic-phase fluids indicates that the concentration and spatial extent of contamination have been reduced and that leaching rates have diminished since the initial discharge. The 2009 OSPAR Assessment of impacts of offshore oil and gas activities in the North‐East Atlantic concluded that disturbance of cuttings piles does not result in significant impacts on the marine environment. Further studies conducted in 2014 (OIC 2014) and 2017 (OIC 2017) and new data support that conclusion: no significant effects on the seabed have been observed, although there may be a temporary effect on the water and sediment quality near the site of the disturbance.

The discharge of drill cuttings and water-based fluids may cause some smothering in the near vicinity of the well location. Water-based cuttings may affect biomarkers in filter feeding bivalves and cause elevated sediment oxygen consumption and mortality in benthic fauna. Effects levels occur within a 0,5-1 km distance and the stress is mainly physical. The impacts of such discharges are localised and transient but may be of concern in areas with sensitive benthic fauna, for example corals and sponges.  

Impacts of discharges from produced water on sediments

It is generally to be expected that produced water is diluted in the water phase. However, the hydrophobic chemicals in it may adsorb to the sediment, especially in shallow water or under downward trajectory of the produced water plume.

Sediment monitoring has been performed by several Contracting Parties. Both Danish and Norwegian studies have found that the concentration in sediments of petrogenic PAH increases in the areas close to the platforms. Biological diversity and evenness were studied in samples from the Danish platforms, and changes to seabed fauna and quality were found to be local and short-term; the seabed was found to be resilient to disturbances associated with oil and gas operational discharges. The results of the seabed monitoring do not indicate that discharges of produced water in general have an impact on the seabed, since the probability of such an impact will, by its nature, be less likely with increasing distance and depth from where the discharges take place.

Physical impacts on the seabed

Contracting Parties do not undertake extensive monitoring programmes to assess the physical impacts of the placement of structures on the seabed. Historical monitoring has demonstrated that the impacts are largely transient, with recolonisation of disturbed seabed habitats occurring within relatively short time scales.

The creation of hard bottom substrate can, over time, give an opportunity for new benthic species to colonise the former sandy / muddy areas. Pipelines, platform legs and subsea templates may act as shelter for fish and other mobile marine organisms and provide a habitat for benthic organisms usually associated with hard substrates.

Benthic communities will be impacted for a variable period of time. In areas of soft sediments, where most pipelines are trenched and buried, the soft bottom fauna recolonises within a year or two. In areas of harder substrates, the recovery of benthic communities may take longer, up to 10 years in deeper and colder water. There are few pipelines that are trenched and buried in these areas. In impacted areas a gradual change occurs in the species composition of benthic communities until equilibrium is achieved, depending on the new local conditions. During the re-establishment of the area, it is also possible that specific diversity will increase due to the colonisation of hard structures by previously absent benthic species.

Impact from decommissioning of offshore installations

OSPAR Decision 98/3 on the Disposal of Disused Offshore Installations prohibits the dumping, and the leaving wholly or partly in place, of disused offshore installations within the OSPAR Maritime Area. It is possible to seek derogation to this Decision if it can be demonstrated that there are significant reasons why an alternative disposal option is preferable. The majority of installations are removed at the time of decommissioning. Reviews of the experience and technical developments relating to the decommissioning of platforms were undertaken in 2013 and 2018. The reviews showed that the number of projects involving concrete structures and substantial steel footings has been very low and that there have been no significant developments in the technical capabilities of the industry which would support a reduction in the categories eligible for derogation. However, as older installations reach their end-of-life, it is anticipated that a number of installations will be decommissioned in the coming decade. Therefore, the 2018 review also agreed that Contracting Parties and Observer Organisations should proactively promote areas of research and scientific understanding so as to provide a wider scope for the upcoming review of derogation categories in Annex 1 of Decision 98/3 to be conducted in 2023.

In the light of experience with the decommissioning of offshore installations, relevant research and the exchange of information, OSPAR aims to ensure that derogations from the dumping ban remain exceptional.

During 2019 to 2020 a consultation process was undertaken under OSPAR Decision 98/3 concerning the United Kingdom’s intention to issue a derogation so as to leave in situ the footings of the Brent Alpha Steel Jacket and Brent Bravo, Brent Charlie and Brent Delta gravity-based concrete installation structures. A Special Consultative Meeting was held in London in October 2019 to discuss the objections raised to the derogation proposal with reference to comparative assessment methodology, long-term risk to the marine environment from the residues in the storage cells and the risk posed by the gravity-based concrete installation legs to shipping and fishing. The meeting agreed that, in view of the upcoming decommissioning projects, the process presented an opportunity to agree on common OSPAR standards for comparable challenging decommissioning cases.

Impact of platform lighting on birds

According to the research into possible effects of offshore platform lighting on specific bird populations (2012 OSPAR Workshop), there is evidence that the conventional lighting on some offshore installations has had an impact on a large number of birds. The evidence is, however, not sufficient to conclude whether or not there has been a significant effect at the population level (E. van der Zee, 2014).

Impact of noise on fish and marine mammals

The potential effects from noise vary depending on the sensitivity of the receptor and its proximity to the sound source. There is potential for increased mortality among juvenile stages of fish, permanent or temporary hearing impairment and the displacement of fish and marine mammals from their normal range (OSPAR, 2009a). There is evidence for several species of cetaceans to suggest avoidance over distances, most commonly around 2 - 5 km from the seismic survey vessel. Changes in acoustic communication have been recorded at much greater distances (up to several hundred km), but there is a lot of uncertainty with regard to the biological significance of these observations. Relatively limited evidence is available for harbour porpoises or other species common in the North Sea; as a conservative assessment, it is reasonable to assume that the firing of airguns during seismic surveys will affect individuals within 10 km of a survey vessel, resulting in changes in distribution and a reduction in foraging activity, although this effect is short-lived.

The impacts of seismic surveys on fish have been shown to include an increase in fish mortality at less than 5 m from the sound source, and temporary threshold shifts, and behavioural responses have also been reported. Evidence from the North Sea indicates potentially large-scale avoidance of areas where seismic surveys are being undertaken, with fish either moving into deeper water or avoiding the area altogether. Experiments undertaken in the North Sea on sand eels have indicated relatively minor responses to seismic surveys and no increases in mortality.