煤层甲烷碳同位素偏轻机理研究进展  

Advance on the genetic mechanism of lighter carbon isotopic composition in coalbed methane

作　　者：鲍园 胡宜亮 李丹 孙学阳[1,2] 琚宜文 BAO Yuan;HU Yiliang;LI Dan;SUN Xueyang;JU Yiwen(College of Geology and Environment,Xi’an University of Science and Technology,Xi’an 710054,China;Geological Research Institute for Coal Green Mining,Xi’an University of Science and Technology,Xi’an 710054,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]西安科技大学地质与环境学院,陕西西安710054 [2]西安科技大学煤炭绿色开采地质研究院,陕西西安710054 [3]中国科学院大学地球与行星科学学院,北京100049

出　　处：《西安科技大学学报》2021年第6期1040-1049,共10页Journal of Xi’an University of Science and Technology

基　　金：国家自然科学基金项目(42172200,41972183,41502156);西安科技大学煤炭绿色开采地质研究院项目(MTy2019-12)。

摘　　要：煤层气勘探开发实践证明煤层甲烷碳同位素组成(δ^(13)C_(1))普遍轻于常规煤成气的δ^(13)C_(1)值。关于煤层甲烷碳同位素组成偏轻的原因,前人提出了多种作用机制,对于解释特定煤层的甲烷δ^(13)C_(1)值偏轻成因仍存在较大差异。通过大量相关文献资料调研与系统分析,对煤层甲烷碳同位素组成变化现象及其偏轻的主要因素进行了归纳总结,对4种主要控制因素的成因机理、适用条件及其资源意义进行讨论。结果表明:解吸-扩散分馏作用主要发生在多煤层的上部,造成上煤层的δ^(13)C_(1)值偏轻;流动地下水溶解作用多发生在径流区,引起煤层甲烷碳同位素组成分布不均;次生生物成因气混合作用主要发生在构造抬升及地下水汇聚带,具有干气特征;CH_(4)与CO_(2)的同位素交换作用多发生煤化作用早期,导致δ^(13)C_(CO_(2))值偏重;构造热事件与母质继承等作用的影响不可忽略。研究成果对丰富煤层气富集机理与指导煤层气的勘探开发具有重要的理论意义。The fact that the carbon isotopic composition of coalbed methane(CBM,δ^(13)C_(1))is generally lighter than conventional coal-derived gas has been confirmed by the CBM exploration and development practice.Although researchers have proposed various mechanisms to explain the phenomenon of delicate carbon isotopic composition of methane in coal seams,many controversies involve a specific coal seam.Based on the investigation of relevant literature and systematic analysis,variation characteristics of carbon isotopic composition in coalbed methane and the main factors causing its lightness were summarized.The genetic mechanism,application conditions,and resource significance of the four main factors were also examined.The results show that the desorption-diffusion fractionation occurs mainly in the upper part of multiple coal seams,which causes theδ^(13)C_(1)value of the upper coal seam to be lighter.The dissolution of flowing groundwater occurs mainly in runoff areas,resulting in the uneven distribution of the methane carbon isotopic composition in the coal seam.Secondary biogenic gas mixing occurs mainly in the tectonic upliftand groundwater convergence zone,which has dry gas characteristics.The isotopic exchange between CH_(4)and CO_(2)occurs primarily in the early stage of coalification,resulting in the heavyδ^(13)C_(CO_(2))value.In addition,we cannot ignore the influence of tectonic heat events and parent material inheritance.The results will be of great theoretical significance for promoting the enrichment mechanism of coalbed methane and guiding the exploration and development of coalbed methane.

关 键 词：煤层气 解吸-扩散 水动力溶解 生物成因气混合 同位素交换 

分 类 号：P593[天文地球—地球化学]