陆相湖盆细粒混积岩的沉积特征与成因机理——以东营凹陷南坡陈官庄地区沙河街组四段上亚段为例

以东营凹陷南坡陈官庄地区沙河街组四段上亚段为例,结合大量基础地质资料,通过岩心观察、岩石薄片鉴定、扫描电镜分析、X射线衍射分析、元素地球化学分析和储层物性测试等技术手段,探讨了湖相细粒混积岩的沉积特征、成因机理、沉积主控因素和储集性,建立了适用于湖相细粒混积岩的岩性定名方案。研究表明,陈官庄地区主要发育含有机质块状灰质粉砂岩、含有机质块状含粉砂砾屑泥晶灰岩、含有机质块状粉砂质泥晶灰岩、富有机质块状含粉砂生屑泥晶灰岩、含有机质条带状粉砂质粉屑泥晶灰岩、含有机质交错层理灰质粉砂岩、富有机质纹层状黏土质泥晶灰岩和富有机质滑塌构造含粉砂黏土质泥晶灰岩8种主要的细粒混积岩岩相。明确了不同岩相的环境指示意义及空间展布特征,认为研究区共存在风暴流和重力流主导的事件性混合沉积、相缘混合沉积、原地混合沉积和生物-化学混合沉积4种混积模式。沉积组分的混合离不开地质营力的驱动;频繁的断层活动为混合沉积提供了动力基础和湖盆底形斜坡条件;气候通过降雨量、温度、生物等因素的变化控制着细粒混积岩的物质条件和混积方式;物源输入提供了陆源碎屑组分;湖平面的升降和水介质条件不仅决定了碳酸盐组分的形成条件和微观结构,对有机质的保存也具有关键作用。湖相细粒混积岩储层的非均质性较强,储集空间类型多样,是十分具有勘探潜力的储层类型。

Sedimentary characteristics and genetic mechanism of fine-grained hybrid sedimentary rocks in continental lacustrine basin: a case study of the upper submember of Member 4 of Shahejie Formation in Chenguanzhuang area,southern slope of Dongying sag

Taking the upper submember of Member 4 of Shahejie Formation in Chenguanzhuang area of the southern slope of Dongying sag as an example, based on a large number of basic geological data, the sedimentary characteristics, genetic mechanism, main controlling factors and reservoir properties of lacustrine fine-grained hybrid sedimentary rocks were explored through core observation, rock thin section identification, scanning electron microscope analysis, X-ray diffraction analysis, element geochemical analysis, reservoir physical property test, and other technical means. Moreover, a lithologic nomenclature scheme suitable for lacustrine fine-grained hybrid sedimentary rocks was also established. The study shows that there are eight major fine-grained hybrid sedimentary lithofacies developed in Chenguanzhuang area, including organic-bearing massive calcareous siltstone, organic-bearing massive silty gravel clastic micrite, organic-bearing massive silty micritic limestone, organic-rich massive silty bioclastic micritic limestone, organic-bearing banded silty clastic micrite, organic-bearing cross-bedding calcareous siltstone, organic-rich laminated clayey micritic limestone, and organic-rich silty clayey micritic limestone with slump structure. As a result, the environmental indication and spatial distribution characteristics of various lithofacies are identified, and it is believed that there are four hybrid sedimentary models in the study area, including the hybrid sediments driven by storm current and gravity flow events, lithofacies margin hybrid sediments, in-situ hybrid sediments and bio-chemical hybrid sediments. The mixing of sedimentary components is driven by geological forces. Frequent fault activities provide dynamic foundation and lakebed slope condition for hybrid sediments. The climate controls the material conditions and hybrid sedimentary modes of fine-grained hybrid sedimentary rocks through the changes of rainfall, temperature, organisms and other factors. The provenances input terrigenous clastic components. The lake level fluctuations and aqueous medium conditions not only determine the formation conditions and microstructures of carbonate components, but also play a key role in the preservation of organic matters. Lacustrine facies fine-grained hybrid sedimentary rocks reservoir has strong heterogeneity and diverse types of reservoir space, which is a kind of reservoir with great exploration potential.