Effect of maceral composition and coal rank on gas diffusion in Australian coals

Based on the experimental data, different synthetic coalbed simulation models were constructed to analyse the impact of CH4 and CO2 diffusion coefficients on ECBM and CO2 sequestration performance. The numerical simulation results showed that CH4 production rate is inversely proportional to the sorption time, if the bulk flow in the cleats does not create any restriction. The results also indicated that CO2 breakthrough time is a function of the CO2 sorption time - if the CO2 adsorption is not fast enough, the injected CO2 will be spread into the seam, resulting in an early breakthrough.