Preparation and Mechanism of Low-Molecular-Weight Amine-Based Inhibitor that Completely Inhibits Surface Hydration of Clay Minerals

The inhibition of surface hydration is the most fundamental technical measure for controlling shale borehole stability, but little research has been conducted on the inhibition of surface hydration. In this study, the low-molecular-weight amine inhibitor NH-2 was prepared. The inhibition performance of the NH-2 inhibitor was studied by linear expansion experiment, shale rolling recovery, isothermal adsorption, X-ray diffraction and thermogravimetric analysis. The inhibition mechanism was studied by X-ray diffraction and X-ray photoelectron spectroscopy. The results showed that 1 wt% NH-2 had a lower linear expansion ratio than did 5 wt% KCl and 1 wt% polyamine. The shale rolling recovery rate of the drilling fluid significantly improved after the addition of the NH-2 inhibitor. After the inhibitor NH-2 was added, the unit adsorbed water content of sodium montmorillonite decreased from 0.1104 g/g to 0.0331 g/g. The basal spacing of dry sodium montmorillonite increased from 1.01 nm to 1.3 nm, while that of wet sodium montmorillonite decreased from 1.9 nm to 1.31 nm. The DTG curve has only one low-temperature peak, and the sodium ion content in sodium montmorillonite was greatly reduced. These results showed that the NH-2 inhibitor has good inhibition performance. The inhibitor NH-2 enters the interlayer space of sodium montmorillonite through intercalation, displaces exchangeable cations, and minimizes the base spacing of sodium montmorillonite. Thus, the surface hydration of sodium montmorillonite was completely inhibited. In addition, the decomposition temperature of the NH-2 inhibitor was 232°C, which indicates good thermal stability. This study provides an inhibitor with high temperature resistance and efficient inhibition of hydration.