吉木萨尔凹陷芦草沟组页岩油地球化学特征与运聚意义

The geochemical characteristics and migration-accumulation significances of shale oil in Lucaogou Formation of Jimsar Sag

准噶尔盆地吉木萨尔凹陷芦草沟组甜点段页岩油资源丰富,前人在页岩油来源、运聚特征及物性差异原因等方面存在争论。结合芦草沟组纵向分子地球化学特征分析,基于其上、下甜点段及邻近层段泥岩、碳酸盐岩与砂岩抽提物的分子化合物组成、地球化学参数的对比分析,揭示了芦草沟组上、下甜点段页岩油生成与运聚特征,并解释了上、下甜点段原油物性差异原因。研究结果表明:芦草沟组上、下甜点段具有更高的总有机碳质量分数、游离烃质量分数及烃类可采系数,显示明显的生烃聚集特征;上、下甜点段沉积环境还原性与水体咸度相较于其他层段更高,藻类输入生源特征更为显著;上、下甜点段内砂岩储集的烃及原油与泥岩、碳酸盐岩抽提物具有相似的分子组成特征,而与上、下甜点之间的层段显著不同,揭示芦草沟组上、下甜点段之间存在一个由分子组成迥异的石油运聚隔断层,上、下甜点段为2套独立的自生自储、内源成藏的油气系统;芦草沟组上、下甜点段页岩油生成与运聚过程的差异性在一定程度影响了原油物性垂向倒置的形成。

There have been a large number of tight oil in the sweet-spots of Lucaogou Formation in jimsar sag, Junggar Basin. The oil source, migration-accumulation characteristics and physical property of shale reservoir in the sweet-spots have been lack of research evidence. In this study, base on the analysis of molecular geochemical characteristics in the vertical direction of Lucaogou Formation and the comparison of molecular compound composition and geochemical parameters of the extracts of mudstone, carbonate rock and sandstone in the upper and lower sweet-spots and their adjacent intervals, the generation and migration-accumulation characteristics of tight oil were revealed in the upper and lower sweet-spots of Lucaogou Formation. And the difference of physical property was interpreted. The results showed that the upper and lower sweet-spots of Lucaogou Formation in jimusar Sag had higher TOC content, free hydrocarbon content and hydrocarbon recovery coefficient, showing obvious characteristics of hydrocarbon generation and migration-accumulation. The reducibility of sedimentary environment, salinity of water column and the content of algae input source in the upper and lower sweet-spots of Lucaogou Formation were higher than those in other layers. The crude oil and extracts of sandstone reservoirs had similar molecular composition with the extracts of mudstone and carbonate rocks in the upper and lower sweet-spots sections, but were significantly different from the extracts of interlayer between the upper and lower sweet-spots, which revealed that there was a crude oil migration-accumulation barrier layer with different molecular composition between the upper and lower sweet-spots of Lucaogou Formation. The upper and lower sweet-spots are two sets of independent oil reservoir of self-generation, self-storage and near-source accumulation. The difference in the formation, migration-accumulation process of shale oil in the upper and lower sweet-spots of Lucaogou Formation leads to the formation of vertical inversion of crude oil physical properties.