Macromolecule simulation studies on mechanical properties and CH4/CO2 adsorption characteristics in bituminous coal matrix based on uniaxial tension-compression effect.

Abstract

With the increasing complication of production and geology conditions, and the increase of mining intensity and depth in coal mine, the coal structure presents varying degrees of deformation. In order to study the influence of uniaxial tension-compression effect on mechanical properties of coal matrix and CH4/CO2 adsorption characteristics, a macromolecular model reflecting the realistic bituminous coal structure was established. Results demonstrate that the influence of tension strain on the microporous structural parameters is greater than that of compression strain, and the tension strain weakens the mechanical properties but enhances the adsorbates adsorption amount. For the pure gases adsorption, there is a negative linear correlation between the total energy and adsorption amount. Additionally, the strain ranging from -0.20 to 0.20, the distribution of punctated adsorbates density develops to that of banded adsorbates density, and the mean adsorption density and saturated adsorption amount increase linearly. For the binary components adsorption (1:1), the CH4 adsorption strength increases while the CO2 adsorption strength slightly decreases. The minimum of total energy decreases in a quadratic polynomial relationship with the strain, and the proportion of van der Waals energy is 75.8-85.5%. Nevertheless, the competitive adsorption and strain have little effect on the potential energy range of the adsorbates. Furthermore, the diffusibility of CO2 molecular layers is relatively good, and the strain enhances the stability of CH4 molecular layers for the saturated binary adsorption. The findings provide essential guidance for the improvement of carbon capture and storage and CO2-enhanced coalbed methane technologies in the deformation area of coal seam.