Isotopic geochemistry of non-hydrocarbons in natural gases from the Sanshui Basin, Guangdong Province, China
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This study is focused on geothermal heat flow and the origin of non-hydrocarbons in natural gases in terms of the isotope geochemical characteristics of Ar, He, CO2 and N2 in natural gases from the Sanshui Basin, Guangdong Province. China.3He/4He ratios are of (1.60-6.39) × 10-6, and40Ar/36Ar ratios of 450–841. The carbon isotopic composition (δl3C PDB) of carbon dioxide ranges from -20‰ to -2‰. δl5N(air) ratios have a wider range of-57 ‰- +95 ‰. The isotope geochemical characteristics of non-hydrocarbons indicate that He, Ar and N2 in the gas reservoirs enriched in non-hydrocarbons were derived largely from the upper mantle. Non-hydrocarbons in gaseous hydrocarbon reservoirs consist mainly of crustal radiogenic He and40Ar and some mantle-derived He and Ar, as well as of13C-depleted carbon dioxide and nitrogen generated as a result of thermal decomposition of organic matter in strata. Carbon dioxide enriched in13C was derived largely from carbonate rocks and partially from the lower crust and upper mantle.
Based on the relationship between geothermal heat flow (Q) and3He/4 He ratio in natural gases, the Q values for the area studied have been calculated. Similar Q values are reported from the upper mantle uplift area (77 mWm-2) in Huabei and the Tancheng-Lujiang Rift Zone (88 mWm-2). More than 60 percent of geothermal heat flow in the Sanshui Basin may have been derived from the upper mantle.
KeywordsCarbonate Rock Kerogen Carbon Isotopic Composition Radiogenic Heat Lanzhou Institute
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- Craig H., Lupton J. E. and Horibe Y. (1987) Mantle helium component in Circum-Pacific volcanic gases: Hakone, the Marianas and Mt. Lassen. Terrestrial Rare Gases (Advances in Earth and Planetary Sciences), Center for Academic Publications, Japan,3, 3 -16.Google Scholar
- Du, J. and Xu, Y. (1988) Geochemical characteristics and origins of natural gases from the Sanshui Basin. Annual Research Report of Biogeochemistry and Gasgeochemistry Laboratory. Lanzhou Institute of Geology, Academia Sinica (1987) Gansu Publishing House of Science and technology, Lanzhou, 150–166 (in Chinese).Google Scholar
- Headlee, A. J. W. (1962) Carbon dioxide, nitrogen crucial to oil migration?World Oil,155 (5), 126–144.Google Scholar
- Hoefs, J. (1980) Stable Isotope Geochemistry. Springer-Verlag, Berlin.Google Scholar
- Liu, W. and Xu, Y. (1987) Relationship between argon in natural gas, and potassium in source rocks. Annual Research Report of Biogeochem. and Gasgeochem. Lab. Lanzhou Institute of Geology, Academia Sinica. Gansu Pub. House of Sci. and Techno., Lanzhou, 191–200 (in Chinese).Google Scholar
- Parada, C. B., Long, A. and Davis, S. N. (1983) Stable-isotopic composition of soil carbon dioxide in the Tucson Basin, Arizona,U. S. A. Isot. Geosci.,1, 219–236.Google Scholar
- Sano, Y. (1988) Helium isotope ratios and tectonics.Geochemistry,22, 1–11 (in Japanese).Google Scholar
- Tang, Z. (1984) Relationship between volcanism and oil, gas in the Sanshui Basin.Oil and Gas Geolo.,5 (2). 89–100 (in Chinese).Google Scholar
- Valyayev, B. M. and Grinchenko, Yu. I. (1985) The origin of isotopically ultraheavy carbon dioxide.Internal. Geol. Rev.,27 (11), 1315–1324.Google Scholar
- Wu, Q., Xian, Y., Zhu, J. and Wang, D. (1985) Terrestrial heat flow and seismicity in North China. Research on Recent Crustal Movement, Seismological Press, Beijing, 133–141 (in Chinese).Google Scholar
- Xu, Y. and Shen, P. (1985) A preliminary study on geochemical characteristics of coal-type gas in Zhongyuan-Huabei oil-gas area. ActaSedimentologica Sinica,3 (2), 37–46 (in Chinese).Google Scholar
- Zhen, G. (1986) Distribution and occurrence of non-hydrocarbon gases in Guangdong Province.Oil and Gas Geol.,7 (4), 404–411 (in Chinese).Google Scholar