Premium
GEOCHEMICAL CHARACTERIZATION OF A BIODEGRADED CRUDE OIL, ASSRAN FIELD, CENTRAL GULF OF SUEZ
Author(s) -
Hegazi A. H.,
ElGayar M. Sh.
Publication year - 2009
Publication title -
journal of petroleum geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.725
H-Index - 42
eISSN - 1747-5457
pISSN - 0141-6421
DOI - 10.1111/j.1747-5457.2009.00454.x
Subject(s) - sterane , hopanoids , kerogen , biodegradation , maturity (psychological) , geology , oleanane , phytane , source rock , environmental chemistry , pristane , carbonate , geochemistry , mineralogy , chemistry , hydrocarbon , organic chemistry , paleontology , triterpene , medicine , psychology , alternative medicine , pathology , structural basin , developmental psychology
A crude oil sample from the Assran field in the Central Gulf of Suez (Egypt) was analysed geochemically and characterized in terms of a variety of source and maturity dependent biomarkers. Biodegradation was indicated by increasing concentration ratios of Pr/n‐C 17 and Ph/n‐C 18 . However, biodegradation was only slight as GC‐MS analyses of the saturate and aromatic fractions showed that hopanes, steranes, aromatic steroids and polycyclic aromatic compounds including sulphur heterocycles remained intact. The sterane and hopane distributions showed a predominance of C 27 steranes, a low diasterane index, an abundance of gammacerane, a high homohopane index and an oleanane index < 0.2. The results indicate that the Assran‐10 crude oil was derived from a marine carbonate source deposited in a highly reducing saline environment with a high bacterial contribution, consistent with the Upper Cretaceous Brown Limestone or Lower Eocene Thebes Formation containing Type IIS kerogen. Maturity parameters based on changes in the stereochemistry at chirality centres in hopane and sterane nuclei, such as C 30 βα/(βα+αβ) and C 31 22S/(22S+22R) hopanes and C 29 ββ/(ββ+αα) and C 29 20S/(20S+20R) steranes, together with triaromatic sterane cracking ratios, indicate that the oil sample was marginally mature. The results also suggest that biodegradation is probably due to sulphate‐reducing anaerobic bacteria.