Fuel, Vol.241, 83-93, 2019
Recent advances of surfactant-stabilized N-2/CO2 foams in enhanced oil recovery
Foam has been applied in enhanced oil recovery (EOR) for more than sixty years. The surfactant-stabilized N-2/CO2 foams are two of the most widely used foams in foam EOR processes, and numerous oil reservoirs could potentially benefit from them. This paper comprehensively reviews the development of these foams over the past decade. We focused on the promising surfactant formulas and their corresponding mechanisms under different reservoir conditions, especially harsh conditions. The most recent studies have shown that low interfacial tension foaming surfactants are efficient in fractured/tight reservoirs, while CO2-switchable surfactants are well suited to CO2 foam in carbonate reservoirs with high temperatures. Pure surfactants and mixed surfactants that combine anions and cations contain superior foam properties. The surfactant aggregates, such as vesicles and wormlike micelles, could distinctly enhance the foam stability. However, the adsorption of the mixed surfactants on reservoir rocks and the temperature sensitivity of the complex structures should be given particular consideration. The phase behaviors involved in foam EOR processes are vital and much more complicated than those in other EOR processes. Thus, a better knowledge of the phase behaviors could further improve foam EOR performance. The results of this paper provide clues to N-2/CO2 foam EOR design and also promote the development of harsh reservoirs.