Surface-active compounds, which are mostly in asphaltene fraction of crude oil, are responsible for binding the oil components to mineral surfaces and, therefore, control wettability changes on reservoir rock/mineral surfaces. Surface wettability change occurs mainly through polar functional groups in these compounds, such as hydroxyl, carboxyl, or carbonyl functional groups. Using an asphaltene removed crude oil (i.e., maltenes), we investigate the effect of hydroxyl and carboxyl functional groups on wettability changes of calcite surfaces. AFM images show significantly increased adsorbates of maltenes for the calcite sample pretreated with two asphaltene surrogates (phenol with a hydroxyl group and benzoic acid with a carboxyl group) than the one treated with water. However, the adsorbate patterns are different between those two asphaltene surrogates, suggesting different aggregation mechanisms. We observed formations of bigger surface-adsorbed droplets on the phenol- or benzoic acid-treated calcite samples even for relatively short exposure times (&lt; 30 min.) to maltenes. Quantum-mechanical calculations were performed to calculate which asphaltene surrogate works better to adsorb oil molecules onto the calcite surface for both terraces and step edges. And classical molecular dynamics simulations show that phenol can behave as an agent to separate oil from the water phase and help bind the oil phase to the calcite surface in the water/oil mixture.<sup>1</sup>

Effects of hydroxyl and carboxyl functional groups on the calcite surface wettability using AFM and computational modeling

ACS Fall 2021

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