Study on the types and formation mechanisms of residual oil after two surfactant imbibition

For investigating the types and formation mechanisms of residual oil after surfactant imbibition, the easyemulsifying surfactant Sodium Dodecylbenzene Sulfonate (SDBS) and ultra-low interfacial tension surfactant Sodium Oleate (SOL) were selected. The visual micromodel was adopted to observe the oil morphologies, while the rheometer and the emulsion stability analyzer were applied to analyze formation mechanisms. According to micro experiments, the main types of residual oil after SDBS imbibition are columnar, cluster, blind-end and small drop residual oil whose structure was small fragmented droplet. As for SOL solution, they are mainly blindend and island residual oil. The formation mechanism of columnar and cluster residual oil is capillary force offsetting, the direction of capillary force forms the blind-end residual oil, while the Marangoni effect and snapoff effect are responsible for island residual oil. The small drop residual oil is from emulsification, which always appears at the intersection of multiple flows. The aromatic groups of SDBS can promote the emulsion more stable by increasing the strength of interfacial film, hence the small drop residual oil only exists after SDBS imbibition.