CONICET | Buscador de Institutos y Recursos Humanos

Asphaltenes play a key role on the oil production and exploration from natural reservoirs. In carbonate reservoirs, the calcite (10.4) surface retains asphaltenes. However, the aggregate structure and deposition processes are not fully understood. By first-principles calculations based on density-functional theory (DFT) with van der Waals (vdW) dispersion, we studied the adsorption of asphaltene, resin and resinasphaltene dimer molecular models on the CaCO3 surface in the presence of water and toluene dielectric environment. These large molecules impose a challenging description at electronic level. Our calculations indicate that there is steric hinderingfor the effective interaction of the aromatic region of the asphaltene on the calcite surface. However, the aliphatic chains with sulphide groups can play a significant role on the adsorption process and its availability to receive electronic charge density from the surface. Accordingly, the preferential LUMO localized in the aromatic region of the asphaltene may also allow the adsorption on the calcite surface by π-π stacking. The resin molecule tends to be firstly trapped in the dimer formation with the asphaltene, whereas a significant intramolecular charge rearrangement due to the heteroatoms is necessary to increase the π-π stacking. For the dimer, the adsorbed form of the asphaltene favors more available electronic states to increase the likelihood of nanoaggregation. For this reason, changes on the continuum dielectric constant only had a minor effect on the calculated adsorption energies. Experimental works related to oil-water interface in presence of toluene show similar behavior of asphaltene adsorption. Our studies indicate that nanoaggregates are grown through resin and the calcite (10.4) surface selectively adsorbs the less polar asphaltenes from oil.