Conclusions
1. Droplet formation observed in the partially-miscible Hele-Shaw studies is associated with emulsion instability: produced emulsions from the droplet morphologies require an external mechanical force to maintain their stability.
2. Emulsion stability is predominantly dependent on the viscosity force. With the increase in the strength of the viscous force, the number of droplets decreases. This effect is especially pronounced at the later stage of the experiment for cases that contain both the surface-active agent and the viscosifying agent. Surfactant-induced fingers are consumed by large and highly-stable polymer-induced fingers via the Ostwald ripening process.
3. Low IFT is associated with the droplet generation after the initiation of the finger break. The opposite is observed to be true (less droplet generation) before the finger stability loss (at earlier stages of the experiment) which implies that low IFT is a leading factor in hydrodynamic stability at the initial stage. However, upon the stability loss, droplets are generated and such droplet generation continues until it begins to plateau.
4. Finger development before and after the stability loss follows separate self-similarity patterns and such divergence in patterns can be noted in saturation profiles plotted with the time variable.
5. Fractal dimensions have a proportional relationship with surface tension and an inversely proportional relationship with viscosity.
6. We presented two types of “self-similar” behaviors per the categorization based on the saturation profiles. However, certain complex colloidal samples may display multiple self-similar fingering behaviors based on the chemical component, mechanism, and subsequently induced hydrodynamic stability (or instability).
7. For the future study (in oil recovery), the impact of droplet generation behavior on heavy oil recovery in the porous media can be investigated. Pore size distribution can be predicted to be the most significant parameter on the droplet retainment behavior which can improve the overall oil recovery via entrapment (mobility control), or reduce it by decreasing the relative permeability to oil.