Carbon and Hydrogen Isotopic Characteristics of Hydrocarbons in Coal Type Gas from China

Chen Jianfa; Li Chunyuan; Shen Ping; Ying Guangguo

The thermogenic gas can be divided into coal type gas originated from humic organic matter and oil type gas formed by sapropel organic matter according to the type of organic matter. The stable isotopic compositions of hydrocarbons of coal type gas and oil type gas from main oil - gas- bearing basins in Chins are relatively systematically studied in this paper. The results show that it is not certain that the methane of coal type gas always enriches the heavy carbon isotope in comparison with oil type gas. At the stage from immature to low mature, there is no obvious difference in carbon isotopic compositions of methane between coal type gas and oil type gas. From low mature stage, in comparison with oil type gas, the methane of coal type gas gradually enriches heavy carbon isotope with the increasing of thermal evolution. When vitrinite renectance (Ro) reaches about 1. 0, the difference in δ¹³C₁ between coal type gas and oil type gas is the largest,about 7～8‰, then gradually decreases with increasing thermal evolution. After thermal evolution reaches the stage of over - maturity(Ro2. 2% ), the carbon isotope composition of coal type gas is basically similar to that of oil type gas. The carbon isotope compositions of heavy gaseous hydrocarbons (ethane to butane) of coal type gas and oil type gas are mainly controlled by the carbon isotopic composition of organic matter in source rock. Therefore, the carbon isotopic composition of heavy gaseous hydrocarbon is an effective indicator for the identification of coal and oil type gas. In general, the δ¹³C₂ of coal type gas is more than -28‰,while the δ¹³C₂ of oil type gas is less than - 28‰. Thermal evolution has no obvious innuence on carbon isotopic composition of heavy hydrocarbons of coal type gas. However, it has certain influence on carbon isotopic composition of heavy hydrocarbons of oil type gas. With the increase of thermal evolution, the ethane of oil type gas gradually enriches heavy carbon isotopes. The hydrogen isotopic composition of methane and heavy gaseous hydrocarbons of coal type gas is mainly related to the salinity of water under which the source rock was deposited. The coal type gas formed by the source rock deposited in terrestrial freshwater environment relatively enriches protium of hydrogen isotope. However, the coal type gas derived from the marine source rock relatively enriches deuterium of hydrogen isotope. In addition, with the increase of carbon number from methane to butane, the hydrogen isotopic composition of hydrocarbons of coal type gas successively becomes heavier, i. e.,δD₁<δＤ₂<δＤ₃<δＤ₄.

Carbon and Hydrogen Isotopic Characteristics of Hydrocarbons in Coal Type Gas from China

State Key Laboratory of Gas Geochemistry, Lanzhou Institute of Geology,Chinese Academy of Sciences, 730000, Lanzbou, P. R. China

Received Date: 1994-10-15

Publish Date: 1995-06-10

Abstract: The thermogenic gas can be divided into coal type gas originated from humic organic matter and oil type gas formed by sapropel organic matter according to the type of organic matter. The stable isotopic compositions of hydrocarbons of coal type gas and oil type gas from main oil - gas- bearing basins in Chins are relatively systematically studied in this paper. The results show that it is not certain that the methane of coal type gas always enriches the heavy carbon isotope in comparison with oil type gas. At the stage from immature to low mature, there is no obvious difference in carbon isotopic compositions of methane between coal type gas and oil type gas. From low mature stage, in comparison with oil type gas, the methane of coal type gas gradually enriches heavy carbon isotope with the increasing of thermal evolution. When vitrinite renectance (Ro) reaches about 1. 0, the difference in δ¹³C₁ between coal type gas and oil type gas is the largest,about 7～8‰, then gradually decreases with increasing thermal evolution. After thermal evolution reaches the stage of over - maturity(Ro2. 2% ), the carbon isotope composition of coal type gas is basically similar to that of oil type gas. The carbon isotope compositions of heavy gaseous hydrocarbons (ethane to butane) of coal type gas and oil type gas are mainly controlled by the carbon isotopic composition of organic matter in source rock. Therefore, the carbon isotopic composition of heavy gaseous hydrocarbon is an effective indicator for the identification of coal and oil type gas. In general, the δ¹³C₂ of coal type gas is more than -28‰,while the δ¹³C₂ of oil type gas is less than - 28‰. Thermal evolution has no obvious innuence on carbon isotopic composition of heavy hydrocarbons of coal type gas. However, it has certain influence on carbon isotopic composition of heavy hydrocarbons of oil type gas. With the increase of thermal evolution, the ethane of oil type gas gradually enriches heavy carbon isotopes. The hydrogen isotopic composition of methane and heavy gaseous hydrocarbons of coal type gas is mainly related to the salinity of water under which the source rock was deposited. The coal type gas formed by the source rock deposited in terrestrial freshwater environment relatively enriches protium of hydrogen isotope. However, the coal type gas derived from the marine source rock relatively enriches deuterium of hydrogen isotope. In addition, with the increase of carbon number from methane to butane, the hydrogen isotopic composition of hydrocarbons of coal type gas successively becomes heavier, i. e.,δD₁<δＤ₂<δＤ₃<δＤ₄.

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[1]

1.沈平，徐永昌，1991，中国陆相成因天然气同位素组成特征，地球化学.(2):1-6.

2.陈文义，朱家蔚，许化政，1987，东浪凹陷不同成因类型的天然气，凝析油地球化学特征及鉴别标志.煤成气地质研究，石油工业出版社，118-130。

3.张士亚、部建军、蒋泰然.1988，利用甲、乙烷碳同位素判识天然气类璧的一种新方法，石油与天然气地质文集，(第1集)，中国煤成气研究，北京:地质出版社.P. 48-58。

4.徐水昌、沈平，1985，中原华北油气区“煤型气，地球化学特征初探.沉积学报，3(2),37-46。

5.徐永昌等.1990，一种新型的天然气成因类蟹一生物热催化过渡带气，中国科学(B)辑.(9)：975 - 980。

6.徐水昌等.1994，天然气的成因理论及应用，北京:科学出版社，102-269。

7.裁金星，戚厚发，1985.鉴别煤成气和油型气若干指标的初步探讨，石油学报，6(2):31一38。

8.戴金星等.1987.鉴别煤成气的指标，煤成气地质研究，北京:石油工业出版社，156-170。

9.段金星、戚厚发，1989.我国煤成烃δC一Ra关系，科学通报，37(9),690 - 692。

10.戴金星.1992，各类烷烃气的鉴别，中国科学(B)辑，(2),183-193.11.Fa6er E.，Stahl. W. and Whiticar M.，1992. Distinction of bacterial and thertnogenic h州rocarbon gases. in 0Bacterial Gas. Edited by Vially. Paris. P.63一74.

12.Gelimov. E.，1988. Sources and mechanism of formation of gaseous harocarbons in sedimentary rocks. Chem. Gaol. Vol. 71，P. 77一95.

13.James. A. T.，1983. Correlation of natural gas by use of isotopic distribution between hydrocarbon components.AAPG. Bull. V. 67 a. P. 1176一1191.

14.James. A. T.，1990. Correlation of reservoired Gases Using the Carbon isotopic rnmposition of Wet Gas. Components.AAPG. Bull. Vol. 74. No. 9. P. 1441一1458.

15.Jenden. P. D.1988.Composition and stable一isotope geochemistry of natural gases Irom Kansas, midrnntinent. U SA. Chem. Geol. Vol.71,P.117-147.

16.Rice.and Claypool. G. E.，1981，Generation. accumulation and resource potential of biogenic gas. Am. Assoc.Pet..Bull.。Vol. 65. P. 5一25.

17.Schoell.M 1980. The hydrogen and carbon isotopic composition of methane from natural gases of various origins. Cosmochim. Acta. Vol. 44. P.649一661.

18.Stahl. W. J. et al.，1975. Source一rock. identification by isotope analyses oI natural gases from fields in the Vol Verdeand Dclawere Basins. West Texas. Chem. Geol. V. 16. N. 4.

19.Stahl. W. J. 1977. Carbon and nitrogen isotopes in hydrocarbon P. 257一267.research and exploration. Chem. Geol. Vol. 20. P. 121一149.

Carbon and Hydrogen Isotopic Characteristics of Hydrocarbons in Coal Type Gas from China

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