柴东三湖地区天然气成因及成藏特征研究

Origin and Accumulation Characteristics of Natural Gas in San-hu Region, Eastern Qaidam Basin

柴达木盆地生物气资源丰富,主要分布在1 800 m埋深以上的第四系地层,是一种持续生烃、动态平衡的成藏模式。根据近期天然气样品和烃源岩样品的分析测试结果,发现三湖地区不仅在浅层第四系发育生物气藏,而且在新近系狮子沟组发现了生物气甚至热成因气存在的证据。从生物气形成机理的角度出发,拓展了柴达木盆地生物气分布的深度下限,在中深层发现热成因气也扩展了三湖地区天然气资源的勘探领域。在分析天然气成因和运聚成藏的基础上,指出三湖地区发育两套含气系统,第四系中下部和新近系上部仍可作为三湖地区天然气勘探的接替领域。

Abundant biogenetic gas resources have been found in Qaidam Basin and are mainly distributed in the Quaternary strata of burial depth above 1800 m. Moreover, for biogenetic gas, the accumulation mode is characterized by continuous hydrocarbon generation and dynamic balance between hydrocarbon generation and dispersion. After a comparison and analysis on some samples from natural gas and source rock, it is demonstrated that in San-hu region, Qaidam Basin, biogenetic gas reservoirs can be found in not only the Quaternary but also the Neogene Shizigou Formation. Even there is thermogenic gas found in the Shizigou Formation. Our study on biogenetic-gas forming mechanisms shows that the lower limit of burial depth inferred is bigger than the previous result. In addition,thermogenic gas found in middle to deep strata expands an exploration domain of natural- gas resources in this area. Based on the analysis on origin and accumulation of natural gas, it is pointed out that there are two gas systems developed, and both the middle to lower Quaternary and the upper Neogene can be taken as the next exploration domains.