Polynuclear aromatic hydrocarbons (PAH) as indicators of the source and maturity of marine crude oils | Academic Article individual record
abstract

Whole oil GC-MS was used to characterize selected polynuclear aromatic hydrocarbons (PAH) in a suite of marine crude oils derived from source rocks deposited under different conditions. The selected PAH consist primarily of 2- and 3-ring aromatic hydrocarbons, including naphthalenes (to C4), fluorenes (to C3), phenanthrenes (to C4) and dibenzothiophenes (to C3), as well as several 4- and 5-ring compounds. Concentrations of the selected PAH range from 2294 to 129,170 ppm and typically comprise between 1% and 20% of the total C12+ aromatic fraction. PAH compositions in all source types are dominated by naphthalenes. These compounds comprise between 41.9% and 88.9% of the total PAH measured. The greatest difference between oils lies in the relative abundance of dibenzothiophenes. Their abundance rivals that of naphthalenes in the carbonate oils (up to 41.7% of total PAH) but is exceedingly low in the paralic oils (< 2.1% of total PAH). These differences, which reflect differences in clastic content, Eh-pH, and availability of reduced sulfur in the source rock depositional environment, are captured in the ratio DBT/P, calculated as the sum of all dibenzothiophenes relative to phenanthrenes DBT/P is greater than 10 in most carbonate-sourced oils but ranges between 0.08 and 0.18 in the paralic-sourced oils. Siliciclastic-sourced oils are intermediate, with values ranging from 0.14 to 0.87 (average 0.40). All oils show a predominance of alkylated PAH homologues over the unsubstituted parent, however, the maximum degree of alkylation (the most abundant alkylated homologues within any given PAH series) varies. Carbonate-sourced oils show a high degree of alkylation, often maximizing at C3 or C4, while paralic-sourced oils generally exhibit a lower degree of alkylation in which the C1 or C2 isomers predominate. Siliciclastic-sourced oils are intermediate, with alkylation maximizing between the C2 and C3 isomers. We propose that these alkylation trends reflect differences in the PAH precursor moieties in source kerogens and/or variations in the thermal history of the source types, i.e. milder thermal history for the carbonate oils relative to paralic and siliciclastic oils.

author list (cited authors)
Requejo, A. G., Sassen, R., McDonald, T., Denoux, G., Kennicutt, M. C., & Brooks, J. M.
publication date
1996
publisher
Elsevier BV Publisher
published in
keywords
  • Alkyl Homologues
  • Crude Oils
  • Dibenzothiophenes
  • Marine Source Rocks
  • Thermal Maturity
  • Aromatic Hydrocarbons
  • PAH
  • Phenanthrenes
  • GC-MS
citation count

47