In our previous work, we examined the potential of divalent cations (Mg2+ and Ca2+) in formation water (FW) for low-salinity (LS) EOR effect, where the increase in divalent cations in FW lowered the impact of LS water EOR.

In this paper, we demonstrate the importance of the same divalent cations in the injected water (both FW and LS water). We also try to relate the percentage of the divalent cations in the injected water to that in the FW to engineer the optimum concentration of the injected water and obtain the maximum oil recovery from sandstone reservoirs.

Berea sandstone cores were successfully flooded with FW and LS water at 90°C. While injecting both brines, samples of the effluent were analyzed for pH. Oil recovery experiments with a double Ca2+ and Mg2+ concentration showed a lower LS water effect, inferring that the cores became more water-wet; however, the LS water effect was much greater when the amount of Ca2+ and Mg2+ in the HS water was decreased by half. The results of this work relate oil recovery with LS water chemical compositions, temperature, ion exchange, and pH.