An integrated membrane system (IMS) of ultrafiltration-nanofiltration (UF-NF) technology has been investigated extensively as a means of seawater softening for offshore oilfield water and polymer flooding. The results showed that the softened water generated by the selected NF membrane could meet the water flooding standard for offshore oilfield. At appropriate mixing ratio of softened water and formation water, scales may be avoided completely. Furthermore, the reservoir formation sensitivity evaluation proved the compatibility of NE permeation water with the formation core, which indicates that the permeation water of the selected NF membrane module could be safely used for offshore oilfield water flooding. The prepared aqueous polymer solution using NF softened seawater showed relatively high viscosity and stability at formation temperature for long time, which could meet the demand for offshore polymer flooding. Therefore, the UF-NF integrated membrane technology could efficiently resolve the softened water shortage problem in offshore oilfield water flooding and polymer flooding and ensure continuous and stable oil production. (C) 2012 Elsevier B.V. All rights reserved.