WO2021120701A1

WO2021120701A1 - Coal seam permeability increasing method utilizing cyclic damage of liquid nitrogen cold impact and phase change gas

Info

Publication number: WO2021120701A1
Application number: PCT/CN2020/113351
Authority: WO
Inventors: 翟成; 张建国; 吕有厂; 丛钰洲; 李喜员; 陈振宇; 刘庆军; 徐吉钊; 孙勇; 郑仰峰; 唐伟
Original assignee: 翟成
Priority date: 2019-12-20
Filing date: 2020-09-04
Publication date: 2021-06-24
Also published as: CN111119829B; CN111119829A

Abstract

Disclosed is a coal seam permeability increasing method utilizing cyclic damage of liquid nitrogen cold impact and phase change gas. According to the method, a through-layer borehole (8) running through a rock layer to a coal seam (1) is first drilled in a tunnel; a plurality of cracks perpendicular to the through-layer borehole (8) are cut from the coal seam (1) in the through-layer borehole (8); a liquid nitrogen injection pipe (6) and an exhaust pipe (9) are inserted into the through-layer borehole (8); the exhaust pipe (9) is connected to two gas pipelines respectively provided with a safety valve (5) and a ball valve (4); the ball valve (4) as a switch controls the discharge of nitrogen when liquid nitrogen is injected into the through-layer borehole (8); after the ball valve (4) is closed, a threshold of the safety valve (5) is set so that the safety valve (5) controls the pressure in the through-layer borehole (8); when air pressure in the through-layer borehole (8) exceeds the threshold, the safety valve is opened so that the internal nitrogen is discharged for pressure relief, and the safety valve (5) is automatically closed after pressure relief. The method can ensure rapid and continuous injection of liquid nitrogen into the through-layer borehole (8); moreover, the cold impact of liquid nitrogen, the expansion pressure of phase change gas, and the frost heaving pressure of moisture in the cracks are utilized to crack the coal seam, and the permeability increasing effect is effectively ensured.

Description

Coal seam anti-reflection method using liquid nitrogen cold shock and phase change gas cycle damage

Technical field

The invention relates to a coal seam anti-reflection method, in particular to a coal seam anti-reflection method using liquid nitrogen cold shock and phase change gas circulation damage.

Background technique

High gas coal seams in my country's coal mines account for 50% to 70%. With the continuous increase of mining depth, coal seam pressure and gas pressure are constantly increasing. The gas problem is becoming more and more serious. Gas explosion and gas outburst have become urgent problems to be solved in mine safety production. . The coal seams in my country are mostly high gas and low gas permeability coal seams. The existing hydraulic fracturing, hydraulic slitting and pre-splitting blasting methods are not enough to overcome the problems of high gas adsorption and low permeability of coal seams, which makes the current concentration of gas drainage Low, small drainage volume, unsatisfactory drainage effect. At present, the method of liquid nitrogen injection has attracted wide attention due to its multiple mechanisms of cold shock, phase change gas expansion force, and water ice phase change frost heave force. However, in actual tests, it was found that the existing liquid nitrogen injection methods and patents all have the following significant problems: due to the severe gasification problem in the liquid nitrogen injection process, the liquid nitrogen gas will be expanded to pure nitrogen at 21°C. The volume has an expansion rate of 696 times, which means that in the initial stage of liquid nitrogen injection, when the liquid nitrogen has not flowed to the position of the coal body, the borehole has been filled with heated gasified nitrogen and the pressure continues to rise. The pressure in the borehole is very high. It quickly reaches dozens of MPa, and because of its poor stability, the effective pressure and flow rate provided by the injection pump are not high due to the poor stability of liquid nitrogen, which is more than 10 times different from the expansion pressure of the gas generated in the borehole. Liquid nitrogen cannot be injected into the borehole quickly and in large quantities. It can only be injected into the borehole at a very small flow rate. However, the advantages of liquid nitrogen cannot be used in this way (that is, the impact of the volume expansion during liquid nitrogen gasification and the impact of liquid nitrogen). Low temperature has superimposed effects on coal freezing, and once the small flow of liquid nitrogen is injected, it will lose the impact of rapid expansion and differential generation); at the same time, it will greatly increase the time required for coal seam anti-reflection and cannot guarantee the anti-reflection effect.

Summary of the invention

In view of the above-mentioned problems in the prior art, the present invention provides a method for anti-reflection of coal seam using liquid nitrogen cold impact and phase change gas circulation damage, which can ensure the rapid and continuous injection of liquid nitrogen into the through-bed borehole while using liquid nitrogen. The cold shock, the expansion pressure of the phase change gas and the frost heave pressure of the moisture in the crack crack the coal, effectively ensuring the anti-reflection effect.

In order to achieve the above-mentioned object, the technical solution adopted by the present invention is: a coal seam anti-reflection method using liquid nitrogen cold shock and phase change gas circulation damage, the specific steps are:

A. Set up at least one through-layer borehole in the roadway, which penetrates the rock layer and extends into the coal seam;

B. Use hydraulic slitting equipment to penetrate the through-bed drilling to reach the coal seam, and cut multiple disc-shaped cracks in the coal seam at equal intervals in the direction perpendicular to the through-bed drilling centered on the through-bed drilling; Full contact with the coal body after liquid nitrogen injection to achieve better cracking and anti-reflection effects;

C. Extend one end of the liquid nitrogen injection pipe and one end of the exhaust pipe into the penetration borehole to reach the coal seam, and then seal the liquid nitrogen injection pipe and the exhaust pipe with the strata section of the penetration borehole; the other end of the exhaust pipe is connected to three Through pipe, the other two ports of the three-way pipe are respectively connected to two gas pipelines; the two gas pipelines are respectively equipped with safety valves and spherical valves;

D. Connect the other end of the liquid nitrogen injection pipe to the liquid nitrogen pump, start the liquid nitrogen pump and open the spherical valve. The liquid nitrogen is injected into the through-layer borehole through the liquid nitrogen injection pipe, and enters the disc-shaped cracks, and the liquid nitrogen is absorbed. The heat causes the temperature of the coal body to decrease rapidly, and the water in the coal body freezes and expands to impose icing expansion force on the coal body to crack; at the same time, the gasified nitrogen volume rapidly expands to impose gas expansion force on the coal body to crack, and penetrate the borehole. The air pressure increases rapidly, and nitrogen is discharged from the gas pipeline where the spherical valve is located through the exhaust pipe to the penetration borehole, thereby reducing the air pressure in the penetration borehole so that the liquid nitrogen is continuously injected;

E. When liquid nitrogen is continuously injected into the gas pipeline where the spherical valve is located, when liquid nitrogen flows out, stop the liquid nitrogen pump and close the spherical valve, set the opening threshold of the safety valve, and the liquid nitrogen continues to vaporize and expand in the borehole. , Apply gas expansion force to the coal to crack. When the air pressure in the borehole exceeds the set opening threshold, the safety valve opens. At this time, the nitrogen in the borehole is discharged from the gas pipeline where the safety valve is located. Drill through the strata to reduce the air pressure inside the borehole. When the air pressure is lower than the set opening threshold, the safety valve will be closed. At this time, the liquid nitrogen will continue to gasify and expand in the drill through the strata, and apply again to the coal. The gas expansion force cracks until the air pressure in the penetration borehole exceeds the set opening threshold, the safety valve is opened to relieve the pressure, and the cycle is repeated, and the coal body is cracked by the gas expansion force for many times until the penetration borehole. After the liquid nitrogen is completely vaporized, the safety valve will no longer be opened; the cracking and anti-reflection process of the penetration drilling is completed;

F. Two gas drainage boreholes are drilled into the coal seam on both sides of the penetration borehole, and the two gas drainage boreholes pass through each disc-shaped crack; finally, the coal seam is carried out through two gas drainage boreholes Gas drainage

G. After completing the gas drainage at this location, repeat steps A to F at another location in the roadway at a certain distance to perform the coal seam penetration enhancement and gas drainage at this location, and so on, until the entire roadway is completed. Drain.

Further, the outer surface of the liquid nitrogen injection pipe is wrapped with a heat insulation layer. Reduce the degree of gasification of liquid nitrogen when it is injected through the liquid nitrogen injection pipe into the penetration borehole, and ensure the amount of liquid nitrogen entering the penetration borehole, thereby improving its cracking effect.

Further, the opening threshold of the safety valve is 30 MPa.

Compared with the prior art, the present invention firstly drills through the rock layer into the coal seam in the roadway, and uses hydraulic slitting equipment to cut the coal seam at equal intervals and perpendicular to the through-layer borehole. Extend the liquid nitrogen injection pipe and exhaust pipe into the penetration borehole, and seal the rock section of the penetration borehole. The exhaust pipe outside the penetration borehole is equipped with a three-way pipe. The other two ports of the pipe are respectively connected to two gas pipelines, and the two gas pipelines are respectively equipped with a safety valve and a spherical valve. Among them, the spherical valve switches and controls the discharge of nitrogen gas when liquid nitrogen is injected into the penetration borehole, so as to control the speed of liquid nitrogen injection into the penetration borehole; when the spherical valve is closed, the threshold value of the safety valve is set, so that the safety valve crosses the hole. The pressure in the borehole is controlled. When the air pressure in the borehole exceeds the threshold, the safety valve is opened to discharge the internal nitrogen to relieve the pressure, and the safety valve is automatically closed after the pressure is relieved. This method makes full use of the cold impact of liquid nitrogen, the expansion pressure of the phase change gas, and the frost heave pressure of the residual moisture in the cracks to crack the coal. The effective fracture area is wide, especially the expansion pressure of the phase change gas increases with the liquid The continuous gasification of nitrogen and the multiple opening of the safety valve enable the air pressure inside the borehole to repeatedly reach the threshold of the safety valve, so that the coal can be repeatedly expanded and damaged, and the fracture network of the coal can be enlarged. At the end of the fracture, two gas drainage boreholes were drilled in the surrounding area for gas drainage. The invention can ensure the rapid and continuous injection of liquid nitrogen into the penetration borehole, and at the same time use the cold impact of liquid nitrogen, the expansion pressure of the phase change gas and the frost heave pressure of the moisture in the cracks to crack the coal, effectively ensuring the anti-reflection effect .

Description of the drawings

Fig. 1 is a schematic diagram of the construction cloth erected body of the present invention.

In the picture: 1. Coal seam, 2. Disc-shaped crack, 3. Rock formation, 4. Spherical valve, 5. Safety valve, 6. Liquid nitrogen injection pipe, 7. Gas drainage hole, 8. Cross-layer drilling, 9. ,exhaust pipe.

Detailed ways

The present invention will be further explained below.

As shown in Figure 1, the specific steps of the present invention are:

A. Two drill holes 8 are drilled in the roadway, and the two drill holes penetrate the rock layer 3 into the coal seam 1;

B. Use hydraulic slitting equipment to extend the penetration borehole 8 into the coal seam 1, and cut out a plurality of discs in the coal seam 1 at medium intervals in the direction perpendicular to the penetration borehole 8 with the penetration borehole 8 as the center. Crack 2; it is used to make full contact with the coal body after the liquid nitrogen is injected, so as to achieve a better effect of cracking and anti-reflection;

C. Extend one end of the liquid nitrogen injection pipe 6 and the exhaust pipe 9 into the penetration borehole 8 to reach the coal seam, and then seal the rock interval between the liquid nitrogen injection pipe and the exhaust pipe 9 and the penetration borehole 8; The other end of the pipe 9 is connected to a three-way pipe, and the other two ports of the three-way pipe are respectively connected to two gas pipelines; the two gas pipelines are respectively equipped with a safety valve 5 and a spherical valve 4;

D. Connect the other end of the liquid nitrogen injection pipe 6 to the liquid nitrogen pump, start the liquid nitrogen pump and open the spherical valve 4, the liquid nitrogen is injected through the liquid nitrogen injection pipe 6 into the penetration borehole 8 and enters each disc-shaped crack 2 , The heat absorption of liquid nitrogen gas makes the temperature of the coal body drop rapidly, the moisture in the coal body freezes and expands to impose icing expansion force on the coal body to crack; at the same time, the rapid expansion of the gasified nitrogen volume exerts gas expansion force on the coal body to crack. The air pressure in the penetration borehole 8 increases rapidly, and the nitrogen gas is discharged from the gas pipeline where the spherical valve 4 is located through the exhaust pipe 9 to the penetration borehole 8, thereby reducing the pressure in the penetration borehole 8 to make the liquid nitrogen continue injection;

E. When liquid nitrogen is continuously injected into the gas pipeline where the spherical valve 4 is located, when liquid nitrogen flows out, stop the liquid nitrogen pump and close the spherical valve 4, set the opening threshold of the safety valve 5, and the liquid nitrogen is in the penetration hole 8 Continue to gasify and expand, and apply gas expansion force to the coal to crack. When the air pressure in the penetration borehole 8 exceeds the set opening threshold, the safety valve 5 opens. At this time, the nitrogen in the penetration borehole 8 flows from the safety valve The gas pipeline where 5 is located is discharged from the penetration borehole 8, so that the air pressure inside the penetration borehole 8 is reduced. When the pressure is lower than the set opening threshold, the safety valve 5 is closed. At this time, the liquid nitrogen is in the penetration borehole. Gasification and expansion continues in 8, and gas expansion force is applied again to the coal to crack until the air pressure in the borehole 8 exceeds the set opening threshold, and the safety valve 5 is opened to relieve the pressure. This cycle is repeated, and the coal is more Perform gas expansion force cracking again until the liquid nitrogen in the penetration borehole 8 is completely vaporized and the safety valve 5 no longer opens; complete the cracking and antireflection process of the penetration borehole 8;

F. Drill two gas drainage boreholes 7 toward coal seam 1 on both sides of the penetration borehole 8, and both gas drainage boreholes 7 pass through each disc-shaped crack 2; finally pass through two gas drainage Drill hole 7 for gas drainage in the coal seam;

Further, the outer surface of the liquid nitrogen injection pipe 6 is wrapped with a heat insulation layer. The degree of gasification of liquid nitrogen when it is injected into the penetration borehole through the liquid nitrogen injection pipe 6 is reduced, and the amount of liquid nitrogen entering the penetration borehole 8 is ensured, thereby improving its cracking effect.

Further, the opening threshold of the safety valve 5 is 30 MPa.

Claims

A coal seam anti-reflection method using liquid nitrogen cold shock and phase change gas cycle damage is characterized in that the specific steps are:

A. Set up at least one through-layer borehole in the roadway, which penetrates the rock layer and extends into the coal seam;

B. Use hydraulic slitting equipment to penetrate the through-bed drilling to reach the coal seam, and cut multiple disc-shaped cracks in the coal seam at equal intervals in the direction perpendicular to the through-bed drilling centered on the through-bed drilling;

C. Extend one end of the liquid nitrogen injection pipe and one end of the exhaust pipe into the penetration borehole to reach the coal seam, and then seal the liquid nitrogen injection pipe and the exhaust pipe with the strata section of the penetration borehole; the other end of the exhaust pipe is connected to three Through pipe, the other two ports of the three-way pipe are respectively connected to two gas pipelines; the two gas pipelines are respectively equipped with safety valves and spherical valves;

D. Connect the other end of the liquid nitrogen injection pipe to the liquid nitrogen pump, start the liquid nitrogen pump and open the spherical valve. The liquid nitrogen is injected into the through-layer borehole through the liquid nitrogen injection pipe, and enters the disc-shaped cracks, and the liquid nitrogen is absorbed. The heat causes the temperature of the coal body to decrease rapidly, and the water in the coal body freezes and expands to impose icing expansion force on the coal body to crack; at the same time, the gasified nitrogen volume rapidly expands to impose gas expansion force on the coal body to crack, and penetrate the borehole. The air pressure increases rapidly, and nitrogen is discharged from the gas pipeline where the spherical valve is located through the exhaust pipe to the penetration borehole, thereby reducing the air pressure in the penetration borehole so that the liquid nitrogen can be continuously injected;

E. When liquid nitrogen is continuously injected into the gas pipeline where the spherical valve is located, when liquid nitrogen flows out, stop the liquid nitrogen pump and close the spherical valve, set the opening threshold of the safety valve, and the liquid nitrogen continues to vaporize and expand in the borehole. , Apply gas expansion force to the coal to crack. When the air pressure in the borehole exceeds the set opening threshold, the safety valve opens. At this time, the nitrogen in the borehole is discharged from the gas pipeline where the safety valve is located. Drill through the strata to reduce the air pressure inside the borehole. When the air pressure is lower than the set opening threshold, the safety valve will be closed. At this time, the liquid nitrogen will continue to gasify and expand in the drill through the strata, and apply again to the coal. The gas expansion force cracks until the air pressure in the penetration borehole exceeds the set opening threshold, the safety valve is opened to relieve the pressure, and the cycle is repeated, and the coal body is cracked by the gas expansion force for many times until the penetration borehole. After the liquid nitrogen is completely vaporized, the safety valve will no longer be opened; the cracking and anti-reflection process of the penetration drilling is completed;

F. Two gas drainage boreholes were drilled into the coal seam on both sides of the penetration borehole, and the two gas drainage boreholes passed through each disc-shaped crack; finally, the coal seam was carried out through two gas drainage boreholes. Gas drainage

G. After completing the gas drainage at this location, repeat steps A to F at another location in the roadway at a certain distance to perform the coal seam penetration enhancement and gas drainage at this location, and so on, until the entire roadway is completed. Drain.
The method for anti-reflection of coal seam using liquid nitrogen cold shock and phase change gas circulation damage according to claim 1, wherein the outer surface of the liquid nitrogen injection pipe is wrapped with a heat insulation layer.
The method for anti-reflection of coal seam using liquid nitrogen cold shock and phase change gas circulation damage according to claim 1, wherein the opening threshold of the safety valve is 30 MPa.