Environmental impacts of oil and gas activities

Published by the Norwegian Environment Agency Lag rapport Les på norsk

Oil and gas activities have impacts on large areas of the sea, the seabed and on land. They affect the environment through emissions to air, noise from seismic surveys and their physical footprint on the seabed.

Emissions to air

The oil and gas industry is the largest source of greenhouse gas emissions in Norway. It is also an important source of emissions of volatile organic compounds (VOCs). Emissions of non-methane VOCs in combination with NOx contribute to the formation of ground-level ozone. NOx also contributes to eutrophication and acidification.

Production of oil and gas requires large amounts of energy. Both drilling of wells and treatment of the oil and gas extracted from the reservoir contribute to this. Gas turbines and diesel engines are used to produce the energy needed. Diesel engines are mainly used on mobile drilling rigs used to drill exploration and production wells.

Transport of oil and gas in pipelines from the offshore fields to land terminals, also requires large amounts of energy.

Offshore oil loading is the most important source of emissions of volatile organic compounds, especially when using shuttle tankers. Fugitive emissions and gas cold venting are also sources of emissions of volatile organic compounds. In addition, gas flaring generates emissions of soot and particles.

Discharges to sea

The concentrations of oil and hazardous substances discharged with produced water are generally low. The total amount is still relatively large given the big water volumes. It is very difficult to document whether these discharges have an impact on marine life. Research has shown that oil and environmentally hazardous substances in produced water may affect the health and reproduction of individuals of fish and invertebrates. The ecological significance of these discharges is still unclear however, because effects measured in individuals cannot be linked to consequences for entire populations and communities.

Concentrations shown to have effects in scientific studies do not normally extend further than about one kilometer from the discharge point. This distance corresponds relatively well with both monitoring and risk assessment results. However, the risk that weak impacts on individual species may have cumulative ecological effects still can not be ruled out.

Both authorities and operators have worked to reduce the use and discharge of environmentally hazardous substances for many years, with good results. Discharges of the most environmentally hazardous substances were reduced by about 75.5 per cent from 2003 to 2015.

Discharges of environmentally hazardous substances to sea will continue to happen in the years to come due to safety and technical considerations. Mature fields with increased water production generally need more chemicals.

Besides produced water, drilling of wells stands for the biggest discharges to sea. Discharges from drilling consist mainly of crushed material from the borehole (cuttings) and chemicals used during the operation. Drilling takes place with a constant supply of drilling fluid, whose main component is a base liquid, water or oil based, and a weight material, most often the naturally occurring mineral barite. Alternatives to discharge may either be injecting everything back into suitable geological formations or taking it to shore for further treatment.

Discharging drill cuttings and associated drilling fluids will cause the death of the benthic (bottom-living) organisms living in and on sediments covered by cuttings in the immediate vicinity of the discharge point (out to about 50 meters). Soft bottom organisms will however normally recolonize the area relatively quickly after the drilling ends. That is why cuttings from drilling with water-based drilling fluids may usually be discharged to sea. Cuttings can, however, cover and harm other organisms that are vulnerable to this kind of influence, and who have a long recovery time if damaged. Examples of such organisms are corals, sponges and sand eels.

Oil and gas activities also affect the seabed through the placement and movement of installations and other necessary equipment such as platform legs, subsea templates, anchor chains and pipelines. An additional pressure for the seabed is particle load from dredging and rock filling when putting in place installations. The physical impact on the seabed is mainly local and limited in extent and scope. Possible negative environmental impacts depend on which areas are affected, and whether valuable and vulnerable species and habitats might be affected or damaged.

Seismic surveys

Seismic surveys are performed to map the geology and geological structures of the sea floor. Noise from such surveys may frighten fish and marine mammals. The noise is not expected to cause significant damage or nuisance to fish, as long as the activity does not take place in spawning areas during the spawning season.

A review of existing knowledge on the possible effects of noise from seismic activity on marine mammals is needed. Based on that the authorities will again look into whether stricter regulation of such activities is required