Performance and mechanism of DL-alanine ionic liquid shale inhibitor

Shale hydration and expansion during drilling can lead to wellbore instability, sticking, and frequent leakage accidents. To prevent these issues, an ionic liquid (IL) inhibitor solution was synthesized using DL-alanine and 98% concentrated sulphuric acid as raw materials. The optimum composition and effect of the synthesized inhibitor in oilfield water-based drilling fluids were evaluated through anti-expansion, linear expansion rate, water washing resistance, and clay hydration dispersion experiments. The inhibition mechanism was investigated by thermogravimetric analysis, infrared spectroscopy, zeta potential, contact angle, and X-ray diffraction analysis. The results show that the optimum IL consists of a 1:1 molar ratio of DL-alanine to concentrated sulphuric acid synthesized under a reaction temperature and time of 70°C and 18 h, respectively. The resulting DL-alanine IL exhibited the best inhibitory effect on the hydration, dispersion, and expansion of clay at a concentration of 0.5% in aqueous solution, and its linear expansion rate was only 18.49%. After adding a quantitative amount of clay to different concentrations of DL-alanine IL aqueous solution, the expansion volume of the clay decreased and the water washing resistance significantly improved. These results provide a theoretical basis for improving the safety and efficiency of shale horizontal well drilling operations.