Comparative Study on Cation Adsorption and Thermodynamic Characteristics of Clay Minerals in Electrolyte Solutions

Abstract

The interaction between clay minerals and electrolyte solutions critically affects waterflooding efficiency in enhanced oil recovery (EOR). This study systematically investigated the adsorption and thermodynamic properties of montmorillonite, illite, and kaolinite in different cationic solutions (K+, Na+, Ca2+, Mg2+), integrating adsorption isotherm analysis with immersion calorimetry for the first time. Montmorillonite showed the highest adsorption capacity, with the cation affinity following K+ > Na+ > Ca2+ > Mg2+. The highest immersion enthalpy was observed in KCl solution, indicating the dominant roles of ionic radius and solvation energy. Cation adsorption induced deformation of clay lamellae and modification of Si-O and Al-OH groups. These findings suggest that optimizing injected ion composition can enhance reservoir stability and waterflood performance, providing thermodynamic insights for EOR process optimization.