Osmosis During Low Salinity Water Flooding

Several research groups have shown that injection of low saline water may yield an Enhanced Oil Recovery (EOR). The mechanisms underlying this “low salinity effect” are, however, still unclear. We believe that osmosis has been overlooked as a possible mechanism for the observed EOR effect. Osmosis is bound to occur in an oil/water/rock system when injecting low salinity water as the system is full of an excellent semi-permeable membrane, namely the oil itself. Hence we believe that this topic deserves more attention. In the present work oil droplets were observed to move under the influence of an osmotic gradient in a simple visualization experiment. The experimental setup consisted of two oil droplets in a ~1 mm diameter glass tube with salt water between them and distilled water on the outside. For a porous rock medium it is proposed that such osmotic gradients relocate oil by expanding an otherwise inaccessible aqueous phase.