A device for coal seam penetration by liquid nitrogen and carbon dioxide and an application method thereof

Abstract

The application discloses a device and application method for coal seam penetration by liquid nitrogen and carbon dioxide, and belongs to the technical field of coal seam penetration. The device comprises a carbon dioxide fracturing pipe, one end of the carbon dioxide fracturing pipe is connected with a liquid nitrogen injection pipe, an outer side of a middle part of the liquid nitrogen injection pipe is sleeved with a water seal bag, an exhaust pipe is arranged through the water seal bag, the exhaust pipe is horizontally arranged with the liquid nitrogen injection pipe, a wind pipe connector is arranged at an end of the exhaust pipe away from the carbon dioxide fracturing pipe, a water pipe is further arranged on the water seal bag and communicates with the water seal bag, a water pipe valve and an exhaust pipe valve are respectively arranged on the water pipe and the exhaust pipe, and the liquid nitrogen can dissolve pores, the energy dissipation of coal wall blasting in the initial stage of gas explosion can be reduced, and then the gas explosion can act on a farther distance.

Description

A device and application method for enhancing the permeability of coal seams using a combination of liquid nitrogen and carbon dioxide. Technical Field

[0001] This invention relates to the field of coal seam permeability enhancement technology, specifically to a device and application method for enhancing coal seam permeability using a combination of liquid nitrogen and carbon dioxide. Background Technology

[0002] To eliminate the threat posed by coal and gas outbursts to safe coal mine production, the technology of drilling for gas extraction has emerged. However, the application of single-hole gas extraction in low-permeability coal seams is not significant, and various coal seam permeability enhancement technologies have gradually been applied. Currently, the mainstream permeability enhancement measures include hydraulic methods, gas blasting, and cryogenic permeability enhancement. Cryogenic permeability enhancement, which uses liquid nitrogen to enhance coal seam permeability, has two problems: firstly, the radius of influence of liquid nitrogen is small; secondly, to achieve a good permeability enhancement effect, a large amount of liquid nitrogen needs to be recycled, resulting in high costs. Hydraulic methods waste a lot of water resources and cause water phase pollution. Gas blasting, namely conventional carbon dioxide fracturing, results in a large amount of the impact energy of the fracturing gas being consumed in the early stage when it forms a gas wedge on the coal and rock borehole wall. This is the main problem currently faced. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a device for enhancing the permeability of coal seams by combining liquid nitrogen and carbon dioxide, so as to solve the objective disadvantages of the mainstream permeability enhancement methods in the above-mentioned background art.

[0004] To address the above problems, the present invention provides the following technical solution:

[0005] A device for enhancing the permeability of coal seams using a combination of liquid nitrogen and carbon dioxide; it includes a carbon dioxide fracturing tube; one end of the carbon dioxide fracturing tube is connected to a liquid nitrogen injection tube; a water seal bag is fitted around the outside of the middle part of the liquid nitrogen injection tube; an exhaust pipe is installed through the water seal bag; the exhaust pipe is installed horizontally with the liquid nitrogen injection tube; an air duct connector is installed at the end of the exhaust pipe away from the carbon dioxide fracturing tube; a water pipe is also installed on the water seal bag and communicates with it; a water pipe valve and an exhaust pipe valve are respectively installed on the water pipe and the exhaust pipe.

[0006] Preferably, it also includes a water supply pipe, an air duct, a liquid nitrogen tank, a first pump body, a second pump body, and a drilling rig connected to the mine roadway; wherein the air duct is connected to the air duct connector through a branch pipe; the water supply pipe is connected to the water pipe through the second pump body; and the liquid nitrogen tank is connected to the first pump body and the liquid nitrogen injection pipe inlet in sequence through a pipeline.

[0007] The carbon dioxide fracturing tube and the liquid nitrogen injection tube are connected by threads; and the electro-excitation wire of the carbon dioxide fracturing tube is wrapped around the outside of the liquid nitrogen injection tube with adhesive tape.

[0008] The liquid nitrogen injection pipe includes a pipe body made of hollow steel pipe; an external threaded section is opened on one end of the pipe body, and a nozzle groove is opened on the side wall of the pipe body near the external threaded section; a limiting washer and a pusher are installed in the pipe on the side of the nozzle groove away from the external threaded section; a part of the pusher extends into the nozzle groove, and the pusher is movable when liquid nitrogen is injected into the liquid nitrogen injection pipe.

[0009] The duct connector on the exhaust pipe is connected to the duct via a slot structure.

[0010] The water seal bag is located behind the nozzle groove on the liquid nitrogen injection pipe, and its position does not interfere with the nozzle groove.

[0011] This invention also discloses a method for using a device for enhancing the permeability of coal seams using a combination of liquid nitrogen and carbon dioxide; it includes the following steps:

[0012] S1. First, drill holes in the rock strata inside the roadway using a drilling rig, and then drill into the coal seam to identify the permeable coal seam. After that, withdraw the drill rod from the drilling rig.

[0013] S2. Remove the drill bit from the drilling rig and install the liquid nitrogen and carbon dioxide combined coal seam permeation enhancement device onto the drilling rig, and push it to the coal seam location using the drilling rig; connect the liquid nitrogen to the inlet end of the first pump body, and connect the outlet end of the first pump body to the liquid nitrogen inlet of the liquid nitrogen injection pipe; connect the water supply pipe to the inlet end of the second pump body, and connect the outlet end of the second pump body to the tail end of the water pipe of the water seal bag; after confirming that there are no leaks, open the exhaust pipe valve;

[0014] S3. Open the water pipe valve and start the second pump body. After the water seal bag is filled with water to form a seal, close the water pipe valve and the second pump body. Then start the first pump body to allow liquid nitrogen to flow into the borehole through the nozzle groove of the liquid nitrogen injection pipe. After the liquid nitrogen flows out through the exhaust pipe, close the first pump body and the exhaust pipe valve.

[0015] S4. Wait 2-3 minutes to allow the liquid nitrogen to dissolve the coal surface in the borehole and expand the coal and rock pores before starting the carbon dioxide fracturing device.

[0016] S5. Connect the air pressure pipe connector to the air duct, open the exhaust pipe valve to allow the gas inside the borehole to be discharged from the borehole, reduce the pressure inside the borehole, and at the same time reduce the concentration of gases such as methane, carbon dioxide, and nitrogen by mixing with the fresh air flow in the air duct.

[0017] S6. On-site operators temporarily disconnect the air duct to determine whether there is gas flowing out of the exhaust pipe. If there is no gas flowing out, the air duct is removed and the exhaust pipe valve is closed. The connection between the water pipe and the liquid outlet of the first pump body is disconnected, the water pipe valve is opened to allow water to flow out of the water seal bag, and the sealing is completed. After the entire set of equipment is removed, the drilling permeability of the coal seam is improved.

[0018] Beneficial effects of this invention:

[0019] The advantages of combining liquid nitrogen and carbon dioxide fracturing are as follows: liquid nitrogen first dissolves the coal and rock borehole walls, forming numerous tiny fissures. When carbon dioxide impacts the coal and rock borehole walls, the pores formed by the initial liquid nitrogen dissolution act as gas wedges, reducing the energy consumption of the impacting gas when it first contacts the coal and rock borehole walls. At the same time, the pores formed by dissolution also conform to the principle of shaped charge blasting, thereby extending the effective radius of carbon dioxide gas fracturing of the coal seam. Therefore, researching and using a combined liquid nitrogen and carbon dioxide permeability enhancement coal seam device has important practical significance.

[0020] This invention sprays liquid nitrogen through a nozzle to dissolve the coal and rock borehole walls during use. Then, carbon dioxide impact gas injected by a carbon dioxide fracturing device enhances the permeability of the coal seam, resulting in a wider range of permeability enhancement and facilitating better extraction of gas from low-permeability coal seams. Attached Figure Description

[0021] Figure 1 is a schematic diagram of the structure of the invention device in this embodiment;

[0022] Figure 2 is a schematic diagram of the state of the invention device applied in the mine in this embodiment;

[0023] Figure 3 is a cross-sectional view of the liquid nitrogen injection tube in this embodiment:

[0024] Figure 4 is a schematic diagram of the liquid nitrogen injection tube pusher and limiting washer structure in this embodiment;

[0025] Figure 5 is a three-dimensional structural schematic diagram of the liquid nitrogen injection tube in this embodiment;

[0026] Figure 6 shows the displacement of the pusher head when liquid nitrogen flows inside the liquid nitrogen injection pipe in the structure shown in Figure 3.

[0027] Explanation of reference numerals in the attached diagram: 1. Carbon dioxide fracturing pipe; 2. Liquid nitrogen injection pipe; 3. Exhaust pipe; 4. Water seal bag; 5. Exhaust pipe valve; 6. Air duct connector; 7. Water pipe; 8. Water pipe valve; 9. Push head; 10. Limiting coil; 11. Nozzle slot; 12. First pump body; 13. Water supply pipe; 14. Air duct; 15. Drilling rig; 16. Second pump body; 17. Liquid nitrogen tank; 18. Coal seam; 19. Rock stratum; 20. Roadway. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0029] Example:

[0030] Referring to Figure 1, this embodiment provides a device for enhancing the permeability of coal seams using a combination of liquid nitrogen and carbon dioxide. It includes a carbon dioxide fracturing tube 1; one end of the carbon dioxide fracturing tube 1 is connected to a liquid nitrogen injection tube 2; a water seal bag 4 is fitted around the outside of the middle part of the liquid nitrogen injection tube 2; an exhaust pipe 3 is provided through the water seal bag 4; the exhaust pipe 3 is arranged horizontally with the liquid nitrogen injection tube 2; an air duct connector 6 is provided at the end of the exhaust pipe 3 away from the carbon dioxide fracturing tube 1; a water pipe 7 communicating with the water seal bag 4 is also provided; a water pipe valve 8 and an exhaust pipe valve 5 are respectively provided on the water pipe 7 and the exhaust pipe 3.

[0031] Preferably, the system also includes a water supply pipe 13, an air duct 14, a liquid nitrogen tank 17, a first pump body 12, a second pump body 16, and a drilling rig 15, all connected to the mine roadway. The air duct 14 is connected to the air duct connector 6 via a branch pipe; the water supply pipe 13 is connected to the water pipe 7 via the second pump body 16; and the liquid nitrogen tank 17 is connected sequentially to the inlet of the first pump body 12 and the liquid nitrogen injection pipe 2 via pipelines. The exhaust pipe 3 is used to discharge the mixed gas inside the borehole after fracturing, allowing the borehole pressure to quickly return to normal levels and preventing injury from pressurized gas inside the borehole when the fracturing equipment is removed. Simultaneously, by connecting the air duct 14, the pressure difference between the inside and outside of the borehole can be increased, accelerating gas outflow; and the fresh airflow inside the air duct 14 can neutralize the mixed gas inside the borehole, reaching a safe gas environment threshold.

[0032] The carbon dioxide fracturing tube 1 and the liquid nitrogen injection tube 2 are connected by threads; and the electro-excitation wire of the carbon dioxide fracturing tube 1 is wrapped around the outside of the liquid nitrogen injection tube 2 with adhesive tape.

[0033] The liquid nitrogen injection pipe 2 includes a pipe body made of hollow steel tubing; an external thread section is formed at one end of the pipe body, and a nozzle groove 11 is formed on the side wall of the pipe body near the external thread section; a limiting washer 10 and a pusher 9 are installed in the pipe on the side of the nozzle groove 11 away from the external thread section; a portion of the pusher 9 extends into the nozzle groove 11, and the pusher 9 can move when liquid nitrogen is injected into the liquid nitrogen injection pipe 2. The addition of the pusher 9 allows the flow of liquid nitrogen to push the pusher 9, thereby pushing coal slime or rock fragments, so that liquid nitrogen can effectively flow out of the nozzle 11. The limiting washer 10 limits the movement distance of the pusher 9, preventing the pusher 9 from separating from the liquid nitrogen injection pipe 2 during pipe removal and causing equipment jamming.

[0034] The duct connector 6 on the exhaust pipe 3 is connected to the duct 14 via a slot structure.

[0035] The water seal bag 4 is located behind the nozzle groove 11 on the liquid nitrogen injection pipe 2, and it does not interfere with the nozzle groove 11 in position.

[0036] When using the device of this embodiment, the following process can be referred to:

[0037] S1. Inside the roadway 20, drill holes in the rock strata using drilling rig 15 and drill into the coal seam to identify the permeable coal seam. Then, withdraw the drill rod from drilling rig 15.

[0038] S2. Remove the drill bit from the drilling rig 15 and install the liquid nitrogen and carbon dioxide combined coal seam permeation enhancement device onto the drilling rig 15, and push it to the coal seam position through the drilling rig 15; connect the liquid nitrogen 17 to the inlet end of the first pump body 12, and connect the outlet end of the first pump body 12 to the liquid nitrogen inlet of the liquid nitrogen injection pipe 2; connect the water supply pipe 13 to the inlet end of the second pump body 16, and connect the outlet end of the second pump body 16 to the tail end of the water pipe 7 of the water seal bag 4; after confirming that there are no leaks, open the exhaust pipe valve 5;

[0039] S3. Open the water pipe valve 8 and start the second pump body 16. After the water seal bag 4 is filled with water to form a seal, close the water pipe valve 8 and the second pump body 16. Then start the first pump body 12 to allow liquid nitrogen 17 to flow into the borehole through the nozzle groove 11 of the liquid nitrogen injection pipe 2. After the liquid nitrogen 17 flows out through the exhaust pipe 3, close the first pump body 12 and the exhaust pipe valve 5.

[0040] S4. Wait 2-3 minutes to allow the liquid nitrogen to dissolve the surface of the drilled coal and expand the coal and rock pores before starting the carbon dioxide fracturing device 1. At this time, the carbon dioxide gas will impact the coal wall. Since the coal and rock firmness coefficient has decreased and the coal wall pores have expanded, according to fracture theory, whether the fracture in the coal and rock will extend depends on the stress intensity factor at the fracture tip and the critical fracture toughness value of the fracture. When the stress intensity factor is greater than the critical fracture toughness value, fracture extension will occur. Since the critical fracture toughness value has been reduced by the liquid nitrogen in the early stage, the impact stress of the carbon dioxide gas is unchanged compared with the impact stress of the single carbon dioxide fracturing gas. Therefore, the impact of carbon dioxide fracturing after the liquid nitrogen action will affect a wider range, and the coal seam permeability will be better.

[0041] S5. Connect the air pressure pipe connector 6 to the air duct 14, open the exhaust pipe valve 5 to allow the gas inside the borehole to be discharged from the borehole, reduce the pressure inside the borehole, and at the same time reduce the concentration of gases such as methane, carbon dioxide, and nitrogen by mixing with the fresh air flow in the air duct 14.

[0042] S6. On-site operators temporarily disconnect the air duct to determine whether there is gas flowing out of the exhaust pipe 3. If there is no gas flowing out, the air duct 14 is removed and the exhaust pipe valve 5 is closed. The connection between the water pipe 7 and the liquid outlet of the first pump body 12 is disconnected, and the water pipe valve 8 is opened to allow water to flow out of the water seal bag 4, thus ending the sealing. After the entire set of equipment is removed, the drilling permeability of the coal seam is improved.

[0043] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0044] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A device for enhancing the permeability of coal seams using a combination of liquid nitrogen and carbon dioxide, characterized in that: It includes a carbon dioxide fracturing tube (1); one end of the carbon dioxide fracturing tube (1) is connected to a liquid nitrogen injection tube (2); a water seal bag (4) is fitted on the outer side of the middle part of the liquid nitrogen injection tube (2); an exhaust pipe (3) is installed through the water seal bag (4); the exhaust pipe (3) is installed flush with the liquid nitrogen injection tube (2); a duct connector (6) is installed at the end of the exhaust pipe (3) away from the carbon dioxide fracturing tube (1); a water pipe (7) connected to the water seal bag (4) is also installed; and the water pipe (7) and the exhaust pipe (3) are connected together. The liquid nitrogen injection pipe (2) is equipped with a water pipe valve (8) and an exhaust pipe valve (5); the liquid nitrogen injection pipe (2) includes a pipe body made of hollow steel pipe; an external thread section is opened on one end of the pipe body, and a nozzle groove (11) is opened on the side wall of the pipe body near the external thread section; a limiting washer (10) and a pusher (9) are installed in the pipe on the side of the nozzle groove (11) away from the external thread section; a part of the pusher (9) extends into the nozzle groove (11), and the pusher (9) can move when liquid nitrogen is injected into the liquid nitrogen injection pipe (2).

2. The device for enhancing the permeability of coal seams using a combination of liquid nitrogen and carbon dioxide according to claim 1, characterized in that: It also includes a water supply pipe (13), an air duct (14), a liquid nitrogen tank (17), a first pump body (12), a second pump body (16), and a drilling rig (15) connected to the mine roadway; wherein the air duct (14) is connected to the air duct connector (6) through a branch pipe; the water supply pipe (13) is connected to the water pipe (7) through the second pump body (16); the liquid nitrogen tank (17) is connected to the inlet of the first pump body (12) and the liquid nitrogen injection pipe (2) in sequence through a pipeline.

3. The device for enhancing the permeability of coal seams using a combination of liquid nitrogen and carbon dioxide according to claim 1, characterized in that: The carbon dioxide fracturing tube (1) and the liquid nitrogen injection tube (2) are connected by threads; and the electro-excitation wire of the carbon dioxide fracturing tube (1) is wrapped around the outside of the liquid nitrogen injection tube (2) with adhesive tape.

4. The device for enhancing the permeability of coal seams using a combination of liquid nitrogen and carbon dioxide according to claim 1, characterized in that: The duct connector (6) on the exhaust pipe (3) is connected to the duct (14) through a slot structure.

5. The device for enhancing the permeability of coal seams using a combination of liquid nitrogen and carbon dioxide according to claim 1, characterized in that: The water seal bag (4) is located behind the nozzle groove (11) on the liquid nitrogen injection pipe (2), and it does not interfere with the nozzle groove (11) in position.

6. The method of using the device for combined liquid nitrogen and carbon dioxide permeability enhancement of coal seams according to any one of claims 1 to 5, characterized in that: Includes the following steps: S1. Drill the rock strata inside the roadway (20) using a drilling rig (15) and drill into the coal seam to determine the permeable coal seam. Then, remove the drill rod from the drilling rig (15). S2. Remove the drill bit from the drilling rig (15) and install the liquid nitrogen and carbon dioxide combined permeable coal seam enhancement device onto the drilling rig (15). Push the device to the coal seam location using the drilling rig (15). Connect the liquid nitrogen tank (17) to the inlet end of the first pump body (12), and connect the outlet end of the first pump body (12) to the liquid nitrogen injection pipe (2). Connect the inlet to the liquid nitrogen port; connect the water supply pipe (13) to the inlet of the second pump body (16), and connect the outlet of the second pump body (16) to the tail of the water pipe (7) of the water seal bag (4); after confirming that there are no leaks, open the exhaust pipe valve (5); S3, open the water pipe valve (8) and start the second pump body (16), and close the water pipe valve (8) and the second pump body (16) after the water seal bag (4) is filled with water to form a seal; then start the first pump body (12) to allow the liquid nitrogen tank (17) to be filled with liquid nitrogen. The nozzle groove (11) of the inlet pipe (2) flows into the borehole; until the liquid nitrogen in the liquid nitrogen tank (17) flows out through the exhaust pipe (3), the first pump body (12) and the exhaust pipe valve (5) are closed; S4, wait 2~3 minutes to allow the liquid nitrogen to dissolve the coal surface in the borehole and expand the coal and rock pores, then start the carbon dioxide fracturing pipe (1); S5, connect the air pressure pipe connector (6) to the air pipe (14), open the exhaust pipe valve (5) to allow the gas inside the borehole to be discharged from the borehole, and reduce the pressure. The low pressure inside the hole is mixed with the fresh air flow in the air duct (14) to reduce the concentration of methane, carbon dioxide and nitrogen gas; S6, the on-site operator determines whether there is gas flowing out of the exhaust pipe (3) by temporarily disconnecting the air duct; if there is no gas flowing out, the air duct (14) is removed and the exhaust pipe valve (5) is closed; the connection between the water pipe (7) and the liquid outlet of the first pump body (12) is disconnected, the water pipe valve (8) is opened to allow water to flow out of the water seal bag (4) and the sealing is ended; after the entire set of equipment is removed, the drilling permeability of the coal seam is increased.

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