Coal seam hard top plate fracturing weakening method

Abstract

The invention discloses a coal seam hard top plate fracturing weakening method. The coal seam hard top plate fracturing weakening method comprises the following steps that firstly a fracturing hole is drilled in the top plate, then a thermal insulation casing pipe is utilized to inject liquid nitrogen into a top plate rock stratum in a pulse mode, the coupling effect of pulse fatigue damage and liquid nitrogen cold shocks can weaken the strength of the top plate rock stratum itself to a large margin, and when gasification pressure exceeds the rock stratum tensile strength, fractures are formed around the fracturing holes, and finally nitrogen is recycled. The method integrates the advantages of fatigue weakening, the cold shocks and gasification inflation, on one hand, by relying on a gas-liquid two-phase flow pressure group of which the size is gradually increased formed in a limited drilling hole space, the temperature inside the rock stratum is sharply reduced, and the generation of the thermal stress is induced, on the other hand, a pulse type injection method makes nitrogen gas-liquid two-phase flow quickly flows to the fractures, the fracture expanding velocity is increased, and finally effective collapse of the top layer rock stratum is achieved. The method is simple and convenient to construct, low in cost and wide in application range.

Description

technical field [0001] The invention relates to a cracking and weakening method for a hard roof of a coal seam, which is mainly suitable for the effective caving work of a dense and hard roof layer rich in clay matrix, and can combine the weakening characteristics of pulsation fatigue, the low-temperature cold impact of liquid nitrogen, and the gas The advantages of the three aspects of the fracturing effect realize the high-efficiency caving of the roof rock formation. Background technique [0002] In China, hard roofs with high strength, large thickness and good integrity are widely distributed in various mining areas. With the mining of coal resources and the gradual advancement of the working face, the area of ​​the roof overhang formed inside the stope is gradually increasing. If it cannot be effectively collapsed, the support strength and difficulty of the stope area will inevitably be increased. During the advancing process of the working face, the step distance of t...

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Problems solved by technology

These technologies all have certain limitations. For example, the shock waves generated by deep hole blasting can easily cause stress disturbances in coal and rock mass, often accompanied by explosion rejection or squibs; high-pressure hydraulic fracturing and water injection weakening consume a lot of water resources , water resources added with chemical reagents are more likely to cause pollution. In addition, when the roof rock layer contains a large amount of clay, it is easy to cause the clay to absorb water and swell, failing to achieve the effect of cracking and caving

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