Numerical simulation on non-Darcy seepage of CBM by means of 3D reconstruction based on computed tomography

In order to study the influence of parameters on the CBM non-Darcy flow, six real models of various coal samples collected from underground mine were created by 3D reconstruction based on computed tomography. The CBM non-Darcy flow was numerically simulated under 30 different pressure gradients based on the six real models. According to the simulation results, some conclusions can be drawn as follows: (1) At the micro-scale (<100 μm), the relationship between the seepage velocity and the pressure gradient is consistent with the Forchheimer high speed non-linear percolation rule; (2) Effective porosity and permeability are positively related, but in the case of larger porosity, local twists and turns occur. Under the same pressure gradient, the seepage velocity increases with the effective porosity, permeability, non-Darcy coefficient increase in a general trend; (3) The non-Darcy coefficient decreases with the increase of effective porosity and permeability. Analysis results obtained by power function fitting and multivariate regression show that the effective porosity is the most significant factor on the non-Darcy coefficient, only consideration on the influence of the effective porosity can be more accurate to estimate the non-Darcy coefficient. Through the calculation by the numerical simulation of non-Darcy, empirical constant is 0.003171, the power of effective porosity is -5.38745.