Study on the differences in microscopic oil displacement effects and action mechanisms of different rhamnolipid systems

Rhamnolipids are a class of anionic glycolipid surfactants produced through microbial metabolism. As a widely researched biosurfactant, rhamnolipids possess several advantages over traditional chemical surfactants, including non-toxicity, eco-friendliness, biodegradability, and biocompatibility, particularly in the context of microbial oil recovery applications. This class of surfactants enhances oil recovery by reducing the interfacial tension between oil and water, emulsifying residual oil, and modifying the wettability of rock surfaces. Furthermore, rhamnolipids maintain stability in high-temperature and high-salinity environments. However, rhamnolipids derived from different fermentation substrates exhibit variations in structure, composition, and properties, resulting in distinct displacement effects and mechanisms of action. This study focuses on two types of rhamnolipids: typical rhamnolipid and high-yield rhamnolipid, which are fermented using glycerol and rapeseed oil, respectively. Based on the characteristics of the target heavy oil reservoir, micromodels were designed and manufactured to conduct microfluidic experiments. The results obtained from imaging and video recording were analyzed qualitatively and quantitatively to explore the differences in effects and mechanisms between the two rhamnolipid systems. Results indicate that typical rhamnolipid increased recovery by 4.41% through delayed mechanisms involving wettability modification and residual oil emulsification. Conversely, high-yield rhamnolipid demonstrates an immediate effect by reducing interfacial tension, resulting in a recovery increase in 5.68%. According to the observed experimental phenomena and analytical trends, the conclusions evaluate the production increase, clarify the differences in mechanisms of action, and enhance the microscopic understanding of these surfactants. These findings provide directions for future investigations and serve as a reference for the design of related schemes.