Excellent foaming properties of anionic-zwitterionic-Gemini cationic compound surfactants for gas well deliquification: Experimental and computational investigations

Foams are often employed as an efficient and cleaner method to remove the liquid accumulated at the bottom of the gas wells and promote the production of natural gas. However, the extreme conditions (e.g., high content of condensate, high salinity, high temperature, etc.) in the wells would retard the performance of the foaming agents. Usually, mixtures of different foaming surfactants were used to achieve high performances under those extreme conditions. In this paper, foams stabilized by surfactant mixtures containing alpha-olefin sulfonate (AOS), synthesized green cocamidopropyl betaine (CAPB) and modified quaternary ammonium Gemini surfactant (CAGB) in a proportion of 0.2:0.2:0.2 (wt%/wt%/wt%) were developed to evaluate their industrial application potential in gas well deliquification. The ternary surfactant (CAPB-CAGB-AOS) foam exhibited higher stability than the other dual surfactant foams and singular surfactant foams. Additionally, the foaming efficiency (defined as the ratio of the mass of water converted into foam to the mass of the initial liquid) and liquid unloading efficiency of the CAPB-CAGB-AOS mixture could be improved with the presence of condensate. Salts and methanol had a weak influence on the performance of the CAPB-CAGB-AOS foam. The introduction of ethylenediamine tetraacetic acid disodium (EDTA‧2Na) can enhance the performance of the CAPB-CAGB-AOS foam against salts. The temperature (> 60 °C) favored the foaming efficiency and liquid unloading efficiency of the CAPB-CAGB-AOS mixture, which reached up to 100% and 88.5% at 90 °C. These results indicated that the synergy effect of these three surfactants on the stability and liquid unloading efficiency of the foam can be confirmed. Moreover, the synergy effect can also be confirmed by the surface tension test, the foam's microstructure observation and the computational studies on calculated binding energies and electrostatic interactions.