Zeta potential in porous rocks in contact with monovalent and divalent electrolyte aqueous solutions

Electrokinetic phenomena are the result of a coupling between a fluid flow and an electric current flow in porous rocks. The zeta potential is an important parameter that influences the electrokinetic coupling. Most reservoir rocks are saturated or partially saturated by natural water containing various types of ions. Therefore, it is important to understand how the zeta potential and therefore the electric double layer (EDL) behave for different types of ions or electrolytes. Types of electrolytes influence the zeta potential most by affecting the surface charge — by changing the thickness of the EDL and the exact location of the shear plane. To study the dependence of the zeta potential on various electrolytes, we have carried out streaming potential measurements for consolidated rock samples saturated by monovalent and divalent electrolytes. From streaming potential coefficients, the zeta potential is obtained for different systems of electrolytes and rocks. The experimental results of silica-based rocks are then compared with theoretical models. For 1:1 or 1:2 electrolytes, a theoretical model for the zeta potential that has been available in literature is used. For 2:2 or 2:1 electrolytes, we have developed a new model to calculate the Stern potential and the zeta potential. The comparison found that the theoretical models can explain the main behavior of the zeta potential against types of electrolytes and types of silica-based rocks. The results show that the zeta potential for monovalent electrolytes is higher than that for divalent electrolytes. The zeta potential of the silica-based samples is higher than that of the nonsilica-based samples when they are saturated by the same types of electrolyte.

A how-to approach for estimation of surface/Stern potentials considering ionic size and polarization

Based on the effects of ionic volume in Stern layer and polarization in diffuse layer, the relationship between surface potential and Stern potential is quantified.

Shear Thinning and Thickening of Alumina Suspensions

The rheological behavior of alumina suspension stabilized with Tri-ammonia citrate (TAC) was studied. It was thought that there would form some particle clusters due to the collisions between particles caused by their relative motion in the suspension, and such particle clusters are classified as thermodynamic clusters and hydrodynamic clusters by their origin. Shear thinning is the result of decomposition of the thermodynamic clusters, while shear thickening is the result of formation of the hydrodynamic clusters. From the view of cluster-forming potential barrier, it was deemed that the viscosities of alumina suspensions at low and high shear rates are respectively determined by zeta potential and Stern potential on the particle surface, and shear thickening behavior can be suppressed with some excessive TAC.