Investigating the impact of relative permeability characteristics and pressure management on oil recovery during low-salinity water injection

• Novel GEM-based modeling of low-salinity water injection in heterogeneous sandstone. • Coupled analysis links intersection point of the relative permeability and BHP effects. • Upward shift of oil–water intersection improved recovery by up to 48% and reduced water cut. • Optimum bottom-hole pressure (∼1000 psia) enhanced sweep and minimized water production. • Provides quantitative guidelines for optimizing LSWI under realistic reservoir conditions. Low-salinity water injection (LSWI) has emerged as a promising enhanced oil recovery (EOR) technique, yet the governing mechanisms remain sensitive to reservoir properties and operational parameters. This study systematically evaluates the impact of relative permeability characteristics and bottomhole production pressure on oil recovery during LSWI using reservoir simulation. Sensitivity analyses were performed on the curvature, endpoints, and intersection point of oil–water relative permeability curves, as well as on interpolation coefficients and minimum bottomhole pressures. The results show that increased curvature of the oil relative permeability curve significantly improves oil mobility, delays water breakthrough, and enhances ultimate recovery, while excessive curvature of the water curve accelerates water channeling and reduces displacement efficiency. The intersection points of the oil and water curves proved critical, where upward shifts improved displacement efficiency and reduced cumulative water production. Similarly, narrowing the interpolation range stabilized the displacement front and maximized recovery. Pressure management was found to be equally decisive: a moderate minimum bottomhole pressure of around 1000 psia achieved the best recovery by sustaining wettability alteration, ionic exchange, and interfacial tension reduction, while excessive pressures (≥3000 psia) limited interlayer communication and shortened residence time, leaving significant residual oil in upper zones. These findings highlight the mechanistic role of relative permeability behavior and pressure conditions in governing LSWI efficiency. The study provides new insights into tuning multiphase flow parameters and pressure strategies, offering practical guidance for optimizing low-salinity water flooding in both laboratory and field applications.