Molecular Dynamics Simulation on the Mechanism of Shale Oil Displacement by Carbon Dioxide in Inorganic Nanopores

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Shale oil reservoirs feature a considerable number of nanopores and complex minerals, and the impact of nano-pore confinement and pore types frequently poses challenges to the efficient development of shale oil. For shale oil reservoirs, CO2 flooding can effectively lower crude oil viscosity, enhance reservoir physical properties, and thereby increase recovery. In this paper, the CO2 displacement process in the nanoscale pores of shale oil was simulated through the molecular dynamic simulation method. The performance disparity of quartz and calcite slit nanopores was discussed, and the influences of nanoscale pore types and displacement rates on CO2 displacement behavior were further analyzed. The results demonstrate that the CO2 displacement processes of different inorganic pores vary. In contrast, the displacement efficiency of light oil components is higher and the transportation distance is longer. Intermolecular interaction has a remarkable effect on the displacement behavior of CO2 in nanopores. On the other hand, it is discovered that a lower displacement rate is conducive to the miscible process of alkane and CO2 and the overall displacement process of CO2. The displacement efficiency drops significantly with the increase in displacement velocity. Nevertheless, once the displacement speed is extremely high, a strong driving force can facilitate the forward movement of alkane, and the displacement efficiency will recover slightly.