Effect of betaine surfactant structure on the properties of CO₂ foam film

The stability of foam system is very important in the application of foam flooding and gas reservoir foam drainage agent. The influence of surfactant molecular structure and interface arrangement on the permeability and stability of foam liquid film is of great significance for the construction of highly stable CO₂ foam, but there is no systematic understanding at present. The betaine surfactant with four molecular structures is used as the research object, and the foam phase property evaluation is used as the research method. For the saturated adsorption capacity, foam liquid film permeability, foam stability and other phase properties, the surfactant molecular structure, interface arrangement, CO₂ foam liquid film permeability, foam stability and their correlation experiments are carried out. The results show that when the molecular head groups of surfactants are consistent, the hydrophobic carbon chain length increases, the hydrophobic effect increases, the molecules on the liquid film surface are arranged more closely, the permeability of foam liquid film decreases, and the stability of foam increases. When surfactant molecules have longer hydrophobic carbon chains, the enhanced hydrophobicity leads to a tighter arrangement of the liquid membrane and an increase in adsorption capacity, hindering the permeation behavior of CO₂ gas within the bubble and weakening the foaming ability of the foaming solution. Based on the regression analysis of the parameters obtained from four foaming systems, the correlation coefficient <i>R</i>² between foam life, foam liquid film molecular adsorption capacity and foaming capacity and foam liquid film permeability <i>K</i> is established. The fitting shows that <i>R</i>²&gt;0.90. Therefore, the permeability of foam liquid film <i>K</i> can be used as one of the parameters to evaluate the stability of foam system and provide a reliable evaluation parameter for the screening of highly stable foam system.