Shale rocks are inherently heterogeneous and the shale matrix pores can be divided into organic and inorganic pores. The transport mechanism of shale gas in organic and inorganic pores is different, and it is necessary to describe the nanoscopic organic and inorganic pore characteristics of shale rocks. In this paper, 2D thin section shale rock images are collected through scanning-electron microscopy (SEM); the first image mainly describes inorganic pore properties while the second image mainly shows organic pore properties. Then, according to the corresponding images, the inorganic pore digital rock and organic pore digital rock are reconstructed with the Markov Chain Monte Carlo (MCMC) method respectively. Next, a two-step superposition method is used to merge the inorganic and organic pore digital rocks together, which can construct the superposition shale digital rock including the characteristics of both inorganic pores and organic pores. Finally, the pore space structure analysis method is used to analyze the pore structure of each digital rock. Results show that, the superposition shale digital rock can recognize the inorganic pore and organic pore structure characteristics simultaneously and has a bimodal pore volume distribution; the first mode reflects the inorganic pores with relatively large pore sizes, while the second mode reflects the organic pores with relatively small pore sizes. This method provides a research platform for the study of different pore structure characteristics and nanoscopic flow mechanisms in shale rocks.

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