REVIEW OF POTENTIAL TECHNOLOGIES FOR THE REMOVAL OF DISSOLVED COMPONENTS FROM PRODUCED WATER

Between March and December 1992, the Environmental Technology Division of Kvaerner Engineering carried out an investigation of potential technologies for removing dissolved components from produced water as part of the OLF (Norwegian Oil Industry Association) Environmental Programme. Dissolved component groups include inorganic compounds (heavy metals and radiochemicals), organic compounds (aliphatic, aromatic, polar and fatty acid components) and various production chemicals. Including fatty acids, the dissolved organic content of produced water greatly exceeds the 40 mg/l dispersed hydrocarbon limit, and regulatory authorities are currently thought to be considering possible controls over dissolved component discharges. A wide range of technologies was assessed for both oil (relatively high produced water flowrates) and gas fields (relatively low produced water flowrates). Technologies that were felt to offer the greatest potential (based on current stages of development) were found to be ion exchange for heavy metal removal, and air (or gas/vapour) stripping, activated carbon adsorption (with regeneration of the carbon by wet air oxidation) and biological treatment for dissolved organic removal. In gas fields, wet air oxidation could be used without the activated carbon adsorption step. However, none of the systems evaluated would be capable of removing all of the groups of dissolved components from produced water alone. This implies that, if removal of all dissolved components is required, 2 or more systems would have to be used in series. In practice, technology selection could be based on the toxicity reduction achieved and/or the organic loading reduction achieved (of the technologies assessed, only biological oxidation and wet air oxidation achieved significant organic loading reduction). The systems generally add significantly to the cost, weight and space requirements of produced water processing systems (and it may not always be practicable to retrofit some of these bulky systems onto existing platforms). In many cases produced water reinjection should also be considered as an alternative water disposal route. Offshore testing known to be underway at present includes air and steam stripping trials on gas platforms in the Dutch sector of the North sea and membrane filter trials on gas platforms in the British sector of the North sea. Whilst the implementation of dissolved component removal technology is already feasible in some cases (particularly on gas platforms), further technology improvements such as combining technologies, developing new technologies and/or reducing equipment size through process intensification may improve the cost effectiveness of these systems and allow retrofitting onto a larger number of existing platforms. It is expected that such technologies could be made available within 3-5 years.