沁水盆地阳泉地区煤层氮气同位素组成及其成因

煤层气地球化学研究对象以煤层甲烷为主，对非烃组分氮气地球化学特征的研究相对较少。采用气相色谱和同位素质谱方法，分析了沁水盆地北部阳泉-寿阳地区煤层排采气中氮气的地球化学特征。结果表明：采集的排采气样中氮气体积分数平均为1.46%，其中大气源氮气为1.05%，有机成因氮气为0.41%。有机成因氮气的δ15N平均为+1.5‰，属于热氨化和热裂解混合成因。阳泉-寿阳地区排采气中有机成因氮气同位素组成主要受地下水动力条件、人为排采活动以及解吸-扩散-运移效应影响，其中，较强的地下水动力条件导致其同位素组成偏轻；产气量越高，氮气同位素组成越重；煤层埋深越深，氮气同位素组成越重。依据多元线性回归分析的结果，各影响因素对有机成因氮气同位素组成影响的程度由高到低依次为：地下水动力条件>排采>解吸-扩散-运移。

Origins and isotopic geochemical characteristics of nitrogen in coalbed methane of Yangquan district,Qinshui Basin

Studies on the geochemistry of coal seam gas (CSG) mainly focus on methane，while on non-hydrocarbon nitrogen are very limited.The nitrogen geochemistry of exploited CGS from Yangquan-Shouyang district，North Qinshui Basin was studied by gas chromatography and isotope mass spectrometry.The results indicate that the N2 proportion of the exploited CGS accounts for an average of 1.46%，and the proportions of atmospheric N2 is 1.05%，and that of organic origin is 0.41%.The N2 of organic origin has an average isotopic ratio of +1.5‰，heavier than atmospheric N2，indicating a mixed origins of organic nitrogen thermal ammoniation and thermal cracking.The major influencing factors on the nitrogen isotopic composition of CGS in Yangquan-Shouyang district include groundwater dynamic condition，exploitation and desorption-diffusion-migration effect.Strong groundwater flow results in a lighter nitrogen isotopic composition and the δ15N of exploited CGS increases as the increase of exploitation intensity.Nitrogen isotopic composition becomes heavier as the increase of coal seam depth.According to the results of multiple linear regression analysis，the influencing factors are shown in the order of influence degree:groundwater dynamic condition>exploitation>desorption-diffusion-migration effect.