Molecular Dynamics Study on Characterization of CO2/Oil Miscibility in Nanopores

CO2 enhanced oil recovery (CO2-EOR) has received significant attention in the field of energy and environment due to its ability to increase oil production and reduce greenhouse gases. Minimum miscibility pressure (MMP) has become a research hotspot as a key parameter in the implementation process of this technology. In this paper, based on molecular dynamics simulation, the MMP of the established complex oil and gas system in the confined state is calculated by applying the diminishing interface method, which quantitatively analyzes the response rules of two-phase miscibility to the external conditions. The proportional distribution of straight-chain alkanes in the oil phase is regulated, which clarifies the dominant sequence of influence on MMP during CO2 displacement. It is found that the system MMP increases linearly with the increase of chain length. The effects of different alkane structures on MMP are compared. The study finds that the presence of cycloalkanes and aromatics greatly increases the pressure required for reservoir exploitation. The study quantitatively analyzes the change mechanism of MMP of CO2-EOR process in the restricted state from the nanoscale, which provides theoretical basis for the development of tight oil reservoirs.