Intercalation behavior of branched polyethyleneimine into sodium bentonite and its effect on rheological properties

Abstract

The inhibitive mechanism of low-molecular-weight branched polyethyleneimine (BPEI) with multiple primary amines and 1,6-hexamethylenediamine (HMDA) with two primary amines adsorbed on sodium bentonite (Na+Bent) has been investigated using isothermal adsorption, adsorption kinetics, scanning electron microscopy (SEM), X-ray diffraction (XRD) and elemental analysis (EA) techniques. The results indicate that as the number of primary amine groups in the inhibitor increases, the saturated adsorption amount decreases, and the adsorption rate increases. Low-molecular-weight BPEI molecules enter the interlayer space of Na+Bent and significantly reduce this space compared to that in hydrated Na+Bent. Moreover, there is no change in the clay interlayer space of Na+Bent with increasing BPEI concentration. A monolayer of BPEI intercalates into the clay interlayer and replaces the sodium ions in the interlayer. The BPEI molecules become firmly embedded in the Na+Bent interlayer between the primary amine groups and Si-O groups, resulting in the removal of water molecules. The inhibitive performance shows that BPEI inhibits clay hydration more effectively than HMDA and other inhibitors, and also indicates that as the number of primary amines increases, the inhibitive performance increases. When <1wt% BPEI was added, the rheological properties improved significantly, and the American Petroleum Institute standard (API) fluid loss could be controlled well, indicating that BPEI can effectively create a balance between swelling inhibition and the rheological properties of water-based drilling fluids. Overall, the results indicate that BPEI is promising as a commercial shale inhibitor.