Three-dimensional reconstruction of coal based on CT scan technology and the study on gas apparent permeability

Based on CT scanning technology, the coal sample is scanned and then filtered and binarized to obtain characteristic parameters such as pore and fracture dimensions, porosity, etc. The fractal dimension of coal samples is calculated using the box dimension method, and the average tortuosity and tortuosity dimension of coal pores and fractures are derived. Combined fractal theory and Knudsen number, the slip modified apparent permeability model for coal is derived and verified. The gas seepage behavior in coal is studied using ANASY finite element software. The results show that the gas pressure changes significantly at the bends of pore-fractures, with maximum seepage velocity, and gas coagulates and does not flow in certain pores. The gas apparent permeability is calculated using the slip modified apparent permeability model, and compared with the gas apparent permeability obtained by fitting the Forchheimer formula and calculated using the FT model. It is found that the slip modified apparent permeability model is suitable for studying the apparent permeability in microscale media.