Exploring the synergistic effects and mechanistic insights of ionic and polyionic liquid combinations as shale inhibitors

A B S T R A C T Ionic liquids (ILs), recognized for their negligible vapor pressure, thermal stability, and structural tailorability, offer targeted inhibition of clay expansion. Compared to ILs, polyionic liquids (PILs) possess stronger mechanical properties and adsorption capabilities, showing even greater potential in inhibiting clay swelling. In this work, we synthesized and characterized an imidazole-based ionic liquid (IL-NH 2 ), a polyionic liquid (PIL-ABHIm), and a PIL/IL combination. Their inhibitory performance was rigorously evaluated under simulated drilling conditions through immersion tests, linear swelling tests, among others. Additionally, the mechanisms underlying their interaction with clay minerals were elucidated through contact angle measurements, Fourier-transform infrared spectroscopy, X-ray diffraction (XRD), Zeta potential analysis, and molecular electrostatic potential (MEP) analysis. This work demonstrates that IL-NH 2 inhibits osmotic hydration by altering the interlayer structure of the clay, while PIL-ABHIm reduces surface hydration by forming a hydrophobic barrier on the clay surface. PIL/IL combines both mechanisms, significantly enhancing the stability of clay through the dual mechanisms of cation exchange and hydrophobic barriers. These findings reveal an innovative mechanism by which PIL/IL combination inhibits clay hydration and swelling, providing a scientific foundation for their application in drilling fluids.