Biosurfactants are surface-active substances produced by the metabolism of microorganisms such as bacteria and yeast. Common types include rhamnolipids, sophorolipids, and lipopeptides. The core mechanism by which they enhance crude oil recovery lies in their ability to significantly reduce the interfacial tension between oil and water. The interfacial tension between crude oil and formation water is typically high, causing the oil to behave like mercury droplets that struggle to deform and flow through narrow rock pores. Biosurfactant molecules adsorb at the oil-water interface, with their hydrophilic groups extending into the water phase and hydrophobic groups inserting into the oil phase. This greatly weakens the attractive forces between molecules at the interface, reducing the interfacial tension from its original level.10⁻¹ mN/mScale down to10⁻³ mN/mEven lower. The reduction in interfacial tension makes it easier for residual oil droplets, previously trapped in rock pores by capillary forces, to deform, break off, and flow toward the production well along with the displacing fluid (water).

Furthermore, biosurfactants can enhance oil recovery efficiency by altering the wettability of rock surfaces. Polar components in crude oil can shift the reservoir rock surface from hydrophilic to oleophilic, causing oil to adhere more firmly. Biosurfactants adsorb onto the rock surface, reversing its property from oleophilic back to hydrophilic. This change makes oil films easier to detach, roll up, and be carried away by the water flow.

Compared to chemically synthesized surfactants, biosurfactants offer superior biodegradability and environmental compatibility. They can be produced in situ by microorganisms or directly injected into reservoirs, even under extreme conditions, allowing for a broader range of applications. Field application examples demonstrate that biosurfactants can effectively enhance oil displacement in challenging development areas such as heavy oil fields and low-permeability reservoirs, providing a viable approach to improving crude oil recovery rates."Green"Solution.