玛湖凹陷玛页1井风城组富硅页岩成因及其油气意义

Genesis and Petroleum Significance of Silica⁃Rich Shale in Fengcheng Formation of Well Maye⁃1,Mahu Sag

准噶尔盆地玛湖凹陷玛北斜坡区玛页1井风城组发育富硅页岩,以富集自生硅质为特征,富硅页岩层段是该区页岩油分布最广的层段。利用岩心描述、岩石薄片鉴定、电镜扫描、古生物分析、地球化学测试等资料,采用多尺度岩矿学和地球化学结合的方法,对玛北斜坡区风城组富硅页岩纵向分布、自生硅质成因、富硅页岩中藻类的类型和生烃情况以及与硅质相关的孔隙结构展开了研究。结果表明,玛页1井风城组自生硅质的发育与碱湖pH值较高有关,火山物质和陆源碎屑在高pH值条件下易释放溶解硅,在持续蒸发或pH值降低条件下重新结晶形成富硅页岩。富硅页岩中的硅质条带和团块中发育大量保存完好的球形生物化石,为古盐藻休眠孢子,生烃效果显著。富硅页岩脆性较高,发育裂缝、晶间孔和晶间溶孔。玛页1井风城组自生硅质在生烃和成储过程中发挥着重要作用,该研究结果可为玛北斜坡区风城组页岩油的进一步勘探提供借鉴。

Silicarich shale is developed in the Fengcheng formation of Well Maye1 in the Mabei slope of the Mahu sag,Junggar basin,and it is characterized by enrichment of authigenic silica.The silicarich shale interval is one of the intervals with shale oil widely distributed.Based on the data from core description,rock thin section,scanning electron microscope,paleontological analysis,and geochemical test,the Fengcheng formation silicarich shale in the Mabei slope was investigated from the aspects of longitudinal distribution,authigenic silica genesis,algae types and hydrocarbon generation and silicarelated pore structure by combining petrology and geochemistry in multiple scales.The results show that the development of the authigenic silica in the Fengcheng formation of Well Maye1 is related to the high pH of the alkaline lake.Volcanic materials and terrigenous debris are likely to release dissolved silica under high pH conditions,which will form silicarich shale after recrystallizing because of continuous evaporation or pH reduction.A large number of wellpreserved spherical biological fossils developed in the flint strips and agglomerates of the silicarich shale are mainly composed of dormant spores of paleosalina,which have a remarkable hydrocarbon generation capability.Fractures,intercrystalline pores,and intercrystalline dissolved pores are found in the silicarich shale which has a high brittleness.The authigenic silica in the Fengcheng formation of Well Maye1 played an important role in the process of hydrocarbon generation and reservoir formation.This recognition can provide references for the further exploration of shale oil in the Fengcheng formation in the Mabei slope.