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澳大利亚Sydney和Bowen盆地二叠纪沥青煤层气具有以下特征:(1) 甲烷/乙烷比值大于或等于1000;(2)甲烷的δ~(13)C和δD值分别为—60±10‰PDB和—217±17‰SMOW;(3) CO_2含量低于5％;(4) CO_2—CH_4的δ~(13)C值为55±10‰PDB。这些数据表明,是CO_2的微生物还原作用,决定气体成分的主要因素,而不是传统的热成因反应。根据CO_2的同位素成分(—7±2‰PDB),容易识别出深层气中是否存在外部成因CO_2的混入。 为了确定气源和生气机理,测定了在Sydney和Bowen盆地(图1)深度可达550m所采二叠纪沥青煤(R_0=0.8—1.2％)期间释放出的气体的同位素成分和化学成分。
Permian bituminous CBM in the Sydney and Bowen basins of Australia has the following characteristics: (1) methane / ethane ratio greater than or equal to 1000; (2) δ 13 C and δ D values of methane are -60 ± 10 ‰ PDB And -217 ± 17 ‰ SMOW; (3) CO_2 content was less than 5%; (4) δ ~ (13) C value of CO_2-CH_4 was 55 ± 10 ‰ PDB. These data suggest that it is the microbial reduction of CO2 that determines the major component of the gas composition rather than the traditional thermogenesis. According to the isotope composition of CO_2 (-7 ± 2 ‰ PDB), it is easy to identify whether there is the mixing of external causes CO 2 in deep gas. In order to determine gas source and gas generation mechanisms, the isotope composition and chemical composition of gases released during Permian bituminous coals (R_0 = 0.8-1.2%) deep up to 550 m in the Sydney and Bowen basins (Figure 1) were determined.