Experimental and computational investigations on foaming properties of anionic-nonionic-zwitterionic surfactants and amino acid compounds to address the liquid loading of natural gas wells

Liquid buildup in gas wells would undoubtedly obstruct the gas production. The use of foaming surfactants to generate foams and remove the loaded liquid is very common. Due to the undesirable conditions (e.g., high condensate cut (ratio of condensate oil volume to total liquid volume) and high salinity, etc.) that often encountered in the wells, different foaming surfactants were often compounded together to unload liquid in gas wells. In this paper, lauramide propyl dimethylamine (C12 Amine), palmitamide propyl dimethylamine (C16 Amine) and cocamidopropyl betaine (CAPB) were synthesized and compounded with L-aspartic acid (Asp) and N-lauroylsarcosine sodium (LSS) to form foaming supramolecular complexes through optimization (with Waring blender method and liquid unloading tests) to quantify their application potentials in foam-based deliquification treatment for gas wells. The C12 Amine-Asp-LSS-CAPB complex (in an optimized mole ratio of 10:4:14:7) exhibited superior condensate tolerance than the C16 Amine-Asp-LSS-CAPB complex (in an optimized mole ratio of 10:4:14:42). The salinity posed a significant influence on the liquid unloading performance (k) and foaming efficiency (ƞ, defined as the ratio of the foam mass to the initial liquid mass) of the C12 Amine-Asp-LSS-CAPB complex, however, the nitrilotriacetic acid trisodium (NTA) can greatly enhance the properties of the C12 Amine-Asp-LSS-CAPB complex against the salinity (up to 6 × 104 mg/L). The temperature (25 °C −90 °C) favored the performances (as indicated by k and ƞ) of the C12 Amine-Asp-LSS-CAPB complex, which achieved k and ƞ values of 85.0% and 100% at 90 °C, respectively. Meanwhile, the synergy observed in the foaming ability, foam stability and liquid unloading performance tests using the C12 Amine-Asp-LSS-CAPB mixture was also proved by the surface tension analysis and the calculations of the supramolecular interactions (interaction energies and electrostatic interactions).