| Composition and Origin of Shallow Biogenetic Gases in the Baise Basin, South China |
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| 作者姓名： | ZHU Yangming WENG Huanxin ZOU Huayao CAI Xunyu HUANG Shaofu LUO Yi |
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| 作者单位： | [1]Department of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027 [2]College of Resource and Information, China University of Petroleum, Beijing 102249 [3]Research Institute of Southern Exploration and Development Corporation, SINOPEC, Kunmi |
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| 摘 要： | Based on the analytical data of over 30 gas samples, combined with geochemical and geological backgrounds, the composition and distribution characteristics of shallow biogenetic gases in the Baise Basin, a Tertiary residual basin in southern China, were extensively investigated, and the origin and formation mechanism tentatively approached. The shallow gases are primarily composed of gaseous hydrocarbons, generally accounting for over 90%. The abundances of methane and C2＋ homologues show a relatively wide range of variation, mainly 50%-100% and 0%-50%, respectively, depending on the mixing proportions between biogenetic and thermogenic gases. A highly negative carbon isotope is the significant signature for the shallow gases with δ^13C1 values of -55‰ to -75‰. According to molecular and isotopic compositions and light hydrocarbon parameters, the shallow gases in the basin can be classified into three types of origins： biogenetic gas, biogenetic/thermogenic mixed gas, and oii-biodegraded gas. They exhibit regular distribution both spatially and temporally, and are believed to be associated with the maturity of adjoining gas source rocks and biodegraded oil accumulation. The Baigang and Nadu source rocks can be considered to have experienced early and late gas generation during early burial and after basin uplift respectively. A late accumulation mechanism of multiple gas sources is put forward for the formation of the shallow gas reservoirs, which is responsible for the variations in chemical and isotopic composition of the gases in depth profile.
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| 关 键 词： | 天然气 生物起源 同位素 地球化学 碳氢化合物 |
| 收稿时间： | 2005-04-26 |
| 修稿时间： | 2005-06-13 |
Composition and Origin of Shallow Biogenetic Gases in the Baise Basin, South China |
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| Authors: | ZHU;Yangming;WENG;Huanxin;ZOU;Huayao;CAI;Xunyu;HUANG;Shaofu;LUO;Yi |
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| Abstract: | Abstract Based on the analytical data of over 30 gas samples, combined with geochemical and geological backgrounds, the composition and distribution characteristics of shallow biogenetic gases in the Baise Basin, a Tertiary residual basin in southern China, were extensively investigated, and the origin and formation mechanism tentatively approached. The shallow gases are primarily composed of gaseous hydrocarbons, generally accounting for over 90%. The abundances of methane and C2+ homologues show a relatively wide range of variation, mainly 50%?100% and 0%?50%, respectively, depending on the mixing proportions between biogenetic and thermogenic gases. A highly negative carbon isotope is the significant signature for the shallow gases with δ3C1 values of ?55‰ to ?75‰. According to molecular and isotopic compositions and light hydrocarbon parameters, the shallow gases in the basin can be classified into three types of origins: biogenetic gas, biogenetic/thermogenic mixed gas, and oil‐biodegraded gas. They exhibit regular distribution both spatially and temporally, and are believed to be associated with the maturity of adjoining gas source rocks and biodegraded oil accumulation. The Baigang and Nadu source rocks can be considered to have experienced early and late gas generation during early burial and after basin uplift respectively. A late accumulation mechanism of multiple gas sources is put forward for the formation of the shallow gas reservoirs, which is responsible for the variations in chemical and isotopic composition of the gases in depth profile. |
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| Keywords: | shallow biogenetic gas origin stable isotope light hydrocarbon accumulation mechanism Baise Basin South China |
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