Multistage hydraulic fracturing of a horizontal well for hard roof related coal burst control: Insights from numerical modelling to field application

Multistage hydraulic fracturing of horizontal wells (MFHW) is a promising technology for controlling coal burst caused by thick and hard roofs in China. However, challenges remain regarding the MFHW control mechanism of coal burst and assessment of the associated fracturing effects. In this study, these challenges were investigated through numerical modelling and field applications, based on the actual operating parameters of MFHW for hard roofs in a Chinese coal mine. A damage parameter (D) is proposed to assess the degree of hydraulic fracturing in the roof. The mechanisms and effects of MFHW for controlling coal burst are analyzed using microseismic (MS) data and front-abutment stress distribution. Results show that the degree of fracturing can be categorized into lightly-fractured (D≤0.3), moderately fractured (0.3<D≤0.6), well-fractured (0.6<D≤0.9), and over-fractured (0.9<D≤0.95). A response stage in the fracturing process, characterized by a slowdown in crack development, indicates the transition to a well-fractured condition. After MFHW, the zone range and peak value of the front-abutment stress decrease. Additionally, MS events shift from near the coal seam to the fractured roof layers, with the number of MS events increases while the average MS energy decreases. The MFHW control mechanisms of coal bursts involve mitigating mining-induced stress and reducing seismic activity during longwall retreat, ensuring stresses remain below the ultimate stress level. These findings provide a reference for evaluating MFHW fracturing effects and controlling coal burst disasters in engineering.