低演化阶段轻烃的生成及地球化学应用

Light hydrocarbon has been widely used to determine the origin and maturity of gas due to a lots of information obtained from C5 to C8 hydrocarbons. A lots of works hve been done on the generation mechanism and geochemical applications of light hydrocarbon in natural gas generated in the high and post mature stages.But few work has been done on the study of the generation mechanisam and its application of light hydrocarbon from sedimentary organic matter in the low thermal evolution stage. This project is suggested to study the generation mechanism of light hydrocarbon from biogenic gas and low mature gas from Chaidam and Songlao basins.The carbon and hydrogen isotope of individual light hydrocarbons from adsorbed gas in gelogical profiles and gas in gas pools. The distribution of individual compounds in light hydrocarbon is also analysed. The content of light hydrocarbon in source rock from geological profiles is suggested to determine and the distribution of light hydrocarbons from simulated biogenic gas and catalyzed low mature gas will be studied. Baesed on the analysed data of biogenic and low mature gases, compared with simulated gases, The geochemical characteristics of light hydrocarbon from biogenic and low mature gases will have been determined. The discrimination parameters of origin,maturity and sedimentary environment of biogenic and low mature gases will have been proposed. This study is very helpful for gas exploration and natural gas geology in the low evolution stage.

天然气中可利用的地球化学参数较少，轻烃含量虽然较低，但可提供丰富的地球化学信息。目前，对高-过成熟阶段油气中轻烃组成及地球化学应用研究报道较多，但低演化阶段（Ro<0.8%）天然气伴生轻烃的生成及地球化学应用研究相对较少。本项研究以柴达木和松辽盆地浅层自然演化剖面中岩石吸附轻烃与典型气藏研究对象，采用烃源岩轻烃定性定量、生物与催化模拟、单体烃碳氢同位素等分析技术或方法，对C1-C4与C5-C8开展单体烃组成及其碳、氢同位素对比分析，研究低演化阶段轻烃的生成特征和分布，探讨其生成机理及与各种成熟度指标（生物标志物和Ro）关系，建立反映天然气成熟度、母源和沉积环境等方面的关键信息，并根据生物气和低熟气轻轻演化特征，为低熟气和生物气成因鉴别提供依据，这对低演化阶段天然气生成理论和天然气勘探基础应用研究方面都具有重要意义。

低演化阶段轻烃的生成机理及其对低熟气、生物气的成因鉴别研究具有重要的理论和实践价值。本项目主要开展了烃源岩轻烃馏分的定量分析方法、探索低演化阶段轻烃生成机理以及生物气与低熟气成因鉴别研究，提出两种成因的轻烃鉴别指标。在 494样次的实验分析基础上，建立了2种烃源岩吸附轻烃的定量方法，提出了低演化阶段轻烃的成因存在微生物作用和催化作用两种，,微生物作用的轻烃富含异构烷烃和芳烃，而催化作用形成的轻烃富含环烷烃，这些轻烃组成的差异性对低演化阶段低熟气和生物气成因鉴别提供了新的指标，本项目成果在松辽盆地、辽河坳陷和柴达木盆地生物气和低熟气的成因鉴别中得到了应用，为这这些地区低演化阶段天然气资源勘探前景评价提供了理论基础。