Experimental investigation and molecular simulations of CQDs for asphaltene deposition inhibition during CO2-EOR

Asphaltene deposition is a significant issue in CO2-EOR, leading to reservoir damage and reduced efficiency. In this study, oil-soluble carbon quantum dots (CQDs) were synthesized to address asphaltene deposition issues, evaluating the inhibitory performance through laboratory experiments and molecular dynamics (MD) simulations. Experimental results demonstrated that CQDs effectively delayed the onset of asphaltene deposition from 45 vol% to 55 vol%, reduced the average particle size of asphaltene aggregates from 1200 nm to approximately 600 nm, and achieved an inhibition rate of 52.7 %. MD simulations revealed that CQDs reduced the mobility of asphaltene molecules and decreased the number of stacked asphaltene model molecules in aggregates from four to two, thereby lowering the risk of aggregation and subsequent deposition. Furthermore, the study showed that CQDs primarily inhibit asphaltene aggregation and deposition by weakening T-shaped or offset stacking interactions between asphaltene molecules. This effect was attributed to the strong interactions between CQDs and asphaltenes, with stabilization energies reaching up to -90 kcal/mol. Asphaltene molecules formed it-it interactions with CQDs through it-electron cloud overlap, dispersing the it-it interactions originally occurring between asphaltene molecules. This ultimately suppressed asphaltene aggregation. These characteristics suggested that CQDs offer a promising new approach to mitigate asphaltene deposition and have the potential to enhance oil recovery in low-permeability reservoirs.