Abstract: The main subjects of study for this paper are from Longmaxi Formation of Lower Silurian in northern Yunnan and Guizhou Province. Based on analysis of whole rock-mineral and observation of core slices, we divide shale lithofacies into 4 types of shale facies, in which the main developed lithofacies in the study area are the clayey shale facies and mixed shale facies. Based on scanning electron microscopy imaging and organic carbon content measurement, and the experiment of nitrogen adsorption at low temperature, we analyzed the pore structure characteristics of different shale facies. The results show that the larger pores in argillaceous shale facies reservoir are mainly flask-shaped pores, open pores and half-closed pores. The larger pore forms in mixed shale facies are mainly open pores with some half-closed pores; the smaller pores in the two facies are mostly half-closed pores. The content of TOC is favorable to the development of micropores and mesopores, while the content of argillaceous minerals is beneficial to the development of macropores. Because the clay mineral content of the clayey shale facies are higher than that of the mixed shale facies, as well as the effect of diagenesis, the macro-pore volume of the clayey shale facies is higher than that of the mixed shale facies, the pore volume of micro-pore and meso-pore is smaller than that of mixed shale facies.

Key words: Longmaxi Formation, shale lithofacies, mineral contents, organic matter, pore structure