东营凹陷沙河街组四段上亚段细粒沉积岩岩相特征及与沉积环境的关系

细粒沉积岩的岩相特征影响泥页岩的生烃能力与储集性能,与沉积环境的相互关系分析亦可丰富细粒沉积的研究。然而目前针对陆相细粒沉积岩岩相的研究较为薄弱,基于岩相成因,与沉积环境相结合的岩相特征分析较少。基于大量岩心、薄片、X射线衍射及地球化学数据,以成分为第一要素,以东营凹陷沙河街组四段上亚段细粒沉积岩为例,划分出4大类、12种岩相类型,分析每一种岩相的宏观、微观、成分及成因特征。通过矿物成分、地球化学等多参数的分析发现,沙河街组四段上亚段沉积环境分为4个阶段。沉积环境通过控制岩相主要成分而控制了岩相的类别与发育;沉积环境的旋回性与阶段性变化导致岩相的旋回性与阶段性变化;沉积环境控制岩相发育,岩相亦能反应沉积环境的变化。在细粒沉积分析中,不能排除突发事件(海侵、浊流等)对岩相及沉积环境的影响。

Lithofacies characteristics of fine-grained sedimentary rocks in the upper submember of Member 4 of Shahejie Formation,Dongying sag and their relationship with sedimentary environment

Lithofacies characteristics of fine-grained sedimentary rocks (FGSR)have impact on the hydrocarbon generation ability and reserving property of shale, and their relationship with sedimentary environment can be analyzed to enrich the research on fine-grained sediment.However, there are insufficient studies regarding the lithofacies of lacustrine FGSR. The lithofacies characteristics are less analyzed based on lithofacies genesis in combination with sedimentary environment. Accordingly, based on massive well cores, thin sections, X-ray diffraction and geochemical data, and the component as the first element, FGSR in the upper submember of Member 4 of Shahejie Formation in Dongying sag was divided into four categories and 12 lithofacies types, so as to analyze the macro, micro, component and genesis characteristics of each lithofacies type. Through analyzing mineral compositions, geochemical indexes and other parameters, it is found that the sedimentary environment in the upper submember of Member 4 of Shahejie Formation can be classified into four stages.The sedimentary environment controls the types and development of lithofacies through controlling the main components of lithofacies;the cyclicity and periodic changes of lithofacies are caused by those in sedimentary environment; the sedimentary environment controls the lithofacies development, and the lithofacies reflects the change of sedimentary environment. During the FGSR analysis, the influences of sudden events (such as transgression and turbidity flow)on lithofacies and sedimentary environment cannot be excluded.