Monitoring Polymer-Enhanced Foam Displacements Through Heterogeneous Porous Media: A Pore-Scale Study

In this work, fundamental understanding of phase displacements involved in polymer-enhanced air foam is investigated which was not well discussed in the available literature. To do this, a series of foam injection experiments were performed on heterogeneous rock-look-alike micromodels in the presence and absence of a single fracture. The models were initially saturated with crude oil and experienced post polymer-enhanced foam injection process. We observed for the first time the mechanism of synergetic upstream snap-off and lamella division in the vicinity of the area where the permeability contrast was obvious. Observations showed two opposite effects of oil emulsioning and bubble coalescence when gas bubbles came in contact with oil in pore bodies. Fractal dimension analysis of front polymer-enhanced foam illustrates a noticeable improvement in oil displacement. Primary enhanced foam injection to oil saturated micromodel causes bubble coarsening which leads to less efficient oil displacement process. The lower the polymer concentration, the less stable the foam; consequently, the less efficient oil displacement is observed. Lower viscosity oil results in lower recovery efficiency as the stability of foam decreases. To shed light on the dynamic behavior of polymer-surfactant interface, some dynamic surface tension tests were conducted. Results showed that repellency between surfactant and polymer molecules causes surfactant molecules to be present on the surface making the initial dynamic interfacial tension (IFT) decrease. Results of this work help to better understand how polymer could enhance the efficiency of foam floods in heterogeneous systems.