不同成煤母质热解烃类气体氢碳同位素组成特征

为了认识草本沼泽和森林沼泽成煤物质以及煤显微组分对热解煤层气同位素，特别是氢同位素的影响，对草本沼泽和森林沼泽泥炭以及具有略微不同显微组分的煤进行了热解模拟实验，研究了它们热解烃类气体氢碳同位素组成差异，以及这种差异随成熟度的变化，讨论了引起这种差异的原因。结果表明:草本沼泽泥炭热解甲烷, 乙烷和丙烷δD平均值分别为-235‰, -200‰和-209‰，森林沼泽泥炭的平均值分别为-226‰, -188‰和-191‰。草本沼泽泥炭热解甲烷, 乙烷和丙烷δ¹³C平均值分别为-36.2‰、-27.4‰和-31.6‰，森林沼泽泥炭的平均值分别为 -33.7‰、-20.7‰和-25.6‰。表现为草本沼泽泥炭热解的烃类气体氢碳同位素组成轻于森林沼泽泥炭，并且从泥炭连续热解至R_O值分别为2.5％, 3.5％和5.5％时，甲烷氢同位素值分别平均低18‰, 11‰和9‰，碳同位素值分别平均低3.4‰, 3.8‰和1.8‰。煤显微组分微小的差异对热解烃类气体碳同位素有明显的影响，表现为具有较高壳质组的煤热解甲烷的碳同位素组成较轻，可是煤热解烃类气体氢同位素组成主要与成煤环境因素有关。这些研究成果为自然煤层气的成因判识提供了科学数据。

Carbon and Hydrogen Isotopic Compositional Features of Hydrocarbon Gases Generated by Different Coal-forming Materials

In order to understand the influence of coal-forming materials from forest and herbaceous swamps and maceral compositions on the isotopic composition of thermogenic coalbed gas, the forest and herbaceous swamp peats and coals with slight differences in maceral compositions were pyrolyzed. The differences in the carbon and hydrogen isotopic compositions of pyrolytic hydrocarbon gases and their evolutions were studied. The results showed that the mean δD values of the pyrolysis methane,ethane and propane were -235‰, -200‰ and -209‰ for the herbaceous swamp peat and -226‰, -188‰ and -191‰ for the forest swamp peat,respectively.The meanδ¹³C values of the pyrolysis methane,ethane and propane were -36.2‰,-27.4‰ and -31.6‰ for the herbaceous swamp peat and -33.7‰,-20.7‰ and -25.6‰ for the forest swamp peat,respectively.These showed that the carbon and hydrogen isotopic compositions of the hydrocarbon gases generated from the herbaceous swamp peat were lighter than those generated from the forest swamp peat.At pyrolytic intervals from peat to 2.5%,3.5% and 5.5%,this difference in the mean δD value of the methane was 18‰,11‰ and 9‰,respectively,and in theδ¹³C value was 3.4‰, 3.8‰ and 1.8‰, respectively. The methane generated from the coal containing slightly higher exinite content has evidently lighter carbon isotopic composition. However, the hydrogen isotopic composition of the pyrolysis methane was possibly related primarily to coal-forming environmental factors.These results provide a basis for studying on the isotopic geochemistry of coalbed gas.