Experimental study on competitive adsorption relationship between CH4 and N2 ,CO2 by NMR

Nuclear magnetic resonance (NMR) technique is used to characterize the different states of CH4 in coal. By testing the NMR signal of interaction between CH4 and CO2 and N2 in coal samples,the whole process of the interac- tion between each gas are described and analyzed by the T2 spectrum morphology and spectral area. The test results show that the T2 spectrum of CH4 adsorption process in coal is double peaks structure,and the smaller relaxation time is the adsorption peak and the other is free peak. With the increase of adsorption time and injection pressure,the total amount of adsorption increased gradually,but the adsorption rate decreased. Strong adsorption gas can displace the weakly adsorbed gas adsorbed in coal,but on the contrary,the effect is not obvious. In the replacement process,the gas in the macropores is easier to replace than the small pores. When the weakly adsorbed gas is injected into the coal, which has been adsorbed strongly adsorbed gas,the primary gas can be transformed from the adsorbed state to the free state. At the same time,a small amount of weakly adsorbed gas can also be adsorbed,and the greater the pressure,the more obvious. The results of NMR test have directly reflected the interaction between CH4 and other gas.