Blasting-enhanced water injection for coal and gas out-burst control

Abstract

Coal and gas out-bursts are a major risk in deep gassy coal mines. In order to minimize the out-burst potential during the mining process, we propose a novel blast-injection integrated (BII) technology. In this technology, a group of de-stress blasts are first used to de-stress the area near the active mining face and push the stress peak further away from the mining face. The cracks generated by the blasting improve the connectivity between the pre-existing fractures and promote gradual release of gas at the mining face. This is followed by water injection directly into the coal seam through the blast holes. The injection of water can greatly improve coal plasticity and reduce the initial speed of gas diffusion, ultimately reducing the potential for violent out-bursts. To implement this technology, a set of devices were developed that include hole packers and transport and safety accessories. The BII technology was subsequently tested at an active mine. It was found that the stress relief zone in front of the coal face increased longitudinally by ∼5m, and the rate of gas emission at the mining face doubled within 30min after the de-stress blasting. The injection water volume after the de-stress blasting also increased by 25 times compared to the un-blasted condition, and the monthly gas concentration in the return airway decreased from 0.58% to 0.36%. Additionally, the concentration of dust in the return airway was found to decrease. Based on the field test results, it was concluded that BII technology is an effective measure to limit coal and gas out-burst potential.