Effect of Alkyl Chain Length on Shale Hydration Inhibitive Performance of Vinylimidazolium-Based Ionic Liquids

Previously, our group developed a vinylimidazolium-based ionic liquid (IL) as an excellent shale hydration inhibitor for water-based drilling fluids (WBDFs). Herein, several ILs with different alkyl-chain lengths on the vinylimidazolium group were successfully synthesized by adjusting the cation composition to study their influence on inhibition performance. The results indicated that the IL with an ethyl group (C2) showed the strongest inhibitory effects for bentonite swelling, shale-cutting dispersion and rheological properties of bentonite suspension. Furthermore, the IL inhibition performance decreased with increasing alkyl-chain length. Accordingly, we concluded that as alkyl-chain length increased, the IL molecular volume increased, while the IL hydrophilicity and solubility decreased; minimizing the interlayer space and decreasing the water activity became more difficult, thus decreasing their inhibiting performance. Simultaneously, the reduction in inhibition performance has little relationship with the ability to suppress the double electron layers. All these findings can serve as a basis for designing ILs for high-performance shale hydration inhibition in WBDFs