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

Abstract

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 CH 4 , N 2 , and H 2 O in coal and N 2 displacement of CH 4 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 CH 4 /N 2 are 0.204/0.189 (cm 3 /g), and at a moisture content of 5.63%, the saturated adsorption capacities of CH 4 /N 2 are 0.151/0.139 (cm 3 / 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 cm 3 /g and the difference in the CH 4 adsorption capacities is 0.473 cm 3 /g, and at a moisture content of 5.63%, the difference in the total gas adsorption capacities is 0.3 cm 3 /g and the difference in CH 4 adsorption capacities is 0.22 cm 3 /g. For the coal samples treated with various moisture phases, the differences in the CH 4 /N 2 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 CH 4 desorption capacity and desorption rate. The study is important to understand the interactions between coal and moisture.