A high interfacial activity system with temperature resistance and salt tolerance from bio-based surfactants through interaction

The development of ultra-low interfacial tension systems is an important direction for enhanced oil recovery (EOR). However, the construction of alkali-free ultra-low interfacial tension systems that are both temperature-resistant and salt-tolerant faces significant challenges. Based on the surface tension before and after the mixing of bio-based surfactants, the intermolecular interaction parameter β^m was calculated using the regular solution theory. The results demonstrated a synergistic effect between N,N-dimethyl-N-[2-hydroxy-3-sulfo-propyl]-N-benzyloxyoctadecanoyl-1,3-propanediamine (SPBOPA) and lauric acid diethanolamide (LDEA) surfactant molecules. Furthermore, owing to the chain length compatibility between SPBOPA and LDEA, an ultra-low interfacial tension system without extra alkali addition was constructed. This bio-based surfactant system exhibits excellent interfacial property within a relatively broad concentration range (0.10–3.0 g/L) and ratio range (4:6–8:2), with the oil-water interfacial tension (IFT) being significantly reduced to ultra-low levels (<10⁻² mN/m). The system can withstand temperatures up to 120 °C, with sodium chloride tolerance increased from 50 g/L to 100 g/L and calcium ions tolerance increased from 500 mg/L to 5000 mg/L at specific concentrations and ratios. The bio-based surfactants system exhibits excellent temperature and salt resistance. Therefore, this binary system is expected to be applicable to oil displacement systems in high-temperature and high-salinity reservoirs.