A system and method for improving gas extraction effect by linking ground drilling groups

Abstract

A method and system for improving gas extraction effect by linkage of ground drilling groups. The method utilizes linkage of ground drilling groups to pressurize gas extracted by the ground drilling groups, directly injects high-concentration gas in the initial stage of extraction, and injects the concentrated high-concentration gas into the ground drilling in the later stage of extraction, and combines with gas extraction to achieve high-concentration gas fracturing, positive and negative pressure alternating stress fatigue fracturing and gas displacement of coal bodies around the ground drilling, thereby improving gas extraction efficiency and concentration. The system part adopts a drying device, a conventional gas injection pipe, a gas purification pipe, a first gas extraction pump, a booster pump, a gas injection pipe, and a second gas extraction pump in combination. Through the action of the first gas extraction pump and the booster pump on the booster pipe, gas with a concentration higher than 30% is directly injected into the ground drilling during the entire extraction cycle, achieving high-concentration gas fracturing of coal bodies, positive and negative pressure alternating stress fatigue fracturing of coal bodies, and gas displacement, thereby achieving efficient and high-concentration gas extraction in ground drilling.

Description

Technical Field

[0001] The present invention relates to a method for improving the gas extraction effect of ground drilling, in particular to a system and method for improving the gas extraction effect by linkage of ground drilling groups, belonging to the technical field of gas extraction. Background Art

[0002] The generally low permeability of coal seams is the main reason that limits the effectiveness of gas extraction by surface drilling.

[0003] In order to improve the permeability of coal seams, hydraulic fracturing technology is generally used to increase the permeability of coal seams. However, relevant research results show that the cracks caused by hydraulic fracturing mainly expand in the direction perpendicular to the minimum principal stress. The number of cracks produced is small, and it is difficult to form longer cracks. It fails to produce a volume rupture effect on the coal seam storage. At the same time, there is also the disadvantage of high fracturing fluid pressure.

[0004] At present, the application effect of this technology in most mining areas in my country is not ideal, and the relevant technical processes need further research. In addition, some scholars have studied the method of injecting nitrogen to suffocate the well to improve the gas extraction effect. This method improves the gas extraction effect, but the injection of nitrogen reduces the gas concentration, resulting in a decrease in gas utilization. Therefore, it is urgent to develop new methods to improve the gas extraction effect of ground drilling without affecting gas utilization. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system for improving the gas extraction effect by linking a ground drilling group, which does not require an external gas source, has a simple process, is easy to operate, and has a low cost. It integrates gas fracturing (well blocking), alternating stress fracturing, and gas displacement, solves the problem of short gas extraction cycle in ground drilling with high concentration, and improves gas extraction efficiency and gas extraction concentration.

[0006] In order to achieve the above object, the present invention provides a method for improving gas extraction effect by linkage of ground drilling groups, comprising the following steps:

[0007] ① According to the coal seam occurrence, underground coal seam tunnel layout and gas mining conditions, several surface drillings are constructed on the ground. After the surface drilling construction is completed, they are sealed according to conventional methods;

[0008] ② For every three surface wells, connect the first surface well, the second surface well and the third surface well to the extraction branch pipe, open the control valves on the gas extraction pipes of the second surface well and the third surface well, and connect the gas injection interface on the gas extraction pipe of the first surface well to the gas injection pipe;

[0009] ③ Open the fifth valve, the fourth valve, the third valve and the first valve in sequence. The gas concentration gushing out of the second surface well and the third surface well is close to 100%. The second gas concentration measuring device transmits the gas concentration signal to the controller. When the gas concentration of the second gas concentration measuring device received by the controller is higher than 30%, the controller transmits a signal through the data line to open the first electric valve. After a delay of 30 seconds, the controller transmits a signal through the data line to sequentially open the booster pump and the first gas extraction pump. Under the negative pressure of the first gas extraction pump, the gas from the second surface well and the third surface well is passed through the drying device to remove the water impurities carried by the gas, and then is injected into the first surface well through the gas extraction pipe after passing through the first branch pipe, the conventional gas injection pipe, the booster pipe, the gas injection pipe, and the gas injection interface. The pressure of the injected gas gas on the coal body around the first surface well is in the same direction as the negative pressure of the extraction of the second surface well borehole, both of which diffuse outward to form a combined force to fracture the coal body and displace the gas in the coal body. The gas injection time is 24-48 hours.

[0010] ④ Remove the gas injection pipe connected to the gas extraction pipe of the first surface drilling well, connect the first surface drilling well to the extraction branch pipe, open the second valve, close the valve on the gas extraction pipe of the second surface drilling well, separate the gas extraction pipe of the second surface drilling well from the extraction branch pipe, connect the gas injection interface of the second surface drilling well to the gas injection pipe, repeat step ③, until the work of injecting high-concentration gas to improve the gas extraction effect is completed in the first surface drilling well, the second surface drilling well, and the third surface drilling well;

[0011] ⑤ Connect the gas extraction pipes of the first surface drilling well, the second surface drilling well, and the third surface drilling well to the extraction branch pipe, and open the fourth electric valve and the second gas extraction pump in sequence through the controller to extract gas. The gas time is 4-6 days;

[0012] ⑥ Repeat steps ②, ③, ④, and ⑤ for 5-7 times to complete the production increase operation of the surface drilling group. During this process, the coal bodies around the first surface drilling well, the second surface drilling well, and the third surface drilling well undergo gas positive pressure fracturing, gas dynamic fatigue fracturing and gas displacement with positive and negative pressure conversion, ensuring efficient and high-concentration extraction of coal seam gas. Then, normal gas extraction is carried out, and the gas injection pipe is kept connected to the gas injection interface of the first surface drilling well;

[0013] ⑦ During the gas extraction process, when the second gas concentration measuring device measures a gas concentration lower than 30%, the second gas concentration measuring device transmits the measured gas concentration signal to the controller through the data line, and the controller closes the fourth electric valve and the second gas extraction pump, and opens the third electric valve, and then opens the fourth valve and the first valve in sequence. After a delay of 30 seconds, the controller transmits a signal through the data line to open the booster pump and the first gas extraction pump in sequence. The gas passes through the deoxygenation device and the denitrogenation device to increase the gas concentration. When the first gas concentration measuring device measures a gas concentration lower than 30%, the controller transmits a signal through the data line to open the second electric valve, and the gas flows back to the extraction branch pipe until the first gas concentration measuring device measures a gas concentration higher than 30%. The controller transmits a signal through the data line to open the first electric valve, and the gas with a concentration higher than 30% is injected into the first surface well. The injection gas pressure is 2-5MPa, and the gas injection time is 8-12h.

[0014] ⑧ Remove the gas injection pipe connected to the gas extraction pipe of the first surface drilling well, connect the first surface drilling well to the extraction branch pipe, open the second valve, close the valve on the gas extraction pipe of the second surface drilling well, separate the gas extraction pipe of the second surface drilling well from the extraction branch pipe, connect the gas injection interface of the second surface drilling well to the gas injection pipe, repeat step ⑦, cycle in sequence, until the work of injecting high-concentration gas into the first surface drilling well, the second surface drilling well, and the third surface drilling well to improve the gas extraction effect is completed;

[0015] ⑨Connect the first surface drilling well, the second surface drilling well, and the third surface drilling well to the extraction branch pipe, open the fourth electric valve and the second gas extraction pump through the controller, and extract gas for 2-3 days;

[0016] ⑩ Repeat steps ⑦, ⑧ and ⑨ until the coal seam gas extraction volume reaches the design requirements. In this process, it is ensured that the extracted gas concentration does not affect gas utilization.

[0017] In step ③, the pressure of the first surface drilling gas injected after being pressurized by the booster pump is 10-14 MPa.

[0018] A system for improving gas extraction effect by linkage of ground drilling groups, comprising a first ground drilling well, a second ground drilling well, a third ground drilling well and a controller, wherein the first ground drilling well, the second ground drilling well and the third ground drilling well are arranged along the ground drilling well and extend to the coal seam, gas extraction pipes are arranged in the first ground drilling well, the second ground drilling well and the third ground drilling well, the bottom ends of the gas extraction pipes extend to the inside of the coal seam, the top ends of the gas extraction pipes extend upward out of the ground and are connected to the branch interface of the extraction branch pipe after the hole is sealed, and the gas extraction pipes are arranged on the gas extraction pipes. A gas injection interface is installed, a control valve is arranged on the gas extraction pipe in the second ground well and the third ground well, a second valve is arranged on the first ground well, and the control valve and the second valve are arranged between the gas injection interface and the extraction branch pipe, and the first valve is arranged on the pipeline of the gas injection interface; the gas outlet of the extraction branch pipe is connected to the gas inlet of the second branch pipe, the gas outlet of the second branch pipe is connected to the gas inlet of the drying device, and the fifth valve and the second gas concentration measuring device are arranged on the second branch pipe in sequence; the gas outlet on one side of the drying device is connected to one end of the first branch pipe, the other end of the first branch pipe is connected to one of the ports of the third three-way valve, and the other two ports of the third three-way valve are respectively connected to one end of the conventional gas injection pipe and one end of the gas purification pipe, and a fourth valve is arranged on the first branch pipe, the other end of the conventional gas injection pipe is connected to one of the ports of the second three-way valve, and the other two ports of the second three-way valve are respectively connected to the other end of the gas purification pipe and one end of the boosting pipe, the third valve and the second check valve are arranged on the conventional gas injection pipe, and the third electric valve and the deoxygenation valve are arranged on the gas purification pipe in sequence A gas extraction device, a denitrification device, a first gas concentration measuring device, and a third check valve are provided; the other end of the boosting pipe is connected to one of the ports of the first three-way valve, and the other two ports of the first three-way valve are respectively connected to the air inlet of the extraction branch pipe and the air inlet of the gas injection pipe. The first gas extraction pump and the boosting pump are sequentially arranged on the boosting pipe, and the second electric valve and the first check valve are sequentially arranged at one end of the extraction branch pipe close to the first three-way valve. The air outlet of the gas injection pipe is connected to the air inlet of the gas injection interface, and the first electric valve is arranged on the gas injection pipe;

[0019] The gas outlet on the other side of the drying device is connected to one end of the third branch pipe, the other end of the third branch pipe is connected to the second gas extraction pump, and a fourth electric valve is arranged on the third branch pipe;

[0020] The controller is respectively connected to the first electric valve, the second electric valve, the first gas extraction pump, the booster pump, the third electric valve, the fourth electric valve, the first gas concentration measuring device, the second gas concentration measuring device and the second gas extraction pump.

[0021] The controller is a programmable logic controller.

[0022] The deoxygenation device is provided with a commercial nitrogen-making carbon molecular sieve; the denitrogenation device is provided with an activated carbon adsorbent with the function of absorbing nitrogen.

[0023] Compared with the prior art, the method of the present invention partially makes full use of the linkage of the ground drilling group, pressurizes the gas extracted by the ground drilling group, directly injects high-pressure and high-concentration gas in the early stage of extraction, and combines it with gas extraction to achieve gas high-pressure (muffled well) fracturing, positive and negative pressure alternating stress fatigue fracturing and gas displacement of the coal body around the ground drilling, thereby significantly improving the gas extraction efficiency and gas extraction concentration. In the later stage of extraction, the low-concentration gas is purified to ensure that the gas concentration is higher than 30%, and low-pressure fracturing, positive and negative pressure alternating stress fatigue fracturing and gas displacement of the coal body around the ground drilling are achieved. In this way, there is no need to add other gases, which ensures the quality of gas utilization. While the surface drilling is being subjected to high-pressure fracturing (stifling the well), the surface drilling also alternates between compressed air flow and extracted air flow, causing the coal body extracted by the surface drilling to repeatedly undergo expansion and contraction. Under the action of this alternating stress, the coal body is prone to reach its fatigue limit and rupture, causing the cracks to continue to expand and gradually develop toward the deep, increasing the radius of gas extraction from the surface drilling, and increasing the total amount of gas extracted from the surface drilling, thereby achieving increased production of the surface drilling group. This method does not require an external gas source, has a simple process, is easy to operate, and is low in cost. It integrates gas fracturing (stifling the well), alternating stress fracturing, and gas displacement, solving the problem of short extraction cycles of high-concentration gas in surface drilling, and has wide practicability.

[0024] The extraction system of the present invention adopts a drying device, a conventional gas injection pipe, a gas purification pipe, a first gas extraction pump, a booster pump, a gas injection pipe, and a second gas extraction pump. The high-concentration gas in the initial stage of extraction is directly injected into the ground well through the first gas extraction pump and the booster pump on the conventional gas injection pipe and the booster pipe. The ground well gas injection and extraction are combined to realize high-concentration gas high-pressure fracture of the coal body (well blocking), positive and negative pressure alternating stress fatigue fracture of the coal body and gas displacement, thereby realizing high-efficiency and high-concentration gas extraction. In the later stage of ground well gas extraction, the low-concentration gas is concentrated (concentration is greater than 30%) and then injected into the ground well. The gas that does not meet the concentration requirement flows back to the extraction branch pipe, thereby realizing low-pressure fracture, positive and negative pressure alternating stress fatigue fracture and gas displacement of the coal body around the ground well, ensuring high-concentration and high-efficiency gas extraction without affecting gas utilization. The present invention makes full use of the cooperation between ground drilling wells, pressurizes the gas extracted by the ground drilling group, and then injects it into the ground drilling well that needs to be increased in production to block the well, and then performs normal gas extraction, and repeats the blocking and gas extraction. In this way, there is no need to add other gases, and the quality of gas utilization is guaranteed. While the ground drilling well is blocked, the ground drilling well also alternately pressurizes and extracts airflow, so that the coal body around the ground drilling well repeatedly bears the effects of expansion and contraction. Under the action of this alternating stress, the coal body is prone to reach the fatigue limit and rupture, so that the cracks continue to expand and gradually develop to the deep, increasing the gas extraction radius of the ground drilling well, and increasing the total amount of gas extraction of the ground drilling well, thereby achieving the increase in production of the ground drilling group. This method does not require an external gas source, has a simple process, is easy to operate, and has low cost. It integrates gas fracturing and alternating stress fracturing, solves the problem of short extraction cycle of high-concentration gas in ground drilling, and has wide practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of the present invention after assembly.

[0026] In the figure: 1, coal seam; 2, first surface drilling; 3, gas extraction pipe; 4, gas injection interface; 5, first valve; 6, gas injection pipe; 7, first electric valve; 8, second valve; 9, extraction branch pipe; 10, first check valve; 11, second electric valve; 12, first three-way valve; 13, booster pipe; 14, booster pump; 15, first gas extraction pump; 16, second three-way valve; 17, second check valve; 18, conventional gas injection pipe; 19, third valve; 20, gas purification pipe; 21 , the third check valve; 22, the first gas concentration measuring device; 23, the denitrification device; 24, the deoxygenation device; 25, the third electric valve; 26, the controller; 27, the third three-way valve; 28, the first branch pipe; 29, the fourth valve; 30, the drying device; 31, the second branch pipe; 32, the second gas concentration measuring device; 33, the fifth valve; 34, the fourth electric valve; 35, the third branch pipe; 36, the second gas extraction pump; 37, the second ground drilling; 38, the third ground drilling. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] like Figure 1 As shown, a method for improving gas extraction effect by linking a surface drilling group includes the following steps:

[0029] ① According to the occurrence of coal seam 1, the layout of underground coal seam tunnels and the gas mining situation, several surface drillings are constructed on the ground. After the surface drilling construction is completed, they are sealed according to conventional methods;

[0030] ② Every three surface drilling wells form a group, connect the first surface drilling well 2, the second surface drilling well 37, and the third surface drilling well 38 to the extraction branch pipe 9, open the control valves on the gas extraction pipes 3 of the second surface drilling well 37 and the third surface drilling well 38, and connect the gas injection interface 4 on the gas extraction pipe 3 of the first surface drilling well 2 to the gas injection pipe 6;

[0031] ③ The fifth valve 33, the fourth valve 29, the third valve 19 and the first valve 5 are opened in sequence. The gas concentration gushing out of the second surface well 37 and the third surface well 38 is close to 100%. The second gas concentration measuring device 32 transmits the gas concentration signal to the controller 26. When the gas concentration of the second gas concentration measuring device 32 received by the controller 26 is higher than 30%, the controller 26 transmits a signal through the data line to open the first electric valve 7. After a delay of 30 seconds, the controller 26 transmits a signal through the data line to open the booster pump 14 and the first gas extraction pump 15 in sequence. The gas from the second surface well 37 and the third surface well 38 is subjected to the negative pressure of the first gas extraction pump 15, passes through the drying device 30 to remove the water impurities carried by the gas, passes through the first branch pipe 28, the conventional gas injection pipe 18, the booster pipe 13, the gas injection pipe 6, and the gas injection interface 4, and is then injected into the first surface well 2 through the gas extraction pipe 3; the pressure of the injected gas gas on the coal body around the first surface well 2 is in the same direction as the negative pressure of the extraction of the second surface well 37, both of which diffuse outward, forming a combined force to fracture the coal body, and can also displace the gas in the coal body, and the gas injection time is 24-48h;

[0032] ④ Remove the gas injection pipe 6 connected to the gas extraction pipe 3 of the first surface drilling well 2, connect the first surface drilling well 2 to the extraction branch pipe 9, open the second valve 8, close the valve on the gas extraction pipe of the second surface drilling well 37, separate the gas extraction pipe of the second surface drilling well 37 from the extraction branch pipe 9, connect the gas injection interface 4 of the second surface drilling well 37 to the gas injection pipe 6, repeat step ③, until the work of injecting high-concentration gas into the first surface drilling well 2, the second surface drilling well 37, and the third surface drilling well 38 to improve the gas extraction effect is completed;

[0033] ⑤ Connect the gas extraction pipes of the first surface drilling well 2, the second surface drilling well 37, and the third surface drilling well 38 to the extraction branch pipe 9, and sequentially open the fourth electric valve 34 and the second gas extraction pump 36 through the controller 26 to extract gas for 4-6 days;

[0034] ⑥ Repeat steps ②, ③, ④, and ⑤ for 5-7 times to complete the production increase operation of the surface drilling group. During this process, the coal bodies around the first surface drilling well 2, the second surface drilling well 37, and the third surface drilling well 38 experience gas positive pressure fracturing, gas dynamic fatigue fracturing and gas displacement by positive and negative pressure conversion, ensuring efficient and high-concentration extraction of coal seam gas. Then, normal gas extraction is carried out, and the gas injection pipe 6 is kept connected to the gas injection interface 4 of the first surface drilling well 2;

[0035] ⑦ During the gas extraction process, when the second gas concentration measuring device 32 measures a gas concentration lower than 30%, the second gas concentration measuring device 32 transmits the measured gas concentration signal to the controller 26 through the data line, and the controller 26 closes the fourth electric valve 34 and the second gas extraction pump 36, and opens the third electric valve 25, and then opens the fourth valve 29 and the first valve 5 in sequence. After a delay of 30 seconds, the controller 26 transmits a signal through the data line to open the booster pump 14 and the first gas extraction pump 15 in sequence, and the gas passes through the deoxygenation device 26. The device 24 and the denitrification device 23 are used to increase the concentration of gas. When the first gas concentration measuring device 22 measures that the gas concentration is lower than 30%, the controller 26 transmits a signal through the data line to open the second electric valve 11, and the gas flows back to the extraction branch pipe 9 until the first gas concentration measuring device 22 measures that the gas concentration is higher than 30%. The controller 26 transmits a signal through the data line to open the first electric valve 7, and the gas with a concentration higher than 30% is injected into the first surface drilling well 2. The injection gas pressure is 2-5MPa, and the injection time is 8-12h.

[0036] ⑧ Remove the gas injection pipe 6 connected to the gas extraction pipe 3 of the first surface drilling well 2, and connect the first surface drilling well 2 to the extraction branch pipe 9, open the second valve 8, close the valve on the gas extraction pipe of the second surface drilling well 37, separate the gas extraction pipe of the second surface drilling well 37 from the extraction branch pipe 9, connect the gas injection interface 4 of the second surface drilling well 37 to the gas injection pipe 6, repeat step ⑦, cycle in sequence, until the work of injecting high-concentration gas into the first surface drilling well 2, the second surface drilling well 37, and the third surface drilling well 38 to improve the gas extraction effect is completed;

[0037] ⑨ Connect the first surface well 2, the second surface well 37, and the third surface well 38 to the extraction branch pipe 9, open the fourth electric valve 34 and the second gas extraction pump 36 through the controller 26, and extract gas for 2-3 days;

[0038] ⑩ Repeat steps ⑦, ⑧ and ⑨ until the coal seam gas extraction volume reaches the design requirements. In this process, it is ensured that the extracted gas concentration does not affect gas utilization.

[0039] In step ③ of the present invention, the pressure of the gas injected into the first surface drilling well 2 after being pressurized by the booster pump 14 is 10-14 MPa.

[0040] A system for improving gas extraction effect by linkage of ground drilling groups, comprising a first ground drilling well 2, a second ground drilling well 37, a third ground drilling well 38 and a controller 26, wherein the first ground drilling well 2, the second ground drilling well 37, and the third ground drilling well 38 are drilled along the ground and extend to a coal seam 1, a gas extraction pipe 3 is arranged in the first ground drilling well 2, the second ground drilling well 37, and the third ground drilling well 38, the bottom end of the gas extraction pipe 3 extends to the inside of the coal seam 1, the top end of the gas extraction pipe 3 extends upward out of the ground and is connected to a branch interface of an extraction branch pipe 9 after sealing, a gas injection interface 4 is installed on the gas extraction pipe 3, and the first ground drilling well 2, the second ground drilling well 37, and the third ground drilling well 38 are ... and the gas extraction pipe 3 is connected to a branch interface of the extraction branch pipe 9 after sealing. A control valve is provided on the gas extraction pipe 3 in the second surface well 37 and the third surface well 38, and a second valve 8 is provided on the first surface well 2, and the control valve and the second valve 8 are provided on the extraction pipeline between the gas injection interface 4 and the extraction branch pipe 9, and a first valve 5 is provided on the pipeline of the gas injection interface 4; the gas outlet of the extraction branch pipe 9 is connected to the gas inlet of the second branch pipe 31, and the gas outlet of the second branch pipe 31 is connected to the gas inlet of the drying device 30, and a fifth valve 33 and a second gas concentration measuring device 32 are provided on the second branch pipe 31 in sequence; the gas outlet on one side of the drying device 30 is connected to one end of the first branch pipe 28 The other end of the first branch pipe 28 is connected to one of the ports of the third three-way valve 27, and the other two ports of the third three-way valve 27 are respectively connected to one end of the conventional gas injection pipe 18 and one end of the gas purification pipe 20. A fourth valve 29 is arranged on the first branch pipe 28, and the other end of the conventional gas injection pipe 18 is connected to one of the ports of the second three-way valve 16, and the other two ports of the second three-way valve 16 are respectively connected to the other end of the gas purification pipe 20 and one end of the boosting pipe 13. A third valve 19 and a second check valve 17 are arranged on the conventional gas injection pipe 18, and a third electric valve 25, a deoxygenating valve 26 and a second check valve 17 are arranged on the gas purification pipe 20 in sequence. Device 24, denitrification device 23, first gas concentration measuring device 22, third check valve 21; the other end of the boosting pipe 13 is connected to one of the ports of the first three-way valve 12, and the other two ports of the first three-way valve 12 are respectively connected to the air inlet of the extraction branch pipe 9 and the air inlet of the gas injection pipe 6, and the first gas extraction pump 15 and the boosting pump 14 are sequentially arranged on the boosting pipe 13, and the second electric valve 11 and the first check valve 10 are sequentially arranged at one end of the extraction branch pipe 9 close to the first three-way valve 12, the air outlet of the gas injection pipe 6 is connected to the air inlet of the gas injection interface 4, and the first electric valve 7 is arranged on the gas injection pipe 6;

[0041] The gas outlet on the other side of the drying device 30 is connected to one end of the third branch pipe 35, the other end of the third branch pipe 35 is connected to the second gas extraction pump 36, and a fourth electric valve 34 is provided on the third branch pipe 35;

[0042] The controller 26 is respectively connected to the first electric valve 7 , the second electric valve 11 , the first gas extraction pump 15 , the booster pump 14 , the third electric valve 25 , the fourth electric valve 34 , the first gas concentration measuring device 22 , the second gas concentration measuring device 32 and the second gas extraction pump 36 .

[0043] The controller 26 is a programmable logic controller.

[0044] The deoxygenation device 24 is provided with a commercial nitrogen-producing carbon molecular sieve; the denitrogenation device 23 is provided with an activated carbon adsorbent having a nitrogen absorbing function.

Claims

1. A system for improving gas extraction effect by linking a group of surface drilling wells, characterized in that: The invention comprises a first ground drilling well (2), a second ground drilling well (37), a third ground drilling well (38) and a controller (26). The first ground drilling well (2), the second ground drilling well (37) and the third ground drilling well (38) are drilled along the ground and extend to the coal seam (1). A gas extraction pipe (3) is arranged in the first ground drilling well (2), the second ground drilling well (37) and the third ground drilling well (38). The bottom end of the gas extraction pipe (3) extends into the interior of the coal seam (1). The top end of the gas extraction pipe (3) extends upward out of the ground and is connected to the branch interface of the extraction branch pipe (9) after sealing. A gas injection interface (4) is installed on the gas extraction pipe (3). A control valve is arranged on the gas extraction pipe (3) in the well (38), a second valve (8) is arranged on the first surface drilling well (2), and the control valve and the second valve (8) are arranged between the gas injection interface (4) and the extraction branch pipe (9), and the first valve (5) is arranged on the pipeline of the gas injection interface (4); the gas outlet of the extraction branch pipe (9) is connected to the gas inlet of the second branch pipe (31), the gas outlet of the second branch pipe (31) is connected to the gas inlet of the drying device (30), and a fifth valve (33) and a second gas concentration measuring device (32) are arranged on the second branch pipe (31) in sequence; the gas outlet on one side of the drying device (30) is connected to one end of the first branch pipe (28), and the other end of the first branch pipe (28) is connected to the gas inlet of the drying device (30). A third three-way valve (27) is connected to one of the ports, and the other two ports of the third three-way valve (27) are respectively connected to one end of a conventional gas injection pipe (18) and one end of a gas purification pipe (20). A fourth valve (29) is arranged on the first branch pipe (28). The other end of the conventional gas injection pipe (18) is connected to one of the ports of the second three-way valve (16). The other two ports of the second three-way valve (16) are respectively connected to the other end of the gas purification pipe (20) and one end of a booster pipe (13). A third valve (19) and a second check valve (17) are arranged on the conventional gas injection pipe (18). A third electric valve (25), a deoxygenation device (24), and a denitrogenation device (25) are arranged on the gas purification pipe (20) in sequence. device (23), a first gas concentration measuring device (22), and a third check valve (21); the other end of the boosting pipe (13) is connected to one of the ports of the first three-way valve (12), and the other two ports of the first three-way valve (12) are respectively connected to the air inlet of the extraction branch pipe (9) and the air inlet of the gas injection pipe (6); a first gas extraction pump (15) and a boosting pump (14) are sequentially arranged on the boosting pipe (13); a second electric valve (11) and a first check valve (10) are sequentially arranged at one end of the extraction branch pipe (9) close to the first three-way valve (12); the air outlet of the gas injection pipe (6) is connected to the air inlet of the gas injection interface (4), and a first electric valve (7) is arranged on the gas injection pipe (6); The gas outlet on the other side of the drying device (30) is connected to one end of the third branch pipe (35), the other end of the third branch pipe (35) is connected to the second gas extraction pump (36), and a fourth electric valve (34) is provided on the third branch pipe (35); The controller (26) is respectively connected to the first electric valve (7), the second electric valve (11), the first gas extraction pump (15), the booster pump (14), the third electric valve (25), the fourth electric valve (34), the first gas concentration measuring device (22), the second gas concentration measuring device (32) and the second gas extraction pump (36).

2. A system for improving gas extraction effect by linking a surface drilling group according to claim 1, characterized in that: The controller (26) is a programmable logic controller.

3. The system for improving gas extraction effect by linking a surface drilling group according to claim 1 is characterized in that: The deoxygenation device (24) is provided with a commercial nitrogen-making carbon molecular sieve; the denitrogenation device (23) is provided with an activated carbon adsorbent having the function of absorbing nitrogen.

4. A method for improving gas extraction effect by linkage of ground drilling groups, which adopts the system for improving gas extraction effect by linkage of ground drilling groups as claimed in any one of claims 1 to 3, characterized in that: The steps include: ① According to the occurrence of coal seams (1), the layout of underground coal seam tunnels and the gas mining conditions, several surface wells are constructed on the ground. After the surface well construction is completed, they are sealed according to conventional methods; ② Every three surface drilling wells form a group, the first surface drilling well (2), the second surface drilling well (37), and the third surface drilling well (38) are connected to the extraction branch pipe (9), the control valves on the gas extraction pipes (3) of the second surface drilling well (37) and the third surface drilling well (38) are opened, and the gas injection interface (4) on the gas extraction pipe (3) of the first surface drilling well (2) is connected to the gas injection pipe (6); ③ The fifth valve (33), the fourth valve (29), the third valve (19) and the first valve (5) are opened in sequence. The gas concentration gushing out of the second surface well (37) and the third surface well (38) is close to 100%. The second gas concentration measuring device (32) transmits the gas concentration signal to the controller (26). When the gas concentration of the second gas concentration measuring device (32) received by the controller (26) is higher than 30%, the controller (26) transmits a signal through the data line to open the first electric valve (7). After a delay of 30 seconds, the controller (26) transmits a signal through the data line to open the booster pump (1) in sequence. 4) and the first gas extraction pump (15), the gas from the second surface well (37) and the third surface well (38) is injected into the first surface well (2) through the gas extraction pipe (3) under the action of the extraction negative pressure of the first gas extraction pump (15), through the drying device (30), the first branch pipe (28), the conventional gas injection pipe (18), the booster pipe (13), the gas injection pipe (6), the gas injection interface (4); the pressure of the injected gas gas on the coal body around the first surface well (2) is in the same direction as the extraction negative pressure of the second surface well (37), forming a combined force to fracture the coal body, and the gas injection time is 24-48 hours; ④ Remove the gas injection pipe (6) connected to the gas extraction pipe (3) of the first surface drilling well (2), connect the first surface drilling well (2) to the extraction branch pipe (9), open the second valve (8), close the valve on the gas extraction pipe of the second surface drilling well (37), separate the gas extraction pipe of the second surface drilling well (37) from the extraction branch pipe (9), connect the gas injection interface (4) of the second surface drilling well (37) to the gas injection pipe (6), repeat step ③, until the work of injecting high-concentration gas into the first surface drilling well (2), the second surface drilling well (37), and the third surface drilling well (38) to improve the gas extraction effect is completed; ⑤ Connect the gas extraction pipes of the first surface drilling well (2), the second surface drilling well (37), and the third surface drilling well (38) to the extraction branch pipe (9), and sequentially open the fourth electric valve (34) and the second gas extraction pump (36) through the controller (26) to extract gas, and the gas extraction time is 4-6 days; ⑥ Repeat steps ②, ③, ④, and ⑤ 5-7 times to complete the production increase operation of the surface drilling group. During this process, the coal bodies around the first surface drilling well (2), the second surface drilling well (37), and the third surface drilling well (38) experience gas positive pressure fracturing, gas dynamic fatigue fracturing with positive and negative pressure conversion, and gas displacement, and then normal gas extraction is carried out, and the gas injection pipe (6) is kept connected to the gas injection interface (4) of the first surface drilling well (2); ⑦ During the gas extraction process, when the second gas concentration measuring device (32) measures a gas concentration lower than 30%, the second gas concentration measuring device (32) transmits the measured gas concentration signal to the controller (26) via the data line, and the controller (26) closes the fourth electric valve (34) and the second gas extraction pump (36), and opens the third electric valve (25), and then opens the fourth valve (29) and the first valve (5) in sequence. After a delay of 30 seconds, the controller (26) transmits a signal via the data line to open the booster pump (14) and the first gas extraction pump (15) in sequence, and the gas After passing through the deoxygenation device (24) and the denitrogenation device (23), when the first gas concentration measuring device (22) measures that the gas concentration is lower than 30%, the controller (26) transmits a signal through the data line to open the second electric valve (11), and the gas flows back to the extraction branch pipe (9), until the first gas concentration measuring device (22) measures that the gas concentration is higher than 30%, the controller (26) transmits a signal through the data line to open the first electric valve (7), and the gas with a concentration higher than 30% is injected into the first surface drilling well (2), the injection gas pressure is 2-5 MPa, and the injection time is 8-12 hours; ⑧ Remove the gas injection pipe (6) connected to the gas extraction pipe (3) of the first surface drilling well (2), connect the first surface drilling well (2) to the extraction branch pipe (9), open the second valve (8), close the valve on the gas extraction pipe of the second surface drilling well (37), separate the gas extraction pipe of the second surface drilling well (37) from the extraction branch pipe (9), connect the gas injection interface (4) of the second surface drilling well (37) to the gas injection pipe (6), repeat step ⑦, cycle in sequence, until the work of injecting high-concentration gas into the first surface drilling well (2), the second surface drilling well (37), and the third surface drilling well (38) to improve the gas extraction effect is completed; ⑨ Connect the first surface drilling well (2), the second surface drilling well (37), and the third surface drilling well (38) to the extraction branch pipe (9), open the fourth electric valve (34) and the second gas extraction pump (36) through the controller (26), and perform gas extraction, and the gas extraction time is 2-3 days; ⑩ Repeat steps ⑦, ⑧ and ⑨ until the coal seam gas extraction volume reaches the design requirements. In this process, it is ensured that the extracted gas concentration does not affect gas utilization.

5. A method for improving gas extraction effect by linkage of ground drilling groups according to claim 4, characterized in that: In step ③, the pressure of the gas injected into the first surface drilling well (2) after being pressurized by the booster pump (14) is 10-14 MPa.

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