Effects on the benthic fauna
As the oil and gas industry has expanded, many platforms and other offshore installations have been built, and large quantities of drill cuttings have been discharged on the seabed, altering the benthic (bottom-living) fauna across large areas of the seabed. It takes time for pollutants to break down, and in the meantime discharges that affect the bottom sediments are continuing. However, oil companies are now only permitted to discharge drilling fluids that are less harmful to the environment and the fauna than those previously used.
Unless performed with care, seismic surveying can injure organisms in the immediate vicinity. The activity may also frighten fish and marine mammals. Therefore, seismic surveying must be conducted when there are no known vulnerable organisms in the area.
Discharges of pollutants can be high during the well drilling and production phases. In addition, extensive works on the seabed are often required before platforms, subsea installations and pipelines can be installed. These may include leveling, trenching and dumping of rock waste.
When fields are closed down and decommissioned, the installations in principle are to be sent onshore, according to international regulations. This can result in further disturbance of the seabed.
Impacts on the North Sea
There has been a tendency to regard pollution from offshore activities in the North Sea as a relatively minor problem, since this area was already relatively heavily polluted by discharges from a number of European countries.
However, this means that we need an overview of the overall pollution load, and ensure that the total load is not too high. The oil and gas industry is only one of many sources of pollution of the North Sea, and all releases of pollution, regardless of the amounts involved, add up to the cumulative effects.
The exact effects of chronic, long-term environmental pressure are difficult to identify, since there are few recognised methods for monitoring impacts in marine ecosystems.
Greater impacts in more vulnerable areas
As the industry moves into deeper water, further north and closer to the coast, it is also moving into more vulnerable areas. We still know too little about ecosystems in deep water and in the far north.
Impacts of emissions to air
Emissions to air from the oil and gas industry include substances that are linked to global warming and others with more local effects, such as acidification of lakes and forests.
The oil and gas industry is the largest source of greenhouse gas emissions in Norway. It is also an important source of emissions to air 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 effects.
Production of oil and gas requires large amounts of energy; both drilling of production wells and treatment of oil and gas as it leaves the reservoir contributes to this. Pipeline transport of oil and gas from the offshore fields to land terminals, also requires large amounts of energy.
Energy is produced in gas turbines and diesel engines. Diesel engines are mainly used on the mobile drilling rigs used for drilling exploration and production wells.
Energy production based on fossil fuels (gas and diesel) and gas flaring generate emissions of CO2 and gases which can cause acidification (NOx and SO2) and contribute to forming ground-level ozone.
Offshore oil loading is the most important source of emissions of volatile organic compounds. 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.