| 非生物成因天然气的稳定同位素地球化学特征与判据 | |
| 胡桂兴 | |
| 1994 | |
| Degree Grantor | 中国科学院地球化学研究所 |
| Place of Conferral | 中国科学院地球化学研究所 |
| Degree Name | 博士 |
| Abstract | 本采自松辽盆地的天然气进行了化学组分和氦、碳同位素分析。经空气校正后的氦同位素组成为 ~3He/~4He＝0.26 * 10~(-6)～7.48 * 10~(-6)，相应的幔源氦的贡献额为 2.3%～63%，显示了明显的幔源氦信息，表明松辽盆地天然气藏中有幔源挥发份加入。烃类气藏甲烷的灿位素组成为 δ~(13)C＝-53.3‰～-16.7‰，δ~(13)C小于-25‰ 的甲烷是生物成因的产物，δ~(13)大于-25‰的甲烷则可能是非生物成因的。甲烷及其同系物的碳同位素组成存在两类不同的分配模式。正序排列的分析模式，即 δ~(13)C_(CH_4) < δ~(13)C_(C_2H_6) < δ~(13)C_(C_3H_8) < δ~(13)C_(C_4H_(10))，表明了生物成因天然气的特征，而反序排列的分配模式，即 δ~(13)C_(CH_4) > δ~(13)C_(C_2H_6) > δ~(13)C_(C_3H_8) > δ~(13)C_(C_4H_(10))的存在则暗示了松辽盆地存在非生物成因的商业天然气藏。模拟原始太阳星云中地球吸积区条件进行了原始宇宙成因烃类的合成实验（费托反应）。对合成气进行了碳同位素组成分析，并结合反应机理讨论了费托反应中碳同位素的分馏和原始宇宙成因烃类的碳同位素分配模式。反应合成气中二氧化碳具有最重的碳同位素组成。甲烷及其同系物的碳同位素分配模式具有与生物成因烃类完全不同的反序排列特征，即 δ~(13)C_(CH_4) > δ~(13)C_(C_2H_6) > δ~(13)C_(C_3H_8) > δ~(13)C_(C_4H_(10))，这表明由原始宇宙成因烃类构成的非生物成因天然气中甲烷及其同系物的碳同位素分配的反序排列的。对非生物成因天然气的判识应依靠多项指标。作为灵敏的幔源挥发份示踪剂的氦同位素是非生物成因天然气有效的间接指示剂，甲烷及其同系物碳同位素的反序排列分配模式加上重的碳同位素组成可作为非生物成因天然气的可靠的内在指标。松辽盆地的区域构造特征，天然气中显著的幔源氦的存在，较重的甲烷同位素组成 (δ~(13)C_(CH_4) > -25‰)和甲烷及其同系物碳同位素的反序排列充分证明了松辽盆地存在非生物成因的商业天然气藏。 |
| Other Abstract | Natural gas samples from Songliao Basin have been analyzed for chemical and helium and carbon isotopic compositions. ~3He/~4He ratios vary from 0.26 * 10~(-6) to 7.48 * 10~(-6) after air-correction. The distribution of mantle-source helium varies from 2.3% to 63% correspondingly, which shows obvious mantle helium information and indicates the injection of mantle volatile components to natural gases reservoirs in Songliao Basin. Methane δ~(13)C values of methane-rich natural gases range from -53.3‰～-16.7‰. The natural gases with light carbon isotope of methane (δ~(13)C_(CH_4)<-25‰) is of biogenic, and those with heavy carbon isotope of methane (δ~(13)C_(CH_4)<-25‰) may be of abiogenic. There are two different carbon isotopic distribution patterns of methane and its homologous in natural gases. The normal distribution pattern in which δ~(13)C_(CH_4) < δ~(13)C_(C_2H_6) < δ~(13)C_(C_3H_8) < δ~(13)C_(C_4H_(10)) shows biogenic natural gas characteristics, however, the existence of reverse distribution pattern in which δ~(13)C_(CH_4) > δ~(13)C_(C_2H_6) > δ~(13)C_(C_3H_8) > δ~(13)C_(C_4H_(10)) suggests the occurrence of abiogenic commercial natural gases in Songliao Basin. Primordial cosmogenic hydrocarbon synthesis experiment (Fischer - Tropsch reaction) has been done in the condition of the Earth's formation region in primordial sular nebula. The carbon isotopic compositions of synthetic gases have been analyzed. Combined with reaction mechanism, carbon isotopic fractionation in the process of FT reaction and carbon isotopic distribution pattern of primordial cosmosgenic hydrocarbons are discussed. Carbon dioxide in synthetic gases has the most heavy carbon isotopic composition. In different to biogenic natural gases, carbon isotopic distribution pattern of synthetic gases yields a reverse distribution pattern, i.e. δ~(13)C_(CH_4) > δ~(13)C_(C_2H_6) > δ~(13)C_(C_3H_8) > δ~(13)C_(C_4H_(10)). It proves that abiogenic natural gases composed by primordial hydrocarbons possesses reverse carbon isotopic distribution pattern among methane and its homologous. The identification of abiogenic natural gases should rely on multiple criteria. As a sensitive indicator of mantle volatile components, helium isotope can be used as a effective indirect indicator of abiogenic natural gases. Reverse carbon isotopic distribution pattern of methane and its homologous and heavy carbon isotopic value of methane can be used as reliable inherent criteria of abiogenic natural gases. Tectonic characteristics of Songliao Basin, significant contribution of mantle source helium, heavy carbon isotopic values of methane (δ~(13)C_(CH_4) > -25‰), and isotopic reversal of the form δ~(13)C_(CH_4) > δ~(13)C_(C_2H_6) > δ~(13)C_(C_3H_8) > δ~(13)C_(C_4H_(10)) fully prove the formation of commercial natural gases by abiogenic hydrocarbons in the basin. |
| Pages | 42 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/352002/3946 |
| Collection | 研究生_研究生_学位论文 |
| Recommended Citation GB/T 7714 | 胡桂兴. 非生物成因天然气的稳定同位素地球化学特征与判据[D]. 中国科学院地球化学研究所. 中国科学院地球化学研究所,1994. |
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