2005/10/30 | 中国主要的煤层序列有机岩石学及地球化学方面的若干问题
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中国主要的煤层序列有机岩石学及地球化学方面的若干问题

Some aspects of the organic petrology and geochemistry of

major coal-bearing sequences in China

Zhong Ningning1, Wang Tieguan1 and Chen Jianping2

1 Faculty of Natural Resource & Information Technology, University of Petroleum, Beijing 102249, China 2 Key Lab of Petroleum Geochemistry, CNPC, Beijing 100083, China

The China's proven gas reserves have risen steadily during the past two decade. The important discoveries are mostly related to the major coal-bearing strata. Coal-related gas therefore play a very important role in the country's gas reserves.

Based on petrographic analyse of more 3000 samples, the maceral compositions and their contours of distributive density of the coal-bearing sequence, such as Permo-carboniferous coal-bearing sequence in the North China, Permo-carboniferous and Jurassic coal-bearing sequences in the Erdos Basin, Upper Permian coal-bearing sequence in the South China, Upper Permian and Upper Triassic coal-bearing sequences in the Southwest China, Jurassic coal-bearing sequence in the Northwest China (including the Tarim, Turpan, Junggar and Santanghu basins), Lower Cretaceous coal-bearing sequence in the Northeast China and inner-Mongolia and Tertiary coal-bearing sequence in the East coast and off-shore are individually discussed in this paper .

Petrographically, the distribution of maceral compostion of the coal-bearing squences in China show three patterns of density, namly vitrinite-exinite assemblage, vitrinite-inertinite assemblage and transitional assemblage (intergradation) . Coal-bearing sequence that shows the pattern of vitrinite-exinite assemblage is likely oil prone one. Coal-bearing sequence that shows the patterns of vitrinite-inertinite or transitional assemblages should be gas prone one.

Geochemically, it is much the same that the saturated fraction of the extracts from the coals whatever they were from different coal-bearing sequence. The biomarkers generally show no clear age-specific features. Although tricyclic terpenoids, resin-input diterpenoids and sesquiterpenoids are widely detected in different coal-bearing sequences, the assembalges of biomarker compounds and their proportions do show some difference from one sequence to another. The stable carbon isotopic value (δ13C) of the coals ranges from –28‰ to –22‰, which slightly vary from those of the major coal-bearing sequences. It has been seen from a case study of Jurassic coal-bearing sequence in the Northwest China that the gas and oil preferences of coal sequences as a whole highly depend on the pattern of distributive density.

Based on experimental data and geological evidence, it is revealed that the geological and geochemical factors control the distribution of the initial gas to oil ratio of the coal sequence. It is evident that the vitrinite-exinite assemblage pattern is the most likely to develop in the sub-sequence of base level up, whereas the vitrinite-inertinite and/or transitional assemblages are often related to the the sub-sequence of base level down. Thefore the coal measure located in descending semi-cycle of sequence base level should be regarded as gas-prone, and one located in ascending semi-cycle should be regarded as oil-prone. It is natural that gas prone is characteristic of most of the major coal-bearing sequences in China.

转自：中国石油网

译－部分：镜质体－壳质体组合体最有可能存在于基准线之上的准层序中，而镜质体－惰质体组合体或过渡形态的组合体则一般出现在基准线之下的准层序中。因此，可认为处于层序基准线半旋回下降位置的煤系更有可能是气源岩；反之则是油源岩。以此来判定，中国大部的的煤系地层具有气源的特征。

基准线？半旋回？

低水位体系域(LST)、海侵体系域(TST)和高水位体系域(HST)；在Ⅱ型层序中自下而上划分出陆棚边缘体系域(SMST)、海侵体系域(TST)和高水位体系域(HST)
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