Novel high-hydrophilic carbon dots from petroleum coke for boosting injection pressure reduction and enhancing oil recovery

Zero-dimensional carbon nanomaterials show intriguing potential in the field of unconventional oil resource development for reducing injection pressure and enhancing oil recovery. However, the complicated synthesis procedure, necessity for surfactant and limited understanding of the mechanism impede their practical applications. In this study, novel high-hydrophilic carbon dots (hh-CDs) with an average particle size of 2.54 ± 0.016 nm were facilely synthesized through an electrochemical approach by employing cost-effective petroleum coke as the carbon source, followed by treating with ozone for further oxidation. The abundant surface functional groups render hh-CDs superior hydrophilicity, dispersibility and stability. Core flooding tests show 0.20 wt% hh-CDs nanofluid delivers a prominent pressure-reducing rate of 23.81% and an enhancement in oil recovery of 26.38% without any surfactant. Analytical results of atomic force microscope (AFM) with hydrophobic probe reveal hh-CDs can adsorb on the rock surface to alter the micro-scale wettability from oil-wet to homogeneous water-wet. The hh-CDs can also efficiently reduce the core surface roughness and afford excess disjoining pressure for oil displacement, accounting for the impressive performance. This work provides a feasible oil systemic circulation for the synthesis of versatile surfactant-free carbon dots for boosting injection pressure reduction and enhancing oil recovery in tight oil reservoirs.