Development of a Green and Sustainable Nanofluid Based on Carbon Dots with Sensing Capability for Enhanced Oil Recovery

Carbon dots (CDs) as a zero-dimensional family of nanocarbon provide a great potential for enhanced oil recovery (EOR) owing to the outstanding physicochemical and optical properties for manipulation and detection of the water–rock–oil ternary system. Herein, CDs were synthesized with citric acid and urea via an easy and fast microwave-assisted carbonization method and characterized by atomic force microscopy (AFM), dynamic light scattering (DLS), ζ-potential, and thermogravimetric analysis (TGA) to prepare nanofluids as a tracing and flooding agent in the oil field. The as-synthesized CDs with a quantum yield of 35% demonstrated a long-time fluorescence emission stability in a brine solution with 50,000 ppm salt concentration for more than 3 months to be used as a tracer for on-site water monitoring to manage and optimize oil production by following the flow path in the oil reservoir. Moreover, the oil sweeping efficiency of CDs on the carbonate rock reservoir was evaluated by controlling the viscosity, wettability alteration, and interfacial tension, and a displacement mechanism was proposed by following the nanofluid flow on the micromodel pattern. Experimental results showed convenient water traceability and around 33% oil recovery for the prepared nanofluid with a low concentration of CDs (ca., 500 ppm).