When produced water is to be discharged to the sea, it will first be subdivided into various pollutants. Each of these is characterised by a threshold value in terms of its predicted no-effect concentration (PNEC).
A dilution model is then used to simulate the predicted environmental concentrations (PEC) of these pollutants in volume terms around a platform as a function of various natural phenomena, such as currents, tides, waves, evaporation and biodegradation.
If the PEC/PNEC ratio visualised by the model is less than one, the untreated discharge will not be harmful. However, a ratio greater than one means that a potential risk to the environment exist.
Computer-generated map of the PEC/PNEC ratio for a produced-water plume originating from the Statfjord field operated by StatoilHydro in the North Sea. The map shows a projection of the ratio onto the sea surface, whereas in reality the plume moves at depth in the water column (upper inset). The inset map (lower left) shows a corresponding dispersion/dilution snapshot of the plume.
