Chemical osmosis as a cause for the improved oil recovery by low-salinity water flooding: Experimental and numerical approaches for detection

Abstract

Crude oil migration induced by chemical osmosis is particularly attractive among the mechanisms explaining the improved oil recovery by low-salinity water flooding (LSWF). Oil migration is caused by the thermodynamic potential transfers between injected low-salinity water (LSW) and connate high-salinity water (HSW) in reservoir rocks with leaky semipermeabilities. The difference in the chemical potentials of water causes chemical osmosis through semipermeable membranes in the reservoir rock. The migrating water molecules induce countercurrent pressure-driven water migration, accompanying crude oil migration toward the LSW. Based on this understanding, this study proposes a chemical osmosis experiment for screening reservoir rocks that can potentially improve oil recovery by potential transfers. An oil-free porcelanite with 11 wt% clay content showed that osmotic pressures greater than 10 kPa were established at the HSW reservoir within 8 h for a core sample with 1-cm-thickness. Subsequent numerical simulations illustrate that the counteracting water migration reaches 1 pore volume within 60 and 6000 h in the cases of 1- and 10-cm thick semipermeable rocks, respectively. These results suggest that chemical osmosis can be effective within a feasible duration for LSWF. However, the rock volume under the influence depends on time and salinity control parameters. The presented experiments and simulations assume the clay-originated semipermeability of reservoir rocks, but they could be applied to preliminarily estimate the effect of chemical osmosis even when oil-originated semipermeabilities are also involved in the process. • Chemical osmosis can be a cause of oil migration in hydraulically stagnant pores. • Chemical osmosis experiment is proposed to detect reservoir rock semipermeability. • Coupled H–C modeling was used to assess the effect of chemical osmosis on the IOR. • Chemical osmosis exerts its effect in a short time duration feasible for LSWF. • The effect is expected for reservoir rocks with leaky semipermeabilities.