More water than oil on the shelf

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The Norwegian shelf currently produces more water than oil. The water must not be released into the ocean until any harmful substances have been removed.

Produced water is water which comes up from the reservoirs along with the oil. Since 2004, more water than oil has been produced on the Norwegian shelf, according to the resource report of the Norwegian Petroleum Directorate, The petroleum resources on the Norwegian shelf 2011. Since 2004, water production has been stable, while oil production has fallen. In 2011, 161 million standard cubic metres of water were produced, compared with 97.5 million cubic metres of oil. The water ratio is expected to increase further in the coming years.

The water ratios are especially high at some of the large, old fields, such as Statfjord, Gullfaks and Troll II. These three fields alone contributed more than half the water production in 2008.

Some of the water exists in the reservoirs from earlier, but the amount of produced water increases as the fields become older. This is primarily due to the fact that water, mostly seawater, is injected into the reservoirs to maintain the pressure and thus increase oil production. For example, water injection has made it possible to increase the recovery rate from Ekofisk. When the field started production, the operator expected a recovery rate of 17-18 per cent, while current calculations show a recovery rate exceeding 50 per cent.

The produced water contains small amounts of oil, even after separation from the oil and cleaning in the processing plant. It also contains natural chemical substances which can be harmful for the environment.

In addition, produced water contains chemicals which are added when the wells are in production.

"A considerable effort was made to replace harmful chemicals with less harmful chemicals from 2000 to 2005," says principal engineer Tor Fadnes in the Norwegian Petroleum Directorate. The discharge of added, potentially harmful chemicals has been reduced by more than 99 per cent on the Norwegian shelf over the course of the last ten years.

Since 1997, Norwegian authorities have expressly stated that the goal is that no environmentally harmful produced water shall be discharged.

The zero harmful discharges goal was laid down in Storting White Paper No. 58 (1996-1997), and later specified in several Storting white papers, most recently in No. 26 (2006-2007). No or minimal discharges of naturally occurring environmentally harmful substances are allowed. Added chemicals in categories "red" or "black" must not be discharged to sea, and must therefore be replaced.

For new discoveries, requirements can be set demanding impact assessments prior to development of the field. Discharge bans may be introduced in areas considered environmentally sensitive.

In 2007, the Oslo-Paris Convention (Ospar) relating to marine environment introduced a requirement stating that the concentration of oil in water must not exceed 30 milligrams per litre on average. The requirement was previously 40 milligrams per litre. 

According to Fadnes, Norway has been a promoter of introducing strict, realistic requirements related to discharges under Ospar. The average oil concentration in water on the Norwegian shelf was 10 milligrams per litre in 2008.

The operators on the shelf are required to monitor the environmental condition around their installations every third year, and report their emissions to the Climate and Pollution Agency (Klif) annually. Fields which do not comply with the discharge requirements may be ordered to upgrade their treatment plants or to inject the water rather than releasing it.  


22.06.2012