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Geoscience ›› 2021, Vol. 35 ›› Issue (02): 301-314.DOI: 10.19657/j.geoscience.1000-8527.2021.032

• Petroleum Geology • Previous Articles     Next Articles

Distribution Characteristics and Geochemical Significances of the Compound Specific Sulfur Isotope of Saline Lacustrine Source Rocks from the North Dongpu Depression, Bohai Bay Basin

KE Changwei1,2(), LI Sumei1,2(), ZHANG Hongan3, XU Tianwu3, ZHANG Yunxian3, ZENG Fangang4, ZHANG Shuhai1, ZHANG Hanjing1   

  1. 1. State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing 102249,China
    2. College of Geosciences,China University of Petroleum,Beijing 102249,China
    3. SINOPEC Zhongyuan Oilfield Company,Puyang,Henan 457001,China
    4. School of Environment & Natural Resources, Renmin University of China,Beijing 100872,China
  • Received:2020-09-23 Revised:2020-12-15 Online:2021-04-25 Published:2021-05-25
  • Contact: LI Sumei

Abstract:

The researches about compound specific sulfur isotopes of saline lacustrine source rocks are rare. Using the technology of gas chromatography with multicollector inductively coupled plasma mass spectrometry (GC-MC-ICP MS), combined with gas chromatography/mass spectrometry (GC/MS), carbon and oxygen isotopic and trace elements to analyze the source rocks (oil sands)from saline lacustrine northern of Dongpu Depression. The analysis results show that the sulfur isotopic values of individual hydrocarbon in source rocks (oil sands) are small, but the δ34S values of different sulfur compounds are quite different (5.16‰ to 44.73‰). Boundary with δ34S=25.00‰ the source rocks (and oil sands) can be divided into two categories, the first type with δ34S>25.00‰ is mainly Weicheng source rock characterized by the sulfur isotope of individual hydrocarbon decreases with the increase of methyl. And the δ34S<25.00‰ is the second type,which characteristics are opposite to Weicheng source rocks. The sulfur isotopes of dibenzothiophenes have obvious positive correlation with the content of saturated hydrocarbon, tricyclic terpane/pentacyclic terpane, and negative correlation with content of “nonhydrocarbon+asphaltene”. The sulfur isotopes of hydrocarbons have obvious positive correlation with gammacerane/C31hopane and C35/C34hopanes, excellent correlation with contents of minerals and ratios of trace elements, indicating that the isotopes of organic sulfur compounds in the closed evaporation environment becomes heavier, and the values in the open terrestrial input environment becomes lighter. The analysis shows that the sulfur isotopes of individual hydrocarbon are significantly controlled by the original sedimentary environment of source rock. Strong reduction and closed evaporation environment are conducive to the sulfuration of organic matter, which makes the sulfur isotope heavier. The sulfur isotopes are also affected by maturity, while the sulfur isotope tends to become heavier with the increase of maturity. Generally speaking, isotopes of organic sulfur compounds have important significance of indicating sedimentary environment and maturity, and the potential of oil-oil and oil-rock correlation.

Key words: Dongpu depression, saline lacustrine, isotopes of organic sulfur compounds, trace elements, sedimentary environment

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