古交区块煤层气地球化学特征及其成因

基于古交区块煤田地质勘探资料以及煤层气井排采气体组分、甲烷碳氢同位素质谱等相关测试分析，查明了该区块煤层气地球化学特征、成因及其地质控制因素。结果显示：煤层气组分主要以甲烷为主，组分浓度介于85.36%～99.23%，其次为氮气，重烃含量最少，属于干气～特别干的气体。煤层气δ13C1介于-62.24‰～-40.70‰，δD介于-244.3‰～-229.3‰。以热成因气为主。煤层气δ13C1随着煤级增加呈变重趋势，随着埋深增加而变化的趋势不明显。古交区块矿化度整体从北向南逐渐增加，说明该地区水动力条件从北向南逐渐增强。南部刑家社矿区甲烷碳同位素较重，而北部镇城底矿区、西曲矿区以及马兰矿区的部分地区甲烷碳同位素较轻。研究区北部(MCQ9)煤层埋藏浅，露头发育，煤的Ro,max介于1.14%～2.18%，且水文地质条件适宜，形成了生物成因与热成因混合气体。

Geochemical characteristics and its origin of CBM in Gujiao blocks

Based on the coal geological exploration data and the data analysis of composition,methane,hydrogen isotope mass spectrometry of gas drainage from CBM well,the geochemical characteristics and its origin of CBM in Gujiao blocks could be found out.The results show that the CBM are mainly composed of methane whose concentration ranges from 85.36% to 99.23%.It belongs to dry gas-extremely dry gas.The nitrogen gas is less than methane and the heavy hydrocarbon content is the least.The δ13C1 of CBM ranges from -62.24‰ to -40.70‰ and the δD ranges from -244.3‰ to -229.3‰.The CBM gives priority to thermogenic gas which has characteristics with proliferation,migration and fractionation.The δ13C1 of CBM shows a heavier trend with the increase of coal rank.With the increase of buried depth,the change trend of the δ13C1 is not obvious.The degree of mineralization increases gradually from north to south which shows that the hydrodynamic conditions gradually enhanced from north to south.The methane carbon isotope is heavier in southern square,such as Xingjiashe mine,and the north is lighter,such as Zhenchengdi mine,Xiqu mine and some parts of Malan mine.The Ro,max of coal ranges from 1.14% to 2.18%.The biogenic and thermogenic mixture gas is formed in the northern study area with the shallow buried depth of coal seam,the outcrop development,and the appropriate hydrogeological condition.