中国西北侏罗纪煤系显微组分生烃潜力、产物地球化学特征及其意义

从吐哈盆地侏罗纪煤中分离富集了藻类体、孢子体、角质体、镜质体、基质镜质体和丝质体6种主要显微组分,进行了热解及热模拟实验,并对各显微组分热模拟生成的产物热解油进行了碳同位素组成等分析。各显微组分热解生烃潜力及其热解产物热解油的碳同位素组成表明,煤系有机质中藻类体的生油潜力最高,生成的液态烃类的碳同位素组成最轻;孢子体、角质体等陆源富氢组分生烃潜力低于藻类体,生成的液态烃类的碳同位素组成重于藻类体生成的液态烃类,与煤系含油气盆地中原油的碳同位素组成基本一致。这些富氢显微组分应该是煤系有机质中主要的生油显微组分。镜质体和基质镜质体的生油潜力相对较低,其生成的液态烃类的碳同位素组成比一般煤系原油重得多,而且这些组分本身对液态烃具有较强的吸附力,尽管其在煤系有机质中所占的比例很大,仍然难以成为生成液态石油的主要显微组分,只能在高成熟演化阶段成为良好的生气显微组分。丝质体等惰性组分生烃潜力极低,不可能成为生油组分。此外,结合原煤的显微组分组成、生烃潜力和元素分析,提出仅仅以壳质组的含量高低来评价煤的生烃潜力不完全可靠,热解是经济、快速、有效的评价方法。

Genetic potential and geochemical features of pyrolysis oils of macerals from Jurassic coal measures, Northwest China

The six macerals, including alginite, sporinite, cutinite, vitrinite, desmocollinite and fusinite, are isolated from Jurassic coals in Northwest China, and are undergone the Rock-Eval and hydrous pyrolysis. A series of geochemical analyses of the pyrolysis oils produced by the macerals are carried out. In terms of the genetic potential of the macerals and the stable carbon isotope of the pyrolysis oils, it is revealed that alginite has the highest potential of hydrocarbon generation in these macerals, with the lightest stable carbon isotope composition of its pyrolysis oil. The genetic potential of hydrocarbon of sporinite and cutinite is largely lower than that of alginite. The stable carbon isotope composition of their pyrolysis oils is heavier than that of alginite, and approximately accords with that of the oils derived from Jurassic coal measures, Northwest China. It is indicated that these hydrogen-rich macerals are main material to generate oil in the Jurassic coal measures. Vitrinite and desmocollinite have a relatively low potential of hydrocarbon generation. The stable carbon isotope composition of their pyrolysis oils is heavier than that of sporinite, cutinite and oils derived from coal-bearing strata. It seems that they cannot be major macerals to generate oil, even if they occupy a majority of proportion in the organic matter of coal and coaly shale, and that they can be good gas-prone macerals at the stage of high-maturity to over-maturity. Fusinite has an extremely low potential of hydrocarbon generation, and cannot be the organic matter of oil generation. The relationship of the content of hydrogen-rich macerals with the genetic potential of the coals containing these macerals suggested that it is not reliable to estimate the oil potential just with the content of hydrogen-rich liptinite, and that Rock-Eval pyrolysis is the economical, fast and effective method.