Simulation of Polymer Flooding for EOR: Effect of Water Salinity on Polymer Solution Displacement in a Sandstone Reservoir with High Porosity and Permeability

In many reservoirs, due to the inappropriate mobility ratio between oil and displacing fluid, the oil recovery factor has no significant increase even after using emerging low salinity water flooding. Polymer solution injection to achieve further oil recovery is limited by water salinity. In this paper, the synergy of low-salinity water flooding and polymer injection is investigated as a potential EOR in an Iranian oil reservoir through coupling fluid flow and geochemical modeling. In order to model change in wettability, the interpolation factor of relative permeability and capillary pressure was obtained using geochemical reactions between rock and low-salinity water. Different scenarios were designed to investigate the effect of water salinity during continuous waterflooding, water flooding before and after polymer injection with different concentrations of polymer, and the effect of the salinity of polymer solution on oil recovery in the reservoir. During low salinity water flooding oil recovery increases by 4.19% in comparison with high salinity water. When low-salinity water is injected before high-salinity polymer, oil recovery increases by less than 1% compared to the high salinity. Low salinity of the chemical solution leads to an increase in the oil recovery performance of polymer flooding due to an increase in solution viscosity. Considering formation breakdown pressure, a low salinity polymer solution with a polymer concentration of 100 ppm is appropriate from an operational viewpoint. Oil recovery increases by 5.05% in comparison with high salinity  polymer. Low salinity water after polymer injection is more effective than high salinity water during tertiary recovery. During low salinity polymer injection with the concentration of 100 ppm followed by low salinity water in the tertiary stage, an increase in oil recovery is 2.27% in comparison with continuous low salinity water flooding. Combined low salinity water and polymer injection in the reservoir can be considered as one of the selected EOR methods to perform on a pilot scale.