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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. [ABSTRACT FROM AUTHOR]

The selective ions permeation through nanofiltration (NF) membranes is the rationale of its application in different fields. However, the correlation of selectivity with membranes properties such as hydrophilicity, surface free energy and electrokinetic potential is not completely understood. Three negatively charged commercial NF membranes (NP010, NP030 and NF90) were characterized by scanning electronic microscopic (SEM), contact angle and zeta potential measurements. The rejection of salts typically present in seawater (NaCl, Na 2 SO 4 , MgSO 4 , K 2 SO 4 , and CaSO 4 ) was evaluated at various transmembrane pressures. Sieve mechanisms, ionic electrical exclusion, dielectric effects and permeate flux coupling of ions to keep electroneutrality contribute simultaneously to ions selective rejection. Permeation with mixture of mono and divalent ions through membranes with higher pore size, NP010 and NP030, showed that high sulfate exclusion leads to increase in the rejection of all cations present in the solution. Conversely, for NF90 membrane steric effects are predominant and high sulfate rejection leads to reduction of monovalent ions rejection. [ABSTRACT FROM AUTHOR]