Effects of Aging on Asphaltene Deposit Composition Using Ultrahigh-Resolution Magnetic Resonance Mass Spectrometry

In this work, the compositional changes of asphaltene deposits as a function of time were analyzed. It has been demonstrated using ultrahigh-resolution magnetic resonance mass spectrometry that the precipitation of asphaltenes is a dynamic process where the composition of the deposit shows variations that are linked to the exchange of molecules between the deposit and fluid. The detailed analysis of the nature of the species that were exchanged during this process indicates that the species that are more aromatic and richer in heteroatom molecules are less soluble and become enriched in the deposit as it ages, as those that are less aromatic with fewer heteroatoms go back into the fluid. It was also found that the oxygen-containing species that precipitate are less aromatic and have smaller sizes than those that do not contain oxygen. This is an indication that for these molecules, hydrogen bond and dipole–dipole interactions might play a significant role in their solubility, while for the species that do not contain oxygen, the driving force for precipitation is aromaticity. These findings support a previously proposed model that suggests that during aging, the aggregates become more organized as the more soluble molecules are expelled, whereas others, the less soluble molecules, are incorporated into the precipitated material.