The organic and inorganic pores exhibit significant differences in pore sizes and surface chemistries that give rise to complex fluid flow behaviours. It is well known that pore size and pore connectivity directly impacts on macroscopic flow properties of a porous medium. Therefore characterization of strong heterogeneous shales with multiscale pore size is indispensable to accurately assess fluid transport properties. Recent advances in pore-scale imaging technique provide practical pathway to understand shale pore structure but the imaging area and resolution is still not available to capture the entire distribution of organic and inorganic pores in a single 2D or 3D image. However, the inorganic pores structure can be accurately captured inthat the inorganic pores sizes are relatively larger. In this work, a multi-scale pore network model is proposed to estimate the fluid transport properties. A 3D binary image is constructed from a section of SEM image which only image inorganic pores. Then the maximal ball fitting method is applied to extract its inorganic pore network. Gas flow inside the nano-porous organic matter considers gas adsorption/desorption, surface diffusion, Knudsen diffusion, viscous flow. Gas flow inside the inorganic pore considers Knudsen diffusion and viscous flow. The constructed multiscale pore network accounts for the distribution of organic matter, organic matter total volume, organic pore size, inorganic pore structure all together. Key analysis results indicate that the distribution of nano-porous organic matter significantly influences the fluid flow ability. Furthermore, the predicted permeability based on the proposed multi-scale pore network model matches well with laboratory measured pressure pulse data.
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