Trial eoalbed methane (CBM) production of the well group in Baode has achieved a relatively satisfactory result but the CBM genesis is still unconfirmed. Based on the data of the components and stable isotope composition of the CBM sampled from the producing wells, the genesis was discussed. Results showed that the CBM is mainly composed of the methane with little heavy hydrocarbons. Carbon isotopic composition of the methane is obviously light, and partial data of the carbon and hydrogen isotopes of the methane plot within the transitional range between the thermogenic and biogenic gases. Carbon isotopic composition of the carbon dioxide of the samples is relatively heavy and is negatively correlated to the carbon isotopic composition of the methane. It was suggested that the coalbed methane in the area has a mixed thermogenic and biogenic origin, but thermogenic gas is the main with composition minor of biogenic gas. Biogenic methane was formed through the reduction of carbon dioxide. The chemistry and hydrodynamics of the coalbed water and the porosity and permeability of the strata in the area were favorable of the active population of the methanogenic bacteria.%鄂尔多斯盆地东北缘保德地区煤层气井组试采取得较好效果,但煤层气成因尚未形成统一认识,影响到对区域煤层气勘探开发潜力的进一步认识.本文基于各类煤层气样品组分和稳定同位素的分析,对其成因进行了探讨.结果表明,煤层气组分以甲烷为主,重烃浓度极低；δ13CCH4明显偏轻,部分δ13CCH4和δDCH4分布在热成因与二氧化碳还原型生物成因气过渡区间；δ13CCO2相对较重,且与δ13CH4之间存在负相关关系.分析认为,该区煤层气具有混合成因,以热成因气为主,兼具生物成因气的特征,生物甲烷形成于二氧化碳还原途径,煤层水的化学和动力条件以及煤岩孔渗条件有利于产甲烷菌的大量繁殖.
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