Study On Phase Behavior And Mass Transfer Of Carbon Dioxide-decane System Based On Micro/Nanofluidic Technology

Micro/nanofluidic technology has the advantages of real-time visualization and micro/nanoscale,which is of great significance to explore the phase behavior and mass transfer characteristics in the process of carbon dioxide flooding to improve oil recovery.Therefore,based on the micro/nanofluidic technology,the phase behavior and mass transfer mechanism of carbon dioxide-decane system were studied in this paper:Firstly,the minimum miscibility pressure(MMP)of carbon dioxide-decane system at micro/nanoscale were measured based on micro/nanofluidic technology and the miscible mechanism was investigated.By characterizing the fluorescence intensity of decane in the dead-end micro/nano channels,carbon dioxide-decane MMP at 5 μm scale and 50 nm scale was measured and compared.It is found that MMP of both 50 nm scale and 5 μm scale is 5.4 MPa at 293.15 K and 6.4 MPa at 303.15 K.Through theoretical calculation,MMP offset was only 0.17%at 50 nm scale.MMP at the 5 nm scale offset reached 2.5%,that is,the nanometer confinement effect occurred.Secondly,the mass transfer coefficient of carbon dioxide-decane system was measured by using self-made polymethyl methacrylate(PMMA)chip and the mass transfer mechanism was explored.It is found that the mass transfer coefficient increases with the increase of gas flow rate and liquid phase flow rate,and increases with the increase of ambient temperature.When the gas flow rate was 0.6-1.2 mL/min and the liquid flow rate is 0.1-0.4 mL/min,the liquid-side volumetric mass transfer coefficients kLa at 25℃,30℃ and 35℃ are 1.0-4.5 s-1,1.0-5.8 s-1 and 1.0-6.8 s-1,respectively.Finally,the carbon dioxide flooding process was simulated based on the microfluidic chip and the displacement mechanism was studied.The oil recovery can be obtained by analyzing the area of residual oil in the experimental photos.The effect of carbon dioxide immiscible flooding becomes better with the increase of displacement pressure.The recovery efficiency of immiscible flooding at 0.1-0.3 bar ranged from 60%to 82%,while almost 100%displacement efficiency can be achieved for miscible flooding at 56.9 bar.