Impact of injection rate on transient oil recovery under mixed-wet conditions: A microfluidic study

Abstract

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.