Excellent condensate and salt-resistant foam by anionic-zwitterionic-cationic Gemini surfactants compounds for gas well deliquification

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.