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The blockage caused by liquid loading poses a major problem to the aged gas wells. Various categories of foaming surfactants including zwitterionic, anionic and cationic surfactants are often used for foam‐based gas well deliquification. In this study, a foaming formula containing anionic (sodium lauroyl sarcosinate, LSS), cationic Gemini (C16AGB and C12AGB) and zwitterionic (C16APB and C12APB) surfactants was developed. This foaming formula was first optimized through the foaming ability and foam stability tests, and then evaluated through liquid unloading performance tests under various salinity, condensate, methanol and temperature conditions. Synergy was observed in the foaming ability and foam stability measurements when LSS, C16AGB, C12AGB, C16APB and C12APB were combined at a molar ratio of 5:4:1:4:1. The foaming formula exhibited excellent liquid unloading performance at high salinity (up to 26 × 104 mg/L), high condensate fraction (up to 25%) and high methanol fraction (up to 50%) conditions. The presence of 10% methanol significantly enhanced foaming efficiency (referred to as the ratio of the foam mass to the initial liquid mass) and liquid unloading efficiency of the foaming formula at 20–90°C. Furthermore, the surface tension measurements and the foam morphological investigation were carried out to reveal the observed synergy. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • A cost-effective ternary surfactant (CAPB-CAGB-AOS) foam was developed for gas well deliquification. • A green cationic Gemini surfactant (CAGB) was synthesized to support the foamability of anionic and betaine surfactant. • Synergy effect was observed in generating and stabilizing the foams when these three surfactant were compounded properly. • The synergy effect among these three surfactants was supported by the binding energies and electrostatic interactions. [ABSTRACT FROM AUTHOR]