A series of microfluidic experiments have been carried out to understand the influence of aspect ratio (AR) and wettability on residual oil saturations (Sor) in water and immiscible gas flooding. Linear and uniform pore network microfluidic chips with various wettability, ARs and depths were used. Water, n-decane, and methane were used as aqueous, oil, and gas phases, respectively. Water and oil were dyed with 1 g/l concentrations of methyl blue and Sudan red, respectively, for better visual contrast for the fluid saturation measurements. 0.1 uL/min flow rate was used during oil saturation and water flooding and 0.3 sccm flow rate was used for gas flooding to maintain the capillary numbers in the range of 10-7 to 10-5 to be in compliance with typical reservoir capillary numbers. An image analysis protocol using ImageJ was used to measure the residual fluid saturations.

Linear pore networks of 20 um and 40 um depths with same ARs were used to study the influence of depth on residual fluid saturations. It has been found that the depth has a significant influence on the pore-scale residual fluid saturations. For 20 um depth chips, pore-scale residual oil saturation after waterflooding (Sorw) increased with the AR semilogarithmically (log AR vs. Sorw) for both hydrophilic and hydrophobic chips. The pore-scale Sorw for 40 um depth hydrophobic chips also followed the same trend, however, the 40 um depth hydrophilic chips exhibited an exponential trend.

Uniform pore networks with same depth were also used to study the effect of AR on residual saturations. For hydrophilic uniform pore networks, the chip-scale Sorw data spread between 41 and 51 %PV for the AR range of 1.97 to 23.94, the data for hydrophobic uniform pore networks fall between 72 and 57 %PV, respectively. For both the hydrophilic and hydrophobic uniform pore networks, there exits strong semilogarithmic relationships between AR and residual oil saturation after gas flooding (log AR vs. Sorg). The data can be used to validate flow simulation models in digital rock analysis.