<![CDATA[Rhamnolipid biosurfactants, derived from microbial sources, gain substantial interest as environmentally sustainable alternatives to synthetic surfactants, particularly in the realm of Microbial Enhanced Oil Recovery (MEOR). Their biodegradability, low toxicity, and effectiveness under extreme conditions make them ideal candidates for improving oil displacement in reservoir. However, the presence of divalent ions, specifically calcium (Ca²⁺) and magnesium (Mg²⁺), which are abundant in brine solutions in reservoirs, significantly affect the performance of these biosurfactants. This research investigates the influence of Ca²⁺ and Mg²⁺ ions on the phase behavior, stability, and interfacial properties of rhamnolipid-based microemulsion systems, which are integral to MEOR processes. A series of experiments analyze the impact of varying concentrations of Ca²⁺ and Mg²⁺ ions on rhamnolipid microemulsions. The study assesses phase transitions, stability, and the microstructure of these emulsions, utilizing spinning drop tensiometer to measure interfacial tension (IFT) and rheological analysis to determine viscosity. The results demonstrate that both Ca²⁺ and Mg²⁺ ions influence the optimal salinity conditions for microemulsion stability, with their presence causing shifts in the phase boundaries. Specifically, Ca²⁺ ions exert a more pronounced effect on phase stability compared to Mg²⁺, leading to increased IFT and viscosity at higher concentrations. The study further elucidates the crucial role of divalent ions in the stability and functionality of biosurfactant systems under reservoir conditions, emphasizing the importance of managing ion concentrations for efficient MEOR applications. These findings provide significant knowledge for optimizing the formulation of rhamnolipid-based systems to enhance oil recovery performance while mitigating the adverse effects of high divalent ion content in brine. The research contributes valuable understanding to ongoing efforts of improving biosurfactant efficacy, offering a pathway for refining MEOR strategies and advancing sustainable oil recovery technologies.]]>
