Abstract: The process and characteristics of hydraulic fracturing in coal shale were studied. The coal shale in the Fuxin Sunjiawan coal mine was regarded as the research object. The test was carried out by using a piece of triaxial hydraulic fracturing equipment. Then the original acoustic emission signal was time-converted by Short-Time Fourier Transform(STFT). The relationships between time-frequency parameters and crack initiation and propagation were obtained. The results show that the amplitude change rate can be used as an index to judge the stage of crack initiation or propagation, that the amplitude change rate of initiation stage increases with the increase of horizontal stress difference, that the amplitude change rate of the propagation stage increases first and then decreases with the increase of horizontal stress difference, that when the horizontal stress difference is 0, 0.2 and 0.4 MPa, the amplitude change rate in initiation stage is 2.88 times, 3.14 times and 5.36 times as high as that in the propagation stage respectively, that there is a linear decreasing relationship between the dominant frequency and the horizontal stress difference in crack initiation and propagation stage, and that in propagation stage, the dominant frequency is 2 times, 1.96 times and 1.99 times as high as that in crack initiation stage respectively.

Key words: hydraulic fracturing, crack initiation, crack propagation, coal shale, acoustic emission, time-frequency analysis