Emissions to air from the petroleum sector

Nationally, petroleum operations account for 31 percent of CO2 emissions, 24 percent of NOx emissions and 41 percent of nmVOC emissions.

Under the Kyoto and Gothenburg protocols, Norway is, among other things, required to reduce emissions of carbon dioxide (CO2), methane (CH4), nitrogen oxides (NOx), non-methane volatile organic compounds (nmVOC) and sulfur dioxide (SO2). The petroleum sector emits environmentally harmful substances like CH4 and SO2, but the most important emissions to air from this sector are CO2 and NOx from energy production and flaring, as well as emissions of nmVOC from storage and loading of crude oil. Nationally, petroleum operations account for 31 percent of CO2 emissions, 24 percent of NOx emissions and 41 percent of nmVOC emissions.

Measuring and reporting of discharges and emissions
Emissions to air are in most cases calculated on the basis of the quantity of combustion gas and diesel used on the installation. The emissions factors employed are based on measurements from suppliers or standard figures prepared by the sector itself, through the Norwegian Oil Industry Association (OLF). For most fields, emissions are calculated using field-spesific factors. Software is also available that can calculate emissions based on measured process parameters. Discharges of produced water to sea are measured by water meters. The oil content of this water is analysed and used to calculate total oil discharges. The discharge of chemicals is calculated from consumption relative to what is recovered and/or injected. The Norwegian Pollution Control Authority (SFT), The Norwegian Petroleum Directorate (NPD) and OLF have set up a joint database for reporting of discharges to sea and emissions to air from petroleum operations. From 2004, all operators of petroleum activities on the Norwegian Continental Shelf (NCS) report discharge and emission data directly into the database. This facilitates both the operators’ and the authorities’ ability to produce analyses of historical discharges and emissions in a way that is more comprehensive and consistent than was previously the case.

Emissions status for CO2
CO2 emissions related to the installations on the NCS derive primarily from the combustion of gas in turbines, flaring of gas and diesel combustion. CO2 is the most important of the climate gases and is closely linked to the burning of fossil fuels, of which natural gas emits the lowest volume of CO2 per unit of energy. The environmental impacts of CO2 include:

  • CO2 contributes to the greenhouse effect, which in turn causes global warming.
  • High concentration of CO2 in the atmosphere makes more CO2 dissolve in water, and this may cause a reduction in the sea’s pH value.

Nationally, petroleum operations account for 27 percent of CO2 emissions. This share is expected to decline during the next years. Other major emission sources in Norway are road traffic and other mobile sources, heating and emissions from various industrial processes.

The majority of CO2 emissions from the petroleum sector relate to offshore installations. Other CO2 emissions come from land based gas terminals and indirectly from VOC emissions (so-called process emissions). Improved energy efficiency and reduced flaring contributed to a reduction in CO2 emissions per produced oil equivalent by around 20 percent from 1990 to 2006. This follows general improvements in technology and emission-reducing measures, as a result, amongst other things, of the introduction of the CO2 tax in 1991. The reduction in CO2 emissions per produced oil equivalent has, however, not been significant enough to counterbalance the increase in energy consumption due to increased activity on the NCS. Especially increased gas production and gas compression for exports have led to increased power consumption which in turn increases CO2 emissions. In general, emissions linked to the production of a unit of oil or gas will vary both between fields and over a single field’s lifetime. Reservoir conditions and transport distances to the gas markets are factors that cause the energy requirements, and hence emissions, to vary from field to field. The variation in emissions over a field’s lifetime is due in part to the fact that the proportion of water in the well stream increases as the field ages. Since it is essentially the total liquid and gas volumes (water, oil and gas) that determine the energy requirements on the processing installation, a field will have higher emissions per produced unit the older it gets. This is one of the reasons we have seen a slight increase in emissions per unit the recent years. The trend on the NCS towards more mature fields and the movement of activities northwards is leading towards increased emissions per produced unit. Processing and transport of produced gas is more energy-intensive than production of liquids. The proportion of produced gas is still on the increase on the NCS. This has a major impact on the development in the indicator showing CO2 emissions per produced unit.

Measures for reducing CO2 emissions
The development of combined solutions for energy production offshore (combined cycle power plants), recirculation of flare gas and injection of CO2 from produced gas at Sleipner West, are examples of the NCS’s leading-edge position in terms of implementing environmentally efficient solutions.

Combined power solutions
Combined cycle power plants represent a solution whereby heat from turbine exhaust gas is used to produce steam, which in turn is used to generate electric power. Combined cycle power plants increase the energy efficiency and are currently in operation on the Oseberg, Snorre and Eldfisk fields. These plants are totally unique in an offshore context.

Storage of CO2
CO2 can be injected and stored in depleted produced oil or gas reservoirs, or in geological formations under water or on land. Since 1996, one million tonnes of CO2 has been stored annually in the Utsira formation in connection with the processing of gas from the Sleipner field. The storage of CO2 in the Utsira formation is unique, because this is the only facility in the world with storage of large amounts of CO2 in a geological formation under the seabed. When the Snøhvit field comes on stream in 2007, CO2 from gas production will be separated out before the natural gas is cooled into liquid gas (LNG). The CO2 gas will be transported in a pipeline from the LNG plant at Melkøya and back to the field for injection into a formation called Tubåen. Every year, around 700 000 tonnes of CO2 will be stored in Tubåen. In the future, Norway will have excellent opportunities for storing CO2 due to its access to large water-filled reservoirs and depleted produced oil or gas reservoirs off the Norwegian coast. Storing of CO2 in depleted produced reservoirs is, geologically speaking, a good solution, since the structure is highly likely to be impermeable in as much as it will have retained gas and oil for millions of years. The Norwegian authorities are working actively to ensure that such CO2 storage can be achieved in a safe and secure manner. Work is therefore being undertaken under the auspices of the OSPAR and London Conventions to ensure that sound international regulations for CO2 storage are established. In November 2006, changes were made to the part of the London Convention that set legal bounds to CO2 storage in geological formations under the seabed. In June 2007, similar changes were made to the OSPAR convention.

Energy installations and energy efficiency
CO2 emissions from power production on the NCS account for around 80 percent of total emissions from offshore operations. In 2004, the authorities, in cooperation with the industry, carried out a report on the potential for more efficient power supply on the NCS. It concluded that a realistic, although ambitious, estimate of potential emission reduction is approximately 5-10 percent over the course of 10 years, an improvement that has already been taken into account in projections of the sector’s CO2 emissions. This is achievable if the industry systematically implements energy management in all aspects of operations. The industry will follow up the authorities’ study, and under the direction of OLF, it is working on developing common guidelines for establishing and implementing energy management. To ensure further increases in energy efficiency in the longer term, a change in technology and energy supply concepts will be required. This calls for a long-term commitment to the development, testing and implementation of new technology.

Flaring is necessary as a security measure on the installations to prevent explosion in pressurised systems. Although flaring accounts for around ten percent of the CO2 emissions from petroleum operations, the Norwegian level is low compared to other countries. The CO2 tax and direct regulation of flaring have triggered a number of emission reducing measures, making Norway a leader in this area.

Emissions trading scheme
In the petroleum sector, only a few facilities on land, such as gas processing plants and gas terminals, are subject to quota obligations in the early phase of the emissions trading scheme from 2005-2007. A proposition on the emissions trading scheme 2008-2012 passed through the Storting in June 2007, and the guidelines are now being developed before the proposition can take effect. If the Emissions Trading Directive is incorporated in the European Economic Agreement (EEA), it implies that the offshore oil and gas sector as well as companies producing pulp and paper will be included in the trading scheme from 2008, along with those already covered in the period 2005-2007. From 2008 the trading sector will represent more than 40 per cent of Norwegian emissions of greenhouse gases. The Directive does not, however, stand in the way for applying other policies and measures such as carbon taxes or technological requirements.

Emission status for NOx
Emissions of CO 2 and NOx are closely connected. Gas combustion in turbines, flaring of gas and diesel consumption on the facilities are, similarly to CO2, also key emission sources for NOx. The volume of emissions depends both on the combustion technology and the quantity of fuel used. The environmental effects of NOx emissions include the following:

  • Impact on fish and other fauna through acidification of watercourses and the ground.
  • Damage to buildings, stone and metalwork resulting from acid rain.
  • Eutrophication, which may lead to a change in the composition of species in ecosystems.
  • Damage to health, crops and buildings due to production of ground-level ozone.

Mobile sources account for the majority of the Norwegian NOx emissions. The petroleum sector contributes with 28 percent. Emissions of NOx per produced oil equivalent have declined by 18 percent from 1990 to 2005. The reductions in emissions per produced oil equivalent are the result of improved technology and measures to reduce emissions. Despite the reduction in emissions per produced oil equivalent, total emissions of NOx from the sector have increased compared with 1991. The main cause of the growth so far is increased activity which has entailed a need for more energy, which in turn means more emissions. Emissions of NOx are expected to fall from 2009 and onwards.

Measures for reducing NOx emissions
Most of the measures designed to reduce CO2 emissions also contribute to reducing NOx emissions from the petroleum sector. Other measures that can help reduce NOx emissions include introducing low-NOx burners as standard on gas turbines on new facilities. NOx emissions can be reduced by as much as 90 percent with no change in CO2 emissions. In some cases, however, use of this technology can lead to increased CO2 emissions. Low-NOx burners can be retrofitted on existing turbines. Studies show that the general cost level associated with retrofitting such burners on existing facilities is considerably higher than previously assumed. Generally speaking, low-NOx technology installed on machinery running at high efficiency will result in significant environmental benefits. On machinery running at low capacity, CO2 emissions increase, while NOx reductions are less than when the utilization of capacity is high. Injection of steam or water in the combustion chamber can reduce NOx emissions. Steam or water will be used to reduce the combustion temperature and thus NOx emissions. This technology requires large quantities of clean water, which is a challenge offshore.

The government introduced a tax on NOx from 1 January 2007.

Emission status for nmVOC
nmVOC is a notion for non-methane volatile organic compounds, which vaporise from substances such as crude oil. In the petroleum sector, most of these emissions derive from offshore and onshore storage and loading of crude oil. The environmental effects of nmVOC include:

  • Formation of ground-level ozone, which can damage health, crops and buildings
  • Direct exposure to nmVOC can cause respiratory tract damage
  • nmVOC contributes indirectly to the greenhouse effect in that CO2 and ozone are formed when nmVOC reacts with air in the atmosphere.

The petroleum sector is the main source of nmVOC emissions in Norway, accounting for approximately 40 percent of total emissions. Emissions of nmVOC largely originate from storage and loading of crude oil offshore. Minor emissions also occur at the gas terminals and in connection with small leaks. Other industrial processes and road traffic are also important sources of nmVOC emissions in Norway. The petroleum sector’s share of this is shrinking due to the phase-in of emission-reducing technology. Emissions of nmVOC per produced unit of oil have also declined in recent years. There are large differences in emissions depending on where the oil is loaded. The main reason for this is that the content of volatile gases in the oil varies from field to field. Several of the newer fields on the Norwegian continental shelf use floating storage facilities. This type of development can result in higher emissions of nmVOC than on fields where oil storage takes place in the base of the platforms (Statfjord, Draugen and Gullfaks). This is because the use of floating storage facilities also causes emissions between production and storage. The forecast for emissions of nmVOC from the sector shows a distinct declining trend in the years to come. Implementation of emission-reducing technology is the reason for this. Moreover, oil production is expected to reach its peak a few years from now.

Measures for reducing nmVOC emissions
For a number of years, the oil companies have worked to make technology for recovering nmVOC available to storage vessels and shuttle tankers. Today, tested technology exists that can reduce emissions from loading by approximately 70 percent. Several vessels have now installed technology to reduce emissions. The field operators with buoy loading on the Norwegian continental shelf have formed a joint venture. A recovery facility for nmVOC was deployed at the crude oil terminal at Stura in 1996. This facility is the first of its kind in a crude oil terminal. In order for loading tankers to use the facility, they must be fitted with coupling equipment. From 1 January 2003, it became a requirement that all vessels must be fitted with equipment for recovering nmVOC. Ships without the necessary equipment are not normally granted access to the facility.


(published August 30, 2007)