Numerical Investigations of Low-Salinity Water Flooding in a Saline Sandstone Reservoir

In the era of dominance of renewable energies and the pandemic-affected world, oil industries must produce oil from extant fields most economically. Further, increasing ecological awareness makes oil companies look forward to cost-effective, eco-friendly and efficient enhanced oil recovery (EOR) techniques like low-salinity water flooding (LSWF). The mechanism behind LSWF in the augmentation of oil recovery has been a prominent research area. The present study gives more profound insights into the impact of divalent cations (${\mathrm{Ca}}^{2+}$ and ${\mathrm{Mg}}^{2+}$) on LSWF in clayey sandstones by considering the multi-ion exchange (MIE) mechanism. The developed mathematical model consists of a fluid transport model, an ion transport module incorporating MIE, and a model for the weighing factor to interpolate between low-saline and high-saline states. The present model was validated and verified with analytical solutions and experimental results in the literature. In this study, the dilution of the ${\mathrm{Ca}}^{2+}$ ion concentration by a factor of $10$ and $100$ times of formation water in injection water led to an enhancement in desorption of ${\mathrm{Ca}}^{2+}$ ions and a relative increase in oil recovery by 9.61% and 12.33%, respectively. Further, the dilution of both ${\mathrm{Mg}}^{2+}$ and ${\mathrm{Ca}}^{2+}$ ions by 100 times led to the highest relative oil recovery of 13.22%. This study also provides fundamental insights into the microscopic displacement efficiency and fractional flow curves in the LSWF, which is a novel attempt. Moreover, this work helps in quantifying oil recovery in clayey sandstone reservoirs and also assists in selecting suitable reservoir candidates for LSWF.