Experimental study on gas-soluble surfactant-assisted CO2 huff-and-puff for enhancing oil recovery in tight reservoirs

The application of CO2 huff-and-puff technology is crucial for enhancing oil recovery and enabling efficient development of tight reservoirs. In this study, physical simulation experiments combined with nuclear magnetic resonance were used to evaluate the improvement in oil recovery from tight reservoirs afforded by gas-soluble surfactant-assisted CO2 huff-and-puff. We performed a comparative analysis of production performance and pore-scale oil-mobilization characteristics for pure CO2 huff-and-puff versus a CO2 + FS-340 hybrid fluid across different pore-size ranges. The experimental results show that the surfactant FS-340 has a relatively high solubility in CO2. As the mass fraction of FS-340 increases, crude-oil viscosity, oil-CO2 interfacial tension (IFT), and the minimum miscibility pressure (MMP) decrease progressively. At an FS-340 mass fraction of 0.8 wt%, crude-oil viscosity was reduced by 55.2%, and the MMP decreased from 31.9 to 24.3 MPa (a 23.8% reduction). Adding 0.8 wt% FS-340 to CO2 substantially improved huff-and-puff efficiency in natural cores over multiple cycles. Total oil recovery after three huff-and-puff cycles reached 59.27%, which is 22.96% higher than that achieved with pure CO2. These findings indicate that gas-soluble surfactants effectively enhance CO2 huff-and-puff performance in tight oil reservoirs and provide useful guidance for the efficient development of tight oil formations.