Biodegraded oils have been widely discovered throughout the world, whereas the alteration of the molecular composition of oils at extreme levels (>PM8) has been insufficiently documented. A suite of crude oils from Carboniferous volcanic reservoirs in the eastern Chepaizi Uplift, Junggar Basin, experienced severe to extreme biodegradation (from PM6+ to PM9+), which provided an ideal case for the present study. This investigation showed that the variations in molecular composition were not strictly consistent with their stepwise fashion in established schemes. The idea that 25-norhopanes are derived from hopanes was confirmed by the sharp decreases in the C₂₉ hopane/gammacerane (C₂₉H/G) and C₃₀ hopane/gammacerane (C₃₀H/G) values at the level of extreme biodegradation, which were associated with the increases in their counterparts of C₂₈ 25-norhopane/gammacerane (C₂₈ 25-NH/G) and C₂₉ 25-norhopane/gammacerane (C₂₉ 25-NH/G). 25-Norhopanes were also biodegraded at an extreme level, with C₂₉ 25-NH being more susceptible than C₂₈ 25-NH. The preferential biodegradation of individual homohopanes by carbon number occurred at an extreme level, whereas C₂₉H featured more bioresistance than C₃₀H and shared a similar susceptibility to biodegradation as 18α-30-norneohopane (C₂₉Ts). The formation of 22R isomers for 25-norhopanes seemed to be favored over that of 22S isomers, although the 22S isomer was degraded faster that the 22R epimer for the C₃₁, C₃₂, and C₃₃ homohopanes. However, the constant values of 22S/(22S + 22R) for the C₃₄ homohopane implied no preferential biodegradation of 22S or 22R isomers for this extended hopane. Lower molecular weight tricyclic terpanes (TTs) were preferentially removed at extreme biodegradation levels, and the late eluting stereoisomers were degraded faster than the early eluting stereoisomers for C₂₆TT, C₂₈TT, and C₂₉TT. C₂₄ tetracyclic terpane (C₂₄Tet) is much more resistant to biodegradation than TTs. Pregnanes have a similar susceptibility to biodegradation as gammacerane, but they are more resistant than C₂₃TT. The biodegradation of regular steranes was characterized by their faster depletion than diasteranes and the preferential depletion of C₂₇ regular sterane to the C₂₉ homologue and the 20R isomers to the 20S isomers. At the extreme level, even C₂₀ and C₂₁ triaromatic steroids (TAS) were distinctively reduced, coexisting with the relatively highly degraded steranes and terpanes, although water washing can also be responsible for the decreases in (C₂₀ + C₂₁)-TAS/C_26–28-TAS values.

中文翻译：

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从严重到极端的生物降解，人们对分子组成的改变有了进一步的了解：以准Jung尔盆地东部车牌子隆起的石炭系油为例

在世界范围内已广泛发现了生物降解的油，而没有充分记录到极端水平（> PM8）时油分子组成的变化。准gar尔盆地Chepaizi隆起东部石炭纪火山岩储层的一组原油经历了严重到极端的生物降解（从PM6 +到PM9 +），这为本研究提供了理想的案例。这项研究表明，分子组成的变化与既定方案中的逐步变化形式并不完全一致。C- ₂₉ ho烷/ γ-庚烷（C ₂₉ H / G）和C ₃₀ ane烷/γ-庚烷（C ₃₀）的急剧下降证实了25-去甲胆烷衍生自hop烷的想法。H / G）值处于极端生物降解的水平，这与C ₂₈ 25-去甲胆烷/γ-庚烷（C ₂₈ 25-NH / G）和C ₂₉ 25-去甲胆烷/γ-甘油（C ₂₉ 25 ）对应物的增加相关-NH / G）。25-Norhopanes也被极端降解，C ₂₉ 25-NH比C ₂₈ 25-NH更易受影响。单个同型人的优先生物降解的碳数发生在一个极端的水平，而C ₂₉ H具有比C ₃₀ H更多的生物抵抗力，并且对生物降解的敏感性与18α-30-正新庚烷（C ₂₉ Ts）类似。22 R的形成尽管22 S异构体的降解速度比C ₃₁，C ₃₂和C ₃₃同型异构体的22 R差向异构体要快，但25-去甲胆碱的异构体似乎比22 S异构体更受青睐。但是，C _34同型半胱氨酸的恒定值22 S /（22 S + 22 R）表示22 S或22 R没有优先的生物降解。延长的hopane的异构体。在极端生物降解水平下，优先去除了较低分子量的三环萜烯（TTs），对于C ₂₆ TT，C ₂₈ TT和C ₂₉ TT ，晚期洗脱的立体异构体的降解速度比早期洗脱的立体异构体要快。C ₂₄四环萜烯（C ₂₄ Tet）比TT更耐生物降解。孕烷对生物降解的敏感性与γcercerane相似，但比C ₂₃ TT具有更高的抵抗力。常规甾烷的生物降解的特征在于其耗竭速度比非甾烷快，并且C ₂₇常规甾烷比C ₂₉优先耗竭同源物和20 R异构体到20 S异构体。在极端水平上，即使C ₂₀和C _21三芳族类固醇（TAS）也明显降低，与相对高度降解的甾烷和萜烯并存，尽管水洗也可能导致（C ₂₀ + C ₂₁）-TAS降低/ C _26–28 -TAS值。