4. Discharge to sea
Discharges to sea consist primarily of discharges from drilling of wells and release of produced water. Produced water is water that accompanies the oil from the reservoirs. Drilling discharges are mainly comprised of rock particles from the bedrock and drilling fluid. Discharges of drill cuttings contaminated with water-based drilling fluid is only allowed with permission from the Norwegian Environment Agency. This also applies to drill cuttings contaminated with oil-based drilling fluid and if contamination from oil-based fluids is less than ten grams of base oil per kilogram of cuttings.
Figure 3 shows that drilling activity decreased slightly from 2023 to 2024, with a total of 178 wells drilled, of which 44 were started exploration wells. Discharges of produced water reached a peak in 2007 at just over 160 million Sm³, as shown in Figure 7. In 2024, total discharges amounted to 116 million Sm³.
4.1 Discharges from drilling
The drilling fluid used in well drilling serves many functions. It transports cuttings to the platform while lubricating and cooling the drill bit. At the same time, the drilling fluid prevents the borehole from collapsing. Most importantly, it keeps the well pressure stable and prevents uncontrolled oil and gas blowouts.
The industry primarily uses two types of drilling fluids: oil-based and water-based.
The discharge of oil-based or synthetic drilling fluids, or cuttings contaminated with these, is prohibited if the oil concentration exceeds one percent by weight. One percent by weight correspond to ten grams of oil per kilogram of cuttings. Drill cuttings discharge contaminated with oil-based or synthetic drilling fluids containing less than one percent by weight of oil is only permitted if authorised 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.
Figure 3: Number of wells drilled on the NCS (Source: the Norwegian Offshore Directorate).
Figure 4: Disposal of oil-based drilling fluid.
Operators use water-based drilling fluids as far as possible to reduce the quantities of waste requiring treatment. Oil-based drilling fluids are more effective from a technical drilling perspective than water-based drilling fluids, and more complex wells will have a greater need for the use of oil-based drilling fluids.
The use of oil-based drilling fluid increased in 2024 compared to 2023. The quantity of oil-based cuttings contaminated by drilling fluids and injected sub-surface have shown a downward trend in recent years but increased slightly from 2023 to 2024, as shown in Figure 4.
The quantities of drill cuttings presented in Figure 5 are based on calculations of the rock which has been drilled out. The quantities of drill cuttings registered as hazardous waste transported onshore (see Chapter 7) are, however, significantly larger. This is because cuttings from many fields are slurrified by adding water to make them easier to handle from the platform to the vessel and then to shore.
The quantity of oil-contaminated drill cuttings transported onshore as waste decreased from 2023 to 2024. In 2023, the amount was just under 88,000 tonnes, and in 2024, 69,000 tonnes. The water and drill cuttings are separated on shore. Whilst the water is treated and discharged to the sea, the cuttings undergo further treatment in accordance with current regulations.
Figure 5: Disposal of drill cuttings contaminated with oil-based drilling fluids.
Figure 6: Disposal of drill cuttings from wells drilled with water-based drilling fluids.
In 2024, discharges from drill cuttings drilled with water-based drilling fluid were approximately 70,000 tonnes, a reduction of 5 percent from the previous year, as shown in Figure 6. Water-based drilling fluids mainly contain natural components such as clay or salts. These substances are classified as green in the NEA’s classification system. According to OSPAR, they pose little or no risk to the marine environment when discharged.
The potential impact of these discharges on the environment is monitored through extensive environmental monitoring (see Chapter 5.5).
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 that accompanies oil and gas from the reservoir. Produced water is complex and can contain several thousand different individual components. Routine analyses of the water are therefore conducted. When water is injected to enhance production, it will mix with formation water. The produced water will also contain various chemical additives, for example, to inhibit bacterial growth, corrosion, and emulsion. On the offshore installations, the water is treated using various treatment technologies before being discharged to the sea. Different treatment technologies help to keep the oil content as low as possible. The regulatory threshold for oil concentration in produced water discharged to the sea is 30 mg/l. - Displacement water
Seawater is used as ballast in storage cells on some platforms. When oil is to be stored in the storage cells, the water must be treated prior to discharge. The seawater has a limited contact area with the crude oil, so the quantity of dispersed oil is usually low. The discharged volume depends on the oil production. - Drainage water
Rainwater and water washed off the decks may contain chemical residues and oil. Drain water discharges make up only a small proportion of the total volume of water discharged.
"Other oily water" is also reported. Other oily water refers to all oily water that is not considered drainage water, produced water or displacement water. For example, particles and oil-contaminated sand that are collected in separators must be flushed out from time to time, known as jetting. Some oil adheres to the particles after the water has been treated according to the requirements, but the volume of oily water discharged to sea is marginal. Oily water can also occur from hosing down processing equipment, in connection with incidents, or from the oil droplets forming when burning oil during well testing and well maintenance work.
Discharges of produced water
Figure 7 shows the historical development of produced water volumes discharged to sea and reinjected into the bedrock. Projections for discharges of produced water from the NCS pointed upward for many years and were expected to exceed 200 million Sm³ from 2012 to 2014. However, discharges peaked at 160 million Sm³ in 2007 and declined significantly in the following years. From 2012 to 2015, discharges increased to nearly 150 million Sm³. However, after 2015, they were reduced once again, and in 2024, they amounted to 116 million Sm³. The industry has worked actively for many years to keep the oil content in produced water low, with BAT assessments for treatment technology and injection for each installation. The quantity of dispersed oil to sea was 1,475 tonnes, distributed across all types of discharges. The largest discharges occur on mature fields with large volumes of produced water and oil from produced water accounts for 95 percent of the oil discharged to sea.
On certain fields, where conditions allow, all or parts of the produced water is reinjected into the bedrock. Since 2002, injection has increased significantly and has been around 20 percent in recent years. In 2024, nearly 30 percent of the produced water was injected (49 million Sm³), a slight increase from the previous year (46 million Sm³).
On new fields, produced water consists solely of water already present in the reservoirs. However, the injection of water leads to an increase in produced water volumes as the field matures. Water is injected to maintain reservoir pressure and increase the oil recovery rate from the reservoir. This is primarily treated seawater. The oil recovery rate from fields on the NCS is generally significantly higher than the recovery rate worldwide. Despite this, discharges from the NCS are comparable to international figures.
Figure 7: Produced water volumes discharged to sea and reinjected into the bedrock.
Figure 8: Concentration of oil in the discharge of produced water to the sea.
Figure 9: Ratio between produced water and oil.
Before oily water is discharged to the sea, it is treated. Different technologies are used on different fields on the NCS. The average oil content in produced water for the entire shelf in 2024 was 11.9 mg/l, while the regulatory threshold is 30 mg/l. As of 1 January 2028, a new regulatory requirement enters into force following an amendment to Section 60 of the Activities Regulations. The amendment stipulates that the oil content must not exceed 15 mg/l, calculated as a weighted average over the calendar year. Offshore Norge submitted a consultation response to the amendment proposal in autumn 2024.
The ratio between the volumes of produced water and produced oil on the NCS, shown in Figure 9, has slightly declined since 2019. This is likely due to the startup of production on several new fields. The startup of the Johan Sverdrup field, for example, contributed to higher oil production while water production did not increase correspondingly.
Both risk-based modelling and environmental monitoring studies have so far not indicated any significant environmental impact caused by discharges of produced water (see Chapter 5.5). An article by Beyer et al. (2020) indicates mild acute environmental impact associated with produced water in the water column, limited to the vicinity of the discharge.
Discharges of other types of water
Figure 10 shows that discharges of other types of water are dominated by displacement water. Discharge volumes decreased steadily until around 2010. Since 2011, discharge volumes have hovered at around 30 million Sm³. In 2024, displacement water discharges totalled approximately 32 million Sm³.
Figure 10: Discharge volumes to the sea of other types of oily water.
The amount of oil discharged to the sea with produced water increased from 1,305 tonnes in 2023 to 1,401 tonnes in 2024, as shown in Figure 11. A total of 1,475 tonnes of oil were discharged with water from drainage, displacement, produced water, and jetting in 2024. In 2023, this figure was 1,377 tonnes.
Figure 11: Oil discharges accompanying water discharges from the NCS.
Discharges of other substances accompanying produced water
Produced water has been in contact with the bedrock over an extended period of time and therefore contains a number of naturally occurring substances. In addition to oil, a typical composition includes mono- and polycyclic aromatic hydrocarbons (PAHs), alkylphenols, heavy metals, naturally occurring radioactive materials, organic matter, organic acids, inorganic salts, mineral particles, sulphur, and sulphides. The composition will vary between fields depending on the properties of the bedrock.
4.2 Chemical discharges
Chemicals are assessed according to their inherent ecotoxicological properties, including their persistence, potential for bioaccumulation, and toxicity. Section 62 of the Activities Regulations stipulates requirements for ecotoxicological testing of chemicals. In addition, Norwegian authorities require comprehensive environmental assessments under Section 64 of the Activities Regulations. These assessments must cover the quantities, timing, and locations of the discharges, as well as the properties of the chemicals involved.
Chemical additives that are subject to discharge permit requirements are divided into the categories green, yellow, red and black, as described in Section 63 of the Activities Regulations.
Chemicals classified in the black and red categories, as well as in yellow subcategories 2 and 3, may only be selected when required for technical or safety reasons, or when they represent the documented option with the lowest environmental risk. These must also be prioritised for substitution.
Replacing chemicals with less environmentally harmful alternatives, known as the substitution obligation, is an important part of the environmental initiative to reduce potentially harmful effects from offshore discharges. Operators regularly assess the chemicals used to determine if they can be substituted. Extensive chemical substitution has reduced the release of the most environmentally hazardous chemicals to a fraction of what they were just ten years ago.
Discharges of chemical additives from Norwegian petroleum operations in 2024 totalled approximately 167,000 tonnes. This is an increase of about 3 percent from 2023. About 90 percent of the discharges were green chemicals. Red and black chemicals together accounted for about 0.25 percent of the discharges, and the discharges of both red and black chemicals have been reduced since 2023. The distribution of the various categories is shown in Figure 12.
Figure 12: Distribution of discharges of chemical additives from the NCS by the NEA’s colour categories.
Discharges of black chemicals in 2024 were 3.5 tonnes, down from 4.1 tonnes in 2023, as shown in Figure 13.
There has been a steady increase in reported discharges of red-category chemicals since 2013, when the volume was down to around 8 tonnes. The apparent increase in recent years is due to changes in reporting requirements. For instance, the antifouling agent sodium hypochlorite, which is also used in drinking water treatment and indoor swimming pools, was reclassified from yellow to red.
In 2024, 408 tonnes of red chemicals were released, roughly the same level as in 2023.
Furthermore, Figure 13 shows an increase of 4,550 tonnes for discharges of green chemicals from 2023 to 2024, while discharges of yellow chemicals increased by 471 tonnes.
Figure 13: Discharges of chemical additives from the NCS categorised by the NEA.
4.3 Unintentional spills
Unintentional spills are defined as unplanned emissions/discharges that occur suddenly and without a permit. The potential environmental impact of such releases will depend on the properties of the substance spilled, the volume, and the time/location of the spill.
Unintentional spills are classified in three main categories:
- Oil: diesel, fuel oil, crude oil, waste oil, and other oils
- Chemicals and drilling fluids
- Gas emissions to sea and air
The oil and gas industry prioritises mitigating measures. These are measures (barriers) that 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.
It has been a priority for the petroleum industry to contribute to increasing knowledge about the actual potential for impact and to develop methods for communicating this in a way that provides a complete picture of possible outcomes and uncertainties. This includes understanding when environmental resources are at their most vulnerable, when they are present, and which activities pose the highest environmental risks. Examples of such activities include the mapping and monitoring of seabirds (SEAPOP and SEATRACK), research on the effects on fish and other resources in the water column (such as PROOFNY and SYMBIOSES), and research and development of models to predict the presence of seabirds and marine mammals (for instance MARAMBS).
Unintentional oil spills
The total number of unintentional spills of all types of oil has generally decreased over the past 20 years. The marked decrease in the number of spills from 2013 to 2014 is due to a clarification of regulations, resulting in fewer oil spills of less than 50 litres, while the number of unintentional chemical releases in the same volume category increased correspondingly.
Figure 14: Number of unintentional oil spills to sea on the NCS.
Figure 15: Number of unintentional crude oil spills to sea on the NCS.
In 2024, there were 36 incidents involving oil spills compared to 41 in 2023, as shown in Figure 14. For discharges exceeding 50 litres, 10 to 15 incidents have been reported annually in recent years (except in 2022, when the number rose to 20). In 2024, there were a total of 12 spills exceeding 50 litres, of which 7 were greater than 1 m³. The largest isolated spill in 2024 was 75 m³, an incident at Njord in December.
On New Year's Eve 2024, around 75 m3 of crude oil was accidentally released through the produced water system at Njord. 25–30 percent of the spill (around 20 m³) was transformed into wax-rich oil lumps, some of which – for the first time on the Norwegian continental shelf – reached the shore. In spring 2025, nearly 10 m3 of oil lumps were collected during an extensive oil spill response operation along the coast from Frøya northwards to Helgeland. No environmental damage was reported, nor were any birds or marine mammals harmed by the oil.
Looking only at crude oil spills in Figure 15, there is also a clear downward trend over the past 10–15 years, with some annual variations. In 2024, there were 24 such spills.
The total oil spill volume from unintentional oil spills varies significantly from year to year, as shown in Figure 16. The statistics are influenced by large single incidents. In 2007, the second-largest oil spill on the NCS occurred, amounting to over 4,000 m³, while total spills since then have ranged between 10 and 200 m³. In 2024, the total volume was 96 m³, dominated by a single spill as described above.
Figure 16: Spill volume from unintentional oil spills on the NCS.
Figure 17: Total unintentional chemical spills on the NCS distributed across three spill sizes.
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 238 spills was attributed to a clarification of regulations, which led to fewer oil spills and more chemical spills. In 2024, the number of spills was 230, of which 32 were larger than 1 m³. Their distribution is shown in Figure 17.
The total volume of unintentional chemical spills in 2024 was 404 m³, an increase from 2023 when the spills totalled 347 m³. The unintentional spills were distributed as follows: 87 percent green chemicals, 11.8 percent yellow, 0.9 percent red, and 0.3 percent black.
In the period from 2007 to 2010, the spill volumes were dominated by individual years where leaks from injection wells were detected. These wells are now permanently plugged.
Figure 18: Total volume of unintentional chemical spills.
Unintentional discharge of gas to sea
From the reporting year 2023, unintentional discharges of gas to the sea are also reported in Footprint. The number of unintentional discharges in 2024 was 25, with a total volume of 7,422 Sm3.
Unintentional gas emissions to air
Unintentional emissions to air are mainly leaks of hydrocarbon gases and refrigerants from processing equipment. In 2024, the number of emissions was 181, up from 154 in 2023. The total mass (kg) increased from 7,198 kg in 2023 to 143,821 kg in 2024. The increase in hydrocarbon gas emissions from 2023 to 2024 was mainly related to gas leaks at Balder. The proportion of methane from the leak is included in the overview of total methane emissions in Figure 27 (Chapter 6.2). Despite the significant increase in unintentional gas emissions to air in 2024, total methane emissions show a decrease of 6 percent from 2023 to 2024.
Figure 19: Unintentional gas emission to air.
Leak detection
A detection system is an important barrier for identifying leaks and other unintentional spills as quickly as possible. The system is designed to provide the necessary data so that relevant actions can be initiated as promptly as possible, also ensuring that spills are notified, reported, and documented in accordance with regulations. All facilities on the NCS currently have one or several leak detection technologies installed.
The number of incidents involving unintentional spills from subsea installations is low and is highlighted each year in the Norwegian Ocean Industry Authority's report RNNP Acute Emissions.
Large spills can be detected immediately through process monitoring, and daily satellite monitoring and radar monitoring of the sea surface. However, it can be more challenging to detect small spills from subsea installations. Modern subsea installations are equipped with local leak detection systems, but this is not always the case for older installations built before such technology was available.
The NEA and the Norwegian Ocean Industry Authority conducted 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. Some common non-conformities were identified among all operators, particularly related to the detection of minor leaks and performance requirement procedures. A work group was therefore established under the directive of Offshore Norge to investigate this jointly. The operators submitted a response to the audit report with a proposed plan for closing the various non-conformities at the beginning of 2021.
The findings from the audits are largely due to insufficient risk assessments of potential spills from individual installations, as well as insufficient documentation and holistic evaluations of the systems’ capabilities/performance. The industry is currently working to address these issues for their fields and installations, and assessments are ongoing to identify gaps and how to close them. Consideration must also be given to the limitations of technology; most leak detection systems can only cover a limited area and cannot always detect small spills from a distance. For the very smallest spills, inspections may therefore be the only option for detection. Inspections are carried out on all fields at regular intervals.
There are also several subsea installations on the NCS that have lower production pressure relative to the ambient pressure. These fields are more likely to experience seawater leaks into the system than oil and gas discharges to sea.