Water vapor adsorption on the mixtures of swelling and non-swelling clays.

This article investigates the adsorption behavior of water vapor on swelling montmorillonite (Mt), non-swelling kaolinite (Kaol), and their mixtures with varying mass ratios, aiming to elucidate water–clay interactions relevant to hydraulic fracturing in shale gas reservoirs. The study finds that Mt exhibits significantly higher water vapor adsorption capacity and affinity than Kaol, with primary adsorption dominating in Mt and secondary adsorption more prominent in Kaol; increasing the Mt proportion in mixtures enhances overall water uptake and adsorption spontaneity. Adsorption isotherms were best described by the D'Arcy and Watt model, and thermodynamic analysis showed that surface potential and Gibbs free energy changes correlate positively with Mt content, while higher temperatures reduce adsorption affinity and spontaneity. These findings highlight the critical role of swelling clays like Mt in controlling water retention and swelling in shale formations during hydraulic fracturing.