In-situ synthesis of high thermal stability and salt resistance carbon dots for injection pressure reduction and enhanced oil recovery

Carbon dots (CDs) show great potential as a new type of oil-displacing agent for unconventional oil and gas development. However, the instability and easy aggregation epitomize the challenges that accompany the application of CDs in high temperature and high salinity (HT/HS) reservoirs. In this research, novel benzene sulfonate-modified carbon dots (BS-CDs) with remarkable thermal stability and salt resistance were fabricated through an in-situ electrochemical exfoliation method. Molecular simulation verifies that the introduction of benzene sulfonate groups substantially strengthens the electrostatic repulsion between BS-CDs, leading to outstanding dispersibility and stability even at a temperature of 100 °C and salinity of 14 × 10⁴ mg/L. Core flooding tests show that 0.05 wt.% BS-CDs nanofluid can significantly reduce the water injection pressure by 50.00% and enhanced oil recovery (EOR) to 68.39% under HT/HS conditions. According to the atomic force microscopy (AFM) scanning results, the adhesion force between the core (after BS-CDs treatment) and oil decreased by 11.94 times, indicating that the hydrophilicity of the core surface was increased. In addition, the distribution of the adhesion force curve is more concentrated, which means that the micro-scale wettability of the core changes from oil-wet to more homogeneous water-wet. This study provides a feasible way for the development and application of good thermal stability and salt resistance CDs in unconventional reservoir development.