4. Discharges to sea
Discharges to sea consist primarily of discharges associated with well drilling and produced water. Produced water is water which follows the oil from the reservoirs. Drilling discharges are mainly comprised of rock particles (drill cuttings) from the borehole and drilling fluid. Discharges are only permitted from wells drilled using water-based fluid. Oil-based fluids can be permitted by NEA if contamination from oil-based fluids stands at less than ten grams of base oil per kilogram of cuttings.
Fig. 3 illustrates that drilling activity in 2022 was significantly lower than in the peak year of 2019, with a total of 182 wells drilled. Thirty-four of these were exploration wells. Discharges from produced water were at their highest in 2007, totaling approximately 160 million Sm3. In 2022 total discharges stood at 116 million Sm3.
4.1 Discharges from drilling
Drilling activity showed a slight decrease in 2022. The number of new production wells drilled in 2022 was 148. The number of exploration wells stood at 34, compared to 40 in 2021.
The fluid used for drilling wells has multiple functions. It transports the drill cuttings up to the platform and is also used to lubricate and cool the drill bit. In addition, it prevents the borehole from collapsing. Last, but not least, it keeps the well pressure stable, preventing uncontrolled oil and gas blowouts.
The industry primarily uses two types of drilling fluid: oil-based and water-based. Synthetic drilling fluids were also used previously, and these were either ether-based, ester-based or olefin-based. In recent years, synthetic-based fluids are rarely used.
The discharge of oil-based or synthetic-based drilling fluids, or cuttings contaminated with these, is prohibited if the oil concentration exceeds one per cent by weight. One per cent by weight equates to 10 grams of oil per kilogram of cuttings. Drill cuttings discharge contaminated with oil-based or synthetic-based drilling fluids containing less than one per cent by weight of oil is only permitted if authorized by the NEA. Used oil-based drilling fluids and contaminated cuttings are either transported onshore as hazardous waste for carefully controlled treatment or injected into specially designated wells beneath the seabed.
Fig. 3: Number of wells drilled on the NCS (Source: Norwegian Petroleum Directorate)
Fig. 4: Disposal of oil-based drilling fluid
Field operators use water-based drilling fluids as far as possible, also to reduce the quantities of waste requiring treatment. Oil-based fluids are more effective from a technical drilling perspective than water-based fluids, and more complex wells will have a greater need to use oil-based fluids.
The use of oil-based drilling fluids dropped by almost 5% in 2022 compared to 2021, as illustrated in Fig. 4. The quantity of oil-based cuttings contaminated by drilling fluids and injected sub-surface shows a downward trend, with the ratio falling from 9% to 7%.
The quantities of drill cuttings presented in Fig. 5 are based on calculations of the rock which has been drilled out. However, the quantities of drill cuttings registered as hazardous waste transported onshore (see Chapter 8) are considerably larger. Cuttings from many fields are slurrified by adding water so that they can be handled more easily from platform to ship to shore. This nonconformity is therefore largely due to water being added to the drill cuttings before they are received onshore.
The quantity of oil-contaminated drill cuttings sent onshore as waste has decreased from 2020 to 2022. This quantity stood at just below 88,000 tons in 2020, compared to 70,000 tons in 2022. The water and drill cuttings are separated onshore. Whilst the water is treated and discharged to sea, the drill cuttings are further treated in compliance with current regulations.
Fig. 5: Disposal of drill cuttings contaminated with oil-based drilling fluids
Fig. 6: Disposal of drill cuttings from wells drilled using water-based drilling fluids
Discharges from drill cuttings drilled with water-based fluids stood at approximately 85,000 tons in 2022, representing a decrease of 17% from the previous year, as illustrated in Fig. 6. Water-based fluids contain largely natural components such as clay or salts. These substances are classified as green in the NEA´s classification system. In accordance with OSPAR, these substances pose little or no risk to the marine environment when discharged.
The potential impact of these discharges is followed closely by extensive environmental monitoring (see Chapter 5.3).
Discharges from oily water
Oily water discharges from petroleum operations on the NCS derive from three main sources, with produced water accounting for the largest contribution.
- Produced water
This is water which comes up from the reservoir along with oil and gas. Produced water is complex and can contain several thousand individual components. Routine analyses are therefore carried out. When produced water is injected to enhance production, the water will mix with formation water. The produced water will also contain various chemical additives in order, for example, to inhibit bacterial growth, corrosion, and emulsion. The water is treated on the offshore installations using various technologies prior to being discharged to sea. These technologies help to keep the oil content as low as possible. The regulatory threshold for the oil concentration in produced water discharged to sea is 30 milligrams per litre (mg/l).
- Displacement water
Seawater is used as ballast in the storage cells on some platforms. If oil is to be stored in these cells, the water must be treated prior to discharge. The seawater has a limited contact area with the crude, so the quantity of dispersed oil is normally small. The discharged volume depends on the level of oil production.
- Drainage water
Water falling as rain and water used to hose down the decks may contain chemical residues and oil. Drain water discharges make up only a small proportion of the total volume of water discharged.
Particles and sand contaminated with oil are collected in separators and must be hosed periodically, known as “jetting”, which also may contribute to discharges to sea. Particles may still be contaminated with oil following treatment in accordance with regulatory requirements, but the volume of oily water discharged to sea is marginal.
Oily water can also occur from hosing down processing equipment, from an incident, or from droplets forming when burning oil for well-testing purposes or when carrying out well maintenance work.
Produced water discharges
Fig. 7 shows the historic development of produced water volumes discharged to sea and volumes reinjected into the bedrock. For many years, produced water discharges from the NCS were predicted to increase and were expected to exceed 200 million Sm3 from 2012 to 2014. However, discharges peaked at 160 million Sm3 in 2007 and declined substantially in the years that followed. From 2012 to 2015, annual discharges rose to almost 150 million Sm3. Since 2015 they have dipped again, and in 2022, they stood at 116,127 million Sm3, which is a decrease from 127 million Sm3 in 2021. The quantity of dispersed oil to sea stood at 1,490 tons, distributed across all types of discharge. The greatest discharges are found on mature fields with large volumes of produced water, where produced water accounts for 97% of the oil discharged to sea.
On certain fields where conditions allow, all or parts of the produced water is injected back into the bedrock. Water injection increased substantially from 2002 and has been at around 20% in recent years. In 2022, approximately 23% of the water, or roughly 43 million Sm3 was injected, which is approximately the same as in the previous year.
On new fields, produced water consists solely of water already present in the reservoirs. Water injection, however, leads to an increase in produced water volumes as the field matures. The water is injected to maintain the reservoir pressure and to improve the recovery factor from the reservoir. This is primarily treated seawater. The recovery factor from fields on the NCS is generally significantly higher than in the rest of the world. However, produced water discharges are comparable to international figures.
Fig.7: Produced water volumes discharged to sea and injected into bedrock
Fig. 8: Ratio between produced water and oil
The ratio between the volumes of produced water and produced oil on the NCS, as illustrated in Fig. 8, has generally shown a tendency to rise, although it dipped in 2016. This is probably due to production starting up on several new fields. The start-up of the Johan Sverdrup field contributed to increased oil production whilst water production did not increase at the same rate.
The results from risk-based modelling and from environmental monitoring have not yet indicated any significant environmental impact caused by discharging produced water (see Chapter 5.3). An article by Beyer et al (2020) indicates mild acute environmental impact associated with produced water in the water column and is limited to the vicinity of the discharge.
Discharges of other water types
Fig. 9 illustrates that displacement water dominates discharges of other water types. Discharge volumes decreased steadily up to 2009-2011. Post-2011, volumes hovered at approximately 30 million Sm3. In 2022, displacement water discharges totalled approximately 32 million Sm3.
Fig. 9: Discharges to sea of other water types
Fig. 10:
Oil Concentration in produced water discharged to sea
Discharge of oil with water
Oily water is treated prior to being discharged to sea. Different types of technology are used on different fields. The average oil content in produced water for the entire NCS in 2022 was 11.8 mg/l, with the government threshold standing at 30 mg/l. The water volume decreased by 11 million m3, whilst the concentration of dispersed oil rose marginally compared to 11.1 mg/l in 2021, as illustrated in Fig. 10. If we look at total water discharges, the average oil content stood at 9.5 mg/l in 2022.
The amount of oil discharged to the sea with produced water went down from 1,409 tons in 2021 to 1,370 tons in 2022, as illustrated in Fig. 11. A total of 1,445 tons of oil were discharged with water from drainage, displacement, produced water and jetting. In 2021, this figure stood at 1,531 tons.
Fig. 11: Oil discharges accompanying water discharges from the NCS
Discharge of other substances accompanying produced water
Produced water has been in contact with the bedrock over a long period of time and therefore contains a number of naturally occurring substances. In addition to oil, a typical composition will include mono- and polycyclic aromatic hydrocarbons (PAH), alkylphenols, heavy metals, naturally radioactive materials, organic substances, organic acids, inorganic salts, mineral particles, sulphur, and sulphides. The composition will vary from field to field, depending on the properties of the bedrock. Generally, the content of environmentally harmful substances is low and similar to the normal base level for these substances in seawater.
An article which describes the potential modelled effects of PAH on cod roe and spawn in the North Sea was published by Nepstad and his colleagues in the 2021 Marine Pollution Bulletin.
The article concludes, inter alia, that “In all simulations we find the predicted total internal PAH concentration (26 components) to be below 1.2 nmol/g, a factor of 1,000 less than concentrations commonly associated with acute narcotic effects.”
Experiments and tests were also carried out as part of the water column monitoring on the Ekofisk field in 2021, with the results thereof being presented in the autumn of 2022 during the Forum for Offshore Environmental Monitoring (see Chapter 5.5).
4.2 Chemical discharges
Chemicals are assessed according to their environmental properties, including persistence, potential for bioaccumulation and toxicity (PBT). The Norwegian government has also specified criteria in the Activities regulations and guidelines for reporting from offshore petroleum operations.
Chemical additives which are controlled by discharge permit requirements are divided into four categories in accordance with the classification system in the Activities regulations:
Green Zero or minimal environmental impact. May be discharged without special conditions.
Yellow Normally acceptable environmental impact. Discharge permit is required, but usually approved.
Red These chemicals must be prioritized for substitution with chemicals in green or yellow categories.
Black Discharge is not permitted. Exceptions may be made under extenuating circumstances, such as if crucial for safety reasons.
A more detailed description of the classification system may be found in the NEA´s M-107 Guidelines on reporting from offshore petroleum operations.
Discharges of chemical additives from Norwegian petroleum operations in 2022 totaled approximately 172,000 tons. This is a decrease of around 9% since 2021. Green chemicals accounted for 90% of the total, whilst red and black chemicals accounted for approximately 0.2% of the total, as illustrated in Fig. 12.
Replacing chemicals with less environmentally harmful alternatives is an important part of the environmental initiative to reduce the potentially harmful effects from offshore discharges. Operators carry out regular assessments on the chemicals used to determine whether they can be substituted. The extensive substitution of chemicals has reduced the release of the most environmentally harmful chemicals to a fraction of its level just ten years ago.
Fig. 12: Breakdown of discharges of chemical additives from the NCS by the NEA´s colour categories
Between 2011 and 2014 there was a substantial increase in the reported discharges of black chemicals. This is primarily because firefighting foam discharges were not previously reported, as fire foam was classified as a contingency chemical. Alternatives with less environmentally harmful properties are now available, meaning that firefighting foam falls into the category of chemicals for substitution. The new alternatives are now implemented on all NCS fields.
The increase observed in 2020 is partly because lubricants leaking from submerged seawater pumps had to be reported as black category discharges. Discharges from black category substances are expected to be reduced further in the coming years, due to the ongoing substitution work. There are now alternatives available to the lubricants used in submerged water pumps.
Black chemical discharges stood at 3.7 tons in 2022, compared to 5.5 tons in 2021, as
illustrated in Fig. 13. Several of the chemicals used in the production of freshwater offshore lack Harmonized Offshore Chemical Notification Format (HOCNF) and are therefore categorized as black.
Fig. 13 shows that red category chemicals experienced a steady increase in reported discharges from 2013, when they were down to approximately 8 tons. In 2022, 419
tons of red chemicals were discharged, down from 450 tons in 2021.
The reason for the apparent increase in recent years is the change in reporting requirements. This also applies to the antifouling agent sodium hypochlorite, used in
the treatment of drinking water and in indoor swimming pools onshore, which has
been reclassified from yellow to red.
2020 also saw the introduction of a new reporting requirement for chemicals used in
the production of freshwater. Several fields use their own hypochlorite, which must now be reported and has been classified as red.
Fig 13: Discharges of chemical additives from the NCS by the NEA´s categories
4.3 Zero emissions target initiative
The zero-emissions target initiative started as a collaboration between the industry and the Norwegian government in the Zero Emissions Project in 1998 and was further developed in 2002 and 2003. The term “zero emissions” has been the subject of debate and interpretation. The Zero Emissions Group – an advisory collaborative body consisting of representatives from the NEA, (formerly the Norwegian Pollution Control Authority), the Norwegian Petroleum Directorate (NPD) and the Norwegian Oil Industry Association (OLF) – clarified in 2003 that a literal interpretation of the zero emissions target for all types of emissions is neither environmentally advisable nor achievable. In many cases, the term “minimization” may also suffice.
The zero-emissions target initiative is anchored in a Risk Based Approach (RBA) from OSPAR, whereby risk assessments are used to implement measures where a) it is most environmentally advantageous to do so and b) a sensible cost/benefit balance can be achieved. The zero emissions initiative has led to a significant reduction in oil and chemical discharges to sea. Oil discharges to sea are reduced by reinjection on many fields and significant investments have been made in water treatment prior to discharge. The most environmentally hazardous chemical additives were reduced by over 99%, - a target which was achieved prior to 2010. Operators continue, however, to work on assessing and phasing out environmentally hazardous chemicals. The discharge of those chemicals categorized as red and black usually accounts for less than 1% of discharges.
The potential environmental impact associated with produced water discharges is assessed for each individual field through analyses and modelling calculations and is referred to as the EIF (Environmental Impact Factor). The oil in produced water accounts for a very small proportion of the risk factor associated with the discharge, whilst chemical additives may play a larger role. The EIF refers to each specific discharge and the purpose is to assess which components in the produced water pose a risk, thus warranting the substitution of chemicals containing these components.
Certain chemical additives and natural components from the bedrock discharged with produced water may potentially have harmful effects on aquatic organisms. This is supported by research and EIF calculations. This applies primarily in concentrations located close to the point of discharge, typically within a hundred to a thousand metres. Chemical additives which contribute to environmental hazards are regularly assessed and substituted. Offshore Norge´s guideline 084 for EIF modelling and calculation was updated and published in the autumn of 2022.
The results obtained from water column monitoring on the NCS in 2021 indicate that significant acute biological effects from the discharges can not be proven beyond the immediate vicinity of the point of discharge. Research and modelling have also been carried out and have not indicated any significant effects from produced water discharges to date. Research was continued in 2022.
Significant investments in treatment technology and injection have been made to reduce oil discharges from produced water. The discharges from most fields are far lower than the regulatory threshold of 30 mg/l. For various reasons, however, certain fields have stability issues with their injection plants and treatment processes, and therefore have a higher level of discharges, particularly when phasing in new well streams.
The Risk Based Approach under OSPAR started with the Offshore Industry Committee (OIC) Decision in 2008. A holistic approach and a set of guidelines for the initiative were developed in 2012. The guidelines recommended that the risk should be characterized by:
- Whole Effluent Testing (WET)
- Substance-based approach applying EIF – SB HC50
- A combination of both
The RBA campaign was approved for introduction to the NCS between 2013 and 2019. Final guidelines were issued in March 2020 by the (OIC) under OSPAR, which discussed the RBA in its Intersessional Correspondence Group (ICG), concluding, inter alia, that;
- A report should be prepared summarizing the findings of RBA
- “Recommendation” 2012/5 and its proposals should potentially be revised according to RBA (OIC19/2/1 Ass.1 & OIC19/2/1 Add.2.
The International Association of Oil and Gas Producers (IOGP) published a guide for RBA in autumn 2020. It describes the RBA approach and the recommended implementation of its principles, where the results determine whether the risk level is acceptable, or whether further measures ought to be implemented.
The NEA tasked its Expert Group with providing an overview of the greater environmental impact from produced water discharges to be expected in the Barents Sea and in arctic conditions, as opposed to on the NCS, and in the Norwegian Sea and North Sea.
The Expert Group concluded towards the end of 2019 that, based on the information gathered, there was no reason to believe that there is a systematic pattern indicating that organisms and ecosystems in the Barents Sea are significantly more sensitive towards chemical pollution and ecotoxicological effects than in other parts of the NCS. This accords with findings made in the PROOFNY study during the Marine and Coastal Program from 2005 to 2015, as well as with environmental monitoring.
Chemicals which contribute towards environmental impact are subject to regular assessment and substitution.
4.4 Unintentional spills
Unintentional spills are defined as unplanned emissions/discharges, occurring suddenly and without a permit. The potential environmental impact of such releases will depend upon the properties and the volume of the substance spilled, and upon the time and place of the spill.
Unintentional spills are classified according to three main categories:
- Oil: diesel, heating, crude, spill oil and others
- Chemicals and drilling fluids
- Emissions to air
The oil and gas industry prioritizes preventive measures very highly. These are measures (barriers) which prevent unwanted incidents from occurring, thereby reducing the number of unintentional spills. All unintentional spills are reported to the NEA in the annual emission/discharge reports.
Unintentional oil spills
The total number of unintentional spills of all oil types has generally declined over the past twenty years. The marked drop in the number of spills from 2013 to 2014 is due to a clarification of the regulations, leading to less spills smaller than 50 litres, whilst the number of unintentional chemical releases in the same volume category increased correspondingly.
Fig. 14: Number of unintentional oil spills to sea on the NCS
Fig. 15: Number of unintentional crude oil spills to sea on the NCS
In 2022 there were 43 incidents involving oil spills, compared to 52 in 2021, as illustrated in Fig. 14. There have been approximately 10 – 15 incidents per year in recent years involving spills of over 50 litres. In 2022 there were a total of 20 spills exceeding 50 litres of oil, 8 of which were larger than 1 m3. The two largest isolated spills in 2022 measured 18 m3 and 16 m3.
There has been a marked decline in crude oil spills over the past 10 – 15 years, as illustrated in Fig. 15. In 2022 there were 25 spills in this category, 5 of which measured over 1 m3.
The total volume of oil unintentionally spilled varies substantially from year to year, as illustrated in Fig. 16. Statistics tend to be characterized by large, isolated incidents. 2007 saw the second-largest spill on the NCS, measuring approximately 4,000 m3, whilst total spills since then have ranged from 10 m3 to 200 m3. In 2022 the total volume stood at 61 m3.
Fig. 16: Discharge volumes from unintentional oil spills on the NCS
Fig. 17: Total unintentional chemical spills on the NCS distributed across three sizes of spill
Unintentional chemical spills
The number of unintentional chemical spills does not show the same downward trend as for unintentional oil spills. The marked increase in 2014 to 237 spills can be attributed to a clarification of the regulations, leading to fewer oil spills being reported and more chemical spills being reported. The number of spills in 2022 totalled 194, of which 27 were larger than 1 m3. Their distribution is illustrated in Fig. 17.
The overall volume of unintentional chemical spills in 2022 was 388 m3, denoting a marked increase from 2021 when they totalled 124 m3. Fig. 18 illustrates a number of larger, isolated incidents which explain the increase in volume; one spill of 160 m3
during the loading of drill water and two spills of over 20 m3 from water-based drilling fluids (56 m3 and 29 m3). The unintentional spills were broken down as follows: 93% green chemicals, 6.6% yellow chemicals, 0.3% red chemicals and 0.2% black chemicals.
Discharged volumes were dominated from 2007 to 2010 by individual years when leaks from injection wells were detected. These wells have now been shut in.
Fig. 18: Total volume of unintentional chemical spills
Subsea leak detection
A detection system is an important barrier used to detect leaks and other unintentional spills as swiftly as possible. The system is designed to provide essential information so that the relevant measures can be implemented as quickly as possible, also ensuring the notification and reporting of the spill in compliance with regulatory requirements. All installations on the NCS today have one or several leak detection technologies installed.
The number of incidents involving unintentional spills from subsea installations is low, and is highlighted annually in the Norwegian Petroleum Authority´s RNNP (Trends in Risk Level) report.
Large spills can be detected immediately by, for example, process monitoring, as well as by daily satellite monitoring and daily radar monitoring of the sea surface. The detection of smaller spills from subsea installations can, however, prove more challenging. Modern subsea installations are equipped with a local system for leakage detection, but this is not always the case for older installations built before this type of technology was available.
The NEA and the PSA (Petroleum Safety Authority) carried out a joint audit initiative in 2020/early 2021 to inspect the operators´ routines and equipment for detecting leaks of oil, gas, and chemicals from subsea installations on the NCS. Common deviations were observed amongst all operators, including routines for the detection of minor leaks and performance requirement procedures. A work group was therefore established under the directive of Offshore Norway to investigate this jointly.
The findings from these audits are largely due to insufficient risk assessments of potential spills from individual installations, as well as insufficient documentation and assessment of the systems´ capabilities. The industry is currently working to resolve these issues, and assessments are ongoing to identify the gaps and how best to close them. Technological limitations must also be considered, as most leak detection systems can only cover a limited area and cannot always detect small spills from a distance. For this reason, inspections may be the only means of detecting the smallest spills. Inspections are carried out regularly on all fields.
There are also several subsea installations on the NCS having low or negative pressure relative to the surrounding water mass. These fields are more likely to experience water leaking into the system than oil and gas discharges to sea.