CO2 adsorption-deformation-percolation characteristics of coals with different degrees of metamorphism and improvement of dynamic prediction model

The deformation and permeability changes occurring during CO2 adsorption in the coal body are important factors affecting CO2 injectability. In order to reveal the characteristic laws of adsorption, deformation and permeability of coal in the process of CO2 adsorption by different coal rank coals, the test experiments of adsorption, deformation and permeability of different coal rank coals under the condition of constant external force were carried out. The adsorption capacity of different coal samples for CO2 was obtained as anthracite > coking coal > long flame coal; The radial deformation e2 and axial deformation e1 of coal after CO2 gas adsorption by anthracite are the closest (e2/e1 is about 1.37), coking coal is the second (e2/e1 is about 1.73), long -flame coal is the largest (e2/e1 is about 2.72), In other words, the higher the coal rank, the more significant the degree of internal homogeneity and isotropy of the coal body, and the mean value of the volume deformation of CO2 adsorbed by long-flame coal is 1.07 and 1.17 times higher than that of coking coal and anthracite. The permeability curves of CO2 adsorption in all three coal samples decreased first and then increased, and the permeability of CO2 in coking coal was the largest, and the sensitivity coefficient of CO2 permeability in coal to adsorption pressure showed a trend of rapid decrease and then small increase. Based on the CO2 adsorption -deformation-percolation variation law of coal, an improved dynamic prediction model of adsorption (fitting accuracy 0.9850 -0.9963), an improved dynamic prediction model of coal body deformation (fitting accuracy 0.9889 -0.9921) and an improved dynamic prediction model of permeability (fitting accuracy 0.9848 -0.9914).