Origin and Accumulation of Natural Gases in the Upper Paleozoic Strata of the Ordos Basin in Central China |
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作者姓名: | ZHU Yangming WANG Jibao LIU Xinse ZHANG Wenzheng |
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作者单位: | Department of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027;Department of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027;Research Institute of Petroleum Exploration and Development, Changqing Oil Field Branch, CNPC, Xi’an, Shaanxi 710021;Research Institute of Petroleum Exploration and Development, Changqing Oil Field Branch, CNPC, Xi’an, Shaanxi 710021 |
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基金项目: | The research was financially supported by the Research Foundation for the Doctoral Program of Higher Education of China (No. 20050335095). |
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摘 要: | The natural gases in the Upper Paleozoic strata of the Ordos basin are characterized by relatively heavy C isotope of gaseous alkanes with δ 13C1 and δ13C2 values ranging mainly from ?35‰ to ?30‰ and ?27‰ to ?22‰, respectively, high δ13C excursions (round 10) between ethane and methane and predominant methane in hydrocarbon gases with most C1/(C1-C5) ratios in excess of 0.95, suggesting an origin of coal-derived gas. The gases exhibit different carbon isotopic profiles for C1-C4 alkanes with those of the natural gases found in the Lower Paleozoic of this basin, and believed to be originated from Carboniferous-Permian coal measures. The occurrence of regionally pervasive gas accumulation is distinct in the gently southward-dipping Shanbei slope of the central basin. It is noted that molecular and isotopic composition changes of the gases in various gas reservoirs are associated with the thermal maturities of gas source rocks. The abundances and δ13C values of methane generally decline northwards and from the basin center to its margins, and the effects of hydrocarbon migration on compositional modification seem insignificant. However, C isotopes of autogenetic calcites in the vertical and lateral section of reservoirs show a regular variation, and are as a whole depleted upwards and towards basin margins. Combination with gas maturity gradient, the analysis could be considered to be a useful tool for gas migration.
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关 键 词: | accumulation autogenetic calcite isotopic composition natural gas Ordos basin upper Paleozoic |
收稿时间: | 2007/9/10 0:00:00 |
修稿时间: | 2008/3/10 0:00:00 |
Origin and Accumulation of Natural Gases in the Upper Paleozoic Strata of the Ordos Basin in Central China |
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Authors: | Yangming ZHU Jibao WANG Xinse LIU Wenzheng ZHANG |
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Institution: | 1. Department of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027;2. Research Institute of Petroleum Exploration and Development, Changqing Oil Field Branch, CNPC, Xi'an, Shaanxi 710021 |
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Abstract: | The natural gases in the Upper Paleozoic strata of the Ordos basin are characterized by relatively heavy C isotope of gaseous alkanes with δ13C1 and δ13C2 values ranging mainly from –35‰ to –30‰ and –27‰ to –22‰, respectively, high δ13C excursions (round 10) between ethane and methane and predominant methane in hydrocarbon gases with most C1/(C1‐C5) ratios in excess of 0.95, suggesting an origin of coal‐derived gas. The gases exhibit different carbon isotopic profiles for C1‐C4 alkanes with those of the natural gases found in the Lower Paleozoic of this basin, and believed to be originated from Carboniferous‐Permian coal measures. The occurrence of regionally pervasive gas accumulation is distinct in the gently southward‐dipping Shanbei slope of the central basin. It is noted that molecular and isotopic composition changes of the gases in various gas reservoirs are associated with the thermal maturities of gas source rocks. The abundances and δ13C values of methane generally decline northwards and from the basin center to its margins, and the effects of hydrocarbon migration on compositional modification seem insignificant. However, C isotopes of autogenetic calcites in the vertical and lateral section of reservoirs show a regular variation, and are as a whole depleted upwards and towards basin margins. Combination with gas maturity gradient, the analysis could be considered to be a useful tool for gas migration. |
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Keywords: | accumulation autogenetic calcite isotopic composition natural gas Ordos basin upper Paleozoic |
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