Interpretation of the extent of hydraulic fracturing for rockburst prevention using microseismic monitoring data

As the mining depths increase, an increasing number of deep coal mines in China encounter frequent intense rockburst problems. Conventional destress measures, employed effectively in shallow mines to reduce rockburst risk, are not suitable to deep coal mines because they are labor-intensive and time-consuming and hence are costly. Hydraulic fracturing in coal seams before mining a particular area has been considered as an effective destressing method for rockburst prevention. This paper focuses on using microseismic data to evaluate the extent of hydraulic fracturing in coal seams. To that purpose, innovative methods are proposed to process and interpret microseismic monitoring data. The proposed methods consist of an improved HHT method for signal filtering, an improved time-window energy eigenvalue method for first arrival picking, and a four-channel combined algorithm for seismic source location determination. Using the elaborate signal processing and interpretation methods, high-precision source locations of microseismic events recorded in a field hydraulic fracturing test at Huafeng Coal Mine are obtained. Microseismic event frequency and energy contours are plotted to characterize the fracture development and propagation process. The interpretation method was successfully applied in the coal seam hydraulic fracturing tests. Direct field observation and stress monitoring were also conducted to verify the results by the microseismic data interpretation method. Compared with conventional monitoring techniques such as stress monitoring and direct field observation, microseismic monitoring can cover a large monitoring volume with a high response sensitivity and it can capture the spatial-temporal fracture evolution process easily. It provides a practical approach to quantify the extent of hydraulic fracturing in coal seams for rockburst prevention.