Offshore Industry Thematic Assessment

Pressures from the oil and gas industry and carbon dioxide storage

Table P.1: Trends in pressures from oil and gas activities

¹The confidence assessment is based on data for discharges, emissions and spills

The pressure intensity from offshore oil and gas activities is greatest in the North Sea, followed by Arctic Waters and the Celtic Seas. In the remaining regions — Bay of Biscay, Iberian Coast and the Wider Atlantic— the number of installations is low and the pressure is considered to be relatively low. These trends are described in the table. Pressure intensity has been stable for all Regions since 2010 and is expected to remain stable towards 2030.

There has been a measurable decrease in emissions and discharges since QSR 2010.This conclusion is based on discharge data reported by Contracting Parties and assessments carried out by the Expert Assessment Panel and published in OSPAR’s Assessment of the OSPAR Report on Discharges, Spills and Emissions from Offshore Installations, 2009 – 2019 . This assessment method used basic linear regression, best professional judgement, and observation. The data is supported by environmental monitoring findings, and the confidence assessment expressed in Table P.1 is based on data for these pressures, as this has been the main work area for the Offshore Industry Committee since 2010. The confidence level for this part of the data can be regarded as very high (high agreement, robust evidence), except for Region IV where reported data on discharges were sparse, and trends could not be determined.

For other pressures, such as physical pressure, noise and light, the confidence level can be regarded as medium to low. However limited evidence is available, and the confidence assessment is therefore uncertain.

Oil and gas industry

Oil and gas exploration and production within the OSPAR Maritime Area have affected the marine environment of the North-East Atlantic. The environmental pressures include discharges of produced water, chemicals, drilling fluids and cuttings, atmospheric emissions, noise, light and the physical impacts from the placement and decommissioning of pipelines and installations.

OSPAR Contracting Parties have conducted studies of historical cuttings piles, discharges of produced water, drilling fluids and chemicals. The results show that the implementation of OSPAR measures has resulted in a measurable decrease in pressures and associated impacts. Where potential impacts may still occur, they have been reduced.

Input of other substances (e.g., synthetic substances, non-synthetic substances, radionuclides), diffuse sources, point sources, atmospheric deposition, and acute events

The different phases of the oil and gas industry will result in pressures stemming from the discharge of produced water, chemicals and drilling muds, accidental spills of oil and chemicals, and atmospheric emissions:

Discharge of produced water

The amount of dispersed oil discharged in 2019 was 16% below that discharged in 2009. While there was no year-on-year decrease, the total quantity of dispersed² oil (aliphatic oil) discharged to the sea from produced water and displacement water decreased from 4 890 tonnes in 2009 to 4 096 tonnes in 2019. There was a notable increase in dispersed oil discharged in 2015 as a result of an increase in the amount of produced water discharged and in average dispersed oil concentrations.

Produced water and displacement water are the main contributors to the oil discharges from offshore oil and gas activities, representing 95-99% of the total amount of oil discharged to the sea during the 2009 to 2019 period. The exception was in 2011 to 2012, when a single large spill event accounted for 11-12% of the total oil to sea.

It should be noted that dispersed oil in displacement water contributes less than 1% to this total. The annual average dispersed oil content of produced water ranged from 12,4 mg/l to 14,1 mg/l over the period, well below the current performance standard of 30 mg/l for dispersed oil in produced water discharged into the sea.

Over the period 2009 to 2019, the total number of installations exceeding the performance standard decreased from 31 to 17. The amount of oil discharged from six of these installations was less than 2 tonnes annually. In total, the discharge of dispersed oil in excess of the performance standard was less than 2% of the total discharge of dispersed oil in the OSPAR area.

In 2013, Contracting Parties provided OSPAR’s Offshore Industry Committee (OIC) with implementation plans under OSPAR Recommendation 2012/5 for a risk-based approach to the management of produced water discharges from offshore installations, and the majority commenced assessments in 2014 with the Recommendation due to be fully implemented by 2018. In 2019, of the 231 installations still included within the risk-based approach process, 216 had been assessed, with 125 installations (54%) determined as having their discharge adequately controlled and 91 installations (39%) as requiring further action to be taken, while the remainder were still awaiting the outcome of an assessment (Figure P.2).

Produced water discharges are the main source of radionuclides from oil and gas operations. Radionuclide discharges from oil and gas operations are covered in the Radioactive Substances Thematic Assessment.

Use and discharge of chemicals

The total quantity of chemicals used offshore decreased from 838 111 tonnes in 2009 to 733 598 tonnes in 2019, of which 69% (wt.) were on the PLONOR list (OSPAR List of substances/preparations used and discharged offshore which are considered to Pose Little or No Risk to the environment) and less than 1% (wt.) contained substances which are candidates for substitution.

The total quantity of chemicals discharged into the sea decreased from a peak of 293 402 tonnes in 2009 to 204 570 tonnes in 2019, of which 84% were on the PLONOR list and less than 0,5% (wt.) contained substances which are candidates for substitution.

The use of ranking³ chemicals increased by 7% and their discharge decreased by 3% between 2009 and 2019. The use and discharge of PLONOR chemicals decreased by 18% and 34% respectively over the same period. It is not entirely clear if this was mainly due to an overall reduction in use and discharge and/or a change in categorisation of chemicals resulting in removal from the PLONOR list.   

The use of added chemicals identified for priority action (LCPA) continued to decrease over the 2009 to 2019 period, from 3 929 kg to 111 kg. 

The discharge of chemicals on the LCPA-list was phased out by 2014, and other than a 3 kg accidental permitting of an LCPA discharge in 2016 in the United Kingdom and a 0,5 kg unpermitted discharge in Denmark in 2019 there were no others.

The discharge of chemicals containing substances that are substitution chemicals fell from about 1 755 tonnes in 2013 to 1 012 tonnes in 2019, a 42% decrease.

The use of substitution chemicals with a biodegradation of < 20% or that meet 2 of the 3 PBT criteria decreased from 11 959 tonnes in 2009 to 7 739 tonnes in 2018, a 36% reduction. Similarly, discharge of these substitution chemicals decreased from 1 753 tonnes to 1 162 tonnes, a 35% reduction.

While progress has been made in reducing the use and discharge of chemicals identified as candidates for substitution since the introduction of OSPAR Recommendation 2006/3, more needs to be done to reduce discharges of substitution chemicals.

Discharge of drilling fluids

The discharge of organic-phase fluids ceased in 1996 and no organic-phase fluid discharges have been reported since 2004 in the OSPAR area. The objective of Decision 2000/3 on the Use of Organic-Phase Drilling Fluids and the Discharge of Organic-Phase Fluids Contaminated Cuttings continues to be fulfilled.

In 2019, a total of 11 wells were drilled with organic-phase fluid with cuttings discharged into the sea after treatment to < 1% oil on cuttings. This is the same number as in 2009, and the annual numbers over the period ranged from 7 to 20 wells. Other organic-phase drilling fluids were used in one well in the United Kingdom in 2019 and all the cuttings were injected or transported to shore.

The availability of thermal desorption treatment technologies, which enable the 1% concentration limit to be achieved, has brought an increase in their use offshore, particularly in the United Kingdom. The use of these technologies led to an increase in the discharge of thermally treated organic-phase drilling contaminated cuttings from 0,3 tonnes in 2009 up to a maximum of 23 tonnes in 2016. However, all discharges were significantly lower than the 1% concentration performance standard (see Figure P.6). Less than 0,01 % of all the organic-phase drilling fluids used is discharged by using this technology.

Accidental spills

Accidents or incidents occurring during the transportation of oil and gas by pipeline or tanker, as well as accidental spills from installations have the potential to cause impacts outside the area of production. 

Accidental spills of oil

Over the period 2009 to 2019, the number of accidental spillages of oil to sea varied widely, with 2014 having the highest number of spills (572) and 2019 the lowest (338). While there has been annual variation, it is possible to identify a downward trend in the number of oil spills being reported since 2014. 

The total quantity spilled each year is variable, with a high of 541 tonnes in 2012 when a single large spill in the United Kingdom contributed approximately 400 tonnes to the total, and a low of 44 tonnes in 2016 (see Figure P.7). In 2019, oil spills contributed less than 2% (wt) (106 tonnes) of the total amount of oil released to the sea from offshore oil and gas installations, the remaining 98% (4 096 tonnes) being dispersed oil discharged with produced water. 

There is no discernible trend in the quantity of oil being spilled annually. Spills over 1 tonne account for just 2–4 % of the number of spills but account for 68–96 % of all the oil spilled on an annual basis. Consequently, the quantity spilled annually is very much the result of a small number of larger spills.

Accidental spills of chemicals

Over the period 2009 to 2019, the number of accidental spillages of chemicals to sea also varied widely, with 2014 having the highest number of spills (488) and 2019 the lowest (346). While there was annual variation, it is a possible to identify a downward trend in the number of chemical spills being reported since 2014. The number of larger spills (> 1 tonne) also trended downwards over the period, from 99 in 2009 to 55 in 2019. 

The total quantity spilled each year was extremely variable, with a high of 14 464 tonnes in 2009 and a low of 728 tonnes in 2011 (see Figure P.8) and there was no discernible trend in the quantity of chemicals being spilled annually. Of the chemicals spilled in each year the vast majority – 97-99%) were either on the PLONOR list or were ranking chemicals.

Atmospheric emissions

Although atmospheric emissions are not covered by OSPAR measures, overall reductions have been reported in all atmospheric emissions across the OSPAR area over the last 10 years, most significantly in methane and SO₂ emissions. Over the 2009 to 2019 period:

• CO₂ emissions decreased by 7,5%;
• NO_X emissions decreased by 9,2%;
• Methane emissions decreased by 35%;
• NMVOC emissions decreased by 7,2%; and
• SO₂ emissions decreased by 33%.

As national and EU legislation is introduced to address local, regional, and international Net Zero commitments it is expected that emissions from offshore installations will continue to fall.
This is further discussed under the climate change section.

Input of anthropogenic sound (impulsive, continuous)

There are a number of distinct phases in oil and gas operations which can introduce pressures in the form of underwater noise, ranging from initial seismic exploration to drilling, production and then decommissioning. The most significant underwater noise associated with each phase is dependent upon the nature and scale of the specific activities. Geophysical surveys associated with the exploration and management of hydrocarbon reserves are a source of anthropogenic noise. Drilling for hydrocarbons requires the use of mobile drilling units or drilling equipment installed on fixed platforms, and the position-keeping propulsion mechanisms of some mobile drilling units are also a notable source of noise. Infrastructure installation activities involving underwater hammer piling, and the occasional use of explosives for well abandonment or the decommissioning of facilities, are also sources of underwater noise.

Anthropogenic noise emitted to the marine environment can potentially affect marine organisms in various ways. Impulsive sound sources have been observed to cause temporary displacement of small cetaceans (e.g., harbour porpoises), increased physiological stress in some fish species (e.g., European seabass) and developmental abnormalities in invertebrate larvae. In some cases, they may also be capable of causing more severe effects such as permanent auditory damage or blast injuries. While the effects on individual animals have been shown for a number of species, there is uncertainty as to whether and how the effects of sound on individuals are translated to the population or on ecosystem scale ( 2021 Indicator Assessment – Distribution of Reported Impulsive Sounds in the Sea ).

Reported impulsive noise activity increased overall during the assessment period (2015 to 2019), with most reported activity occurring in the Greater North Sea Region. Seismic airgun surveys were the dominant sound source ( Underwater Noise Thematic Assessment ). Activity can change markedly between years. While it is notable that large-scale seismic surveys were carried out in United Kingdom waters during 2015 and 2016, significant change in activity trends is not expected.

Input of other forms of energy (including electromagnetic fields, light and heat)

Flaring and lighting from offshore installations contribute to the pressures on migratory birds. A significant number of birds of different species migrate across OSPAR Region II (Greater North Sea) at least twice a year or use the Greater North Sea as a feeding and resting area. This migratory behaviour is an essential part of the birds’ natural life cycle. Some species crossing or using the area may become attracted to offshore light sources, especially in deteriorating weather conditions which restrict visibility (e.g., low clouds, mist, drizzle). This attraction can be fatal and may involve large numbers of individuals of many species of birds. OSPAR Region II contains a substantial number of illuminated offshore installations where such attraction can potentially result in mortality. The OSPAR Workshop on research into possible effects of offshore platform lighting on specific bird populations (January 2012) noted that there is evidence that conventional lighting of some offshore installations has an impact on a large number of birds. The evidence is, however, not sufficient to conclude whether or not there is a significant effect at the population level. (See:  Marine Birds Thematic Assessment )

Input of litter (solid waste matter, including micro-sized litter)

A limited number of offshore chemicals contain plastic or microplastic substances which are used and discharged during other offshore operations. 

Man-made infrastructures such as pipelines, cables and structures placed on the seabed are normally protected for a number of reasons, including protection from trawl boards, scouring and pipeline / cable crossings, as well as to provide foundation support, prevent buoyancy and provide stability.

The protection materials include concrete mattresses and sand or grout bags. Sand or grout bags are typically contained in polypropylene sacks. Concrete mattresses are often held together by polypropylene ropes. The life span of these protection materials is such that the plastic substances they contain deteriorate and eventually disintegrate over the extended periods for which they are deployed on the seabed, thus contributing to marine plastic litter and the presence of microplastics. (See:  Marine Litter Thematic Assessment ).

Physical disturbance to the seabed (temporary or reversible) and Physical loss (due to permanent change of seabed substrate or morphology and the extraction of seabed substrate)

Physical impact

Physical disturbance to the seabed and physical loss of seabed will result from the placement of pipelines, installations, cables, and associated structures. Owing to the number and length of pipelines placed on or under the seabed, their overall physical impact is greater than that from other installations.

Pipelines are either placed on the seabed or buried partly or completely in the sediment. The actual placement of the pipelines causes impacts, particularly in areas where they are to be trenched and buried. Pipelines are buried to ensure that they are not buoyant and remain in place; this also reduces the potential hazards for fishing activities.

The footprint of the pipeline, or the affected zone around it, depends on length, diameter, the depth of burial or build-up of gravel, the presence of hard substrate, and other factors. Pipeline burial causes the largest impact during the installation phase because of the considerable disturbance to the seabed and to the mobilisation of sediment. The area of impact during pipeline burial is considered to be within 10–20 m of the line, but once buried, pipelines usually have insignificant impacts.

Due to differences in bottom topography, geology, water mass movement and other environmental factors such as the sensitivity of benthic species and habitats (particularly cold-water corals and sponges), the pressures resulting from the introduction of these structures will vary according to the natural conditions in the different OSPAR Regions.

The decommissioning of pipelines and removal of installations and associated infrastructure can cause sediment disturbance and subsequent localised impacts. Similarly, if there is a cuttings pile at the base of the platform this may be disturbed and the contaminated cuttings re-suspended. On occasions it may not be possible to remove the lower parts of a platform, such as concrete substructures and the footings of the largest steel installations.

Cuttings

The drilling of both hydrocarbon and injection wells generates drill cuttings, which are particles of crushed rock produced by the action of the drill bit as it penetrates the earth. The chemical and mineral composition of drill cuttings reflects that of the rock layers penetrated by the drill. Cuttings contain the residues of the drilling fluids used in the wells, and in some cases also reservoir hydrocarbons. Cuttings piles arise from drilling operations where the drilled cuttings and associated drilling fluids are discharged at the location of the well and then accumulate depending on the water current in the region. It is more than 20 years since the discharge of organic-phase fluid-contaminated drill cuttings was prohibited, but historic cuttings piles are still present under some platforms. Such cuttings piles have been identified as a possible source of oil release into the marine environment, due to remobilisation of residues and natural leaching into the water column. Studies have shown that the leakage of oil from these cuttings piles is low, and their individual footprints are contracting due to natural degradation. However, concerns have been expressed about possible releases of oil, chemicals, and heavy metals from the disturbance of historic cuttings piles, either during decommissioning activities or from bottom trawling after decommissioning. 

The discharge of cuttings drilled with water-based fluids and discharge of treated cuttings drilled with organic-phase fluids may cause sediment modification and some smothering in the near vicinity of the well location. The impacts from such discharges are localised and transient but may be of concern in areas with sensitive benthic fauna, for example corals and sponges.

Input or spread of non-indigenous species

The introduction of hard substrates such as offshore installations and of protection material including sand, rock, gravel, and concrete mattresses facilitates the establishment of invasive species by providing stepping stones. However, healthy ecosystems established on/around installations may also offer protection against invasive species. This is further elaborated in the thematic assessment covering non-indigenous species. (See:  Non-Indigenous Species Thematic Assessment )

Carbon dioxide storage

The pressures from carbon dioxide storage, including development and decommissioning activities, could be similar to pressures from offshore oil and gas activities. There is the risk of carbon dioxide leakage from the storage site, which may have negative effects on the receptors in the marine environment, including the potential for ocean acidification if carbon dioxide leakage were to occur. While scientific knowledge of the environmental risks of carbon dioxide storage in geological formations is developing, the need for improving and refining the reporting to OSPAR on environmental monitoring of carbon dioxide storage projects has been identified.

Footnotes

²“Aliphatics” and “aromatics” are defined by the reference method set in OSPAR Agreement 2005-15 (Solvent extraction, Infra-Red measurement at 3 wavelengths). In that context, “aliphatics” and “dispersed oil” mean the same thing.

³Ranking chemicals being the combination of inorganic chemicals with LC50 or EC50 greater than 1 mg/l and ranking chemicals, which includes substances ranked according to OSPAR Recommendation 2000/2 and don’t fall into another category.