Effects of Maturity on the Pr/Ph Ratio of the Soluble Organic Matters in the Terrestrial Source Rocks
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摘要: Pr/Ph比值一直作为重要的生物标志物参数，其不仅与生源、沉积环境条件有关，而且在一定程度上还受成熟度影响。本论文对取自南海珠江口盆地西部不同有机相的陆相烃源岩样品进行了生排烃热模拟实验，获取了不同温度点的可溶有机质（油），结合对不同成熟度地质烃源岩样品抽提物的分析，较系统的研究了油/抽提物的Pr/Ph比值随着成熟度的变化规律。研究结果表明，在Ro为0.6%～1.8%阶段，中深湖相Ⅱ型和浅湖相—河沼相Ⅲ型烃源岩生成油的Pr/Ph比值随着成熟度的增高而降低，并且Ⅲ型烃源岩降低的幅度明显大于II型烃源岩，而到高成熟度阶段，两类烃源岩的Pr/Ph比值相近。应用Pr/Ph比值进行油—油对比、油—源对比、判识古沉积环境等，需要充分考虑成熟度对该比值的影响，尤其是对于含有陆相Ⅲ型烃源岩的沉积盆地，应结合其它地球化学参数综合对比分析。Abstract: The Pr/Ph ratio has been used widely as a significant biomarker. Except for the sources and palaeosedimentary environments, the Pr/Ph ratio is also affected by the maturity. In this paper, the terrestrial source rocks of different organic phases, taken from the western Pearl River Mouth Basin, were thermally simulated by the hydrocarbon generation-expulsion experiments and the soluble organic matters were obtained, then the tendency of the Pr/Ph ratio following the maturity was relatively systematically researched in the generated oils/extracts and the samples from strata. The results showed that, from Ro=0.6％ to Ro=1.8％, the Pr/Ph ratios in both the medium-deep (terrestrial kerogen of type Ⅱ) and the shallow lacustrine (terrestrial kerogen of type Ⅲ) source rocks were decreasing with the increase of maturity and the latter decreased more obviously than the former; However, the Pr/Ph ratios in the two source rocks were almost similar in high maturity phases. This research indicated that the effects of maturity on the Pr/Ph ratio should be considered in identifying palaeosedimentary environments and the correlations of oil-oil and oil-source rocks and it was necessary to combine with other geochemical parameters for the applications of the Pr/Ph ratio to the basins containing terrestrial Ⅲ source rocks.
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Key words:
- maturity /
- the Pr/Ph ratio /
- hydrocarbon generation-expulsion /
- organic phase
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