Minimum Miscibility Pressure of the CO₂-Hydrocarbon System Based On Nanofluidics

The large-scale development of onshore shale oil is not only an inevitable choice under the current oil and gas resource endowment in China but also a vivid practice to ensure national energy security. The CO2 Huff-n-Puff method, as one of the main ways to enhance the recovery factor of shale oil, has broad application prospects. In view of the complex interaction mechanism of the CO2-hydrocarbon system in the nanospace, which is still poorly understood and lacks experimental means, this paper designs two types of terminal-closed single tubes and porous medium tubes in a nanochip. This design, different from the open-ended single tube, can effectively eliminate the influence of convection and more realistically simulate the fluid mobilization process in the dead-end pores of shale. Based on the nanofluidics experimental, we utilized fluorescence and bright-field imaging to further clarify the gas–liquid miscible process. Additionally, we determined the minimum miscibility pressure (MMP) of CO2 with seven single-component alkanes and multicomponent mixtures at a high temperature of 70 °C and a scale of 30 nm. Notably, we first discovered that the MMP of a multicomponent mixture composed of C6, C10, and C16 in a 10:44:16 molar ratio at a size of 30 nm was 4.37% lower than that in the bulk, providing evidence for the presence of a confinement effect. In addition, we find that the nanofluidics not only has extremely low time cost and minimal sample usage but also has good accuracy (maximum error not exceeding 5%). This effective method, combined with a large amount of MMP values for CO2 and elemental alkanes as well as multicomponent mixtures at reservoir temperatures, may provide theoretical support for CO2-enhanced oil recovery.