Differential Analysis of Various Moisture Phases on N2 Displacement of CH4 in Coal

The aim of the study was to elucidate the impact of different moisture phases during gas injection on coalbed methane displacement. The coal samples were treated with two methods: water vapor adsorption and liquid water stirring. The differences in the coal samples treated with various moisture phases during gas injection for coalbed methane displacement were investigated by using the isothermal adsorption curves of CH4, N2, and H2O in coal and N2 displacement of CH4 in coal. The results indicate that variations in the gas adsorption capacity of coal are treated with different moisture phases. The gas adsorption capacities and displacement capacities of the coal samples treated with the water vapor adsorption methods are better than those treated with the stirring methods. In the isothermal adsorption experiment, for the coal samples treated with different moisture phases, at a moisture content of 2.75%, the saturated adsorption capacities of CH4/N2 are 0.204/0.189 (cm3/g), and at a moisture content of 5.63%, the saturated adsorption capacities of CH4/N2 are 0.151/0.139 (cm3/g). In addition, in the displacement experiment, for the coal samples treated with different moisture phases, at a moisture content of 2.75%, the difference in the total gas adsorption capacities is 0.62 cm3/g and the difference in the CH4 adsorption capacities is 0.473 cm3/g, and at a moisture content of 5.63%, the difference in the total gas adsorption capacities is 0.3 cm3/g and the difference in CH4 adsorption capacities is 0.22 cm3/g. For the coal samples treated with various moisture phases, the differences in the CH4/N2 adsorption and displacement capacities are greater at a moisture content of 2.75% than at 5.63%. Notably, the moisture phase has only a marginal influence on the CH4 desorption capacity and desorption rate. The study is important to understand the interactions between coal and moisture.