A volume of fluid (VOF) method is used to study the immiscible gas-liquid two-phase flow in a microchannel T-junction, through which the accurate interface of the Taylor bubble flow inside the microchannel is captured and compared with visualization experiment of Taylor bubbles' generation inside a Tjunction microfluidic chip. The numerical results are in good agreement with the experimental measurements, which confirms the validation of our model. Then the length of gas-liquid slugs and velocity distribution inside slugs at various conditions are investigated with the superficial velocity of gas and liquid phase ranging from 0.01 to 0.90 m/s, and capillary number ranging from 6.4 × 10 −4 to 1.7 × 10 −2 . A comprehensive description of mechanism of bubbles' break-off is achieved and the transition capillary number from squeezing regime to shearing regime is found around 5.8 × 10 −3 . Finally the influences of fluid viscosity, surface tension of the gasliquid interface and the velocity of both gas and liquid phases on the characteristic of the gas-liquid two-phase flow in micro-channel are also discussed in detail.

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Four typical types of residual oil, residual oil trapped in dead ends, oil ganglia in pore throats, oil at pore corners and oil film adhered to pore walls, were studied. According to main pore structure characteristics and the fundamental morphological features of residual oil, four displacement models for residual oil were proposed, in which pore-scale fl ow behavior of viscoelastic fl uid was analyzed by a numerical method and micro-mechanisms for mobilization of residual oil were discussed. Calculated results indicate that the viscoelastic effect enhances micro displacement effi ciency and increases swept volume. For residual oil trapped in dead ends, the fl ow fi eld of viscoelastic fl uid is developed in dead ends more deeply, resulting in more contact with oil by the displacing fl uid, and consequently increasing swept volume. In addition, intense viscoelastic vortex has great stress, under which residual oil becomes small oil ganglia, and fi nally be carried into main channels. For residual oil at pore throats, its displacement mechanisms are similar to the oil trapped in dead ends. Vortices are developed in the depths of the throats and oil ganglia become smaller. Besides, viscoelastic fl uid causes higher pressure drop on oil ganglia, as a driving force, which can overcome capillary force, consequently, fl ow direction can be changed and the displacing fl uid enter smaller throats. For oil at pore corners, viscoelastic fl uid can enhance displacement effi ciency as a result of greater velocity and stress near the corners. For residual oil adhered to pore wall, viscoelastic fl uid can provide a greater displacing force on the interface between viscoelastic fl uid and oil, thus, making it easier to exceed the minimum interfacial tension for mobilizing the oil fi lm.

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