Colloidal stability and rheological behavior of a hydrophilic nanofluid for wettability modification, interfacial tension reduction, and improving sweep efficiency at the pore scale of carbonate formations

This study introduces a novel hydrophilic nanofluid composed of multi-walled carbon nanotubes, chitosan biopolymer, and a zwitterionic surfactant (cocamidopropyl betaine) to address Enhanced Oil Recovery (EOR) challenges in carbonate reservoirs, including oil-wetness, high interfacial tension, and asphaltene instability. The optimized formulation at 200 ppm demonstrated excellent colloidal stability at 80 °C for 15 days (zeta potential: −58.74 mV) and enhanced viscosity relative to the pristine polymer solution. Wettability was drastically altered from an oil-wet state (136°) to a strongly water-wet condition (19.11°), while interfacial tension was reduced by 94% to an ultra-low value of 1.06 mN/m. Core flooding experiments yielded an incremental oil recovery of 35.84%. Asphaltene dispersant tests confirmed 93.43% efficiency at the optimal dosage. This work offers a scalable and environmentally conscious nanofluidic strategy for enhancing production from challenging asphaltenic carbonate formations.