Visualization of CO2-oil vanishing interface to determine minimum miscibility pressure using microfluidics

The determination of the minimum miscibility pressure (MMP) assumes paramount significance in evaluating CO2 enhanced-oil recovery strategies. We created a microfluidic method for determining the MMP of CO2 and oil samples by integrating the direct observation of the vanishing interface and the analysis of fluorescence intensity exhibited by oil samples. A microfluidic chip is designed with closed-end microchannels to mimic the blind-end fractures which contributes to reveal the complete picture of residual oil mobilization during CO2 miscible flooding. The maximum deviation of 3.83 % and 5.47 % unequivocally attested to the accuracy of our method by comparing measured MMPs with those reported in the literature and theoretically calculated in this study. The effects of alkane types, temperature and oil compositions on MMP was investigated. The MMPs for binary synthetic oils (C8 + C14) increased non-linearly with contents of tetradecane and increased significantly at C14 > 75 vol%. MMPs of nine n-alkanes, seven binary synthetic oils, four ternary synthetic oils and kerosene were provided reliably as the unprecedented new data. Such unique advantages as in-situ visualization, chip pattern customizability, user-independence, and the clear criterion render this research highly valuable for determining the MMP as well as elucidating the microscopic mechanisms underlying residual oil mobilization.