SYNERGISM IN BINARY SURFACTANT MIXTURES CONTAINING A PH-RESPONSIVE SURFACTANT TO OBTAIN STABLE FOAMS CONTAINING CO2 UNDER SALINITY, HIGH PRESSURE AND TEMPERATURE CONDITIONS

The use of foams in enhanced oil recovery (EOR) applications requires the formation of stable foams under harsh reservoir conditions, such as a wide pH range, brines and high temperature and pressure. In this work, mixtures of the pH-responsive surfactant bis-(2-hydroxyethyl) cocoalkylamine (C12) with nonionic (tallow fatty amine, TFA) and zwitterionic (cocamidopropyl hydroxysultaine, CAHS) surfactants were evaluated to obtain foams with improved stability under conditions relevant to CO2-based EOR. The presence of TFA in the formulations increased the solubility of C12 at basic pH values, but impaired foam stability. In contrast, the formulations containing CAHS exhibited a significant synergy regarding surface tension reduction and foam stabilization. The synergy was confirmed by the negative value of the interaction parameter, indicating strong attraction, likely electrostatic, between the surfactant molecules at the interface.1 This effect was evidenced in the decrease in the bubble growth rate obtained with the C12:CAHS (1:2) mixture, compared to the individual components, suggesting a reduction coarsening and coalescence due to higher packing density of surfactants in the interfacial film. This mixture allowed obtaining foams with improved stability at pH 4, under high pressure (100 bar) and high temperature (65 °C) conditions. The results showed the potential of using synergic mixtures to tailor the solubility and foaming properties of pH-responsive surfactants for enhanced performance in EOR methods.