Study on pore structure characteristics of mud shale in Wuxiang Block of eastern Qinshui Basin

Coal-bearing associated shale in Wuxiang Block of eastern Qinshui Basin is widely developed and has great potential for shale gas resources.Strengthening the study of pore structure characteristics of shale is of great significance to the evaluation of shale gas-bearing property and the realization of co-exploration and co-exploitation of coalbed gas and shale gas.Therefore，the pore structure of the shale of the Permian Shanxi Formation of Well X in Wuxiang Block is studied by means of high pressure mercury injection and low temperature liquid nitrogen experiments.The results show that the adsorption curve of mudstone samples in Wuxiang Block of Qinshui Basin is inverted S-shaped，which belongs to Type II curve of Brunauer classification scheme.The desorption line belongs to the H2 type (both Type H1 and Type H3) in the IUPAC classification scheme，and belongs to the Type B(both Type E and Type C) in the De Boer classification scheme.Fractured holes are mainly developed，followed by ink bottle holes，with good sorting，fewer open holes and poor connectivity.Target layer belongs to the reservoir with poor shale gas，which is not conducive to the adsorption，diffusion and permeability of reservoir，but can be improved by fracturing.The pore size of shale is mainly about 5 ～7 nm and 15 nm by mercury injection test.The pore size of mudstone in Wuxiang Block of Qinshui Basin is concentrated at about 1.18 nm measured by liquid nitrogen experiment.BET specific surface area ranges from 10.022 to 15.454 m2/g，with an average of 13.342 m2/g.Micropore is the main contributor to shale specific surface area.The average pore diameter ranges from 5.56 to 6.50 nm，with an average of 5.75 nm.The average pore size is in the range of mesoporous.The total pore volume is between 0.008 12 and 0.012 54 cm3/g，and the average pore volume is 0.01 cm3/g.According to the experimental results of liquid nitrogen mercury injection，the pore size of shale in Shanxi Formation of Well X in Wuxiang Area is less than 50 nm，and the pore size of 2～50 nm is the main contributor to the total pore volume.