Varying characteristics of electromagnetic radiation from coal failure during hydraulic flushing in coal seam

Abstract

A large amount of gas, which will do great damage to the environment as a kind of greenhouse gas, is discharged directly into the air in the process of coal mining in China. Majority of coal mines in China are characterized by low permeability, great gas pressure, and low strength feature. These features make it difficult for the extraction of gas, which increases the risk of coal and gas outbursts. In order to improve the permeability of coal seam, hydraulic flushing (HF) technology is adopted. So, the effect of hydraulic flushing will be necessary to be analyzed before gas extraction. In this paper, an electromagnetic radiation (EMR) experiment system of coal seam during hydraulic flushing was established, electromagnetic radiation (EMR) signals produced by the deformation and fracture of coal were studied during hydraulic flushing in coal seam in the Songhe coal mine, Guizhou province, China. The results showed that abundant EMR signals could be produced because of coal deformation and fracture. EMR signals were positively associated with the degree of coal failure. In different coal seams, EMR signals had different features during hydraulic flushing. The greater the gas pressure in the coal seam, the more dilatation energy was released. Higher rupture velocity could generate stronger magnetic signals. During hydraulic flushing, the more serious the rupture of coal, the higher the count of EMR pulses, and the higher the frequency of EMR. The principal frequencies and the amplitudes of waves increased gradually with gradually increasing ruptures. The change of EMR signals after hydraulic flushing was more dramatic than before hydraulic flushing. So, it is feasible and dependable to evaluate the effect of coal seam hydraulic flushing by EMR.