Effect of seawater ionic composition modified by nanofiltration on enhanced oil recovery in Berea sandstone

Water ionic composition significantly influences reservoir wettability and hence microscopic oil sweep. However, there is no clear explanation of how the ion composition of injection water influences the oil displacement. In this work, aqueous solutions were formulated from seawater using nanofiltration (NF) membranes, which has been currently used to remove sulfate from seawater in offshore oil prospecting. The effect of the interfacial tension (IFT) of water/crude oil, zeta potential and contact angle (CA) at water/crude oil/rock interface was evaluated to identify changes in wettability and also to relate with spontaneous imbibition experiments. The main objective of this study is to investigate the effect of the injection aqueous solutions composition on wettability and oil recovery in sandstone reservoirs.The results demonstrate that it is possible to improve the oil recovery efficiency by controlling the injection water salinity using NF process. Increased water salinity resulted in lower electrokinetic potential near the sandstone surface, approaching null values, suggesting adsorption of cations. The oil droplet interface also was affected in a similar way. Furthermore, in the presence of low salinity water, both rock and oil zeta potential was negative, which leads the electrical double layer (EDL) expansion, changing wettability and intensifying spontaneous imbibition.

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