The operators on the Norwegian Continental Shelf (NCS) and the Norwegian Authorities have agreed to work towards a reduction of the environmental impacts from produced water releases (and from drill cuttings and mud releases as well) down to a level of “zero harmful effects”. To more clearly define this goal, the EIF (Environmental Impact Factor) has been developed as an indicator of the potential impacts from produced water releases. The EIF is used as a measure of the environmental benefit achieved when alternate measures are considered for reducing environmental impacts.
The method has the advantage that it gives a quantitative measure of the environmental risks involved when produced water is released into the sea, and is thus able to form a basis for reduction of impacts in a systematic and a quantitative manner.
This method is based on the calculation of the EIF using the numerical model DREAM (Dose-related Risk and Effects Assessment Model) developed by SINTEF, with financial support from Statoil, Norsk Hydro, ENI, Total, ExxonMobil, Petrobras, ConocoPhillips, and Shell.
DREAM is a three-dimensional Lagrangian particle model (Reed and Hetland, 2002). The model is based on:
- A generalised transport equation, accounting for advection and turbulent diffusion
- several transformative processes such as sinking, dissolution, sedimentation and biodegradation.
The numerical solution of the transport equation uses the Lagrangian frame of reference, with numerical parcels following the ocean current. For a continuous release of produced water or cuttings and mud, the numerical parcels are created with fraction of the released mass, and then tracked through the water column, while being subject to the physio-chemical processes already mentioned. Essential parameters of the released material, including grain size distribution, attached chemicals and heavy metals are similarly tracked.