Emulsion flooding has been proposed for enhanced oil recovery (EOR) since it blocks the pores and diverts the preferential flow path. However, a new mechanism of the microemulsion flooding is hypothesized that the oil phase is displaced through miscible interface where capillary forces could be negligible, thereby leading to a higher oil recovery in this study. To this end, we use high-resolution X-ray CT imaging technique to help understand the EOR process by microemulsion flooding in water-wet and oil-wet porous media at the pore scale. After immiscible water flooding, oil recovery in water-wet reservoir is much higher than that in oil-wet reservoir. Compared with water-wet case, the capillary pressure in oil-wet case shows negative which is very decremental to the oil removal. After microemulsion flooding, oil recovery increases significantly even in the oil-wet reservoir. The pore-scale imaging shows miscible displacement interface causes the oil solubilization into the flowing microemulsion, thereby eliminating the capillary pressure.
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