The oil content in the produced water discharged from StatoilHydro's installations on the Norwegian continental shelf has been significantly reduced over the past years.
Many of the installations have an oil content far below the authorities' requirements.
Beside oil and gas, old wells on the Norwegian continental shelf produce large volumes of water. This is quite normal for a "mature" shelf, but it is challenging to clean oil from large volumes of water.
The injection of produced water is not always possible, unfortunately. Our goal is to reduce the oil content in water as much as practically possible. There is an equilibrium between the volume of oil droplets in the water and the dissolved oil components (the "water soluble fraction"). Removal of the oil droplets will also remove the dissolved components from the water.
The current regulations define 30 milligrams of oil per litre of water as the maximum limit if discharged to sea. Many of our installations discharge water with no more than three to four milligrams of oil per litre. There are, however, large individual differences between the different installations. Under certain circumstances a few of our installations discharged water containing more than the general limit of 30 milligrams of oil per litre of water. The authorities' acceptance was granted in all these cases.
Local production conditions vary a great deal. However, there are no results from environmental monitoring that indicate any harm to the environment from the permitted discharges.
Our goal, however, is to continuously reduce the oil content in water where discharges are the only option. It is not physically possible to achieve zero oil content in water, but all our installations should clean produced water to the maximum of their capacity before discharging it into the sea.
