Method for sealing borehole in soft coal seam by air-water linkage

Abstract

This invention discloses a method for sealing boreholes in soft coal seams using a gas-water linkage system. First, the actual condition of the current gas drainage borehole is obtained to determine the sealing status of the peri-hole fractures. Then, gas drainage pipes are laid out so that the farthest boundary of the peri-hole fracture zone is located between the second and third air bladders. Next, water is injected into the sealed space between the second and third air bladders. The water diffuses within the fractures of the soft coal body, and after combining with the soft coal body, it forms an impermeable, mud-like coal body, similar to dough. This mud-like coal body then blocks the air transport channels, ensuring that the injected water has diffused to the farthest boundary of the peri-hole fractures, thus forming a sealing layer and achieving high-quality and efficient sealing of the borehole. Furthermore, after the gas drainage borehole is completed, water and gas are released. Then, the first end pipe, middle pipe, last end pipe, and each air bladder are recovered for reuse, significantly reducing the sealing cost of the gas drainage borehole.

Description

Technical Field

[0001] This invention relates to a method for sealing boreholes in soft coal seams, specifically a method for sealing boreholes in soft coal seams using a gas-water linkage mechanism. Background Technology

[0002] Gas drainage is the fundamental measure and main approach to coal mine gas control. The sealing of the drainage borehole has a significant impact on the drainage effect. Specifically, if the borehole seal fails during drainage, external air will enter the drainage borehole, leading to leakage and a decrease in the gas concentration. This directly results in many coal mines failing to achieve usable gas concentrations, forcing large amounts of gas to be directly released into the atmosphere, causing not only a huge waste of resources but also environmental pollution.

[0003] Currently, the most common borehole sealing method is the "two-plug-one-injection" approach. This involves first sealing both sides of the extraction sealing section inside the borehole with a specialized plugging device or polyurethane, and then injecting cement grout into the sealed space between the two plugs to achieve sealing. This method is affected by many factors, including the underground working environment, operator skill, and grout mixing ratio, and the process is relatively cumbersome, making it difficult to achieve satisfactory sealing results. This is especially true for soft coal seams, where the lower coal hardness leads to even worse results. Furthermore, after this method of sealing, the hardened sealing material can create new leakage channels under the influence of mining dynamic pressure, further reducing the sealing effect, and causing severe leakage under the negative pressure of extraction. In addition, the existing borehole sealing process generally uses disposable devices and materials, resulting in resource waste and high sealing costs. Therefore, how to provide a new sealing method that can ensure the sealing effect of gas drainage boreholes in soft coal seams, and enable the sealing device to be recycled and reused after gas drainage is completed, thereby reducing sealing costs and realizing resource reuse, is one of the research directions that this industry needs to explore. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for sealing boreholes in soft coal seams using a gas-water linkage system. This method ensures the sealing effect of boreholes used for gas extraction in soft coal seams and allows for the recycling and reuse of the sealing device after gas extraction is completed, thereby reducing sealing costs and achieving resource reuse.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a method for drilling holes in soft coal seams using a gas-water linkage system, the specific steps of which are as follows:

[0006] A. Determine the farthest boundary of the fracture zone and the construction water diffusion detection hole: First, drill a gas extraction borehole into the soft coal seam, then conduct geological exploration to obtain the depth and dip angle of the soft coal seam, coal body parameters, roadway layout parameters, borehole parameters, and the distribution of overlying coal and rock mass. Then, use mechanical software to perform numerical simulation calculations to obtain the distribution of the fracture zone around the current gas extraction borehole, and determine the position of the farthest boundary of the fracture zone from the gas extraction borehole based on the distribution. Since water is affected by its own gravity when diffusing in the fracture zone, the farthest boundary directly above the borehole during subsequent water injection is the last place where water diffuses in the fracture zone. Drill a water diffusion detection hole into the soft coal seam at the same height as the farthest boundary of the fracture zone directly above the borehole, so that the water diffusion detection hole passes through the farthest boundary of the fracture zone and continues to extend a certain distance.

[0007] B. Laying out the gas extraction pipe: The gas extraction pipe consists of a head pipe, an intermediate pipe, and a tail pipe. The head pipe is equipped with a first air bladder, the intermediate pipe is equipped with a second and a third air bladder, and the tail pipe is equipped with a fourth air bladder. The head pipe, intermediate pipe, and tail pipe are coaxially connected in sequence to form the gas extraction pipe. One end of the water injection pipe passes through the fourth and third air bladders in sequence and extends between the second and third air bladders. The water injection pipe is equipped with a first control valve, and the air bladders are interconnected through the air injection pipe. The air injection pipe is equipped with a second control valve. Then the gas extraction pipe is sent into the gas extraction borehole, so that the head pipe and the intermediate pipe are both inside the gas extraction borehole, and the tail pipe extends into the gas extraction borehole. This ensures that the farthest boundary of the peri-hole fracture zone is located between the second and third air bladders, thus completing the laying out of the gas extraction pipe.

[0008] C. Preliminary sealing: Connect the gas injection pipe outside the gas extraction borehole to the downhole compressed air system, open the second control valve, and inject gas into each airbag. When the pressure inside each airbag is equal to the air pressure, close the second control valve. Connect the other end of the water injection pipe outside the gas extraction borehole to the borehole filling device, open the first control valve, and the borehole filling device blows polyurethane particles between the second and third airbags through the water injection pipe. After filling a certain amount, the preliminary sealing process is completed.

[0009] D. Secondary sealing with water injection: Remove the borehole filling device connected to the water injection pipe, then connect the other end of the water injection pipe to the downhole pressure water pipe, open the first control valve, and inject water between the second and third airbags through the water injection pipe at a pressure of 0.3-0.4 MPa. The injected water continuously diffuses within the peri-hole fracture zone of the soft coal body, and the soft coal body continuously mudsifies upon contact with water, forming an impermeable mud-like coal body similar to dough. During the water injection process, continuously observe the water diffusion detection hole. When water begins to flow out from the water diffusion detection hole, seal the water diffusion detection borehole, close the first control valve, and disconnect the connection with the downhole pressure water pipe. At this time, the impermeable mud-like coal body diffuses within the peri-hole fracture zone to the farthest boundary of all fracture zones, forming a sealing layer to seal the peri-hole fracture zone, thus completing the secondary sealing with water injection.

[0010] E. Gas extraction: Connect the other end of the end pipe located outside the gas extraction borehole to the downhole gas extraction system to continuously extract gas.

[0011] F. Secondary water injection and sealing: During the extraction process, if the extracted gas concentration is found to decrease to 30%, it indicates that the moisture in the coal body after cementing continues to be absorbed by the surrounding dry coal body, or that the fractures around the borehole redevelop during the extraction process, causing the previously formed sealing layer to fail to seal the fracture zone around the borehole, resulting in a gas leakage channel. At this time, the water injection pipe is reconnected to the downhole pressure water pipe, the first control valve is opened, and the water injection pressure is set to 0.3-0.4 MPa. The injected water will further expand in the fracture zone around the borehole, thereby forming a new sealing layer to seal the fracture zone around the borehole. By observing the extracted gas concentration in real time, when the gas concentration recovers to 50%, the first control valve is closed to stop water injection.

[0012] G. Continue water injection sealing and gas extraction: When the gas concentration drops to 30% again, repeat step F. Repeat this process multiple times until the gas extraction work of the gas extraction borehole is completed.

[0013] H. Recovering the gas extraction pipe: Open the first control valve and the second control valve to allow the gas in each airbag to be discharged from the gas injection pipe, and at the same time allow the water between the second and third airbags to be discharged from the water injection pipe. Finally, remove the gas extraction pipe from the gas extraction borehole and separate the head pipe, middle pipe and end pipe to complete the recovery work.

[0014] Furthermore, each airbag is made of rubber with a thickness of 0.2 to 0.5 cm, and the outer diameter of the airbag is 1.1 to 1.2 times the diameter of the drill hole.

[0015] Furthermore, the distance between the second and third airbags is 0.4 to 0.6 m.

[0016] Furthermore, the polyurethane particles are polyurethane spheres with a diameter of 0.5 to 1 cm.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. This invention first obtains the actual situation of the current gas drainage borehole and performs numerical simulation calculations to obtain the sealing situation of the peri-hole fractures, which helps to accurately seal the borehole and arrange the airbags. This invention first deploys four airbags to achieve preliminary sealing of the borehole, and places the farthest boundary of the peri-hole fracture zone between the second and third airbags. Then, water is injected into the sealed space between the second and third airbags. The water diffuses in the fractures of the soft coal body. After the water combines with the soft coal body, it forms an impermeable mud-like coal body similar to dough (especially for soft coal bodies with a hardness coefficient f value of less than 0.5, the sealing effect after mud-forming is better). This mud-forming coal body blocks the air transport channel, ensuring that the injected water has diffused to the farthest boundary of the peri-hole fractures, so that the mud-forming coal body forms a sealing layer, separating and sealing the peri-hole fracture zone, minimizing air leakage from the peri-hole fractures, and achieving high-quality and efficient sealing of the borehole.

[0019] 2. Before water injection, this invention first blows polyurethane balls with a diameter of 0.5 to 1 cm into the water injection pipe between the second and third airbags to complete the filling of the borehole in the water injection section. The gaps between the polyurethane balls will not affect the subsequent water injection process, thereby supporting the coal body in the water injection section and preventing the coal body from collapsing after cementing, which would affect the sealing effect of the borehole.

[0020] 3. After the gas extraction borehole is completed, the present invention first performs water and gas release operations, and then recovers the head pipe, middle pipe, end pipe and each airbag for reuse, thereby greatly reducing the sealing cost of the gas extraction borehole. Moreover, the sealing effect can be guaranteed when reused, so it has wide applicability. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall layout of the present invention.

[0022] In the diagram: 1. Soft coal seam; 2. Peri-hole fracture zone; 3. Gas drainage borehole; 4. Water injection pipe; 5. First control valve; 6. End pipe; 7. Gas injection pipe; 8. Second control valve; 9. Water diffusion detection hole; 10. Head pipe; 11. First airbag; 12. Intermediate pipe; 13. Second airbag; 14. Coal body after mudification; 15. Polyurethane ball; 16. Third airbag; 17. Fourth airbag. Detailed Implementation

[0023] The present invention will be further described below.

[0024] like Figure 1 As shown, the specific steps of the present invention are as follows:

[0025] A. Determine the farthest boundary of the fracture zone and the construction water diffusion detection hole: First, construct a gas extraction borehole 3 into the soft coal seam 1, then conduct geological exploration to obtain the depth and dip angle of the soft coal seam, coal body parameters, roadway layout parameters, borehole parameters, and the distribution of the overlying coal and rock mass. Next, use existing mechanical software to perform numerical simulation calculations to obtain the distribution of the fracture zone 2 around the current gas extraction borehole, and determine the position of the farthest boundary of the fracture zone 2 from the gas extraction borehole 3 based on the distribution. Since water is affected by its own gravity when diffusing in the fracture zone, the farthest boundary directly above the borehole during subsequent water injection is the last place where water diffuses in the fracture zone. Construct a water diffusion detection hole 9 into the soft coal seam 1 at the same height as the farthest boundary of the fracture zone directly above the borehole, so that the water diffusion detection hole 9 passes through the farthest boundary of the fracture zone and continues to extend a certain distance.

[0026] B. Deployment of gas extraction pipes: The gas extraction pipe consists of a head pipe 10, a middle pipe 12 and a tail pipe 6. The head pipe 10 is equipped with a first airbag 11, the middle pipe 12 is equipped with a second airbag 13 and a third airbag 16, and the tail pipe 6 is equipped with a fourth airbag 17. All airbags are made of rubber with a thickness of 0.2 to 0.5 cm, and the outer diameter of the airbag is 1.1 to 1.2 times the diameter of the borehole. The first end pipe 10, the middle pipe 12 and the last end pipe 6 are coaxially connected in sequence to form a gas extraction pipe. One end of the water injection pipe 4 passes through the fourth airbag 17 and the third airbag 16 in sequence and extends into the space between the second airbag 13 and the third airbag 16. The water injection pipe 4 is equipped with a first control valve 5 and the airbags are connected to each other through the air injection pipe 7. The air injection pipe 7 is equipped with a second control valve 8. Then the gas extraction pipe is sent into the gas extraction borehole 3 so that the first end pipe 10 and the middle pipe 12 are both in the gas extraction borehole 3 and the last end pipe 6 extends into the gas extraction borehole 3. This ensures that the farthest boundary of the peri-hole fracture zone 2 is located between the second airbag 13 and the third airbag 16. The distance between the second airbag 13 and the third airbag 16 is 0.4 to 0.6 m, thus completing the layout of the gas extraction pipe.

[0027] C. Preliminary sealing: Connect the gas injection pipe 7 outside the gas extraction borehole 3 to the downhole compressed air system, open the second control valve 8, and inject gas into each airbag. When the pressure in each airbag is equal to the air pressure, close the second control valve 8. Connect the other end of the water injection pipe 4 outside the gas extraction borehole 3 to the borehole filling device, open the first control valve 5, and the borehole filling device blows polyurethane balls with a diameter of 0.5 to 1 cm into the space between the second airbag 13 and the third airbag 16 through the water injection pipe 4. After filling a certain amount, the preliminary sealing process is completed.

[0028] D. Secondary sealing with water injection: Remove the borehole filling device connected to the water injection pipe 4, then connect the other end of the water injection pipe 4 to the downhole water supply pipe, open the first control valve 5, and inject water between the second airbag 13 and the third airbag 16 through the water injection pipe 4. The water injection pressure is 0.3-0.4 MPa. The injected water continuously diffuses in the peri-hole fracture zone 2 of the soft coal body, and the soft coal body continuously mudsifies after encountering water, forming an impermeable mud-like coal body 14 similar to dough. During the water injection process, continuously observe the water diffusion detection hole 9. When water begins to flow out from the water diffusion detection hole 9, seal the water diffusion detection borehole 9, close the first control valve 5, and disconnect the connection with the downhole water supply pipe. At this time, the impermeable mud-like coal body 14 diffuses in the peri-hole fracture zone 2 to the farthest boundary of all fracture zones, forming a sealing layer to seal the peri-hole fracture zone 2, thus completing the secondary sealing with water injection.

[0029] E. Gas extraction: Connect the other end of the end pipe 6 outside the gas extraction borehole 3 to the downhole gas extraction system to continuously extract gas.

[0030] F. Secondary sealing with water injection: During the extraction process, if the extracted gas concentration is found to decrease to 30%, it indicates that the moisture in the coal body 14 after cementing continues to be absorbed by the surrounding dry coal body, or that the fractures around the borehole redevelop during the extraction process, causing the previously formed sealing layer to fail to seal the peri-hole fracture zone 2, resulting in a gas leakage channel. At this time, the water injection pipe 4 is reconnected to the downhole pressure water pipe, and the first control valve 5 is opened to make the water injection pressure 0.3-0.4MPa. The injected water will further expand in the peri-hole fracture zone 2, thereby forming a new sealing layer to seal the peri-hole fracture zone 2. By observing the extracted gas concentration in real time, when the gas concentration recovers to 50%, the first control valve 5 is closed to stop water injection.

[0031] G. Continue water injection sealing and gas extraction: When the gas concentration drops to 30% again, repeat step F. Repeat this process multiple times until the gas extraction work of the gas extraction borehole is completed.

[0032] H. Recovering the gas extraction pipe: Open the first control valve 5 and the second control valve 8 to allow the gas in each airbag to be discharged from the gas injection pipe 7, and at the same time allow the water between the second and third airbags to be discharged from the water injection pipe 4. Finally, remove the gas extraction pipe from the gas extraction borehole 3, and separate the head pipe 10, the middle pipe 12 and the end pipe 6 to complete the recovery work.

[0033] The aforementioned borehole filling device, underground pressurized water pipe, and underground compressed air system are all existing equipment within the mine.

[0034] 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 method for sealing boreholes in soft coal seams using a gas-water linkage system, characterized in that, The specific steps are as follows: A. Determine the farthest boundary of the fracture zone and the construction water diffusion detection hole: First, drill a gas extraction borehole into the soft coal seam, then conduct geological exploration to obtain the depth and dip angle of the soft coal seam, coal body parameters, roadway layout parameters, borehole parameters, and the distribution of overlying coal and rock mass. Then, use mechanical software to perform numerical simulation calculations to obtain the distribution of the fracture zone around the current gas extraction borehole. Based on the distribution, determine the position of the fracture zone from the farthest boundary of the gas extraction borehole. Drill a water diffusion detection hole into the soft coal seam at the same height as the farthest boundary of the fracture zone directly above the borehole, so that the water diffusion detection hole passes through the farthest boundary of the fracture zone and continues to extend a certain distance. B. Laying out the gas extraction pipe: The gas extraction pipe consists of a head pipe, an intermediate pipe, and a tail pipe. The head pipe is equipped with a first air bladder, the intermediate pipe is equipped with a second and a third air bladder, and the tail pipe is equipped with a fourth air bladder. The head pipe, intermediate pipe, and tail pipe are coaxially connected in sequence to form the gas extraction pipe. One end of the water injection pipe passes through the fourth and third air bladders in sequence and extends between the second and third air bladders. The water injection pipe is equipped with a first control valve, and the air bladders are interconnected through the air injection pipe. The air injection pipe is equipped with a second control valve. Then the gas extraction pipe is sent into the gas extraction borehole, so that the head pipe and the intermediate pipe are both inside the gas extraction borehole, and the tail pipe extends into the gas extraction borehole. This ensures that the farthest boundary of the peri-hole fracture zone is located between the second and third air bladders, thus completing the laying out of the gas extraction pipe. C. Preliminary sealing: Connect the gas injection pipe outside the gas extraction borehole to the downhole compressed air system, open the second control valve, and inject gas into each airbag. When the pressure inside each airbag is equal to the air pressure, close the second control valve. Connect the other end of the water injection pipe outside the gas extraction borehole to the borehole filling device, open the first control valve, and the borehole filling device blows polyurethane particles between the second and third airbags through the water injection pipe. After filling a certain amount, the preliminary sealing process is completed. D. Secondary sealing with water injection: Remove the borehole filling device connected to the water injection pipe, then connect the other end of the water injection pipe to the downhole pressure water pipe, open the first control valve, and inject water between the second and third airbags through the water injection pipe at a pressure of 0.3-0.4 MPa. The injected water continuously diffuses within the peri-hole fracture zone of the soft coal body, and the soft coal body continuously mudsifies upon contact with water, forming an impermeable mud-like coal body similar to dough. During the water injection process, continuously observe the water diffusion detection hole. When water begins to flow out from the water diffusion detection hole, seal the water diffusion detection borehole, close the first control valve, and disconnect the connection with the downhole pressure water pipe. At this time, the impermeable mud-like coal body diffuses within the peri-hole fracture zone to the farthest boundary of all fracture zones, forming a sealing layer to seal the peri-hole fracture zone, thus completing the secondary sealing with water injection. E. Gas extraction: Connect the other end of the end pipe located outside the gas extraction borehole to the downhole gas extraction system to continuously extract gas. F. Secondary water injection and sealing: During the extraction process, if the extracted gas concentration is found to decrease to 30%, it indicates that the moisture in the coal body after cementing continues to be absorbed by the surrounding dry coal body, or that the fractures around the borehole redevelop during the extraction process, causing the previously formed sealing layer to fail to seal the fracture zone around the borehole, resulting in a gas leakage channel. At this time, the water injection pipe is reconnected to the downhole pressure water pipe, the first control valve is opened, and the water injection pressure is set to 0.3-0.4 MPa. The injected water will further expand in the fracture zone around the borehole, thereby forming a new sealing layer to seal the fracture zone around the borehole. By observing the extracted gas concentration in real time, when the gas concentration recovers to 50%, the first control valve is closed to stop water injection. G. Continue water injection sealing and gas extraction: When the gas concentration drops to 30% again, repeat step F. Repeat this process multiple times until the gas extraction work of the gas extraction borehole is completed. H. Recovering the gas extraction pipe: Open the first control valve and the second control valve to allow the gas in each airbag to be discharged from the gas injection pipe, and at the same time allow the water between the second and third airbags to be discharged from the water injection pipe. Finally, remove the gas extraction pipe from the gas extraction borehole and separate the head pipe, middle pipe and end pipe to complete the recovery work.

2. The method for sealing soft coal seams using gas-water linkage according to claim 1, characterized in that, Each airbag is made of rubber with a thickness of 0.2 to 0.5 cm, and the outer diameter of the airbag is 1.1 to 1.2 times the diameter of the drill hole.

3. The method for sealing soft coal seams using gas-water linkage according to claim 1, characterized in that, The distance between the second and third airbags is 0.4 to 0.6 m.

4. The method for sealing soft coal seams using gas-water linkage according to claim 1, characterized in that, The polyurethane particles are polyurethane spheres with a diameter of 0.5 to 1 cm.

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