Abstract:In order to analyze the characteristics of natural gas occurrence of the lacustrine shale in Da'anzhai member in Yuanba area. Using scanning electron microscope (SEM), nitrogen adsorption, high-pressure mercury injection and other analytical techniques, the pore types and pore size distribution of lacustrine shale in Da'anzhai member of Yuanba area were studied, and the effects of the pore structure of shale on the occurrence state of shale gas were discussed. Inorganic pores (76.92%), organic pores (9.17%), and microfractures (13.91%) are developed in the shale. Among them, the inorganic pores are mainly clay mineral pores formed during the smearing of montmorillonite. The organic pores are underdeveloped. The reason is related to the fact that the type of organic matter is mainly type III and the TOC content is low. In the whole-aperture pore size distribution of shale pores, the micropore, mesopore and macropore contributed 6.76%, 76.92% and 16.30% of pore volume espectively. It can be seen that the shale in the Da'anzhai member of the Yuanba area is dominated by inorganic pores, mainly meso-macropores, together with the high temperature and high pressure of the reservoir controlled the occurrence of shale gas in this area is mainly free gas.