Imidazoline-Based Fatty Acid Derivatives as Novel Shale Inhibitors for Water-Based Drilling Fluids

Water-based drilling fluids (WBMs) are widely applied in petroleum engineering due to their lower cost and reduced environmental impact compared to oil-based muds. However, their performance is severely limited in shale formations, where hydration and swelling of clay minerals lead to wellbore instability. In this study, two novel imidazoline-type inhibitors were synthesized from fatty acids: A-Lin (derived from linoleic acid) and A-Lau (derived from lauric acid). The synthesis involved amidation followed by cyclization, and the products were characterized using FTIR and TGA. Their performance as shale hydration inhibitors was evaluated in WBM formulations and compared with commercial additives (Amine NF and Glycol). The FTIR spectra confirmed successful imidazoline ring formation, while TGA demonstrated good thermal stability up to 150 °C, with A-Lin exhibiting superior resistance due to its unsaturated structure. Rheological tests showed that the synthesized additives reduced plastic viscosity, thereby improving cuttings transport efficiency. Swelling tests revealed that A-Lin achieved the lowest final swelling (6.3%), outperforming both commercial inhibitors and the saturated A-Lau analogue. Furthermore, A-Lin provided the best lubricity coefficient (0.148), reducing torque and drag during drilling. Overall, A-Lin demonstrated strong potential as an efficient, thermally stable, and environmentally compatible shale inhibitor for advanced WBM formulations. Compared to conventional inhibitors such as KCl, glycol, and amine-based additives, A-Lin uniquely combines superior swelling inhibition, enhanced lubricity, and good thermal stability, highlighting its novelty as an imidazoline derivative derived from renewable fatty acids