Modified Carbon Dots with Lowered Retention and Improved Colloidal Stability for Application in Harsh Reservoir Condition

Abstract Tracer technology has been increasingly used in inter-well tests to investigate reservoir performance, reservoir connectivity and residual oil saturation for providing useful information to improve decision making in reservoir management. Stable nanoparticle tracers with high-sensitive real-time detectability are highly desired, and as one of the nanoparticles tracers, carbon dots (C-dots) have been studied and tested as nano-agent tracer in field trial for reservoir monitoring. In this research, we report a modified method to synthesize fluorescent C-dots and fluorinated, sulfonated or zwitterionic functional groups were incoprtated into the C-dots. The synthesis reaction occurs at hydrothermal conditions with inexpensive starting materials and is readily to scale up for industrial application. Optical properties of the synthesized colloidal C-dots were studied by UV-visible and fluorescence spectroscopies. Colloidal stability was studied by dynamic light scattering (DLS) measurements, and retention of the C-dots in porous medium was evaluated by adsorption experiment with limestone rock. The synthesized C-dots are readily dispersible in freshwater and synthetic brines and exhibit improved colloidal stability in hot brine and lowered retention in reservoir rocks. In comparison with those C-dots reported in literatures, our results suggest that the synthesized C-dots using the modified procedure have excellent fluorescence properties, improved thermal stability, photostability, and water dispersibility, enabling their use as optically detectable nano-agent tracer in oil field application.