Mitigating shale swelling in deep drilling: Novel natural deep eutectic solvent vs hybrid additives system

Shale instability during shale drilling poses significant challenges that require effective additives to control swelling and enhance water-based drilling fluids. This study investigates the effectiveness of various shale inhibitors, both individually and in combination, and compares them to the latest innovation i.e, Natural Deep Eutectic Solvents (NADES) as a promising alternative. Various additives including Potassium Chloride (KCl), 1-Ethyl-3-methylimidazolium chloride. ([EMIM]Cl), SiO 2 nanoparticles, amine terminated polyetheramine (ATPE), Okra mucilage, Choline Chloride:Urea Deep Eutectic Solvent (DES), and Citric acid:Glycerine Natural Deep Eutectic Solvent (CA NADES) and their combinations were subjected to rigorous examination to delineate their impact on shale stability and drilling fluid properties. Notably, CA NADES reduced mudcake thickness by 42.8 %, filtrate volume by 40.3 %, and linear swelling by 76.1 %, while improving shale recovery by 51.7 %. Among the additive combinations, SET B (0.5 % KCl + 0.5 % ATPE) and SET G (0.5 % KCl + 0.5 % [EMIM]Cl) demonstrated particularly effective performance. Surface tension measurements revealed favorable interfacial properties, X-ray diffraction analysis confirmed effective intercalation, and zeta potential assessments indicated improved colloidal stability. Overall, these findings highlight the critical role of optimized additive formulations in mitigating shale instability and enhancing drilling fluid performance, offering promising strategies for more efficient and reliable drilling operation. • Introduces Natural Deep Eutectic Solvent as an eco-friendly mud additive. • Demonstrates significant improvements with Citric acid based NADES. • Identifies promising hybrid additive combinations. • Provide insights into interfacial and colloidal stability mechanisms.