Formulation and Performance of a Rhamnolipid-Based Nanoemulsion for Enhanced Heavy Oil Recovery in Offshore Reservoirs.

Heavy oil resources are abundant, yet their high viscosity imposes severe difficulties in both recovery and pipeline transport. Conventional viscosity reducers suffer from inherent limitations, including poor environmental compatibility, insufficient stability, and low efficiency. In this work, we developed an eco-friendly nanoemulsion system that can efficiently reduce heavy oil viscosity, offering a new pathway for the green exploitation of heavy oil resources. This study employed the hydrophilic-lipophilic balance (HLB) method to screen surfactant formulations. A composite surfactant system consisting of rhamnolipid and AEO-9 at a mass ratio of 2:1 (HLB = 20.44) was used in 0.5 mol/L CaCl2 aqueous solution, with glycerol as the cosurfactant at a surfactant/cosurfactant mass ratio (Km ) of 3 and palm oil as the oil phase, to prepare microemulsion precursor #5. Upon 500-fold dilution, this precursor yielded nanoemulsion #5-500. Dynamic light scattering characterization revealed a narrow particle size distribution centered at 60-80 nm, with a zeta potential of - 52.8 mV. At 55 °C, the nanoemulsion reduced the viscosity of heavy crude oil by 91.85% and lowered the oil-water interfacial tension to 0.15 mN/m. The contact angle on an oil-wet surface decreased from 106° to 74°, crossing the 90° threshold, indicating a wettability reversal from oil-wet to water-wet. Core flood experiments demonstrated that sequential injection of the diluted nanoemulsion followed by the neat formulation at 55 °C enhanced oil recovery by 68.79%. This green nanoemulsion system offers a feasible and environmentally friendly technological pathway for efficient heavy oil recovery.