Chemical flooding is a beneficial approach to enhance oil recovery from hydrocarbon reservoirs. Surfactant flooding due to the capability of oil/water interfacial tension (IFT) reduction is a very well-known approach. However, the adsorption of surfactants on the rocks' surface makes this approach less feasible and too complex to model. This study attempts to analyze the adsorption behavior of saponin on sandstone rocks. Saponin is a natural surfactant found in more than 500 plant species. The adsorption behavior of this surfactant follows the Langmuir isotherm model with a negligible error of 0.98%. Experimental studies revealed that saponin adsorption capacity decreases when the temperature rises, but the behavior still follows the Langmuir isotherm model in elevated temperatures. Furthermore, the effect of particle size on adsorption behavior was also investigated experimentally, whereas smaller particles were found to provide higher adsorption capacities for saponin molecules. In the current research, a model based on thermodynamic equations has been constructed capable of predicting the adsorption behavior of saponin on sandstone rocks in extended conditions. Experimental data were also employed to verify the model performance. Moreover, the core plug and batch adsorption capacities were compared to each other, which showed that the core adsorption capacity is much lower than the batch condition. Comparing results achieved in this study with other natural surfactants, it is explicit that saponin induces a ten times lower critical micelles concentration (CMC) and adsorption tendency on sandstone rocks, which can make saponin a superior natural surfactant with invaluable applications in chemical EOR jobs.
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