(85e) The Influence of the Reservoir Acidity on Asphaltenes Dissolution in Aromatic Solvent Using Microsystems with in Situ Spectroscopy

Asphaltenes give rise to flow assurance issues in upstream petroleum and natural gas production.^1,2 The molecular structure of asphaltene includes an aromatic core, heteroatoms (e.g., N, O, and S), and a trace amount of metals (e.g., V, Ni). Their complex structures lead to five different types of molecular interactions: van der Waals, acid-base, metal coordination, hydrogen bonding, and p-p stacking.³ The fact that the structure and composition of asphaltenes vary from reservoir-to-reservoir adds to the complexity of flow assurance problems. Molecular-level information on asphaltenes that explains production-scale phenomena is critical to their remediation, and microfluidics with in situ spectroscopy are appropriate experimental methods.

In the present work, the deposition and the dissolution mechanisms of asphaltenes in aromatic solvent were studied at ambient temperature in a micro-packed-bed reactor with the help of in-line UV-Vis spectroscopy and in situ Raman spectroscopy. Measurement of the bed occupancy yielded the asphaltene distribution within the porous media. Zeolite (H-ZSM5) with different ratio of Al₂O₃/SiO₂ were also injected to study the influence of surface acidity of porous media. According to our results, the dissolution percentage of asphaltene in xylenes increases from 20.15 wt% to 51.00 wt% as the Al₂O₃ content increased. Measurements of the asphaltenes sheet-size distributions provided insight on the interaction mechanisms. Asphaltene molecules with larger sheet sizes tend to have stronger affinity with aromatic solvents than those with smaller sheet sizes.⁴ The mean sheet size was observed to decrease from 2.97 ± 0.25 nm to 2.74 ± 0.26 nm. Our findings support that p-p stacking is significant among the different interactions of asphaltenes in the aromatic solvent.⁵ General guidelines based on our observations could be prescribed for the design of asphaltenes remediations in the near-wellbore region.

References:

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2 O. C. Mullins, Annu. Rev. Anal. Chem., 2011, 4, 393–418.

3 M. R. Gray, R. R. Tykwinski, J. M. Stryker and X. Tan, Energy and Fuels, 2011, 25, 3125–3134.

4 E. Rogel, Energy & Fuels, 2000, 14, 566–574.

5 J. J. Adams, Energy and Fuels, 2014, 28, 2831–2856.