热成熟及水的作用对热解烃同位素组成的影响

对Ⅱ型未成熟源岩采用高压釜热模拟实验方法,研究了在有水及无水条件下,生成的热解烃中正构烷烃单体氢同位素随热成熟作用的变化情况。实验结果表明,在无水条件下,随热解温度的升高(290-400℃),热解烃中正构烷烃呈现富D(2H)趋势,氢同位素发生了20‰左右的分馏;而在有水条件下,由于相同热解温度点所达到的成熟度低于无水条件下的,所以产生的氢同位素分馏相对要小。热模拟实验中水的存在对热解烃中正构烷烃单体氢同位素组成并没有产生明显的影响。因此,热成熟作用及成岩作用过程中的氢同位素交换均不能在很大程度上改变脂类化合物本身的同位素组成,脂类化合物的氢同位素能够用来评价有机质的来源、进行油源对比以及地质历史时期沉积古环境的恢复。 

THE INFLUENCES OF MATURATION AND WATER IN THE ISOTOPIC COMPOSITIONS OF PYROLYSIS

In order to characterize the influences of maturation and water in the hydrogen isotopic compositions of individual n-alkanes from the pyrolysis,the simulation test of typeⅡsource rock was made by high-pressure autoclave.The analytical results indicate that in the condition of non-hydrous pyrolysis,with the rise of temperature(290～400℃),the individual n-alkanes have the shift toward enriched hydrogen,the difference is over 20‰.But in hydrous pyrolysis,the hydrogen isotopic fractionation is smaller because the lower maturation at the same temperature.Moreover,water has no obvious effect on the hydrogen isotopic compositions of individual n-alkanes in the simulation test.So,the hydrogenisotopic compositions of lipid biomarkers were not obviously influenced by maturation and the hydrogen isotopic exchange during diagenesis.The hydrogen isotopes of lipid biomarkers from source rock can be used to discuss the differences of source rocks and depositional environments and to correlate oil/oil and oil/source.