Experimental and computational insights into a highly salt-tolerant foaming complex containing a pseudo-Gemini supramolecular surfactant for gas well deliquification

Foam drainage is a critical technique for enhancing gas production in water-producing natural gas wells during mid-to-late operational stages. In this study, we hypothesized that constructing a pseudo-Gemini supramolecular surfactant complex through non-covalent interactions between a hydroxy tertiary amine (HTA) and 2-hydroxyterephthalic acid (HTPA) would significantly enhance foam stability and liquid-carrying performance under harsh downhole conditions. To realize this, we developed a novel five-component foam drainage agent by integrating the HTA/HTPA complex with cocamidopropyl betaine (CAPB), α-olefin sulfonate (AOS), and sodium carboxymethyl cellulose (NaCMC). The optimized molar ratio and total dosage of HTA:HTPA:AOS:CAPB:NaCMC were found to be 12:6:42:40:25 and 15 mM/L respectively, at which this foaming system exhibited a foaming volume of 390 mL and a half-life time of 23.07 min. Critically, liquid-carrying rate tests demonstrated that moderate contents of condensate and methanol enhanced drainage efficiency, the presence of 30 % condensate yielded a liquid-carrying rate of 43.06 %, while the presence of 20 % methanol increased it to 47.10 %. Remarkably, the system maintained 100 % foaming efficiency over a wide range of methanol or condensate concentrations (0–50 % v/v). This foaming system also exhibited excellent tolerance to salinity (up to 300 g/L, enabled by nitrilotriacetic acid) and temperature (up to 90 ℃), at which produced a liquid-carrying rate of 91.98 % while foaming efficiency remained at 100 % across 20–90 ℃. Besides, surface tension measurements, shear viscosity tests, microscopic foam morphology analysis, interaction energy calculations, and electrostatic surface potential analyses confirmed strong synergistic effect among the components. These findings validate the rational design of the supramolecular system and underscore its high potential as a novel foam drainage agent for efficient gas well deliquification.