鄂尔多斯盆地延长组绿泥石膜的形成机制

通过包裹体、铸体薄片、带有能谱仪的扫描电镜技术对鄂尔多斯盆地延长组长8砂岩中的绿泥石膜进行分析测试,研究其形成机制和过程及其与物性的关系。研究表明:绿泥石膜具有双层膜结构,由骨架颗粒向孔隙方向依次为里层膜和外层膜;等厚的外层膜发育在压实作用之后,由孔隙水中析出的绿泥石晶体聚集在骨架颗粒表面形成,由于原生孔隙提供了充足的生长空间,致使生成的绿泥石晶粒大,晶形好,集合体有规律地排列;在外层膜的双向阻滞作用下,里层膜开始在骨架颗粒边缘溶蚀产生的小孔腔中生长,因空间狭小造成绿泥石晶体小,晶形差,集合体杂乱堆积;随成岩环境的变化,碎屑石英表面在外层膜形成后,经历了里、外层膜同时生长和停止的反复交替,而碎屑长石表面的里、外层膜则表现为此长彼停的循环过程;绿泥石膜胶结是一种破坏性成岩作用,其发育的砂岩物性好仅仅是表象,本质是物性好的砂岩有助于绿泥石膜发育。

Forming mechanisms of chlorite films in Yanchang Formation, Ordos Basin

Using inclusion analysis, casting slice, scanning electron microscope analysis with energy disperse spectroscopy, the chlorite films in Chang 8 sandstones of the Yanchang Formation in the Ordos Basin were observed and probed, in order to analyze the forming mechanisms and processes of the films and the relationship between the films and the physical property. The results show that the chlorite films have double layers, referred to as the inside layer film and the outside layer film from the surface of the grain to the pore, respectively. The outside layer film with the isopachous feature was developed after the compaction,whose chlorite crystals precipitated from the pore fluid and densely cover the grain. The primary porosity provides enough space for the outside layer film, which leads to large chlorite crystals with uniform shape and regular accumulation. Owing to bi-directional blocking of the outside layer film, the inside layer film was developed in the small cavity formed by the dissolution of the framework grain. The cavity is narrow which leads to small chlorite crystals of the inside layer with irregular shape and chaotic mélange. With the change of the diagenetic environment, the inside and outside films around the quartz fragment simultaneously grow and cease repeatedly after the first formation of the outer layer, but the growth of the inside layer alternates with the growth of the outside layer around the felspar fragment. The cementation of the chlorite films is a destructive diagenesis process, such that the formation of the chlorite films does not lead to good physical properties in sandstones; on the contrary the good physical properties of sandstones facilitate formation of chlorite films.