Desalination method

A method of recovering hydrocarbons from a porous subterranean hydrocarbon-bearing formation comprising the steps of: a) feeding to at least on reverse osmosis unit of a desalination assembly a high salinity water feed stream having a total dissolved solids content (total salinity) of at least 10,000 ppm; b) driving a portion of the high salinity water feed stream across a membrane in the reverse osmosis unit of the desalination assembly at a pressure above the osmotic pressure of the high salinity water feed stream while excluding at least a portion of the dissolved solids from crossing said membrane to produce a treated low salinity water product stream having a total salinity of less than 5,000 ppm and a concentrated waste brine stream wherein the hydrostatic head exerted by the high salinity water feed stream on the feed side of the membrane provides at least a major component of the pressure required to overcome the osmotic pressure; c) injecting the low salinity water product stream into the hydrocarbon-bearing formation from an injection well; d) displacing the hydrocarbons with the low salinity water product stream toward an associated production well; and e) recovering hydrocarbons from the formation via the production well.