Biomass-Derived Carbon Quantum Dots for Wettability Alteration of Oil-Wet Carbonate Rocks: A Micromodel Flooding Study

Abstract

Restoring the water-wet state of oil-wet carbonate rocks through wettability alteration is one of the most effective approaches for improving oil recovery. Although conventional surfactants and nanomaterials have been widely investigated for this purpose, carbon quantum dots (CQDs) synthesized from sustainable biomass precursors have received limited attention in enhanced oil recovery applications. This study investigates the effect of CQDs derived from brewed coffee grounds on altering the wettability of oil-wet carbonate rocks and, consequently, improving oil recovery. CQDs were synthesized using a modified hydrothermal method and comprehensively characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), and dynamic light scattering (DLS). Contact angle measurements demonstrated a significant reduction from 123° for untreated oil-wet rocks to 52° following treatment with a 3 vol.% CQD suspension, indicating a substantial shift toward water-wet conditions. In contrast, the CQDs showed no significant effect on the interfacial tension (IFT) between crude oil and water. Micromodel flooding experiments resulted in an incremental oil recovery of approximately 15.8% compared with DI water flooding. Overall, the results indicate that the spent-coffee-ground-derived material altered the wettability of oil-aged carbonate surfaces and improved oil recovery in the tested oil-wet micromodel.

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