Liquid-nitrogen circulation cold-shock permeability increasing method based on multi-parameter monitoring

Abstract

The invention discloses a liquid-nitrogen circulation cold-shock permeability increasing method based on multi-parameter monitoring. A video monitoring lens is used for shooting and monitoring the size of bubbles generated in liquid nitrogen in a layer-through borehole and the flow rate of generated bubbles in real time and feeding the size of the bubbles and the flow rate back to a monitoring control center for storage; a mass sensor monitor the mass loss rate of liquid nitrogen in the layer-through borehole in real time and feeds the mass loss rate back to the monitoring control center for storage; and a gas monitoring device detects gas pressure, gas flow and gas temperature in a pressure relief pipe in real time and feeds the gas pressure, the gas flow and the gas temperature back to the monitoring control center for storage; after one-time cracking is completed, a SF6 gas detector, an acoustic wave transmitter and an acoustic wave receiver are used for detecting the permeability increasing cracking effect, that is, the acoustic wave speed can be used for detecting the number of cracks generated after permeability increasing, and the SF6 gas can be used for detecting the mutualconnectivity of the cracks. By monitoring the data, the cold shock of liquid nitrogen, the expansion pressure of phase change gas and cracking of a coal body by means of frost heaving pressure of moisture in the cracks are achieved, and the permeability increasing effect can be effectively monitored.

Description

technical field [0001] The invention relates to a coal seam anti-permeability method, in particular to a liquid nitrogen circulation cold shock anti-permeability method based on multi-parameter monitoring. 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 wells h...

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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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