Five crude oil samples from the Quiriquire field (Maturin sub-basin, Eastern Venezuelan Basin) were analysed to evaluate their levels of biodegradation. The oils were obtained from coarse sandstones and conglomerates of the Pliocene Quiriquire Formation at depths <1000 m. Analyses of the samples’ bulk physicochemical parameters indicate variations in API gravity and in the content of saturated hydrocarbons and NSO+asphaltenes, and also in the saturate/aromatic ratio which increases in more biodegraded oils. n-Alkane distributions are characterized by a dominant unresolved complex mixture (UCM) or hump under an envelope of peaks which lack the acyclic isoprenoids pristane and phytane. The alteration of steranes and terpanes together with the presence of 25-norhopanes and 17-nor-tricyclic terpanes, and the alteration of low molecular-weight (C₂₀-C₂₁) triaromatic steroids, phenanthrene, methyl-phenanthrene, dibenzothiophene and methyl-dibenzothiophene, indicate that the oils have undergone severe biodegradation.

中文翻译：

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委内瑞拉东部 QUIRIQUIRE 油田原油的严重生物降解

对来自 Quiriquire 油田（Maturin 子盆地，委内瑞拉东部盆地）的五个原油样品进行了分析，以评估其生物降解水平。这些油是从上新世 Quiriquire 地层的粗砂岩和砾岩中获得的，深度小于 1000 米。样品整体理化参数的分析表明 API 比重以及饱和烃和 NSO+沥青质含量的变化，以及饱和/芳烃比率的变化，在更多生物降解油中增加。正烷烃分布的特征在于主要的未解析复杂混合物 (UCM) 或峰包络下的驼峰，而这些峰包络缺乏无环类异戊二烯类异戊二烯和植烷。甾烷和萜烷的变化以及 25-去甲霍烷和 17-去甲三环萜烷的存在，以及低分子量（C₂₀ -C ₂₁ ) 三芳族类固醇、菲、甲基菲、二苯并噻吩和甲基-二苯并噻吩，表明油已经经历了严重的生物降解。