Quantitative investigation of anisotropic characteristics of methane-induced strain in coal based on coal particle tracking method with X-ray computer tomography

In order to quantify the anisotropic characteristics of coal swelling deformation during the process of methane adsorption, the inner mesoscopic structures of coal are scanned with computerized tomography (CT) and a coal particle tracking method (CPTM) is proposed to quantitatively calculate the strain of coal particulates in view of the pixel gray level matrix of CT image. The results show that the spatio-temporal distribution of coal mesoscopic deformation is inhomogeneous during the process of methane adsorption. From the spatial distribution, some parts of coal swell and other parts shrink. The mineral phase and porosity or fracture inside them are mainly swelling deformation and little shrinkage deformation. The swelling and shrinkage deformation is varying constantly with different gas pressure in the organic lithotypes of varying macerals and pore or fracture inside them. The expansion deformation tends to first squeeze the original pore or fracture inside them for more expansion space. From the temporal distribution, the magnitudes of adsorption deformation is also not uniform along with the decrease of gas pressure. After the adsorption balance, the change magnitudes of strain tend to decrease. The mesoscopic deformation of coal samples is anisotropic and the macroscopic deformation is swelling. This is verified by the cumulative total strain values of coal, which are obtained from the mesoscopic strain calculation results. This study presents mesoscopic CT and strain calculation results images of coal deformation. These data will provide the basis for the study of physical structure and mechanical properties of coal with adsorbing methane.