Mechanisms of high-temperature inhibition of montmorillonite surface hydration by polyethyleneimine additives

The hydration swelling of clay minerals during oil and gas production can severely compromise wellbore stability, particularly under deep, high-temperature, and high-pressure conditions, where the thermal limitations of drilling fluids exacerbate downhole accidents. This study employs molecular dynamics (MD) simulations to investigate the interactions between water molecules, clay, and polyethyleneimine (PEI) under high-temperature and high-pressure conditions. Key parameters, including dynamic parameters, hydration characteristics, adsorption conformations of water, Na⁺, and PEI, and intermolecular interaction energies, were analyzed to elucidate how PEI molecules inhibit montmorillonite surface hydration. The results reveal that PEI primarily hinders hydration through Coulombic interactions and hydrogen bonding with the Na-montmorillonite surface, with inhibition significantly declining above 473 K. Functional groups like -NH₂ and -OH enhance PEI adsorption at high-temperature, while -SO₃⁻ and -COO⁻ groups improve both the hydration resistance of PEI and its disruption of the montmorillonite hydration layer at high-temperature. These findings provide a theoretical basis for the design of shale inhibitors in high-temperature drilling fluids and offer insights into the underlying mechanisms. The research has significant implications for developing drilling fluids capable of maintaining stability under high-temperature conditions.