摘要
松辽盆地徐家围子断陷深层天然气甲烷碳同位素重,且烷烃碳同位素序列大部分为倒转和反序。关于这些碳同位素反序的天然气是有机成因还是无机成因,一直存在争议。为此,进行了一系列烃类生成和合成实验。利用徐家围子断陷幔源二氧化碳进行了费-托合成实验,其烃产物大部分未发生碳同位素反序。选取松辽盆地深层沙河子组低成熟烃源岩,开展了生气模拟实验,并在对模拟产物进行化学组成和碳同位素测定的基础上,根据模拟实验温度条件与地质条件的差异,客观地选定了化学组成和碳同位素特征均与徐家围子断陷深层天然气一致的端元气,进行泥岩和煤生成的烃气产物在理论上的混合。混合结果表明,两种有机成因的端元气,在一定的混合比例区间内,会发生碳同位素倒转和反序。因此,无机合成的烃气碳同位素并不一定反序,而有机成因天然气混合也可能出现碳同位素反序现象。对生气模拟实验结果、现代火山泉水逸出气以及研究区源岩生烃条件综合分析表明,徐家围子断陷深层天然气以有机成因气为主。
Gaseous alkanes from the Xujiaweizi fault depression in the Songliao Basin are characterized by heavier stable carbon isotopes,mostly showing a inverse order or a reverse order.It is still in debate whether these gases are biogenic or abiogenic.To determine the potential origin of these natural gases,a series of experiments concerning the generation and synthesis of gaseous alkanes have been conducted.Mantle-derived carbon dioxide sampled from the Xujiaweizi fault depression was used to synthesize hydrocarbon gas through the Fishcher-Tropsch reaction,and the produced gaseous alkanes yielded a normal stable carbon isotope trend.Meanwhile,some source rocks with low maturity were sampled from the Shahezi Formation to conduct pyrolysis experiments,the produced gases were then determined for chemical components and stable carbon isotopes.Based on the possible end-member gases in the Xujiaweizi fault depression and geological conditions,the produced gases generated by shales and coals at different heating rate were mixed to determine the trend of stable carbon isotopes.The results showed that the mixed biogenic end-member gases could also lead to an inverse stable carbon isotopic order,whereas the mixed abiogenic gases are not necessarily reversal.Integrated with the results of pyrolysis experiments discussed in this paper,comprehensive analyses both on gases released from modern volcanic springs and on source-rock characteristics of the Xujiaweizi fault depression have suggested that natural gases from the Xujiaweizi fault depression are mainly biogenic.
出处
《石油学报》
EI
CAS
CSCD
北大核心
2011年第1期54-61,共8页
Acta Petrolei Sinica
基金
国家重点基础研究发展规划(973)项目(2009CB219308)资助
关键词
徐家围子断陷
天然气成因
碳同位素
反序
费-托合成实验
生气模拟实验
混合
Xujiaweizi fault depression
gas genesis
carbon isotope
inverse order
Fishcher-Tropsch synthesis
experimental simulation of gas generation
mixture
