川东北南江地区大隆组页岩孔隙结构特征及控制因素

Pore Structure Characteristics and Controlling Factors of Dalong Formation Shale in Nanjiang Area, Northeastern Sichuan Basin

摘要: 为明确川东北南江地区二叠系大隆组海相页岩孔隙结构特征及控制因素，选取LB1井大隆组岩心作为研究对象，通过扫描电镜、低温氮吸附、高压压汞及FIB三维扫描对比实验分析，对页岩孔隙类型和结构进行定量表征。实验表明：LB1井大隆组页岩以有机孔为主，形态主要为墨水瓶状，孔隙连通性相对较差；孔径主要分布在<2 nm和10~50 nm，比表面积平均27.2 m²/g；有机质丰度、粘土矿物含量与页岩孔隙度及微孔、中孔孔容有较好正相关性，I型干酪根有机质孔隙发育程度大于II1型，斑脱岩发育情况与Ba含量较好对应，表明TOC、有机质类型、粘土矿物及凝灰质矿物含量是控制南江地区大隆组页岩孔隙发育的主要控制因素。本文为南江地区新层系二叠系大隆组页岩气勘探突破提供理论支撑。

Abstract: In order to clarify the pore structure characteristics and controlling factors of Permian Dalong Formation marine shale in Nanjiang area of northeastern Sichuan, the core of Dalong Formation in Well LB1 was selected as the research object, and the pore types and structures of shale were quantitatively characterized by scanning electron microscopy, low temperature nitrogen adsorption, high pressure mercury injection and FIB three-dimensional scanning comparative experimental analysis. The result shows that the shale of the Dalong Formation in Well LB1 is dominated by organic pores, the shape is mainly ink-bottle, and the pore connectivity is relatively poor. The pore size is mainly distributed in <2 nm and 10~50 nm, and the average specific surface area is 27.2 m²/g. The organic matter abundance and clay mineral content have a good positive correlation with shale porosity, micropore and mesopore volume. The development degree of type I kerogen organic matter pore is greater than that of type II1, and the development of bentonite is well corresponding to the content of Ba, indicating that TOC, organic matter type, clay mineral content and tuffaceous mineral content are the main controlling factors for the development of shale pores in the Dalong Formation in Nanjiang area. This paper provides theoretical support for the breakthrough of shale gas exploration in the Permian Dalong Formation of the new strata in Nanjiang area.