Gas extraction treatment method for secondary hole forming of goaf penetrating through protective layer

Abstract

The invention discloses a gas extraction treatment method for secondary hole forming through a protective layer goaf, which comprises the following steps of: firstly, constructing a first-stage drill hole from a current coal seam to the protective layer goaf, injecting filling colloid into the protective layer goaf through the first-stage drill hole after the first-stage drill hole is completed, and after the filling colloid and broken rock mass in the goaf are cemented and solidified, injecting the filling colloid into the protective layer goaf; forming a coal rock cementitious body for connecting the goaf top and bottom plates; construction continues to be conducted along the first-stage drill hole, the drill hole extends into the roof rock stratum through the coal rock cementitious body until the fissure zone is reached, and second-stage drilling is completed; and finally, a gas extraction pipe is arranged in the drill hole to perform gas extraction on the fissure zone, by forming a coal rock cementitious body in the protective layer goaf and combining a two-stage secondary hole forming mode, gas extraction is performed on the upper fissure zone by penetrating through the goaf from the current coal seam, and the goaf does not interfere with gas extraction. Therefore, the effect of gas extraction of the fissure zone is guaranteed, and subsequent safe mining of a coal seam is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of gas extraction technology, specifically a gas extraction and control method that involves secondary drilling through a protective layer goaf. Background Technology

[0002] Coal mining follows a pattern of progressing from shallow to deep. For closely spaced coal seams, the upper seam, once mined, acts as a protective layer to reduce the gas hazard associated with mining adjacent lower seams. However, during coal seam mining, gas in the goaf often accumulates from the caving zone to the fracture zone. When this accumulation becomes excessive, it can erupt from the upper corner of the currently mined coal seam, causing gas levels to exceed limits at the upper corner of the working face. Therefore, to extract gas from the fracture zone of the goaf, it is necessary to construct high-level cross-seam boreholes through the current coal seam into the fracture zone above. However, during high-level borehole construction, the goaf, formed after the protective layer above the coal seam is mined, contains a lot of gravel, making borehole drilling difficult. If the borehole directly passes through the goaf and is drilled into the fracture zone above it for gas extraction, the extracted gas will escape into the protective layer goaf and may re-enter the fracture zone, ultimately failing to achieve gas extraction from the fracture zone. As coal mining continues, gas accumulates in the fracture zones. If it cannot be extracted in time, it will surge into the working face in large quantities, causing the risk of gas exceeding the limit or even gas explosion, which seriously affects mining efficiency and the safety of workers' lives.

[0003] Therefore, the research direction of this invention is to provide a new gas extraction and control method that can extract gas from the current coal seam through the goaf to the fracture zone above, without the goaf interfering with the gas extraction, thereby ensuring the effectiveness of gas extraction from the fracture zone and facilitating the safe mining of subsequent coal seams. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a gas extraction and control method for secondary drilling through the goaf of the protective layer. By forming a coal-rock cemented body in the goaf of the protective layer and combining it with secondary drilling, gas extraction can be carried out from the current coal seam through the goaf to the upper fracture zone. The goaf will not interfere with the gas extraction, thereby ensuring the effectiveness of gas extraction from the fracture zone and facilitating the safe mining of subsequent coal seams.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a method for gas extraction and control through secondary drilling in goaf areas traversing protective layers, comprising the following steps: Step 1: First stage of drilling: Drilling site is constructed within the currently mined coal seam. Then, upward drilling is carried out in the fracture zone above the protective layer. If the drill bit falls off during the drilling process, it means that the drilling has reached the goaf of the protective layer. At this time, drilling is stopped and the first stage of drilling is completed.

[0006] Step 2, cementation and solidification: Filling colloid is injected into the goaf of the protective layer through the first stage borehole. After the filling colloid cements and solidifies with the broken rock mass in the goaf, a coal-rock cemented body connecting the top and bottom plates of the goaf is formed in the goaf of the protective layer.

[0007] Step 3: Drilling the second stage: Continue drilling along the first stage, drilling through the coal-rock cemented body and into the roof strata until reaching the fracture zone, thus completing the second stage drilling. If the drill bit falls off during drilling, it means that the coal-rock cemented body is not connected to the roof of the goaf. At this time, stop drilling and repeat step 2. After completion, continue drilling to complete the second stage drilling.

[0008] Step 4: Gas Drainage: Gas drainage pipes are laid from the drilling site into the borehole and connected to the underground gas drainage network to drain gas from the fracture zone, thereby achieving gas drainage and control of the current coal seam.

[0009] Furthermore, the criteria for judging the phenomenon of drill bit loss are as follows: if the drill pressure of the drill rod suddenly decreases or disappears from a constant value during the drilling process, and the drilling depth exceeds 1m under this condition, it is judged as drill bit loss.

[0010] Furthermore, both the first and second stage drilling were carried out using a high-torque drilling rig to drive the drill rod.

[0011] Further, step two specifically involves: inserting a colloid grouting pipe equipped with an external sealing device into the first-stage borehole, with one end of the colloid grouting pipe positioned within the goaf of the protective layer and the other end connected via a pipeline to a colloid mixer and pump located within the drilling site; connecting the sealing device to the colloid mixer and pump via the sealing grouting pipe; first placing sealing slurry in the colloid mixer and pump, then conveying the sealing slurry to the sealing device via the colloid mixer and pump, causing the sealing device to expand and inject the colloid grout. The gap between the grout pipe and the first-stage borehole is sealed; then, filling colloid is placed into the colloid mixer and pump, and the filling colloid is transported through the colloid grouting pipe to the goaf area of ​​the protective layer where the first-stage borehole is located through the colloid mixer and pump. After the injection is completed, the sealing state is maintained until the filling colloid cements and solidifies with the broken rock mass in the goaf area. Then, the sealing grout in the sealing device is discharged through the sealing grouting pipe, and the colloid grouting pipe and sealing device are removed to complete the cementing and solidification process.

[0012] Furthermore, the filling colloid is a high-viscosity mixture with poor flowability, such as concrete or water glass gel. This ensures the stability of the coal-rock cemented body and achieves the required strength.

[0013] Furthermore, the colloid mixer and pump is equipped with a pressure gauge and a valve, wherein the pressure gauge is used to monitor the pressure of the sealing slurry injected into the sealing device; and the valve is used to control the connection and disconnection between the colloid mixer and pump and the sealing grouting pipe and the colloid grouting pipe.

[0014] Furthermore, the sealing pressure of the sealing device is 6 MPa. This pressure value ensures that the required sealing effect is achieved, allowing the filling colloid to fully enter the fractures of the broken coal and rock in the goaf, and finally solidify to form a coal-rock cemented body.

[0015] Compared with existing technologies, this invention first constructs a first-stage borehole from the current coal seam into the protective goaf area. After completion, a filling colloid is injected into the protective goaf area through the first-stage borehole. After the filling colloid cements and solidifies with the fractured rock mass in the goaf area, a coal-rock cemented body connecting the roof and floor of the goaf area is formed. Then, construction continues along the first-stage borehole, with the borehole extending through the coal-rock cemented body into the roof strata until it reaches the fracture zone, completing the second-stage borehole. Finally, a gas extraction pipe is installed into the borehole to treat the fracture zone. Gas drainage, because the second-stage drilling passes through the goaf within the coal-rock cemented body, is not affected by the fractured coal and rock fissures within the goaf. This means that the extracted gas will not escape into the goaf. By forming a coal-rock cemented body within the protective goaf and combining it with the two-stage secondary drilling method, gas drainage can be achieved from the current coal seam through the goaf to the upper fracture zone. The goaf will not interfere with the gas drainage, thus ensuring the effectiveness of gas drainage from the fracture zone and facilitating the safe mining of subsequent coal seams. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the construction layout of the present invention.

[0017] In the diagram: 1-Roof strata; 2-Protective layer goaf; 3-Borehole; 4-Drill rod; 5-Coal-rock cemented body; 6-Fractured zone; 7-Collapse zone; 8-High torque drilling rig; 9-Sealing device; 10-Colloid grouting pipe; 11-Sealing grouting pipe; 12-First valve; 13-Pressure gauge; 14-Second valve; 15-Colloid agitator and pump; 16-Coal seam; 17-Drilling site. Detailed Implementation

[0018] The present invention will be further described below.

[0019] like Figure 1 As shown, the present invention includes the following steps: Step 1: Drilling the first stage of the project: Drilling site 17 is constructed within the currently mined coal seam 16. Then, drilling hole 3 is constructed from drilling site 17 towards the fracture zone 6 above the protective layer. If the drill bit falls off during the drilling process, it means that the drill hole 3 has reached the goaf area 2 of the protective layer. At this point, drilling is stopped and the first stage of drilling hole 3 is completed.

[0020] Step 2, cementation and solidification: Inject filling colloid into the goaf area 2 of the protective layer through the first stage borehole 3. The filling colloid is a high-viscosity mixture with poor flowability, such as concrete or water glass gel. This ensures the stability of the coal-rock cemented body 5 and achieves the required strength. After the filling colloid cements and solidifies with the broken rock mass in the goaf, the fissures in the broken coal-rock mass are sealed and solidified, forming a coal-rock cemented body 5 connecting the top and bottom plates of the goaf within the protective layer goaf 2. Specifically, the colloid injection pipe 10, equipped with a sealing device 9, is inserted into the first-stage borehole 2, with one end of the colloid injection pipe 10 inside the protective layer goaf 2 and the other end connected to the colloid mixer and pump 15 located in the drilling site 17 via a pipeline. The sealing device 9 is connected to the colloid mixer and pump 15 via the sealing injection pipe 11. First, sealing slurry is placed in the colloid mixer and pump 15, and then the sealing slurry is transported to the sealing device 9 through the colloid mixer and pump 15. The sealing device 9 expands to seal the gap between the colloid injection pipe 10 and the first stage borehole 3. Then, filling colloid is placed into the colloid mixer and pump 15. The filling colloid is transported through the colloid injection pipe 10 to the goaf area 2 of the protective layer where the first stage borehole 3 is located by the colloid mixer and pump 15. After the injection is completed, the sealing state is maintained until the filling colloid cements and solidifies with the broken rock mass in the goaf area. Then, the sealing grout in the sealing device 9 is discharged through the sealing grout pipe 11, and the colloid injection pipe 10 and the sealing device 9 are taken out (since the filling colloid above the sealing device 9 has solidified, the sealing device 9 itself and the colloid injection pipe 10 below the sealing device 9 to the drilling site 17 can be taken out from the borehole 3), completing the cementing and solidification process.

[0021] Step 3: Construction of the second stage of drilling: Continue construction along the first stage of drilling. Drill hole 3 passes through the coal-rock cemented body 5 and extends into the roof strata until it reaches the fracture zone, completing the second stage of drilling 3. If the drill bit falls off during the drilling process, it means that the coal-rock cemented body 5 is not connected to the roof of the goaf. At this time, stop drilling and repeat step 2. After completion, continue construction to complete the second stage of drilling 3. Both the first stage of drilling and the second stage of drilling are formed by using a high-torque drilling rig 8 to drive the drill rod.

[0022] Step 4: Gas Drainage: A gas drainage pipe is laid from drilling site 17 into borehole 3, and the gas drainage pipe is connected to the underground gas drainage network to drain gas from fracture zone 6. Since borehole 3 passes through the goaf by drilling into the coal-rock cemented body 5, the borehole 3 is not affected by the fractured coal-rock fissures in the goaf. That is, the extracted gas will not escape into the goaf and can directly enter the underground gas drainage network along borehole 3 and gas drainage pipe, thereby realizing the gas drainage and treatment of the current coal seam 16.

[0023] Step 5: Based on the mining progress of coal seam 16, repeat steps 1 to 4 above along the mining direction of coal seam 16, and carry out gas drainage in fracture zone 6 by constructing multiple secondary boreholes, thereby ensuring the gas drainage and control effect throughout the entire coal seam mining process.

[0024] As an improvement of the present invention, the colloid mixer and pump 15 is equipped with a pressure gauge 13, a first valve 12, and a second valve 14. The pressure gauge 13 is used to monitor the pressure of the sealing slurry injected into the sealing device 9; the first valve 12 is used to control the connection between the colloid mixer and pump 15 and the colloid injection pipe 10; and the second valve 14 is used to control the connection between the colloid mixer and pump 15 and the sealing injection pipe 11. The sealing pressure of the sealing device 9 is 6 MPa. This pressure value ensures the desired sealing effect, allowing the filling colloid to fully enter the fractures of the broken coal and rock in the goaf, ultimately solidifying to form a coal-rock cemented body 5.

[0025] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A gas extraction treatment method for secondary hole formation through a protective layer goaf, characterized in that, Includes the following steps: Step 1: Drilling in the first stage of construction: Drilling site is constructed within the currently mined coal seam, and then upward drilling is carried out in the fracture zone above the protective layer. If the drill bit falls off during the drilling process, it means that the drilling has reached the goaf of the protective layer. At this time, drilling is stopped and the first stage of drilling is completed. Step 2, cementation and solidification: Filling colloid is injected into the goaf of the protective layer through the first stage borehole. After the filling colloid cements and solidifies with the broken rock mass in the goaf, a coal-rock cemented body connecting the top and bottom plates of the goaf is formed in the goaf of the protective layer. Step 3: Drilling the second stage: Continue drilling along the first stage, drilling through the coal-rock cemented body and into the roof strata until reaching the fracture zone, thus completing the second stage drilling; if the drill bit falls off during the drilling process, it means that the coal-rock cemented body is not connected to the roof of the goaf. At this time, stop drilling and repeat step 2. After completion, continue drilling to complete the second stage drilling. Step 4: Gas Drainage: Gas drainage pipes are laid from the drilling site into the borehole and connected to the underground gas drainage network to drain gas from the fracture zone, thereby achieving gas drainage and control of the current coal seam.

2. The gas extraction treatment method for the secondary hole-forming in the goaf crossing the protective layer according to claim 1, characterized in that, The criteria for judging the phenomenon of drill bit loss are as follows: if the drill pressure of the drill rod suddenly decreases or disappears from a constant value during the drilling process, and the drilling depth exceeds 1m under this condition, it is judged as drill bit loss.

3. The gas drainage and control method for secondary drilling through the goaf of the protective layer according to claim 1, characterized in that, Both the first and second stage drilling were carried out using a high-torque drilling rig to drive the drill rod.

4. The gas drainage and control method for secondary drilling through the goaf of the protective layer according to claim 1, characterized in that, Step two specifically involves: inserting a colloid grouting pipe equipped with an external sealing device into the first-stage borehole, ensuring that one end of the colloid grouting pipe is within the goaf area of ​​the protective layer, and the other end is connected via a pipeline to a colloid mixer and pump located within the drilling site; connecting the sealing device to the colloid mixer and pump via the sealing grouting pipe; first placing sealing slurry in the colloid mixer and pump, then conveying the sealing slurry to the sealing device via the colloid mixer and pump, causing the sealing device to expand and press against the colloid grouting pipe. The gap between the first-stage borehole and the first-stage borehole is sealed. Then, filling colloid is placed into the colloid mixer and pump. The filling colloid is transported through the colloid grouting pipe to the goaf area of ​​the protective layer where the first-stage borehole is located. After the injection is completed, the sealing state is maintained until the filling colloid cements and solidifies with the broken rock mass in the goaf area. Then, the sealing grout in the sealing device is discharged through the sealing grouting pipe. The colloid grouting pipe and the sealing device are then removed to complete the cementing and solidification process.

5. The gas drainage and control method for secondary drilling through a goaf area in a protective layer according to claim 1, characterized in that, The filling colloid is a high-viscosity mixture with poor flowability.

6. The gas drainage and control method for secondary drilling through the goaf of the protective layer according to claim 4, characterized in that, The colloid mixer and pump is equipped with a pressure gauge and a valve. The pressure gauge is used to monitor the pressure of the sealing slurry injected into the sealing device. The valve is used to control the connection and disconnection between the colloid mixer and pump and the sealing grouting pipe and the colloid grouting pipe.

7. The gas drainage and control method for secondary drilling through the goaf of the protective layer according to claim 4, characterized in that, The sealing pressure of the sealing device is 6 MPa.

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