Ethanol enhanced anionic surfactant solubility in CO2 and CO2 foam stability: MD simulation and experimental investigations

CO2 foam has been widely scrutinized as a potential candidate in enhanced oil recovery while reducing CO2 emissions through geo-sequestration due to the high-efficiency CO2 mobility control ability. However, its application has been retarded partially because of the limited solubility of commercial and environmentally friendly surfactants in supercritical CO2. In this work, the challenge of limited solubility of surfactant sodium bis (2-ethylhexyl) sulfosuccinate (AOT) in CO2 is overcome by using ethanol as a co-solvent. The presented MD simulation reveals the underlying mechanism of the ethanol increased solubility of AOT in CO2 and the subsequently water-CO(2 )interfacial properties favorable for a stable CO2 foam. Experimental observation is in good accordance with the MD simulation that foamability and foam stability both significantly increase with ethanol as co-solvent, and their dependence on ethanol content. With ethanol as co-solvent to assist the dissolution of AOT in CO2, the CO2 foam has a high stiffness and the foam film has a high dilational modulus under high pressure of 15 MPa, which explain the stable CO2 foam. Experiments also show that ethanol helps the foam regeneration, making the practical oil field application of the presented system even more promising.