Abstract The Vankor Field, located in the West Siberia Basin, Russia, contains oils at various levels of biodegradation. A study of reservoir oils and rock extracts from the Lower Cretaceous sandstones in the Nkh 3-4 interval reveals that increasing biodegradation when moving from the gas-oil contact (GOC) towards the oil-water contact (OWC) is strongly controlled by rock properties. Biodegradation is most advanced where the OWC is located in the high permeability reservoir interval. High permeability rocks also allow for more extensive upward mixing of biodegraded oil. Changes in the oil and gas fractions due to biodegradation also affect the gas-oil ratio as dry gas is less soluble in heavy oil. This explains the presence of reservoir oil saturated with gas near the OWC. The latter also can be partly due to the admixture of methane through methanogenic processes at the OWC. Upward movement of microbial gas bubbles enhances the mixing of biodegraded oil in the high permeability reservoir intervals.

中文翻译：

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Vankor 油田（俄罗斯西西伯利亚盆地）Nkh 3-4 油藏的生物降解受到岩石性质的强烈控制

摘要 位于俄罗斯西西伯利亚盆地的 Vankor 油田含有不同程度的生物降解油。对 Nkh 3-4 层段下白垩统砂岩储层油和岩石提取物的研究表明，当从气油界面 (GOC) 向油水界面 (OWC) 移动时，增加的生物降解受到岩石性质的强烈控制. 当 OWC 位于高渗透储层层段时，生物降解最为先进。高渗透性岩石还允许更广泛地向上混合生物降解油。由于干气在重油中的溶解度较低，因此生物降解引起的石油和天然气馏分的变化也会影响气油比。这解释了在 OWC 附近存在饱和气体的储层油。后者也可能部分是由于通过 OWC 的产甲烷过程混合了甲烷。微生物气泡的向上运动增强了高渗透油藏层段中生物降解油的混合。