Nano-surfactant of sodium dodecyl sulfate (SDS) was synthesized to be evaluated as a new chemical enhanced oil recovery agent for the application in an Iranian carbonate oil reservoir. Particle size analysis showed that the nano-SDS emulsions with 0.3 and 0.45 wt% concentrations contain particles smaller than 100nm. SDS nano-surfactant in the form of emulsion was relatively more stable than those of the conventional SDS, detected by the zeta potential measurements. Also, nano- SDS was slightly more effective in lowering crude oil–aqueous phase interfacial tension, compared to the conventional SDS. The results of wettability studies indicated that the SDS emulsions, either in the form of surfactant or nano-surfactant, could similarly modify the wettability of the oil-wet rock surfaces (in the forms of both slice and powder) toward water-wet conditions. The spontaneous imbibition experiments on the reservoir limestone core samples at 50°C resulted in up to 6% percent incremental oil recovery. The maximum incremental oil recovery happened as the SDS nano-surfactant was imbibed into the core samples at the second stage, after the formation brine.

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