Investigation on microseismic activity and time frequency characteristics of coal seam hydraulic fracturing

In order to study the microseismic activity and time frequency characteristics of coal seam hydraulic fracturing,we developed a series of research about staged fracturing technology including theoretical research and field test in Shandong Province.The main works were carried out as follows:in the filed tests,the small shear failures were triggered by high response microseismic monitoring system.And we proposed a denoising method Singular Value Decomposition (SVD) for those microseismic signals.Short-Time Fourier Transform (STFT) was proposed in this paper to extract feature from microseismic signals in different stages.Microseismic event frequency and energy contours were plotted to characterize the fracture development and propagation process.The interpretation method was initially and successfully applied in the coal seam hydraulic fracturing tests.The test of on-site application shows that the method described above serve as a description method for hydraulic fracturing very well,signal amplitude increases firstly and then decreases (increase from 6.64 mV to 97.51 mV,and decrease to 30.61 mV),signal frequency shows a slow rise tendency (increase from 64 Hz to 109.5 Hz,and keep at 105.3 Hz) and in the range of 30 ～250 Hz.Based on the events number and energy distribution,the initial extent of hydraulic fracturing and regular of stress migration is evaluated.The conclusions above can provide some useful idea to quantitative evaluation of hydraulic fracturing in coal mines.