Oil Recovery from Micropores in Heterogeneous Tight Conglomerate Rocks Using a Diluted Rhamnolipid Microemulsion

Abstract Oil recovery from micropores in heterogeneous tight conglomerates is limited by pore-scale heterogeneity and surfactant retention. This study evaluates a diluted rhamnolipid microemulsion (DME) in Mahu conglomerate cores with permeabilities of 0.01–1.6 mD using interfacial measurements, dynamic adsorption, coreflooding, NMR, and CT. DME has a mean hydrodynamic diameter of 7.7 nm. At 0.1 wt % DME, the oil–water interfacial tension is 1.2 mN/m, and the aqueous-phase contact angle decreases from 109° to 60° after treatment of an oil-wet surface. At the same working formulation concentration of 0.1 wt %, DME exhibits 78–80% lower cumulative adsorption than RL in two cores. This formulation-dose result does not establish intrinsic adsorption reduction at equal active-RL concentration. DME increases oil recovery by 8–14 percentage points relative to RL in three cores with permeabilities of 0.01–0.03 mD. Dynamic NMR indicates an earlier small-pore response with DME while large-pore oil production continues. Cumulative NMR analysis gives lower equivalent mobilization cutoff radii, and CT-derived estimates support a more uniform axial sweep. Fracture-network microfluidics provides qualitative supporting evidence. Together, these results suggest that lower adsorption losses, alongside improved interfacial and wetting properties, contribute to recovery and small-pore oil mobilization under the tested formulation and laboratory conditions.