--> Abstract: Biomarker Classification of Seepage Oils from Western Greece, by Nickos Rigakis, Konstantinos A. Nicolaou, Peter H. Nytoft, Jørgen A. Bojesen-Koefoed, and Ioannis Abatzis; #90072 (2007)

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Biomarker Classification of Seepage Oils from Western Greece

Nickos Rigakis1, Konstantinos A. Nicolaou2, Peter H. Nytoft3, Jørgen A. Bojesen-Koefoed4, and Ioannis Abatzis5
1Hellenic Petroleum SA, Maroussi, Greece
2Hellenic Petroleum SA, Greece
3Geological Survey of Denmark and Greenland (GEUS), Denmark
4Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark
5Geological Survey of Denmark and Greenland, Copenhagen, Denmark

A selection of the numerous western Greece oil shows was analyzed for their distribution of biomarkers, trying to ascertain their origin. Most oils are severely biodegraded with only trace amounts of n-alkanes and isoprenoids. Steranes are partly degraded making them useless for maturity assessment or source correlation. Some samples contain the full suite of C27-C35 hopanes, whereas others have lost all regular hopanes above C29. Hopanes can be biodegraded with or without the formation of 25-norhopanes. 25-norhopanes were not detected in any of these oils. 30-norhopanes and gammacerane are not degraded.
Biodegradation, evaporation and water-washing has changed the composition of aromatic hydrocarbons. Phenanthrenes are absent in most cases, and other polar compounds such as triaromatic steranes are generally found in very low concentrations. Various monoaromatic hydrocarbons are resistant to biodegradation and appear to be the only useful compounds for correlation and can be used even when saturated steranes and hopanes are degraded.
Most seep oils from the north have almost identical distributions of monoaromatic steranes. The separation based on monoaromatic steranes is largely supported by the composition of monoaromatic 8, 14-secohopanes and demethylated monoaromatic 8, 14-secohopanes. Oils from the south are slightly different and more variable.
Traces of a rare and unusual tetracyclic compound (baccharane) have been detected in most seep oils. Samples from the North showed a higher than average content of baccharane, and a few immature samples from the same area had a high content of baccharane and dammarenes.

 

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece