准噶尔盆地玛湖凹陷风城组页岩油储层岩相划分与类型评价

Lithofacies Division and Type Evaluation of Shale Oil Reservoir in Fengcheng Formation of Mahu Sag,Junggar Basin

准噶尔盆地玛湖凹陷风城组页岩油藏是继吉木萨尔凹陷芦草沟组页岩油藏之后的又一重大发现,风城组沉积期玛湖凹陷具有近陆源供给、火山活动频发、气候干旱炎热的特点,为独具特色的盐碱化湖泊沉积环境创造了条件,也是风城组岩性复杂多变的重要原因。火山岩、内源岩、陆源碎屑岩以及多源混积岩纵向频繁叠置,形成米级到厘米级页岩油储层。结合岩性变化特征,以构造样式作为突破口,厘米级尺度岩心观察为基础,高频沉积构造分析为辅助,利用亚离子抛光电镜、能谱测试、荧光分析等多种技术手段对准噶尔盆地玛湖凹陷风城组页岩油储层进行岩性岩相分析,认为玛湖凹陷风城组页岩油储层可划分为4大类(砂砾岩类、火山岩类、混积岩类与内源岩类)、8小类储层。4大类储层储集性能逐渐减弱,其中混积岩类储层因其构造与成分差异可进一步划分为混积页岩、纹层-似纹层状混积泥岩、树根状-网状混积泥岩、雪花-星点状混积泥岩;页理发育情况、云质含量以及其产出样式成为混积岩类储层储集物性差异的重要控制因素。

Shale reservoir of Fengcheng Formation in Mahu Sag,Junggar Basin is another important discovery after Lucaogou Formation in Jimusar Sag.During the sedimentary period of Fengcheng Formation,Mahu sag is characterized by near-terrigenous source supply,frequent volcanic activity and arid and hot climate,which creates conditions for the unique saline and alkaline lake sedimentary environment and is also an important reason for the complex and changeable lithology of Fengcheng Formation.Volcanic rock,internal rock,terrigenous clastic rock and multi-source mixed rock are frequently stacked longitudinally,forming shale oil reservoirs of meter to centimeter size.Based on the characteristics of lithologic changes,the lithology and lithofacies of shale oil reservoirs in Fengcheng Formation in Mahu Sag,Junggar Basin were analyzed by means of sub-ion polishing electron microscopy,energy spectrum testing and fluorescence analysis,with the structural style as the breakthrough point,cm-scale core observation as the basis and high-frequency sedimentary structure analysis as the auxiliary.The shale oil reservoirs of Fengcheng Formation in Mahu sag can be divided into 4 types and 8 types.The reservoir properties of glutenite,volcanic rock,mixed rock and internal rock are gradually weakened.Due to the differences in structure and composition,the mixed mudstone reservoir can be divided into mixed shale,laminate-laminate-like mixed mudstone,root-reticular mixed mudstone,snowflake-star-point mixed mudstone.Foliation development,dolomite content and its occurrence pattern are the important controlling factors for the difference of reservoir of reservoir physical properties of mixed rock reservoirs.