Intercalation Inhibits the Surface Hydration of Sodium Montmorillonite: Experiments and Density Functional Theory Simulation

Abstract

In order to use water-based drilling fluids to substitute for oil-based drilling fluids in the drilling industry, one of the main challenges is the inhibiting the surface hydration of clay to further develop oil and gas resources. In this work, low-molecular weight branched polyethylenimine (BPEI) and hexamethylenediamine (HMDA) as inhibitors were used to investigate the inhibitory mechanism of surface hydration on sodium montmorillonite (Mt) using isothermal adsorption, X-ray diffraction (XRD), thermogravimetric analysis (TGA), low field nuclear magnetic resonance (LF-NMR), the Brunner–Emmet–Teller (BET) technique, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), and density functional theory (DFT) simulations. The XRD results confirmed that HMDA and BPEI could decrease the d001 values of hydrated Mt from 1.91 to 1.32 and 1.39 nm, respectively. These results verified that the interlamellar space of Mt-HMDA and Mt-BPEI may contain one layer of water molecules. TGA and LF-NMR analyses further confirmed that HMDA can restrict Mt to one-layer hydration, while BPEI can completely inhibit the interlayer surface hydration of Mt. The HMDA and BPEI could displace the exchangeable cations in the interlamellar space of Mt, whereas as the number of primary amine groups increased, both the displaced exchangeable cations and the inhibition performance increased. The DFT simulation results showed that, as the number of primary amine groups increased, both the adsorption energy of the inhibitor on the Mt surface and the inhibition performance increased. Finally, the mechanism of the inhibition of the clay surface hydration through intercalation adsorption was put forward. The theory and method can be helpful in designing inhibitors that completely inhibit the surface hydration of clay.

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