Fractionation and Characterization of Acidic Compounds of Flowline and Separator Asphaltene Deposits from a Gulf of Mexico Field

Asphaltenes represent the most complex fraction of crude oil, consisting of a diverse range of species with varying sizes, solubilities, aggregation states, structural motifs, and heteroatom contents. In prior work, we identified differences between asphaltenes that deposit in subsea flowlines and those that settle in topside processing facilities. These differences were determined through a variety of techniques, including near-infrared absorbance, bulk elemental analyses, saturates, aromatics, resins, asphaltenes composition profiling, and sequential precipitation using alkanes of different carbon numbers (e.g., C5, C6, and C7). This study extends that research by using high-resolution mass spectrometry to identify molecular-level differences between flow-line and separator deposits. Recent advances in separation methods, such as extrography coupled with high-field Fourier transform ion cyclotron resonance mass spectrometry (21 T FT-ICR MS), have minimized the selective ionization effects of ultracomplex asphaltene samples, thereby enhancing our understanding of their molecular composition, including contributions from both island and archipelago structural motifs. In this work, the two deposit samples were fractionated by extrography and characterized by negative-ion electrospray ionization 21 T FT-ICR MS. Our results reveal significant molecular-level differences between the deposits. The flowline deposit is dominated by species with lower aromaticity and molecular weight, which suggests aggregation behaviors driven by hydrogen bonding and acid–base interactions. In contrast, the separator deposit contains highly aromatic species with higher carbon numbers, indicating a stronger tendency for aromatic stacking and, thus, aggregation. These findings imply that the molecular mechanisms driving subsea deposition differ from those responsible for topside settling. Understanding these distinctions can improve our ability to correlate laboratory results with field data and aid in the development of more effective asphaltene control chemicals.