A shale formation contains numerous organic nano-pores and microscopic fractures, which natural gas flows through during production period. In shale formations, the flow mechanism and the characterization of petrophysical parameters are open and challenging topics for researchers since shale has significantly different characteristics from conventional rocks. Knudsen diffusion is considered as the main flow mechanism in nanoscale pores as the Knudsen number is finite. Many conventional methods have encountered challenges to model natural gas flow in organic nano-pores due to their continuum assumption. The lattice Boltzmann method (LBM) is a good candidate for modelling shale gas flows because it arises from the gas kinetic theory. In this work, three-dimensional (3D) pore structures of a shale core sample are reconstructed based on the Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) technique. The multiple-relaxation-time LBE is used to model gas flows. A slip boundary condition is implemented to capture boundary flows in pores to describe the Klinkenberg effect. In addition, intermolecular forces between pore walls and gas molecules are incorporated to capture the adsorption effects to flow. Methane gas flows driven by gravitational force in square ducts with different sizes have been simulated in order to observe slippage. Permeability of methane gas in 3D complex kerogen pore structures has been investigated. It has been found that the permeability decreases with the pore pressure increases, which follows the Klinkenberg theory.

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