Abstract: In order to clarify the differences between the pore characteristics of marine and paralic transitional shale, in the case study of Upper Yangtze Region, Northwest Guizhou, the pore characteristics of Longmaxi Formation marine shale, Niutitang Formation shale and Longtan Formation paralic transitional shale widely distributed in the area were studied, and the types and development and distribution patterns of pores inside the shale were analyzed to further explore the causes of difference. The study showed that, the overall pore distribution pattern of marine shale was dominated by organic pores and followed by rigid intergranular pores such as quartz and carbonate minerals, with the relative content of organic pores accounting for more than 50% of the total pores; the diameter of pores in marine-continental transitional shale was greater and more variable than that of marine shale, and the pore distribution pattern was dominated by inorganic intergranular/intragranular pores and microfractures, followed by organic pores, with a large number of dissolved pores/fractures developed in carbonate minerals, and the relative content of organic pores only accounting for about 20% of the total pores. The difference of sedimentary conditions in formation period was the root cause for the difference of pore development between marine and marine-continental transitional shale, and the different preservation conditions in the later stage also had a certain influence. Differential analysis of reservoir pore characteristics provides an important guidance to the exploration and development of shale gas resources.

Key words: marine shale, marine-continental transitional shale, pore characteristics, difference analysis, northwestern Guizhou