Multi-stage pulse high-frequency dynamic load fracturing method

Abstract

A multistage pulse high-frequency dynamic load fracturing method comprises the steps that a coal seam and a cover layer horizontal well are drilled out, supercritical CO2 is used for fracturing an upper cover layer of the coal seam, and fracturing cracks are expanded to a target coal seam to form a crack network; injecting high-pressure oxygen into the horizontal well of the cover layer, and enabling the high-pressure oxygen to enter the low-permeability target coal seam to form an oxygen-enriched coal seam; tripping in a bridge plug; operation gas and fuel are charged into the burning and explosion tool, the burning and explosion tool is lowered, and the packer is set; high-pressure nitrogen is used for pushing a piston to move downwards, a constant pressure valve is opened, and a gaseous combustion improver enters a combustion explosion cavity to be mixed with a liquid alkyl compound; the piston is used for pushing the trigger needle to move downwards, so that the trigger linkage rod relieves limiting of the firing pin, the firing pin rapidly strikes gunpowder, and ignition operation is completed. The liquid alkyl compound is quickly burnt and exploded, potassium permanganate in the detachable hollow pipe is decomposed to generate a large amount of oxygen, and methane-oxygen mixed gas in a gap network is ignited while secondary burning and explosion occur. The method can obviously improve the mining efficiency of the coal bed gas.

Description

Technical Field

[0001] The invention belongs to the technical field of coal and unconventional natural gas development, and specifically relates to a multi-stage pulse high-frequency dynamic load fracturing method. Background Art

[0002] Although my country has abundant reserves of unconventional natural gas, the low permeability of its reservoirs leads to low mining efficiency and difficulty. In actual operations, fracturing and permeability enhancement operations are often required to achieve continuous mining operations. At present, hydraulic fracturing technology is mainly used to enhance the permeability of reservoirs. Although hydraulic fracturing technology has accelerated the development of unconventional natural gas, this technology has many problems such as large water resource consumption, reservoir clay expansion, groundwater pollution, and difficulty in handling return fluid. In addition, conventional hydraulic fracturing has problems such as insufficient reservoir fracture degree and single crack expansion direction in shale gas development. In order to overcome the problems of conventional hydraulic fracturing, a method of in-situ methane explosion fracturing in reservoirs has been developed. Methane in-situ explosion fracturing technology is a new type of fracturing technology that uses a waterless method to fracture shale reservoirs to avoid damage to water-sensitive formations. This technology can also be used for coalbed methane development. It has the characteristics of simple operation and low cost, and provides new ideas for cost reduction, efficiency improvement and economic exploitation of unconventional oil and gas.

[0003] Conventional explosive fracturing technology uses reservoir methane as fuel, releases an oxidant on the ground and mixes it with reservoir methane at the bottom of the well to form an explosive fluid, and then uses the high pressure generated by the explosion of methane-oxidant to fracture the reservoir, forming a complex fracture network. On this basis, in order to solve the problem of the difficulty in continuous release of oxidants caused by the narrow space and great depth of deep coal seams, a new type of oxidant pre-charged mixed oxidant tool has been developed, which can pre-mix methane-oxidant in the oxidant device, and arrange fracturing tools and ignite explosive fracturing operations on the reservoir according to needs. This technology makes the explosive fracturing process more modular and convenient. However, due to the limitations of reservoir space and tool size, the oxidant cannot be continuously supplied, and the explosive fracturing operation is usually dominated by a single instantaneous explosive impact, so a multi-stage explosive tool is required to cooperate with the operation to meet the needs of high-quality fracturing. Therefore, it is urgent to further improve the pre-charged mixed explosion tool. At the same time, the fracturing coal seam needs to be transformed into an oxidative one to provide a multi-stage pulse high-frequency dynamic fracturing method for deep coal seams. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a multi-stage pulse high-frequency dynamic load fracturing method. This method can achieve efficient fracturing and crack expansion of coal seams through the construction of oxygen-rich coal seams and continuous combustion and explosion impact fracturing operations, and can significantly improve the extraction efficiency of coalbed methane. At the same time, it can make the fracturing process green and environmentally friendly, and has significant technical advantages and application prospects.

[0005] In order to achieve the above object, the present invention provides a multi-stage pulse high-frequency dynamic load fracturing method, comprising the following steps:

[0006] Step 1: Preparation;

[0007] S11: Collect geological parameters and exploration data of target coal seams, and analyze the structure and density of coal seams based on the geological parameters and exploration data; at the same time, analyze the well logging data to determine the thickness and distribution of coal seams, coal seam physical properties, coal seam gas content and water content;

[0008] S12: Based on the analysis results of well logging data, combined with the assessment of coal seam structure and density, select areas with thick coal seams, high permeability and rich gas content as well as well-laying sections. At the same time, ensure that the well-laying sections avoid areas with developed fault and fold geological structures, as well as unfavorable areas with thin coal seams and low permeability.

[0009] S13: Analyze the cap rock conditions above the coal seam to ensure that the cap rock can effectively isolate the coalbed methane; based on the cap rock condition analysis results, design the cap rock horizontal well drilling location in the area where the cap rock is stable and of moderate thickness to ensure safe drilling and long-term production of the cap rock horizontal well;

[0010] S14: Design reasonable coal seam horizontal well drilling parameters according to coal seam structure and geological conditions;

[0011] Step 2: Wellbore layout and caprock horizontal well fracturing;

[0012] S21: Drill two vertical main shafts at a set distance according to the well logging data and the coal seam distribution interval, and make the lower ends of the two vertical main shafts stop at the target coal seam and the cap layer above the target coal seam respectively, and then extend two horizontal well sections relatively from the ends of the two vertical main shafts, wherein the horizontal well section located in the cap layer is used as the cap layer horizontal well, and the horizontal well section located in the target coal seam is used as the coal seam horizontal well, and the cap layer horizontal well and the coal seam horizontal well constitute a counter well layout;

[0013] S22: Use supercritical CO2 concentrated energy fracturing technology to perform fracturing and fracture creation operations on the cap layer, and use the strong fracturing shock wave generated by supercritical CO2 under high pressure conditions to promote the generated fracturing cracks to expand toward the target coal seam to form a fracture network connecting the cap layer horizontal well and the target coal seam. After the fracture network is formed, the fracturing and fracture creation operations are stopped;

[0014] Step 3: Placement of combustion aid in caprock horizontal wells;

[0015] The combustion-aid delivery tool is connected to the end of the oil pipe, and the head end of the oil pipe is connected to the ground fracturing vehicle. The ground fracturing vehicle, the oil pipe and the combustion-aid delivery tool are used to inject high-pressure oxygen into the cap layer horizontal well. At the same time, the fracture network formed by the fracturing operation is used as a permeation channel, and the injection pressure is used to drive the high-pressure oxygen into the low-permeability target coal seam, so that the oxygen is widely distributed in the coal seam, thereby forming an oxygen-rich coal seam;

[0016] At the same time, according to the geological parameters and exploration data of the coal seam, a measuring wellbore is drilled vertically from the ground downward using coalbed methane drilling equipment, and the end of the measuring wellbore reaches the oxygen-rich coal seam. The oxygen concentration in the oxygen-rich coal seam is measured using the measuring wellbore. When the oxygen concentration reaches the appropriate combustion and explosion standard, the high-pressure oxygen injection operation of the cap layer horizontal well is stopped.

[0017] Step 4: Lower and seal the blasting tools;

[0018] S41: placing a drillable bridge plug in a horizontal well in the coal seam and setting it;

[0019] S42: Prepare the explosion tool; the explosion tool includes a delivery bin, an upper isolation block, an isolation bin, a lower isolation block, an explosion bin, an upper end plate, a lower end plate, an annular piston, an ignition device, a constant pressure valve, a one-way valve, a detachable hollow tube and a center tube; the outer contours of the delivery bin, the upper isolation block, the isolation bin, the lower isolation block and the explosion bin are all circular, and have the same outer diameter, and at the same time, they are coaxially fixedly connected in sequence from top to bottom to form an explosion carrier; an axially penetrating upper center through hole is provided in the center of the upper isolation block, and two axially penetrating upper air passages are provided on opposite sides of the outer side of the upper center through hole in the horizontal direction, and at the same time, two L-shaped sliding channels are provided inside the upper isolation block on opposite sides of the outer side of the upper center through hole in the longitudinal direction, and the L-shaped sliding channels It includes a vertical sliding section and a transverse sliding section; the connecting parts of the vertical sliding section and the transverse sliding in the two L-shaped sliding channels are located in the middle section of the upper isolation block, and the upper ends of the two vertical sliding sections extend to the upper end surface of the upper isolation block, and the outer ends of the two transverse sliding sections extend to the outer circular surfaces on the opposite sides, and the outer ends of the transverse sliding sections are encapsulated with outer sealing plates; the upper isolation block is provided with two axially penetrating stepped mounting cavities on the opposite sides of the longitudinal direction outside the upper center through hole, and the stepped mounting cavities include a small-diameter mounting cavity located at the upper part and a large-diameter mounting cavity located at the lower part, and the upper end of the small-diameter mounting cavity is encapsulated with an upper sealing plate, and the lower end of the large-diameter mounting cavity is encapsulated with a lower sealing plate, and the large-diameter mounting cavity is blocked by the lower sealing plate to form a gunpowder bin, and Gunpowder is loaded in the gunpowder bin; the two small-diameter section installation cavities are located on the outsides of the two vertical sliding sections, and at the same time, the lower parts of the two small-diameter section installation cavities are respectively connected with the two horizontal sliding sections; the two stepped installation cavities and the two L-shaped sliding channels are connected to form two ignition installation channels; an axially penetrating lower center through hole is provided in the center of the lower isolation block, and two axially penetrating lower air passages are provided on opposite sides of the outside of the lower center through hole; the aperture of the lower center through hole is consistent with the aperture of the upper center through hole; a plurality of perforations are provided on the wall of the combustion and explosion bin, and a perforation plug is packaged on the outside of each perforation; the upper end plate is fixedly packaged on the upper end of the delivery bin, and an air inlet is provided in the center, and on the outside of the air inlet An air inlet joint is fixedly connected; the lower end plate is fixedly packaged at the lower end of the combustion and explosion chamber, and an air outlet is opened in the central area thereof; a delivery chamber, an isolation chamber and a combustion and explosion chamber are respectively formed inside the delivery chamber, the isolation chamber and the combustion and explosion chamber; the annular piston is slidingly and sealingly assembled in the delivery chamber, and the aperture of its center hole is consistent with the aperture of the upper center through hole; the number of the ignition devices is two, corresponding to the two ignition installation channels respectively; the ignition device comprises a spring one, a firing pin, a spring two, a trigger linkage rod and a trigger pin; the spring one and the firing pin are sequentially installed in the small-diameter section installation cavity from top to bottom, and the upper end of the spring one is in contact with the upper sealing plate, the upper end of the firing pin is in contact with the lower end of the spring one, and its lower end extends to a position close to the upper end of the large-diameter section installation cavity;The spring 2 and the trigger linkage rod are slidably installed in the lateral sliding section from the outside to the inside, and the outer end of the spring 2 is in contact with the outer sealing plate, and the outer end of the trigger linkage rod is in contact with the inner end of the spring 2, and the inner end thereof extends to the lower end of the vertical sliding section; a section on the inner side of the trigger linkage rod is provided with a limiting structure at the position corresponding to the firing pin, and the limiting structure realizes the vertical limiting action of the firing pin under the elastic action of the spring 2; the trigger pin is axially slidably installed in the vertical sliding section, and its upper end extends above the upper end of the upper isolation block, and its lower end extends to the lower end of the vertical sliding section, and cooperates with the inner section of the trigger linkage rod, and is used to push the trigger linkage rod to slide outward by extrusion, and make the limiting structure release the firing pin; two constant pressure valves are correspondingly installed on the two upper air passages The cam is an airtight container, and the cam is connected to the bottom of the container to form a seal. The cam is connected to the bottom of the container to form a seal. The cam is connected to the bottom of the container to form a seal. The cam is connected to the bottom of the container to form a seal.

[0020] S43: according to the required combustion-supporting amount, the required amount of gaseous combustion-supporting agent is filled into the delivery cavity, nitrogen is injected into the isolation cavity to improve the sealing effect of the isolation chamber by using nitrogen, liquid alkyl compound is injected into the explosion cavity, and potassium permanganate is filled into four detachable hollow tubes; a steel ball with a size matching the shrinkage part of the central tube is put into the central tube through the air inlet joint, and the lower end of the central tube is blocked by the steel ball;

[0021] S44: Connect the air inlet joint of the blasting tool to the end of the coiled tubing, and at the same time, set a packer on the outside of the end section of the coiled tubing, and then connect the head end of the coiled tubing to the ground fracturing vehicle; first, use the coiled tubing to lower the blasting tool to a predetermined position in the coal seam horizontal well, and then slowly inject high-pressure nitrogen into the coiled tubing through the ground fracturing vehicle, and let the high-pressure nitrogen enter the packer to seal the packer; after the packer is sealed, a closed working space is formed between the packer and the drillable bridge plug;

[0022] Step 5: Mix and place the combustion aid in the explosion tool;

[0023] S51: high-pressure nitrogen is continuously pumped into the coiled tubing through the fracturing truck, and the high-pressure nitrogen with increasing pressure acts on the upper end surface of the annular piston to move the annular piston downward; at the same time, the pressure inside the delivery chamber is continuously increased by the compression effect of the annular piston, and when the pressure reaches the opening pressure of the constant pressure valve, the constant pressure valve opens and opens the upper gas passage;

[0024] S52: Using pressure to make the gaseous combustion-supporting agent enter the isolation chamber through the upper gas passage, and then enter the combustion and explosion chamber through the one-way valve, and be fully mixed with the liquid alkyl compound;

[0025] Step 6: Trigger the firing pin to ignite;

[0026] The continuously pumped high-pressure nitrogen is used to push the annular piston to continue to move downward, and the combustion-supporting agent is continuously discharged until the annular piston moves to the upper end of the upper isolation block. In the process of the annular piston contacting the upper isolation block, the annular piston is used to push the trigger needle to move downward and squeeze the inner end of the trigger linkage rod, so that the trigger linkage rod slides outward and releases the limit state of the striker; the elastic action of the spring 1 pushes the striker to quickly hit the gunpowder in the gunpowder chamber, and the gunpowder is burned and exploded. At the same time, the flame stimulated by the explosion passes through the isolation chamber and enters the explosion chamber to complete the ignition operation;

[0027] Step 7: Explosive fracturing of oxygen-rich coal seams;

[0028] The ignition of flame and the combustion-supporting effect of combustion-supporting agent are used together to promote the rapid combustion and explosion of liquid alkyl compound. Under the action of instantaneous impact of combustion and explosion, the explosion gas breaks through the perforation plugging and rapidly expands into the wellbore through the perforation; the high temperature of combustion and explosion is used to quickly melt the outer wall of the detachable hollow tube, and at the same time, potassium permanganate is quickly decomposed and continuously produces a large amount of oxygen. With the continuous supply of oxygen, secondary combustion and explosion further occur; the multi-frequency shock waves and the continuously generated flames generated by the combustion and explosion process are used together to act on the oxygen-rich coal seam, thereby forming a radial volume fracture group in the coal seam, and at the same time ignite the methane-oxygen mixed gas enriched in the gap, causing further combustion and explosion in the fracture group, further strengthening the expansion and transformation effect of the fracture network, thereby forming a higher quality radial three-dimensional fracture network.

[0029] Preferably, in step 1 S11, the geological parameters and exploration data include coal seam thickness, coal seam burial depth, coal seam top and bottom lithology, geological structure, and coal seam permeability.

[0030] As a preferred embodiment, in step 1 S13, when analyzing the cap layer conditions, the lithology, thickness and stability of the cap layer are analyzed.

[0031] Furthermore, in order to enable the potassium permanganate in the detachable hollow tube to quickly release oxygen during the combustion and explosion process, in step 4 S42, the detachable hollow tube is made of a fusible material.

[0032] Furthermore, in order to ensure that the perforation plug is effective in sealing the perforation and to ensure good sealing performance in the explosion chamber, in step four S42, the perforation is a stepped through hole, and the perforation plug is installed on the outside of the perforation and sealed by an O-ring to enhance the sealing effect.

[0033] Furthermore, in order to ensure the best explosion effect, in step 4 S43, the injection amount of the liquid alkyl compound is two-thirds of the total height of the explosion chamber when the explosion tool is in a vertical state.

[0034] The present invention adopts a technical method that combines coal seam oxidation-enrichment transformation with continuous explosion impact fracturing. First, up and down opposite horizontal wells are directionally drilled to build a basic framework, and then conventional fracturing methods are used to communicate the fractures. The target coal seam is oxygen-enriched by oxygen injection and diffusion through the extended fracture gaps in the coal seam cap layer. On this basis, a special structural design is made for the explosion tool. The piston is used to compress the combustion aid and the annular piston is used to trigger the trigger pin to unlock the firing pin to fire the gunpowder chamber to complete the ignition process. Liquid alkyl compounds are used as fuel in the explosion chamber, and potassium permanganate tube columns are installed to continuously supply oxygen by heating and decomposing potassium permanganate. Compared with the traditional single explosion impact method, it not only improves the explosion intensity, but also effectively improves the continuous explosion effect of the liquid alkyl compound. It can then act on the oxygen-rich coal seam through multi-frequency and continuously generated flames and shock waves to form cracks with better three-dimensional effects. At the same time, it can effectively ignite the methane-oxygen mixed gas enriched in the gaps during the explosion process, and then further explosions can occur in the crack group, further expanding the crack network, thereby forming a higher quality radial three-dimensional crack network.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] 1. The present invention uses a trigger to unlock the firing pin and fire the ignition cartridge to complete the ignition process, taking into full account the possibility that the bumps and collisions that occur during the transportation and installation of the explosive tool may cause the firing pin to loosen and unlock the ignition cartridge to fire prematurely, and then innovatively installs a trigger linkage rod that serves as a safety pin at the firing pin to effectively limit the movement of the firing pin. The present invention innovatively sets an isolation chamber between the delivery chamber and the explosive chamber, which can effectively avoid direct contact between the ignition cartridge and the explosive chamber below. At the same time, a certain amount of inert gas is filled in the isolation chamber, further ensuring the safety of the explosive tool in a non-working state.

[0037] 2. The present invention achieves efficient fracturing and permeability enhancement of the upper cap layer of the coal seam by directional drilling of upper and lower opposite horizontal wells, combined with supercritical CO2 energy-concentrated fracturing technology, and expands the cracks to the target coal seam, significantly improving the permeability of the coal seam. Then, by injecting high-pressure oxygen into the horizontal well of the upper cap layer of the coal seam and utilizing the fracturing fracture network, oxygen is driven into the low-permeability target coal seam to form an oxygen-rich coal seam. The presence of the oxygen-rich coal seam not only provides sufficient oxygen supply for subsequent explosive fracturing, but also promotes the oxidation reaction of organic matter in the coal seam, enhancing the desorption and migration efficiency of coalbed methane.

[0038] 3. The present invention designs a special structure of the explosion tool, which realizes the continuous explosion of liquid alkyl compounds through the mechanisms of piston compression of combustion aid, firing of the striker, and continuous oxygen supply by potassium permanganate decomposition. The multi-frequency and continuous flames and shock waves act on the oxygen-rich coal seam, forming a radial volume crack group, and through the further explosion of the methane-oxygen mixed gas enriched in the cracks, the crack network is efficiently expanded, and a higher quality three-dimensional crack network is constructed.

[0039] 4. The present invention realizes the modular operation of fracturing bomb arrangement and ignition explosion fracturing by combining methane in-situ explosion with reservoir transformation technology. The special structural design of the explosion tool makes the combustion aid placement, ignition and explosion process more convenient and controllable. It avoids a series of problems such as water resource consumption, reservoir clay expansion, groundwater pollution, etc. caused by conventional hydraulic fracturing, and realizes the green and efficient mining of coalbed methane. At the same time, the formation of oxygen-rich coal seams and the continuous explosion mechanism improve the mining efficiency of coalbed methane, providing new ideas for the commercial development of coalbed methane resources.

[0040] In summary, this method achieves efficient fracturing and crack expansion of coal seams through the construction of oxygen-rich coal seams and continuous explosion impact fracturing operations, improves the efficiency of coalbed methane extraction, and at the same time has the characteristics of green and environmental protection, with significant technical advantages and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of well layout and early stage fracturing state in the present invention;

[0042] Figure 2 It is a schematic diagram of oxygen delivery and diffusion state in the present invention;

[0043] Figure 3 It is a schematic diagram of the logging and tool lowering state in the present invention;

[0044] Figure 4 It is a schematic diagram of the three-dimensional structure of the explosion tool in the present invention;

[0045] Figure 5 is a cross-sectional view of the explosion tool of the present invention;

[0046] Figure 6 It is a schematic diagram of the structure of the ignition device in the explosion tool of the present invention;

[0047] Figure 7 It is a schematic diagram of the assembly of the ignition device and the constant pressure valve in the present invention;

[0048] Figure 8 It is a schematic diagram of the state of placing the combustion aid in the present invention;

[0049] Fig. 9 It is a schematic diagram of the ignition process state in the present invention;

[0050] Fig.10 It is a schematic diagram of the state of explosive fracturing of an oxygen-rich coal seam in the present invention.

[0051] In the figure: 1. vertical main wellbore, 2. cap layer horizontal well, 3. fracturing fracture, 4. ground fracturing vehicle, 5. cap layer, 6. coal seam, 7. coal seam horizontal well, 8. oil pipe, 9. combustion aid delivery tool, 10. high pressure oxygen, 11. measuring wellbore, 12. drillable bridge plug, 13. combustion tool, 14. packer, 15. continuous oil pipe, 16. delivery chamber, 17. isolation chamber, 18. combustion chamber, 19. annular piston, 20. center tube, 21. ignition device, 22. constant pressure valve, 23. one-way valve, 24. removable hollow tube, 25. , perforation plug, 26, trigger needle, 27, spring one, 28, firing pin, 29, trigger linkage rod, 30, gunpowder magazine, 31, nitrogen, 32, combustion aid, 33, potassium permanganate, 34, liquid alkyl compound, 35, steel ball, 36, flame, 37, perforation, 38, oxygen-rich coal seam, 39, upper isolation block, 40, lower isolation block, 41, upper end plate, 42, lower end plate, 43, air inlet joint, 44, stepped installation cavity, 45, upper sealing plate, 46, lower sealing plate, 47, outer sealing plate, 48, spring two, 49, L-shaped sliding channel. DETAILED DESCRIPTION

[0052] In order to realize the fracturing transformation of deep low-permeability coal seams, the present invention proposes a multi-stage pulse high-frequency dynamic load fracturing method for low-permeability coal seams, adopts the method of directional drilling of opposite horizontal wells, and oxygen-enriches the target coal seam by oxygen injection and diffusion through the extended fracturing gaps in the upper cover layer of the coal seam. Combined with the special structural design of the explosive tool, three-dimensional explosive fracturing operations such as combustion-aid mixing, striker firing ignition, potassium permanganate decomposition and oxygen supply continuous explosion, and oxygen-enriched coal layer primary explosion are completed, so as to realize the multi-stage pulse high-frequency dynamic load fracturing transformation operation of the coal seam and construct a higher quality radial three-dimensional fracture network.

[0053] The following is a more detailed description of the continuous explosion impact fracturing method for oxygen-rich coal seams of the present invention in conjunction with the accompanying drawings and specific embodiments. The following embodiments only describe the general process of implementing the method in a coal mine, and are not targeted at a specific mine. Therefore, the various parameters described below are only qualitatively described and are not intended to limit the present invention.

[0054] like Figures 1 to 10 As shown, the present invention provides a multi-stage pulse high-frequency dynamic load fracturing method, comprising the following steps:

[0055] Step 1: Preparation;

[0056] S11: Collect geological parameters and exploration data of the target coal seam 6. As a preferred method, the geological parameters and exploration data include coal seam thickness, coal seam burial depth, coal seam top and bottom lithology, geological structure, coal seam permeability, etc., and analyze the coal seam structure and density based on the geological parameters and exploration data; at the same time, analyze the well logging data to determine the thickness and distribution of the coal seam, coal seam physical properties, coal seam gas content and water content;

[0057] S12: Based on the analysis results of well logging data and combined with the assessment of coal seam structure and density, areas with thick coal seams, high permeability and rich gas content are selected as well-laying sections. At the same time, ensure that the well-laying sections avoid areas with developed geological structures such as faults and folds, as well as unfavorable areas with thin coal seams and low permeability, so as to reduce the risks and costs of operations such as fracturing;

[0058] S13: Analyze the conditions of the cap layer 5 above the coal seam 6. As a preferred method, it is necessary to analyze the lithology, thickness and stability of the cap layer 5 to ensure that the cap layer 5 can effectively isolate the coal seam gas and prevent the coal seam gas from escaping. Based on the analysis results of the cap layer conditions, design the drilling position of the cap layer horizontal well 2 in an area where the cap layer 5 is stable and of moderate thickness to ensure the safe drilling and long-term production of the cap layer horizontal well 2.

[0059] S14: Design reasonable coal seam horizontal well 7 drilling parameters according to coal seam structure and geological conditions;

[0060] Step 2: Wellbore layout and caprock horizontal well 2 fracturing, such as Figure 1 As shown;

[0061] S21: Drill two vertical main shafts 1 at a set distance according to the well logging data and the distribution interval of the coal seam 6, and make the lower ends of the two vertical main shafts 1 stop at the target coal seam 6 and the cap layer 5 above the target coal seam 6 respectively, and then extend two horizontal well sections relatively from the ends of the two vertical main shafts 1, wherein the horizontal well section located in the cap layer 5 is used as the cap layer horizontal well 2, and the horizontal well section located in the target coal seam 6 is used as the coal seam horizontal well 7, and the cap layer horizontal well 2 and the coal seam horizontal well 7 constitute a counter-well layout;

[0062] The drilling position of the cap layer horizontal well 2 is in the upper cap layer 5 of the coal seam 6 and is close to the target fracturing coal seam;

[0063] S22: Figure 1 The schematic diagram of the early stage fracturing state is shown; the supercritical CO2 energy-concentrated fracturing technology is used to perform fracturing and seam-making operations on the cap layer 5, and the strong fracturing shock wave generated by supercritical CO2 under high pressure conditions is used to promote the generated fracturing cracks 3 to expand toward the target coal seam 6 to form a fracture network connecting the cap layer horizontal well 2 and the target coal seam 6. After the fracture network is formed, the fracturing and seam-making operations are stopped;

[0064] Supercritical CO2 can generate strong fracturing shock waves under high pressure conditions due to its unique physical and chemical properties, which can effectively penetrate and expand the network of fracturing cracks 3 in the upper cover layer 5, thereby extending the fracturing cracks 3 to the lower target coal seam 6.

[0065] Step 3: placing the combustion aid 32 in the cap rock horizontal well 2; Figure 2 As shown, a schematic diagram of the delivery and diffusion state of high-pressure oxygen 10 is shown;

[0066] The combustion-aiding agent delivery tool 9 is connected to the end of the oil pipe 8, and the head end of the oil pipe 8 is connected to the ground fracturing vehicle 4. The ground fracturing vehicle 4, the oil pipe 8 and the combustion-aiding agent delivery tool 9 are used to inject high-pressure oxygen 10 into the cap layer horizontal well 2. At the same time, the fracture network formed by the fracturing and seaming operation is used as a permeation channel, and the injection pressure is used to drive the high-pressure oxygen 10 into the low-permeability target coal seam 6, so that the oxygen is widely distributed in the coal seam 6, thereby forming an oxygen-rich coal seam 38; the formation of the oxygen-rich coal seam 38 not only provides more favorable conditions for the subsequent coalbed methane mining, but also promotes the oxidation reaction of organic matter in the coal seam 6, which helps to improve the desorption and migration efficiency of the coalbed methane. Among them, the combustion-aiding agent delivery tool 9 is a combustion-aiding agent delivery tool in the prior art, which can be a delivery cylinder with a plurality of delivery holes, or a delivery pipe with a plurality of delivery holes.

[0067] At the same time, according to the geological parameters and exploration data of the coal seam 6, a coalbed methane drilling device is used to vertically drill a measuring wellbore 11 from the ground downward, and the end of the measuring wellbore 11 reaches the oxygen-rich coal seam 38. The oxygen concentration in the oxygen-rich coal seam 38 is measured by the measuring wellbore 11. When the oxygen concentration reaches the appropriate combustion and explosion standard, the high-pressure oxygen 10 injection operation into the cap layer horizontal well 2 is stopped;

[0068] Step 4: lowering and sealing the blasting tool 13;

[0069] S41: Figure 3 As shown, a drillable bridge plug 12 is lowered into a coal seam horizontal well 7 and is set;

[0070] S42: Prepare the blasting tool 13, such as Figure 4 , Figure 5 , Figure 6 and Figure 7As shown; the explosion tool 13 includes a delivery bin 16, an upper isolation block 39, an isolation bin 17, a lower isolation block 40, an explosion bin 18, an upper end plate 41, a lower end plate 42, an annular piston 19, an ignition device 21, a constant pressure valve 22, a one-way valve 23, a detachable hollow tube 24 and a center tube 20; the outer contours of the delivery bin 16, the upper isolation block 39, the isolation bin 17, the lower isolation block 40 and the explosion bin 18 are all circular, and have the same outer diameter. At the same time, they are coaxially fixedly connected from top to bottom to form an explosion carrier; an axially penetrating upper center through hole is opened in the center of the upper isolation block 39, and two axially penetrating upper gas passages are opened on opposite sides of the upper center through hole. At the same time, the interior of the upper isolation block 39 is outside the upper center through hole. Two L-shaped sliding channels 49 are provided on opposite sides of the upper isolation block 39 in the longitudinal direction, and the L-shaped sliding channels 49 include a vertical sliding section and a transverse sliding section; the connecting parts of the vertical sliding section and the transverse sliding section in the two L-shaped sliding channels 49 are located in the middle section of the upper isolation block 39, and the upper ends of the two vertical sliding sections extend to the upper end surface of the upper isolation block 39, and the outer ends of the two transverse sliding sections extend to the outer circular surfaces on the opposite sides, and the outer ends of the transverse sliding sections are both encapsulated with outer sealing plates 47; the upper isolation block 39 is provided with two axially penetrating stepped mounting cavities 44 on opposite sides of the longitudinal direction outside the upper center through hole, and the stepped mounting cavities 44 include a small-diameter mounting cavity located at the upper part and a large-diameter mounting cavity located at the lower part, and the upper end of the small-diameter mounting cavity is encapsulated with an upper sealing plate 45, a lower sealing plate 46 is encapsulated inside the lower end of the large diameter section installation cavity, and the large diameter section installation cavity is blocked by the lower sealing plate 46 to form a gunpowder chamber 30, and gunpowder is loaded in the gunpowder chamber 30; the two small diameter section installation cavities are located on the outside of the two vertical sliding sections, and at the same time, the lower parts of the two small diameter section installation cavities are respectively connected with the two horizontal sliding sections; the two stepped installation cavities 44 and the two L-shaped sliding channels 49 are connected to form two ignition installation channels; the center of the lower isolation block 40 is provided with an axially penetrating lower center through hole, and two axially penetrating lower gas passages are provided on the opposite sides of the lower center through hole; the aperture of the lower center through hole is consistent with the aperture of the upper center through hole; the wall surface of the chamber body of the explosion chamber 18 is provided with a plurality of perforations 3 7, and a perforation plug 25 is packaged on the outside of each perforation 37. In order to ensure that the perforation plug effectively blocks the perforation and ensure that the combustion chamber has good sealing performance, the perforation 37 is a step-shaped through hole. The perforation plug 25 is installed on the outside of the perforation 37 and seals it through an O-ring to enhance the sealing effect, and can be separated from the perforation 37 when the internal pressure or impact force is greater than the set value; the upper end plate 41 is fixedly packaged at the upper end of the delivery bin 16, and an air inlet hole is opened in the center, and an air inlet joint 43 is fixedly connected to the outside of the air inlet hole; the lower end plate 42 is fixedly packaged at the lower end of the combustion chamber 18, and an air outlet hole is opened in the central area; a delivery chamber, an isolation chamber and a combustion chamber are formed inside the delivery bin 16, the isolation bin 17 and the combustion chamber 18 respectively;The annular piston 19 is slidably and sealingly assembled in the delivery cavity, and the aperture of its center hole is consistent with the aperture of the upper center through hole; the number of the ignition devices 21 is two, corresponding to the two ignition installation channels respectively; the ignition device 21 includes a spring 27, a firing pin 28, a spring 248, a trigger linkage rod 29 and a trigger needle 26; the spring 27 and the firing pin 28 are sequentially installed in the small diameter section installation cavity from top to bottom, and the upper end of the spring 27 is in contact with the upper sealing plate 45, and the upper end of the firing pin 28 is in contact with the lower end of the spring 27, and its lower end extends to a position close to the upper end of the large diameter section installation cavity; the spring 248 and the trigger linkage rod 29 are laterally slidably installed from outside to inside It is installed in the transverse sliding section, and the outer end of the spring 2 48 is in contact with the outer sealing plate 47, and the outer end of the trigger linkage rod 29 is in contact with the inner end of the spring 2 48, and its inner end extends to the lower end of the vertical sliding section; a section on the inner side of the trigger linkage rod 29 is provided with a limiting structure at the position corresponding to the firing pin 28, and under the elastic action of the spring 2 48, the limiting structure realizes the vertical limiting action of the firing pin 28. As a preference, the limiting structure can be an arc-shaped pressing piece fixedly connected to the trigger linkage rod 29, and the length direction of the arc-shaped pressing piece extends along a direction perpendicular to the length direction of the transverse sliding section, and its size is small, it can slide laterally in the transverse sliding section, and can act on the side of the firing pin 28. , in order to limit and tighten it; wherein, spring 1 27 is used to provide pre-tightening elastic force, so that when the trigger linkage rod 29 releases the limiting state of the firing pin 28, the firing pin 28 can hit the gunpowder in the gunpowder chamber 30 at high speed, and spring 2 48 is used to provide elastic thrust to the trigger linkage rod 29. Under the action of the elastic thrust, the limiting structure on the trigger linkage rod 29 can squeeze the firing pin 28 inward, thereby realizing the limiting fixation of the firing pin 28; the trigger needle 26 is axially slidably installed in the vertical sliding section, and its upper end extends above the upper end of the upper isolation block 39, and its lower end extends to the lower end of the vertical sliding section, and cooperates with the inner section of the trigger linkage rod 29, which is used to pass The trigger linkage rod 29 is pushed to slide outward by extrusion, and the limiting structure releases the firing pin 28; two constant pressure valves 22 are correspondingly installed in the two upper gas passages; two one-way valves 23 are correspondingly installed in the two lower gas passages, so that it can be ensured that the external gas can only flow into the combustion chamber, and the fuel leakage in the chamber can be effectively prevented; four detachable hollow tubes 24 are located in the combustion chamber, and are evenly distributed around the periphery of the lower center through hole, and their upper ends are closed, and their lower open ends are fixedly connected to the upper end surface of the lower end plate 42. In order to enable the potassium permanganate in the detachable hollow tubes to quickly release oxygen during the combustion process, the detachable hollow tubes 24 are made of easily fusible materials;The central tube 20 is arranged at the center of the explosion carrier, and its upper open end is a flared structure, and its upper open end is located below the upper end plate 41, and is in clearance with the lower end of the air inlet joint 43, and its lower open end is a contracted structure, and its lower open end sequentially passes through the center hole of the annular piston 19, the upper center through hole of the upper isolation block 39, the lower center through hole of the lower isolation block 40 and the air outlet of the lower end plate 42, and then stops at the bottom of the lower end plate 42, wherein the central tube 20 and the annular piston 19 are in sliding sealing cooperation, and the central tube 20 and the upper isolation block 39, the lower isolation block 40 and the lower end plate 42 are all fixedly connected;

[0071] As a preferred embodiment, the detachable hollow tube 24 is a disposable item, and the material used is a fusible material, which can be replaced at any time from the bottom of the explosion chamber.

[0072] S43: Figure 8 As shown, according to the required amount of combustion-supporting agent 32, the required amount of gaseous combustion-supporting agent 32 is filled into the delivery cavity, nitrogen 31 is injected into the isolation cavity to utilize nitrogen to enhance the sealing effect of the isolation chamber 17, liquid alkyl compound 34 is injected into the explosion cavity, and potassium permanganate 33 is filled into the four detachable hollow tubes 24; a steel ball 35 having a size matching the shrinkage portion of the central tube 20 is introduced into the central tube 20 through the air inlet joint 43, and the lower end of the central tube 20 is blocked by the steel ball 35;

[0073] In order to ensure the best explosion effect, the injection amount of the liquid alkyl compound 34 is two-thirds of the total height of the explosion chamber (when the explosion tool 13 is in a vertical state), wherein the liquid alkyl compound 34 serves as the fuel for the subsequent explosion;

[0074] S44: Connect the air inlet connector 43 of the blasting tool 13 to the end of the coiled tubing 15, and at the same time, set the packer 14 on the outside of the end section of the coiled tubing 15, and then connect the head end of the coiled tubing 15 to the ground fracturing vehicle 4; first, use the coiled tubing 15 to lower the blasting tool 13 to a predetermined position in the coal seam horizontal well 7, and then slowly inject high-pressure nitrogen 31 into the coiled tubing 15 through the ground fracturing vehicle 4, and allow the high-pressure nitrogen 31 to enter the packer 14, so that the packer 14 is set; after the packer 14 is set, a closed working space is formed between the packer 14 and the drillable bridge plug 12;

[0075] Step 5: Mixing and placing the combustion aid 32 in the explosion tool 13; Figure 8 This is a schematic diagram of the introduction of the combustion aid in the method of the present invention;

[0076] S51: The high-pressure nitrogen 31 is continuously pumped into the coiled tubing 15 through the fracturing vehicle 4, and the high-pressure nitrogen 31 with increasing pressure acts on the upper end surface of the annular piston 19, so that the annular piston 19 moves downward; at the same time, the pressure inside the delivery chamber is continuously increased by the compression effect of the annular piston 19, and when the pressure reaches the opening pressure of the constant pressure valve 22, the constant pressure valve 22 opens and opens the upper gas passage;

[0077] S52: Using the pressure, the gaseous combustion aid 32 enters the isolation chamber 17 through the upper gas channel, and then enters the combustion chamber through the one-way valve 23, and is fully mixed with the liquid alkyl compound 34; the setting of the one-way valve 23 can ensure that the liquid alkyl compound 34 in the combustion chamber will not leak.

[0078] Step 6: Trigger the firing pin 28 to ignite the device. Fig. 9 As shown;

[0079] The annular piston 19 is pushed to continue to move downward by the continuously pumped high-pressure nitrogen 31, and the combustion-supporting agent 32 is continuously discharged until the annular piston 19 moves to the upper end of the upper isolation block 39. In the process of the annular piston 19 contacting the upper isolation block 39, the annular piston 19 is used to push the trigger needle 26 to move downward and squeeze the inner end of the trigger linkage rod 29, so that the trigger linkage rod 29 slides outward and releases the limit state of the striker 28; the elastic action of the spring 27 pushes the striker 28 to quickly hit the gunpowder in the gunpowder chamber 30, and the gunpowder is burned and exploded. At the same time, the flame 36 stimulated by the combustion and explosion passes through the isolation chamber into the combustion and explosion chamber, completing the ignition operation;

[0080] Step 7: Explosion fracturing of oxygen-rich coal seam 38, such as Fig.10 As shown;

[0081] The liquid alkyl compound 34 is a highly flammable organic compound. The ignition of the flame 36 and the combustion-supporting effect of the combustion-supporting agent 32 are used together to promote the rapid combustion and explosion of the liquid alkyl compound 34. Under the action of the instantaneous impact of the combustion and explosion, the combustion and explosion gas breaks through the perforation plug 25 and rapidly expands into the wellbore through the perforation 37. The high temperature of the combustion and explosion is used to quickly melt the outer wall of the detachable hollow tube 24, and at the same time, the potassium permanganate 33 is quickly decomposed and continuously produces a large amount of oxygen 10. Under the continuous supply of oxygen 10, a secondary combustion and explosion further occurs, which can effectively improve the combustion and explosion intensity and the continuous combustion and explosion effect of the liquid alkyl compound 34. The multi-frequency shock waves generated by the combustion and explosion process and the continuously generated flame 36 act together on the oxygen-rich coal seam 38, thereby forming a radial volume fracture group in the coal seam 6, and at the same time ignite the methane-oxygen mixed gas enriched in the gap, so that further combustion and explosion occur in the fracture group, further strengthening the expansion and transformation effect of the fracture network, thereby forming a higher quality radial three-dimensional fracture network.

[0082] The present invention adopts a technical method that combines coal seam oxidation-enrichment transformation with continuous explosion impact fracturing. First, up and down opposite horizontal wells are directionally drilled to build a basic framework, and then conventional fracturing methods are used to communicate the fractures. The target coal seam is oxygen-enriched by oxygen injection and diffusion through the extended fracture gaps in the coal seam cap layer. On this basis, a special structural design is made for the explosion tool. The piston is used to compress the combustion aid and the annular piston is used to trigger the trigger pin to unlock the firing pin to fire the gunpowder chamber to complete the ignition process. Liquid alkyl compounds are used as fuel in the explosion chamber, and potassium permanganate tube columns are installed to continuously supply oxygen by heating and decomposing potassium permanganate. Compared with the traditional single explosion impact method, it not only improves the explosion intensity, but also effectively improves the continuous explosion effect of the liquid alkyl compound. It can then act on the oxygen-rich coal seam through multi-frequency and continuously generated flames and shock waves to form cracks with better three-dimensional effects. At the same time, it can effectively ignite the methane-oxygen mixed gas enriched in the gaps during the explosion process, and then further explosions can occur in the crack group, further expanding the crack network, thereby forming a higher quality radial three-dimensional crack network.

[0083] Compared with the prior art, the present invention has the following advantages:

[0084] 1. The present invention uses a trigger to unlock the firing pin and fire the ignition cartridge to complete the ignition process, taking into full account the possibility that the bumps and collisions that occur during the transportation and installation of the explosive tool may cause the firing pin to loosen and unlock the ignition cartridge to fire prematurely, and then innovatively installs a trigger linkage rod that serves as a safety pin at the firing pin to effectively limit the movement of the firing pin. The present invention innovatively sets an isolation chamber between the delivery chamber and the explosive chamber, which can effectively avoid direct contact between the ignition cartridge and the explosive chamber below. At the same time, a certain amount of inert gas is filled in the isolation chamber, further ensuring the safety of the explosive tool in a non-working state.

[0085] 2. The present invention achieves efficient fracturing and permeability enhancement of the upper cap layer of the coal seam by directional drilling of upper and lower opposite horizontal wells, combined with supercritical CO2 energy-concentrated fracturing technology, and expands the cracks to the target coal seam, significantly improving the permeability of the coal seam. Then, by injecting high-pressure oxygen into the horizontal well of the upper cap layer of the coal seam and utilizing the fracturing fracture network, oxygen is driven into the low-permeability target coal seam to form an oxygen-rich coal seam. The presence of the oxygen-rich coal seam not only provides sufficient oxygen supply for subsequent explosive fracturing, but also promotes the oxidation reaction of organic matter in the coal seam, enhancing the desorption and migration efficiency of coalbed methane.

[0086] 3. The present invention designs a special structure of the explosion tool, which realizes the continuous explosion of liquid alkyl compounds through the mechanisms of piston compression of combustion aid, firing of the striker, and continuous oxygen supply by potassium permanganate decomposition. The multi-frequency and continuous flames and shock waves act on the oxygen-rich coal seam, forming a radial volume crack group, and through the further explosion of the methane-oxygen mixed gas enriched in the cracks, the crack network is efficiently expanded, and a higher quality three-dimensional crack network is constructed.

[0087] 4. The present invention realizes the modular operation of fracturing bomb arrangement and ignition explosion fracturing by combining methane in-situ explosion with reservoir transformation technology. The special structural design of the explosion tool makes the combustion aid placement, ignition and explosion process more convenient and controllable. It avoids a series of problems such as water resource consumption, reservoir clay expansion, groundwater pollution, etc. caused by conventional hydraulic fracturing, and realizes the green and efficient mining of coalbed methane. At the same time, the formation of oxygen-rich coal seams and the continuous explosion mechanism improve the mining efficiency of coalbed methane, providing new ideas for the commercial development of coalbed methane resources.

[0088] In summary, this method achieves efficient fracturing and crack expansion of coal seams through the construction of oxygen-rich coal seams and continuous explosion impact fracturing operations, improves the efficiency of coalbed methane extraction, and at the same time has the characteristics of green and environmental protection, with significant technical advantages and application prospects.

Claims

1. A multi-stage pulse high-frequency dynamic fracturing method, characterized in that: The following steps are involved: Step 1: Preparation; S11: Collect geological parameters and exploration data of the target coal seam (6), and analyze the structure and density of the coal seam based on the geological parameters and exploration data; at the same time, analyze the well logging data to determine the thickness and distribution of the coal seam, coal seam physical properties, and coal seam gas and water content; S12: Based on the analysis results of well logging data, combined with the assessment of coal seam structure and density, select areas with thick coal seams, high permeability and rich gas content as well as well-laying sections. At the same time, ensure that the well-laying sections avoid areas with developed fault and fold geological structures, as well as unfavorable areas with thin coal seams and low permeability. S13: Analyze the conditions of the cap rock (5) above the coal seam (6) to ensure that the cap rock (5) can effectively isolate the coal seam gas; based on the analysis results of the cap rock (5) conditions, design a drilling position for the cap rock horizontal well (2) in an area where the cap rock (5) is stable and has a moderate thickness to ensure safe drilling and long-term production of the cap rock horizontal well (2); S14: Design reasonable coal seam horizontal well (7) drilling parameters according to coal seam structure and geological conditions; Step 2: Wellbore arrangement and caprock horizontal well (2) fracturing; S21: Drill two vertical main wellbores (1) at a set distance according to the well logging data and the distribution interval of the coal seam (6), and make the lower ends of the two vertical main wellbores (1) stop at the target coal seam (6) and the cap layer (5) above the target coal seam (6), respectively, and then extend two horizontal well sections relatively from the ends of the two vertical main wellbores (1), wherein the horizontal well section located in the cap layer (5) is used as the cap layer horizontal well (2), and the horizontal well section located in the target coal seam (6) is used as the coal seam horizontal well (7), and the cap layer horizontal well (2) and the coal seam horizontal well (7) constitute a counter-well layout; S22: using supercritical CO2 energy-concentrated fracturing technology to perform fracturing and fracture-forming operations on the cap layer (5), and utilizing the strong fracturing shock wave generated by supercritical CO2 under high pressure conditions to cause the generated fracturing cracks (3) to expand toward the target coal seam (6) to form a fracture network connecting the cap layer horizontal well (2) and the target coal seam (6), and stopping the fracturing and fracture-forming operations after the fracture network is formed; Step 3: placing the combustion aid (32) in the cap rock horizontal well (2); The combustion-aiding agent delivery tool (9) is connected to the end of the oil pipe (8), and the head end of the oil pipe (8) is connected to the ground fracturing vehicle (4). The ground fracturing vehicle (4), the oil pipe (8) and the combustion-aiding agent delivery tool (9) are used to inject high-pressure oxygen (10) into the cap layer horizontal well (2). At the same time, the fracture network formed by the fracturing operation is used as a permeation channel, and the injection pressure is used to drive the high-pressure oxygen (10) into the low-permeability target coal seam (6), so that the oxygen is widely distributed in the coal seam (6), thereby forming an oxygen-rich coal seam (38); At the same time, according to the geological parameters and exploration data of the coal seam (6), a measuring wellbore (11) is vertically drilled from the ground downward using coal seam gas drilling equipment, and the end of the measuring wellbore (11) reaches the oxygen-rich coal seam (38). The oxygen concentration in the oxygen-rich coal seam (38) is measured using the measuring wellbore (11). When the oxygen concentration reaches a suitable combustion and explosion standard, the high-pressure oxygen (10) injection operation into the cap layer horizontal well (2) is stopped; Step 4: The blasting tool (13) is lowered and sealed; S41: inserting a drillable bridge plug (12) into the coal seam horizontal well (7) and setting it; S42: Prepare an explosion tool (13); the explosion tool (13) comprises a delivery bin (16), an upper isolation block (39), an isolation bin (17), a lower isolation block (40), an explosion bin (18), an upper end plate (41), a lower end plate (42), an annular piston (19), an ignition device (21), a constant pressure valve (22), a one-way valve (23), a detachable hollow tube (24) and a center tube (20); the delivery bin (16), the upper isolation block (39), the isolation bin (17), the lower isolation block (40) and the explosion bin (18) are all circular in profile and have the same outer diameter, and are coaxially fixedly connected from top to bottom to form an explosion carrier; the center of the upper isolation block (39) is provided with an axially penetrating upper center through hole, and Two upper air passages are axially connected on opposite sides of the upper central through hole. At the same time, two L-shaped sliding passages (49) are provided inside the upper isolation block (39) on opposite sides of the upper central through hole in the longitudinal direction. The L-shaped sliding passages (49) include a vertical sliding section and a horizontal sliding section. The connecting parts of the vertical sliding section and the horizontal sliding section in the two L-shaped sliding passages (49) are located in the middle section of the upper isolation block (39). The upper ends of the two vertical sliding sections extend to the upper end surface of the upper isolation block (39). The outer ends of the two horizontal sliding sections extend to the outer circular surfaces on the opposite sides. The outer ends of the horizontal sliding sections are both sealed with outer sealing plates (47). The upper isolation block (39) is axially connected on opposite sides of the upper central through hole in the longitudinal direction. Two stepped mounting cavities (44), the stepped mounting cavities (44) comprising a small diameter segment mounting cavity located at the top and a large diameter segment mounting cavity located at the bottom, the upper end of the small diameter segment mounting cavity is encapsulated with an upper sealing plate (45), the lower end of the large diameter segment mounting cavity is encapsulated with a lower sealing plate (46), the large diameter segment mounting cavity is sealed by the lower sealing plate (46) to form a gunpowder chamber (30), and gunpowder is loaded in the gunpowder chamber (30); the two small diameter segment mounting cavities are located outside the two vertical sliding sections, and at the same time, the lower parts of the two small diameter segment mounting cavities are respectively connected to the two horizontal sliding sections; the two stepped mounting cavities (44) and the two L-shaped sliding channels (49) are connected to form two ignition mounting channels; the center of the lower isolation block (40) is provided with an axially penetrating lower center passage The lower central through hole has two axially extending lower air passages on opposite sides of the lower central through hole; the aperture of the lower central through hole is consistent with the aperture of the upper central through hole; a plurality of perforations (37) are distributed on the wall of the combustion and explosion chamber (18), and a perforation plug (25) is packaged on the outside of each perforation (37); the upper end plate (41) is fixedly packaged on the upper end of the delivery chamber (16), and an air inlet hole is opened in the center thereof, and an air inlet joint (43) is fixedly connected to the outside of the air inlet hole; the lower end plate (42) is fixedly packaged on the lower end of the combustion and explosion chamber (18), and an air outlet hole is opened in the center thereof; a delivery chamber, an isolation chamber and a combustion and explosion chamber are formed inside the delivery chamber (16), the isolation chamber (17) and the combustion and explosion chamber (18), respectively;The annular piston (19) is slidably and sealingly assembled in the delivery cavity, and the diameter of the center hole thereof is consistent with the diameter of the upper center through hole; the number of the ignition devices (21) is two, corresponding to the two ignition installation channels respectively; the ignition device (21) comprises a spring one (27), a firing pin (28), a spring two (48), a trigger linkage rod (29) and a trigger pin (26); the spring one (27) and the firing pin (28) are sequentially installed in the small diameter section installation cavity from top to bottom, and the upper end of the spring one (27) is in contact with the upper sealing plate (45), the upper end of the firing pin (28) is in contact with the lower end of the spring one (27), and the lower end thereof extends to a position close to the large diameter section. The position of the upper end of the section installation cavity; the spring 2 (48) and the trigger linkage rod (29) are slidably installed in the horizontal sliding section from the outside to the inside, and the outer end of the spring 2 (48) is in contact with the outer sealing plate (47), and the outer end of the trigger linkage rod (29) is in contact with the inner end of the spring 2 (48), and the inner end extends to the lower end of the vertical sliding section; a section on the inner side of the trigger linkage rod (29) is provided with a limiting structure at the position corresponding to the firing pin (28), and the limiting structure realizes the vertical limiting action of the firing pin (28) under the elastic action of the spring 2 (48); the trigger pin (26) is slidably installed in the vertical sliding section axially, and its upper end The trigger linkage rod (29) is used to push the trigger linkage rod (29) to slide outward by extrusion, and to release the firing pin (28) by the limiting structure; two constant pressure valves (22) are correspondingly installed in the two upper air passages; two one-way valves (23) are correspondingly installed in the two lower air passages; four detachable hollow tubes (24) are located in the explosion chamber and are evenly distributed around the periphery of the lower central through hole, and their upper ends are closed and their lower open ends are fixedly connected to the upper end surface of the lower end plate (42); the central tube (20) is provided with At the center of the explosion carrier, its upper open end is a flared structure, and its upper open end is located below the upper end plate (41) and is in clearance with the lower end of the air inlet joint (43), and its lower open end is a contracted structure, and its lower open end sequentially passes through the center hole of the annular piston (19), the upper center through hole of the upper isolation block (39), the lower center through hole of the lower isolation block (40) and the air outlet of the lower end plate (42) and ends at the bottom of the lower end plate (42), wherein the center tube (20) and the annular piston (19) are in sliding sealing cooperation, and the center tube (20) and the upper isolation block (39), the lower isolation block (40) and the lower end plate (42) are all fixedly connected; S43: according to the required amount of combustion-supporting agent (32), the required amount of gaseous combustion-supporting agent (32) is filled into the delivery cavity, nitrogen (31) is injected into the isolation cavity, so as to utilize the nitrogen (31) to enhance the sealing effect of the isolation chamber (17), liquid alkyl compound (34) is injected into the explosion cavity, and potassium permanganate (33) is filled into four detachable hollow tubes (24); a steel ball (35) having a size matching the constricted portion of the central tube (20) is introduced into the central tube (20) through the air inlet joint (43), and the lower end of the central tube (20) is blocked by the steel ball (35); S44: Connect the air inlet joint (43) of the blasting tool (13) to the end of the coiled tubing (15), and at the same time, set the packer (14) on the outside of the end section of the coiled tubing (15), and then connect the head end of the coiled tubing (15) to the ground fracturing vehicle (4); first, use the coiled tubing (15) to lower the blasting tool (13) to a predetermined position in the coal seam horizontal well (7), and then slowly inject high-pressure nitrogen (31) into the coiled tubing (15) through the ground fracturing vehicle (4), and allow the high-pressure nitrogen (31) to enter the packer (14) to seal the packer (14); after the packer (14) is sealed, a closed working space is formed between the packer (14) and the drillable bridge plug (12); Step 5: Mixing and placing the combustion aid (32) in the explosion tool (13); S51: The high-pressure nitrogen (31) is continuously pumped into the coiled tubing (15) through the fracturing vehicle (4), and the high-pressure nitrogen (31) with increasing pressure is used to act on the upper end surface of the annular piston (19), so that the annular piston (19) moves downward; at the same time, the pressure inside the delivery chamber is continuously increased by the compression effect of the annular piston (19), and when the pressure reaches the opening pressure of the constant pressure valve (22), the constant pressure valve (22) is opened and the upper gas passage is opened; S52: Using pressure, the gaseous combustion-supporting agent (32) enters the isolation chamber through the upper gas passage, and then enters the combustion chamber through the one-way valve (23), and is fully mixed with the liquid alkyl compound (34); Step 6: Trigger the firing pin (28) to perform ignition; The annular piston (19) is pushed to continue to move downward by the continuously pumped high-pressure nitrogen (31), and the combustion-supporting agent (32) is continuously discharged until the annular piston (19) moves to the upper end of the upper isolation block (39). In the process of the annular piston (19) and the upper isolation block (39) contacting each other, the annular piston (19) is used to push the trigger needle (26) to move downward and squeeze the inner end of the trigger linkage rod (29), so that the trigger linkage rod (29) slides outward and releases the limit state of the striker (28); the elastic action of the spring 1 (27) pushes the striker (28) to quickly strike the gunpowder in the gunpowder chamber (30), and the gunpowder is caused to explode. At the same time, the flame (36) stimulated by the explosion passes through the isolation chamber and enters the explosion chamber, completing the ignition operation; Step 7: Explosion fracturing of oxygen-rich coal seam (38); The ignition of the flame (36) and the combustion-supporting effect of the combustion-supporting agent (32) are used together to promote the rapid combustion and explosion of the liquid alkyl compound (34). Under the action of the instantaneous impact of the combustion and explosion, the combustion and explosion gas breaks through the perforation plug (25) and rapidly expands into the wellbore through the perforation (37); the high temperature of the combustion and explosion is used to rapidly melt the outer wall of the detachable hollow tube (24), and at the same time, the potassium permanganate (33) is rapidly decomposed and continuously produces a large amount of oxygen (10). Under the continuous supply of oxygen (10), a secondary combustion and explosion further occurs; the multi-frequency shock waves generated by the combustion and explosion process and the continuously generated flame (36) act together on the oxygen-rich coal seam (38), thereby forming a radial volume fracture group in the coal seam (6), and at the same time ignite the methane-oxygen mixed gas enriched in the fracture, so that further combustion and explosion occur in the fracture group, further strengthening the expansion and transformation effect of the fracture network, thereby forming a higher quality radial three-dimensional fracture network.

2. A multi-stage pulse high-frequency dynamic fracturing method according to claim 1, characterized in that: In step 1 S11, the geological parameters and exploration data include coal seam thickness, coal seam burial depth, coal seam top and bottom lithology, geological structure, and coal seam permeability.

3. A multi-stage pulse high-frequency dynamic fracturing method according to claim 1 or 2, characterized in that: In step 1 S13, when analyzing the condition of the cap layer (5), the lithology, thickness and stability of the cap layer (5) are analyzed.

4. A multi-stage pulse high-frequency dynamic fracturing method according to claim 3, characterized in that: In step 4 S42, the detachable hollow tube (24) is made of a fusible material.

5. A multi-stage pulse high-frequency dynamic fracturing method according to claim 4, characterized in that: In step 4 S42, the perforation (37) is a stepped through hole, and the perforation plugging piece (25) is installed on the outside of the perforation (37) and improves the plugging effect through an O-ring.

6. A multi-stage pulse high-frequency dynamic fracturing method according to claim 5, characterized in that: In step 4 S43, the injection amount of the liquid alkyl compound (34) is two-thirds of the total height of the explosion chamber when the explosion tool (13) is in a vertical state.

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