Abstract: This study focuses on the Lucagou Formation of Jimusaer sag in Junggar Basin. Based on the lithological and reservoir pore characteristics, the migration and enrichment mechanisms of shale oil were determined using geochemical analysis data. The analysis of biomarkers shows that the lower section of sweet spots and the central thick mudstone interval of Lucagou Formation are independent petroleum systems without the occurrence of mixed shale oil source in the longitudinal direction, and the crude oil in reservoir sandbodies is derived from adjacent hydrocarbon source rocks, and characterized with near-source migration and in-situ accumulation, displaying a self-generation, self-reservoir and near-source accumulation model. Besides originating from nearby hydrocarbon source rocks, the shale oil in the upper section of sweet spots is mainly derived from deep hydrocarbon source rocks, and characterized with lateral migration and enrichment of shale oil, displaying a mixed accumulation model based on long-distance lateral migration and vertical near-source migration. The analyses of well profiles, rock thin sections, and high-pressure mercury injection experiments show that the upper section of sweet spots has the characteristics of low crude oil density, large reservoir thickness (single sandbody with the thickness of more than 1.6 m), well-developed intergranular pores, and good horizontal permeability, providing favorable conditions for the lateral migration of shale oil. By contrast, the crude oil density is higher, the reservoir thickness is thinner, and intergranular pores are not well developed in the central mudstone interval and the lower section of sweet spots, which is unfavorable for the lateral migration and enrichment of shale oil. The research results have identified two favorable depth intervals for the development of sweet spots of shale oil in the upper section of Lucagou Formation, i.e., the shallow depth section with high porosity and the deep depth section with developed secondary dissolution pores. The lateral migration distances of shale oil during enrichment in these two sections are 7300 m and 4100 m respectively. The shale oil enrichment in the lower section of sweet spots and the central thick mudstone interval needs to consider the hydrocarbon generation intensity and expulsion amount of adjacent source rocks. The favorable exploration interval in the lower section of sweet spots is below the peak oil generation depth (over 3 300 m). The research results have certain guiding significance for the discovery of interbedded shale oil sweet spots and the shale oil exploitation.

Key words: Lucaogou Formation, Jimusaer sag, accumulation model, oil-source correlation, shale oil

摘要： 以准噶尔盆地吉木萨尔凹陷芦草沟组为研究对象,结合地层岩性特征与储层孔隙特征,应用地球化学分析资料厘定了芦草沟组页岩油的运移特征和富集机制。生物标志化合物分析表明:芦草沟组下甜点段和中部厚层泥岩段作为独立的含油气系统,页岩油在纵向上不存在不同油源混合现象,储层砂体内的原油均来自邻近烃源岩,具有近源运移和原位聚集的特征,为自生自储、近源成藏模式;上甜点段的页岩油除来自邻近烃源岩外,主要来源于深部烃源岩,具有侧向运移富集的特征,为远距离侧向运移和近源垂向运移混合成藏模式。连井剖面、岩石薄片和高压压汞实验分析表明:上甜点段具有原油密度低、储层厚度大(单层砂体厚度>1.6 m)、粒间孔隙发育以及水平渗透性好的特征,为页岩油的侧向运移提供了有利条件;而中部泥岩段和下甜点段的原油密度较大,储层厚度较薄,粒间孔隙不发育,不利于页岩油的侧向运移富集。研究结果确定了芦草沟组上甜点段的2个页岩油有利开发深度段,即浅部高孔隙度深度段和深部次生溶蚀孔隙发育段,这两个深度段的页岩油在富集过程中的侧向运移距离分别为7300 m和4100 m。芦草沟组下甜点段和中部厚层泥岩段页岩油的富集需要考虑邻近烃源岩的生烃强度和排烃量,下甜点段的有利勘探层段在生油高峰深度以下(>3 300 m)。研究成果对寻找夹层型页岩油甜点和页岩油开采具有一定的指导意义。

关键词: 芦草沟组, 吉木萨尔凹陷, 成藏模式, 油源对比, 页岩油