Method for efficiently improving permeability of coal body utilizing liquid nitrogen-hot gas cold and hot cycle impact

Abstract

The invention discloses a method for efficiently improving the permeability of a coal body by utilizing liquid nitrogen-hot gas cold and hot cycle impact. Liquid nitrogen is injected and gasified forabsorbing heat to quickly reduce the temperature of the coal body, and water in the coal body is iced and expanded to apply icing expansive force to the coal body for cracking; meanwhile, the gasifiednitrogen rapidly expands in volume to apply gas expansion force to the coal body for cracking, the gas pressure in a drill hole is rapidly increased, and the nitrogen is exhausted through an exhaustpipe; then, after liquid nitrogen injection is stopped, the liquid nitrogen is continuously gasified and expanded in the layer-crossing drill hole to apply gas expansion force to the coal body for cracking, and the gasified nitrogen flows back and is recycled, so that subsequent repeated use is facilitated; hot steam is injected to apply gas impact force to the coal body for cracking, meanwhile, the temperature of the coal body is rapidly increased, and the coal body is cracked through the temperature difference; then the hot steam is discharged out of the layer-crossing drill hole, so that the gas pressure in the layer-crossing drill hole is reduced, and the hot steam can be continuously injected; and the steps are repeated for cycle to carry out cold and hot alternation to impact the coal body, therefore, the permeability improvement time is effectively shortened, and the permeability improvement effect is ensured.

Description

technical field [0001] The invention relates to a coal seam anti-permeability method, in particular to a high-efficiency anti-permeability method for coal by using liquid nitrogen-hot air cold and heat cycle impact. 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 in...

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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 superimposes the freezing effect of coal, and once the liquid nitrogen is injected with a small flow rate, it will lose the impact force generated 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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