Abstract Large amounts of light oil have been produced from carbonate reservoirs at depths below 7 km in the recently discovered Shunbei and Yuecan oil fields within the north Tarim Basin. Eighteen samples were investigated for molecular and isotopic compositions to help understand the origin of these deep oil accumulations. Several ratios based on C6 and C7 hydrocarbons suggest that they were not affected by evaporative fractionation. Linear relationships between the carbon number and log of the mole fraction of n-alkanes support no fractionation alteration. The correlation between concentrations of methyldiamantanes and stigmastane indicates that these oils were not severely cracked and probably at the beginning or an early stage of intense oil cracking. C29 sterane isomerization ratios 20S/(20S + 20R) and ββ/(ββ + αα) have reached their equilibrium points while a good linear relationship between the concentrations of terpanes and steranes suggests variations in maturity. Calculated vitrinite reflectance of source rocks based on phenanthrene and diamondoid hydrocarbons shows different ranges, which may reflect multiple oil charges to these deep oil accumulations. A narrow range of δ13C values of whole oil and oil fractions suggest a genetic correlation of these oils. Triangular plots based on C6 and C7 hydrocarbons and diamantanes also indicate a very similar source. In addition, several ratios based on n-alkanes, isoprenoids, tri-, tetra-, and pentacyclic saturated hydrocarbons support a common source. However, oil SB7 seems to differ from the others in terms of source rock depositional environment, indicated by its much higher pristane/phytane ratio and lower dibenzothiophene/phenanthrene ratio as well as a much lower dibenzothiophenes concentration.

中文翻译：

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塔里木盆地北部碳酸盐岩储层深层油藏成因：分子和同位素组成的洞察

摘要 塔里木盆地北部新发现的顺北油田和月灿油田在7 km以下深度碳酸盐岩油藏中开采了大量轻质油。研究了 18 个样品的分子和同位素组成，以帮助了解这些深层石油聚集的起源。基于 C6 和 C7 烃的几个比率表明它们不受蒸发分馏的影响。正构烷烃摩尔分数的碳数和 log 之间的线性关系支持没有分馏改变。甲基二金刚烷和柱头烷的浓度之间的相关性表明这些油没有被严重裂化，并且可能处于强油裂化的开始或早期阶段。C29 甾烷异构化比率 20S/(20S + 20R) 和 ββ/(ββ + αα) 已达到其平衡点，而萜烷和甾烷浓度之间的良好线性关系表明成熟度的变化。基于菲和金刚石类烃源岩计算的镜质体反射率显示出不同的范围，这可能反映了这些深层石油聚集的多种石油电荷。全油和油馏分的 δ13C 值范围很窄，表明这些油存在遗传相关性。基于 C6 和 C7 碳氢化合物和金刚石的三角图也表明了一个非常相似的来源。此外，基于正烷烃、类异戊二烯、三环、四环和五环饱和烃的几个比率支持一个共同的来源。然而，