System for å tilveiebringe en tilførsel av vann med kontrollert saltholdighet for økt oljeutvinning

A method for providing controlled salinity water for enhanced oil recovery begins by raising the pressure of, and then splitting, a treated seawater feed into two supply streams which are then processed in parallel. One supply stream is passed thorough a nanofiltration membrane system while the other is passed through a reverse osmosis membrane system. The permeate streams are then combined for an overall recovery factor in a range of 50% to 65%. The pressure of the first supply stream is preferably reduced prior to treatment and the nanofiltration membrane system may be housed in a pressure vessel rated for use with a reverse osmosis membrane system. Energy can be recovered from the nanofiltration reject stream or the reverse osmosis reject and used to reduce the feed pumping power or provide an inter-stage pressure boost. The single seawater feed allows for a simplified pumping and piping arrangement.