Modeling of the equivalent permeability for an underground coal fire zone, Xinjiang region, China

Underground coal fires (UCFs) constitute severe disasters, yet the quantification of the process of coal fire propagation, the first step in knowing how to extinguish a UCF, remains a great challenge even after decades of research. An important feature for understanding oxygen supply to a coal fire is the permeability of the UCF zone. Here, we propose a model for a typical UCF zone based on an analysis of the deformation of the overlying rocks caused by the UCF. We delineate the physical boundaries of the UCF and show how the zone includes both porous media and fractured zones. We then attempted to quantify the permeability of these porous and fractured zones and use the quantitative model to design, build, and employ an elementary UCF air/smoke flow experimental apparatus to run a permeability experiment. Subsequent to the experiments, we used simulation software to build a numerical model of the experimental apparatus. Calculated results from the numerical model agreed reasonably well with results from the physical experiments, though for this model to be applied in practice to quantify UCF propagation, further research on problems such as the size and distribution of the fractures and the relationship between the fractures and stress in the rock matrix will be required.