Modified permeability extraction system and process for high-gas low-permeability coal seams

Abstract

The application discloses a modified permeability increasing extraction system and process for high-gas low-permeability coal seams, which comprises a drill rod, an outer wall of the drill rod is provided with a sunken annular space, and the annular space is provided with a mechanical reaming mechanism, a plurality of acid injection holes, and an isolation protection mechanism.

Description

Technical Field

[0001] This invention relates to the field of coal mine gas extraction technology, specifically to a high-gas, low-permeability coal seam modification and permeability enhancement extraction system and process. Background Technology

[0002] Gas drainage is a crucial link in coal mine safety production and gas resource utilization. Most coal seams in my country's mining areas are low-permeability seams with generally low permeability, making gas drainage a core issue restricting coal mine safety production and gas control efficiency.

[0003] Currently, there are two main types of permeability enhancement technologies for low-permeability coal seams: one is mechanical cavity creation technology, which involves constructing large-diameter cavities in the coal seam to create macroscopic pressure relief spaces and gas flow channels; the other is acid injection technology, which involves injecting acid into the coal seam to dissolve minerals blocking pores and clear microscopic seepage channels. However, in existing technologies, mechanical cavity creation and acid injection are usually implemented in separate steps. That is, first, a steel drill pipe is lowered for mechanical hole enlargement, and then the drill pipe is pulled out and a corrosion-resistant tubing string is lowered for acid injection. This results in cumbersome construction procedures and low efficiency. Moreover, if the borehole collapses during the lowering of the acid injection tubing, it will affect the lowering process.

[0004] Although there have been explorations in recent years to integrate hole creation and permeability enhancement, the following technical challenges are generally faced: First, the reaming tool is directly exposed to acid during the acidizing process, making it susceptible to corrosion and hydrogen embrittlement fracture; Second, the acid injection hole is easily blocked by coal slag during drilling and reaming; These problems limit the engineering application of composite permeability enhancement technology.

[0005] Therefore, it is necessary to provide a high-gas, low-permeability coal seam modification and permeability enhancement extraction system and process to solve the problems mentioned in the background technology. Summary of the Invention

[0006] To achieve the above objectives, the present invention provides the following technical solution: a high-gas, low-permeability coal seam modification and permeability enhancement extraction system, comprising a drill rod, wherein a sunken annular space is formed on the outer wall of the drill rod, and a mechanical reaming mechanism is provided within the annular space, comprising multiple storage slots formed circumferentially at the bottom of the annular space, and reaming cutters rotatably disposed in each of the storage slots, one end of the reaming cutter being rotatably connected to one end of the storage slot, and a first hydraulic drive component being hinged between the middle of the reaming cutter and the other end of the storage slot; and multiple acid injection holes, wherein the multiple acid injection holes are respectively opened... The drill rod is disposed on the wall between two adjacent storage slots; the isolation and protection mechanism includes an annular sleeve fixedly disposed at one end of the annular space, an isolation sleeve slidably disposed within the annular sleeve, a sealing sleeve fixedly disposed at the other end of the annular space, and a drive bar slidably disposed between two adjacent storage slots. The drive bar is axially fixedly connected to the isolation sleeve and can rotate relative to it in the circumferential direction. A second hydraulic drive component is connected between the drive bar and the drill rod. The drive bar has multiple first through holes, and the isolation sleeve has multiple second through holes.

[0007] Preferably, the inner wall of the isolation sleeve has multiple composite guide grooves circumferentially formed, and the bottom of the annular sleeve is fixedly provided with multiple guide blocks that slide in cooperation with the composite guide grooves circumferentially. The composite guide groove includes a straight groove section extending axially and a spiral groove section communicating with the straight groove section. When the guide block slides along the straight groove section, the isolation sleeve only moves axially. When the guide block slides along the spiral groove section, the isolation sleeve rotates circumferentially while moving axially.

[0008] Preferably, when the drive bar slides, it causes the isolation sleeve to slide axially between the annular sleeve and the sealing sleeve, so that the isolation protection mechanism switches between the initial state, the hole expansion state and the acid injection state.

[0009] Preferably, an annular plug is slidably disposed inside the sealing sleeve, and an elastic element is disposed between the annular plug and the sealing sleeve. When the isolation sleeve exits the sealing sleeve, the annular plug slides out of the sealing sleeve under the drive of the elastic element and blocks the entrance of the sealing sleeve.

[0010] Preferably, the drive bar has a first drive stroke and a second drive stroke, wherein the guide block slides in the straight groove section during the first drive stroke and slides in the spiral groove section during the second drive stroke.

[0011] Preferably, sealing rings are provided on the outer walls of both ends of the isolation sleeve, and the sealing rings are used to form a sliding seal between the isolation sleeve and the annular sleeve and between the isolation sleeve and the sealing sleeve.

[0012] Preferably, the system further includes an acid supply system, a hydraulic control system, and a gas extraction structure. The acid supply system is connected to the acid injection port, the hydraulic control system is connected to the first hydraulic drive and the second hydraulic drive, and the gas extraction structure is connected to the inner cavity of the drill pipe.

[0013] The process for modifying and enhancing the permeability of high-gas, low-permeability coal seams includes the following steps:

[0014] S1. The drill rod is inserted into the target coal seam borehole, at which point the isolation sleeve is in the initial state of covering the reaming tool;

[0015] S2. The second hydraulic drive unit drives the drive bar to slide, causing the isolation sleeve to retract into the annular sleeve and exit the sealing sleeve, so that the reaming tool is exposed in the annular space. At the same time, the annular plug slides towards the opening end of the sealing sleeve under the drive of the elastic element, blocking the entrance of the sealing sleeve.

[0016] S3. Drive the reaming tool to unfold using the first hydraulic drive component, and rotate the drill rod to mechanically create a cavity;

[0017] S4. After the cavity is created, the hole-reaming tool is retracted, and the drive bar is driven in the opposite direction by the second hydraulic drive component, so that the isolation sleeve extends out of the annular sleeve and covers the hole-reaming tool, and the isolation sleeve returns to its initial state.

[0018] S5. The second hydraulic drive unit continues to drive the drive bar to slide, the isolation sleeve slides into the sealing sleeve and pushes the annular block to overcome the elastic force of the elastic element and slide into the sealing sleeve. At the same time, the guide block enters the spiral groove section to make the isolation sleeve rotate circumferentially until the acid injection hole, the first perforation hole and the second perforation hole are aligned in sequence, and acid is supplied to the acid injection hole to carry out acidification and penetration enhancement operation.

[0019] S6. After acidification is completed, the residual acid is discharged and gas is extracted through the inner cavity of the drill pipe.

[0020] Compared with existing technologies, this invention provides a high-gas, low-permeability coal seam modification and permeability enhancement extraction system and process, which has the following beneficial effects:

[0021] First, it achieves "one-trip drilling" composite permeability enhancement; it integrates mechanical hole enlargement, acidizing permeability enhancement, and gas extraction functions into the same drill pipe, so that hole creation, permeability enhancement, and extraction operations can be completed sequentially without repeatedly raising and lowering the drill pipe, greatly simplifying the construction process and improving work efficiency.

[0022] Secondly, it effectively protects the reaming tool; by covering the reaming tool with an isolation sleeve during acid injection, the precision tool is physically isolated from the acid environment, avoiding the risk of corrosion of the cemented carbide blades and hydrogen embrittlement fracture caused by the acid, thus extending the tool's service life.

[0023] Third, it effectively prevents the acid injection hole from becoming blocked; through the multiple staggered sealing of the drive bar and the isolation sleeve, the acid injection hole is completely sealed during the drilling and hole enlargement stages, preventing coal slag from entering; during the acid injection stage, it is reliably opened through precise mechanical linkage, ensuring the smooth progress of the acidizing operation.

[0024] Fourth, the synergistic permeability enhancement effect is significant; mechanical cavity creation constructs a macroscopic pressure relief space and gas flow channel, while acidification and permeability enhancement unblock the microscopic seepage pores. The synergistic effect of the two fundamentally improves the permeability of the coal seam, effectively increasing the gas extraction efficiency and concentration. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0026] Figure 2 This is a schematic diagram of the drill pipe structure in this invention;

[0027] Figure 3 This is a schematic diagram of the structure of the isolation sleeve in this invention;

[0028] Figure 4 This is a schematic diagram of the composite guide groove in the present invention;

[0029] Figure 5 This is a schematic diagram of the drive bar structure in this invention;

[0030] Figure 6a This is a schematic diagram of the isolation and protection mechanism in its initial state in this invention;

[0031] Figure 6b This is a schematic diagram of the isolation and protection mechanism in the acid injection state in this invention;

[0032] In the diagram: 1. Drill rod; 11. Annular space; 12. Storage groove; 3. Reamer; 31. First hydraulic drive component; 4. Acid injection hole; 5. Annular sleeve; 51. Guide block; 6. Isolation sleeve; 61. Second perforation; 62. Composite guide groove; 621. Straight groove section; 622. Spiral groove section; 7. Sealing sleeve; 71. Annular sealing block; 8. Drive bar; 81. First perforation; 82. Receiving cavity. Detailed Implementation

[0033] Please see Figure 1Figure 6 shows the high-gas, low-permeability coal seam modification and permeability enhancement extraction system in this embodiment of the invention. It mainly includes a drill pipe 1, a mechanical reaming mechanism, an acid injection hole 4, and an isolation and protection mechanism installed on the drill pipe 1. A recessed annular space 11 is formed on the outer wall of the drill pipe 1. The outer diameter of the annular space 11 is smaller than the maximum outer diameter of the drill pipe 1, thus forming a recessed area on the outer wall of the drill pipe 1 for installing the mechanical reaming mechanism and the isolation and protection mechanism. The inner cavity of the drill pipe 1 serves as an acid delivery channel and a gas extraction channel. The surface of the drill pipe 1 is coated with an anti-corrosion and wear-resistant coating to resist the harsh underground environment and acid corrosion.

[0034] The mechanical reaming mechanism is disposed within the annular space 11, including multiple storage slots 12 circumferentially formed at the bottom of the annular space 11, and reaming cutters 3 rotatably disposed within each storage slot 12; such as Figure 1 As shown, there are preferably three reaming tools 3, evenly distributed along the circumference of the drill rod 1 to ensure balanced force during reaming; one end of the reaming tool 3 is rotatably connected to one end of the storage groove 12 via a hinge shaft, and a first hydraulic drive 31 is hinged between the middle of the reaming tool 3 and the other end of the storage groove 12; the first hydraulic drive 31 is a hydraulic telescopic rod, which drives the reaming tool 3 to rotate around the hinge shaft during its telescopic movement, thereby realizing the expansion or contraction (retraction into the storage groove 12) of the reaming tool 3; the cutting edge of the reaming tool 3 is made of cemented carbide to ensure wear resistance when cutting coal seams.

[0035] There are multiple acid injection holes 4, which are respectively opened on the wall surface of the drill rod 1 between two adjacent storage tanks 12.

[0036] In this embodiment, the isolation and protection mechanism is set in the annular space 11 to protect the acid injection hole 4 from being blocked by coal slag during the drilling and reaming stages, and to protect the reaming tool 3 from being corroded by acid during the acid injection stage. The isolation and protection mechanism mainly includes an annular sleeve 5, an isolation sleeve 6, a sealing sleeve 7, and a drive bar 8. The annular sleeve 5 is fixedly set at one end of the annular space 11, and its inner hole slides with the outer wall of the isolation sleeve 6. Multiple guide blocks 51 (preferably 2 to 3, evenly distributed along the circumference) are fixedly set at the bottom of the annular sleeve 5 facing the inner wall of the isolation sleeve 6.

[0037] The isolation sleeve 6 is slidably disposed inside the annular sleeve 5 and can slide along the axial direction of the drill rod 1 between the annular sleeve 5 and the sealing sleeve 7. The isolation sleeve 6 is made of acid-resistant stainless steel, and sealing rings (not shown in the figure) are respectively provided on the outer walls of both ends of the isolation sleeve 6. The sealing rings are made of acid-resistant fluororubber and are used to form a sliding seal between the isolation sleeve 6 and the annular sleeve 5 and between the isolation sleeve 6 and the sealing sleeve 7 to prevent leakage of coal slag and acid. Multiple composite guide grooves 62 are opened circumferentially on the inner wall of the isolation sleeve 6. The composite guide grooves 62 slide in cooperation with the guide block 51 at the bottom of the annular sleeve 5.

[0038] The sealing sleeve 7 is fixedly disposed at the other end of the annular space 11, and its inner hole is slidably fitted with the outer wall of the isolation sleeve 6; an annular block 71 is slidably disposed inside the sealing sleeve 7, and an elastic element (preferably a compression spring made of acid-resistant stainless steel) is disposed between the annular block 71 and the sealing sleeve 7; a sealing surface is provided on the side of the annular block 7 facing the opening end of the sealing sleeve 7, which is used to block the entrance of the sealing sleeve 7 when the isolation sleeve 6 exits the sealing sleeve 7, so as to prevent coal slag from entering the interior of the sealing sleeve 7.

[0039] The drive bar 8 is slidably disposed at the bottom of the annular space 11 between two adjacent storage slots 12. The drive bar 8 is axially fixedly connected to the isolation sleeve 6 and can rotate relative to it in the circumferential direction. A second hydraulic drive component is connected between the drive bar 8 and the drill rod 1. The second hydraulic drive component is used to drive the drive bar 8 to slide along the axial direction of the drill rod 1. A plurality of first through holes 81 are provided on the drive bar 8. The number and position of the first through holes 81 correspond one-to-one with the acid injection holes 4. A plurality of second through holes 61 are provided on the isolation sleeve 6. The number and position of the second through holes 61 correspond one-to-one with the first through holes 81.

[0040] It should be noted that the second hydraulic drive unit is used to drive the drive bar 8 to slide along the axial direction of the drill rod 1. It has a first drive stroke and a second drive stroke. In order to save the axial and circumferential space of the drill rod 1, reduce the outer diameter of the drill rod 1, and avoid interference between the external pipeline and the underground coal wall, the second hydraulic drive unit can be set in an embedded manner.

[0041] Specifically, such as Figure 5 As shown, a receiving cavity 82 is provided on the drive bar 8, and the second hydraulic drive component can be disposed in the receiving cavity 82; the receiving cavity 82 extends along the length direction of the drive bar 8, and its shape and size match the shape of the second hydraulic drive component; the second hydraulic drive component adopts a double-stroke limiting hydraulic cylinder; the hydraulic cylinder includes a cylinder body, a primary piston rod and a secondary piston rod; the cylinder body is fixedly installed in the receiving cavity 82 (it can be fixed by bolt connection or welding), the primary piston rod is slidably disposed in the cylinder body and can extend axially, and the secondary piston rod is slidably disposed in the primary piston rod and can extend axially; the extended ends of the primary piston rod and the secondary piston rod are respectively fixedly connected to the wall surface of the drill rod 1 (or fixedly connected to the wall surface of the drill rod 1 through a connector).

[0042] The action sequence of the two-stage telescopic hydraulic cylinder is as follows: when extending, the first-stage piston rod extends first, followed by the second-stage piston rod; when retracting, the second-stage piston rod retracts first, followed by the first-stage piston rod; that is, the first-stage piston rod extends first and retracts later, while the second-stage piston rod extends later and retracts first. The above action sequence is automatically realized by the internal oil circuit design and mechanical limit structure of the hydraulic cylinder, without the need for external position detection and electrical control. The specific structure can refer to the relevant designs in the existing technology.

[0043] The specific structure of the aforementioned double-stroke limiting hydraulic cylinder can refer to the relevant designs in the prior art; and in other embodiments, the second hydraulic drive component can also be an existing hydraulic mechanism that can realize two-stage drive, such as a segmented piston double-acting short-stroke hydraulic cylinder or a sequential hydraulic cylinder group, which is also embedded in the receiving cavity 82 of the drive bar 8.

[0044] In this embodiment, the composite guide groove 62 is formed on the inner wall of the isolation sleeve 6, including a straight groove section 621 extending axially and a spiral groove section 622 communicating with the straight groove section 621; the extension direction of the straight groove section 621 is parallel to the axis of the drill rod 1, and the spiral groove section 622 is set at the end of the straight groove section 621, and its channel extends spirally along the circumference of the isolation sleeve 6.

[0045] The guide block 51 is fixedly disposed at the bottom of the annular sleeve 5, embedded in the composite guide groove 62 and can slide therein; when the guide block 51 slides along the straight groove section 621, the isolation sleeve 6 only makes axial linear movement; when the guide block 51 slides along the spiral groove section 622, due to the guiding effect of the spiral groove, the isolation sleeve 6 continues to move axially while rotating circumferentially.

[0046] When the drive bar 8 slides, it drives the isolation sleeve 6 to slide axially between the annular sleeve 5 and the sealing sleeve 7, so that the isolation protection mechanism switches between the initial state, the hole expansion state and the acid injection state.

[0047] Initial state: In the initial state, the isolation sleeve 6 extends out of the annular sleeve 5 and covers the entire annular space 11. The reaming tool 3 is covered by the isolation sleeve 6 (that is, the reaming tool 3 is retracted into the storage groove 12 and is shielded and protected by the isolation sleeve 6). One end of the isolation sleeve 6 is in sliding sealing fit with the annular sleeve 5, and the other end extends into the sealing sleeve 7 and is in sealing fit with the sealing surface of the annular plug 71. At this time, the annular plug 71 maintains sealing contact with the end face of the isolation sleeve 6 under the action of the elastic element.

[0048] In this state, the first-stage piston rod in the second hydraulic drive is extended, the acid injection hole 4 is axially offset from the first perforation 81 (i.e., the acid injection hole 4 is covered by the outer wall of the drive rod 8), and the first perforation 81 is circumferentially offset from the second perforation 61 (i.e., the first perforation 81 is covered by the inner wall of the isolation sleeve 6); the acid injection hole 4, the first perforation 81 and the second perforation 61 are not connected to each other, forming multiple physical barriers, effectively preventing the coal slag generated during drilling from entering the acid injection channel and the inner cavity of the drill rod 1.

[0049] Hole enlargement state: such as Figure 1As shown, when drill rod 1 reaches the target coal seam section and mechanical cavity creation is required, the secondary piston rod of the second hydraulic drive component extends (at this time, the primary piston rod remains extended and stationary), driving the drive bar 8 to slide along the first drive stroke; the drive bar 8 drives the isolation sleeve 6 to retract into the annular sleeve 5, and the isolation sleeve 6 exits the sealing sleeve 7; during this process, the guide block 51 slides along the straight groove section 621 of the composite guide groove 62, and the isolation sleeve 6 only makes axial linear movement and does not rotate.

[0050] When the isolation sleeve 6 retracts from the sealing sleeve 7, the annular plug 71 slides towards the open end of the sealing sleeve 7 under the drive of the elastic element. The sealing surface of the annular plug 71 seals the entrance of the sealing sleeve 7, preventing coal slag from entering the interior of the sealing sleeve 7. At the same time, the isolation sleeve 6 retracts completely into the annular sleeve 5, the annular space 11 is opened, and the reaming tool 3 is exposed in the annular space 11. At this time, the reaming tool 3 is driven to unfold by the first hydraulic drive 31 (that is, the reaming tool 3 rotates outward from the storage groove 12 around the hinge axis). Then, the drill rod 1 is rotated, and the reaming tool 3 can cut and enlarge the surrounding coal seam to form a cavity with a diameter larger than the original drill hole. During the reaming process, since the drive bar 8 covers the acid injection hole 4, the acid injection hole 4 is effectively blocked, and coal slag cannot enter the acid injection hole 4.

[0051] Acid injection state: After mechanical cavity creation is completed, the first hydraulic drive 31 drives the reaming cutter 3 to retract back into the storage groove 12; then the second hydraulic drive retracts the secondary piston rod in the second hydraulic drive (at this time, the primary piston rod remains extended and stationary), so that the isolation sleeve 6 extends out of the annular sleeve 5 and enters the sealing sleeve 7. That is, the isolation sleeve 6 returns to the initial state first, and then the primary piston rod of the second hydraulic drive retracts, driving the drive bar 8 to slide along the second drive stroke; during this process, the guide block 51 enters the spiral groove section 622 from the straight groove section 621 of the composite guide groove 62; due to the guiding effect of the spiral groove, the isolation sleeve 6 rotates circumferentially while continuing to slide axially (further extending into the sealing sleeve 7); when the isolation sleeve 6 extends into the sealing sleeve 7, its end face pushes the annular plug 71 to overcome the elastic force of the elastic element and slide into the sealing sleeve 7.

[0052] As the isolation sleeve 6 slides axially and rotates circumferentially, the first perforation 81 on the drive bar 8 will align with the acid injection hole 4 on the wall of the drill rod 1; at the same time, the second perforation 61 on the isolation sleeve 6 will align with the first perforation 81; at this point, the acid injection hole 4, the first perforation 81 and the second perforation 61 are aligned, forming a complete acid channel from the outside of the drill rod 1 to the inside of the drill rod 1.

[0053] In this state, the reaming tool 3 is completely covered and protected by the isolation sleeve 6, which physically isolates it from the acid environment and prevents the acid from corroding the reaming tool 3. At the same time, the acid can be injected into the target coal seam through the acid injection hole 4, the first perforation hole 81 and the second perforation hole 61 to carry out acidizing and permeability enhancement operations. During the acid injection process, the drill rod 1 can be slowly rotated to make the acid evenly distributed on the inner wall of the borehole and improve the acidizing effect.

[0054] It should be noted that the length of the straight groove section 621 is not less than the axial stroke required for the isolation sleeve 6 to switch from the initial state to the reaming state, so as to ensure that the isolation sleeve 6 will not rotate before the reaming tool 3 is exposed.

[0055] The process of acidizing and improving permeability extraction in a high-gas, low-permeability coal seam modification and extraction system includes the following steps:

[0056] S1. Drill rod insertion: Drill rod 1 is inserted into the target coal seam borehole. At this time, the isolation protection mechanism is in the initial state, that is, the isolation sleeve 6 covers the reaming tool 3, the acid injection hole 4, the first perforation hole 81 and the second perforation hole 61 are staggered, and the acid injection channel is in a closed state.

[0057] S2. Switch to the reaming state; the secondary piston rod of the second hydraulic drive extends, driving the drive bar 8 to slide along the first drive stroke (sliding away from the sealing sleeve 7), causing the isolation sleeve 6 to retract into the annular sleeve 5 and exit the sealing sleeve 7, exposing the reaming tool 3 in the annular space 11; at the same time, the annular block 71 slides towards the opening end of the sealing sleeve 7 under the drive of the elastic element, blocking the entrance of the sealing sleeve 7 and preventing coal slag from entering; during this process, the guide block 51 slides along the straight groove section 621 of the composite guide groove 62, and the isolation sleeve 6 only makes axial linear movement and does not rotate.

[0058] S3, Mechanical cavity creation; The first hydraulic drive unit 31 drives the reaming cutter 3 to unfold and rotate the drill rod 1 to mechanically create a cavity; The reaming cutter 3 cuts the coal body in the target coal seam section to form a large-sized cavity; During the cavity creation process, the drive bar 8 covers the acid injection hole 4 to prevent coal slag from entering the acid injection channel.

[0059] S4. The tool is retracted. After the cavity is created, the first hydraulic drive 31 drives the reaming tool 3 to retract back into the storage groove 12. The second hydraulic drive reverses the drive bar 8 (i.e., the secondary piston rod retracts) so that the isolation sleeve 6 extends out of the annular sleeve 5 and covers the reaming tool 3. The isolation sleeve 6 returns to its initial state. At this time, one end of the isolation sleeve 6 slides and seals with the annular sleeve 5, and the other end extends into the sealing sleeve 7 and seals with the annular plug 71. The reaming tool 3 is completely covered and protected by the isolation sleeve 6.

[0060] S5. Switch to acid injection mode and perform acidification and permeation enhancement; retract the first-stage piston rod of the second hydraulic drive component, causing the drive bar 8 to slide along the second drive stroke; while the isolation sleeve 6 continues to slide axially, it rotates circumferentially due to the guide block 51 entering the spiral groove section 622; the isolation sleeve 6 extends into the sealing sleeve 7 and pushes the annular plug 71 to overcome the elastic force of the elastic element and slide into the sealing sleeve 7. As the isolation sleeve 6 rotates, the acid injection hole 4, the first perforation 81 and the second perforation 61 are aligned in sequence to form a complete acid channel.

[0061] Subsequently, acid (such as hydrochloric acid, hydrofluoric acid or a mixture thereof) is supplied to the acid injection hole 4. The acid enters the target coal seam section through the first perforation 81 and the second perforation 61, and reacts chemically with minerals such as carbonates and silicates in the coal, dissolving the minerals blocking the pores and clearing the microscopic seepage channels. During the acid injection process, the drill rod 1 is slowly rotated to make the acid evenly distributed on the inner wall of the borehole. The acidification time is determined according to the mineral composition of the coal seam and the acid formula. During the acidification process, the reaming tool 3 is completely covered by the isolation sleeve 6, which physically isolates it from the acid environment and prevents it from being corroded by the acid.

[0062] S6. Gas extraction; After acidification is completed, residual acid is discharged through the inner cavity of drill pipe 1 (which can be recycled or neutralized before discharge); After the residual acid is discharged, the inner cavity of drill pipe 1 is connected to the gas extraction structure, and negative pressure extraction is started; Due to the mechanical cavity creation forming a large-sized macroscopic pressure relief space, acidification and permeability enhancement have cleared the microscopic seepage channels, improved the permeability of the coal seam, and gas can be smoothly extracted.

[0063] After the extraction meets the standard, the second hydraulic drive unit reverses the drive bar 8 to reset the isolation protection mechanism to its initial state. Then, the drill rod 1 is withdrawn from the borehole to complete the "one-pass drilling" composite permeability enhancement extraction operation for a single borehole.

[0064] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-gas, low-permeability coal seam modification and permeability enhancement extraction system, comprising a drill pipe (1), characterized in that, The outer wall of the drill pipe (1) is provided with a recessed annular space (11), and the annular space (11) is provided with: The mechanical hole-reaming mechanism includes a plurality of storage slots (12) circumferentially opened at the bottom of the annular space (11), and a hole-reaming cutter (3) rotatably disposed in each of the storage slots (12). One end of the hole-reaming cutter (3) is rotatably connected to one end of the storage slot (12), and a first hydraulic drive component (31) is hinged between the middle part of the hole-reaming cutter (3) and the other end of the storage slot (12). Multiple acid injection holes (4) are respectively opened on the wall surface of the drill rod (1) between two adjacent storage slots (12); The isolation and protection mechanism includes an annular sleeve (5) fixedly disposed at one end of the annular space (11), an isolation sleeve (6) slidably disposed within the annular sleeve (5), a sealing sleeve (7) fixedly disposed at the other end of the annular space (11), and a drive bar (8) slidably disposed between two adjacent storage slots (12). The drive bar (8) is axially fixedly connected to the isolation sleeve (6) and can rotate relative to it in the circumferential direction. A second hydraulic drive component is connected between the drive bar (8) and the drill rod (1). The drive bar (8) has a plurality of first through holes (81), and the isolation sleeve (6) has a plurality of second through holes (61).

2. The high-gas, low-permeability coal seam modification and permeability enhancement extraction system according to claim 1, characterized in that, The inner wall of the isolation sleeve (6) has multiple composite guide grooves (62) circumferentially formed. The bottom of the annular sleeve (5) is fixedly provided with multiple guide blocks (51) that slide in cooperation with the composite guide grooves (62). The composite guide groove (62) includes a straight groove section (621) extending axially and a spiral groove section (622) communicating with the straight groove section (621). When the guide block (51) slides along the straight groove section (621), the isolation sleeve (6) only moves axially. When the guide block (51) slides along the spiral groove section (622), the isolation sleeve (6) rotates circumferentially while moving axially.

3. The high-gas, low-permeability coal seam modification and permeability enhancement extraction system according to claim 2, characterized in that, When the drive bar (8) slides, it drives the isolation sleeve (6) to slide axially between the annular sleeve (5) and the sealing sleeve (7), so that the isolation protection mechanism switches between the initial state, the hole expansion state and the acid injection state.

4. The high-gas, low-permeability coal seam modification and permeability enhancement extraction system according to claim 2, characterized in that, An annular plug (71) is slidably disposed inside the sealing sleeve (7). An elastic element is disposed between the annular plug (71) and the sealing sleeve (7). When the isolation sleeve (6) exits the sealing sleeve (7), the annular plug (71) slides out of the sealing sleeve (7) under the drive of the elastic element and blocks the entrance of the sealing sleeve (7).

5. The high-gas, low-permeability coal seam modification and permeability enhancement extraction system according to claim 2, characterized in that, The drive bar (8) has a first drive stroke and a second drive stroke. In the first drive stroke, the guide block (51) slides in the straight groove section (621), and in the second drive stroke, the guide block (51) slides in the spiral groove section (622).

6. The high-gas, low-permeability coal seam modification and permeability enhancement extraction system according to claim 1, characterized in that, The outer walls at both ends of the isolation sleeve (6) are respectively provided with sealing rings, which are used to form a sliding seal between the isolation sleeve (6) and the annular sleeve (5) and between the isolation sleeve (6) and the sealing sleeve (7).

7. The high-gas, low-permeability coal seam modification and permeability enhancement extraction system according to claim 1, characterized in that, It also includes an acid supply system, a hydraulic control system and a gas extraction structure. The acid supply system is connected to the acid injection hole (4), the hydraulic control system is connected to the first hydraulic drive (31) and the second hydraulic drive, and the gas extraction structure is connected to the inner cavity of the drill rod (1).

8. A high-gas, low-permeability coal seam modification and permeability enhancement extraction process, which employs the high-gas, low-permeability coal seam modification and permeability enhancement extraction system as described in claim 4, characterized in that... Includes the following steps: S1. The drill rod (1) is sent into the target coal seam borehole. At this time, the isolation sleeve (6) is in the initial state of covering the hole-reaming tool (3). S2. The second hydraulic drive unit drives the drive bar (8) to slide, causing the isolation sleeve (6) to retract into the annular sleeve (5) and exit the sealing sleeve (7), so that the hole-reaming tool (3) is exposed in the annular space (11). At the same time, the annular block (71) slides towards the opening end of the sealing sleeve (7) under the drive of the elastic element, blocking the entrance of the sealing sleeve (7). S3. Drive the reaming tool (3) to unfold by the first hydraulic drive (31) and rotate the drill rod (1) to create a mechanical cavity; S4. After the cavity is created, the reaming tool (3) is retracted, and the driving bar (8) is driven in reverse by the second hydraulic drive component, so that the isolation sleeve (6) extends out of the annular sleeve (5) and covers the reaming tool (3), and the isolation sleeve (6) returns to its initial state. S5. The second hydraulic drive unit continues to drive the drive bar (8) to slide, the isolation sleeve (6) slides into the sealing sleeve (7) and pushes the annular block (71) to overcome the elastic force of the elastic element and slide into the sealing sleeve (7). At the same time, the guide block (51) enters the spiral groove section (622) to make the isolation sleeve (6) rotate circumferentially until the acid injection hole (4), the first perforation (81) and the second perforation (61) are aligned in sequence, and acid is supplied to the acid injection hole (4) for acidification and permeation operation. S6. After acidification is completed, the residual acid is discharged and gas is extracted through the inner cavity of the drill pipe (1).

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