Study on microscopic deformation fractal characteristics of methane adsorbed by coal based on CT images

In order to quantify the anisotropic characteristics of mesoscopic deformation during the process of coal adsorbing methane, the CT scanning experiment of adsorption deformation was conducted during the methane adsorption process of anthracite coal under constant temperature using the ACTIS-CT scanning experimental system, the strain deformation of meso-structure of coal was quantitatively calculated during the adsorption process based on the particle tracking strain calculation algorithm of CT image, and the change regulation was discussed. On this basis, a quantitative research method for the heterogeneity of micro deformation of coal adsorbing methane based on CT technology was proposed, and the fractal dimension D was calculated using the fractal dimension method to quantitatively evaluate the heterogeneity of micro deformation of coal. Based on the physical description of fractal geometry and micro-strain deformation distribution, the relationship between fractal dimension D and anisotropic deformation characteristics of methane adsorption was also discussed. The results indicate that: the expansion deformation of coal adsorbing gas first compresses pores or cracks to obtain a larger expansion space; the heterogeneity of microscopic deformation caused by coal adsorbing methane conforms to the fractal characteristics; the fractal dimension is negatively correlated with the expansion and deformation rate of coal after methane adsorption; the higher the expansion and deformation rate is, the lower the fractal dimension is. In other words, the larger the expansion of coal after methane adsorption is, the lower the irregularity of the overall heterogeneous strain deformation of coal is. On the contrary, the lower the value of expansion deformation rate, the higher the fractal dimension, and the higher the irregularity of the whole heterogeneous strain deformation of coal.