Zeta potential of porous rocks in contact with mixtures of monovalent and divalent electrolytes

Abstract

A B S T R A C TThe zeta potential is one of the most important parameters influencing the electrokinetic coupling. Most reservoir rocks are saturated or partially saturated by natural water containing various types of ions (mostly monovalent and divalent ions). Therefore, understanding how the zeta potential behaves for mixtures of electrolytes is very important. In this work, measurements of the zeta potential for four different silica-based samples saturated by seven different mixtures of monovalent and divalent electrolytes are then carried out at a fixed ionic strength. It is seen that the magnitude of the measured zeta potential decreases with increasing divalent cation fraction. The experimental results are then explained by a model developed for mixtures of monovalent and divalent electrolytes. The result shows that the theoretical model is able to reproduce the main trend of the variation of the zeta potential with divalent cation fractions. Additionally, the model can fit the experimental data reported in literature well for reasonable values of the input parameters.

Streaming Potential Coefficient Measurements in Porous Rocks Saturated by Divalent Electrolytes

“…5 is the same for two other electrolytes (CaCl2 and CaSO4). It is seen that the SPC in magnitude decreases with an increase of the electrolyte concentration for all studied rocks and that is in good agreement with published data in literature for monovalent electrolytes [e.g., [12][13][14][15]. Figure 6 shows the variation of the SPC in magnitude with rock types for all studied electrolytes at a representative concentration of 10 -4 M. It is seen that the SPC of Bentheim sandstone and Artificial ceramic are almost the same but significantly higher than that of Berea sandstone (more than three times) at a given electrolyte concentration.…”