正构烷烃单体烃的氢同位素分析方法及应用

以渤海湾盆地东营凹陷古近系沙河街组烃源岩及原油为研究对象,通过气相色谱仪—GC/TC接口—同位素质谱仪的联用,构建了正构烷烃单体烃氢同位素在线分析方法,对正构烷烃的单体烃氢同位素组成进行了测定,揭示了不同沉积环境中氢同位素的组成特征。沙四上亚段烃源岩的正构烷烃单体烃氢同位素组成较重,分布于-161‰^-111‰,沙三下亚段烃源岩的氢同位素组成较轻,分布在-186‰^-134‰,指示了从微咸水到咸水的沉积环境,随着沉积环境水体盐度的增加,氢同位素值具有明显变重的趋势,成熟度差异较大的样品,其氢同位素组成的差异相对较小。表明在正常生油窗范围内,正构烷烃单体烃的氢同位素受成熟度影响相对较小,主要与母质来源和沉积环境有关,可为油源对比、母质来源和古沉积环境判识提供科学依据。

Method and application of hydrogen isotope analysis of n-alkanes

The source rock and crude oil from the Shahejie Formation in the Dongying Sag of the Bohai Bay Basin were studied. Hydrogen isotopic compositions of n-alkanes from different sedimentary environments were determined using a combination of gas chromatograph, GC/TC interface and an isotope mass spectrometer. In the upper section of the fourth member of Shahejie Formation, the hydrogen isotopic composition of source rocks was heavy, ranging from -161‰ to -111‰. While the hydrogen isotopic composition of source rocks in the lower section of the third member of Shahejie Formation was relatively lighter, ranging from -186‰ to -134‰. The results suggested that from brackish water to saline water sedimentary environment, the hydrogen isotope value shifted toward heavier composition following the increasing of salinity in water. The difference of hydrogen isotopic composition was relatively smaller for samples with large maturity differences. The results indicated that the influence of maturity on hydrogen isotopes of a single hydrocarbon was relatively smaller in the range of the normal oil generation window, which was mainly related to the source of parent material and the sedimentary environment. The characteristics of hydrogen isotopic composition of n-alkanes could provide an important scientific basis for the correlation of oil and source rock and the identification of parent material source and paleosedimentary environment.