Investigation of anionic group effects on the shale inhibition performance of fatty acid-based ionic liquids and their inhibition mechanism

Ionic liquids (ILs) have been introduced as novel high-performance shale inhibitors. The inhibition performance and mechanism of the cation groups in ILs have been widely investigated, whereas the effects of the anionic groups in ILs on the inhibitory capacity have rarely been reported. In this work, a series of fatty acid-based ionic liquids (FAILs) with different anionic groups, methyltrioctylammonium octanoate ([N 8881 ][C 8:0 ]), methyltrioctylammonium laurate ([N 8881 ][C 12:0 ]), and methyltrioctylammonium palmitate ([N 8881 ][C 16:0 ]), were synthesized to evaluate their inhibition ability via the sodium bentonite (Na-Bent) immersion test, the linear swelling test, and the shale hot-rolling recovery test. Compared with the traditional inhibitor KCl (2 wt%), FAIL [N 8881 ][C 8:0 ] showed greater inhibition performance at a much lower concentration (0.1 wt%). The inhibition mechanism of FAILs was further analysed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), zeta potential measurements, and contact angle measurements. It was speculated that the best inhibition ability and thermal stability of [N 8881 ][C 8:0 ] should be attributed to the intensive interaction and the size-matching effect between cationic and anionic groups. The present study provided novel insight into the research and development of high-efficiency shale inhibitors.