Construction and Oil Displacement Properties of Amphiphilic Carbon Nanofluid Composite

Carbon dots are suitable for low-permeability reservoirs owing to their particle size below 10 nm. However, their low interfacial activity limits their practical applications. In this work, lauryl amine-modified carbon dots were synthesized using citric acid and lauryl amine as raw materials, and an amphiphilic carbon nanofluid composite with high interfacial activity was constructed by compounding the as-prepared carbon dots with sodium laureth carboxylate. The morphology and chemical structure of the lauryl amine-modified carbon dots were characterized via field-emission transmission electron microscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The interfacial activity, wettability regulation capacity, oil film stripping performance, and core flooding efficiency of the amphiphilic carbon nanofluid composite were systematically investigated. Experimental results reveal that the synthesized lauryl amine-modified carbon dots possess an average particle size of 4.28 nm. When compounded with sodium laureth carboxylate at a ratio of 1:1, the composite exhibits interfacial tensions lower than 0.1 mN/m within the concentration range of 0.02–0.5% and can withstand four cycles of adsorption on oil sands. The amphiphilic carbon nanofluid composite is able to reduce the water contact angle to 18.63° and has a stripped oil film area fraction up to 94.22% at the concentration of 0.5%. Core flooding tests demonstrate that injecting one pore volume of carbon nanofluid composite after water flooding can enhance oil recovery efficiency by 11.05%. This study provides a reference for the research of carbon-dot-based nanofluid systems for enhanced oil recovery.