Simulations on the micro-seepage rules of gas and water based on micro-CT/CFD and the related contrastive analysis

Abstract

This study first employed micro-computed tomography technique for scanning the gas-fat coal sample; then, using Avizo software, coal’s micro-pore structure model was established; finally, seepage behaviors of gas and water in the coal under a pressure of 3 MPa were simulated. Through comparison, it can be concluded that both gas pressure and water pressure decreased gradually along the seepage direction; at a same seepage length, water’s maximum seepage pressure significantly exceeded that of gas; gas’s velocity flow lines were overall fuller than water’s flow lines; using a same pore model, gas’s migration velocity far exceeded that of water; In terms of mass flow rate, water exceeded gas. The effluent mass flow rate at the outlet was smaller than the influent mass flow rate at the inlet. Overall, with the increase in the seepage length, gas and water’s mean seepage pressures and mass flow rates all decreased gradually, while their mean seepage velocities fluctuated greatly. Since the pores at the different coal cross-sections were developed to different degrees, the heterogeneity of the coal structure meant that the cross-sectional area of the pore channel varied irregularly along the seepage direction. The fitting curve can be reduced to three classes: logistic linear regression curve, Boltzmann function curve, Exp Dec curve, or poly curve.