Influence of Potassium Salts on Adsorption and Surface Hydration Inhibition of Hexane-1,6-Diamine Clay Mineral Inhibitor: A Molecular Dynamics Study

Abstract Most shale formations, contain a large amount of expansive sodium montmorillonite (Na-Mnt), have high water adsorption, and hydration swelling, causing unstable wellbore wall, resulting from formation shrinkage, sticking, balling, time-wasting, and well collapse in extreme cases causing complex downhole accidents, and high costs. Polyamines like hexane-1, 6-diamine (HEDA), are shale inhibitors in shallow drilling. Inorganic, and organic K-salts can improve the inhibitory performance of polyamine inhibitors. Molecular dynamics (MD) simulations were applied to investigate K-salts' influence on the inhibition mechanism of HEDA to the Na-Mnt. The adsorption configuration is mainly by terminal amine groups with a flat-lying alkyl hydrophobic chain. Interaction with clay surface decreased the H2O-clay H-bonds, electrostatic, and van der Waals interactions, neutralised Mnt surface negative charge, reducing its surface hydration. HCO2K significantly improved the inhibition ability, and coordination of interlayer ions with H2O as they were replaced by K+, and H2O-HCOO- coordination reduced H2O-Mnt interactions, mobility capability of H2O molecules was significantly decreased. Its maximum concentration noted in this study is 1.65 wt.%. While KCl showed little ability, it also caused more hydration with time. HCO2K could be an alternative for offshore drilling instead of toxic KCl. This study provides a theoretical explanation for the inhibition mechanism and adsorption characteristics of HEDA inhibitor on Na-Mnt surfaces in the presence of K+-salts and may provide more insight into the evaluation, selection, and molecular design of new clay-swelling high-performance WBDF systems used in oil and gas complex offshore drilling well sections.