Reliability Assessment of the Hydraulic Fracturing Process in Coal Mine Based on the Analysis of Micro-Seismic Source Parameters

Abstract

In a reliability assessment of hydraulic fracturing, the efficacy of hydraulic fracturing must be evaluated, and the source properties and magnitude of micro-earthquakes induced by hydraulic fracturing in a coal mine need to be quantified. Firstly, the changing trends of the number and energy of micro-seismic events induced by hydraulic fracturing with high-pressure water were examined, and the hydraulic fracturing effect was evaluated by micro-seismic location. Then, the source parameters (seismic moment M0, source radius R, corner frequency f0, radiated seismic energy E, stress drop △σ, and apparent stress σa) were calculated using the Brune model and the grid-search method, and the relationships between M0 and other source parameters were analyzed. Finally, the source parameters between micro-earthquakes induced by hydraulic fracturing and those induced by mining were compared, and the relationship between Mw (moment magnitude) and ML (local magnitude) of a micro-earthquake induced by hydraulic fracturing was ascertained. The results show that most micro-earthquakes occur in the initial stage of water pressure increase during hydraulic fracturing. In addition, the occurrence of several micro-earthquakes does not correspond strictly to the significant decrease of water pressure; the locations of micro-earthquakes can be used to evaluate the effect of hydraulic fracturing. The source parameters of micro-earthquakes induced by hydraulic fracturing in the Xieqiao coal mine can be obtained from the Brune model and the grid-search method. Corner frequency f0 decreases with increase in seismic moment M0, source parameters of R and E, as well as △σ increase with increase in seismic moment M0, but the apparent stress σa fluctuates around a certain value; the relationships between the other source parameters and M0 of micro-earthquake induced by hydraulic fracturing are consistent with that of a micro-earthquake induced by coal mining. Considering Mw, ML1 can be better used to calculate the magnitude of micro-earthquakes induced by hydraulic fracturing. Through Mw and ML1, the magnitude of a micro-earthquake induced by hydraulic fracturing can be evaluated. Our results improve the evaluation of the hydraulic fracturing effect, the understanding of source properties, and evaluation of the magnitude of micro-earthquakes induced by hydraulic fracturing. It is found that these micro-earthquakes are within the safe controllable range, and the hydraulic fracturing process of the Xieqiao coal mine is reliable and safe.