Abstract:

Oil discovered from the Lengdong Oilfield, Liaohe Basin has similar source and maturity. Biodegradation is main cause leading to concentration and distribution variations of alkylated phenanthrenes. The concentrations and molecular distributions show systematic variations at different biodegradation levels.The concentration decreases significantly from level 3 to 5 while isomer distribution varies in slightly advanced biodegradation stage(＞level 4). Alkylated phenanthrene maturity parameters remain valid till biodegradation level 4. Degree of alkylation is a critical factor to control the rate of biodegradation.The C₃-phenanthrenes show high ability to resist biodegradation compared to their low alkylated counterparts, however, we do observed methylphenanthrenes decrease faster than phenanthrene. Demethylation of a substituted compound during biodegradation was inferred as one of biodegradation reaction process. Alkylated isomer specific degradations are also observed in our sample set. Alkylphenanthrenes with substituents at the 9th or 10th position are more resistant to biodegradation than alkylphenanthrenes with substituents at other positions. The relative susceptibility to biodegradation for the individual methylphenanthrene(MP), C₂-phenanthrene and C₃-phenanthrene isomers were determined by their concentration variations.This result provides practical guide for aromatic hydrocarbon maturity parameter selection and further insight into mechanism and quantification of biodegradation in reservoired oils.

Key words: alkylated phenanthrene, isomer, alkylation, biodegradation, Liaohe Basin