Abstract
Efficient extraction of coal bed methane before coal mining is essential to eliminate the risk of coal-gas outbursts. However, stimulation technologies should be implemented to enhance the conductivity of the coal seam. In this study, we propose a novel method to create a complex fracture network in underground coal mines with the integration of multiple hydraulic slotting and hydraulic fracturing. In this method, hydraulic slots are used to direct hydraulic fractures and initialize branch fractures, while hydraulic fracturing is used to extend the fractures. Given the mutually exclusive and attractive propagation of multiple fractures, a relatively evenly distributed fracture network can be generated. The results show that (1) the dynamically induced stress shadows of hydraulic fractures can cause exclusive and attractive propagation of multiple hydraulic fractures; (2) a preset slot that deviates from the principal stress can direct hydraulic fractures to a certain extent and generate branch fractures; and (3) with a staggered distribution of preset slots, a relatively large volume of the coal seam in both the minimum and maximum horizontal stress directions can be stimulated, creating a complex fracture network including many vertical branch fractures and a large area of horizontally layered directional fractures.
Highlights
Coal is currently the major primary energy source based on China’s basic national conditions, accounting for 58% of the total energy consumption in 2018 [1], and it will remain at 50% in 2030 based on the long-term energy strategy
This paper is aimed at enhancing methane-extraction efficiency in underground coal mines, and we present a novel method to create a complex fracture network with the integration of multiple preset slots and hydraulic fracturing
Based on the principle of branch fracture generation and the competitive propagation phenomenon of multiple hydraulic fractures, we proposed a novel method to create a complex hydraulic fracture network in underground coal mines with the integration of hydraulic technologies including staggered distributed multiple slotting
Summary
Coal is currently the major primary energy source based on China’s basic national conditions, accounting for 58% of the total energy consumption in 2018 [1], and it will remain at 50% in 2030 based on the long-term energy strategy. Efficient and safe mining of coal is a major demand supporting economic development in China. Coal mining disasters, including roof collapses, coal-gas outbursts, water inrushes, fires, and explosions, frequently restrict efficient coal mining. China experiences serious gas disasters, which are considered the “first killer” in underground coal mining. A total of 3284 coal mines distributed in 26 main coal production provinces have a high risk of coal-gas outbursts due to their high gas content [2]. Eliminating the risk of coal-gas outbursts in coal mines with high gas content is essential
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