Foams can be considered as air-water emulsions. Just as in oil-water emulsions, surfactant molecules are required to decrease the surface tension between the air-water interface to form a foam.
Gas injection (such as CO2, methane or N2) has been routinely used in enhanced oil recovery. However, as gases have low viscosity and density compared to both water and oil, problems such as gas channeling through high permeability zones and gas migration to upper parts of the porous media occur. Thus, the volumetric sweep efficiency of the gas flooding is often poor. To improve the efficiency of the flooding, foam injections have been proposed.
Foams provide one way of reducing the gas mobility to increase both displacement and sweep efficiency. One major concern in foam-based EOR methods is the foam stability. The foam must remain stable in the porous formation to be an effective recovery agent. Surfactants are in key position when it comes to foam stability. For example, to produce stable CO2-in-water foams (one of the most studied foam systems), it is critical to develop surfactants that can stabilize the CO2-water interface at reservoir condition.