GEOCHEMICAL SIGNIFICANCE OF FATTY ACIDS IN CRUDE OILS AND RELATED SOURCE ROCKS FROM EGYPT

ABSTRACT

The acid fraction of crude oils and related source rocks of different stratigraphic units from the Gulf of Suez and Western Desert, Egypt were analyzed by GC and GC/MS. Normal alkanoic acids (n-C₉?n-C₃₀) were the dominant series (with the predominance of even-carbon numbers maximizing at n-C₁₆, n-C₁₈ or n-C₂₂while iso- and anteiso- branched acids were minor constituents. All samples showed a preference of short chain acids (n-C₁₀?n-C₁₉ with respect to long chain acids (n-C₂₀+) typical of marine oils and source rocks. The n-alkanoic acids distribution suggests a predominant algal and/or bacterial contribution. The presence of high relative abundance of mono and di-unsaturated carboxylic acids in a number of samples point to recent microbial activity. Distributions of n-alkanoic acids in the range (C₁₂?C₂₂) show striking similarities with the n-alkane distributions, indicating that both series may, at least in part, be diagenetically related by decarboxylation of the acids. Dehydroabietic acid has been identified in only one sample from Balaim Marine source rock. This resin-derived compound has probably been transported as pollen to the marine environment.