Synthesis and mechanism research of a new low molecular weight shale inhibitor on swelling of sodium montmorillonite

Shale gas as green and clean energy is attracting more interest. However, shale hydration and swelling have become the major challenges using water‐based drilling fluids, replacing oil‐based drilling fluids, for developing shale gas. In this work, a low molecular weight branched polyamine (NETS) as clay swelling inhibitor was synthesized. The NETS performed excellent inhibition property by linear expansion experiments and cuttings hot‐rolling recovery. The inhibition mechanism of NETS was investigated using X‐ray diffraction, fourier transform infrared spectroscopy, cation exchange capacity, X‐ray photoelectron spectroscopy, scanning electron microscopy, and zeta potential. The results show that the NETS can adsorb on Na‐Mt, decrease the basal spacing of wet Na‐Mt from 1.91 to 1.43 nm, and replace majority sodium ions from interlayer of Na‐Mt. However, replaceability of sodium ions and inhibition of water molecules of ethylenediamine are worse than NETS. These indicate that the primary amines of NETS had strong interaction with Na‐Mt, tensed clay layers and decrease the basal spacing. The combination of long hydrophobic chain and primary amines makes NETS to adsorb on surface of Na‐Mt, intercalate into interlayer of Na‐Mt with tilted monolayer arrangement, and replace sodium ions. The more the number of primary amine groups, the better the inhibition performance. Therefore, NETS has a great potential to be an outstanding shale inhibitor of water‐based drilling fluids in the future. A kind of shale inhibitor (NETS) with four primary amine groups was synthesized. The inhibition mechanism and performance of NETS were investigated. NETS can replace water molecule and sodium ions and decrease the basal spacing of interlayer.