“…Because we focus on the behavior of replacement between CO 2 and methane, we assume coalbed condition to be a saturated coal. Balan and Gumrah (2009) proposed that CO 2 diffusivity is hundred times greater than methane diffusivity into coal matrix. For considering these condition, the sorption times are set to value of 0.24 day for CO2 and 24 day for methane.…”