Occurrence and geochemical significance of carbazoles and xanthones in crude oil from the Western Desert, Egypt

الملخص EN

This paper describes an approach that involves the evaluation of the occurrence and distributions of nitrogen-and oxygen-containing aromatic compounds in Egyptian crude oils and source rocks.

Carbazoles and xanthones represent nitrogen-and oxygen-containing aromatic compounds, respectively.

Alkylcarbazoles and benzocarbazoles were quantitatively studied in crude oils taken from the Abu Gharadig and Shushan basins in north Western Desert of Egypt in order to investigate their occurrence, concentrations and distributions.

The abundances of carbazole, methylcarbazoles and dimethylcarbazoles in the marine Abu Gharadig oils are much higher than that of the terrestrial Shushan oils.

The results presented here indicate that thermal maturation can be ruled out as a major factor in controlling the changes in the carbazole ratios in the crude oils.

Most likely, source characteristics of the studied samples play a significant role in controlling the distribution of carbazole compounds in reservoired oils.

The alkylcarbazoles 1 MC / 1 MC + 1 EC, 3 MC / 4 MC and 18 DMC / 18 DMC + 1 EC when correlated with specific biomarker signatures provide background information discriminating between two main types of depositional setting : 1) Terrestrial dominated source deposited in oxidizing conditions for the Shushan oils and, 2) marine shale dominated sourced oils deposited in suboxic environments for the Abu Gharadig samples.

Similarly, benzocarbazole distributions were found to be independent of maturity, but influenced by organic facies and depositional environments.

Therefore, in this study, alkylcarbazole and benzocarbazoles compounds are well suited for the differentiation of Abu Gharadig and Shushan crude oils with respect to origin and variations of facies and depositional environment.

Using various kinds of Egyptian crude oils derived from marine carbonates, marine clastics and terrestrial sources, the current study indicates that xanthones and its alkylated homologues are abundant only in source extracts and crude oils that have terrestrial organic matter input.

This is the second description of xanthones in crude oils, and the first in Egyptian petroleum systems.

Overall, based on the data of this study, xanthones signatures show great promise as terrestrial source markers in a given petroleum system.