Oil Displacement Mechanism of a Novel Surfactant

China’s low-permeability reservoirs possess abundant resources characterized by poor rock properties, strong heterogeneity, and fine pore throats, leading to low displacement efficiency. This study expands the concentration window for achieving ultra-low interfacial tension (ULT) by adding co-surfactants to the primary surfactant. Research indicates that the critical micelle concentration (cmc) and corresponding interfacial tension (γcmc) of the compounded system are lower than those of individual components. When the molar ratio of M to Q is 1:1, the interaction parameter βm reaches its minimum value, indicating the strongest synergistic effect within the system. The compounded system achieves an oil-water interfacial tension as low as 0.0021 mN/m at 0.25% M + 0.025% Q, enhancing recovery efficiency by 0.88% compared to the single component M. Utilizing micro-etching microscopy and natural core physical model experiments, the compounded surfactant system’s recovery efficiency increment reaches 19.7%, significantly surpassing water flooding effects. This provides robust support for the efficient development of the Jiyuan X reservoir.