Pore-Scale Mechanisms During Low Salinity Waterflooding: Water Diffusion and Osmosis for Oil Mobilization

Abstract

Abstract This work study pore-level oil mobilization by water diffusion and osmosis during low salinity waterflooding using microscopic visualization in sandstone silicon-wafer micromodels. The twodimensional water-wet micromodels apply a high accuracy pore network with sharp edges and surface roughness to observe displacement processes during low salinity water injection. Residual and capillary trapped oil was mobilized when a salinity gradient between high-saline connate water in matrix and low salinity water flowing in an adjacent fracture was established. Transport of water by diffusion occurred through film-flow resulting in film-expansion and droplet growth along the water-wet grains. Water transport was also driven by osmosis due to the difference in chemical potential between the high and low-saline phases. The oil-phase acted as a semi-permeable membrane in presence of an osmotic gradient to transport low salinity water into high-saline water-in-oil emulsions. The identified pore-scale displacement mechanisms, observed using a controlled state-of-the-art experimental approach, contribute to the fundamental understanding of improved oil recovery during low salinity waterflooding.