Investigation of interactions of diluted microemulsions with shale rock and sand by adsorption and wettability measurements

Water-in-oil, oil-in-water and balanced microemulsions made with ethoxylated alcohol surfactant and d-limonene as the oil phase were diluted with distilled water and 2% KCl solutions. The interactions between these diluted microemulsions and Marcellus shale rock were studied by performing adsorption and wettability measurements. Interaction of the balanced microemulsion solutions with sand was studied by monitoring change in the surface tension and droplet size distributions before and after solution exposure to sand. It was established that adsorption of both surfactant and d-limonene took place on both sand and shale. It was discovered that the behavior in adsorption and wetting studies of diluted balanced microemulsion was significantly different as compared to the adsorption from diluted o/w and w/o microemulsions. Balanced microemulsion produced highest value of Γmax and highest contact angle on Marcellus shale. The results of wettability studies were in many aspects similar to those previously established in quartz-surfactant solution system, but with a number of significant differences. Inflection points in adhesion tension–surface tension curves were observed. Such points were previously seen in quartz-cationic surfactants systems, but were not observed in systems with nonionic surfactants.

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► We studied interaction between diluted microemulsions, shale and sand substrates.
► Adsorption on shale depended on oil-to-water weight ratio in microemulsions.
► Results suggest that both surfactant and solubilized oil adsorbed on substrates.
► Unexpected trends in wettability of shale by diluted microemulsions were observed.
► Possible structure of adsorption layer containing oil and surfactant was proposed.