The environmental impact factor (EIF) is invaluable for quantifying the potential benefits of new, cleaner water technologies and for reducing the use of potentially damaging chemicals.
Computing individual EIFs is a complex process, and involves several steps. A greatly oversimplified description follows below.
Produced water to be discharged to the sea is first subdivided into various pollutants, each characterised by a threshold value in terms of its predicted no-effect concentration (PNEC).
The dilution and dispersion of pollutant groups is then modelled as a basis for determining predicted environmental concentrations (PECs).
Finally, an EIF index is established by estimating the volume of potentially harmful discharge water in the area under consideration.
The maximum resolution of the dilution model for EIF calculations is 100 x 100 x 10 metres (where 10 metres represents the water depth). That represents a volume of 100,000 cubic metres.
If this is the total volume containing a potentially harmful discharge, the EIF index will be 1. If the volume is twice the size – at 200,000 cubic metres - the EIF index will be 2, and so forth.
EIF indices are thus expressed as whole numbers.
They may be used to characterise either a single platform or discharge outlet, a producing oilfield with several platforms and outlets, or an area comprising several fields.
A grand regional EIF can also be determined, such the entire North Sea or the whole Norwegian continental shelf.
EIF forecasts can also be made for the lifespan of individual fields, including prognoses for each outlet. The higher the EIF index, the greater the potential for environmental damage.
The mathematical procedure also generates a spreadsheet listing the contribution of each produced water group, both natural and human-induced, to the EIF.
These data can be manipulated to achieve systematic testing of the impact on the EIF produced by new technologies for cleaning discharges and/or by substituting or phasing-out certain production chemicals.
North Sea operators can thereby make informed decisions about measures to be adopted, on the basis of a rigorous environmental and cost-benefit ranking.
However, a full environmental risk assessment is needed for proper testing of those measures which are finally selected or to help weigh up the pros and cons of injection.
So far, the technique has been fully implemented on all StatoilHydro-operated fields for discharges from single outlets. It is also used as a key performance indicator (KPI).
The EIF has been accepted by the Norwegian Pollution Control Authority (SFT).
