Non-ionic alkyl polyglucoside (APG) surfactants have been considered as eco-friendly, nontoxic and biodegradable surfactants. In this study, the physicochemical properties of two APG surfactants under high-temperature and high-salinity conditions were evaluated. The effectiveness of the surfactants as imbibition agents on improving oil production in carbonate reservoirs was investigated. A formulation with ultra-low interfacial tension (IFT) was introduced and the mechanisms resulting in such low IFT were probed and discussed.

Two APG surfactants were studied. Compatibility was evaluated by the transparency in brine solutions after aging. IFT was measured with the formulations of surfactant/additives. The morphology of network formed by surfactant/additives was observed via scanning electron microscope (SEM). The static adsorption of the APGs onto carbonate powder was determined by total organic carbon (TOC) analyzer. The contact angle of oil droplet on surface of carbonate core was measured in surfactant solution. The oil production via spontaneous imbibition of water in carbonate core was obtained using Amott cell. An imbibition simulation model was validated by the experimental results using UTCHEM simulator.

Both surfactants APG-1 and APG-2 exhibited excellent compatibility with the simulated high salinity water at reservoir temperature. They also demonstrated low static adsorption on carbonate reservoir. The surfactant containing larger hydrophobic carbons (APG-1) showed more incremental oil production potential than the other one bearing shorter hydrophobic chain (APG-2). At a concentration of 0.2 wt%, APG-1 yielded a low IFT in the order of 10-2 mN/m and an ultra-low IFT in the order of 10-3 mN/m was obtained upon addition of a small amount of additives. SEM pictures indicated that APG-1 and the additives synergistically generated a more compact structure via interaction between hydrophobic moieties of the chemicals compared to the aggregated structure formed by APG-1 alone. Such an effect could eventually lead to a decrease in IFT between oil and water. APG-1 slightly altered the wettability of carbonate core surface toward water-wet. The experimental results of spontaneous imbibition tests showed an oil production of 28% and 21% by APG-1 and APG-2, respectively. After parameter tuning, the yielded curves from numerical simulation by UTCHEM simulator perfectly matched the experimental data.

A new APG-based formulation was designed with an ultra-low IFT resulting in a much more compact amphiphilic structure along the oil-water interface. This study shows a great potential of APG surfactants and the relevant derivative formulations in improving oil production application for high-temperature and high-salinity carbonate reservoirs.

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