CN117646649A - Positive and negative pressure combined drainage device and method for double-layer casing pipe of gas extraction drilling hole - Google Patents

Abstract

The invention discloses a double-layer casing positive and negative pressure combined drainage device for gas extraction boreholes, which is installed in the borehole and includes a round head of a gas injection screen tube, a triangular cone, a drainage screen tube, an outer tube, an inner tube, and a tee. head, a gas-water separator, a gas injection hose, a gas injection valve, a gas injection main pipe, a drainage valve and a drainage main pipe. A method for combined positive and negative pressure drainage of a double-layer casing in a gas drainage borehole is also disclosed. The invention uses The high-pressure gas reaches the water accumulation point in the borehole from the inner tube and the round head of the gas injection screen tube, forming a gas-liquid mixture fluid. Under the dual effects of the positive pressure of the injected gas and the negative pressure of the extraction, the gas-liquid mixture fluid enters the inner tube along the drainage screen tube. The annular space between the outer pipe and the outer pipe then enters the gas-water separator. Under the action of gravity, the water remains in the box, and the gas moves upward and enters the gas drainage system from the main drainage pipe, thereby removing the accumulated water in the borehole. It is discharged out of the hole in sections to reduce the borehole gas drainage resistance and improve the gas drainage effect.

Description

Gas drainage borehole double-layer casing positive and negative pressure combined drainage device and method

Technical field

The invention belongs to the technical field of gas drainage, and particularly provides a positive and negative pressure combined drainage device and method for a double-layer casing of a gas drainage borehole.

Background technique

As my country pays more and more attention to coal mine safety and invests more and more in safety, the gas drainage rate of coal mines has increased significantly, but the gas drainage effect has not been significantly improved. The problems of rapid decay of borehole gas drainage flow and low gas drainage concentration are common. One of the important reasons is that water and sediment accumulate in the borehole, which blocks the flow of gas in the borehole channel, making the gas drainage borehole effective. The mining length is reduced, and the borehole construction length cannot be converted into an effective drainage length, resulting in low drainage efficiency. Due to the limited drainage negative pressure, it is difficult to pump out the accumulated water deep in the borehole simply by using negative pressure drainage. There is still no effective solution to the problem of water accumulation in boreholes.

Contents of the invention

In order to solve the above problems, the present invention provides a double-layer casing positive and negative pressure combined drainage device and method for gas drainage boreholes.

In order to achieve the above object, the technical solution adopted by the present invention is: a double-layer casing positive and negative pressure combined drainage device for gas extraction boreholes, which is installed in the borehole and includes a gas injection screen round head, a triangular cone, a drainage screen pipe, The outer pipe, the inner pipe, the three-way variable head, the gas-water separator, the gas injection hose, the gas injection valve, the gas injection main pipe, the extraction valve and the drainage main pipe. The round head of the gas injection screen pipe is assembled on the triangular pyramid. The front end, the rear end of the triangular cone is equipped with a drainage screen tube and an inner tube, the rear end of the drainage screen tube is equipped with an outer tube, and the inner tube is placed inside the drainage screen tube and the outer tube, and the inner tube passes through The triangular cone is connected to the round head of the air injection screen tube. The rear end of the outer tube is assembled on the first end of the three-way change head. The second end of the three-way change head is equipped with an air injection hose, and the air injection soft The pipe is connected to the inner pipe. The third end of the three-way variable head is equipped with a gas-water separator. The outer end of the gas injection hose is connected to the gas injection main pipe after passing through the gas injection valve. The gas-water separator is The upper end is connected to the main drainage pipe through the drainage valve, and the main pipe is connected to the gas drainage system.

Further, the front end of the round head of the air injection screen tube is a hemispherical entity, the rear end of the round head of the air injection screen tube is a screen tube, the length of the screen tube is 1m, the outer diameter is 20mm, and the screen tube There are sieve holes with a diameter of 5mm evenly arranged on the surface.

Further, the triangular cone is made of aluminum alloy material. One end of the triangular cone connecting the drainage screen pipe and the inner pipe has an inner and outer double-layer pipeline structure, and the outer pipe at the other end of the triangular cone gradually shrinks to be in contact with the inner pipe. tube merge.

Further, the drainage screen pipe has a double-layer structure. The inner structure of the drainage screen pipe has the same diameter as the outer pipe, and the surface of the inner structure is processed with small holes with a diameter of 10 mm. The outer surface of the drainage screen pipe has a double-layer structure. The layer structure is a stainless steel gauze with 2mm holes.

Further, the outer tube has a diameter of 40mm and a wall thickness of 4mm, and the inner tube has a diameter of 20mm and a wall thickness of 4mm.

Further, the rear end of the inner tube is located in the tee changer, and the rear end of the inner tube is assembled on the second end of the tee changer.

Further, the gas-water separator includes a separator box, the upper side of the outer wall of the separator box is equipped with an exhaust valve and an air inlet elbow, and the air inlet elbow is installed on the third of the three-way change head. At three ends, the lower side of the outer wall of the separator box is equipped with a drain outlet, and the drain outlet is equipped with a drain valve. The lower wall of the separator box is equipped with a bracket, and the upper wall of the separator box is equipped with a drain outlet. There is a drainage port connected to the drainage valve.

Further, a hole sealing tube is assembled at the hole opening of the drilled hole, and the outer tube penetrates the hole sealing tube. A metal baffle and sealing rubber are installed at the hole opening of the hole sealing tube, and the sealing rubber is assembled on the hole sealing tube. between the tube and the outer tube.

The double-layer casing positive and negative pressure combined drainage method for gas drainage boreholes adopts the above-mentioned double-layer casing positive and negative pressure combined drainage device for gas drainage boreholes, which specifically includes the following steps:

Step 1. When the gas drainage borehole is a downward ordinary borehole or a directional long borehole with undulating trajectories, and there is water accumulation inside the borehole that affects the gas drainage effect, remove the drainage pipeline from the hole sealing pipe. Connect the round head of the air injection screen pipe, triangular cone, drainage screen pipe, outer pipe, and inner pipe in sequence from the hole sealing pipe to the inside of the borehole. The round head of the air injection screen pipe enters the accumulated water for 2 to 5 meters and then is fixed;

Step 2, install the metal baffle and sealing rubber at the opening of the sealing tube;

Step 3: Install a tee changer at the orifice of the sealing pipe. The first end of the tee changer is connected to the outer pipe, the second end is connected to the air injection hose connected to the inner pipe, and the third end is connected to the air inlet elbow. head;

Step 4. Install the gas-water separator. Place the separator box 2m away from the opening of the sealing pipe. Connect the exhaust valve, drain valve, drain port, bracket, extraction port, and air inlet elbow respectively. Installed on the separator box, the extraction port is connected to the extraction valve, and the air inlet elbow is connected to the tee changer;

Step 5: After the installation of the gas-water separator is completed, inject positive gas pressure and negative extraction pressure at the same time, keep the exhaust valve and the drainage valve closed, inject positive gas pressure, open the gas injection valve and the extraction valve, The high-pressure gas passes through the gas injection hose, tee changer, inner tube, and gas injection screen round head in order to accumulate water in the borehole. The injected air and the water in the borehole form a gas-liquid mixture fluid, which flows to the upper part of the borehole;

Step 6: Negative pressure is generated from the main drainage pipe, and then passes through the drainage valve, separator box, air inlet elbow, tee changer, outer pipe, and drainage screen pipe to the inside of the borehole. To carry out extraction work;

Step 7: Under the dual effects of the positive pressure of the injected gas and the negative pressure of the extraction, the gas-liquid mixture flows along the drainage screen pipe into the annular space between the inner pipe and the outer pipe. After passing through the tee, it passes through the air inlet bend. The head enters the separator box;

Step 8: The mixed flow of gas and water enters the separator box. Under the action of gravity, the water flows downward and remains in the separator box. The gas moves upward and enters the gas drainage system from the main drainage pipe;

Step 9: When the accumulated water fills the separator box, close the gas injection valve and the extraction valve, open the exhaust valve and the drain valve, and discharge the accumulated water from the separator box;

Step 10: When no accumulated water is discharged within 5 minutes of the gas injection process, continue to extend the accumulated water drainage pipeline system 2-5m deeper into the borehole, and perform drainage operations for the next stage of the borehole according to steps 5 to 9. After all the accumulated water in the borehole is drained, stop the operation, withdraw the round head, triangular cone, drainage screen pipe, outer pipe, and inner pipe of the gas injection screen, and reconnect the borehole to the gas drainage system for drainage. Mining work.

The beneficial effects of using the present invention are:

The invention proposes a combined positive and negative pressure drainage device for a double-layer casing in a gas extraction borehole. The high-pressure gas reaches the water accumulation point in the borehole from the inner pipe and the round head of the gas injection screen tube to form a gas-liquid mixture fluid. The gas-liquid mixture fluid is injected into the gas Under the dual action of positive pressure and extraction negative pressure, it enters the annular space between the inner pipe and the outer pipe along the drainage screen pipe, and then enters the gas-water separator. Under the action of gravity, the water remains in the box and the gas moves upward. Move from the main drainage pipe into the gas drainage system, thereby draining the accumulated water in the borehole out of the borehole in sequence, reducing the gas drainage resistance of the borehole and improving the gas drainage effect.

The invention combines the inner pipe and the outer pipe, can apply positive pressure of injection gas and negative pressure of extraction at the same time, and effectively distinguish the positive and negative pressures through the three-way variable head, making the entire device simple in structure and able to effectively complete drilling operations. Extraction of pore water.

Description of drawings

Figure 1 is a schematic structural diagram of a double-layer casing positive and negative pressure combined drainage device for gas drainage boreholes according to the present invention.

Reference symbols include: 1. Round head of air injection screen tube, 2. Triangular cone, 3. Drainage screen tube, 4. Outer tube, 5. Inner tube, 6. Tee changer, 7. Air-water separator, 7 -1. Separator box, 7-2. Exhaust port valve, 7-3 Drainage port valve, 7-4. Drainage port, 7-5. Bracket, 7-6. Drainage port, 7-7. Inlet Gas elbow, 8. Gas injection hose, 9. Gas injection valve, 10 Gas injection main pipe, 11. Drainage valve, 12. Drainage main pipe, 13. Sealing pipe, 14. Metal baffle, 15. Sealing rubber , 16. Sealing cement, 17. High-pressure gas, 18. Gas-liquid mixture fluid, 19. Borehole water accumulation.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Embodiment 1

Referring to Figure 1, a double-layer casing positive and negative pressure combined drainage device for gas extraction boreholes is installed in the borehole, including a gas injection screen round head 1, a triangular cone 2, a drainage screen pipe 3, an outer pipe 4, and an inner pipe. 5. Tee changer 6, gas-water separator 7, gas injection hose 8, gas injection valve 9, gas injection main pipe 10, extraction valve 11 and extraction main pipe 12, gas injection screen round head 1 is assembled on the triangle The front end of the cone 2 and the rear end of the triangular cone 2 are equipped with a drainage screen pipe 3 and an inner pipe 5. The rear end of the drainage screen pipe 3 is equipped with an outer pipe 4, and the inner pipe 5 is placed between the drainage screen pipe 3 and the outer pipe 4. Inside, the inner tube 5 is connected to the round head 1 of the air injection screen through the triangular cone 2. The rear end of the outer tube 4 is assembled on the first end of the tee changer 6. The second end of the tee changer 6 is equipped with an air injection pipe. hose 8, and the gas injection hose 8 is connected with the inner pipe 5. The third end of the tee changer 6 is equipped with a gas-water separator 7. The outer end of the gas injection hose 8 passes through the gas injection valve 9 and is connected to the gas injection valve 9. The main pipe 10 is connected, the upper end of the gas-water separator 7 is connected to the main pipe 12 through the drainage valve 11, and the main pipe 12 is connected to the gas drainage system.

The round head 1 of the air injection screen pipe is made of aluminum alloy material, which can better bring the subsequent triangular cone 2, drainage screen pipe 3, outer pipe 4 and inner pipe 5 into the drilling hole.

The round head 1 of the gas injection screen pipe is connected with the inner tube 5, the gas injection hose 8, the gas injection valve 9 and the gas injection main pipe 10, and is used to inject high-pressure gas 17 to form a positive pressure. The high-pressure gas 17 flows from the round head 1 of the gas injection screen pipe. The outflow is mixed with the borehole water 19 to form a gas-liquid mixture fluid 18. The gas-liquid mixture fluid 18 flows toward the upper side of the borehole under the action of air pressure and air flow.

The drainage screen pipe 3 is connected with the outer pipe 4, the tee changer 6, the gas-water separator 7, the extraction valve 11, and the extraction main pipe 12, and is used to transmit the negative pressure of the extraction, and the negative pressure will cause the gas-liquid mixture fluid 18 to enter The drainage screen pipe 3 finally flows into the gas-water separator 7, and the gas-water separation is completed at the gas-water separator 7.

Specifically, the front end of the round head 1 of the air injection screen tube is a hemispherical entity, and the rear end of the round head 1 of the air injection screen tube is a screen tube. The length of the screen tube is 1m, the outer diameter is 20mm, and the surface of the screen tube is uniform. Sieve holes with a diameter of 5 mm are arranged.

The hemispherical entity at the front end of the round head 1 of the gas injection screen can push away the coal slime and prevent the coal slime from entering the pipeline.

The high-pressure gas 17 flowing in through the inner tube 5 finally flows into the borehole through the screen holes of the gas injection screen round head 1 .

Specifically, the triangular cone 2 is made of aluminum alloy material. One end of the triangular cone 2 connecting the drainage screen pipe 3 and the inner pipe 5 has an inner and outer double-layer pipeline structure, and the outer pipe of the other end of the triangular cone 2 gradually shrinks to Inner tubes merge.

The inner tubes at both ends of the triangular cone 2 have the same size, and the triangular cone 2 and the air injection screen round head 1 are connected by welding. The triangular cone 2 is connected to the drainage screen pipe 3 and the inner pipe 5 using quick joints.

Specifically, the drainage screen pipe 3 has a double-layer structure and is made of aluminum alloy material. The diameter of the inner structure of the drainage screen pipe 3 is the same as that of the outer pipe 4, and the surface of the inner structure is processed with small holes with a diameter of 10 mm. The outer structure of the drainage screen pipe 3 is a stainless steel gauze with small holes of 2 mm in diameter.

The gas-liquid mixture fluid 18 flows into the annular space between the outer tube 4 and the inner tube 5 through the drainage screen tube 3 .

Specifically, the outer tube 4 has a diameter of 40 mm and a wall thickness of 4 mm, and the inner tube 5 has a diameter of 20 mm and a wall thickness of 4 mm.

The outer tube 4 and the inner tube 5 are both made of PE material, and both the outer tube 4 and the inner tube 5 are made of continuous tube coils.

Specifically, the rear end of the inner tube 5 is located in the tee changer 6 , and the rear end of the inner tube 5 is assembled on the second end of the tee changer 6 .

The tee changer 6 is made of aluminum alloy material and is a separation device for the outer tube 4 and the inner tube 5 .

Specifically, the gas-water separator 7 includes a separator box 7-1. The upper side of the outer wall of the separator box 7-1 is equipped with an exhaust port valve 7-2 and an air inlet elbow 7-7, and the air inlet The elbow 7-7 is assembled at the third end of the tee changer 6, the lower side of the outer wall of the separator box 7-1 is equipped with a drain outlet 7-4, and the drain outlet 7-4 is equipped with a drain outlet valve 7- 3. The lower wall of the separator box 7-1 is equipped with a bracket 7-5, and the upper wall of the separator box 7-1 is provided with a extraction port 7-6 connected to the extraction valve 11.

The gas-water separator 7 is made of stainless steel and is mainly used to separate water and gas in the gas-liquid mixture fluid 18. After the gas-liquid mixture fluid 18 enters the gas-water separator 7, the liquid is stored in the separator box 7-1. The gas is extracted. When the liquid is fully stored in the separator box 7-1, open the exhaust valve 7-2 and the drain valve 7-3 to discharge the liquid.

Specifically, a hole sealing tube 13 is assembled at the hole of the drilled hole, and the outer tube 4 penetrates the hole sealing tube 13 . A metal baffle 14 and a sealing rubber 15 are assembled at the hole of the hole sealing tube 13 , and the sealing rubber 15 It is assembled between the sealing tube 13 and the outer tube 4.

The metal baffle 14 and the sealing rubber 15 are used to seal the gap between the sealing tube 13 and the outer tube 4 to reduce the loss of air pressure.

Sealing between the hole sealing pipe 13 and the borehole is achieved by sealing cement 16 .

Embodiment 2

The method for combined positive and negative pressure drainage of double-layer casing in gas drainage boreholes adopts the positive and negative pressure combined drainage device of double-layer casing in gas drainage boreholes as in Embodiment 1, which specifically includes the following steps:

Step 1: When the gas drainage borehole is a downward ordinary borehole or a directional long borehole with undulating trajectories, and there is water accumulation inside the borehole that affects the gas drainage effect, the drainage pipeline is removed from the hole sealing pipe 13 , connect the air injection screen round head 1, triangular cone 2, drainage screen pipe 3, outer pipe 4, and inner pipe 5 in sequence from the sealing pipe 13 to the inside of the borehole, and the air injection screen round head 1 enters the water accumulation 2 Fixed after ~5m;

Step 2, install the metal baffle 14 and the sealing rubber 15 at the opening of the sealing tube 13;

The metal baffle 14 and sealing rubber 15 are used to seal the gap between the hole sealing tube 13 and the outer tube 4 to reduce the loss of air pressure during air injection;

Step 3: Install the tee changer 6 at the orifice of the hole sealing pipe 13. The first end of the tee changer 6 is connected to the outer pipe 4, and the second end is connected to the gas injection hose 8 connected to the inner pipe 5. Three ends are connected to the air inlet elbow 7-7;

Step 4, install the gas-water separator 7, place the separator box 7-1 2m away from the hole of the sealing pipe 13, and connect the exhaust port valve 7-2, the drain valve 7-3, and the drain port respectively. 7-4, bracket 7-5, extraction port 7-6, and air inlet elbow 7-7 are installed on the separator box 7-1. The extraction port 7-6 is connected to the extraction valve 11 and the air inlet elbow. 7-7 connects tee changer 6;

Step 5: After the installation of the gas-water separator 7 is completed, inject positive gas pressure and extraction negative pressure at the same time, keep the exhaust port valve 7-2 closed and the drain valve 73 closed, perform positive gas pressure injection, and open the gas injection valve. 9 and the extraction valve 11, the high-pressure gas 17 passes through the gas injection hose 8, the three-way change head 6, the inner pipe 5, the gas injection screen round head 1, and collects water in the borehole. The injected air and the borehole water 19 form a gas-liquid mixture. Fluid 18 flows to the upper part of the borehole;

Step 6, negative pressure is extracted from the main extraction pipe 12, and then passes through the extraction valve 11, the separator box 7-1, the air inlet elbow 7-7, the tee changer 6, and the outer pipe 4 in sequence. , the drainage screen pipe 3 reaches the inside of the borehole and is used for drainage work;

Since the gap between the sealing tube 13 and the outer tube 4 is sealed by the metal baffle 14 and the sealing rubber 15, the bore hole is blocked, and the only pressure relief flow channel for the gas-liquid mixture fluid 18 is the drainage screen tube 3;

Step 7: Under the dual effects of the positive pressure of the injected gas and the negative pressure of the extraction, the gas-liquid mixture fluid 18 enters the annular space between the inner pipe 5 and the outer pipe 4 along the drainage screen pipe 3, and passes through the tee changer 6 , enters the separator box 7-1 through the air inlet elbow 7-7;

Step 8: The mixed flow of gas and water enters the separator box 7-1. Under the action of gravity, the water flows downward and remains in the separator box 7-1. The gas moves upward and enters the gas from the drainage main pipe 12. extraction system;

Step 9: When the accumulated water fills the separator box 7-1, close the gas injection valve 9 and the extraction valve 11, open the exhaust valve 7-2 and the drain valve 7-3, and drain the accumulated water from the separator. Discharged from box 7-1;

Step 10: When no accumulated water is discharged within 5 minutes of the gas injection process, continue to extend the accumulated water drainage pipeline system 25m deep into the borehole. Follow steps 5 to 9 to perform drainage operations for the next stage of the borehole until the After all the accumulated water within the borehole is drained, stop the operation, withdraw the gas injection screen round head 1, triangular cone 2, drainage screen pipe 3, outer pipe 4, and inner pipe 5, and reconnect the borehole to the gas drainage. The system performs extraction work.

The above contents are only preferred embodiments of the present invention. For those of ordinary skill in the art, many changes can be made in the specific implementation modes and application scope according to the ideas of the present invention. As long as these changes do not deviate from the concept of the present invention, they are not affected by the present invention. belong to the protection scope of the present invention.

Claims (9)

1. Positive and negative pressure combined drainage device for double-layer casing pipe of gas extraction drilling hole is arranged in the drilling hole, and is characterized in that: including gas injection screen pipe button head (1), triangular cone (2), drainage screen pipe (3), outer tube (4), inner tube (5), tee bend change head (6), gas-water separator (7), gas injection hose (8), gas injection valve (9), gas injection main pipe (10), extraction valve (11) and extraction main pipe (12), gas injection screen pipe button head (1) is assembled in the front end of triangular cone (2), the rear end of triangular cone (2) is equipped with drainage screen pipe (3) and inner tube (5), the rear end of drainage screen pipe (3) is equipped with outer tube (4), and the inside of drainage screen pipe (3) and outer tube (4) is arranged in to inner tube (5), inner tube (5) are through the inside of triangular cone (2) and gas injection screen pipe button head (1), the rear end of outer tube (4) is assembled in the first end of tee bend change head (6), the second end of tee bend change head (6) is assembled in gas injection hose (8), and gas injection hose (5) and tee bend change head (6) are equipped with through tee bend change head (6) and the inside of pipe (4), the upper end of the gas-water separator (7) is communicated with a main extraction pipe (12) through an extraction valve (11), and the main extraction pipe (12) is connected with a gas extraction system.

2. The positive and negative pressure combined drainage device for the double-layer casing of the gas extraction drill hole according to claim 1, wherein the positive and negative pressure combined drainage device is characterized in that: the front end of the gas injection screen pipe round head (1) is a hemispherical entity, the rear end of the gas injection screen pipe round head (1) is a screen pipe, the length of the screen pipe is 1m, the outer diameter of the screen pipe is 20mm, and screen holes with the diameter of 5mm are uniformly distributed on the surface of the screen pipe.

3. The positive and negative pressure combined drainage device for the double-layer casing of the gas extraction drill hole according to claim 1, wherein the positive and negative pressure combined drainage device is characterized in that: the triangular cone (2) is made of an aluminum alloy material, one end of the triangular cone (2) connected with the drainage screen pipe (3) and the inner pipe (5) is of an inner-outer double-layer pipeline structure, and the outer pipe at the other end of the triangular cone (2) is gradually contracted to be combined with the inner pipe.

4. The positive and negative pressure combined drainage device for the double-layer casing of the gas extraction drill hole according to claim 1, wherein the positive and negative pressure combined drainage device is characterized in that: the drainage screen pipe (3) is of a double-layer structure, the diameter of an inner layer structure of the drainage screen pipe (3) is the same as that of the outer pipe (4), small holes with the aperture of 10mm are machined in the surface of the inner layer structure, and the outer layer structure of the drainage screen pipe (3) is a stainless steel gauze provided with small holes with the aperture of 2 mm.

5. The positive and negative pressure combined drainage device for the double-layer casing of the gas extraction drill hole according to claim 1, wherein the positive and negative pressure combined drainage device is characterized in that: the pipe diameter of the outer pipe (4) is 40mm, the wall thickness is 4mm, the pipe diameter of the inner pipe (5) is 20mm, and the wall thickness is 4mm.

6. The positive and negative pressure combined drainage device for the double-layer casing of the gas extraction drill hole according to claim 1, wherein the positive and negative pressure combined drainage device is characterized in that: the rear end of the inner tube (5) is positioned in the three-way variable head (6), and the rear end of the inner tube (5) is assembled at the second end of the three-way variable head (6).

7. The positive and negative pressure combined drainage device for the double-layer casing of the gas extraction drill hole according to claim 1, wherein the positive and negative pressure combined drainage device is characterized in that: the gas-water separator (7) comprises a separator box body (7-1), an exhaust port valve (7-2) and an air inlet elbow (7-7) are arranged on the upper side of the outer wall of the separator box body (7-1), the air inlet elbow (7-7) is arranged at the third end of the three-way variable head (6), a water outlet (7-4) is arranged on the lower side of the outer wall of the separator box body (7-1), a water outlet valve (7-3) is arranged on the water outlet (7-4), a support (7-5) is arranged on the lower wall of the separator box body (7-1), and a pumping port (7-6) communicated with a pumping valve (11) is formed in the upper wall of the separator box body (7-1).

8. The positive and negative pressure combined drainage device for the double-layer casing of the gas extraction drill hole according to claim 1, wherein the positive and negative pressure combined drainage device is characterized in that: the hole opening of the drill hole is provided with a hole sealing pipe (13), the outer pipe (4) penetrates through the hole sealing pipe (13), the hole opening of the hole sealing pipe (13) is provided with a metal baffle (14) and sealing rubber (15), and the sealing rubber (15) is arranged between the hole sealing pipe (13) and the outer pipe (4).

9. The positive and negative pressure combined drainage method for the double-layer casing of the gas extraction drill hole adopts the positive and negative pressure combined drainage device for the double-layer casing of the gas extraction drill hole according to any one of claims 1 to 8, and specifically comprises the following steps:

step 1, when a gas extraction borehole is a down common borehole or a long directional borehole with a fluctuant track and water accumulation in the borehole affects the gas extraction effect, a gas extraction pipeline is detached from a hole sealing pipe (13), a gas injection screen pipe round head (1), a triangular cone (2), a drainage screen pipe (3), an outer pipe (4) and an inner pipe (5) are sequentially connected and sent into the borehole from the hole sealing pipe (13), and the gas injection screen pipe round head (1) enters the water accumulation for 2-5m and is fixed;

step 2, mounting a metal baffle plate (14) and sealing rubber (15) at the orifice of the hole sealing tube (13);

step 3, a three-way change head (6) is arranged at the orifice of the hole sealing pipe (13), the first end of the three-way change head (6) is connected with the outer pipe (4), the second end is connected with an air injection hose (8) communicated with the inner pipe (5), and the third end is connected with an air inlet elbow (7-7);

step 4, installing a gas-water separator (7), placing a separator box body (7-1) at a position 2m away from an orifice of a hole sealing pipe (13), respectively installing an exhaust port valve (7-2), a water outlet valve (7-3), a water outlet (7-4), a bracket (7-5), a suction port (7-6) and an air inlet elbow (7-7) on the separator box body (7-1), wherein the suction port (7-6) is connected with a suction valve (11), and the air inlet elbow (7-7) is connected with a three-way variable head (6);

after the installation of the gas-water separator (7) is finished, positive gas pressure and negative extraction pressure are injected at the same time, the exhaust port valve (7-2) is kept closed, the water outlet valve (7-3) is kept closed, positive gas injection pressure work is carried out, the gas injection valve (9) and the extraction valve (11) are opened, high-pressure gas (17) sequentially passes through the gas injection hose (8), the three-way variable head (6), the inner pipe (5) and the round head (1) of the gas injection sieve tube to accumulate water in a drill hole, and the injected air and the accumulated water (19) in the drill hole form gas-liquid mixture fluid (18) to flow to the upper part of the drill hole;

step 6, extracting negative pressure, namely generating negative pressure from an extraction main pipe (12), and sequentially passing through an extraction valve (11), a separator box body (7-1), an air inlet elbow (7-7), a three-way variable head (6), an outer pipe (4) and a drainage screen pipe (3) to reach the inside of a drill hole for carrying out extraction work;

step 7, under the dual actions of positive pressure and negative extraction pressure of injected gas, the gas-liquid mixture fluid (18) enters an annular space between the inner pipe (5) and the outer pipe (4) along the drainage screen pipe (3), passes through the three-way variable head (6), and enters the separator box body (7-1) through the air inlet elbow (7-7);

step 8, the gas-water mixed flow enters a separator box body (7-1), water flows downwards under the action of gravity and stays in the separator box body (7-1), gas moves upwards, and enters a gas extraction system from an extraction main pipe (12);

step 9, when the separator box body (7-1) is full of accumulated water, the gas injection valve (9) and the extraction valve (11) are closed, the gas exhaust valve (7-2) and the water outlet valve (7-3) are opened, and the accumulated water is discharged from the separator box body (7-1);

and 10, after no accumulated water is discharged in the gas injection process for 5min, continuing to extend the accumulated water pumping and discharging pipeline system to the depth of the drilled hole for 2-5m, performing water discharging operation on the next stage of the drilled hole according to the steps 5 to 9 until all accumulated water in the range of the drilled hole is discharged, stopping operation, withdrawing the round head (1) of the gas injection sieve tube, the triangular cone (2), the water discharging sieve tube (3), the outer tube (4) and the inner tube (5), and reconnecting the drilled hole to the gas pumping and discharging system to perform the gas pumping and discharging operation.