Salinity-dependent adhesion of model molecules of crude oil at quartz surface with different wettability

Abstract The adhesion forces between model chemical moieties of oil molecules (CH 3 –, C 6 H 5 –, COOH–, and NH 2 –) and quartz surfaces with different wettability were investigated by the aid of chemical force microscopy at low and high salinity (10 mM and 100 mM). Our results showed that the adhesion force on hydrophilic surfaces decreased as in the order: –NH 2  > –COOH > –C 6 H 5  ≈ –CH 3 , due to the contribution of hydrogen bonding interactions between polar groups of functionalized tips and Si-OH groups of quartz surfaces. By comparison, the adhesion force decreased almost in an opposite order: –CH 3  > –C 6 H 5  > –COOH ≈ –NH 2 , in the case of hydrophobic surfaces, attributed to the strong trend of hydrophobic interactions between nonpolar oil groups and hydrophobic surface (modified with alkyl chains). A high potential of low salinity effect on improving oil recovery can be found in polar oil system in the presence of hydrophilic surfaces, as well as in nonpolar oil system in the presence of hydrophobic surfaces, because of the significantly reduced adhesion forces from high to low salinity environment. Thus it can be concluded that for hydrophilic reservoirs, the low salinity effect may be remarkable in the case of crude oil containing more polar components. And for hydrophobic reservoirs, crude oil with more nonpolar components would exhibit a significant low salinity effect. All these provide a better understanding in the molecular level for low salinity water flooding applications.