Investigating the Role of Alkyl Chain Length of the Inhibitors on Its Intercalation Inhibiting Mechanism in Sodium Montmorillonite

Shale hydration and swelling are the major problems in using water-based drilling fluids in developing shale gas. In this work, the intercalation inhibiting mechanism of alkyl chain length on the swelling of sodium montmorillonite (Na-MMT) has been innovatively investigated using isothermal adsorption, adsorption kinetics, scanning electron microscopy, X-ray diffraction, cation exchange capacity, elemental analysis, and X-ray photoelectron spectroscopy techniques. The results indicate that an increase in the alkyl chain length of the inhibitor reduces the saturated adsorption capacity of the inhibitor on Na-MMT accordingly, thus reducing the dosage of the inhibitor. The adsorption rate constant increased rapidly when the length of the alkyl chain was increased, which also reduced the degree of hydration of the clay minerals and improved the inhibitory potential. When a flat-lying monolayer of alkyl chain containing four to seven carbon atoms was inserted, the d-spacing of Na-MMT was minimized compared to the hydrated Na-MMT, which in turn replaced the sodium ions in the interlayer space of Na-MMT. The inhibitor was strongly attached in the Na-MMT interlayer between the silicon–oxygen tetrahedron and the primary amine groups. Finally, the water molecules were expelled from the interlayer of Na-MMT. Therefore, the alkyl chain length inhibitors should be considered to design a better class of inhibitors when using the water-based drilling fluid system.