Fluorinated protic ionic liquids for clay swelling inhibition in water based drilling fluids

Wellbore instability caused by clay hydration, swelling, and dispersion remains a major challenge in water-based drilling fluids. Although conventional inhibitors such as KCl can suppress clay hydration, they provide limited molecular level control over clay surface interactions, interlayer hydration, and water accessibility. Moreover, the role of fluorinated protic ionic-liquid architecture in simultaneously regulating these processes remains insufficiently understood. Here, three fluoro-based protic ionic liquids (FIL 2 , FIL 4 , and FIL 6 ) were systematically investigated to establish a structure-property-performance relationship between molecular design and shale inhibition. FIL 6 exhibited the strongest inhibition, reducing the final swelling ratio to 105.16%, compared with 147.59% in deionized water and 129.01% with KCl, corresponding to reductions of approximately 28.7% and 18.5%, respectively. Capillary suction time decreased from 262.1 to 13.8 s, indicating reduced water retention and enhanced dewaterability. The median particle diameter (D 50 ) increased from 2.33 to 6.10 μm, while the zeta potential shifted from − 32.1 to − 23.9 mV, indicating enhanced aggregation and reduced electrostatic stabilization. Complementary structural, morphological, and thermal analyses further supported FIL-clay interactions and suppressed hydration. Collectively, the results support a complementary inhibition mechanism in which electrostatic interactions and charge screening reduce interparticle repulsion and promote clay aggregation, while fluorinated hydrophobic shielding restricts water accessibility. These findings demonstrate the potential of molecularly tailored fluoro-based protic ionic liquids as effective shale inhibitors for water-based drilling fluids.