The study of the local area density homogenization effect of meso-structures in coal during methane adsorption

摘要

The swelling deformations of coal structures during the methane adsorption cause the changes of the gas migration channels such as mesopores and fractures, which poses a great challenge to evaluate the methane migration efficiency in pore-fracture network structures of coal. Because of the complexity of the multi-scale inhomogeneity meso-structure in coal, the previous studies were failed to propose a unified equation to accurately describe and predict the complex deformation of coal structures during methane adsorption. Through lots of researches of meso structures deformation during methane adsorption in coal, the local area density homogenization effect of the meso structures in coal during methane adsorption was discovered. In view of this, the mechanism of the local area density homogenization effect was analyzed by establish a new model of coal structure, and the local area density homogenization equation of methane adsorption in coal was derived. It indicated that the deformation of meso target structure in coal during the methane adsorption is mainly determined by the density ratio of the target structure to the local area, and the swelling deformation of the local area that contains the target structure, as well as the density homogenization coefficient. Through multi-scale three-dimensional segmentation and statistics of the Computed Tomography (CT) scan data of anthracite sample adsorbed methane under different adsorption pressures, the rule of the local area density homogenization effect was verified. It was found that the deformations of the meso structures in coal during the methane adsorption was capable to fit to the local area density homogenization equation of methane adsorption in coal under different adsorption pressures and observation scales. The calculation accuracy of this equation was determined by the analysis of the 95% confidence intervals of the density homogenization coefficient.. The local area density homogenization equation provides a way to describe and predict deformation behavers of coal structures based on the their density information obtained by CT scanning, and has great significance for the numerical simulation of methane dynamic seepage characteristics in multi-scale structures of coal in the CBM exploitation process.