For years, discharging produced water (PW) from offshore installations (after treatment) into the open sea has been the most common way to proceed. So far there is little evidence, if any, of harmful effect from PW currently discharged into the seas, when these discharges are treated by ad hoc technologies and meet the performance standard set up by regional UNEP Conventions or equivalent regulatory authorities (OSPAR, in the North Sea). Nevertheless the pressure made by stakeholders continuously pushes the regulators into taking tougher measures. Such is the case in the North Sea, where a new set of regulations has been issued in 2001 regarding the "dispersed" hydrocarbons and where additional, new prescriptive measures directed at other contaminants, such as chemicals used offshore and aromatic compounds, are investigated. But how clean is clean? How to set up the balance between additional measures, taking into account their cost, their efficiency, and the inevitable drawback of their additional impact on other compartments of the environment? To answer these two questions, it requires both a consensus on how to assess long-term effects of PW discharges, and that the issue is examined from a different point of view: the ecosystem, and its sustainability. From a technical point of view, tremendous research efforts have been made by the industry during the last decade to design more efficient treatment facilities. As a result the 90's can be considered as the hydrocyclones decade, at least in the North Sea, while the 2000's will see a wider range of techniques used, a holistic approach of water management, and the implementation of more preventive measures for reducing the overall load such as re-injection of PW or water shut-off techniques. Finally it must be highlighted that the North Sea features many local characteristics which differ from other maritime areas. Therefore if the process set up by the regulators and the industry could be adapted to other seas, the recently-set North Sea standards should not without a thorough investigation on the local characteristics.

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