Contribution of osmotic transport on oil recovery from rock matrix in unconventional reservoirs

In this study, a model for the mass transport between the rock matrix and the fractures has been formulated and validated with the experimental data. The numerical results showed that osmosis is an important force imbibing water into low permeability rock matrix and enhancing the effectiveness of low salinity waterflooding on oil recovery. The imbibition of water into oil-wetted shale matrix is mainly driven by the osmotic transport and wettability alteration. The contribution of the osmotic transport on oil recovery continues a long period of time, typically in a few years. This contribution increases if the membrane efficiency is high and the matrix block size is small. However, shale membrane efficiency is typically less than 10% considerably reducing the oil recovery factor by osmosis to less than 5%. Higher membrane efficiency and lower diffusion coefficient of dissolved ions increase the contribution of osmosis on the oil recovery from shale matrix.