Dynamic model of coal porosity considering the influence of gas adsorption layer.

Coal porosity prediction is normally based on the matrix deformation caused by effective stress and adsorption/desorption effect. However, the gas adsorption layer attached to the coal pore surface occupies the pore volume and ultimately reduces the coal porosity. Therefore, the porosity dynamic evolution is the result of the matrix deformation and gas adsorption layer variation. According to the basic definition of porosity and the porous media effective stress theory, a dynamic porosity model was developed to explicitly consider the influence of gas adsorption layer. Furthermore, the effects of temperature, gas pressure, adsorption swelling effect, and adsorption layer on coal porosity were analyzed. The model was verified with the field data under the different buried depth conditions. [ABSTRACT FROM AUTHOR]