塔里木盆地深层碳酸盐岩中有机质特征

Organic matter in deep carbonate rocks of the Tarim Basin,NW China

通过对塔里木盆地塔参1井深层碳酸盐岩中游离有机质和包裹有机质组成及正、异构烷烃单体烃碳同位素组成特征的对比研究发现,在高—过成熟演化阶段,不同赋存形式有机质中常用生物标志化合物成熟度参数存在明显不同的响应。Ro值为1.0%～1.3%时,Ts/Tm和Σ三环萜/Σ藿烷参数仍可用作成熟度指标;当Ro值大于1.3%时,这两项参数变化趋势发生反转,不能用以表征有机质的热演化程度。C29甾烷两项成熟度参数20S/(20S+20R)和有机质宏观组成及微观分子组成有明显的差别,但同一样品两种赋存形式有机质的正、异构烷烃碳同位素组成特征基本一致,说明两者有机质来源一致,其有机组成特征的差异主要是后期差异性热成熟作用造成的。

Compositions of free and inclusion organic matter and the individual hydrocarbon isotopic compositions of n-alkanes and isoalkanes were investigated in deep carbonate rocks from the Tacan 1 well of the Tarim Basin.The comparison reveals that there are different evolutional trends for biomarker maturity parameters in different occurrences of organic matter at the high-and over-mature stage.The biomarker thermal maturity parameters of Ts/Tm for C27 hopanes and tricyclics/hopanes ratio can still be used to estimate the maturity of source-rock extracts when Ro is in the range of 1.0%–1.3%.Whereas,these biomarker parameters showed reverse trends and are not useful for maturity assessment when Ro is over 1.3%.The two ratios of C29 sterane isomerization,20S/（20S＋20R） and ββ/（ββ＋αα）,also showed reverse change trends and can not be used to indicate the level of maturity when Ro is more than 1.1%.Although there are obvious different molecular compositions between free organic matter（chloroform bitumen A） and inclusion organic matter（chloroform bitumen C） in the deep carbonate rocks,the carbon isotopic values of n-alkanes and isoalkanes have similar values for the same samples with two different existence states,which indicates that the organic matters in the two existence states are derived from the same precursor,and their differences in molecular composition characteristics are due to the difference in thermal maturity.