Abstract: The Permian Fengcheng Formation is a key stratigraphic unit for shale oil exploration in the northern Mahu sag (Mabei area) of Junggar Basin. Exploration breakthroughs in multiple wells have confirmed the substantial shale oil potential in Mabei area, Due to unique geological settings, the lithological classification schemes for global analogues cannot be directly applied to Fengceng Formation shale, thus posing challenges to hydrocarbon accumulation mechanisms research and sweet-spot assessment in this area. Based on a substantial dataset of petrographic identification and X-ray diffraction (XRD) quantitative mineralogical analyses, combined with extensive exploration practice, this study establishes a new lithological classification scheme for the hybrid shales of Fengcheng Formation in Mabei area. The research results show as follows. (1) Applying the classification scheme based on a ternary diagram that incorporates carbonate minerals, clay minerals, and felsic minerals (containing authigenic silica and reedmergnerite) as end-members, shales are categorized into four primary types: argillaceous shale, carbonate-rich shale, felsic shale, and hybrid shale. For felsic lithologies, a secondary ternary classification system based on the relative contents of feldspar, quartz, and reedmergneriteis established for further subdivision. (2) Argillaceous shale is not observed in the Fengcheng Formation of Mabei area. The shale lithologies predominantly include calcareous shale, dolomite-bearing calcareous shale, dolomitic shale, calcite-bearing dolomitic shale, siliceous shale, feldspathic shale, reedmergnerite shale, felsic shale, clay-bearing felsic shale, carbonate-bearing felsic shale, and hybrid shale. (3) Siliceous shale, felsic shale, and reedmergnerite shale are the most favorable lithologies for hydrocarbon generation and accumulation, with high potential to form self-generated and self-accumulated petroleum systems within the shales. In contrast, carbonate-rich shales exhibits the poorest hydrocarbon generation capacity. These findings provide positive guiding for the exploration and evaluation of shale oil in Fengcheng Formation of Mabei area.

Key words: Junggar Basin, alkali lake, hybrid shale, authigenic silica, fine-grained rock, rock classification, Permian Fengcheng Formation, northern Mahu sag

摘要： 准噶尔盆地玛湖凹陷北部(玛北)地区二叠系风城组是页岩油勘探的重点领域,多口井已获得勘探突破,证实玛北地区页岩油勘探潜力巨大。受独特的地质背景制约,国内外其他盆地中页岩的岩石分类方案很难应用于风城组页岩的岩性划分,严重制约了该地区页岩油的成储、成藏研究和"甜点"评价工作。基于大量岩矿鉴定和X射线衍射(XRD)岩石矿物定量结构组分分析资料,结合长期勘探实践经验,建立了适用于玛北地区风城组混积型页岩的岩石分类方案。研究结果表明:①以碳酸盐矿物、黏土矿物、长英质矿物(含自生硅和硅硼钠石矿物)为三端元建立的三角图分类方案,可将岩石划分为黏土质岩类页岩、碳酸盐岩类页岩、长英质岩类页岩和混合岩类页岩,并将长英质岩类进一步按照长石、石英、硅硼钠石的相对含量建立次级小三角分类体系进行细分;②玛北地区风城组不发育黏土质页岩,页岩的岩石类型主要包括灰质页岩、含白云石灰质页岩、白云质页岩、含灰白云质页岩、硅质页岩、长石质页岩、硅硼钠石页岩、长英质页岩、含黏土矿物长英质页岩、含碳酸盐长英质页岩和混合质页岩;③硅质页岩、长英质页岩和硅硼钠石页岩是有利的烃源岩类型及储集岩类型,表现为"自生自储"的总体特征,碳酸盐岩类页岩的生烃能力及储集性能最差。研究成果对于玛北地区风城组的页岩油勘探及评价具有积极的指导意义。

关键词: 准噶尔盆地, 碱湖, 混积型页岩, 自生硅, 细粒岩, 岩石分类, 二叠系风城组, 玛北地区