Characteristics and evolutions of gas dynamic disaster under igneous intrusions and its control technologies

Globally, thermal events related to igneous intrusions are widespread in major coal-producing countries. The occurrence, size and distribution of these events play important roles in coal mining safety. The sill distribution area is relatively large in China, which has a particularly serious influence on the damage of coal seams and mining safety. In the Haizi coal mine, magmatic activity is intense and widely distributed and has resulted in 11 coal and gas outburst accidents under a 120-m-thick igneous sill. To study the effect of sill intrusions and their relationship with gas outbursts, samples from the outburst coal seams (Nos. 7, 8, 9 and 10) were taken from the Haizi coal mine at various distances from the sill. We found that under the effect of entrapment and thermal evolution of the igneous sill, the coal pore structure was developed, the gas adsorption capacity was enhanced, and gas outburst risk was increased. The rules of bed separations evolution under the sill were analyzed which indicated that large separation quantities are developed as gas enrichment areas in the bending zone after mining, which brings dynamic disasters risk and good drainage conditions at the same time. The gas pre-extraction technology for the first mining seam and the pressure relief gas drainage technologies via surface wells and distant penetration boreholes were established. Given the practice in the Haizi coal mine, it was determined that the gas drainage technologies could eliminate gas outbursts and promote mining safety under this unique geologic condition.