Abstract: To deeply study the micropore characteristics of the 5th shale member of the Xujiahe Formation of Upper Triassic in Sichuan Basin, the microscopic pore structures of the shale reservoir were systematically studied by using Argoion polishing Scanning Electron Microscope(SEM), low temperature nitrogen adsorptiondesorption technology and related geochemical experiments. Meanwhile, the influences on the development of nanopore were discussed. The studies revealed that the micropores in shale can be classified into organic pores, inorganic pores (intergranular pores, intragranular, intercrystalline pores and dissolution pores) and the microcrack can be classified into structure microcrack, pressure crack form hydrocarbon generating and expelling, diagenetic constricted crack. Whats more, the pore structures can be mainly divided into three kinds, such as cylindrical pore with both ends open, Slit shaped holes between the parallel planes and taper pipe bore. The micropore diameters are largely ranged from 1 to 80 nm and the peak is distributed in 2 to 8 nm. The pore volume is mainly composed of mesopores (2 to 50 nm) with the proportion of 6021% (or mainly composed of the pores of clay mineral with the proportion of 4462%). In addition, organic richness and the content of clay minerals are believed to be the main controlling factors of nanopore development.

Key words: Sichuan Basin, Upper Triassic, the 5th shale member of the Xujiahe Formation, shale gas, pore type, pore structure, controlling factor