Evaluation of gas drainage and coal permeability improvement with liquid CO 2 gasification blasting

With the increasing mining depths of underground coal mines, gas drainage and coal permeability improvement with conventional coal seam fracture stimulating methods have shown some deficiencies. In this work, an application of liquid CO 2 gasification blasting is proposed for increasing gas drainage and fracturing coal seam with high-gas content and low permeability. The methods of theoretical analysis, numerical simulation as well as field experiments are involved to build up a comprehensive understanding of this promising application. The variation of gas pressure for the gasification blasting is quantitatively determined by using a modified van der Waals equation of state. It is shown that the maximum pressure generated by the rapid thermal expansion of liquid CO 2 could induce the initiation and propagation of coal cracks and fractures. To testify the fracturing effects of liquid CO 2 gasification blasting on gas drainage, field experiments were carried out on two transportation roadways of Yuwu coal mine in China. It is found that (a) the effective fracturing radius could be about 3 m around the blasting borehole, (b) the quantities of gas extraction and gas emission are increased significantly, and (c) the outburst risk indices for drilling cutting fall below their critical values.