Multisource Gas Control Technology in Goaf Based on a Three-Dimensional O-Ring Model

To address the challenges of gas accumulation in the goaf and excessive gas concentrations in the upper corner, a comprehensive investigation was conducted at a coal mine in Shanxi Province. The study utilized theoretical calculations, numerical simulations, and field experiments to analyze the porosity distribution within a three-dimensional “O”-ring model, as well as the sources, emission rates, and migration patterns of gas. The research identified the optimal configuration for three-dimensional gas extraction, which involved the integration of long boreholes drilled along the roof strike and embedded pipes in the upper corner. The corresponding layout parameters were successfully implemented in the field. The results indicated that the primary sources of gas emissions were the working face, adjacent coal seams, and residual coal, with respective emission rates of 31.25, 18.65, and 7.11 m3/min. The porosity distribution within the mined-out area exhibited a symmetrical pattern along the centerline of the working face (y=150 m), with elevated values at both ends and lower values at the center, thus forming an overall “O”-ring shape. Under normal ventilation conditions, gas concentrations were observed to increase exponentially along the strike, reaching a plateau at high levels beyond 250 m. Notably, gas accumulation was more pronounced on the return air side along the dip, where concentrations significantly exceeded those on the intake air side. Through a combination of numerical simulations and field experiments, the joint extraction method involving long boreholes along the roof strike and embedded pipes in the upper corner proved highly effective in maintaining gas concentrations in the upper corner at approximately 0.24%. Similarly, gas concentrations in the return airway stabilized at around 0.23%, while those at the working face were consistently maintained at approximately 0.26%, thus achieving the desired control outcomes. The findings of this study provide significant insights for gas control strategies in mined-out areas, offering valuable guidance for similar applications in adjacent mines.