Bundled sleeve combined with porous screen pipe for hole sealing and extraction device

Abstract

This utility model discloses a combined multi-hole screen pipe and perforation sealing extraction device, belonging to the field of coal mine gas extraction technology. Addressing the problem that traditional extraction pipes in soft coal seams struggle to balance structural strength, ventilation performance, and anti-clogging capability, a nested structure of outer screen and inner bundle is proposed. The device includes a slag-preventing guide cone, a non-metallic multi-hole screen pipe, a bundled perforated pipe assembly (31), and a sealing unit. The non-metallic multi-hole screen pipe has ventilation holes, and its inner cavity is coaxially fitted with the bundled perforated pipe assembly (31). Ventilation holes are provided on the perforated pipe, forming an annular gas collection gap between the two. The sealing unit is located at the borehole opening behind the screen pipe, employing a two-block, one-injection structure consisting of a front bladder, a rear bladder, and an injection pipeline to achieve reliable sealing. Through the synergistic effect of primary filtration by the outer screen pipe and perforation protection, and redundant extraction by the inner multi-pipe system, this device significantly improves resistance to confining pressure and anti-clogging performance, extends the effective life of the extraction hole, and is suitable for safe and efficient gas extraction in high-gas, soft coal seams.

Description

Technical Field

[0001] This utility model relates to the field of coal mine gas extraction technology, and in particular to a combined multi-hole screen pipe and gas extraction device for gas extraction, which is used for gas extraction, sealing and filtration of coal slag in high-pressure soft coal seams. Background Technology

[0002] In the field of coal mine gas disaster prevention and control, soft coal seams, due to their low permeability, high gas content, and poor self-supporting capacity, have become a key and challenging area for gas drainage. To achieve effective gas control, it is usually necessary to drill in-seam boreholes within the coal seam and maintain their long-term patency through the installation of borehole protection devices, thereby ensuring continuous and efficient gas drainage. Existing technologies commonly employ borehole protection measures such as running metal screens throughout the borehole or using large-diameter perforated pipes. The core significance of these measures lies in: supporting the borehole wall with rigid pipes to prevent surrounding rock collapse; and simultaneously utilizing the perforated structure on the pipe wall to create gas seepage channels, allowing gas from the coal seam to enter the pipe and be extracted under negative pressure. Such structures can effectively extend the life of the drainage borehole and improve gas drainage efficiency in stable coal seams with low confining pressure, and are therefore widely used in engineering practice.

[0003] However, under high confining pressure in soft coal seams, the aforementioned existing technologies reveal significant shortcomings.

[0004] First, although traditional metal screens or large-diameter perforated pipes have a certain compressive strength, when the confining pressure on the borehole exceeds its structural strength limit, the pipe body will still be crushed and deformed, causing the borehole channel to be squeezed and blocked by broken coal slag, and the effective extraction length will be greatly shortened.

[0005] Secondly, blindly increasing the thickness of the metal pipe wall to improve compressive strength may partially alleviate the crushing problem, but it also brings new problems such as a surge in material consumption, increased pipe weight, and difficulties in transportation and underground pushing, which seriously reduces the convenience of construction.

[0006] Third, for sparsely ventilated metal screens, the number of openings is small and the diameter is large. Although this is beneficial to improve local strength, in low-permeability, soft coal seams, high negative pressure tends to concentrate in a few large holes, causing fine coal powder to be sucked into the holes and quickly blocked, resulting in a sharp reduction in the effective extraction area and a significant decrease in extraction efficiency.

[0007] Fourth, existing sealing processes mostly use simple bags or cement mortar for direct sealing, which makes it difficult to form a reliable seal under dynamic confining pressure and complex borehole wall conditions. This can easily lead to gas leakage or air infiltration, affecting the purity of the extraction and the stability of the system's negative pressure.

[0008] In the development of gas extraction and protection technology in soft coal seams, the design paradigm of metal materials and single large-diameter structure has long been used. The technical approach is to enhance the mechanical strength of a single pipe to cope with the confining pressure, which is the traditional idea of ​​"using rigidity to overcome rigidity". This ignores the need for coordinated optimization of "anti-blocking-ventilation-lightweighting" under the dual constraints of high confining pressure and low permeability.

[0009] Existing technologies focus on improving the strength of a single pipe (such as a full-length metal screen pipe or a large-diameter perforated pipe) or reducing the number of holes. They fail to solve the fundamental contradiction that "high strength inevitably leads to low open area ratio, and high open area ratio weakens structural strength." They also fail to design multi-level protection and distributed extraction channels to address the characteristics of soft coal seams where coal slag is easy to intrude and the channels are easy to block.

[0010] Accordingly, this patent application establishes a technical route for combined hole protection using a combination of "non-metallic dense pore screen tube + clustered flower tube". Through material substitution, structural differentiation and functional synergy, it simultaneously achieves high pressure resistance, high air permeability and strong anti-clogging.

[0011] In summary, there is an urgent need for a gas drainage well protection device that can withstand the high confining pressure of soft coal seams, prevent coal slag blockage, and simultaneously ensure ease of construction and reliable well sealing. This necessity for improvement is precisely the core problem that this patented "bundled sleeve combined with porous screen pipe well protection and sealing drainage device" aims to solve: by providing high opening rate and lightweight main support through non-metallic porous screen pipes, combined with bundled perforated pipes to form distributed pressure-resistant and anti-blockage drainage channels, it achieves long-term, efficient, and stable operation of gas drainage wells in soft coal seams. Utility Model Content

[0012] The purpose of this utility model is to provide a combined multi-hole screen pipe hole protection and sealing extraction device to solve the technical problem that hole protection devices in high-pressure soft coal seams cannot achieve both structural strength and ventilation and anti-blocking performance due to the use of a single pipe structure, and to overcome the defects caused by this, such as borehole crushing, extraction channel blockage and significantly shortened effective extraction life.

[0013] To achieve the above objectives, the present invention provides a combined multi-porous screen tube and hole sealing extraction device for bundled sleeves, including a slag-preventing guide cone, a non-metallic multi-porous screen tube, a bundled flower tube assembly, and a hole sealing unit. The anti-slag guide cone is fixedly connected to the front end of the non-metallic porous protective screen tube; the non-metallic porous protective screen tube is a tubular body extending along the borehole axis, and its tube wall is provided with multiple vent holes to support the borehole wall and allow gas to seep in; the bundled perforated tube assembly is composed of multiple perforated tubes with an outer diameter of 10-50mm arranged in parallel, and is integrally set in the inner cavity of the non-metallic porous protective screen tube, and is arranged coaxially with the non-metallic porous protective screen tube; each perforated tube is provided with multiple vent holes; the sealing unit is set at the borehole opening behind the non-metallic porous protective screen tube to seal the borehole opening area and form a closed extraction channel.

[0014] The non-metallic porous screen tubes of adjacent segments are connected by a threaded fixing device.

[0015] The clustered flower tube assembly has multiple segments, and adjacent segments are connected by a clustered flower tube positioning connecting sleeve. The clustered flower tube positioning connecting sleeve has multiple circular through holes that correspond one-to-one with the flower tubes along the axial direction inside. The inner diameter of the circular through holes is slightly smaller than the outer diameter of the flower tubes to form an interference fit, and the two ends of the circular through holes are provided with flared chamfers to facilitate the insertion of the flower tubes.

[0016] The sealing unit includes a front bladder, a rear bladder, and a grouting pipeline. The front and rear bladders are spaced apart along the borehole axis at the borehole opening behind the non-metallic porous screen pipe. The grouting pipeline connects the front and rear bladders and passes through the rear bladder. The front and rear bladders, together with the borehole wall, form a grouting area. The pipe section of the grouting pipeline within the grouting area has a bursting pressure greater than the sealing pressure required for the front and rear bladders to expand and seal the borehole. A return grouting pipe is connected to the grouting area. The return grouting pipe extends backward through the rear bladder and out of the borehole opening, with its front end located at the rear end of the grouting area.

[0017] The non-metallic porous screen tube has a ventilation hole opening rate of 35%–40% and an inter-hole rib width of not less than 1.5mm.

[0018] The anti-slag guide cone has a conical structure, with its large end fixedly connected to the front end of the non-metallic porous screen tube, and its small end being a closed end.

[0019] An annular gap is left between the non-metallic porous screen tube and the clustered flower tube assembly, which forms a gas collection channel.

[0020] This utility model has the following advantages: This invention utilizes a nested structure of "outer screen and inner bundle." The outer layer of non-metallic porous screen provides high-density ventilation holes for primary anti-clogging and hole protection. The inner layer of bundled perforated tube assembly shares the confining pressure and forms redundant extraction channels in a parallel multi-tube configuration, fundamentally solving the technical bottleneck of the trade-off between strength and ventilation performance in single-tube structures. A slag-preventing guide cone reduces propulsion resistance and physically isolates large pieces of coal slag. The sealing unit ensures the system's airtightness. These three elements work synergistically to significantly extend the effective lifespan of extraction holes in soft coal seams.

[0021] Threaded connections provide reliable axial locking force and a certain degree of sealing, adapting to the needs of downhole segmented pushing construction and avoiding the non-removability and safety hazards caused by adhesive bonding or welding.

[0022] The cluster tube positioning connector maintains the relative position of the tubes through an internal porous positioning structure, preventing them from scattering and misaligning during pushing and pressing, and ensuring the integrity of the cluster structure; the interference fit provides radial clamping force, serving both positioning and sealing functions; the flared chamfer reduces assembly resistance and improves construction efficiency.

[0023] The "two-plug-one-injection" structure uses front and rear bladders to expand and seal the borehole wall, while the middle grouting chamber is filled with grout to form a permanent seal. This effectively adapts to irregular borehole walls and resists creep of the surrounding rock, preventing gas leakage.

[0024] This range of opening ratios ensures sufficient gas seepage area while maintaining the pipe's resistance to external pressure at no less than 4MPa through rib widths of ≥1.5mm, thus achieving a balance between strength and ventilation.

[0025] The tapered structure of the anti-slag guide cone reduces drilling resistance, and the closed end prevents coal slag from directly impacting the screen tube inlet.

[0026] The annular gap collects the gas that seeps in from the sieve holes (i.e., the vent holes) of the non-metallic porous screen pipe and distributes it evenly to the inlet of each perforated pipe (i.e., the vent hole), thus avoiding excessive local negative pressure that could lead to the inhalation of coal dust. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of this utility model.

[0028] Figure 2 This is a cross-sectional structural diagram of the clustered flower tube assembly.

[0029] Figure 3 This is a schematic diagram of the structure of a non-metallic porous screen tube.

[0030] Figure 4 This is a schematic diagram of the connection between the extraction pipe and the clustered flower pipe assembly. Detailed Implementation

[0031] like Figures 1 to 4As shown, the combined multi-hole screen tube and hole sealing extraction device of this utility model includes a slag-preventing guide cone 1, a non-metallic multi-hole screen tube 2, a bundled flower tube assembly 31, and a hole sealing unit. The anti-slag guide cone 1 is fixedly connected to the front end of the non-metallic porous protective screen 2; the non-metallic porous protective screen 2 is a tubular body extending along the axial direction of the borehole 32, with multiple vent holes spaced apart on its wall to support the borehole wall of the borehole 32 and allow gas to seep in, while preventing most of the coal slag from entering (the diameter of its vent holes is constrained to be smaller than the diameter of most of the coal slag); the bundled perforated tube assembly 31 is composed of multiple perforated tubes 12 with an outer diameter of 10–50 mm arranged in parallel, and is integrally set in the inner cavity of the non-metallic porous protective screen 2, and is coaxially arranged with the non-metallic porous protective screen 2; each perforated tube 12 is provided with multiple vent holes 33; the sealing unit is set at the borehole 32 opening behind the non-metallic porous protective screen 2, and is used to seal the borehole 32 opening area to form a closed extraction channel.

[0032] When the outer diameter of the flower tube 12 is less than 10mm, the tube body is not rigid enough and is easily flattened under confining pressure; when it is greater than 50mm, it cannot achieve effective bundling and the advantage of multi-channel redundancy is weakened. Therefore, the outer diameter of the flower tube 12 is limited to 10–50mm, including the two ends.

[0033] This invention utilizes a nested structure of "outer screen and inner bundle." The outer non-metallic porous screen tube 2 provides high-density ventilation holes for primary anti-clogging and hole protection. The inner bundled flower tube assembly 31 distributes the confining pressure and forms redundant extraction channels in a multi-tube parallel configuration, fundamentally solving the technical bottleneck of the trade-off between strength and ventilation performance in single-tube structures. The anti-slag guide cone 1 reduces propulsion resistance and physically isolates large pieces of coal slag. The sealing unit ensures the airtightness of the system. The synergy of these three elements significantly extends the effective lifespan of extraction holes in soft coal seams.

[0034] The perforated tube 12 has an outer diameter of 10-50mm and micropores in its wall. The sealing unit adopts a double-bag "two-block, one-injection" structure. The "two-block, one-injection" structure refers to the sealing unit consisting of the front bag 4, the rear bag 5, and the middle injection area 34. If any main component is missing (e.g., without the clustered perforated tube, there is no redundant channel; without the screen tube, there is no primary filtration), the core problem cannot be solved.

[0035] The adjacent segments of the non-metallic porous screen pipe 2 are connected by a threaded fixing device 3. The thread is a trapezoidal thread or a sawtooth thread, with a nominal diameter of 50–75 mm and a pitch of 4–6 mm; the threaded fixing device 3 is a nut with a sealing ring or a flange pressure ring. Threaded connection is a necessary step to achieve "assembled" screen pipe. Threaded connection provides reliable axial locking force and a certain degree of sealing, adapting to the needs of downhole segmented pushing construction, and avoiding the non-removability and safety hazards caused by adhesive bonding or welding.

[0036] The clustered flower tube assembly 31 has multiple segments, and adjacent segments of the clustered flower tube assembly 31 are connected by a clustered flower tube positioning connecting sleeve 14. The clustered flower tube positioning connecting sleeve 14 has multiple circular through holes along the axial direction inside, which correspond one-to-one with the flower tubes 12 of the clustered flower tube positioning connecting sleeve 14. The inner diameter of the circular through holes is slightly smaller than the outer diameter of the flower tubes 12 to form an interference fit, and the two ends of the circular through holes are provided with flared chamfers to facilitate the insertion of the flower tubes 12.

[0037] The cluster tube positioning connecting sleeve 14 maintains the relative position of the tube 12 through the internal porous positioning structure, preventing scattering and misalignment during pushing and pressing, and ensuring the integrity of the cluster structure; the interference fit provides radial clamping force, which also serves as positioning and sealing; the flared chamfer reduces assembly resistance and improves construction efficiency.

[0038] The clustered flower tube positioning connector 14 is made of polyurethane rubber, fluororubber, or glass fiber reinforced nylon; the circular through holes are arranged in a hexagonal lattice pattern to ensure high space utilization. The clustered flower tube positioning connector 14 is a necessary structure to realize the "clustering" function. If binding or no positioning connection is used, the clustering advantage will be lost.

[0039] The sealing unit includes a front bladder 4, a rear bladder 5, and a grouting pipe 6. The front bladder 4 and the rear bladder 5 are arranged axially along the borehole 32 at intervals behind the borehole opening of the non-metallic porous protective screen pipe 2. The grouting pipe 6 connects the front bladder 4 and the rear bladder 5 and passes through the rear bladder 5. The front bladder 4 and the rear bladder 5, together with the borehole wall of the borehole 32, form a grouting area 34. The pipe section of the grouting pipe 6 within the grouting area 34 has a bursting pressure, which is greater than the sealing pressure required for the front bladder 4 and the rear bladder 5 to expand and seal the borehole 32. The grouting area 34 is connected to a return grout pipe 23, which extends rearward through the rear bladder 5 and out of the borehole opening of the borehole 32. The front end of the return grout pipe 23 is located at the rear end of the grouting area 34.

[0040] During grouting, the sealing pressure is reached before the grouting pressure reaches the burst pressure, allowing the front bladder 4 and rear bladder 5 to fully expand and seal the borehole 32. After the grouting pressure continues to rise to the burst pressure, the grouting pipe 6 bursts, allowing grout to enter the grouting area 34 and gradually fill it, achieving a two-plug-one-injection sealing method. When a large amount of grout flows out of the return grout pipe 23, it means the grouting area 34 is full of grout. At this point, grouting can be stopped, and the rear ends of the grouting pipe 6 and the return grout pipe 23 can be sealed to maintain pressure.

[0041] The "two-plug-one-injection" structure uses front and rear bladders to expand and seal the borehole wall, while the middle grouting chamber is filled with grout to form a permanent seal. This effectively adapts to irregular borehole walls and resists creep of the surrounding rock, preventing gas leakage.

[0042] The front bladder 4 is positioned 0.5–1.0m from the orifice, and the rear bladder 5 is positioned 1.5–2.0m from the front bladder; the grouting pressure is 2–5MPa; the bladder material is flame-retardant and antistatic rubber. The "two-plug-one-grout" sealing structure is the preferred solution for achieving a highly reliable seal, unlike single-bladder or pure grouting sealing.

[0043] The non-metallic porous screen pipe 2 has a venting opening ratio of 35%–40%, and the rib width between pores is not less than 1.5 mm. This venting ratio range ensures sufficient gas seepage area while maintaining the pipe body's external pressure resistance of not less than 4 MPa through the ≥1.5 mm rib width, achieving a balance between strength and ventilation. The venting ratio is achieved through a hexagonal arrangement of pores with a diameter of 2.5–3.0 mm and a center distance of 4.5–5.5 mm.

[0044] The slag-prevention guide cone 1 has a conical structure, with its large end fixedly connected to the front end of the non-metallic porous screen tube 2, and its small end being a closed end. The conical structure of the slag-prevention guide cone 1 reduces the drilling resistance of the borehole 32, and the closed end prevents coal slag from directly impacting the inlet of the screen tube.

[0045] The anti-slag guide cone 1 has a cone angle of 30°–45°, is made of the same material as the screen tube, and can be integrally injection molded. The absence of the anti-slag guide cone 1 will lead to an increase in the clogging rate.

[0046] An annular gap (3–10 mm wide) is left between the non-metallic porous screen tube 2 and the clustered flower tube assembly 31, which forms a gas collection channel.

[0047] A bracket is provided between the positioning connecting sleeve 14 of each bundle flower tube and the inner wall of the non-metallic porous screen tube 2, thereby forming the annular gap. This annular gap is also the key to achieving fluid coupling for the coordinated operation of the "outer screen and inner bundle".

[0048] The annular gap collects the gas that seeps in from the sieve holes (i.e., the vent holes) of the non-metallic porous screen pipe 2 and distributes it evenly to the inlet of each perforated pipe 12 (i.e., the vent hole 33) to avoid excessive local negative pressure that could lead to the inhalation of coal dust.

[0049] The positioning connecting sleeve 14 of the clustered flower tube is made of glass fiber reinforced nylon (a preferred material for high confining pressure conditions). Glass fiber reinforced nylon provides high rigidity and dimensional stability, and is not easily deformed under high confining pressure, ensuring long-term positioning accuracy. The glass fiber content is preferably ≥30%, and the tensile strength is ≥120MPa.

[0050] The non-metallic porous screen pipe 2 (hereinafter referred to as screen pipe 2) has a wall thickness of 3-5 mm, preferably 4 mm (too thin and it is easy to be crushed, too thick and it increases cost and weight). This thickness range ensures compressive strength while controlling the amount of material used and weight, which facilitates downhole transportation and pushing.

[0051] The working process of this utility model is as follows: I. Drilling Preparation Stage 32

[0052] Before construction, drilling borehole 32 (e.g., Φ89mm or Φ108mm) is first carried out to the designed depth, typically 80–150m, depending on the coal seam occurrence conditions. After drilling borehole 32, the borehole is thoroughly cleaned using high-pressure air or clean water to remove sediment at the bottom and coal dust adhering to the borehole wall, ensuring the borehole wall is intact and the borehole diameter is regular. Subsequently, a borehole 32 inspection instrument is used to check the borehole diameter, depth, and any collapse. If localized narrowing or collapse is found, borehole enlargement or grouting reinforcement is required.

[0053] II. Assembly and Deployment Stage of the Well Protection and Extraction System.

[0054] The slag-preventing guide cone 1 is fixedly connected to the front end of the non-metallic porous screen tube 2. Its conical structure has a cone angle of 30°–45°, with the large end sealed to the screen tube 2 and the small end closed. During the pushing process, the slag-preventing guide cone 1 guides the coal slag in front along the cone surface to the annulus between the non-metallic porous screen tube 2 and the borehole 32 wall, reducing the pushing resistance by 40%–50% and physically isolating large pieces of coal slag to prevent them from directly impacting the inlet of the screen tube 2.

[0055] The non-metallic porous screen pipe 2 is made of glass fiber reinforced polypropylene with a wall thickness of 3–5 mm. It has hexagonal ventilation holes with a diameter of 2.5–3.0 mm, a center-to-center distance of 4.5–5.5 mm, an opening rate of 35%–40%, and a rib width ≥1.5 mm between holes. This structure effectively prevents most coal slag particles larger than 3.0 mm from entering, while ensuring sufficient gas seepage area and maintaining a compressive strength of at least 4 MPa. Adjacent screen pipe sections 2 are connected by a trapezoidal threaded connection via a threaded fixing device 3 with a thread pitch of 4–6 mm. The engagement length is sufficient to withstand an axial tensile force of over 8 kN, and the clearance is less than 0.2 mm, preventing coal slag from intruding into the gaps between sections. Each screen pipe section 2 is 1–2 m long and can be pushed by two people, significantly improving construction efficiency.

[0056] Inside the screen tube 2, the clustered perforated tube assembly 31 consists of multiple perforated tubes 12 with an outer diameter of 10–50 mm arranged in parallel, and coaxially arranged within the inner cavity of the screen tube 2. Each perforated tube 12 has multiple vent holes 33 on its wall, preferably with a diameter of 2.0–2.5 mm (slightly smaller than the vent holes of the screen tube), which are spirally distributed with a spacing of 15–20 mm. This ensures uniform gas intake and forms a secondary microporous filtration system to further intercept fine coal dust.

[0057] Adjacent flower tube segments 12 are connected by a clustered flower tube positioning connecting sleeve 14. The clustered flower tube positioning connecting sleeve 14 has multiple circular through holes corresponding to the flower tubes 12, arranged in a hexagonal lattice. The inner diameter of the circular through holes is slightly smaller than the outer diameter of the flower tubes 12 by 0.1–0.3 mm, forming an interference fit to ensure that the flower tubes 12 maintain a stable relative position during the pressure and pushing process. The circular through-hole has flared chamfers at both ends to facilitate rapid assembly underground. A bracket is provided between the outer periphery of the cluster tube positioning connecting sleeve 14 and the inner wall of the screen tube 2, thus forming an annular gap with a width of 3–10 mm. This gap serves as a gas collection channel, which evenly distributes the gas seeping from the vent holes of the screen tube 2 to the vent holes 33 of each tube 12, avoiding excessive local negative pressure that could lead to the inhalation of coal dust.

[0058] The rear end of the clustered flower tube assembly 31 is connected to the large-diameter single-hole extraction tube 16 via an interface converter 15. The interface converter 15 has a tapered, gradually changing flow channel structure with a flow channel cone angle of 8°–10°. It is connected via a socket and clamp method, allowing the airflow to smoothly transition from the multi-hole cluster to the single hole. The large-diameter single-hole extraction tube 16 has no vent holes, an outer diameter of 80–100 mm, and extends 1.5–2 m beyond the borehole 32 at its rear end for connection to the surface extraction system.

[0059] III. Sealing Stage.

[0060] Once the device is lowered into place, the sealing unit is activated. This unit includes a front bladder 4, a rear bladder 5, a grouting pipeline 6, and a return grout pipe 23, and is positioned as a whole at the borehole 32 opening behind the non-metallic porous protective screen pipe 2. The front bladder 4 is 0.5–1.0m from the borehole opening, and the rear bladder 5 is 1.5–2.0m from the front bladder 4, with the two arranged at intervals along the axial direction of the borehole 32. In the initial stage of grouting, the grouting pressure is increased to 0.3–0.5MPa (sealing pressure), causing the front bladder 4 and the rear bladder 5 to fully expand and adhere tightly to the borehole wall of the borehole 32, forming an initial sealing barrier. The pressure is further increased to 4–6MPa (bursting pressure), and the grouting pipeline 6 undergoes a controlled burst in the grouting area 34, immediately injecting fast-setting cement grout (water-cement ratio 0.8:1) into the annular grouting area 34 between the front bladder 4 and the rear bladder 5. The front end of the return grout pipe 23 is located at the rear end of the grouting area 34, and the rear end extends out of the orifice. When thick grout continues to flow from the return grout pipe 23 for more than 30 seconds, it indicates that the grouting area 34 is full. At this time, grouting is stopped and the rear end of the pipe is sealed. The grout initially sets in 30 minutes, and its compressive strength reaches 5-8 MPa after 24 hours, forming a permanent seal that effectively resists the creep of the surrounding rock and prevents gas leakage.

[0061] IV. Gas Drainage Operation Phase.

[0062] After the sealing body has solidified, the surface extraction pump is turned on, and a negative pressure of 15–25 kPa is applied. Gas seeps from the coal seam into the annular gap through the vents of the non-metallic porous screen 2, where it collects and is evenly distributed to the vents 33 of each perforated pipe 12. Due to the small diameter and high flow velocity of the vents 33, a self-cleaning effect is generated, flushing out small particles and maintaining unobstructed passages. After entering the inner cavity of the perforated pipe 12, the gas flows through the bundled perforated pipe assembly 31 and the interface converter 15 into the large-diameter single-hole extraction pipe 16, and is finally transported to the surface system. Even if one or two perforated pipes 12 are partially blocked, the remaining channels can still maintain more than 70% extraction capacity, resulting in extremely high system reliability. The entire device systematically solves the technical problem of the incompatibility between the strength and ventilation performance of the hole protection device in high-pressure soft coal seams through the nested structure of "outer screen and inner bundle", the mechanical isolation of the anti-slag guide cone 1, the rapid assembly of the threaded and positioning connection, and the reliable sealing of the "two plugs and one injection" sealing unit. It significantly extends the effective life of the extraction hole to 6-12 months, improves the gas extraction concentration and efficiency, and achieves safe and efficient production.

[0063] The above embodiments are only used to illustrate and not limit the technical solutions of this utility model. Although the utility model has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the utility model without departing from the spirit and scope of the utility model. Any modifications or partial substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A combined multi-hole screen tube and perforation sealing extraction device, characterized in that: It includes a slag-preventing guide cone (1), a non-metallic porous screen tube (2), a clustered flower tube assembly (31), and a sealing unit; The anti-slag guide cone (1) is fixedly connected to the front end of the non-metallic porous screen (2); the non-metallic porous screen (2) is a tubular body extending along the borehole axis, and its wall is provided with multiple vent holes to support the borehole wall and allow gas to seep in; the bundled flower tube assembly (31) is composed of multiple flower tubes (12) with an outer diameter of 10–50 mm arranged in parallel, and is integrally set in the inner cavity of the non-metallic porous screen (2), and is coaxially arranged with the non-metallic porous screen (2); each flower tube (12) is provided with multiple vent holes (33); the sealing unit is set at the borehole opening behind the non-metallic porous screen (2) to seal the borehole opening area and form a closed extraction channel.

2. The combined bundled casing and perforated screen hole protection and sealing and extraction device of claim 1, wherein: The non-metallic porous screen tubes (2) of adjacent segments are connected by a threaded fixing device (3).

3. The combined bundled casing and perforated screen hole protection and sealing and extraction device of claim 1, wherein: The clustered flower tube assembly (31) has multiple segments, and the clustered flower tube assemblies (31) of adjacent segments are connected by the clustered flower tube positioning connecting sleeve (14). The clustered flower tube positioning connecting sleeve (14) has multiple circular through holes that correspond one-to-one with the flower tube (12) along the axial direction inside. The inner diameter of the circular through hole is slightly smaller than the outer diameter of the flower tube (12) to form an interference fit, and the two ends of the circular through hole are provided with flared chamfers to facilitate the insertion of the flower tube (12).

4. The combined bundled casing and perforated screen hole protection and sealing and extraction device of claim 1, wherein: The sealing unit includes a front bladder (4), a rear bladder (5), and a grouting pipeline (6); the front bladder (4) and the rear bladder (5) are arranged at intervals along the borehole axis at the borehole opening behind the non-metallic porous screen pipe (2); the grouting pipeline (6) connects the front bladder (4) and the rear bladder (5) and passes through the rear bladder (5); the front bladder (4) and the rear bladder (5) together with the borehole wall form a grouting area; the pipe section of the grouting pipeline (6) in the grouting area has a bursting pressure, which is greater than the sealing pressure required for the front bladder (4) and the rear bladder (5) to expand and seal the borehole; the grouting area is connected to a return grouting pipe, which passes through the rear bladder (5) and extends out of the borehole opening, with the front end of the return grouting pipe located at the rear end of the grouting area.

5. The combined bundled casing and perforated screen hole protection and sealing and extraction device of claim 1, wherein: The non-metallic porous screen tube (2) has a ventilation hole opening rate of 35%–40% and a rib width between holes of not less than 1.5 mm.

6. The combined multi-hole screen tube and perforation sealing extraction device according to claim 1, characterized in that: The anti-slag guide cone (1) has a conical structure, with its large end fixedly connected to the front end of the non-metallic porous screen tube (2), and its small end being a closed end.

7. The combined bundled casing and perforated screen hole protection and leak-off extraction device of claim 1, wherein: An annular gap is left between the non-metallic porous screen tube (2) and the clustered flower tube assembly (31), which forms a gas collection channel.

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