| Geochemical Characteristics of the Upper Triassic Xujiahe Formation in Sichuan Basin, China and its Significance for Hydrocarbon Accumulation |
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| 作者姓名： | XIE Zengye LI Jian LI Zhisheng GUO Jianying LI Jin ZHANG Lu DONG Caiyuan |
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| 摘 要： | The alternative development of coal-bearing hydrocarbon source rocks and low-porosity and low-permeability tight sandstone reservoirs of the Triassic Xujiahe Formation in the Sichuan Basin is favorable for near-source hydrocarbon accumulation. The natural gas composition of the Xujiahe Formation in the Sichuan Basin is dominated by hydrocarbon gases, of which the methane content is80.16%-98.67%. Typically, the C_2~+ content is larger than 5% in main wet gas. The dry gas is mainly distributed in the western and northern regions of the basin. The non-hydrocarbon gases mainly contain nitrogen, carbon dioxide, hydrogen, and helium, with a total content of 2%. The carbon isotope ranges of methane and its homologues in natural gas are: δ~(13)C_1 of-43.8‰ to-29.6‰, δ~(13)C_2 of-35.4‰ to-21.5‰, δ~(13)C_3 of-27.6‰ to-19.8‰,and δ~(13)C_4 of-27.7‰ to-18.8‰. δ~(13)C_3δ~(13)C_4 occurs in some natural gas with a low evolution degree; such gas is mainly coal-related gas from humic-type source rocks of the Xujiahe Formation. As for the natural gas, δ~2 H_(CH4) values ranged from-195‰ to-161‰,δ~2 H_(C2H6) values ranged from-154‰ to-120‰, and δ~2 H_(C3H8) values ranged from-151‰ to-108‰. The dry coefficient,δ~(13)C and δ~2 H_(CH4) are all positively correlated with the maturity of source rocks. The higher the maturity of source rocks is, the larger the natural gas dry coefficient is and the larger the δ~(13)C and δ~2 H_(CH_4) values are, indicative of the characteristic of near-source accumulation. The δ~2 H_(C2H6) value of natural gas is influenced by paleosalinity to a relatively large extent; the higher the paleosalinity is, the larger the δ~2 H_(C2H6) value is. The Pr/Ph value of the condensate oil ranged from 1.60 to 3.43, illustrating light oxidization-light reduction and partial-oxidization characteristics of the depositional environment of coal-bearing source rocks of the Xujiahe Formation. The natural gas light hydrocarbon(C_5-C_7) from the Xujiahe Formation presented two characteristics: the first was the relatively high aromatic hydrocarbon content(19%-32.1%), which reveals the characteristic of natural gas with humic substances of high-maturity; the second was the low content of aromatic hydrocarbon(0.4%-9.3%),reflecting water-washing during the accumulation of the natural gas. The reported research outcomes indicate a potential mechanism for natural gas accumulation in the Xujiahe Formation, which will further guide natural gas exploration in this region.
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| 收稿时间： | 2016/2/4 0:00:00 |
| 修稿时间： | 2015/8/10 0:00:00 |
Geochemical Characteristics of the Upper Triassic Xujiahe Formation in Sichuan Basin, China and its Significance for Hydrocarbon Accumulation |
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| Authors: | XIE Zengye LI Jian LI Zhisheng GUO Jianying LI Jin ZHANG Lu and DONG Caiyuan |
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| Institution: | 1 Petrochina Research Institute of Petroleum Exploration and Development, Langfang 065007, Hebei, China
2 Key Laboratory of Gas Reservoir Formation and Development, CNPC, Langfang 065007, Hebei, China,1 Petrochina Research Institute of Petroleum Exploration and Development, Langfang 065007, Hebei, China
2 Key Laboratory of Gas Reservoir Formation and Development, CNPC, Langfang 065007, Hebei, China,1 Petrochina Research Institute of Petroleum Exploration and Development, Langfang 065007, Hebei, China
2 Key Laboratory of Gas Reservoir Formation and Development, CNPC, Langfang 065007, Hebei, China,1 Petrochina Research Institute of Petroleum Exploration and Development, Langfang 065007, Hebei, China
2 Key Laboratory of Gas Reservoir Formation and Development, CNPC, Langfang 065007, Hebei, China,1 Petrochina Research Institute of Petroleum Exploration and Development, Langfang 065007, Hebei, China
2 Key Laboratory of Gas Reservoir Formation and Development, CNPC, Langfang 065007, Hebei, China,1 Petrochina Research Institute of Petroleum Exploration and Development, Langfang 065007, Hebei, China
2 Key Laboratory of Gas Reservoir Formation and Development, CNPC, Langfang 065007, Hebei, China and 1 Petrochina Research Institute of Petroleum Exploration and Development, Langfang 065007, Hebei, China
2 Key Laboratory of Gas Reservoir Formation and Development, CNPC, Langfang 065007, Hebei, China |
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| Abstract: | The alternative development of coal‐bearing hydrocarbon source rocks and low‐porosity and low‐permeability tight sandstone reservoirs of the Triassic Xujiahe Formation in the Sichuan Basin is favorable for near‐source hydrocarbon accumulation. The natural gas composition of the Xujiahe Formation in the Sichuan Basin is dominated by hydrocarbon gases, of which the methane content is 80.16%–98.67%. Typically, the C2+ content is larger than 5% in main wet gas. The dry gas is mainly distributed in the western and northern regions of the basin. The non‐hydrocarbon gases mainly contain nitrogen, carbon dioxide, hydrogen, and helium, with a total content of <2%. The carbon isotope ranges of methane and its homologues in natural gas are: δ13C1 of ?43.8‰ to ?29.6‰, δ13C2 of ?35.4‰ to ?21.5‰, δ13C3 of ?27.6‰ to ?19.8‰, and δ13C4 of ?27.7‰ to ?18.8‰. δ13C3>δ13C4 occurs in some natural gas with a low evolution degree; such gas is mainly coal‐related gas from humic‐type source rocks of the Xujiahe Formation. As for the natural gas, δ2HCH4 values ranged from ?195‰ to ?161‰, δ2HC2H6 values ranged from ?154‰ to ?120‰, and δ2HC3H8 values ranged from ?151‰ to ?108‰. The dry coefficient, δ13C and δ2HCH4 are all positively correlated with the maturity of source rocks. The higher the maturity of source rocks is, the larger the natural gas dry coefficient is and the larger the δ13C and δ2HCH4 values are, indicative of the characteristic of near‐source accumulation. The δ2HC2H6 value of natural gas is influenced by paleosalinity to a relatively large extent; the higher the paleosalinity is, the larger the δ2HC2H6 value is. The Pr/Ph value of the condensate oil ranged from 1.60 to 3.43, illustrating light oxidization–light reduction and partial‐oxidization characteristics of the depositional environment of coal‐bearing source rocks of the Xujiahe Formation. The natural gas light hydrocarbon (C5–C7) from the Xujiahe Formation presented two characteristics: the first was the relatively high aromatic hydrocarbon content (19%–32.1%), which reveals the characteristic of natural gas with humic substances of high‐maturity; the second was the low content of aromatic hydrocarbon (0.4%–9.3%), reflecting water‐washing during the accumulation of the natural gas. The reported research outcomes indicate a potential mechanism for natural gas accumulation in the Xujiahe Formation, which will further guide natural gas exploration in this region. |
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| Keywords: | natural gas geochemistry isotopes light hydrocarbon Xujiahe Formation Sichuan Basin |
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