Abstract: The microscopic pore structure characteristics of reservoirs are important factors in evaluating the reservoir performance, resource abundance and "sweet spot" of shale reservoirs. To address the problem of unclear microscopic pore structure characteristics of the shale in Member 1 of Qingshankou Formation, Daan Area of southern Songliao Basin, argon ion polishing and scanning electron microscope, high-pressure mercury injection, constant-speed mercury injection,CT scanning and nuclear magnetic resonance were used to jointly characterize the reservoir space type, pore throat radius distribution, connectivity and fluid mobility of the Member 1 of Qingshankou Formation. The results of the study show that the reservoir in Member 1 of Qingshankou Formation, Daan Area belongs to clay shale facies and mixed shale facies, with an average porosity of 5.95% and an average permeability of 0.041 6 mD, and belongs to extra-low pore ultra-low permeability, ultra-low pore ultra-low permeability tight and ultra-tight reservoir space. Eight types of reservoir space types are divided.Micro-fractures and throats connect the reservoir space, improving the reservoir physical properties, and the percentage of mobile fluid in the reservoir ranges from 27% to 47%. Combined with the oil-bearing characteristics of the reservoir, it is predicted that the area of favorable reservoir of Class I in the study area is about 300 km², and that of Class Ⅱ is about 650 km², which has good prospect of exploration and development. The study results can provide a more accurate scheme for microscopic pore structure evaluation of shale reservoirs in the study area.

Key words: shale reservoir, Qingshankou Formation, microscopic pore structure, reservoir space, Songliao Basin, Daan Area