At present time, North Sea is the main offshore exploration and production (E&P) area in Europe. Due to ageing of the fields, produced water (PW) has now become the prime source of oily discharge to the marine environment from E&P activities.

So far, measures taken to regulate these discharges, at regional or national level, have focused chiefly on "dispersed" hydrocarbons. Although there is little evidence, if any, of harmful effect from PW actually discharged into the North Sea, when these discharges met the performance standard set up and are treated according to Best Available Technologies (BAT) as defined in 1992 by the Convention for the Protection of the North-East Atlantic (OSPAR), the pressure made by stakeholders has recently led regulators to take tougher measures regarding the "dispersed" hydrocarbons and to embark on the definition of additional, new prescriptive measures directed at other contaminants, such as chemicals used offshore and aromatic compounds.

During the last decade, tremendous research efforts have been made by the industry to design more efficient treatment facilities. As a result the 90's can be considered as the hydrocyclones decade, while the 2000's will see a wider range of techniques used, and the implementation of more preventive measures for reducing the overall load such as re-injection of PW or water shut-off techniques.

But the ongoing discussion on performance standards, and the competition for continuous reduction of the content of contaminants in PW at whatever the cost can be – even when it represents only a small percentage of the total input of contaminants in the North Sea – conceals two key questions: 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 (CO2 emissions, energy and non-renewable resources consumption)?

To answer these two questions, it requires (1) a consensus on how to assess long-term effects of PW discharges and (2) that the issue is examined from a different point of view: the ecosystem, and its sustainability. Extensive research has been undertaken to develop tools for a better understanding and assessment of the long-term effects, while a new approach has recently emerged since the entry into force of Annex V of the OSPAR Convention, which should lead to the definition of Ecological Quality Objectives in the future. But this approach could be hampered by a recent initiative from the European Commission, which could lead to a total ban of produced water discharges by 2020. Notwithstanding, at present time, operators strive to encompass a holistic approach of water management.

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