【摘要】 柴达木盆地三湖（台吉乃尔湖、涩聂湖、达布逊湖）地区第四系生物气区是我国最大的生物气区。笔者系统采集了该气区21个天然气样品,测量了其组分和碳同位素组成,重点探讨了生物气形成途径和运聚方式。生物气δ¹³C₁和δ¹³C_CO2均随深度增大而变重,显示了CO₂还原途径成气的特征。生物气δ¹³C₁、δ¹³C_CO2和δD分布与CO₂还原方式形成的生物气的相应同位素值分布范围接近。在有关成因图解中这些数据主要位于CO₂还原途径成气范围内。生物气CO₂和CH₄之间的碳同位素分馏系数α_c>1.055,具有CO₂还原途径成气的特征。柴达木盆地第四纪干旱的古气候、较低的古温度、较高的沉积速率和水体中较高的硫酸盐含量使得甲烷菌的大量繁殖只能在较大的深度范围内才能实现,从而,有利于CO₂还原途径成气作用进行。涩北一号、涩北二号气田生物气δ¹³C₁组成分布可能表明,生物气形成以后沿疏导层水平运移进入气藏,基本不存在垂向运移。该项研究对于进一步深入探讨生物气成因、形成条件,确定生物气模拟实验方式与条件,计算生物气资源量,建立成藏模式和选择天然气有利勘探区块均具有重要价值。更多还原

【Abstract】 The Quaternary biogenic gas province in the Taijnar Lake-Suli Lake-Dabsan Lake area (Sanhu area, means three lakes area), Qaidam basin is the largest biogenic gas province in China. 21 gas samples were collected from different gas-pay beds of the Sebei 1 gas field and the Sebei 2 gas field. The chemical composition and carbon isotope of them were measured, and the microbial pathway, migration and accumulation, and significance of the biogenic gases were emphatically investigated. CH4 and CO2 of the biogenic gases are enriched in 13C with increasing depth, indicating that they are CO2 reduction-derived gases. The δ13C1, δ13Cco2 and δD values of the biogenic gases approximate the range of the corresponding values of the gases formed by the CO2 reduction pathway. The values fall in the field of CO2 reduction pathway on genetic diagrams. The fractionation coefficients (αc) of the CH4 and CO2 of the biogenic gases are more than 1. 055, characteristic of the CO2 reduction pathway. During the Quaternary due to the dry climate, low temperature, high sedimentary rate and a high content of sulfate methane backteria could not propagate until sediments are buried in deeper layers. These conditions benefit the CO2 reduction pathway. The distribution ofδ13C1 of the biogenic gases in the Sebei 1 and the Sebei 2 gas fields probably shows that the gases migrated horizontally into gas pools along leading layers rather than vertically. This research is of important value for further discussing the origin and formation conditions of biogenic gases, determining the method and conditions of biogenic gas simulation, accessing biogenic gas resource yield, establishing a pool-forming model and selecting targets of natural gas exploration.更多还原