陕北侏罗纪富油煤有机地球化学特征

Organic geochemistry of the Jurassic tar-rich coal in Northern Shaanxi Province

  • 摘要: 富油煤的有机地球化学特征对研究其形成时期的古沉积环境和演化过程具有重要意义。以陕北地区侏罗纪延安组6个主采煤层为研究对象,运用煤质分析和气相色谱–质谱联用方法分析其有机地球化学特征。结果表明:陕北地区延安组主采煤的氯仿沥青“A”含量较高,饱芳比较低;正构烷烃呈单峰型分布,中链饱和烃占优势,Pr/nC17、Ph/nC18、Pr/Ph的值较高;C28和C29的规则甾烷和重排甾烷占主导地位。分析表明:陕北地区延安组主采煤层处于低热–成熟阶段,为富氢基质镜质体和壳质组生油的有利阶段;有机质来源以陆生高等植物为主并有部分水生生物混入,形成于贫氧的泥炭沼泽环境,且经历了较强的生物降解作用,为富氢组分的形成提供了有利的条件。

     

    Abstract: The organic geochemical characteristics of tar-rich coal are of great significance to study the paleosedimentary environment and evolution of coal seams. Taking coal samples from 6 main coal seams of Yan'an Formation in Northern Shaanxi Province as the research object, this paper analyses the organic geochemical characteristics of coal seams by coal quality analysis and gas chromatography-mass spectrometry. The results showed that coal samples had a high abundance of chloroform asphalt "A" and a low saturated hydrocarbon/aromatic hydrocarbon ratios, characterized by the unimodal pattern of n-alkanes and dominated by medium chainsaturated hydrocarbons. The ratios of Pr/C17, Ph/C18and Pr/Ph were relatively high, regular sterane and diasteranes of C28 and C29 were dominant in steranes. The organic matter was in the low-mature-mature stage, which was a favorable stage for perhydrousvitrinite and lipinite to generate oil. The source of organic matter were from terrestrial organic matte and aquatic organisms and which formed in the anoxic environment and undergoed strong biodegradation. All of these provided favorable conditions for the formation of perhydrousvitrinite.

     

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