Structure-Modified Fluorescent Carbon-Dots with Improved Colloidal Stability in Porous Media at High Salinity and Temperature for Reservoir Tracer Application

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. In this research, we report a modified method to synthesize fluorescent C-dots with enhanced colloidal stability at ultra-high salinity and lowered retention in reservoir rocks for tracer application.<br/> <br/>With a modified synthesis procedure, fluorinated and sulfonated functional groups were incorporated into the C-dots. The synthesis reaction occurs at hydrothermal condition 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. Retention and transport the C-dots in carbonate rocks were evaluated by core flooding experiments. The synthesized C-dots were readily dispersible in brines with extremely high salinity (TSD &gt;120,000ppm) at high temperature (95°C), and still exhibit high quantum yield for fluorescence, enabling sensitive detectability by optical spectroscopic or imaging techniques. Coreflooding experiments revealed neglectable adsorption of the C-dots on reservoir rocks.<br/> <br/>The synthesized C-dots exhibit improved stability at simulated oil reservoir conditions and lowered retention in reservoir rocks, while remained high fluorescence property, enabling their use as optically detectable nano-agent tracer in oil field application.