Distribution of gob empty space for methane drainage during the longwall mining: A case study

In China, there are a large number of coal mine gobs have been formed as a result of longwall mining processes. These mine gobs contain an enormous amount of methane storage spaces within the gob formations. The methane storage spaces as well as guide methane drainage via vertical boreholes require quantitative measurements. In this study, physical simulation experiments were conducted for the purpose of obtaining digital images of gobs at various working face advance distances. Then, a Matlab-based digital image processing and analysis program was developed to process the obtained high-definition images, extract the geometrical parameters, and calculate the areas of methane storage spaces within the gobs. The results showed that the heights of the methane storage spaces first increased, and then stabilized as the gob lengths increased. The area sizes of the gobs increased gradually with the lengths, while the methane storage space areas were observed to first increase steadily to a maximum, and then decrease sharply. The main methane storage spaces exhibited a decreasing trend stage as the gob lengths increased. Whereas, the secondary methane storage spaces showed the characteristics of increasing trends. These research findings provide a theoretical foundation for the accurate predictions of both the methane storage capacities and methane drainage efficiency of longwall mining gobs.