Long carbon chain-modified carbon nanoparticles for oil displacement in harsh-condition reservoirs

Carbon nanoparticles, as an emerging type of enhanced oil recovery agent, promising broad prospects in unconventional oil and gas development. However, limitations such as low interfacial activity due to the strong hydrophilicity of carbon nanoparticles and tendency to aggregate under high-temperature and high-salinity conditions restrict their further application. In this study, activity carbon dots (S-CDs) were prepared via a simple two-step hydrothermal reaction. A range of physicochemical techniques characterized S-CDs, revealing their small particle size (1.4 ± 0.01 nm) and narrow distribution, maintaining strong dispersion stability in mineralized water at 130 °C with a concentration of 16 × 104 mg/L. The AFM scanning results indicated that S-CDs possessed strong interfacial wetting control capability, the adhesion force between oil and rock cores (after S-CDs treatment) decreased by 25 times. Particle Image Velocimetry (PIV) confirmed that S-CD adsorbed at the oil-water interface could formed a solid film, which could rupture into smaller oil droplets for convenient backward migration. The results demonstrated that S-CDs improved the interfacial activity while maintaining the hydrophilicity of CDs. In core displacement experiments, 0.05 wt% S-CDs nanofluid reduced injection pressure by 32.4 % and increased recovery rates by 34.9 %. This work provides new insights for the development of high-temperature, high-salinity displacement agents in harsh-condition reservoirs.