马朗凹陷低熟页岩油地球化学特征及成烃机理

勘探实践和研究表明，马朗凹陷二叠系芦草沟组源内油气为页岩油，该原油C₂₉甾烷立体异构化参数w(20S)/w(20S+20R)、w(ββ)/w(αα+ββ)均为0.2~0.4，为典型低熟原油。通过对芦草沟组烃源岩地球化学和有机岩石学特征的综合研究，发现低熟页岩油的生烃母质为原生的富氢无定形体，这些无定形体在沉积早期经历过细菌的改造作用，致使其具有特殊的生烃演化模式，即低熟-成熟阶段早期（R_o为0.55%~0.75%）处于生油高峰，对应埋深为1 800~2 900 m，埋深大于或小于该主峰带，烃源岩生烃能力急剧降低。泥岩生烃模拟实验、热解、抽提等实验数据表明:芦草沟组低熟页岩油正是位于该主生带的源岩所生，处于生烃带的源岩区即为马朗凹陷低熟页岩油富集的有利地区。

Geochemical Characteristics and Hydrocarbon-Generating Mechanism of Low-Mature Shale Oil in Malang Sag

Exploration practices and researches show that hydrocarbon in the source rocks of the Lucaogou Formation of the Permian, Malang sag was shale oil and also a typical low-mature oil with both sterane isomerization parameters (20S/(20S+20R) and ββ/(αα+ββ)) between 0.2 and 0.4. Through comprehensive study of geochemical and organic petrology characteristics in the hydrocarbon source rock of Lucaogou Formation, we find that the parent material of this low-mature shale oil was hydrogen-rich amorphous solid and experienced the bacteria transformation in the early sedimentary stage, which resulted in the formation of the particular hydrocarbon-generating evolution model. Namely, during the low-mature and early mature stage with R_o values 0.55%-0.75%, there is an oil generation peak whose burial depth ranges from 1 800 to 2 900 m, and the hydrocarbon-generating potential of source rock drops sharply beyond the main hydrocarbon-generating zone. The results of hydrocarbon-generating simulation experiments, rock pyrolysis analysis and organic extraction of mudstone prove that the low-mature shale oil in Lucaogou Formation was generated by the hydrocarbon source rocks within the range of main hydrocarbon-generating zone, where was the beneficial places of shale oil accumulation.