A system and method for enhancing gas extraction in low-permeability coal seams by injecting gas to increase permeability

Abstract

The present invention discloses a gas injection permeability enhancement and low-permeability coal seam gas extraction system, comprising a gas injection and sealing assembly, a drainage and sealing assembly, a pressurizing assembly, a gas injection assembly, and a drainage assembly. The low-permeability coal seam is provided with a gas injection hole and a drainage hole, a gas injection screen is provided in the gas injection hole, one end of the gas injection screen is connected to the gas injection pipe, the other end of the gas injection pipe is provided with a gas injection pipeline and a drainage assembly in parallel, the other end of the gas injection pipeline is provided with a pressurizing assembly, the other end of the pressurizing assembly is connected to the gas injection assembly via a first pipeline, and the gas injection and sealing assembly is used to achieve sealing of the gas injection hole after the gas injection screen is placed. A gas injection and permeability enhancement and gas extraction method for low-permeability coal seam gas extraction is also disclosed. The system can effectively increase the internal gas pressure of the coal body, increase the spacing between cracks, and accelerate gas desorption within the matrix by utilizing the adsorption differences of different gases by the coal matrix, providing sufficient power and a reliable channel for gas migration within the coal seam, thereby ensuring efficient gas extraction.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal seam gas extraction devices, and in particular relates to a system and method for enhancing gas extraction in low-permeability coal seams by injecting gas to increase permeability. Background Art

[0002] my country's coal seams are complex in geological structure, with low-permeability coal seams accounting for 95% of all mined coal seams. Gas control in low-permeability coal seams is challenging, and conventional drilling extraction struggles to achieve acceptable gas extraction within the specified timeframe. Underground gas drilling extraction processes exhibit rapid gas flow attenuation, easy closure of gas-connecting fissures, and time-consuming gas removal, seriously impacting mining safety. Blasting permeability enhancement technology uses blasting energy to fracture the coal, creating a network of fractures and fissures, thereby increasing the permeability of the coal seam. While this achieves a certain degree of permeability enhancement, the internal pressure of the low-permeability coal seam remains unchanged, preventing efficient desorption of adsorbed gas within the matrix, and resulting in a rapid decline in extraction efficiency. Furthermore, over 50% of low-permeability coal seams are soft, powdery, and highly water-sensitive. Hydraulic fracturing not only decompresses and absorbs energy from the loose coal mass, but also easily transforms the coal into mud upon contact with water, blocking flow channels. At present, various permeability enhancement methods or technologies for low-permeability coal seams have poor versatility, especially efficient permeability enhancement of low-permeability and soft coal seams remains a difficult problem in the industry. Summary of the Invention

[0003] Based on the low pressure difference and low gas flow rate inside low-permeability coal seams, the present invention proposes a gas injection and permeability-enhanced low-permeability coal seam gas extraction system, which can effectively increase the gas pressure inside the coal body, increase the spacing between cracks, and utilize the differences in the adsorption of different gases by the coal matrix to accelerate the desorption of gas within the matrix, providing sufficient power and reliable channels for gas migration within the coal seam, ensuring efficient gas extraction.

[0004] To this end, the technical solution adopted by the present invention is: a gas injection permeability enhancement and low-permeability coal seam gas extraction system, comprising a gas injection and sealing assembly, an extraction and sealing assembly, a pressurizing assembly, a gas injection assembly and an extraction assembly, wherein a gas injection hole and an extraction hole are provided in the low-permeability coal seam, a gas injection screen is provided in the gas injection hole, one end of the gas injection screen close to the gas injection hole orifice is connected to the gas injection pipe, a first multi-function control valve is provided on the gas injection pipe, a gas injection pipeline and an extraction assembly are provided in parallel at the other end of the gas injection pipe, a pressurizing assembly is provided at the other end of the gas injection pipeline, the other end of the pressurizing assembly is connected to the gas injection assembly through a first pipeline, a first control valve is provided on the first pipeline, and a gas injection control valve and a gas injection pressure gauge are provided on the gas injection pipeline, and the gas injection and sealing assembly is used to achieve the sealing of the gas injection hole after the gas injection screen is placed;

[0005] An extraction screen pipe is provided in the extraction hole, and one end of the extraction screen pipe close to the extraction hole opening is connected to the extraction pipe. A second multifunctional control valve is provided on the extraction pipe. An extraction assembly is provided at the other end of the extraction pipe. The extraction sealing assembly is used to seal the extraction hole after the extraction screen pipe is placed in.

[0006] As a preferred option in the above scheme, the gas injection sealing assembly includes a first grouting bag, a second grouting bag and a liquid injection bag, a first slurry connecting pipe is provided between the first grouting bag and the second grouting bag, the first grouting bag and the second grouting bag are spaced apart and sleeved on the gas injection screen tube, the second grouting bag is provided with a first grouting pipe for injecting slurry into the first grouting bag and the second grouting bag, the liquid injection bag is sleeved at the connection position between the gas injection screen tube and the gas injection pipe, and the liquid injection bag is provided with a liquid injection pipe for injecting liquid into the liquid injection bag.

[0007] Further preferably, the boosting assembly includes a pneumatic booster pump and an air storage tank, the pneumatic booster pump and the air storage tank are connected by a second pipeline, a gas parameter meter is provided in the air storage tank, the pneumatic booster pump is connected to the compressed air system through a boosting pneumatic pipeline, an exhaust pipe is provided on the pneumatic booster pump, a boosting pneumatic control valve is provided on the boosting pneumatic pipeline, the compressed air system is also connected to the gas injection pipeline through a drive pipeline, and a drive control valve is provided on the drive pipeline.

[0008] Further preferably, the gas injection assembly includes a carbon dioxide tank and a nitrogen tank, the carbon dioxide tank is connected to the first pipeline through a third pipeline, the nitrogen tank is connected to the first pipeline through a fourth pipeline, the third pipeline is provided with a third control valve, the fourth pipeline is provided with a fourth control valve, the first pipeline is also provided with an exhaust pipeline, and the exhaust pipeline is provided with an exhaust control valve.

[0009] Further preferably, the extraction component includes an extraction pipeline, on which a gas-liquid separation component and a gas collection component are sequentially arranged, a multi-function parameter meter is arranged at the other end of the gas collection component, an extraction pressure gauge and an extraction control valve located between the gas-liquid separation component and the gas collection component are arranged on the extraction pipeline, and the other ends of the two extraction pipelines are connected to the extraction system.

[0010] Further preferably, the extraction and sealing assembly includes a third grouting bag and a fourth grouting bag, a second slurry connecting pipe is provided between the third grouting bag and the fourth grouting bag, the third grouting bag and the fourth grouting bag are spaced apart and sleeved on the extraction screen pipe, and the fourth grouting bag is provided with a second grouting pipe for injecting slurry into the third grouting bag and the fourth grouting bag.

[0011] A method for enhancing gas extraction in low-permeability coal seams by injecting gas to increase permeability is also disclosed. The method is based on the above-mentioned extraction system and includes the following steps:

[0012] S1: device connection;

[0013] Construct gas injection holes and extraction holes in the target coal seam, then place the gas injection screen and extraction screen in the holes accordingly, connect the extraction screen to the extraction pipe, connect the gas injection screen to the gas injection pipe, and then seal the gas injection hole with the gas injection sealing assembly, and seal the extraction hole with the extraction sealing assembly;

[0014] S2: displacement gas injection;

[0015] Open the first multi-function control valve, the gas injection control valve, and the first control valve. Pressurize the gas through the gas injection assembly and the booster assembly and then let it flow into the gas injection hole along the gas injection pipeline. When the gas injection pressure gauge drops significantly, stop the gas injection. First inject nitrogen and then carbon dioxide. After the gas injection is completed, close the gas injection control valve and the first control valve.

[0016] S3: gas injection and drainage;

[0017] Through two extraction components, the gas in the gas injection hole and the extraction hole is extracted by negative pressure. During the extraction process, the residual gas pressure and residual gas content of the coal seam are tested. When the requirements are met, the free carbon dioxide in the gas injection hole is driven out. If the residual gas pressure and residual gas content of the coal seam do not meet the requirements, S2 is repeated until the extracted gas meets the requirements.

[0018] Further preferably, in S2, nitrogen is injected at a high pressure of 4-6 MPa, and carbon dioxide is injected at a low pressure of 0.8-2.8 MPa.

[0019] Beneficial effects of the present invention:

[0020] 1) The gas injection sealing assembly used in this application uses two grouting bags to achieve hard fixation of the gas injection screen tube. At the same time, a liquid injection bag is provided at the connection between the gas injection screen tube and the gas injection pipe for soft connection, which can greatly avoid fatigue damage to the pressure-bearing orifice and pipeline rupture and other problems.

[0021] 2) First, high-pressure, low-adsorption gas nitrogen is injected into the gas injection hole to promote gas flow in the coal seam and at the same time produce a squeezing effect on the gas. Continuous injection can reduce the effective stress of the coal body (ground stress minus gas stress), and closed fracture channels can also reopen, thereby increasing the permeability of the coal seam; then low-pressure, highly adsorbable gas carbon dioxide is injected to absorb and desorb the adsorbed gas in the matrix into a free state, thereby increasing the concentration of gas in the coal matrix and enhancing the diffusion capacity of the gas. That is, this application can achieve the triple effects of promoting flow, increasing permeability and replacement.

[0022] 3) This application is proposed based on the actual situation that low-permeability coal seams are difficult to extract. It is applicable to most low-permeability coal seams and is still applicable to complex working conditions where it is difficult to increase the permeability of low-permeability and soft coal seams. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the device of the present invention.

[0024] Figure 2 for Figure 1 A magnified view of center.

[0025] Figure 3 Schematic diagram of the extraction method of the present invention.

[0026] Figure 1: Injection hole 1, extraction hole 2, injection screen 3, injection pipe 4, first multifunctional control valve 5, injection pipeline 6, first pipeline 7, second slurry connecting pipe 8, first control valve 9, injection control valve 10, injection pressure gauge 11, extraction screen 12, extraction pipe 13, second multifunctional control valve 14, first grouting bag 15, second grouting bag 16, liquid injection bag 17, first slurry connecting pipe 18, first grouting pipe 19, liquid injection pipe 20, pneumatic booster pump 21, gas storage tank 22, second pipeline 23, gas parameter meter 24, booster pneumatic pump Pipeline-25, compressed air system-26, exhaust pipe-27, booster pneumatic control valve-28, expulsion pipeline-29, expulsion control valve-30, carbon dioxide tank-31, nitrogen tank-32, third pipeline-33, fourth pipeline-34, third control valve-35, fourth control valve-36, exhaust pipeline-37, exhaust control valve-38, extraction pipeline-39, gas-liquid separation component-40, gas collection component-41, multi-function parameter instrument-42, extraction pressure gauge-43, extraction control valve-44, extraction system-45, third grouting bag-46, fourth grouting bag-47, second grouting pipe-48. DETAILED DESCRIPTION

[0027] The present invention will be further described below by way of examples and in conjunction with the accompanying drawings:

[0028] like Figure 1-3 As shown, a gas injection permeability enhancement and low permeability coal seam enhanced gas extraction system is mainly composed of a gas injection and sealing assembly, an extraction sealing assembly, a pressurizing assembly, a gas injection assembly and an extraction assembly, wherein the gas injection and sealing assembly is used to seal the gas injection holes, the extraction sealing assembly is used to achieve the sealing of the extraction holes, the pressurizing assembly is used to pressurize the gas entering and exiting and then inject it into the injection hole, the gas injection assembly is used to inject gas into the gas injection hole, and the extraction assembly is used to achieve the extraction of gas in the gas injection hole or the extraction hole.

[0029] A gas injection hole 1 and a drainage hole 2 are provided in the low-permeability coal seam. A gas injection screen 3 is provided in the gas injection hole 1. One end of the gas injection screen 3, close to the orifice of the gas injection hole 1, is connected to a gas injection pipe 4. A first multifunctional control valve 5 is provided on the gas injection pipe 4. At the other end of the gas injection pipe 4, a gas injection pipeline 6 and a drainage assembly are provided in parallel. A booster assembly is provided at the other end of the gas injection pipeline 6. The other end of the booster assembly is connected to the gas injection assembly via a first pipeline 7. A first control valve 9 is provided on the first pipeline 7. A gas injection control valve 10 and a gas injection pressure gauge 11 are provided on the gas injection pipeline 6.

[0030] An extraction screen tube 12 is provided in the extraction hole 2. One end of the extraction screen tube 12 close to the orifice of the extraction hole 2 is connected to the extraction pipe 13. A second multifunctional control valve 14 is provided on the extraction pipe 13. The other end of the extraction pipe 13 is provided with an extraction component. The extraction sealing component is used to achieve the sealing of the extraction hole 2 after the extraction screen tube 12 is placed.

[0031] The gas injection sealing assembly specifically includes a first grouting bag 15, a second grouting bag 16 and a liquid injection bag 17. To facilitate the injection of slurry between the two bags, a first slurry connecting pipe 18 is provided between the first grouting bag 15 and the second grouting bag 16, a first grouting pipe 19 for injecting slurry into the first grouting bag 15 and the second grouting bag 16 is provided on the second grouting bag 16, and a liquid injection pipe 20 for injecting liquid into the liquid injection bag 17 is provided on the liquid injection bag 17. When sealing the gas injection hole, the first grouting bag 15 and the second grouting bag 16 are sleeved on the gas injection screen 3 at intervals, and the liquid injection bag 17 is sleeved at the connection position between the gas injection screen 3 and the gas injection pipe 4. The gas injection pipe and the gas injection screen are connected by threads so that the gas injection pipe can be recovered after the displacement is completed.

[0032] The boosting assembly includes a pneumatic booster pump 21 and a gas tank 22, and the pneumatic booster pump 21 and the gas tank 22 are connected by a second pipeline 23. A gas parameter meter 24 for detecting the gas parameters in the gas tank is provided in the gas tank 22. The pneumatic booster pump 21 is connected to the compressed air system 26 via a boosting pneumatic pipeline 25. An exhaust pipe 27 is provided on the pneumatic booster pump 21, and a boosting pneumatic control valve 28 is provided on the boosting pneumatic pipeline 25, so that the pneumatic booster pump can be driven by the compressed air system, so that it does not need to be connected to electricity. The compressed air system 26 is also connected to the gas injection pipeline 6 through a drive pipeline 29. A drive control valve 30 is provided on the drive pipeline 29, so that the compressed air system can enter the gas injection hole through the drive pipeline and the gas injection pipeline, thereby driving out the free carbon dioxide in the gas injection hole after the displacement is completed, thereby effectively preventing the carbon dioxide from exceeding the limit during the recovery process.

[0033] The gas injection assembly includes a carbon dioxide tank 31 and a nitrogen tank 32, each equipped with corresponding valves. The carbon dioxide tank 31 is connected to the first pipeline 7 via a third pipeline 33, and the nitrogen tank 32 is connected to the first pipeline 7 via a fourth pipeline 34. A third control valve 35 is provided on the third pipeline 33, and a fourth control valve 36 is provided on the fourth pipeline 34. An exhaust pipeline 37 is also provided on the first pipeline 7, and an exhaust control valve 38 is provided on the exhaust pipeline 37.

[0034] The extraction assembly includes an extraction pipeline 39, on which are sequentially installed a gas-liquid separation assembly 40 and a gas collection assembly 41. A multifunctional parameter meter 42 is located at the other end of the gas collection assembly 41. The extraction pipeline 39 also includes an extraction pressure gauge 43 and an extraction control valve 44 located between the gas-liquid separation assembly 40 and the gas collection assembly 41. The other ends of both extraction pipelines 39 are connected to an extraction system 45. The multifunctional parameter meter 42 is connected to the gas collection assembly only during testing, and both extraction assemblies share the same multifunctional parameter meter. Both the gas-liquid separation assembly and the gas collection assembly utilize existing technology.

[0035] The drainage and sealing assembly includes a third grouting bag 46 and a fourth grouting bag 47. A second slurry connection pipe is provided between the third and fourth grouting bags 46, 47. A second grouting pipe 48 is provided on the fourth grouting bag 47 for injecting slurry into the third and fourth grouting bags 46, 47. During sealing, the third and fourth grouting bags 46, 47 are spaced apart and sleeved on the drainage screen 12.

[0036] Based on the above-mentioned gas injection permeability enhancement and low permeability coal seam enhanced gas extraction system, the specific gas injection permeability enhancement and low permeability coal seam enhanced gas extraction method includes the following steps:

[0037] Step 1: Device connection.

[0038] Construct gas injection hole 1 and extraction hole 2 in the target coal seam, then place the gas injection screen pipe 3 and the extraction screen pipe 12 in the holes accordingly, connect the extraction screen pipe 12 with the extraction pipe 13, connect the gas injection screen pipe 3 with the gas injection pipe 4, and then seal the gas injection hole 1 through the gas injection sealing assembly, and seal the extraction hole 2 through the extraction sealing assembly.

[0039] The specific process of sealing the gas injection hole is as follows: first, the gas injection screen tube is placed into the gas injection hole, and then the first grouting bag and the second grouting bag are alternately put on the gas injection screen tube, and the second grouting bag is placed on the side close to the gas injection hole opening. At the same time, the first grouting bag and the second grouting bag can only be put on the gas injection screen tube to realize the rear of gas injection (the rear refers to the side close to the gas injection hole), and then slurry is injected into the first grouting bag and the second grouting bag through the first grouting pipe. After the slurry injection is completed; first put the liquid injection bag on the gas injection screen tube, and then connect the gas injection pipe to the gas injection screen tube, and then move the liquid injection bag to the connection between the gas injection pipe and the gas injection screen tube, and then inject liquid into the liquid injection bag through the liquid injection pipe to achieve soft fixation at the connection to prevent damage caused by intermittent gas injection and pipeline rupture.

[0040] The sealing process of the extraction hole is specifically as follows: first, the extraction screen pipe is placed into the extraction hole, and then the third grouting bag and the fourth grouting bag are placed on the extraction screen pipe at intervals, and the fourth grouting bag is placed on the side close to the extraction hole mouth. At the same time, the third grouting bag and the fourth grouting bag can only be placed on the extraction screen pipe to realize the rear of gas extraction (the rear refers to the side close to the extraction hole), and then slurry is injected into the third grouting bag and the fourth grouting bag through the second grouting pipe until the slurry injection is completed.

[0041] Step 2: Displacement gas injection. Open the first multi-function control valve 5, the gas injection control valve 10, and the first control valve 9. The gas is pressurized by the gas injection assembly and the booster assembly and then flows along the gas injection pipeline 6 into the gas injection hole 1. When the gas injection pressure gauge 11 shows a significant drop, stop the gas injection. During the gas injection, first inject nitrogen and then carbon dioxide. After the gas injection is completed, close the gas injection control valve 10 and the first control valve 9.

[0042] The specific gas injection operation is as follows: first open the booster pneumatic control valve, let the compressed air of the compressed air system enter the pneumatic booster pump through the booster pneumatic pipeline, drive the pneumatic booster pump to work, and then open the fourth control valve, the first control valve and the control valve of the nitrogen tank, so that the nitrogen in the nitrogen tank is pressurized by the pneumatic booster pump and enters the gas storage tank, and use the gas parameter meter to observe the parameters such as the air pressure and volume in the gas storage tank. When the stored gas parameters reach the predetermined value, first close the fourth control valve and the control valve of the nitrogen tank, and then open the gas injection control valve and the first multi-function control valve at the same time, so that the nitrogen enters the gas injection hole along the gas injection pipeline, the gas injection pipe and the gas injection screen tube, and pay attention to the gas injection pressure gauge at the same time, so that the nitrogen is injected at a high pressure of 4-6MPa. When the gas injection pressure gauge shows a significant drop, close the gas injection control valve. Then open the third control valve and the control valve of the carbon dioxide gas tank to allow the carbon dioxide to enter the gas storage tank after being pressurized. When the stored gas parameters reach the predetermined value, first close the third control valve and the control valve of the carbon dioxide gas tank, and then open the gas injection control valve at the same time to allow the carbon dioxide to enter the gas injection hole along the gas injection pipeline, gas injection pipe and gas injection screen tube. At the same time, pay attention to the gas injection pressure gauge to allow carbon dioxide to be injected at a low pressure of 0.8-2.8MPa. When the gas injection pressure gauge shows a significant drop, close the gas injection control valve.

[0043] Step 3: Gas Injection and Extraction. The gas in the injection and extraction holes is extracted using negative pressure through two extraction components. During the extraction process, the residual gas pressure and residual gas content of the coal seam are tested. When the requirements are met, the free carbon dioxide in the injection hole 1 is driven out. If the residual gas pressure and residual gas content of the coal seam do not meet the requirements, the second step is repeated until the extracted gas meets the requirements.

[0044] The specific process of gas injection and extraction is: first open the extraction system, then open the two extraction control valves, and observe through the corresponding extraction pressure gauge to make the extraction negative pressure meet the requirements of the "Coal Mine Safety Regulations". At the same time, the extracted gas is detected by the multi-function parameter instrument for gas concentration and purity after passing through the gas-liquid separation component and the gas collection component; during the extraction process, the residual gas pressure and residual gas content of the coal seam are detected through the extraction pressure gauge and the multi-function parameter instrument connected to the gas injection hole. When the requirements of the "Coal Mine Safety Regulations" are met, the compressed air system and the expulsion control valve are opened, and the free carbon dioxide in the gas injection hole is expelled through the compressed air system. At the same time, pay attention to the carbon dioxide content in the multi-function parameter instrument on the extraction pipeline connected to the gas injection pipeline. After the carbon dioxide meets the requirements of the regulations, close the expulsion control valve and stop the compressed air system. If the residual gas pressure and residual gas content of the coal seam do not meet the requirements, repeat the second step until the extracted gas meets the requirements.

Claims

1. A method for enhancing gas extraction in a low-permeability coal seam by injecting gas to increase permeability, wherein a gas injection hole (1) and an extraction hole (2) are provided in the low-permeability coal seam, and the method is characterized by: The invention comprises a gas injection permeability enhancement low permeability coal seam gas extraction system for realizing extraction, wherein the gas injection permeability enhancement low permeability coal seam gas extraction system comprises a gas injection sealing assembly, an extraction sealing assembly, a pressurizing assembly, a gas injection assembly and an extraction assembly, wherein a gas injection screen tube (3) is provided in the gas injection hole (1), and one end of the gas injection screen tube (3) close to the orifice of the gas injection hole (1) is connected to the gas injection pipe (4), and a first multifunctional control valve (5) is provided on the gas injection pipe (4). ) is provided with an injection pipeline (6) and an extraction component in parallel at the other end thereof, a boosting component is provided at the other end thereof, and the other end thereof is connected to the injection component via a first pipeline (7), a first control valve (9) is provided on the first pipeline (7), an injection control valve (10) and an injection pressure gauge (11) are provided on the injection pipeline (6), and the injection sealing component is used to achieve the sealing of the injection hole (1) after the injection screen tube (3) is placed therein; An extraction screen tube (12) is provided in the extraction hole (2), one end of the extraction screen tube (12) close to the orifice of the extraction hole (2) is connected to the extraction pipe (13), a second multifunctional control valve (14) is provided on the extraction pipe (13), and an extraction assembly is provided at the other end of the extraction pipe (13), and the extraction sealing assembly is used to achieve sealing of the extraction hole (2) after the extraction screen tube (12) is placed in. The boosting assembly includes a pneumatic boosting pump (21) and an air storage tank (22), the pneumatic boosting pump (21) and the air storage tank (22) are connected via a second pipeline (23), a gas parameter meter (24) is provided in the air storage tank (22), the pneumatic boosting pump (21) is connected to a compressed air system (26) via a boosting pneumatic pipeline (25), an exhaust pipe (27) is provided on the pneumatic boosting pump (21), a boosting pneumatic control valve (28) is provided on the boosting pneumatic pipeline (25), and the compressed air system (26) is also connected to the gas injection pipeline (6) via a driving pipeline (29), and a driving control valve (30) is provided on the driving pipeline (29); The following steps are also included: S1: device connection; Constructing a gas injection hole (1) and a drainage hole (2) in the target coal seam, then placing a gas injection screen tube (3) and a drainage screen tube (12) in the holes accordingly, connecting the drainage screen tube (12) to the drainage tube (13), connecting the gas injection screen tube (3) to the gas injection tube (4), and then sealing the gas injection hole (1) with a gas injection hole sealing assembly, and sealing the drainage hole (2) with a drainage hole sealing assembly; S2: displacement gas injection; Open the first multifunctional control valve (5), the gas injection control valve (10), and the first control valve (9), and pressurize the gas through the gas injection assembly and the booster assembly, and then enter the gas injection hole (1) along the gas injection pipeline (6). When the gas injection pressure gauge (11) is observed to drop significantly, stop the gas injection. During the gas injection, first inject nitrogen and then inject carbon dioxide. After the gas injection is completed, close the gas injection control valve (10) and the first control valve (9); S3: gas injection and drainage; The gas in the gas injection hole and the extraction hole is extracted by negative pressure through two extraction components. During the extraction process, the residual gas pressure and residual gas content of the coal seam are detected. When the requirements are met, the free carbon dioxide in the gas injection hole (1) is driven out. If the residual gas pressure and residual gas content of the coal seam do not meet the requirements, S2 is repeated until the extracted gas meets the requirements.

2. The method for enhancing gas extraction in low-permeability coal seams by gas injection according to claim 1, characterized in that: The gas injection sealing assembly comprises a first grouting bag (15), a second grouting bag (16) and a liquid injection bag (17); a first slurry connecting pipe (18) is provided between the first grouting bag (15) and the second grouting bag (16); the first grouting bag (15) and the second grouting bag (16) are sleeved on the gas injection screen tube (3) at intervals; the second grouting bag (16) is provided with a first grouting pipe (19) for injecting slurry into the first grouting bag (15) and the second grouting bag (16); the liquid injection bag (17) is sleeved at the connection position between the gas injection screen tube (3) and the gas injection pipe (4); and the liquid injection bag (17) is provided with a liquid injection pipe (20) for injecting liquid into the liquid injection bag (17).

3. The method for enhancing gas extraction in low-permeability coal seams by gas injection according to claim 1, characterized in that: The gas injection assembly comprises a carbon dioxide gas tank (31) and a nitrogen gas tank (32); the carbon dioxide gas tank (31) is connected to the first gas tank (7) via a third gas tank (33); the nitrogen gas tank (32) is connected to the first gas tank (7) via a fourth gas tank (34); a third control valve (35) is provided on the third gas tank (33); a fourth control valve (36) is provided on the fourth gas tank (34); the first gas tank (7) is further provided with an exhaust gas tank (37); and an exhaust control valve (38) is provided on the exhaust gas tank (37).

4. The method for enhancing gas extraction in low-permeability coal seams by gas injection according to claim 1, characterized in that: The extraction component includes an extraction pipeline (39), on which a gas-liquid separation component (40) and a gas collection component (41) are sequentially arranged, and a multifunctional parameter meter (42) is arranged at the other end of the gas collection component (41). The extraction pipeline (39) is provided with an extraction pressure gauge (43) and an extraction control valve (44) located between the gas-liquid separation component (40) and the gas collection component (41), and the other ends of the two extraction pipelines (39) are both connected to the extraction system (45).

5. The method for enhancing gas extraction in low-permeability coal seams by gas injection according to claim 1, characterized in that: The extraction and sealing assembly includes a third grouting bag (46) and a fourth grouting bag (47), a second slurry connecting pipe (8) is provided between the third grouting bag (46) and the fourth grouting bag (47), the third grouting bag (46) and the fourth grouting bag (47) are spaced apart and sleeved on the extraction screen pipe (12), and a second grouting pipe (48) for injecting slurry into the third grouting bag (46) and the fourth grouting bag (47) is provided on the fourth grouting bag (47).

6. The method for enhancing gas extraction in low-permeability coal seams by gas injection according to claim 1, characterized in that: In S2, nitrogen is injected at a high pressure of 4-6 MPa, and carbon dioxide is injected at a low pressure of 0.8-2.8 MPa.

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