A coal seam permeability enhancement method using liquid nitrogen cold shock and phase change gas circulation damage

Abstract

The invention discloses a coal seam permeability enhancement method utilizing liquid nitrogen cold impact and phase change gas cycle damage. Firstly, a layer-penetrating drilling hole is drilled into the coal seam through the rock layer in the roadway, and the coal seam is cut in the layer-penetrating drilling hole. A plurality of cracks perpendicular to the piercing borehole are produced, and the liquid nitrogen injection pipe and the exhaust pipe are extended into the piercing borehole, and the exhaust pipe is connected to two gas pipelines equipped with a safety valve and a spherical valve respectively. Among them, the spherical valve switches and controls the discharge of nitrogen gas when liquid nitrogen is injected into the piercing hole; when the spherical valve is closed, the threshold of the safety valve is set, so that the safety valve can control the pressure in the piercing hole. When the air pressure in the borehole exceeds the threshold, the safety valve opens to discharge the internal nitrogen to relieve the pressure, and the safety valve automatically closes after the pressure is relieved. It can ensure the rapid and continuous injection of liquid nitrogen into the drilled hole, and at the same time use the cold shock of liquid nitrogen, the expansion pressure of phase change gas and the frost heaving pressure of water in the crack to crack the coal body, effectively ensuring the anti-permeability effect.

Description

technical field [0001] The invention relates to a coal seam anti-permeability method, in particular to a coal seam anti-permeability method utilizing liquid nitrogen cold shock and phase change gas cycle damage. Background technique [0002] High-gas coal seams account for 50% to 70% of my country's coal mines. With the continuous increase of mining depth, the pressure of coal seams and gas pressure are constantly increasing, and the gas problem is becoming more and more serious. Gas explosion and gas outburst have become problems that need to be solved urgently in mine safety production. . Most of the coal seams in our country are high-gas and low-permeability coal seams. Existing methods such as hydraulic fracturing, hydraulic slotting and pre-splitting blasting are not enough to overcome the problems of high adsorption and low permeability of coal seam gas. Low, small drainage volume, unsatisfactory drainage effect. At present, the way of liquid nitrogen injection into w...

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Problems solved by technology

However, in the actual test, it was found that the existing liquid nitrogen injection methods and patents have the following significant problems: due to the severe gasification problem in the liquid nitrogen injection process, the gasification and expansion of liquid nitrogen into pure nitrogen at 21 °C will make it The volume has an expansion rate of 696 times, which means that at the initial stage of liquid nitrogen injection, the borehole has been filled with heated and gasified nitrogen before the liquid nitrogen has flowed to the coal body, and the pressure in the borehole is very high. It quickly reached tens of MPa, and the poor stability of liquid nitrogen led to the low effective pressure and flow rate that the well injection pump could provide, which was more than 10 times different from the expansion pressure of the gas generated in the borehole, which eventually led to Liquid nitrogen cannot be injected into boreholes in large quantities quickly, and liquid nitrogen can only be injected into boreholes with a very small flow rate, but in this way, the advantages of liquid nitrogen anti-reflection cannot be exerted (that is, the impact force of volume expansion during gasification of liquid nitrogen and the impact of liquid nitrogen Low temperature will superimpose the freezing effect of coal body, and once the liquid nitrogen is injected with a small flow rate, it will lose the impact force caused by rapid expansion; at the same time, it will greatly increase the time required for coal seam anti-reflection and cannot guarantee the effect of anti-reflection

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