Method for injecting high-temperature nitrogen gas for improving coal body permeability after liquid nitrogen gasification circulation

Abstract

The invention discloses a method for injecting high-temperature nitrogen gas for improving coal body permeability after liquid nitrogen gasification circulation. A gas extraction drill hole is constructed inside a working face roadway; magnetic water is injected into the gas extraction drill hole through a magnetic water injection pipe, and then the magnetic water permeates into a coal body around the gas extraction drill hole; the gas extraction drill hole is filled with liquid nitrogen inside a liquid nitrogen tank; the liquid nitrogen is frozen to permeate into the magnetic water inside the coal body and gasified into nitrogen gas, and the pressure inside the gas extraction hole is increased; the gasified nitrogen gas inside the gas extraction drill hole enters a nitrogen gas heating tank to be collected; the step of freeze thawing is repeatedly executed, and repeated liquid nitrogen gasification circulation is implemented on the gas extraction drill hole; the nitrogen gas collected inside the nitrogen gas heating tank is heated, high temperature nitrogen gas is injected into the gas extraction drill hole, and the coal body is subjected to fracturing through the high temperature nitrogen gas. The coal body is made to generate a weakening region, and then the coal body is subjected to fracturing and permeability improvement, so that the heat storage time of nitrogen gas is shortened, and meanwhile the coal body permeability improvement range is enlarged.

Description

technical field [0001] The invention relates to a method for increasing coal gas permeability by using nitrogen, in particular to a method for injecting high-temperature nitrogen gas after a liquid nitrogen gasification cycle to increase coal gas permeability. Background technique [0002] The structure of coal seams in my country is complex, and the permeability is generally low. Many high-gassy coal bodies are low-permeability coal bodies. At the same time, with the gradual increase of coal mining depth, the stress increases, which further reduces the gas permeability of coal. In mines with poor air permeability, the effect of gas pre-pumping of coal without unloading pressure is often not ideal, so it is particularly important to increase the air permeability of coal. At present, hydraulic measures, such as hydraulic fracturing and hydraulic cutting, are mainly used in the process of increasing coal gas permeability in my country. When the hydraulic anti-permeability me...

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Problems solved by technology

When the hydraulic anti-permeability measures are adopted, the coal body is easily muddy after being soaked in water, which will block the gas flow channel, and the range of anti-permeability is limited by the surface tension of the water; The crack initiation pressure is required to be at least 25MPa, so under the action of high-pressure water, it is very easy to induce coal and gas outburst, which brings serious safety hazards to the efficient production of coal mines

[0003] The Chinese patent with the application number 201210056438.2 discloses a method of injecting nitrogen under the coupling effect of temperature and pressure to enhance the drainage of gas. Under the coupling effect of nitrogen, the coal body is enhanced. The specific principle is that the nitrogen pressure opens small-scale cracks in the coal body, so that the original closed cracks in the coal body expand and the cracks expand further. After the permeability enhancement, the gas will be discharged from the coal body through the crack channel. Although the method will not block the gas flow channel, in the process of increasing the gas permeability of the coal body, the nitrogen needs a long heat storage time to cause the coal body to rupture and increase the permeability. limited questions

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