Role of asphaltene and resin in oil field emulsions

Asphaltenes and resins are the principal constituents of polar fractions of crude oils. These polar molecules combine with and/or adsorb on other organic and inorganic solids producing emulsion stabilizing films at oil-water interfaces, and contribute to the formation of tight emulsions which are difficult to process at the surface facilities. These emulsion-stabilizing organic constituents, namely the asphaltenes and resins, have been characterized in our laboratories after their separation from unstable, moderately stable and highly stable emulsions obtained from a carbonate reservoir in Saudi Arabia. These constituents were studied in detail in terms of their molecular parameters by proton and carbon-13 NMR and FT-IR spectroscopy and GC-MS under pyrolytic conditions. There is evidence that factors such as increased aromaticity, decreased alkyl side chain lengths, and reduced chain branching are associated with the formation of stable emulsions involving asphaltenes. Also, the presence of aromatic quaternary carbons (bridged as well as substituted) shows a direct correlation with the tendency of asphaltenes to form stable emulsions. NMR and IR spectroscopy also indicate that the condensed ring character of asphaltenes increases with increasing emulsion stability as indicated by parameters such as the percentage of bridged and substituted aromatic carbons, alkyl chain branching, and side chain length. The data indicate that the increasing ring condensation in asphaltenes and resins is associated with an increase in both the degree of alkyl substitution and alkyl branching on the aromatic ring and not with the alkyl side chain elongation. Also, the spectral data for asphaltenes and resins indicate very low concentration of OH and N-H groups, which are often considered important for asphaltene aggregation through hydrogen bonding. These findings have been applied in developing molecular models for asphaltenes and resins from Arab Light crude oil. (C) 1999 Elsevier Science B.V. All rights reserved.