Pore-fracture structures and seepage flow characteristics during spontaneous coal combustion based on CT 3D reconstruction

To study the evolution characteristics of the pore-fracture structures and seepage properties of coal in the process of spontaneous combustion, a high-temperature tube furnace was used to heat the coal samples. The coal samples were scanned using Xray-CT scanning technology, and the CT 3D reconstruction technology was used to extract the 3D pore structure and equivalent pore network model of each group of coal samples. Firstly, the specific surface area and volume of pore cleavage is statistically characterized; the change rules of Ep, Et, Lc, and Cn are quantitatively analyzed. At 200 °C, the coal body produces a large number of pore fractures, the development of coal samples is more significant, and the pore-specific surface area and the number of pore throats reached their maximum value. In addition, the changes of fractal dimension, porosity, connectivity, and permeability of coal with temperature were discussed, and the best permeability of the coal was achieved at 200 °C. The connectivity and permeability were weakened with the further increase of temperature, and the structural changes had a close influence on the gas seepage pressure and seepage flow rate. The results of the study provide important engineering guidance for deepening fire prevention in coalfields.