It is a key step for reservoir evaluation and development of shale gas to analyze characteristics of the microscopic pores in organic-rich shale and quantitatively characterize their pore size distribution.Based on core description

thin section inspection

X-diffraction

SEM and nitrogen adsorption test

this paper analyzed mineral components

classified microscopic pore types and also quantitatively characterized pore size in organic-rich shale samples of the Shahejie Formation in the Zhanhua sag

Bohai Bay Basin.The results show that the samples are characterized by high carbonate content and low clay content.According to their positions in the formation

genetic origin and occurrence

the reservoir spaces are divided into two types

namely pores and fractures

and their size classification criteria are determined.The pores consist of mineral matrix pores and organic pores.The fractures include structural

inter-bedded

over-pressure induced

diagenetic and organic shrinkage fractures.Nitrogen adsorption test mainly displays three types of curves which represent the spatial distribution of micropores

mesopores and macropores in the shale samples respectively.While nitrogen adsorption test mainly measures the mesopores and is relatively insensitive to other pore size types

SEM can reveal the characteristics of macropores much more clearly.It is suggested to further perform measurements of carbon dioxide adsorption

Nano-CT and mercury injection to quantitatively characterize the size and spatial distribution of the micropores and macropores in the shale.