Excellent foaming properties of alcohol ether sulfate (AEnS) for gas well deliquification: Experimental and computational investigations

Abstract

In the later stages of natural gas extraction, fluid buildup often leads to clogging of gas well passages, which can severely impact the extraction efficiency. Current technologies to solve this problem still face multiple challenges due to the harsh operation conditions, such as high condensate content, high temperatures, and high salinity, which often significantly influence the performance of the blowing agent. Alcohol ether sulfates (AE_nS) with varying numbers of ethylene oxide (EO) units demonstrated excellent liquid unloading efficiency and foam stability during the screening process of blowing agents. In particular, at 353.15 K, high NaCl concentrations (100‑200 g/L), and high condensate content (up to 20 %), AE_nS with three EO units (AE₃S) demonstrated excellent performance, with unloading efficiencies consistently not less than 85 %. Dynamic surface tension showed that AE₃S could achieve lower surface tension in the equilibrium region, and the increased liquid film thickness (62.19 μm) was beneficial in enhancing the mechanical strength and liquid-carrying capacity of the foam. In addition, viscosity tests and transmission electron microscopy (TEM) showed that increasing the NaCl concentration led to diversification of the aggregation morphology in the AE_nS solution, which significantly improved the viscosity and stability of the foam. Molecular dynamics simulations further confirmed that a stable composite structure could be formed between the hydrophilic chains of AE_nS, NaCl, and H₂O, which is beneficial for foam stabilization. These findings reveal the reasons for the excellent liquid-carrying performance of AE₃S on both the macro- and micro-scales and demonstrate the great potential of AE₃S foams for gas well deliquefaction.