Distribution and geological significance of 17α(H)-diahopanes from different hydrocarbon source rocks of Yanchang Formation in Ordos Basin |
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| Authors: | WenZheng Zhang Hua Yang LiHui Hou Fei Liu |
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| Institution: | (1) Institute of Exploration, Development and Research of PetroChina Company Limited Changqing Oilfield Branch, Xi’an, 710018, China;(2) PetroChina Company Limited Changqing Oilfield Branch, Xi’an, 710018, China;(3) Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China |
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| Abstract: | Based on GC-MS testing data of many saturated hydrocarbon samples, 17α(H)-C30 diahopanes (C30
*) are extensively distributed in the lacustrine hydrocarbon source rocks of the Yanchang Formation in Ordos Basin, but show
remarkable differences in relative abundance among various source rocks. Generally, Chang 7 high-quality source rock (oil
shale) developed in deep lake anoxic environment shows lower C30
* content, whereas Chang 6–9 dark mudstone developed in shallow to semi-deep lake, sub-oxidizing environment shows relatively
high to high C30
* value. Particularly, Chang 7 and Chang 9 black mudstones in Zhidan region in the northeast of the lake basin show extremely
high C30
* value. A comparative analysis was made based on lithology, organic types and various geochemical parameters indicative of
redox environment, and the results indicate that environmental factors such as redox settings and lithology are key factors
that control the C30
* relative abundance, while organic types and maturity may be minor factors. High to extremely high C30
* values are indicative of sub-oxidizing environment of fresh-brackish water and shallow to semi-deep lake. Therefore, research
on C30
* relative content and distribution in lacustrine hydrocarbon source rocks in the Yanchang Formation, especially on the difference
in C30
* between Chang 7 high-quality source rocks (oil shale) and Chang 6–91 source rocks (dark mudstone), will provide an important approach for classification of Mesozoic lacustrine crudes and detailed
oil-source correlation in the basin.
Supported by National Natural Science Foundation of China (Grant No. 40773028) |
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| Keywords: | Diahopane neohopane sedimentary environment Yanchang Formation Ordos Basin |
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