The Isotopic Tracer and Resource Value of Microbial Gas Production in Coalbeds—ACase Study of Coalbed Gas in Enhong, China
The Isotopic Tracer and Resource Value of Microbial Gas Production in Coalbeds—ACase Study of Coalbed Gas in Enhong, China
复制标题
煤层微生物产气同位素示踪及资源价值——以恩洪煤层气为例
DOI：
10.1021/ef502565g
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发表时间：
2015
期刊：
影响因子：
5.3
通讯作者：
Aihua Zhang
中科院分区：
文献类型：
--
作者：
Mingxin Tao;Yuzhen Ma;Zhongping Li;Jing Li;Pengyang Liu;Yanlong Wang;Xiangrui Chen;Aihua Zhang
从微生物动态同位素分馏和煤层中次生生物气与热成因气混合的新视角，评价了恩洪混合煤层气的地球化学特征。此外，还利用同位素示踪了微生物活动及其结果，如细菌产甲烷等，揭示了煤层气的形成机制和成因类型。煤层气样品的δ 13 C1测定值为−54.5‰ ~ −32.0‰。根据R 0值和δ 13 C2值计算，热成因甲烷的δ 13 C1值分别为−30.6‰ ~ −28.1‰和−30.7‰ ~ −28.3‰。两次计算结果高度一致，均比实测值高出约20‰。δ DCH 4实测值介于−217‰ ~ −196‰之间，介于热成因甲烷和微生物成因甲烷之间; δ 13 CCO 2实测值介于−30.5‰ ~ −23.9‰之间，相对于原始热成因气而言，其质量逐渐增大; δ 13 C2实测值介于−25.7‰ ~ −22.6‰之间，估算值介于−21.8‰ ~ −21.2‰之间，其质量逐渐增大。δ 13 C1和δ 13 C2值呈负相关，Δδ 13 CCO 2-C1和Δδ 13 CCO 2-C1值均呈上升趋势。上述特征表明CO2被产甲烷菌还原为微生物成因甲烷并与热成因气混合，是存在次生生物成因气的新证据。利用δ 13 C1、δ 13 C2、Ro等数据计算，发现热成因甲烷约占总量的38%~ 58%，微生物成因甲烷约占42%~ 62%。微生物甲烷所占比例自上而下逐渐降低，在埋深1000 m以内的煤层中，微生物甲烷所占比例超过50%。使煤层气含量提高1倍以上。在1000 m深度范围内，煤层温度一般低于40 ℃，是产甲烷菌活动和二次生物气生成的最适宜地段。煤层晚期向浅部隆起是次生生物气形成的基本地质条件，具有重要的资源价值。
From the new perspective of the dynamic isotopic fractionation of microbes and the mixture of secondary biogenic gas and thermogenic gas in coalbeds, this study evaluates the geochemical characteristics of mixed coalbed gas in Enhong. Additionally, by using isotopes, the study traces the microbial activities and the results of those activities, such as the methane production of bacteria, and reveals the formation mechanism and genetic types of coalbed gas. The measured δ13C1values of the coalbed gas samples are from −54.5‰ to −32.0‰. Based on the values ofRoand δ13C2, by calculation, the δ13C1values of thermogenic methane range from −30.6‰ to −28.1‰ and from −30.7‰ to −28.3‰, respectively. The results of the two calculations are highly consistent, and both are approximately 20‰ higher than the measured values. The measured δDCH4values are from −217‰ to −196‰, being between thermogenic methane and microbiogenic methane; the δ13CCO2values are from −30.5‰ to −23.9‰, growing heavier with respect to the original thermogenic gas; the measured δ13C2values are from −25.7‰ to −22.6‰, and the estimated δ13C2values are from −21.8‰ to −21.2‰, also indicating growing heavier. The δ13C1and δ13C2values are negatively correlated; both the Δδ13CC2–C1and Δδ13CCO2–C1values are increasing. All of the above characteristics indicate that CO2is reduced into microbial genetic methane by methane-producing bacteria and it mixes with thermogenic gas, which is new evidence showing the existence of secondary biogenic gas. Via calculations using a variety of data, such as the values of δ13C1, δ13C2andRo, it is found that thermogenic methane accounts for approximately 38% to 58% of the total amount, and microbial genetic methane accounts for approximately 42% to 62%. The proportion of micro-biogenic methane reduced from the top down, which occupied more than 50% of that in the coalbed buried within 1000 m deep. It increased the content of coalbed gas by more than 1 times. Within 1000 m deep, coalbed temperatures are generally lower than 40 °C, which is the most appropriate section for methanogenic bacteria activity and secondary biogenic gas generation. Coalbed uplift to the shallow parts in the late stage is the basic geological condition for the formation of secondary biogenic gas, which has significant resource value.