Development and Microscopic Oil Displacement Mechanisms of Active Quantum Dot Fluids for Chemical Flooding in Low-Permeability Reservoirs

Low-permeability reservoirs hold substantial reserves, accounting for approximately 38% of global crude oil reserves. However, their strong heterogeneity and significant capillary resistance lead to severe pressure loss during water flooding, resulting in poor oil mobilization and an average recovery rate of less than 20%. Regulating capillary resistance through interfacial manipulation is crucial for improving development efficiency in such reservoirs. Therefore, a green active quantum dot material A-QDs was synthesized via the hydrothermal method and surface modification. Its main performance and microscopic oil displacement mechanisms were systematically investigated. The results indicate that A-QDs have a particle size of approximately 7 nm and exhibit excellent dispersion stability under conditions of 70 °C and a salinity of 62 179 mg/L. Thanks to their amphiphilic structure, A-QDs significantly reduce the oil/water interfacial tension and alter the rock wettability from strongly oleophilic to strongly hydrophilic, and the adsorption capacity is low, with only 1.02 mg/g adsorbed at low concentration. The results of the CT scan displacement experiments and digital core analysis indicate that A-QDs exert a synergistic effect through “small size, ultra-low interfacial tension, and wettability alteration,” effectively transforming capillary force from a resistance into a driving force for oil displacement. This mechanism breaks through the limitation of small pore throats, thereby significantly improving the sweep efficiency and oil recovery efficiency of the remaining oil. The results show that A-QDs can effectively promote the activation and migration of residual oil, and provide technical support for the green and efficient development of low-permeability reservoirs.