中文摘要：

大宛齐油田全油样品的GC分析显示，部分样品经受了不同程度的微生物降解作用。对原油C，轻烃组成分析发现，随微生物降解程度的增加，链烷烃、环烷烃的相对丰度呈现规律性的变化。对不同支链烷烃而言，单甲基链烷烃比双甲基链烷烃和三甲基链烷烃优先降解，2，3-二甲基戊烷是C7支链烷烃中抗微生物降解能力最强的；2-甲基己烷比3-甲基己烷优先降解，甲基位于末端位置的比位于中间位置的异构体更易于被细菌攻击；烷基化程度和烷基化位置是影响微生物降解的两个主要因素。对于环烷烃，在较为强烈的微生物降解条件下，只剩下1，1-二甲基环戊烷，1，1-二甲基环戊烷是所有C7类烃中抗微生物降解能力最强的。随微生物降解程度的增加，Mango轻烃参数K1值减小、K2值增大，正庚烷值和异庚烷值减小，甲基环己烷指数增加，Halpem变化参数Tr2、Tr3、Tr4、Tr5均减小。

英文摘要：

GC analysis of crude oil samples from Dawanqi Oilfield in Tarim Basin reveals that some samples have been biodegraded but to different degrees. According to the analytical results of C7 light hydrocarbons in crude oils, the relative abundances of chain alkanes and cycloalkanes show regular changes with increasing degree of biodegradation. For branched hydrocarbons, monomethylalkanes are biodegraded earlier than dimethylalkanes and trimethylalkanes, while 2,3-dimethylpentane is the most resistant to biodegradation among the C7 branched hydrocarbons. Moreover, 2-Methylhexane is biodegraded earlier than 3-methylhexane; terminal methyl groups are more susceptible to bacterial attack than mid-chain isomers. It was found that degree of alkylation and position of alkylation are two main factors controlling the susceptibility to biodegradation. For cycloalkanes, 1,1-dimethylcyclopentane is preserved even under relative severe biodegradation, suggesting that 1,1-dimethylcyclopentane is the most resistant,to biodegradation among the C7 light hydrocarbons. With increasing degree of biodegradation, Mango＇s light hydrocarbon parameters such as K1 values decrease, K2 values increase, Heptane value and Isoheptane value decrease, Methylcyclohexane index increases, and Halpern parameters such as Tr2, Tr3, Tr4 and Tr5 values decrease.