Research on Gas Emission Characteristics During Dynamic Coal Breaking in Boreholes Based on Bidisperse Diffusion Model and Coal Dust Desorption Calculation Model: Under Different Original Gas Pressures and Overburden Loads

ABSTRACT Accurately grasping the law of gas occurrence is of vital importance for the prevention and control of coal and gas outbursts. Traditional methods have problems such as low identification accuracy and insufficient predictability. Therefore, this study constructed a gas diffusion‐seepage fluid‐solid coupling model that can reflect the non‐homogeneity of coal matrix pores, and combined it with a calculation model of gas desorption from coal chips during dynamic drilling. The characteristics of gas emission during the entire process of dynamic coal breaking by drilling were studied through COMSOL numerical simulation. The research results were verified on‐site using a self‐developed intrinsically safe wireless multiparameter gas detector for mining. The gas emission laws under different initial gas pressures, overburden loads, and drilling speeds were analyzed. It was found that the gas emission rate rose sharply at the beginning of coal breaking and then quickly stabilized, while the cumulative emission volume increased linearly. The initial gas pressure was positively correlated with the emission volume and emission rate. The overburden load suppressed gas emission by compressing pores, and there was a marginal effect. Increasing the drilling speed reduced the cumulative emission volume but increased the instantaneous peak rate. Based on the analysis of the laws, a multifactor relationship model of cumulative gas emission from the borehole during dynamic coal breaking with the initial gas pressure, overburden load, drilling speed, and hole depth was established. The determination coefficient R 2 of the model fitted by multiple linear regression was 0.996, with a small prediction error. It is suitable for engineering estimation and trend analysis, providing a new method for the advanced identification of gas abnormal zones.