Visualization and Quantification of Mobility Reduction in Porous Media Flow Associated with Pore Blocking by Emulsion Drops

Water injection typically leads to relatively low oil recovery due to an unfavorable mobility ratio between the injected aqueous phase and the displaced oil phase and reservoir heterogeneity, which create preferential flow paths. Experiments have shown that an oil-in-water emulsion can be used as an effective enhanced oil recovery (EOR) method. The aqueous phase mobility reduction associated with the trapping of the dispersed oil drops leads to a more uniform displacement front and also to a reduction of the residual oil saturation. Despite recent developments on emulsion injection as an EOR method, fundamental aspects of the pore-scale flow of oil-in-water emulsion and its relation to the observed macroscopic flow mobility reduction are still not completely understood. One important aspect of the design of an efficient emulsion injection process is the effect of the emulsion drop size, pore throat distribution, and injection flow rate (pressure gradient) on the mobility reduction of the aqueous phase. This work uses a microfluidic porous medium model to visualize details of the dynamics of drop retention and release and to determine how pore-scale phenomena affect the aqueous phase mobility reduction, which was quantified by a resistance factor (RF) and a residual resistance factor (RRF). The results show that mobility reduction can be controlled by the capillary number and drop diameter distribution. At a high enough capillary number, the pressure difference in most of the pore throats is strong enough to overcome the capillary pressure needed to push a drop through the constriction; the number of trapped drops is relatively small, and mobility reduction is weak. At low capillary numbers, the number of trapped drops is large; the mobility reduction is large and strongly dependent on the drop size distribution. The results can be used to determine the characteristics of oil-in-water emulsions to be injected in a reservoir with a known pore throat size distribution in order to achieve the necessary water mobility reduction that leads to a higher oil recovery factor.