Optical microscopy was used to measure depth-averaged oil distribution in a quasi-monolayer of crushed marble packed in a microfluidic channel as it was displaced by water. By calibrating the transmitted light intensity to oil thickness, we account for depth variation in the fluid distribution. Experiments reveal that oil saturation at water breakthrough decreases with increasing Darcy velocity, U w , between capillary numbers Ca = w U w ∕ = 9 × 10 −7 and 9 × 10 −6 , where w is the dynamic viscosity of water and is the oil/water interfacial tension, under the conditions considered presently. In contrast, end-point (long-time) remaining oil saturation depends only weakly on U w . This transient dependence on velocity is attributed to the competition between precursor film flow, which controls early time invasion dynamics but is inefficient at displacing oil, and piston-like displacement, which controls ultimate oil recovery. These results demonstrate that microfluidic experiments using translucent grains and fluids are a convenient tool for quantitative investigation of sub-resolution liquid/liquid displacement in porous media.

Lab-on-a-chip methods were used to visualize the pore-scale distribution of oil within a mixed-wet, quasi-monolayer of marble grains packed in a microfluidic channel as the oil was displaced by water. Water injection rates corresponding to microscopic capillary numbers between Ca = 5 × 10-8 and 2 × 10-4 (Darcy velocities between 0.3 and 1100 ft/d) were considered. As expected, early-time water invasion transitions from stable displacement to capillary fingering with decreasing Ca, with capillary fingering observed at Ca ≤ 10-5. End-point oil saturation decreases with Ca over the entire range of Ca considered, consistent with the canonical capillary desaturation curve. In contrast, Sor derived from approximate numerical simulations using reasonable Pc(Sw) do not display a strong dependence on Ca. These results suggest that the Ca dependence of end-point oil saturation is largely due to capillary end effects which, under conditions considered presently, affect the entire length of the packed bed.

This paper presents static oil/brine contact angles measured using the sessile drop method on soda lime glass and polished marble. Pure n -decane and three 66 mM naphthenic acid solutions in n -decane were considered as model oils. Selected naphthenic acids were: cyclohexanecarboxylic acid (CHCA), cyclohexanebutyric acid (CHBA), and cyclohexanepentanoic acid (CHPA); all oils were dyed with Oil Red O (ORO) at a concentration of 0.9 mM. Also presented are complementary density and viscosity measurements by rotational viscometry at selected temperatures ranging from T = 16.00–28.00 °C. For the application of the data to interpret microfluidic experiments, see Tanino et al. [1] and Christensen et al. [2].