Characteristics of microseismic waveforms induced by hydraulic fracturing in coal seam for coal rock dynamic disasters prevention

Coal rock dynamic disasters have been a persistent threat to mine safety. Hydraulic fracturing(HF) technique has been proved to be an effective method for preventing coal rock dynamic disasters in underground coal mines. In order to monitor the crack extent of HF in coal seam, highly precision microseismic(MS) data acquisition apparatus and sensitive sensors are employed to monitor the cracks induced by coal seam HF in Xiecliao Coal Mine. Lots of effective and weak MS waveforms induced by HF are successfully recorded. Some useful methods such as wavelet transformation, Hilbert-Huang transformation, envelope analysis and curve fitting method help to make comprehensive insights into the amplitude-frequency, time-frequency, duration and peak following attenuation characteristics of these HF induced MS waveforms. The frequency, duration time and peak following attenuation characteristics of MS waveforms induced by mining, blast and coal seam HF are statistically studied. The results show that these characteristic parameters, peak frequency, duration time and peak following attenuation, are very sensitive to distinguish these three typical kinds of induced MS waveforms. Further study shows that the principles of fractures' propagation influenced by the pressurized water and the backfill effect of pores by large volume of pressurized water injection and the pressurized water itself are the key factors influencing the characteristics of MS waveforms. The conclusions are the theoretical basis of locating the cracks and monitoring the effect of HF in coal seams by using MS technique, which can provide the basis reference for designing optimized, safe and effective HF program to prevent the coal rock dynamic disasters, and will be of great significance to coal mine safety.