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

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 m 2 /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 ke-rogen organic matter pore is greater than that of type II 1 , 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 Nan-jiang area.