Insights into Effects of Surfactant Concentration on Foam Behavior in Porous Media

A potential solution to mitigate the adverse effects of viscous fingering, gravity override, and reservoir heterogeneity on the efficiency of gas injection in porous media is to inject the gas with a solution containing surface-active agents such as surfactants or nanoparticles. The efficiency of these processes largely depends on the generation and stability of the lamellae residing in the pores, both of which are influenced by the physicochemical properties of the rock and the surfactant solution. This study investigates the effect of surfactant concentration on the transient and steady-state behaviors of foam in porous media. It is found that the rate of foam generation is affected by the surfactant concentration, i.e., the transition from coarse-textured to fine-textured (strong) foam occurs earlier with the increasing surfactant concentration. However, when a sufficient amount of the surfactant is injected, strong foam is generated even with a very low surfactant concentration in the low-quality regime. Furthermore, because foam stability is governed by the limiting capillary pressure in the high-quality regime, the steady-state pressure behavior of foam (or foam strength) in this regime is significantly impacted by the surfactant concentration. We find that the current (equilibrium or steady-state) foam models cannot mimic the observed behavior in our experiments because it scales both high-and low-quality regimes with the surfactant concentration. Consequently, modifications are suggested to overcome the shortcomings of the model.