Characterization of Asphaltene Deposits by Using Mass Spectrometry and Raman Spectroscopy

Abstract

Crude oil deposition in oil transfer pipelines and bore wells afflicts many oil reservoirs. Asphaltenes play a major role in this process because of their tendency to precipitate in pipelines upon changes in temperature and/or pressure. Asphaltenes are defined by their lack of solubility in n-alkane solvents, which means that they likely contain many compounds that do not actively contribute to the deposition of crude oil in pipelines. The preponderance of studies in the literature have focused on asphaltenes derived from crude oil, whereas far fewer investigations have focused on asphaltenes derived from oil deposits. In this study, structural parameters of oil-deposit asphaltenes were examined using Raman spectroscopy and tandem mass spectrometry and compared to results reported previously for petroleum asphaltenes. On the basis of D1 and G band intensities in the Raman spectrum of oil-deposit asphaltenes, the average aromatic sheet size of these molecules was 21.0 Å, slightly larger than earlier values reported for petroleum asphaltenes (15.2−18.8 Å). Mass spectrometric experiments of oildeposit asphaltenes ionized via atmospheric pressure chemical ionization (APCI) using CS 2 solvent were used to measure the molecular weight distribution (MWD), saturated carbon content, and the number of fused aromatic rings in the cores of the asphaltene molecules. The MWD was found to be 150−1050 Da with an average molecular weight (average M W ) of 497 Da, which are significantly lower than those reported previously for petroleum asphaltenes (200−1500 Da and 570−700 Da, respectively). Aromatic core sizes were estimated to contain 8 fused rings on average for the most abundant species in oil-deposit asphaltenes, with 5−15 carbons in their alkyl side chains, as compared to averages of 3−7 aromatic rings and 17−41 alkyl carbons for petroleum asphaltenes.

Investigation of Island/Single-Core- and Archipelago/Multicore-Enriched Asphaltenes and Their Solubility Fractions by Thermal Analysis Coupled with High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…Similar results were observed for model compounds as well as asphaltenes by using mass spectrometry with collision-induced dissociation (CID) fragmentation, which results in an average number of 3-8 fused rings with up to 20 carbon atoms in alkyl-side chains. [19,[28][29][30] Nonetheless, although the island model serves to describe some asphaltene properties, such as reservoir geodynamics, it is incongruent with asphaltene behavior in several scenarios, e.g., products observed after thermal upgrading or pyrolytic degradation. After thermal cracking, the newly formed maltene fraction has been found to consist of alkylated 1-5-ring aromatics, alkanes, and alkenes, as well as naphthenes.…”

On the use of nanomechanical atomic force microscopy to characterise oil-exposed surfaces

“…Understanding the nature of these deposits and their interaction with the relevant surfaces is the rst step towards being able to mitigate against them. A wide variety of characterisation techniques have been employed in recent years [1][2][3][4][5][6][7][8][9] to explore these deposits including electron microscopy and spectroscopy, infra-red spectroscopy, QCM and AFM.…”

Asphaltenes: Separations, structural analysis and applications

“…MS has identified tens of thousands of unconventional compounds in asphaltenes, moreover, it elucidates the carbon number of alkyl chains, aromatic core sizes, functional heteroatom groups, M W distributions, and interactions between asphaltenes and rock surfaces as "wettability state" and so on [28,52,[108][109][110][111][112] .…”

“…As complementary to IR, Raman is caused by molecular vibration of polarizability changes and mainly for measuring average size of aromatic fused rings and their boundaries in asphaltenes, while IR absorption is due to molecular vibration of dipole moment changes [164] . Asphaltenes and microcrystalline graphite-like substances are alike in Raman spectrum since both of them have aromatic fused rings [112] . The common bands and applications are listed in Table 6 [112,145,155] .…”

“…Asphaltenes and microcrystalline graphite-like substances are alike in Raman spectrum since both of them have aromatic fused rings [112] . The common bands and applications are listed in Table 6 [112,145,155] .…”