柴北缘下侏罗统煤系不同岩性烃源岩显微组分组成及其生烃意义差异性探讨

Discussion on Differences of Macerals Composition and Hydrocarbon Generation Significance of Different Lithologic Source Rocks from the Lower Jurassic Coal Measures in the Northern Qaidam Basin

煤系中常存在三种不同类型的烃源岩,即煤系泥岩、炭质泥岩和煤。由于沉积环境、有机质来源、有机质堆积方式及生物化学作用程度的差异,不同岩性烃源岩的显微组分组成和生烃潜力存在明显的差异性。对柴达木盆地北缘(柴北缘)下侏罗统煤系的对比研究表明,不同岩性烃源岩中显微组分、亚组分的组成普遍存在一定的差异性,同时生烃显微组分的化学组成和生烃潜力也存在明显的差异性。煤系泥岩中“壳质组+腐泥组”相对含量较高,壳质组组成以壳屑体为主,镜质组中镜屑体十分发育,有机质氢指数明显较低;煤和炭质泥岩中,壳质组相对含量低,但以完整形态的显微组分为主。镜质组中基质镜质体含量明显较高,壳屑体不发育,有机质的氢指数相对较高。煤系不同岩性烃源岩中显微组分、亚组分组成的差异及有机质生烃潜力的差异性,是沉积环境、有机质来源、堆积方式和生物化学作用阶段的细菌微生物的代谢作用强度和有机质的保存条件等的综合反映。柴北缘煤系不同岩性烃源岩中显微组分组成、亚组分组成的差异及生烃意义的差异可能具有普遍意义。细菌微生物的分解代谢和合成代谢作用不仅可以消耗、分解原始输入有机质、形成具有自身特点的再生有机质、消耗环境中的游离氧,同时也可降低原始有机质的丰度和富氢程度。煤系中壳屑体是壳质组前身通过细菌代谢作用的残余物。煤系中基质镜质体的生烃作用主要与细菌有机质形成的再生有机质有关,形成基质镜质体的腐殖凝胶体,为再生有机质保存提供了有利条件。

There are three different types of source rocks in coal measures,namely coal-measure mudstone,carbonaceous mudstone and coal.Due to the differences in sedimentary environment,organic matter source,organic matter accumulation mode and biochemical action degree,there are obvious differences in maceral composition and hydrocarbon generation potential of source rocks with different lithology.The comparative study of the Lower Jurassic coal measures in the Northern Qaidam Basin shows that there are some differences in the composition of macerals and subcomponents in different lithologic source rocks,and the chemical composition and hydrocarbon generation potential of hydrocarbon-generating macerals are also obviously different.The relative content of“exinite+sapropelinite”in coal-measure mudstone is high,the exinite is mainly composed of liptodetrinite,and the vitrodetrinite in vitrinite group is well developed,and the hydrogen index of organic matter is obviously low.In coal and carbonaceous mudstone,the relative content of exinite is low,but it is mainly composed of intact macerals.The desmocollinit content in vitrinite is obviously higher,the liptodetrinite is not developed,and the hydrogen index of organic matter is relatively higher.The differences in the composition of macerals,sub-compositions and hydrocarbon generation potential of organic matter in different lithologic source rocks of coal measures are the comprehensive reflection of sedimentary environment,source of organic matter,accumulation mode,metabolic intensity of bacteria and preservation conditions of organic matter in biochemical stage.The differences may have general significance.The catabolism and anabolism of bacterial can not only consume and decompose the original input organic matter,form regenerated organic matter with its own characteristics,consume free oxygen in the environment,but also reduce the abundance and hydrogen enrichment of the original organic matter.Liptodetrinite in coal measures is the residue of exinite precursor by bacterial metabolism.The hydrocarbon generation of desmocollinit is mainly related to the regenerated organic matter formed by bacterial organic matter.The humus gel that forms the desmocollinit provides favorable conditions for the preservation of regenerated organic matter.