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A series of novel, nonionic gemini surfactants (GSs) with varying spacer lengths were synthesized from sunflower (Helianthus) oil for application in enhanced oil recovery (EOR). The surfactants were characterized by 1H-NMR and thermogravimetric analyses (TGA). Critical micelle concentration values increased with temperature due to a delay in micellization of GS molecules in bulk phase. Hydrolytic stability studies revealed that GS solutions possess the ability to displace acidic crude oil through reservoir pores. Crude oil miscibility studies showed the formation of stable emulsion systems. Ultralow interfacial tension was achieved at the oil–aqueous interface in the presence of salt. Surfactant solutions exhibited good tolerance to varying salinity and hardness conditions. GS solutions showed favorably low lime soap dispersion requirement, indicating improved dispersing ability. GS-based foam systems showed enhanced kinetic stabilities with increasing concentration and pseudoplastic flow character that are considered desirable for EOR operations. Half-life times decreased with temperature due to thinning and subsequent rupture of the foam film boundary. Single-phase continuous emulsion(s) were observed during 15 days for n-heptane/GS/aqueous-based emulsions. Dynamic light scattering and microscopic investigations showed that emulsion stability decreased with time due to gradual coalescence of oil droplets. Therefore, studies pertaining to characterization and performance evaluation of synthesized GSs confirm their potentiality as effective oil-displacing agents under reservoir conditions.

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Stabilizing mechanism of silica nanoparticles on gelled foam prepared with a very low concentration of polymer (xanthan gum) and surfactant (α-olefin sulfonate) is reported in the present study. The morphology of the foam at optimized composition reveals its improved stability, owing to the adsorption of silica nanoparticles on the bubble interface, which was further confirmed by microscopic images. The foam decay experiments confirmed the slower drainage of liquids through the strong and rough bubble interface in the presence of nanoparticles. The synergistic effects of nanoparticles–polymer–surfactant help to improvise rheology, viscoelastic properties and enhanced static proppant suspension capacity of the foam. Addition of nanoparticles helps in reducing the polymer concentration in the foam fluid without compromising in stability criterion. Thus, the prepared gelled foam offers less formation damage with improved rheology, and proppant carrying capacity without any limitation to low-temperature application.