Effect of Divalent Cations in Low Salinity Water Flooding in Sandstone Reservoirs


The never ending challenge for petroleum engineers is to improve recovery from existing reservoirs. One promising and relatively low cost method for improving recovery is low salinity (LS) waterflooding. Previously [1], we studied the effects that divalent cations (Ca2+ and Mg2+) in formation water (FW) have on LS water EOR tests, and we found that higher concentrations of divalent cations generally and specifically Ca2+ in FW lowered the performance of LS water EOR. In this study, we probe the significance of the Ca2+ and Mg2+ concentrations in the injected LS water. We also measured the wettability index to investigate the wettability alteration resulted after changing the divalent cations concentrations. Berea sandstone cores were saturated with oil and connate FW. Each core was flooded with two pore volumes (PV) of FW followed by two PVs of various LS waters at reservoir temperature (90 °C). During flooding, aqueous samples of the effluent were analyzed for pH, Ca2+ and Mg2+ concentration. Six LS water flood cases were investigated: (a) 3× dilution of Ca2+ with original Ca2+ concentration; (b) 3× dilution of Mg2+ with original Mg2+; (c) 3× dilution of both Ca2+ and Mg2+; (d) 10× dilution of Ca2+ with original Ca2+ concentration; (e) 10× dilution of Mg2+ with original Mg2+; (f) 10× dilution of both Ca2+ and Mg2+. Overall, both Ca2+ dilution cases achieved a positive LS effect (higher incremental oil recovery), with the 10× Ca2+ dilution producing a larger effect than the 3× dilution. The Mg2+ dilution cases produced either zero or small LS effects. When both Ca2+ and Mg2+ were diluted, there was a positive LS effect but less than for just Ca2+. The presence of Mg2+ inhibited the full benefit of the Ca2+ dilution.


Geosciences and Geological and Petroleum Engineering

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Article - Journal

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© 2019 Elsevier, All rights reserved.

Publication Date

01 Jun 2019