生物气的形成机理及源岩的地球化学特征――以柴达木盆地生物气为例

生物气形成于有机质演化的未成熟―低成熟阶段,形成过程非常复杂和多元化;主要通过H2+CO2生物化学还原反应和乙酸发酵两条途径完成。通过研究柴达木盆地生物气认为:生物气气源岩的地球化学特征均与细菌的产甲烷活动有关,有机质中存留被细菌改造的遗迹;生气母质多为混合型,有机质含碳量低,IHC+IH和IO指数主要分布在大于100mg/g?TOC值域范围内;氯仿沥青"A"族组成中非烃含量较高,多数样品的正构烷烃分布模式与脂肪酸化合物相似;植烷类、甾萜烷类化合物主要被细菌生源烃以及其它被细菌改造后的生源烃所表征;有机母质沉积在强还原环境中。

BIOGAS FORMING MECHANISM AND GEOCHEMICAL CHARACTERISTICS OF ITS SOURCE ROCK

Biogas has been formed in the immature and/or lowe-mature stage of organic matter, which generating process is very complex and divers, mainly including two ways of H-2+CO-2 biochemical reduce and the acetate fermentation. According to biogas forming machine, the geochemical characteristics of its source rocks are relation to the action of bacteria-generating methane.;The source materirals mainly are mixed type. The content of organic carbon is low, and I {HC}+IH>100 mg/g·TOC, but also IO>100 mg/g·TOC. The abundance of non-hydrocarbon is higher in chloroform extracts. The distributional pattern of n-alkane is similar to that of fatty acid compound. The phytane, terpane and sterane compounds have been characterized by bacterial source and other source transformed by bacteria. Some terpane compositions of indicating environment suggest that organic matter has been deposited in strong reducing conditions.