A coal seam permeability enhancement device and method for improving gas drainage efficiency

Abstract

The present invention discloses a coal seam permeability enhancement device and method for improving gas drainage efficiency. The liquid carbon dioxide phase change fracturing mechanism of the present invention includes multiple sections of phase change fracturing pipe components. Adjacent two sections of phase change fracturing pipe components are coaxially connected, and the constant pressure shear slices of each section of phase change fracturing pipe component are exactly arranged opposite to the rotary cutting grooves. The setting of the rotary cutting grooves can effectively improve the effect of instantaneously releasing high-pressure and high-speed supercritical carbon dioxide gas to impact the inside of the coal seam, and ensure the contact area of the gas impacting the coal seam instantaneously, improve the impact permeability enhancement ability, and ensure the effect and reliability of coal seam fracturing. The present invention can automatically adjust the distance between each section of phase change fracturing pipe components according to the distance between the drill holes and the cutting grooves, with a simple, convenient and highly controllable structure.

Description

Technical Field

[0001] The present invention specifically relates to a coal seam permeability enhancement device and method for improving the gas drainage efficiency, and pertains to the related field of gas extraction and permeability enhancement. Background Art

[0002] During the coal mining process, as the mining depth of the coal seam increases, the permeability of the coal seam decreases accordingly, which severely restricts the gas extraction rate and extraction effect of the coal seam. In this regard, it is necessary to drill holes into the coal seam and the gas accumulation area, connect the drilled holes to a dedicated pipeline, and use extraction equipment to extract the gas in the coal seam and the goaf to the ground for utilization; or discharge it into the main return air current. However, if the permeability of the coal seam reaches a certain level with the increase of the coal seam depth, it is difficult to ensure the extraction efficiency only by extraction after drilling, and it is very difficult to achieve the purpose of effectively extracting the gas in the coal seam. In this regard, it is necessary to adopt permeability enhancement technology and equipment to perform permeability enhancement treatment on the coal seam. Currently, the main permeability enhancement methods include high-pressure water fracturing technology, blasting technology, and carbon dioxide phase change fracturing technology, etc. The size of the equipment required in the high-pressure water fracturing technology is extremely large, and the limitation of the fracturing equipment makes it difficult to achieve effective underground operation. The blasting technology has high efficiency, but has high requirements for the blasting technology and is prone to accidents and other problems. The carbon dioxide phase change fracturing technology is not only efficient but also easy to control. Therefore, this technology is widely used. However, the current technology only relies on extending liquid carbon dioxide into the drilled hole, and it is difficult for the carbon dioxide to maximize the fracturing effect of the instantaneous volume increase during phase change, which affects the fracturing ability. Summary of the Invention

[0003] Therefore, in order to solve the above deficiencies, the present invention provides a coal seam permeability enhancement device and method for improving the gas drainage efficiency herein.

[0004] The present invention is implemented as follows. A coal seam permeability enhancement device for improving the gas drainage efficiency is constructed, which includes a drilling and high-pressure jetting and rotary cutting mechanism and a liquid carbon dioxide phase change fracturing mechanism. Among them, the drilling and high-pressure jetting and rotary cutting mechanism includes a drilling mechanism and a rotary cutting mechanism arranged coaxially. The drilling mechanism is used to drill holes in the coal seam, and the rotary cutting mechanism rotarily cuts out a plurality of rotary cutting grooves at intervals along the depth direction of the drilled hole. It is characterized in that the liquid carbon dioxide phase change fracturing mechanism includes multiple sections of phase change fracturing pipe components, and adjacent two sections of phase change fracturing pipe components are coaxially connected, and the constant-pressure shear slices of each section of phase change fracturing pipe component are exactly arranged opposite to the rotary cutting grooves. The drilling and high-pressure jetting and rotary cutting mechanism is controlled by a controller so as to control the operation of the rotary cutting mechanism according to the depth of the drilled hole, and make the distance between adjacent two rotary cutting grooves equal to the distance between the constant-pressure shear slices of adjacent two sections of phase change fracturing pipe components.

[0005] Further, preferably, the drilling mechanism includes a drill pipe, a drill pipe mounting seat, a rotary drive mechanism, and a drill bit assembly. Among them, the drill pipe is rotatably sleeved and installed on the drill pipe mounting seat, the drill pipe mounting seat is fixedly supported and arranged at the position to be drilled, the drill pipe is driven to rotate by the rotary drive mechanism, and the drill bit assembly is further provided at the front end of the drill pipe. The front drill bit of the drill bit assembly can rotate relative to the drill pipe.

[0006] Further, preferably, the drill bit assembly includes a drill bit, a front-end waterproof motor, and a guiding cutter head. The front-end waterproof motor is fixedly provided at the front end of the drill pipe. The drill bit is fixedly installed at the output end of the front-end waterproof motor. The overall shape of the drill bit is a conical structure, and spiral blades are provided around the drill bit. A guiding cutter head coaxial with the drill pipe is provided at the front end of the drill bit. The guiding cutter head is a cylindrical structure, and the diameter of the guiding cutter head is 8-20 mm, and the length is 20-80 mm. The rotation speed of the front-end waterproof motor is at least three times that of the drill pipe, and the rotation directions of the two are the same.

[0007] Further, preferably, the outer diameter at the maximum outer diameter of the drill bit is greater than the outer diameter at the maximum outer diameter of the front-end waterproof motor, and the outer diameter at the maximum outer diameter of the drill bit is greater than the outer diameter at the maximum outer diameter of the rotary cutting mechanism. During drilling, the rotary cutting mechanism can spray water into the drill hole. The drill pipe is a hollow structure to provide a space for accommodating and arranging the power cord of the front-end waterproof motor through the central hole of the drill pipe.

[0008] Further, preferably, the rotary cutting mechanism includes a pressure stabilizing valve, a connecting seat, an inner pipe, an outer pipe, a rotary cutting spray disc, an inner high-pressure spray head group, and an outer high-pressure spray head group. Among them, the pressure stabilizing valve is fixedly provided on the connecting seat. The drill pipe includes an inner pipe and an outer pipe arranged coaxially. The pipe hole of the inner pipe is configured as the central hole of the drill pipe. The cavity between the inner pipe and the outer pipe is configured as a high-pressure water chamber. The high-pressure water chamber is communicated with the rotary cutting spray disc, and the rotary cutting spray disc and the connecting seat are fixedly connected by a reinforcing connecting rib. The connecting seat is coaxially fixedly installed on the drill pipe. The inner high-pressure spray head group and the outer high-pressure spray head group are circumferentially arranged on the rotary cutting spray disc. Both the inner high-pressure spray head group and the outer high-pressure spray head group include a plurality of high-pressure spray heads arranged in a circumferential array. The angle between the spraying direction of the high-pressure spray heads of the inner high-pressure spray head group and the central axis of the drill pipe is the same as the angle between the spraying direction of the high-pressure spray heads of the outer high-pressure spray head group and the central axis of the drill pipe. The spraying direction of the high-pressure spray heads of the inner high-pressure spray head group faces the inner side direction of the drill hole, and the spraying direction of the high-pressure spray heads of the outer high-pressure spray head group faces the outer side direction of the drill hole.

[0009] Further, preferably, the end of the drill pipe is also connected to the high-pressure pump set by a high-pressure resistant rotary sealing ring, and the high-pressure pump set is connected to the water tank. During drilling, the high-pressure pump set provides high-pressure water to the high-pressure nozzle at a first pressure, and during rotary cutting, the high-pressure pump set provides high-pressure water to the high-pressure nozzle at a second pressure, and the first pressure is less than one-third of the second pressure.

[0010] Further, preferably, each phase change fracturing pipe member includes a storage pipe, a control seat body, a heating temperature control component, a constant pressure shear slice, an auxiliary safety cap, a connection positioning chuck, and a connection positioning hole. The storage pipe is coaxially and fixedly arranged at the front end of the control seat body. Liquid carbon dioxide is stored in the storage pipe. A heat conducting rod is also arranged at the center inside the storage pipe. The auxiliary safety cap is coaxially and fixedly arranged at the position corresponding to the constant pressure shear slice on the heat conducting rod. The auxiliary safety cap is a cylindrical structure with a blind hole, and the inner cavity of the auxiliary safety cap communicates with the inner cavity of the storage pipe and is filled with liquid carbon dioxide. The auxiliary safety cap is a thin metal sheet structure, and bursting orifice openings are arranged in a circumferential array on the storage pipe. The constant pressure shear slice is fixedly arranged on the bursting orifice openings. The end of the heat conducting rod is connected to the heating temperature control component inside the control seat body. The connection positioning hole is arranged at the end of the control seat body, and the connection positioning chuck is arranged at the front end of the storage pipe.

[0011] Further, preferably, adjacent two phase change fracturing pipe members are coaxially butted together directly or indirectly through a connecting column by using the connection positioning chuck and the connection positioning hole, and a spring locking chuck is also arranged in the connection positioning hole.

[0012] Further, preferably, a control circuit board or a control coil connected to the heating temperature control component is arranged inside the control seat body, and the wires of the control circuit board or the control coil can extend out from the control seat to uniformly control each phase change fracturing pipe member.

[0013] Further, the present invention also provides a coal seam permeability enhancement method for improving the gas drainage efficiency, which is characterized in that it uses the coal seam permeability enhancement device for improving the gas drainage efficiency of the present invention, and it includes the following steps:

[0014] (1)Drill high-pressure fracturing holes and cut rotary slots: Connect and install the drill hole with the high-pressure jet rotary cutting mechanism, and make the drill pipe connected to the water tank through the high-pressure pump set. When drilling, start the rotary drive mechanism to drive the drill pipe to rotate, and at the same time start the front-end waterproof motor to drive the drill bit and the guiding cutter head to rotate simultaneously. The guiding cutter head plays a guiding role during the drilling process to avoid deviation. At the same time, the high-pressure pump set provides high-pressure water for the high-pressure nozzle at the first pressure, which is convenient for discharging the drilled debris and cooling the drill bit. When the controller controls the drill bit to drill to the set depth, the drill bit stops advancing axially, closes the front-end waterproof motor, and starts the high-pressure pump set to provide high-pressure water for the high-pressure nozzle at the second pressure. Utilize the high-pressure water jets ejected by the high-pressure nozzles of the inner high-pressure nozzle group and the outer high-pressure nozzle group on the rotary cutting injection disc to perform slot cutting operations on the drill hole, thereby cutting out rotary slots; According to this method, successively cut out multiple rotary slots at intervals along the depth direction of the drill hole;

[0015] (2)Remove the drill hole and the high-pressure jet rotary cutting mechanism. When removing, the high-pressure pump set provides high-pressure water for the high-pressure nozzle at the first pressure to clean the debris in the drill hole and the rotary slots;

[0016] (3)Liquid carbon dioxide phase change fracturing: Determine the distance between adjacent two-phase change fracturing pipe components according to the drill hole depth and the distance between two adjacent rotary slots. According to this distance, make the adjacent two-phase change fracturing pipe components coaxially docked together directly or indirectly by using connecting columns until the required length of the liquid carbon dioxide phase change fracturing mechanism matching the drill hole is connected. Then insert the liquid carbon dioxide phase change fracturing mechanism into the drill hole, and ensure that the fixed-pressure shear slices of each phase change fracturing pipe component are exactly facing the rotary slots. Then seal the end of the drill hole and the phase change fracturing pipe component, and control the heating temperature control component to generate heat. Through the instantaneous heating of the heating temperature control component, make the liquid carbon dioxide in the storage pipe instantaneously boost pressure and vaporize, break the fixed shear slice, and thus instantaneously release high-pressure and high-speed supercritical carbon dioxide gas to achieve the purpose of fracturing and enhancing the permeability of the coal seam.

[0017] The present invention has the following advantages: A coal seam permeability enhancement device and method for improving gas drainage efficiency provided by the present invention have the following advantages compared with the same type of devices:

[0018] The present invention relates to a coal seam permeability enhancement device and method for improving gas drainage efficiency. The liquid carbon dioxide phase change fracturing mechanism of the present invention includes multiple sections of phase change fracturing pipe components, which are coaxially connected between adjacent two sections of phase change fracturing pipe components. And the constant pressure shear slice of each section of phase change fracturing pipe component is exactly set facing the rotary cutting groove. The setting of the rotary cutting groove can effectively improve the effect of instantaneously releasing high-pressure and high-speed supercritical carbon dioxide gas impacting the inside of the coal seam, and ensure the contact area of the gas instantaneously impacting the coal seam, improve the impact permeability enhancement ability, and ensure the effect and reliability of coal seam fracturing. The present invention can automatically adjust the distance between each section of phase change fracturing pipe components according to the distance between the drill holes and the cutting grooves, with a simple, convenient and strong controllability structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of the drill hole and high-pressure jet rotary cutting mechanism of the present invention during drilling and rotary cutting;

[0020] Figure 2 is a schematic installation structure diagram of the liquid carbon dioxide phase change fracturing mechanism of the present invention;

[0021] Figure 3 is a partially enlarged front view structural diagram of the drill hole mechanism and rotary cutting mechanism of the present invention;

[0022] Figure 4 is a three-dimensional structural diagram of the drill hole mechanism and rotary cutting mechanism of the present invention;

[0023] Figure 5 is a schematic structural diagram of each section of the phase change fracturing pipe component of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following will combine the attached Figures 1-5 The present invention will be described in detail. The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0025] The present invention provides an equipment for enhancing coal seam permeability to improve the gas drainage efficiency through improvement. The equipment includes a drilling and high-pressure jet rotary cutting mechanism and a liquid carbon dioxide phase change fracturing mechanism. Among them, the drilling and high-pressure jet rotary cutting mechanism includes a drilling mechanism 7 and a rotary cutting mechanism 6 arranged coaxially. The drilling mechanism 7 is used for drilling the coal seam, and the rotary cutting mechanism 6 rotates and cuts out a plurality of rotary cutting grooves 8 at intervals along the depth direction of the drill hole. It is characterized in that the liquid carbon dioxide phase change fracturing mechanism includes multiple sections of phase change fracturing pipe members 11. The adjacent two sections of phase change fracturing pipe members 11 are coaxially connected, and the constant-pressure shear slices 10 of each section of phase change fracturing pipe member are exactly arranged opposite to the rotary cutting grooves 8. The drilling and high-pressure jet rotary cutting mechanism is controlled by a controller to control the operation of the rotary cutting mechanism according to the depth of the drill hole, and make the distance between adjacent two rotary cutting grooves equal to the distance between the constant-pressure shear slices of adjacent two sections of phase change fracturing pipe members.

[0026] In the present invention, the drilling mechanism 7 includes a drill pipe 3, a drill pipe mounting seat 9, a rotary drive mechanism (not shown in the figure, which can be driven by a motor and a transmission mechanism such as gears or belts), and a drill bit assembly. Among them, the drill pipe 3 is rotatably sleeved and installed on the drill pipe mounting seat 9. The drill pipe mounting seat 9 is fixedly supported and arranged at the position to be drilled. The drill pipe is driven to rotate by the rotary drive mechanism. The front end of the drill pipe is also provided with the drill bit assembly, and the front drill bit of the drill bit assembly can rotate relative to the drill pipe.

[0027] Among them, the drill bit assembly includes a drill bit, a front-end waterproof motor 12, and a guiding cutter head 20. The front end of the drill pipe 3 is fixedly provided with the front-end waterproof motor 12. The drill bit is fixedly installed at the output end of the front-end waterproof motor. The overall shape of the drill bit is a conical structure, and spiral edges are arranged around the drill bit. The front end of the drill bit is provided with a guiding cutter head coaxial with the drill pipe. The guiding cutter head 20 is a cylindrical structure, and the diameter of the guiding cutter head is 8-20 mm, and the length is 20-80 mm. The rotation speed of the front-end waterproof motor 12 is at least three times that of the drill pipe, and their rotation directions are the same.

[0028] The outer diameter at the maximum outer diameter of the drill bit is greater than the outer diameter at the maximum outer diameter of the front-end waterproof motor, and the outer diameter at the maximum outer diameter of the drill bit is greater than the outer diameter at the maximum outer diameter of the rotary cutting mechanism. During drilling, the rotary cutting mechanism can spray water into the drill hole. The drill pipe is a hollow structure to provide an accommodation and arrangement space for the power supply line of the front-end waterproof motor through the central hole of the drill pipe.

[0029] The rotary cutting mechanism includes a pressure stabilizing valve 13, a connecting seat 28, an inner pipe 16, an outer pipe 14, a rotary cutting injection disc 17, an inner high-pressure nozzle group 19 and an outer high-pressure nozzle group 18. Among them, the pressure stabilizing valve 13 is fixedly arranged on the connecting seat 28. The drill pipe includes an inner pipe 16 and an outer pipe 14 arranged coaxially. The pipe hole of the inner pipe 16 is configured as the central hole of the drill pipe, and the cavity between the inner pipe and the outer pipe is configured as a high-pressure water chamber 15. The high-pressure water chamber 15 is communicated with the rotary cutting injection disc 17, and the rotary cutting injection disc 17 is fixedly connected to the connecting seat 28 by a reinforcing connecting rib. The connecting seat is coaxially and fixedly installed on the drill pipe. The inner high-pressure nozzle group 19 and the outer high-pressure nozzle group 18 are arranged in a circumferential array on the rotary cutting injection disc. Both the inner high-pressure nozzle group and the outer high-pressure nozzle group include a plurality of high-pressure nozzles arranged in a circumferential array. The angle between the injection direction of the high-pressure nozzles in the inner high-pressure nozzle group and the central axis of the drill pipe is the same as the angle between the injection direction of the high-pressure nozzles in the outer high-pressure nozzle group and the central axis of the drill pipe. And the injection direction of the high-pressure nozzles in the inner high-pressure nozzle group faces the inner side direction of the drill hole, and the injection direction of the high-pressure nozzles in the outer high-pressure nozzle group faces the outer side direction of the drill hole.

[0030] The end of the drill pipe is also connected to a high-pressure pump group 2 by a high-pressure resistant rotary sealing ring. The high-pressure pump group 2 is connected to a water tank 1. During drilling, the high-pressure pump group provides high-pressure water for the high-pressure nozzles at a first pressure. During rotary cutting, the high-pressure pump group provides high-pressure water for the high-pressure nozzles at a second pressure, and the first pressure is less than one-third of the second pressure.

[0031] Each phase change fracturing pipe component includes a storage pipe 21, a control seat body 31, a heating temperature control component 22, a constant pressure shear slice 10, an auxiliary safety cap 27, a connecting positioning chuck 29 and a connecting positioning hole 24. The storage pipe 21 is coaxially and fixedly arranged at the front end of the control seat body 31. Liquid carbon dioxide is stored in the storage pipe 21. A heat conducting rod 30 is also arranged at the center of the inside of the storage pipe 21. The auxiliary safety cap 27 is coaxially and fixedly arranged at the position corresponding to the constant pressure shear slice 10 on the heat conducting rod 30. The auxiliary safety cap 27 is a cylindrical structure with a blind hole, and the inner cavity of the auxiliary safety cap 27 is communicated with the inner cavity of the storage pipe and is filled with liquid carbon dioxide. The auxiliary safety cap is a thin metal sheet structure, and bursting orifice openings are arranged in a circumferential array on the storage pipe. The constant pressure shear slice 10 is fixedly arranged on the bursting orifice openings. The end of the heat conducting rod 30 is connected to the heating temperature control component in the control seat body. The connecting positioning hole 24 is arranged at the end of the control seat body 31, and the connecting positioning chuck 29 is arranged at the front end of the storage pipe.

[0032] The adjacent two-phase change fracturing pipe components are coaxially butted together directly or indirectly through a connecting column by using the connecting positioning chuck and the connecting positioning hole. A spring locking chuck 23 is also arranged in the connecting positioning hole.

[0033] A control circuit board or a control coil 25 connected to the heating temperature control component is arranged in the control seat body. The wires of the control circuit board or the control coil can extend out from the control seat so as to uniformly control each section of the phase change fracturing pipe component.

[0034] The invention also provides a coal seam permeability enhancement method for improving the gas drainage efficiency, which is characterized in that the coal seam permeability enhancement equipment for improving the gas drainage efficiency described in the invention is adopted, and the method comprises the following steps:

[0035] (1) Drilling a high-pressure fracturing hole and opening a rotary cutting groove: Connect and install the drilling hole with the high-pressure jet rotary cutting mechanism, and make the drill pipe connected to the water tank through the high-pressure pump group. When drilling, start the rotary drive mechanism to drive the drill pipe to rotate, and at the same time start the front waterproof motor to drive the drill bit and the guide bit to rotate simultaneously. The guide bit plays a guiding role during the drilling process to avoid deviation. At the same time, the high-pressure pump group provides high-pressure water for the high-pressure nozzle at the first pressure, which is convenient for discharging the drilled debris and cooling the drill bit. When the controller controls the drill bit to drill to the set depth, the drill bit stops advancing axially, closes the front waterproof motor, and starts the high-pressure pump group to provide high-pressure water for the high-pressure nozzle at the second pressure. Utilize the high-pressure water jets sprayed by the high-pressure nozzles of the inner high-pressure nozzle group and the outer high-pressure nozzle group on the rotary cutting jet disc to perform the grooving operation on the drilling hole, so as to open the rotary cutting groove; According to this method, a plurality of rotary cutting grooves are successively cut at intervals along the depth direction of the drilling hole;

[0036] (2) Remove the drilling hole and the high-pressure jet rotary cutting mechanism. When removing, the high-pressure pump group provides high-pressure water for the high-pressure nozzle at the first pressure so as to clean the debris in the drilling hole and the rotary cutting groove.

[0037] (3) Liquid carbon dioxide phase change fracturing: Determine the distance between adjacent two-phase change fracturing pipe components according to the drilling depth and the distance between two adjacent rotary cutting grooves. According to this distance, the adjacent two-phase change fracturing pipe components are coaxially butted together directly or indirectly through a connecting column until the required length of the liquid carbon dioxide phase change fracturing mechanism matching the drilling hole is connected. Then, insert the liquid carbon dioxide phase change fracturing mechanism into the drilling hole, and ensure that the constant-pressure shear slices of each section of the phase change fracturing pipe component are exactly opposite to the rotary cutting grooves. Then, seal the end of the drilling hole and the phase change fracturing pipe component. Control the heating temperature control component to generate heat. Through the instantaneous heating of the heating temperature control component, the liquid carbon dioxide in the storage pipe is instantaneously pressurized and vaporized, destroying the fixed shear slices, so as to instantaneously release high-pressure and high-speed supercritical carbon dioxide gas to achieve the purpose of fracturing and enhancing the permeability of the coal seam.

[0038] The coal seam permeability enhancement equipment and method for improving gas drainage efficiency according to the present invention. The liquid carbon dioxide phase change fracturing mechanism of the present invention includes multiple sections of phase change fracturing pipe components, which are coaxially connected between adjacent two sections of phase change fracturing pipe components, and the constant pressure shear slices of each section of phase change fracturing pipe component are exactly arranged opposite to the rotary cutting grooves. The setting of the rotary cutting grooves can effectively improve the effect of instantaneously releasing high-pressure and high-speed supercritical carbon dioxide gas to impact the inside of the coal seam, and ensure the contact area of the gas impacting the coal seam instantaneously, improve the impact permeability enhancement ability, and ensure the effect and reliability of coal seam fracturing. The present invention can automatically adjust the distance between each section of phase change fracturing pipe components according to the spacing of the drill holes and the cutting grooves, with a simple, convenient and strong controllability structure.

[0039] The above shows and describes the basic principles, main features and advantages of the present invention. Moreover, the standard parts used in the present invention can all be purchased from the market, the special-shaped parts can be customized according to the records in the specification and the drawings, the specific connection methods of each part all adopt the mature conventional means such as bolts, rivets and welding in the prior art, the machines, parts and equipment all adopt the conventional models in the prior art, and the circuit connection adopts the conventional connection method in the prior art, which will not be elaborated herein.

[0040] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A coal seam permeability enhancement device for improving gas drainage efficiency, comprising a drilling hole, a high-pressure jet rotary cutting mechanism, and a liquid carbon dioxide phase change fracturing mechanism. The drilling hole and the high-pressure jet rotary cutting mechanism include a drilling mechanism and a rotary cutting mechanism arranged coaxially. The drilling mechanism is used for drilling the coal seam, and the rotary cutting mechanism is used for cutting a plurality of rotary cutting grooves at intervals along the depth direction of the drilling hole in the drilling hole. It is characterized in that, The liquid carbon dioxide phase change fracturing mechanism includes multiple sections of phase change fracturing pipe components, which are coaxially connected between adjacent two sections of phase change fracturing pipe components. The constant-pressure shear slices of each section of phase change fracturing pipe component are exactly arranged opposite to the rotary cutting grooves. The drilling hole and the high-pressure jet rotary cutting mechanism are controlled by a controller to control the operation of the rotary cutting mechanism according to the depth of the drilling hole, and make the distance between two adjacent rotary cutting grooves equal to the distance between the constant-pressure shear slices of two adjacent sections of phase change fracturing pipe components; The drilling mechanism includes a drill pipe, a drill pipe mounting seat, a rotary drive mechanism, and a drill bit assembly. The drill pipe is rotatably sleeved and installed on the drill pipe mounting seat. The drill pipe mounting seat is fixedly supported and arranged at the position to be drilled. The drill pipe is driven to rotate by the rotary drive mechanism. A drill bit assembly is also provided at the front end of the drill pipe. The front drill bit of the drill bit assembly can rotate relative to the drill pipe; The drill bit assembly includes a drill bit, a front-end waterproof motor, and a guide cutter head. The front-end waterproof motor is fixedly provided at the front end of the drill pipe. The drill bit is fixedly installed at the output end of the front-end waterproof motor. The overall drill bit is a conical structure. Spiral edges are provided around the drill bit. A guide cutter head coaxial with the drill pipe is provided at the front end of the drill bit; The rotary cutting mechanism includes a pressure stabilizing valve, a connecting seat, an inner pipe, an outer pipe, a rotary cutting injection disc, an inner high-pressure nozzle group, and an outer high-pressure nozzle group. The pressure stabilizing valve is fixedly provided on the connecting seat. The drill pipe includes an inner pipe and an outer pipe arranged coaxially. The pipe hole of the inner pipe is configured as the central hole of the drill pipe. The cavity between the inner pipe and the outer pipe is a high-pressure water cavity. The high-pressure water cavity is communicated with the rotary cutting injection disc. The rotary cutting injection disc and the connecting seat are fixedly connected by a reinforcing connecting rib. The connecting seat is coaxially fixedly installed on the drill pipe. The inner high-pressure nozzle group and the outer high-pressure nozzle group are circumferentially arranged on the rotary cutting injection disc. Both the inner high-pressure nozzle group and the outer high-pressure nozzle group include multiple high-pressure nozzles arranged circumferentially. The angle between the injection direction of the high-pressure nozzles of the inner high-pressure nozzle group and the central axis of the drill pipe is the same as the angle between the injection direction of the high-pressure nozzles of the outer high-pressure nozzle group and the central axis of the drill pipe. The injection direction of the high-pressure nozzles of the inner high-pressure nozzle group faces the inner side direction of the drilling hole, and the injection direction of the high-pressure nozzles of the outer high-pressure nozzle group faces the outer side direction of the drilling hole.

2. The coal seam permeability enhancement device for improving the gas drainage efficiency according to claim 1, wherein: The outer diameter at the maximum outer diameter of the drill bit is greater than the outer diameter at the maximum outer diameter of the front-end waterproof motor, and the outer diameter at the maximum outer diameter of the drill bit is greater than the outer diameter at the maximum outer diameter of the rotary cutting mechanism. And during drilling, the rotary cutting mechanism can inject water into the drilling hole. The drill pipe is a hollow structure to provide an accommodation and arrangement space for the power supply line of the front-end waterproof motor through the central hole of the drill pipe.

3. The coal seam permeability enhancement device for improving the gas drainage efficiency according to claim 1, characterized in that: The end of the drill pipe is also connected to a high-pressure pump group by a high-pressure resistant rotary seal ring. The high-pressure pump group is connected to a water tank. During drilling, the high-pressure pump group provides high-pressure water for the high-pressure nozzles at a first pressure. During rotary cutting, the high-pressure pump group provides high-pressure water for the high-pressure nozzles at a second pressure, and the first pressure is less than one-third of the second pressure.

4. A coal seam permeability enhancement device for improving the gas drainage efficiency according to claim 1, characterized in that: Each phase change fracturing pipe component includes a storage pipe, a control seat body, a heating temperature control component, a constant pressure shear slice, an auxiliary safety cap, a connection positioning chuck and a connection positioning hole. The front end of the control seat body is coaxially and fixedly provided with a storage pipe, in which liquid carbon dioxide is stored. A heat conducting rod is also arranged at the center inside the storage pipe. An auxiliary safety cap is coaxially and fixedly arranged on the heat conducting rod corresponding to the position of the constant pressure shear slice. The auxiliary safety cap is a cylindrical structure with a blind hole, and the inner cavity of the auxiliary safety cap communicates with the inner cavity of the storage pipe and is filled with liquid carbon dioxide. The auxiliary safety cap is a thin metal sheet structure, and bursting orifice openings are arranged in a circumferential array on the storage pipe. A constant pressure shear slice is fixedly arranged on the bursting orifice openings. The end of the heat conducting rod is connected with the heating temperature control component in the control seat body. A connection positioning hole is arranged at the end of the control seat body, and a connection positioning chuck is arranged at the front end of the storage pipe.

5. The coal seam permeability enhancement device for improving gas drainage efficiency according to claim 4, characterized in that: Two adjacent phase change fracturing pipe components are coaxially butted together directly or indirectly through a connecting column by using the connection positioning chuck and the connection positioning hole. A spring locking chuck is also arranged in the connection positioning hole.

6. The coal seam permeability enhancement device for improving the gas drainage efficiency according to claim 5, characterized in that: A control circuit board or a control coil connected with the heating temperature control component is arranged in the control seat body. The wires of the control circuit board or the control coil can extend out from the control seat so as to uniformly control each phase change fracturing pipe component.

7. The coal seam permeability enhancement device for improving gas drainage efficiency according to claim 1, characterized in that: The guiding cutter head is a cylindrical structure. The diameter of the guiding cutter head is 8 - 20 mm, and the length is 20 - 80 mm. The rotational speed of the front-end waterproof motor is at least three times that of the drill pipe, and their rotational directions are the same.

8. A method for enhancing the permeability of coal seams to improve the efficiency of gas drainage, characterized in that, It adopts a coal seam permeability enhancement device for improving the gas drainage efficiency described in any one of claims 1 - 7, and comprises the following steps: (1) Drilling a fracturing hole under high pressure and opening a rotary cutting groove: Connect and install the drilling hole with the high-pressure jet rotary cutting mechanism, and make the drill pipe connect with the water tank through the high-pressure pump set. When drilling, start the rotary drive mechanism to drive the drill pipe to rotate, and at the same time start the front-end waterproof motor to drive the drill bit and the guiding cutter head to rotate simultaneously. The guiding cutter head plays a guiding role during the drilling process to avoid deviation. Meanwhile, the high-pressure pump set provides high-pressure water for the high-pressure nozzle at a first pressure, which is convenient for discharging the drilled debris and cooling the drill bit. When the controller controls the drill bit to drill to the set depth, the drill bit stops advancing axially, turn off the front-end waterproof motor, and start the high-pressure pump set to provide high-pressure water for the high-pressure nozzle at a second pressure. Utilize the high-pressure water jets sprayed by the high-pressure nozzles of the inner high-pressure nozzle group and the outer high-pressure nozzle group on the rotary cutting spray disc to perform the grooving operation on the drilling hole, thereby opening a rotary cutting groove; According to this method, a plurality of rotary cutting grooves are sequentially cut at intervals along the depth direction of the drilling hole; (2) Remove the drilling hole and the high-pressure jet rotary cutting mechanism. When removing, the high-pressure pump set provides high-pressure water for the high-pressure nozzle at a first pressure to clean the debris in the drilling hole and the rotary cutting groove; (3) Liquid carbon dioxide phase change fracturing: Determine the distance between adjacent two-phase change fracturing pipe components according to the drilling depth and the distance between two adjacent rotary cutting grooves. According to this distance, make the adjacent two-phase change fracturing pipe components coaxially docked directly or indirectly through a connecting column until the required length of the liquid carbon dioxide phase change fracturing mechanism matching the drilling hole is connected. Then, insert the liquid carbon dioxide phase change fracturing mechanism into the drilling hole, and ensure that the constant-pressure shear slices of each phase change fracturing pipe component are exactly facing the rotary cutting grooves. Then, seal the end of the drilling hole and the phase change fracturing pipe component, control the heating of the heating temperature control component, and make the liquid carbon dioxide in the storage pipe instantaneously boost pressure and gasify through the instantaneous heating of the heating temperature control component, breaking the constant-pressure shear slices, so as to instantaneously release high-pressure and high-speed supercritical carbon dioxide gas to achieve the purpose of fracturing and enhancing the permeability of the coal seam.

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