A deep coal seam permeability improvement system and method based on microwave pre-splitting and directional jetting expansion slit cooperation

Abstract

The application discloses a kind of based on microwave pre-splitting-directional jet flow slit expansion synergy deep coal seam permeability improvement system and permeability improvement method, belong to coal mine gas extraction permeability improvement technical field.The system of the present application includes high-pressure jet preparation system, multi-frequency microwave generating system and intelligent monitoring control system, high-pressure jet preparation system is mainly composed of superhigh pressure plunger pump, high-frequency pressure stabilizer, directional jet flow casing and directional jet flow nozzle, multi-frequency microwave generating system is mainly composed of multi-frequency microwave emission source, multi-frequency microwave power compensator, inner microwave waveguide tube and microwave energy-gathering radiation head.The present application breaks through the bottleneck of deep coal seam permeability improvement technology through the synergistic effect of "microwave multi-point synchronous preheating seam creation + directional jet flow slit expansion", solves the problem of few initial cracks, inaccuracy of slit expansion direction and poor stability in traditional permeability improvement technology, thereby promoting the construction of deep coal seam fracture network and the improvement of extraction efficiency.

Description

Technical Field

[0001] This invention belongs to the field of coal mine gas extraction and permeability enhancement technology, specifically a deep coal seam permeability enhancement system and method based on microwave pre-splitting-directional jet expansion synergy. Background Technology

[0002] As coal mining and coal seam tunneling extend to deeper levels, the geological conditions become increasingly complex, making it difficult for existing permeability enhancement technologies to meet the demands of efficient gas control. Specific challenges include:

[0003] Deep coal seams are characterized by high pressure (high ground stress, high gas pressure, and high fissure water pressure), high temperature, and low permeability. Therefore, the core challenge in gas extraction through tunnels in deep coal seams lies in improving the permeability of the coal seam. Traditional permeability enhancement technologies are difficult to effectively enhance the permeability of coal seams with high ground stress, high gas pressure, and low permeability. First, single microwave permeability enhancement technology uses fixed-frequency microwave heating, resulting in uneven heating of the coal body. The fissures are concentrated around the borehole and are mostly isolated, short, and thin. The fissure opening is low and the extension is insufficient, making it impossible to form a through extraction channel. In addition, single directional jet technology requires high pressure of 30MPa or higher to break the coal body. The equipment has high energy consumption, and the jet energy is prone to diffuse into weak areas, which not only wastes energy but also easily causes the collapse of coal pores. Furthermore, the fissures are prone to close under high ground stress.

[0004] Although many engineering practices have adopted composite permeability enhancement technologies, such as microwave-hydraulic fracturing composite technology, hydraulic fracturing will cause a large amount of water to enter the coal body, causing the coal body to become muddy, and the fracturing fluid remaining in the coal body will trigger a water-locking effect, causing the coal seam permeability to decrease rapidly and the effective extraction period to be short. Summary of the Invention

[0005] The purpose of this invention is to solve the problems existing in the prior art, and to provide a deep coal seam permeability enhancement system and method based on microwave pre-splitting-directional jet expansion synergy.

[0006] This invention is achieved through the following technical solution:

[0007] One aspect of the present invention provides a deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet expansion synergy, comprising a high-pressure jet preparation system, a multi-frequency microwave generation system, and an intelligent monitoring and control system.

[0008] The high-pressure jet preparation system includes a water storage tank, a purification filter and sterilizer, an ultra-high pressure plunger pump, a high-frequency pressure stabilizer, a directional jet sleeve, and directional jet nozzles. The water storage tank is connected to the purification filter and sterilizer, the purification filter and sterilizer is connected to the ultra-high pressure plunger pump, the ultra-high pressure plunger pump is connected to the high-frequency pressure stabilizer, the high-frequency pressure stabilizer is connected to the directional jet sleeve, and the directional jet nozzles are evenly distributed on the directional jet sleeve on the section of the pipe located in the pre-acting coal seam.

[0009] The multi-frequency microwave generation system includes a multi-frequency microwave transmitter, a multi-frequency microwave power compensator, an inner microwave waveguide, and a microwave focusing radiator. The multi-frequency microwave transmitter and the multi-frequency microwave power compensator are connected, and the multi-frequency microwave power compensator is connected to the inner microwave waveguide. The microwave focusing radiator is evenly distributed on the inner microwave waveguide on the section of the pipe located in the pre-acting coal seam. The inner microwave waveguide and the directional jet sleeve adopt a nested structure, and the inner microwave waveguide is inserted and fixed inside the directional jet sleeve.

[0010] The intelligent monitoring and control system includes a PLC controller and sensors. The PLC controller is connected to the ultra-high pressure plunger pump, the multi-frequency microwave emission source, and the sensors.

[0011] As a preferred technical solution, in the high-pressure jet preparation system, the rated pressure of the ultra-high pressure plunger pump is 50MPa, and the output pressure is continuously adjustable to 22MPa and above; the directional jet sleeve is made of Φ60mm ultra-high strength alloy steel sleeve with a pressure resistance of ≥55MPa, the inner wall is sprayed with a wear-resistant layer to reduce flow resistance, and the outer wall is wrapped with a heat insulation layer; the directional jet nozzles are arranged in an array along the circumference of the directional jet sleeve, and a jet delivery pipe is installed along its length inside the directional jet sleeve. The jet delivery pipe is connected to the high-frequency pressure stabilizer, and the directional jet nozzles are connected to the jet delivery pipe.

[0012] As a preferred technical solution, in the multi-frequency microwave generator system, the output power of the multi-frequency microwave transmitter is continuously adjustable from 8 to 20 kW; the inner microwave waveguide is a Φ30mm gold-plated circular waveguide, and an insulating frame for limiting and fixing the conductor line is set inside. The microwave focusing radiator is evenly distributed on the outermost ring of the insulating frame, and the microwave focusing radiator is connected to the multi-frequency microwave power compensator through the conductor line.

[0013] As a preferred technical solution, in the intelligent monitoring and control system, the PLC controller adopts an industrial-grade dual-core PLC controller; the sensors include distributed stress sensors, temperature sensors, pressure sensors, and flow sensors, which are connected to the PLC controller through signal transmitters.

[0014] In another aspect, the present invention provides a permeability enhancement method for the aforementioned deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet expansion synergy, comprising the following steps:

[0015] 1) Construction of extraction wells:

[0016] Construction of extraction wells and lowering of gas extraction pipes.

[0017] 2) Directional drilling construction:

[0018] The drilling was carried out using an ultra-high pressure directional drilling rig, and the coal dust in the hole was cleaned using a gas-water mixed slag removal process. The directional jet casing and the inner microwave waveguide were lowered into the borehole as a whole, and the directional jet nozzle and the microwave focusing radiator were located in the pre-acting coal seam.

[0019] 3) Microwave seam creation:

[0020] Start the multi-frequency microwave generation system, first preheat the multi-frequency microwave transmitter for 10 minutes, and simultaneously turn on the multi-frequency microwave power compensator to ensure stable output power and frequency. Finally, radiate the pre-treated coal seam through the microwave focusing radiator at a preset frequency, and use the thermal shock effect of multi-frequency microwaves to generate initial cracks in the pre-treated coal seam, forming a microwave pre-fracture zone.

[0021] 4) Jet expansion joint:

[0022] The high-pressure jet preparation system is started. The water in the storage tank is filtered and sterilized by a purification filter and sterilizer. Then, an ultra-high pressure plunger pump is used to pressurize the water to an initial pressure of 20 MPa. The high-frequency pressure stabilizer is then used to adjust the directional jet pressure to a stable output to the jet delivery pipe inside the directional jet sleeve. Finally, the jet is ejected from the directional jet nozzle, precisely impacting the microwave pre-fracture zone, expanding the initial fracture opening, and promoting the formation of a network of transverse branch fractures.

[0023] 5) Collaborative Closure:

[0024] After the microwave slit creation and jet slit expansion are completed, the microwave power is first reduced to 5kW and maintained for 15 minutes, then the directional jet pressure is gradually reduced to 10MPa, and finally the equipment is shut down.

[0025] 6) Acceptance evaluation:

[0026] The concentration and flow rate of gas were tested through the gas extraction pipe and monitored continuously for 15 days. Once the permeability enhancement effect was confirmed to meet the standard, normal extraction operations were resumed.

[0027] As a preferred technical solution, in step 3) of the above-mentioned permeability enhancement method, the pre-treated coal seam is heated to 120~150℃ at a gradient heating rate of 10℃ / min, and the total microwave cracking time is 30min.

[0028] As a preferred technical solution, in step 4) of the above-mentioned anti-penetration method, the directional jet pressure is increased in a stepwise manner from 20MPa to 25MPa to 30MPa to 35MPa, with each step lasting 15 minutes, and the total jet expansion time lasting 60 minutes.

[0029] As a preferred technical solution, during the microwave fracture formation and jet fracture expansion process, intelligent monitoring and control system is used for intelligent monitoring. The system collects temperature, flow rate, pressure parameters and pre-acting coal seam stress distribution change signals through sensors, and transmits the collected signals to the PLC controller through a signal transmitter.

[0030] This invention is a permeability enhancement technology that combines microwave active fracture creation with directional jet targeted fracture expansion. It is suitable for deep coal seams and tunnels penetrating coal seams with burial depths of 800-1200m, high ground stress, and low permeability. Through the synergistic effect of "microwave multi-point synchronous preheating fracture creation + directional jet fracture expansion," it overcomes the bottleneck of deep coal seam permeability enhancement technology, solving the problems of insufficient initial fractures, inaccurate fracture expansion direction, and poor stability in traditional permeability enhancement technologies. This promotes the construction of fracture networks in deep coal seams and improves extraction efficiency.

[0031] This invention employs a four-level linkage system: "ground energy supply - downhole energy transmission - drilling operation - intelligent monitoring and control." It achieves innovation in coal seam permeability enhancement technology through the following three objectives: ① By combining "microwave multi-point synchronous preheating for fracture creation + directional jet fracture expansion," the permeability enhancement radius is expanded, maximizing fracture connectivity; ② Through an intelligent monitoring and control system, dynamic matching of permeability enhancement parameters with coal seam geological conditions is achieved; ③ The use of directional jets replaces traditional high-flow-rate hydraulic fracturing, saving water consumption, improving permeability enhancement accuracy, eliminating water-locking effects and borehole collapse, and enhancing safety.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1) Outstanding synergistic fracture creation and expansion effect: The synergistic effect of microwave multi-frequency fracture creation and directional jet expansion results in high fracture density, well-developed fracture network, and good connectivity.

[0034] 2) High long-term stability of fractures: The combined effect of thermal shock fracture creation and stepped fracture expansion stabilizes the fracture opening. The use of intelligent control can avoid coal seam disturbance caused by excessive parameters. The fracture closure rate is low and the extraction attenuation rate is low.

[0035] 3) Good construction safety and economy: The jet pressure is reduced by 30%~40% compared with traditional technology, the risk of borehole wall collapse is reduced, there is no groundwater pollution, the water lock effect is reduced, the equipment energy consumption is effectively reduced, and the labor cost is significantly reduced.

[0036] 4) High intelligence and adaptability: Multi-frequency microwave + stepped jet parameters can be adapted to coal seams with different burial depths and hardness. Intelligent control enables unmanned operation. The modular structure is conducive to step-by-step operation, step-by-step installation and maintenance. The device is directly connected to the extraction system, which has high reliability. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the overall structure of the system of the present invention.

[0039] Figure 2 This is a schematic diagram of the structure of the directional jet sleeve, directional jet nozzle, inner microwave waveguide, and microwave focusing radiator in the system of the present invention.

[0040] Figure 3 This is a schematic diagram of microwave slit creation in the anti-reflection method of the present invention.

[0041] Figure 4 This is a schematic diagram of the jet expansion in the anti-reflection method of the present invention.

[0042] In the diagram: 1-Water storage tank; 2-Purification filter and sterilizer; 3-Ultra-high pressure plunger pump; 4-High frequency pressure stabilizer; 5-Multi-frequency microwave transmitter; 6-Multi-frequency microwave power compensator; 7-PLC controller; 8-Signal transmitter; 9-Sensor; 10-Microwave fracture creation and jet fracture expansion; 11-Directional jet sleeve; 12-Directional jet nozzle; 13-Inner layer microwave waveguide; 14-Microwave focused radiator; 15-Pre-acting coal seam; 16-Insulation skeleton; 17-Jet delivery pipe; 18-Gas extraction well; 19-Coal seam roof; 20-Coal seam floor; 21-Multi-frequency microwave; 22-Initial fracture; 23-Directional jet fracture expansion. Detailed Implementation

[0043] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore merely examples and should not be used to limit the scope of protection of the present invention. It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art to which this invention pertains. Example 1

[0044] like Figure 1 and Figure 2 As shown, this embodiment provides a deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet expansion synergy, including: a high-pressure jet preparation system, a multi-frequency microwave generation system, and an intelligent monitoring and control system.

[0045] The high-pressure jet preparation system includes a water storage tank 1, a purification filter and sterilizer 2, an ultra-high pressure plunger pump 3, a high-frequency pressure stabilizer 4, a directional jet sleeve 11, and directional jet nozzles 12. The water storage tank 1 is connected to the purification filter and sterilizer 2, the purification filter and sterilizer 2 is connected to the ultra-high pressure plunger pump 3, the ultra-high pressure plunger pump 3 is connected to the high-frequency pressure stabilizer 4, the high-frequency pressure stabilizer 4 is connected to the directional jet sleeve 11, and the directional jet nozzles 12 are evenly distributed on the directional jet sleeve 11 on the section of the pre-acting coal seam 15. Specifically, the ultra-high pressure plunger pump 3 has a rated pressure of 50MPa and an output pressure of 20MPa and above that is continuously adjustable; the directional jet sleeve 11 is made of Φ60mm ultra-high strength alloy steel sleeve with a pressure resistance of ≥55MPa, the inner wall is coated with a wear-resistant layer to reduce flow resistance, and the outer wall is wrapped with a heat insulation layer; the directional jet nozzles 12 are arranged in an array along the circumference of the directional jet sleeve 11, and a jet delivery pipe 17 is provided along its length inside the directional jet sleeve 11. The jet delivery pipe 17 is connected to the high-frequency pressure stabilizer 4, and the directional jet nozzles 12 are connected to the jet delivery pipe 17. The directional jet nozzles 12 are made of boron nitride material to ensure that the jet is accurately applied to the microwave pre-crack area.

[0046] The multi-frequency microwave generation system includes a multi-frequency microwave transmitter 5, a multi-frequency microwave power compensator 6, an inner microwave waveguide 13, and a microwave focusing radiator 14. The multi-frequency microwave transmitter 5 and the multi-frequency microwave power compensator 6 are connected, and the multi-frequency microwave power compensator 6 is connected to the inner microwave waveguide 13. The microwave focusing radiator 14 is evenly distributed on the inner microwave waveguide 13 on the section of the pre-acting coal seam 15. The inner microwave waveguide 13 and the directional jet sleeve 11 adopt a nested structure, and the inner microwave waveguide 13 is inserted and fixed inside the directional jet sleeve 11. Specifically, the multi-frequency microwave generation system adopts a solid-state microwave source group, supports multi-frequency switching, and has an output power that is continuously adjustable from 8 to 20 kW. It is also equipped with a microwave reflector absorber to prevent energy reflection from damaging the equipment. The inner microwave waveguide 13 is a Φ30mm gold-plated circular waveguide with an insulating frame 16 inside for limiting and fixing the conductor lines. The microwave focusing radiator 14 is evenly distributed on the outermost ring of the insulating frame 16 to achieve precise focusing of microwave energy. The microwave focusing radiator 14 is connected to the multi-frequency microwave power compensator 6 through the conductor lines.

[0047] The intelligent monitoring and control system includes a PLC controller 7 and sensors 9. The PLC controller 7 is connected to the ultra-high pressure plunger pump 3, the multi-frequency microwave transmitter 5, and the sensors 9. Specifically, the PLC controller 7 adopts an industrial-grade dual-core PLC controller; the sensors 9 include stress sensors, temperature sensors, pressure sensors, and flow sensors. Among them, several temperature sensors are installed on the inner and outer walls of the pipeline before the flow split in the inner layer microwave waveguide 13 on the surface, and several temperature sensors are installed on the inner and outer walls of the inner layer microwave waveguide 13 located in the underground part of the permeability enhancement well; the flow sensors are installed on the inner wall of the directional jet casing 11, starting from the output of the directional jet from the high-frequency pressure stabilizer 4, with a set of flow sensors installed every 30m until the directional jet nozzle 12 in the underground part; the pressure sensor and stress sensor are installed on the outer wall of the directional jet casing 11 in the pre-acting coal seam 15 part, and on the inner wall of the gas extraction well 18, to monitor the gas extraction pressure and stress changes in the pre-acting coal seam 15; the stress sensor, temperature sensor, pressure sensor, and flow sensor are connected to the PLC controller 7 through a signal transmitter 8.

[0048] In this embodiment, the water storage tank 1, purification filter and sterilizer 2, ultra-high pressure plunger pump 3, high-frequency pressure stabilizer 4 in the high-pressure jet preparation system, and the multi-frequency microwave transmitter 5 and multi-frequency microwave power compensator 6 in the multi-frequency microwave generation system constitute the ground preparation unit. This unit serves as the core of energy and medium supply, providing stable microwave energy and high-pressure jet medium for the system. The directional jet casing 11 and directional jet nozzle 12 in the high-pressure jet preparation system, and the inner microwave waveguide 13 and microwave focusing radiator 14 in the multi-frequency microwave generation system constitute the downhole transmission unit. Its purpose is to achieve efficient transmission of microwave energy and jet medium within the same borehole and synergistic effect at the bottom of the borehole. The intelligent monitoring and control system aims to achieve real-time monitoring and dynamic control of coal seam stress and fracture parameters, ensuring safe and efficient permeability enhancement. Sensors 9 form a multi-parameter monitoring component, synchronously acquiring key parameters; the PLC controller 7 is the control core, achieving real-time data transmission and visual management via a 5G network, enabling remote control of the equipment, receiving signals from sensors 9, and using remote control to rapidly adjust microwave frequency, power, jet pressure, and flow rate. Example 2

[0049] like Figures 1 to 4 As shown, this embodiment provides a permeability enhancement method for a deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet fracture widening synergy, as described in Embodiment 1, including the following steps:

[0050] 1) Construction of extraction wells:

[0051] Construction was carried out on 18 gas extraction wells, and gas extraction pipes were lowered.

[0052] 2) Directional drilling construction:

[0053] The drilling was carried out using an ultra-high pressure directional drilling rig, and the coal dust in the hole was cleaned using a gas-water mixed slag removal process to form a permeability enhancement implementation well. The directional jet casing 11 and the inner microwave waveguide 13 were lowered into the permeability enhancement implementation well as a whole, so that the directional jet nozzle 12 and the microwave focusing radiator 14 were both located in the pre-acting coal seam 15.

[0054] 3) Microwave seam creation:

[0055] Start the multi-frequency microwave generation system, first preheat the multi-frequency microwave transmitter 5 for 10 minutes, and simultaneously turn on the multi-frequency microwave power compensator 6 to ensure stable output power and frequency. Finally, radiate the pre-treated coal seam 15 through the microwave focusing radiator 14 at a preset frequency. Utilize the thermal shock effect of the multi-frequency microwave to generate initial fractures (3-5 fractures) in the pre-treated coal seam 15, forming a microwave pre-fracture zone.

[0056] Specifically, the multi-frequency microwave generation system heats the pre-treated coal seam at a gradient heating rate of 10℃ / min to 15 to 120~150℃. The total microwave cracking time is 30 minutes. That is, when the temperature rises to 120~150℃, the microwave cracking time has not yet reached 30 minutes, so microwave cracking continues at this temperature until it reaches 30 minutes.

[0057] 4) Jet expansion joint:

[0058] The high-pressure jet preparation system is started. The water in the water tank 1 is filtered and sterilized by the purification filter sterilizer 2. Then, the water is pressurized to an initial pressure of 20 MPa by the ultra-high pressure plunger pump 3. The directional jet pressure is then adjusted by the high-frequency pressure stabilizer 4 to stabilize the output to the jet delivery pipe 17 in the directional jet sleeve 11. Finally, the water is ejected from the directional jet nozzle 12 to precisely impact the microwave pre-fracture zone, thereby expanding the initial fracture opening and promoting the formation of a network of transverse branch fractures.

[0059] Specifically, the directional jet pressure of the high-pressure jet preparation system is increased in stages from 20MPa to 25MPa to 30MPa to 35MPa, with each stage lasting 15 minutes, and the total jet expansion time lasting 60 minutes.

[0060] 5) Intelligent monitoring:

[0061] During the microwave fracture formation and jet fracture expansion process, intelligent monitoring and control system is used to collect temperature, flow rate, pressure parameters and stress distribution change signals of pre-acting coal seam 15 through sensor 9, and transmit the collected signals to PLC controller 7 through signal transmitter 8.

[0062] In practice, based on monitoring data, the PLC controller 7 optimizes and adjusts parameters such as microwave power and directional jet pressure. When the pre-acting coal seam 15 stress exceeds the critical value, the microwave power and directional jet pressure are reduced; when the fracture density is low (e.g., less than 3 fractures), the microwave power and directional jet pressure are increased; when the coal body temperature is high (e.g., above 150°C), the microwave frequency is reduced. The specific adjustment amounts mentioned above can be achieved by those skilled in the art based on actual conditions and in combination with conventional technical means in this field.

[0063] 6) Collaborative Closure:

[0064] After the microwave slit creation and jet slit expansion are completed, i.e., after a total action time of 90 minutes, the microwave power is first reduced to 5kW and maintained for 15 minutes, then the directional jet pressure is gradually reduced to 10MPa, and finally the equipment is shut down.

[0065] 7) Acceptance evaluation:

[0066] The concentration and flow rate of gas were tested through the gas extraction pipe and monitored continuously for 15 days. Once the permeability enhancement effect was confirmed to meet the standard, normal extraction operations were resumed.

[0067] Figure 1 This is a schematic diagram of a deep coal seam permeability enhancement system based on microwave pre-fracture and directional jet expansion. The blue part in the diagram represents the directional jet effect, and the red part represents the microwave effect. Ultimately, microwave fracturing and jet expansion 10 are formed in the pre-treated coal seam 15. Figure 3 This is a schematic diagram of microwave fracture creation in the permeability enhancement method. The microwave focusing radiator 14 in the diagram emits multi-frequency microwaves 21. The thermal shock effect of the multi-frequency microwaves 21 causes the pre-treated coal seam 15 to generate initial fractures 22, forming a microwave pre-fracture zone. Figure 4 The diagram shows a jet expansion method for enhancing penetration. The directional jet nozzle 12 ejects a jet that precisely impacts the microwave pre-fracture zone, causing the initial fracture 22 to expand and form a directional jet expansion fracture 23, which in turn promotes the formation of a network of transverse branch fractures. Example 3

[0068] In this embodiment, the No. 25 coal seam of a certain mine with a burial depth of 1200m is used as an example. This coal seam is a typical deep coal seam that is extremely difficult to extract. The permeability coefficient is 0.0002m² / (MPa²·d), the ground stress is 55MPa, the coal body is solid, and the gas pressure and content are high.

[0069] Based on Examples 1 and 2, the anti-reflection system is used for anti-reflection construction, which specifically includes the following steps:

[0070] 1) Construction of extraction wells: Construction of 18 gas extraction wells and lowering of gas extraction pipes.

[0071] 2) Directional drilling construction: Ultra-high pressure directional drilling rigs are used for drilling, and gas-water mixed slag removal process is used to clean coal dust in the hole and conduct sealing and pressure resistance tests; various parameter sensors are calibrated and installed.

[0072] 3) System settings: Set the multi-frequency microwave generation system to 5.8GHz intermediate frequency microwave and pre-action temperature to 120℃; simultaneously, set the high-pressure jet preparation system to an initial jet pressure of 20MPa and a step-up pressure of 35MPa; simultaneously, set the intelligent monitoring and control system to an intelligent control threshold of stress of 60MPa and temperature of 160℃.

[0073] 4) System preheating and pressure adjustment: Start the multi-frequency microwave generation system and the high-pressure jet preparation system, and perform system preheating and jet pressure adjustment respectively. Use the multi-frequency microwave power compensator and the high-frequency pressure stabilizer to adjust the microwave frequency and jet pressure to stabilize.

[0074] 5) Lowering the downhole transmission unit: The directional jet casing 11 and the inner microwave waveguide 13 are lowered into the borehole as a whole, so that the directional jet nozzle 12 and the microwave focusing radiation head 14 are both located in the pre-acting coal seam 15 between the coal seam roof 19 and the coal seam floor 20.

[0075] 6) Microwave seam creation: Start the multi-frequency microwave generation system, directionally irradiate the coal seam 15 at the preset frequency, heat the coal body to 120℃ at a gradient heating rate of 10℃ / min, and continue to act for 30min;

[0076] 7) Jet expansion: Start the ultra-high pressure jet, and increase the directional jet pressure in a stepwise manner from 20MPa to 25MPa to 30MPa to 35MPa, increasing the pressure to 35MPa. Each step lasts for 15 minutes, and the process continues for 60 minutes.

[0077] 8) Monitor and adjust the parameters and stress distribution of each sensor using the PLC controller 7.

[0078] 9) After 90 minutes of synergistic action, reduce the microwave power to 5kW and maintain it for 15 minutes, then gradually reduce the jet pressure to 10MPa and turn off the equipment.

[0079] 10) Test the gas extraction concentration and flow rate through the gas extraction pipe, monitor continuously for 15 days, and switch to normal extraction operation after confirming that the permeability enhancement effect meets the standard.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A permeability enhancement method for deep coal seams based on a microwave pre-fracture-directional jet fracture widening synergy system, characterized in that: The deep coal seam permeability enhancement system based on microwave pre-splitting and directional jet expansion includes a high-pressure jet preparation system, a multi-frequency microwave generation system, and an intelligent monitoring and control system. The high-pressure jet preparation system includes a water tank (1), a purification filter sterilizer (2), an ultra-high pressure plunger pump (3), a high-frequency pressure stabilizer (4), a directional jet sleeve (11), and directional jet nozzles (12). The water tank (1) is connected to the purification filter sterilizer (2), the purification filter sterilizer (2) is connected to the ultra-high pressure plunger pump (3), the ultra-high pressure plunger pump (3) is connected to the high-frequency pressure stabilizer (4), the high-frequency pressure stabilizer (4) is connected to the directional jet sleeve (11), and the directional jet nozzles (12) are evenly distributed on the directional jet sleeve (11) on the pipe section located in the pre-acting coal seam (15). A jet delivery pipe (17) is installed along its length inside the directional jet sleeve (11), and the jet delivery pipe (17) is connected to the high-frequency pressure stabilizer (4). The directional jet nozzle (12) is connected to the jet delivery pipe (17); the multi-frequency microwave generation system includes a multi-frequency microwave emission source (5), a multi-frequency microwave power compensator (6), an inner microwave waveguide (13), and a microwave focusing radiator (14); the multi-frequency microwave emission source (5) and the multi-frequency microwave power compensator (6) are connected, the multi-frequency microwave power compensator (6) is connected to the inner microwave waveguide (13), and the microwave focusing radiator (14) is evenly distributed on the inner microwave waveguide (13) on the pipe section located in the pre-acting coal seam (15); the inner microwave waveguide (13) and the directional jet sleeve (11) adopt a nested structure, and the inner microwave waveguide (13) is inserted and fixed in the directional jet sleeve (11); the intelligent monitoring and control system includes a PLC controller (7) and a sensor (9), the PLC controller (7) is connected to the ultra-high pressure plunger pump (3), the multi-frequency microwave emission source (5), and the sensor (9) respectively; The permeability enhancement method of the deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet fracture expansion synergy includes the following steps: 1) Construction of extraction wells: Construct gas extraction well (18) and lower gas extraction pipe; 2) Directional drilling construction: The drilling was carried out using an ultra-high pressure directional drilling rig, and the coal dust in the hole was cleaned using a gas-water mixed slag removal process. The directional jet casing (11) and the inner microwave waveguide (13) were lowered into the borehole as a whole, and the directional jet nozzle (12) and the microwave focusing radiation head (14) were both located in the pre-acting coal seam (15). 3) Microwave seam creation: Start the multi-frequency microwave generator system, first preheat the multi-frequency microwave transmitter (5) for 10 minutes, and simultaneously turn on the multi-frequency microwave power compensator (6) to ensure stable output power and frequency. Finally, radiate the pre-acted coal seam (15) at a preset frequency through the microwave focusing radiator (14). Utilize the thermal shock effect of the multi-frequency microwave (21) to generate initial cracks (22) in the pre-acted coal seam (15) and form a microwave pre-crack zone. 4) Jet expansion joint: The high-pressure jet preparation system is started. The water in the water tank (1) is filtered and sterilized by the purification filter sterilizer (2). Then, the water is pressurized to the initial pressure of 20MP by the ultra-high pressure plunger pump (3). The directional jet pressure is then adjusted by the high-frequency pressure stabilizer (4) to be output to the jet delivery pipe (17) in the directional jet sleeve (11). Finally, it is ejected from the directional jet nozzle (12) to accurately impact the microwave pre-crack zone, so that the opening of the initial crack (22) expands and promotes the formation of a network of transverse branch cracks. 5) Collaborative Closure: After the microwave slit creation and jet slit expansion are completed, the microwave power is first reduced to 5kW and maintained for 15 minutes, then the directional jet pressure is gradually reduced to 10MPa, and finally the equipment is turned off. 6) Acceptance evaluation: The concentration and flow rate of gas were tested through the gas extraction pipe and monitored continuously for 15 days. Once the permeability enhancement effect was confirmed to meet the standard, normal extraction operations were resumed.

2. The permeability enhancement method of a deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet fracture widening synergy as described in claim 1, characterized in that: In the high-pressure jet preparation system, the rated pressure of the ultra-high pressure plunger pump (3) is 50MPa, and the output pressure is continuously adjustable to 20MPa and above; the directional jet sleeve (11) is made of Φ60mm ultra-high strength alloy steel sleeve with a pressure resistance of ≥55MPa, the inner wall is sprayed with a wear-resistant layer to reduce flow resistance, and the outer wall is wrapped with a heat insulation layer; the directional jet nozzles (12) are arranged in an array along the circumference of the directional jet sleeve (11), and a jet delivery pipe (17) is installed along its length inside the directional jet sleeve (11). The jet delivery pipe (17) is connected to the high-frequency pressure stabilizer (4), and the directional jet nozzles (12) are connected to the jet delivery pipe (17).

3. The permeability enhancement method of a deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet fracture expansion synergy as described in claim 2, characterized in that: In the multi-frequency microwave generation system, the output power of the multi-frequency microwave transmitter (5) is continuously adjustable from 8 to 20 kW; the inner microwave waveguide (13) adopts a Φ30mm gold-plated circular waveguide, and an insulating frame (16) for limiting and fixing conductor lines is set inside. The microwave focusing radiator (14) is evenly distributed on the outermost ring of the insulating frame (16), and the microwave focusing radiator (14) is connected to the multi-frequency microwave power compensator (6) through the conductor line.

4. The permeability enhancement method of a deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet fracture widening synergy as described in claim 3, characterized in that: In the intelligent monitoring and control system, the PLC controller (7) adopts an industrial-grade PLC dual-core controller; the sensors (9) include stress sensors, temperature sensors, pressure sensors and flow sensors. The stress sensors, temperature sensors, pressure sensors and flow sensors are connected to the PLC controller (7) through a signal transmitter (8).

5. The permeability enhancement method of a deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet fracture expansion synergy as described in claim 1, characterized in that: In step 3), the multi-frequency microwave generator heats the pre-treated coal seam (15) to 120~150℃ at a gradient heating rate of 10℃ / min, and the total microwave cracking time lasts for 30min.

6. The permeability enhancement method of a deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet fracture expansion synergy as described in claim 1, characterized in that: In step 4), the directional jet pressure of the high-pressure jet preparation system is increased in a stepwise manner from 20MPa to 25MPa to 30MPa to 35MPa, with each step lasting 15 minutes, and the total jet expansion time lasting 60 minutes.

7. The permeability enhancement method of a deep coal seam permeability enhancement system based on microwave pre-fracture-directional jet fracture widening synergy as described in claim 1, characterized in that: During the microwave seam making and jet seam expansion process, intelligent monitoring is carried out through an intelligent monitoring and control system. The temperature, flow rate, pressure parameters and stress distribution change signals of the pre-acting coal seam (15) are collected by the sensor (9), and the collected signals are transmitted to the PLC controller (7) through the signal transmitter (8).

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