Quantitative Investigation of the Hydration Behavior of Sodium Montmorillonite by Thermogravimetric Analysis and Low-Field Nuclear Magnetic Resonance

Shale hydration and swelling are major hindrances for using water-based drilling fluids to develop shale gas. Quantitative investigation of the hydration behavior of clay minerals is helpful to further develop high-performance inhibitors to use with water-based drilling fluids. In this work, the hydration behavior of sodium montmorillonite (Na-MMT) was investigated by isothermal adsorption, X-ray diffraction, and thermogravimetric analysis (TGA) with microporous crucible technology and low-field nuclear magnetic resonance (LF-NMR). The adsorbed water content and the basal spacing of Na-MMT were found to be a function of relative humidity. The adsorbed water on Na-MMT of the first step by TGA was the cationic interlayer water. The adsorbed water of the second step was the interlayer surface water. The adsorbed water of the third step was the sum of the part of interlayer surface water and free water. The experimental results of the cationic interlayer water and interlayer surface water measured using LF-NMR were consistent with the TGA results. According to the above results, it was inferred that if the cationic interlayer water and interlayer surface water can be removed, the surface hydration of Na-MMT could be completely inhibited.