Abstract Fifteen natural gas samples were collected from the autochthonous Miocene strata between Debica and Przemyśl towns in the eastern sector of the Polish Carpathian Foredeep. The samples were analysed for the molecular and stable isotope compositions of carbon (δ13C in CH4, C2H6, C3H8, i-C4H10, n-C4H10 and CO2), hydrogen (δ2H in CH4, C2H6 and C3H8), nitrogen (δ15N in N2), and all stable isotopes of noble gases (He, Ne, Ar, Kr and Xe) in order to reveal the origin and migration pathway of these gases. Methane concentrations usually exceeded 90 vol%. Methane was mainly generated by microbial carbon dioxide reduction. The rhythmic and cyclic deposition of clays, muds and sands in the Miocene marine basin facilitated and intensified microbial processes. Microbial ethane can be produced by methanogenic Archaea from acetate via reduction. Ethane partly contains a minor component generated from early mature thermogenic process. Propane and butanes were also generated thermogenically. The hydrocarbon gases in the Miocene horizons IIA and IIIA of the Gora Ropczycka field were generated at higher maturity thermogenic process than the rest of the analysed Miocene gases probably from the Middle Jurassic type III kerogen. They migrated to the Miocene horizons from the underlying Upper Jurassic horizon IV of the same field along a fault. Carbon dioxide of the analysed Miocene gases was mainly generated by primary microbial processes. Moreover, the total carbon constrained in the analysed Miocene gases from 0.1 to 6 wt% contained mantle-derived carbon, and thus carbon dioxide mantle component. Molecular nitrogen was mainly generated during low-temperature thermal transformation of organic matter. It might also involve a relatively insignificant component released from NH4-rich illites of the clayey facies of Miocene strata and an atmospheric component delivered by recharge of air-saturated seawater to the reservoir. Inorganic fluid supply from greater lithospheric depth would not be responsible for the promotion of thermal transformation of organic matter. Molecular nitrogen from Miocene horizons in the Gora Ropczycka field was generated during the thermal transformation of organic matter of higher maturity than the rest of Miocene gases, and migrated from the Upper Jurassic horizon along a fault. Helium is dominated by its radiogenic component, with a minor contribution from the mantle. The almost constant mixing ratios of the two helium components in the natural gases from Miocene horizons of various depths suggest that He migrated from a common inorganic deep-seated source in the lithosphere. The other noble gases are dominated by atmospheric components delivered to the hydrocarbon reservoirs by recharge of air-saturated seawater, with minor nucleogenic 21Ne, radiogenic 40Ar, and sedimentary Kr and Xe contributions. The atmospheric component is isotopically fractionated for Ne, and elementally fractionated with various degrees. The ratios of radiogenic 4He to nucleogenic 21Ne or radiogenic 40Ar are higher than the crustal production ratios, suggesting fractionation during thermal release from their host minerals and/or phase related fractionation during their transport to the gas reservoirs. The striking similarity in noble gas isotopic/elemental ratios of the Gora Ropczycka gas from the Miocene horizon IIIA to the nearby reservoir in Mesozoic strata is consistent with gas migration along a fault system.

中文翻译：

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波兰喀尔巴阡山脉东部中新世地层中碳氢化合物和惰性气体、二氧化碳和分子氮的起源：同位素和地质方法

摘要 从波兰喀尔巴阡山脉东段的 Debica 和 Przemyśl 城镇之间的本土中新世地层中采集了 15 个天然气样品。分析样品中碳（CH4、C2H6、C3H8、i-C4H10、n-C4H10和CO2中的δ13C）、氢（CH4、C2H6和C3H8中的δ2H）、氮（N2中的δ15N）的分子和稳定同位素组成，以及稀有气体（He、Ne、Ar、Kr和Xe）的所有稳定同位素，以揭示这些气体的起源和迁移途径。甲烷浓度通常超过 90 vol%。甲烷主要由微生物二氧化碳还原产生。中新世海盆中粘土、泥土和沙子的有节奏和循环沉积促进并强化了微生物过程。微生物乙烷可以由产甲烷古细菌通过还原从乙酸盐中产生。乙烷部分含有由早期成熟产热过程产生的少量成分。丙烷和丁烷也是产热产生的。Gora Ropczycka 油田中新世层 IIA 和 IIIA 中的烃类气体是在比其他分析的中新世气体更高的热成因过程中产生的，这些气体可能来自中侏罗世 III 型干酪根。他们沿着断层从下伏的上侏罗统IV层迁移到中新世层。所分析的中新世气体中的二氧化碳主要由初级微生物过程产生。此外，所分析的中新世气体中总碳含量为 0.1 至 6 重量％，其中包含地幔衍生的碳，因此包含二氧化碳地幔成分。分子氮主要在有机物的低温热转化过程中产生。它还可能涉及从中新世地层粘土相的富含 NH4 的伊利石释放的相对微不足道的成分，以及通过空气饱和海水补给储层输送的大气成分。来自更大岩石圈深度的无机流体供应不会促进有机物质的热转化。Gora Ropczycka油田中新世层位的分子氮是在比其他中新世气体成熟度更高的有机质热转化过程中产生的，并从上侏罗统层位沿断层运移。氦主要由其放射成因组成，地幔的贡献很小。来自不同深度的中新世层的天然气中两种氦组分的几乎恒定的混合比表明，He 是从岩石圈中常见的无机深层源迁移而来的。其他稀有气体主要是通过空气饱和海水的补给输送到碳氢化合物储层的大气成分，还有少量的成核 21Ne、放射成因 40Ar 以及沉积的 Kr 和 Xe。大气成分按 Ne 进行同位素分馏，并按不同程度进行元素分馏。放射成因 4He 与成核 21Ne 或放射成因 40Ar 的比率高于地壳生产比率，表明在从其寄主矿物热释放过程中分馏和/或在它们向气藏输送过程中与相相关的分馏。