生物降解作用对原油中烷基菲分布的影响

The Effect of Biodegradation on Alkylated Phenanthrene Distributions in Reservoired Oils

辽河盆地冷东油田原油来源单一,成熟度相近,生物降解是导致原油中烷基菲含量和组成发生变化的主要原因。通过对不同降解程度油砂样品中烷基菲含量和分布的详细地球化学分析,发现中等程度生物降解(3到5级)使烷基菲含量大大降低,而异构体相对含量的变化主要发生在中等程度生物降解之后(4级以上),原油遭受4级以下生物降解影响时,烷基菲参数仍能有效指示成熟度。烷基菲生物降解的难易程度明显受烷基化程度的控制,C3-菲比低烷基取代化合物的抗生物降解能力强,但甲基菲比菲更容易降解,推测这与甲基菲的脱甲基作用有关。生物降解对烷基菲各异构体的消耗有强烈的选择性,在9位或10位上取代的烷基菲比其他位置取代的烷基菲抗生物降解能力强,根据烷基菲系列中化合物相对含量随生物降解程度的变化,确定了甲基菲、C2-菲和C3-菲各异构体的生物降解顺序,研究成果为芳烃成熟度参数的合理选用和生物降解定量评价提供了依据。

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.