Microfluidic and Molecular Insights into Enhanced Recovery and Asphaltene Deposition Behavior during CO2 Miscible Flooding.

CO2 miscible flooding is an effective enhanced oil recovery (EOR) technique. However, its application is constrained by unclear microscopic displacement mechanisms and the risk of asphaltene deposition. Furthermore, conventional macroscopic experiments and microscopic simulation often fail to adequately address the conditions of medium-deep reservoirs. This study employs an integrated approach combining high-pressure, high-temperature microfluidic experiments with molecular simulations. The microfluidic experimental system enables direct visualization of CO2-crude oil interface dynamics and asphaltene deposition, while quantifying oil recovery. Concurrently, simplified molecular models were constructed based on representative hydrocarbon components of authentic shale oil (i.e., light to heavy alkanes C7H16-C18H38, verified by GC-MS analysis) to analyze alkane adsorption, diffusion on different mineral wall surfaces, and the underlying mechanisms of asphaltene deposition. The results demonstrate that miscible conditions significantly enhance displacement efficiency, with miscible flooding achieving oil recoveries of 84% at 50 °C and 91% at 80 °C, which are significantly higher than those of immiscible flooding (59% and 65%, respectively). However, an increased temperature increases the risk of asphaltene precipitation. Molecular simulations confirm that CO2 exhibits higher solubility in light alkanes (e.g., C7H16) and that high temperature weakens the adsorption of alkane molecules onto quartz surfaces. This study provides critical insights for optimizing CO2 miscible flooding in shale oil reservoirs, proposing a near-miscible strategy at 80 °C that balances high recovery (82%) with economic viability.