Synergistic biosurfactant-integrated hydrogels mitigate washout for sustainable enhanced oil recovery in harsh...

Eco friendly biosurfactants present outstanding interfacial properties for enhanced oil recovery (EOR). However, their direct injection often leads to rapid downhole washout and severe sacrificial loss, negating the process efficacy. To overcome such a critical limitation, we engineered a rhamnolipid-integrated hydrogel as a highly synergistic system. Interestingly, the physical entrapment turns the biosurfactant into an active filler rather than a simple additive. Rheological data confirmed that this internal remodeling strengthens the hydrogel matrix, with an increase in elastic modulus from 14.1 to 17 kPa along with a significant expansion in the linear viscoelastic region. Furthermore, this designed dense structure limited the equilibrium swelling ratio in high salinity brine (200,000 ppm) to 36%, indicating the excellent tolerance of the biosurfactant integrated hydrogel in harsh reservoir conditions (90 °C). The robust matrix is essential in preventing premature washout by allowing the sustained and localized release of rhamnolipids at the displacement front. This continuous delivery significantly changes the wettability of the rock, shifting its surface state from strongly oil-wet (116.8°) to water-wet (58.48°), while also greatly reducing the interfacial tension. Glass micromodel flooding validated this dual action mechanism. The synergistic hydrogel achieved an outstanding final oil recovery of 82% OOIP in secondary recovery mode, and a remarkable 90% OOIP in tertiary recovery scenarios. These findings present a practical framework for designing green EOR fluids where structural resilience and active interfacial chemistry are mutually reinforced for sustainable hydrocarbon production.