A secondary grouting plugging device in a borehole

Abstract

The present invention discloses a secondary grouting plugging device in a borehole, comprising an injection pipe composed of a plurality of single-section pipes connected in sequence, each of which comprises an injection pipe and a grouting pipe, wherein the grouting pipe is sleeved inside the injection pipe, wherein the grouting pipe is connected to the grouting pipe, and the injection pipe is connected to the injection pipe; the inner ends of the plurality of connected injection pipes extend out of the inner end of the gas extraction pipe and cross the fissure area of ​​the borehole, and are connected and communicated with the inner end airbag, the inner end of the plurality of connected injection pipes located at the gas extraction pipe is connected and communicated with the outer end airbag, and a sealing body is further provided at one end of the gas extraction pipe and the entrance of the borehole; the plurality of injection pipes of the injection pipe are located at one end of the borehole entrance and connected to the gas supply equipment, and the plurality of grouting pipes of the injection pipe are located at one end of the borehole entrance and connected to the grouting equipment. The device of the present invention can accurately perform pressure grouting on the development position of the fissure of the failed borehole, thereby activating and restoring the extraction function of the failed borehole for gas extraction, and improving the concentration and pure amount of gas extraction.

Description

Technical Field

[0001] The invention relates to the technical field of gas extraction, and in particular to a secondary grouting plugging device in a borehole. Background Art

[0002] There are two main types of air leakage in drilling holes, namely, air leakage inside the hole and air leakage outside the hole. Figure 1 As shown in the figure, the gas leakage in the hole exists in the area between the extraction pipe and the borehole wall, including the gas leakage of the sealing material itself and the gas leakage between the sealing material and the borehole wall. The gas leakage outside the hole exists in the crack area outside the borehole wall. Under the action of negative pressure, the outside air enters the coal body through the cracks around the borehole. In order to more comprehensively analyze the reasons for the attenuation of gas extraction concentration, it is necessary to comprehensively consider the gas leakage inside the hole and the gas leakage outside the hole, so as to provide a scientific basis for the sealing technology of the borehole. In the past, it was generally believed that the gas leakage inside the hole caused by the presence of pores or shrinkage in the sealing material itself and the loose contact with the borehole wall during the borehole sealing process was the main cause of the gas leakage in the borehole. In recent years, with the improvement of the performance of the sealing material, affected by the drilling construction, tunnel excavation, and the dynamic pressure of the working face recovery, the gas leakage around the borehole (gas leakage outside the hole) under the condition of high negative pressure extraction has become the main cause of extraction failure.

[0003] During the gas extraction process, negative pressure is formed at the bottom of the extraction pipe, which creates a pressure difference between the inside and outside of the borehole, providing power for the air outside the hole to flow into the borehole. Under the action of the pressure difference, the air will enter the borehole from the coal body cracks. There are two main ways for air to enter the borehole:

[0004] 1) Tunnel pressure relief zone: In the range of the tunnel pressure relief zone, the coal body is relatively broken and the cracks extend and penetrate;

[0005] 2) Plastic zone around the borehole: In this area, the permeability of the coal body increases significantly due to the reduction of stress.

[0006] The main reason for gas extraction failure is borehole leakage, which can be divided into coal wall leakage on one side of the tunnel and leakage in the borehole sealing section according to the cause and form. Among them, the coal wall leakage on one side of the tunnel includes the broken leakage zone of the coal wall in the axial direction of the drill hole and the leakage circle of the surrounding rock in the radial direction of the drill hole; the sealing effect of the sealing section is not good, resulting in leakage channels, which are divided into leakage of the sealing material itself and leakage of the contact surface between the sealing material and the borehole wall.

[0007] The existing sealing technologies, such as hole sealers and capsule sealing, all have certain shortcomings. Among them, the hole sealer sealing device is relatively bulky and inconvenient to operate. The hole sealer sealing device is used for drilling holes on the side of coal seam tunnels. Since the shape of the drilled hole is difficult to maintain a regular circle and the hole wall is broken, the sealing effect is often poor and the sealing quality is difficult to guarantee. Therefore, it is generally only suitable for temporary extraction sealing; the capsule sealing device is labor-intensive to use and relatively expensive, and is almost useless for sealing the development and expansion of fractures. Summary of the invention

[0008] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a secondary grouting plugging device in a borehole, which can accurately perform pressure grouting on the development position of cracks in the failed borehole, thereby activating and restoring the gas extraction function of the failed borehole and improving the gas extraction concentration and pure amount.

[0009] The technical solution of the present invention is: a secondary grouting plugging device in a borehole, comprising a plurality of single-section pipes, each of which comprises an air injection pipe and a grouting pipe, the grouting pipe is sleeved inside the air injection pipe, the gap between the two pipes serves as a ventilation channel, a connecting piece is fixed between the air injection pipe and the grouting pipe, and the relative position between the two pipes is fixed by the connecting piece; the plurality of single-section pipes are sequentially connected end to end to form an injection pipe, wherein the grouting pipes of two adjacent single-section pipes are connected, and the air injection pipes of two adjacent single-section pipes are connected; the injection pipe is inserted from the gas extraction pipe when the borehole is subjected to secondary grouting plugging, wherein the inner ends of the plurality of connected air injection pipes extend out of the inner end of the gas extraction pipe and pass over The fissure area of ​​the borehole is connected and communicated with the inner end airbag, the inner end airbag is used to seal the drilling part of the inner end of the multiple air injection pipes after being inflated by the air injection pipe, and the inner end of the gas extraction pipe of the multiple connected air injection pipes is connected and communicated with the outer end airbag, the outer end airbag is used to seal the annular space between the air injection pipe and the gas extraction pipe after being inflated by the air injection pipe; the gas extraction pipe and the borehole entrance end are also provided with a sealing body for sealing the annular space between the borehole and the gas extraction pipe; the multiple air injection pipes of the injection pipe are located at one end of the borehole entrance and connected to the air supply equipment, and the multiple grouting pipes of the injection pipe are located at one end of the borehole entrance and connected to the grouting equipment.

[0010] The air injection pipe and grouting pipe of each single-section pipe mentioned above are concentric reducer pipes which are sleeved together, and the connecting piece between the two pipes is an annular metal plug. A metal plug is arranged at both ends of each single-section pipe, wherein the annular inner wall of the metal plug is provided with an internal thread, and the outer wall of the grouting pipe is provided with an external thread matching the internal thread. Through the screw connection of the internal and external threads, the metal plug seals the annular gap between the air injection pipe and the grouting pipe at the metal plug, wherein an air vent is opened on the end face of the metal plug.

[0011] A connecting joint is provided on the inner end of the multiple gas injection pipes, and the connecting joint includes two ports, one of which is connected to the inner end air bag, and the other port is connected to the slurry output end of the multiple grouting pipes for outputting slurry from the grouting pipes.

[0012] The air injection pipe and grouting pipe at one end of each single-section pipe are both provided with external threads, and the air injection pipe and grouting pipe at the other end of each single-section pipe are both provided with internal threads. The air injection pipes and grouting pipes of two adjacent single-section pipes are screwed together through internal and external threads.

[0013] The above-mentioned inner airbag and outer airbag both include an elastic cylinder, which is sleeved on the air injection tube, and the sleeved air injection tube portion is provided with a row of inflation holes along the longitudinal direction of the air injection tube. Both ends of the elastic cylinder are sealed and fixed to the air injection tube by crimping cylindrical metal rings with a crimping machine.

[0014] The outer diameter of the portion of the gas injection pipe where the elastic cylinder is sleeved is smaller than the outer diameter of the remaining portions of the gas injection pipe, so that the outer diameter of the portion of the gas injection pipe where the elastic cylinder is sleeved is equivalent to that of the remaining portions after the elastic cylinder is sleeved, to ensure that the outer diameter of each gas injection pipe remains smooth as a whole after assembly, which is convenient for use in drilling.

[0015] Beneficial effects of the present invention: The present invention provides a secondary grouting and plugging device in a borehole, which can perform precise pressure grouting on the development position of failed borehole cracks, activate and restore the gas extraction function of failed boreholes, and improve the gas extraction concentration and purity. Slurry is injected into a borehole with coal wall cracks through special grouting equipment. As the slurry flows, the cracks (cracks) are filled, and the slurry solidifies over time, thereby compensating for the cracks (cracks), which plays the role of grouting and plugging, thereby improving the gas extraction concentration. The present invention can not only perform grouting and plugging, but also has a borehole leakage detection function. The technical advantages of the present invention specifically include: first, the entire section is recyclable and the sections are adjustable. The present invention can be reused many times during actual use, so the average utilization cost is low, and the airbags, air injection pipes, and grouting pipes included therein can be replaced and adjusted, which can improve the overall service life; second, the depth and length of the sealing section are adjustable. The various parts of the present invention are independent of each other. During actual use, the length and depth of the sealing section can be determined according to specific needs, mainly by controlling the overall length of the device and the length of the grouting pipe with grouting holes to adjust the depth and length of the sealing section; third, the sealing material is injected under pressure to secure the gas extraction borehole; during use, the device first inflates the airbags, and the two airbags form a closed space in the borehole fissure area. Pressurized grouting is used during the grouting process, which can ensure that the slurry flows into and fills the fissures better under pressure, thereby ensuring the grouting effect. The present invention combines the principle of "two plugging and one injection", integrating the advantages of sealing with a sealer and sealing with a capsule, using high-strength and high-rebound capsule material as the plug and lightweight metal material as the main body, to produce a device with good sealing effect, adjustable length, easy operation and durability, and relatively low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the drilling leakage diagram;

[0017] Figure 2 This is a schematic diagram of the borehole gas leakage detection principle of the present invention;

[0018] Figure 3 It is a schematic diagram of the structure of the device of the present invention.

[0019] Explanation of the accompanying reference numerals: 1. gas extraction pipe; 2. gas injection pipe; 3. grouting pipe; 4. sealing body; 5. drilled crack; 6. air bag; 6-1. inner end air bag; 6-2. outer end air bag. DETAILED DESCRIPTION

[0020] A specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation.

[0021] See also Figure 1-Figure 3The embodiment of the present invention provides a secondary grouting plugging device in a borehole, comprising a plurality of single-section pipes, each of which comprises an air injection pipe 2 and a grouting pipe 3, wherein the grouting pipe 3 is sleeved inside the air injection pipe 2, and the gap between the two pipes serves as a ventilation channel, and a connecting piece is fixed between the air injection pipe 2 and the grouting pipe 3, and the relative position between the two pipes is fixed by the connecting piece; the plurality of single-section pipes are sequentially connected end to end to form an injection pipe, wherein the grouting pipes 3 of two adjacent single-section pipes are connected, and the air injection pipes 2 of two adjacent single-section pipes are connected; the injection pipe is inserted from the gas extraction pipe 1 when grouting and plugging the borehole, wherein the inner ends of the plurality of connected air injection pipes 2 extend out of the inner end of the gas extraction pipe 1 and cross the crack area of ​​the borehole, and It is connected and communicated with the inner end airbag 6-1, which is used to seal the part of the borehole where the inner ends of the multiple air injection pipes 2 are located after being inflated by the air injection pipe 2. The inner ends of the multiple connected air injection pipes 2 located at the gas extraction pipe 1 are connected and communicated with the outer end airbag 6-2, which is used to seal the annular space gap between the air injection pipe 2 and the gas extraction pipe 1 after being inflated by the air injection pipe 2; a sealing body 4 for sealing the annular space gap between the borehole and the gas extraction pipe 1 is also provided at one end of the gas extraction pipe 1 and the entrance of the borehole; the multiple air injection pipes 2 of the injection pipe are located at one end of the borehole entrance and are connected to the air supply equipment, and the multiple grouting pipes 3 of the injection pipe are located at one end of the borehole entrance and are connected to the grouting equipment.

[0022] Furthermore, the air injection pipe 2 and the grouting pipe 3 of each single-section pipe are concentric reducer pipes that are sleeved together, and the connecting piece between the two pipes is an annular metal plug. A metal plug is arranged at both ends of each single-section pipe, wherein the annular inner wall of the metal plug is provided with an internal thread, and the outer wall of the grouting pipe 3 is provided with an external thread matching the internal thread. Through the screw connection of the internal and external threads, the metal plug seals the annular gap between the air injection pipe 2 and the grouting pipe 3 at the metal plug, wherein a vent hole is opened on the end face of the metal plug.

[0023] Furthermore, a connecting joint is provided on the inner end of the multiple air injection pipes 2, and the connecting joint includes two ports, one of which is connected to the inner end air bag 6-1, and the other port is connected to the slurry output end of the multiple grouting pipes 3 for the grouting pipes 3 to output slurry.

[0024] Furthermore, the air injection pipe 2 and the grouting pipe 3 at one end of each single-section pipe are provided with external threads, and the air injection pipe 2 and the grouting pipe 3 at the other end of each single-section pipe are provided with internal threads, and the air injection pipes 2 and the grouting pipes 3 of two adjacent single-section pipes are screwed together through internal and external threads.

[0025] Furthermore, the inner airbag 6-1 and the outer airbag 6-2 each include an elastic cylinder, which is sleeved on the air injection tube 2, and a row of inflation holes along the longitudinal direction of the air injection tube 2 are provided on the sleeved air injection tube 2. Both ends of the elastic cylinder are sealed and fixed to the air injection tube 2 by crimping cylindrical metal rings with a crimping machine.

[0026] Furthermore, the outer diameter of the portion of the air injection tube 2 where the elastic cylinder is sleeved is smaller than the outer diameter of the remaining portions of the air injection tube 2, so that the outer diameters of the portion of the air injection tube 2 where the elastic cylinder is sleeved and the remaining portions after the elastic cylinder is sleeved are equivalent, thereby ensuring that the outer diameter of each air injection tube 2 remains smooth as a whole after assembly, which is convenient for use in drilling.

[0027] When the device of the present invention is used, slurry is injected into a borehole with coal wall cracks through a special grouting device. As the slurry flows, the cracks (cracks) are filled. The slurry solidifies over time, thereby filling the cracks (cracks). This plays the role of grouting to plug leaks, thereby increasing the gas extraction concentration. The present invention can not only achieve grouting to plug leaks, but also has the function of drilling leakage detection. Figure 2 As shown, the device is placed in the borehole, and after passing through the 16m extraction pipe of the sealing section, the gas extraction concentration at the depth of 16-20m in the borehole is gradually detected through the inner pipe (connected to the extraction pipe through the mouth hole tee to maintain the drilling state), and the specific leakage area of ​​the borehole is obtained, thereby determining the specific position and length of the borehole that needs to be blocked. Figure 3 As shown, the inner airbag of the device is inserted into a suitable position in the hole so that the detected leakage area is located between the two cloth bags. By injecting air into the airbag to make it expand, the outer airbag blocks the end of the gas extraction pipe, and the inner airbag blocks the borehole. The two airbags and the coal wall therebetween form a sealing area, and then pressurized grouting is performed into the sealing area. After the slurry fills the sealing area, it is squeezed into the cracks of the coal wall of the borehole to achieve the sealing of the leakage area.

[0028] The secondary grouting device in the hole mainly consists of four parts, namely the bag short-circuit, the sealing section grouting short-circuit, the grouting connecting pipe, and the orifice three-way device. In order to realize the separate inflation and grouting of the bag and the grouting section, the device adopts a concentric structure of inner and outer tubes, in which the outer tube has an outer diameter of 45mm, a wall thickness of 3.5mm, and an inner diameter of 38mm; the inner tube has an outer diameter of 28mm, a wall thickness of 7mm, and an inner diameter of 14mm. The size of the tube has a good ability to penetrate the sealing hole tube and can meet the requirements of outer tube inflation and inner tube grouting. In addition, the two ends of the tube are threaded and equipped with "O" type sealing rings to ensure the airtightness of the device.

[0029] The first-generation test device is made of aluminum alloy. Although it has the advantages of light weight and easy to push manually, it also has the disadvantages of easy deformation and disengagement of the joints. During the test in the well, the threads of many test pipe joints were deformed and damaged. In addition, the capsule manufacturing process is an outward protruding rod body, which is easy to be stuck by the pumping pipe head during the expansion and contraction process in the hole. In view of this, the device was improved and the second-generation test device was developed. The main improvement was the rod body material, stainless steel. Although it is twice as heavy as aluminum, the device is more sturdy and durable, and it can be smoothly pushed into the hole by humans without damage during the test. Secondly, the threaded connection process was improved, and a large pitch coarse thread was used to facilitate manual disassembly and assembly. The inner tube was replaced with an outer groove "O" ring side wall sealing process, and the sealing ring is not easy to fall off and damage. Finally, the capsule manufacturing process was improved, and the outer diameter of the rod at the capsule part was made thinner, so that the outer diameter of the air bag after crimping is consistent with the outer diameter of other rods of the device, eliminating the "mutation" phenomenon of the first-generation device.

[0030] The grouting pump selected in this embodiment is a downhole grouting and sealing pump. The sealing pump used is a commonly used SZKF-3.0QB grouting and sealing pump with a maximum output pressure of 3.2MPa. After downhole testing, the grouting pump can smoothly inject slurry into the hole and the cracks in the hole wall, and most boreholes can continue to grout after the grouting volume exceeds the expected grouting volume. The grouting pump has no pressure, so the grouting pump can meet the secondary sealing grouting pressure requirements. The parameters of the grouting pump are shown in Table 1.

[0031] Table 1 Main performance parameters of grouting pump

[0032] Product Model SZKF-3.0QB Grouting pump weight 16kg Working air pressure 0.3~0.7MPa Barrel size Φ500×1350 Maximum output pressure 3.2MPa Maximum range 0～30m Maximum output flow 20L / min Ventilation pipe diameter 3 / 4 3 / 4 Gas consumption <![CDATA[≤0.28m 3 / min]]> Reciprocating times ≤150 times / min

[0033] Since the core of the technology of the present invention is to grout and seal the leaking cracks around the borehole wall, this requires that the grouting liquid has good fluidity and at the same time ensures that the slurry has a certain degree of expansion and does not shrink after solidification in the cracks. In addition, since the grouting equipment needs to be recycled, the initial setting time of the slurry in the sealing section cannot be too fast (it must be greater than the sealing grouting time). The initial setting must be carried out after the sealing grouting device is depressurized and exits the borehole to prevent the device from being unable to exit the borehole, thereby realizing the reuse function of the device.

[0034] The cement used for sealing holes in mines is KFGP-III gas hole sealing material produced by Suzhou Kunfa Company. This material is micro-expansive cement. The test shows that its expansion coefficient is 1.203 and the initial setting time is 40 minutes (the slurry completely loses fluidity). After laboratory tests, the slurry water-cement ratio is controlled at 1.2:1 to 1.6:1, and the slurry fluidity and solidification properties are good. During the field test, the water-cement ratio is basically around 1.2:1. During grouting, the slurry fluidity and solidification properties are good, and there is no pipe blocking or failure to inject slurry. After the slurry is injected, the device can be withdrawn smoothly, and there is no drill jamming caused by the slurry solidifying too quickly. Therefore, the sealing material and slurry ratio can meet the requirements of secondary grouting.

[0035] The specific working principle of the device of the present invention is as follows: the device of the present invention is placed in a gas-failed borehole, the inner airbag 6-1 and the outer airbag 6-2 seal the two ends of the crack area, the airbag 6 is inflated to form a closed space in the area, and the area is pressurized for grouting so that the slurry can fully fill the cracks, thereby restoring the function of the failed borehole and improving the gas extraction effect.

[0036] Working steps: The working process of the device mainly includes two parts, one is to detect the leakage part of the failed borehole; the other is to perform precise grouting according to the detection results. The steps for detecting the leakage part of the failed borehole are as follows: stop the drilling with pumping state, put the device into the borehole to be detected in sections, and the placement order is: outer end air bag, grouting pipe with grouting hole, inner end air bag, ordinary grouting pipe; put the grouting pipe with grouting hole into the position of 16m, 17m, 18m, and 19m of the borehole depth respectively, restore the drilling with pumping state for 5 to 10 minutes and then turn it off, install a special pointed object at the outer end of the device to connect the vacuum pump for pumping, and send the extracted gas to the optical gas detector for gas concentration detection, record and analyze the detection data. According to the data, if the gas concentration decreases the most in a certain interval, it is determined to be the leakage part of the borehole.

[0037] Steps for accurate grouting of failed boreholes: turn off the pumping state of the borehole, put the device into the borehole in sections, put the outer end airbag 6-2 into the borehole first, put the grouting pipe with the grouting hole into the detected leaking part, put the inner end airbag 6-1 into the inside of the gas extraction pipe, and then connect the ordinary grouting pipe in this way. Connect the downhole pressure air pipe with the air path designed at the front end of the device, turn on the control switch to inflate the airbag 6, when the inflation pressure reaches 0.35-0.4MPa (the diameter of the inner section airbag can expand to 130mm), close the inflation valve to stop inflation, and observe whether the pressure gauge reading is stable. If the reading is stable, it means that the device is not leaking, and the next test operation can be carried out; if the pressure gauge reading drops slowly, it means that there is a slight leak in the system. At this time, keep the inflation valve in the open state and adjust the valve switch size so that the pressure gauge reading is stable at 0.4MPa; if the pressure gauge reading drops rapidly after closing the inflation valve, it means that there is a serious leak in the system. At this time, exit the device and recheck the air tightness before pushing it into the hole. Connect the grouting pump compressed air pipeline, add clean water into the grouting pump, add sealing cement while stirring, and prepare the grouting liquid according to the water-cement ratio of 1:1 to 1.2:1; after the slurry is fully stirred, connect the device of the present invention to the grouting pump outlet (the grouting outlet of the grouting equipment) through the high-pressure grouting pipe, open the valve to start grouting, and observe the grouting pressure change in the hole through the grouting pressure gauge on the device during the grouting process. When the grouting pressure rises to 0.5MPa, appropriately reduce the grouting frequency of the grouting pump, and slowly pressurize the hole for grouting until the grouting pressure rises to 1MPa or the grouting pump is blocked and stopped; after the grouting is completed, close the grouting pipe valve, maintain the pressure for 2 minutes and then release the pressure; open the device airbag inflation valve to release the pressure on the airbag, and after the pressure is released, use the grouting pump to inject clean water into the hole through the device grouting pipe to dilute the sealing section slurry (about 2min); withdraw the entire set of equipment in the hole, clean the grouting pump, and clean the inside and outside of the device.

[0038] In summary, the present invention provides a secondary grouting and plugging device in a borehole, which can perform precise pressure grouting at the location where cracks in failed boreholes are developed, activate and restore the gas extraction function of failed boreholes, and improve the gas extraction concentration and purity. Slurry is injected into a borehole with coal wall cracks through special grouting equipment. As the slurry flows, the cracks (cracks) are filled, and the slurry solidifies over time, thereby compensating for the cracks (cracks), which plays the role of grouting and plugging, thereby improving the gas extraction concentration. The present invention can not only perform grouting and plugging, but also has a borehole leakage detection function. The technical advantages of the present invention specifically include: first, the entire section is recyclable and the sections are adjustable. The present invention can be reused many times during actual use, so the average utilization cost is low, and the airbags, air injection pipes, and grouting pipes included therein can be replaced and adjusted, which can improve the overall service life; second, the depth and length of the sealing section are adjustable. The various parts of the present invention are independent of each other. During actual use, the length and depth of the sealing section can be determined according to specific needs, mainly by controlling the overall length of the device and the length of the grouting pipe with grouting holes to adjust the depth and length of the sealing section; third, the sealing material is injected under pressure to secure the gas extraction borehole; during use, the device first inflates the airbags, and the two airbags form a closed space in the borehole fissure 5 area. Pressurized grouting is used during the grouting process, which can ensure that the slurry flows into and fills the fissures better under pressure, thereby ensuring the grouting effect. The present invention combines the principle of "two plugging and one injection", integrating the advantages of sealing with a sealer and sealing with a capsule, using high-strength and high-rebound capsule material as the plug and lightweight metal material as the main body, to produce a device with good sealing effect, adjustable length, easy operation and durability, and relatively low cost.

[0039] The above disclosures are only several specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A secondary grouting plugging device in a borehole, characterized in that: The invention comprises a plurality of single-section pipes, each of which comprises an injection pipe (2) and a grouting pipe (3). The grouting pipe (3) is sleeved inside the injection pipe (2). The gap between the two pipes serves as a ventilation channel. The relative position between the injection pipe (2) and the grouting pipe (3) is fixed by a connecting piece. The plurality of single-section pipes are connected end to end in sequence to form an injection pipe, wherein the grouting pipes (3) of two adjacent single-section pipes are connected, and the injection pipes (2) of two adjacent single-section pipes are connected. The injection pipe is inserted from the gas extraction pipe (1) when secondary grouting is performed on the borehole to plug leaks, wherein the inner ends of the plurality of connected injection pipes (2) extend out of the inner end of the gas extraction pipe (1) and pass over the crack area of ​​the borehole, and are connected and communicated with the inner end air bag (6-1). The inner end air bag (6-1) is connected to the injection pipe. The bag (6-1) is used to seal the drilling parts at the inner ends of the multiple gas injection pipes (2) after being inflated by the gas injection pipe (2); the parts of the multiple gas injection pipes (2) located at the inner ends of the gas extraction pipe (1) are connected and communicated with the outer end bag (6-2); the outer end bag (6-2) is used to seal the annular gap between the gas injection pipe (2) and the gas extraction pipe (1) after being inflated by the gas injection pipe (2); a sealing body (4) for sealing the annular gap between the borehole and the gas extraction pipe (1) is also provided at one end of the gas extraction pipe (1) and the entrance of the borehole; the multiple gas injection pipes (2) of the injection pipe are located at one end of the borehole entrance and connected to the gas supply equipment, and the multiple grouting pipes (3) of the injection pipe are located at one end of the borehole entrance and connected to the grouting equipment; The gas injection pipe (2) and the grouting pipe (3) of each single-section pipe are concentric reducers that are sleeved together, and the connecting piece between the two pipes is an annular metal plug. A metal plug is provided at both ends of each single-section pipe, wherein the annular inner wall of the metal plug is provided with an internal thread, and the outer wall of the grouting pipe (3) is provided with an external thread matching the internal thread. The metal plug seals the annular gap between the gas injection pipe (2) and the grouting pipe (3) at the metal plug through the screw connection of the internal and external threads, wherein a vent hole is provided on the end surface of the metal plug; A connecting joint is provided on the inner end of the plurality of gas injection pipes (2), the connecting joint comprising two ports, one of which is connected to the inner end air bag (6-1), and the other is connected to the slurry output end of the plurality of grouting pipes (3) for outputting slurry from the grouting pipes (3).

2. A secondary grouting plugging device in a borehole as claimed in claim 1, characterized in that: The air injection pipe (2) and the grouting pipe (3) at one end of each single-section pipe are both provided with external threads, and the air injection pipe (2) and the grouting pipe (3) at the other end of each single-section pipe are both provided with internal threads. The air injection pipes (2) and the grouting pipes (3) of two adjacent single-section pipes are both screwed together via internal and external threads.

3. A secondary grouting plugging device in a borehole as claimed in claim 1, characterized in that: The inner airbag (6-1) and the outer airbag (6-2) both include an elastic cylinder, which is sleeved on the gas injection pipe (2), and the sleeved gas injection pipe (2) is provided with a row of inflation holes along the longitudinal direction of the gas injection pipe (2). Both ends of the elastic cylinder are sealed and fixed to the gas injection pipe (2) by crimping cylindrical metal rings with a crimping machine.

4. A secondary grouting plugging device in a borehole as claimed in claim 3, characterized in that: The outer diameter of the portion of the gas injection pipe (2) sleeved with the elastic cylinder is smaller than the outer diameter of the remaining portion of the gas injection pipe (2), so that the outer diameter of the portion of the gas injection pipe (2) sleeved with the elastic cylinder and the remaining portion after the elastic cylinder is sleeved are equal, so as to ensure that the outer diameter of each gas injection pipe (2) remains smooth as a whole after assembly, which is convenient for use in drilling.

Images