Charging behaviour at the carbonate rock‐water interface in low‐salinity waterflooding: Estimation of zeta potential in high‐salinity brines

Abstract

Abstract The study of zeta potential using electro‐kinetic analyzers that measure streaming potential has limitations of measurements to relatively low ionic strength solutions (<0.1 mol/L) due to the threshold limit of streaming potential signal above a certain limit of ionic strength. The objective of this study is to indirectly estimate the zeta potential for higher salinity brine using the zeta potential measurements for low salinity brine, develop an understanding of electrostatic shielding as predicted by the electric double layer (EDL) model, and overcome the limitation of the apparatus. Zeta potential become less negative as ionic strength increases, as per the Gouy–Chapman–Stern theory. It explains the suppression of electro‐kinetic phenomena due to the gradual compression of the diffuse layer. Our calculations show that the zeta potential and the Debye length become nearly constant at higher ionic strength. The ability to estimate zeta potential by the Gouy‐Chapman‐Stern theory at increasing ionic strength is limited. This theory predicts that the concentration of counter‐ions in the Stern layer increases with increasing ionic strength of the brine until the surface charge becomes neutralized and the diffuse layer collapses. However, it ignores the spatial extension of ions. It considers them as a point charge and may not accurately predict the zeta potential at higher ionic strength. The extent of diffuse layer compression is thus limited to the size of the hydrated counter‐ion. It is very unlikely that the measured zeta potential will become zero at higher ionic strength of brines and our calculations show the same.