Method and system for coal bed methane exploitation and separation and utilization based on frequency-converted acoustic wave assistance

Abstract

This invention discloses a method and system for coalbed methane extraction and separation based on variable frequency acoustic wave assistance, belonging to the field of unconventional natural gas development and low-carbon utilization technology. A piezoelectric ceramic vibrator is driven by an acoustic wave frequency stabilizer generator to apply three frequency-modulated acoustic waves—38-42Hz low frequency, 58-62Hz medium frequency, and 75-80Hz high frequency—to the coal seam, stimulating coal resonance, expanding fractures, and enhancing reagent seepage. Simultaneously, an isopropanol-based solution containing a slow-release self-heating agent is injected into the injection well, along with 8.2MPa supercritical carbon dioxide to displace the coalbed methane. The extracted gas undergoes two-stage cyclone separation, amine desulfurization, and condensation dehydration, followed by high-purity methane and CO2 separation via a polyimide hollow fiber membrane. The CO2 is purified by a molecular sieve membrane and then recycled back into the system. Low-calorific-value impurities are used for catalytic power generation, and tail gas is reinjected into the goaf. The system is equipped with intelligent monitoring and safety control, achieving integrated operation of efficient coalbed methane extraction, gas purification, resource recycling, and safety, significantly improving the recovery rate and resource utilization rate of low-permeability coalbed methane.

Description

Technical Field

[0001] This invention relates to the field of unconventional natural gas development and low-carbon utilization technology, and in particular to a method and system for coalbed methane extraction and separation based on variable frequency acoustic wave assistance, applicable to CO2-driven coalbed methane multiphase enhanced gas extraction, separation and utilization based on variable frequency acoustic wave-chemical synergistic excitation. Background Technology

[0002] Coalbed methane (CBM) resources are abundant, but due to geological conditions such as low permeability and uneven fracture development in coal seams, the resource recovery rate of existing mining technologies is generally low, and a large amount of high-quality CBM resources have long remained undeveloped within the coal matrix. This not only causes serious energy waste but also leads to a significant increase in safety risks such as gas exceedances and outbursts during coal mining. Furthermore, the direct emission of untreated CBM generates a strong greenhouse effect, posing a dual burden on the ecological environment. Therefore, developing efficient, safe, and low-carbon CBM extraction and separation technologies is of great practical significance for improving energy efficiency, ensuring coal mining safety, and promoting the achievement of "dual-carbon" goals.

[0003] Traditional coalbed methane extraction technologies, such as vertical well fracturing and horizontal well open-hole completion, generally suffer from core drawbacks. Vertical well fracturing has limited effectiveness in modifying low-permeability, tight coal seams, and the obstructed desorption-diffusion-seepage pathways for coalbed methane result in low well production, long extraction cycles, and poor economic returns. While horizontal well open-hole completion can expand the drainage area, it is limited by a single physical modification method, making it difficult to achieve deep expansion and connectivity of coal seam fractures, and it is prone to problems such as excessively rapid energy decay in the gas reservoir. In addition, traditional technologies often lack efficient means of separating and recovering produced gases, making it difficult to guarantee methane purity and failing to recycle carbon dioxide, which reduces resource value and increases environmental emissions.

[0004] Supercritical CO2 combines the high solubility of liquids with the high diffusivity of gases. After being injected into coal seams, it can efficiently replace the methane adsorbed by the coal matrix and has a significant coal seam permeability enhancement effect. Meanwhile, variable frequency sound waves can stimulate the development of coal seam fractures through resonance. Combined with specific chemical agents, it can further enhance fracture connectivity and agent penetration. The three work together to form a composite mechanism of "physical excitation-chemical permeability enhancement-fluid displacement".

[0005] Given the current technological bottlenecks and industry demands in coalbed methane extraction, there is an urgent need for a collaborative innovation method that integrates the advantages of variable frequency acoustic waves, chemical agents, and supercritical CO2 to optimize the entire process of efficient desorption, enhanced extraction, precise separation, and recycling of coalbed methane. This would improve the level of coalbed methane resource development and utilization, and promote the low-carbon and sustainable development of the unconventional natural gas industry. Summary of the Invention

[0006] Technical Problem: The purpose of this invention is to overcome the technical bottlenecks in traditional coalbed methane extraction, such as low desorption-seepage efficiency of low-permeability coalbed methane, insufficient gas separation purity, low carbon dioxide recycling rate, and uneven expansion and poor connectivity of coal seam fractures. This invention provides a method and system for coalbed methane extraction and separation based on variable frequency acoustic wave assistance. Through the synergistic effect of supercritical CO2 displacement and permeability enhancement, the fracture excitation effect of variable frequency acoustic waves, and the penetration enhancement effect of chemical agents, efficient desorption, precise separation, and CO2 recycling of coalbed methane are achieved, simultaneously improving resource development efficiency, product purity, and low-carbon benefits.

[0007] Technical solution: To achieve the above objectives, the present invention provides a method for coalbed methane extraction and separation based on frequency conversion acoustic wave assistance, comprising the following steps: (a) Based on the geological structure map of the coal seam, the distribution characteristics of the coalbed methane reservoir and the development plan, after determining the spatial location of the injection well and the gas production well on the ground, drilling should be carried out in a flat area with a topographic slope of <12°, avoiding fault fracture zones, groundwater bodies and areas with potential geological hazards, and ensuring that the well site covers an area of ​​≥1800m². (b) Dedicated equipment is installed on the ground around the injection well and the gas production wellhead; the raw material CO2 is stored in the carbon dioxide storage tank in the dedicated equipment, the temperature is adjusted to 31.1-75℃ by the carbon dioxide heating equipment, and then pressurized to 8.2MPa supercritical state by the booster injection pump; the carbon dioxide storage tank is designed with a pressure ≥30MPa, the volume is determined to be 200m³ according to the daily injection volume, and is equipped with a pressure warning device that automatically starts the pressure relief program when the pressure exceeds 5%; (c) Open the nitrogen cylinder group in the special equipment, and at the same time start the three-component solid-liquid mixing tank equipped with an ultrasonic dispersion device. Mix the isopropanol-based carrier liquid, surface-oxidized and passivated aluminum powder particles, and CuO powder coated with an 80nm silane film in a molar ratio of 1:1.5:1. The stirring speed is controlled at 300-500r / min, the mixing time is ≥30min, and the mixing uniformity is ensured to be ≥98%. The nitrogen doping ratio is controlled to be 2-4% by the nitrogen mass flow meter, the nitrogen-copper oxide mixed fluid mass flow meter, and the isopropanol-based carrier liquid mass flow meter in the special equipment, so that it can be fully integrated with supercritical CO2 and mixed agents in the static mixing section. (d) The fully mixed fluid from the static mixing section is pressurized to 10-18 MPa by a permeation enhancer injection pump in a special device. The parameters are monitored in real time by the injection fluid temperature and pressure monitoring device. The fluid is injected into the injection well at a rate of 1-4 m³ / h. Simultaneously, the acoustic wave frequency generator is started to drive the piezoelectric ceramic vibrator to emit segmented frequency-modulated acoustic waves: 38-42 Hz low frequency band for 8 minutes, 58-62 Hz mid frequency band for 25 minutes, and 75-80 Hz high frequency band for continuous operation until the injection is completed. The acoustic wave power is controlled at 8-12 kW. Vibration expands the coal seam fractures and promotes the penetration of the agent. (e) The mixed gas produced from the gas well is extracted by the extraction pump and first enters the primary cyclone separator to remove solid particles with a diameter >20μm. Then it is deeply filtered by the secondary cyclone separator with a filtration accuracy of 2μm. Subsequently, it enters the gas capture tower and is desulfurized and impurities removed by MDEA amine liquid adsorption method. The concentration of MDEA amine liquid is 25-30%, and the liquid-to-gas ratio is controlled at 20-25L / m³. The waste liquid generated by filtration is discharged into the waste liquid pool for centralized treatment. (f) The desulfurized and impurity-removed gas enters the gas condensation and dehydration equipment, where the temperature is reduced to 3-6℃ to achieve condensation and dehydration. The dew point of the dehydrated gas is ≤-40℃. The dried gas enters the polyimide hollow fiber membrane gas separation tower. Utilizing the excellent gas separation characteristics of polyimide material, the separation of methane and carbon dioxide with a purity ≥98% is completed under the conditions of pressure 3-5MPa and temperature 35-45℃ in the operating tower. (g) Real-time control of the entire process is achieved through the signal processing console in the dedicated equipment. The distributed fiber optic sensors in the injection well are spirally laid along the well wall with a spacing of ≤4m to monitor the temperature and pressure stability of the injected fluid and the response of the coal seam fracture. They are connected in series with carbon dioxide anti-high pressure stop switches and nitrogen cylinder group anti-high pressure stop switches. The proportion of produced gas components is detected in real time by a TDLAS laser spectrometer on the gas production well side. The first-level laser scattering sensor and the second-level laser scattering sensor monitor the particle residue. The infrared temperature sensor and piezoelectric accelerometer of the integrated spectrometer collect the equipment operating parameters. All data are transmitted to the signal processing console and the injection well signal processing system. When the parameters are abnormal, the gas production well stop switch is triggered to ensure the safe operation of the system. (h) The methane separated in step (f) is pressurized to 2-4 MPa by a self-priming diaphragm compressor in a dedicated device and transported to a CH4 self-pressurized gas storage tank for later use; the separated carbon dioxide enters the carbon dioxide storage tank after separation and is buffered, and then purified by a spiral wound DD3R carbon dioxide molecular sieve membrane to a CO2 purity of ≥99%. It is then pressurized to the injection pressure by a spiral wound compressor, and after depressurization and cooling, the temperature is adjusted by a supercritical carbon dioxide temperature control device before being returned to the carbon dioxide storage tank for recycling; the low-calorific-value impurities generated by separation are introduced into a steam turbine for catalytic combustion, with an inlet steam pressure of 4-6 MPa and a power generation efficiency of ≥32%, which drives the battery pack for energy storage. The exhaust gas (CO2+H2O) after combustion is stored in the after-combustion impurity gas storage tank and finally reinjected into the goaf.

[0008] In step (a), the distance between the injection well and the gas production well is adjusted according to the coal seam permeability. The distance between the wells is reduced to 30-50m in areas with permeability below 0.08mD, and the distance between the wells with permeability of 0.08-0.5mD is set to 60-80m. A fire lane with a width of ≥5m must be set up at the well site and equipped with a foam fire extinguishing system. Flammable, explosive and corrosive materials are prohibited from being piled up within 80m of the well site.

[0009] In step (b), the carbon dioxide storage tank is made of 316L stainless steel with polished inner wall and a polishing degree Ra≤0.6μm; the injection well is equipped with a P110 grade casing with a casing wall thickness ≥14.5mm; the cementing in the injection well is brought up to 60m below the surface; the cement slurry density is controlled at 1.90-2.00g / cm³; and the setting time is ≥72h to ensure the wellbore sealing.

[0010] In step (c), the three-component solid-liquid mixing tank equipped with an ultrasonic dispersion device is equipped with a CS-3000 ultrasonic dispersion device with a dispersion power of 1500-3000W, ensuring that the suspension stability of aluminum powder and CuO powder in the carrier liquid is ≥96h; the outlet of the nitrogen cylinder group is equipped with a pressure reducing and stabilizing valve, and the output pressure is stable at 0.8-1.2MPa. The nitrogen mass flow meter has a measurement accuracy of ±0.3%, accurately controlling the proportion of each medium.

[0011] In step (e), both the primary cyclone separator and the secondary cyclone separator adopt a tangential inlet design with a separation efficiency of ≥98%; the gas capture tower is equipped with a multi-layer spray device with a gas-liquid contact time of ≥4s.

[0012] In step (f), the gas condensation and dehydration equipment adopts a vortex refrigeration unit with a cooling capacity of 80-120kW and a cooling rate of ≥5℃ / min; the single-strand polyimide hollow fiber membrane has an area of ​​≥60m², and is backwashed with dry nitrogen once a month during operation, with a backwashing pressure of 0.6-0.9MPa and a backwashing time of 15-20min each time.

[0013] In step (g), the bending radius of the distributed optical fiber sensor in the injection well is ≥35mm, and the attenuation rate is ≤0.15dB / km when the signal transmission distance is ≤15km; the measurement accuracy of the TDLAS laser spectrometer is ≤±0.1%, and it can monitor the changes in CH4 and CO2 component concentrations in real time, with a data wireless transmission delay of ≤0.5s.

[0014] In step (h), the spiral wound DD3R carbon dioxide molecular sieve membrane adopts a three-layer composite structure, with a honeycomb guide net between each layer of membrane to improve the gas permeation rate; the spiral wound compressor is divided into four stages of compression, with an exhaust temperature ≤90℃, a lubricating oil flash point ≥220℃, and the filter element is replaced every 800 hours of operation to ensure that the oil content of the compressed gas is ≤3ppm.

[0015] A system for implementing the above-mentioned method for coalbed methane extraction and separation based on variable frequency acoustic wave assistance includes a dedicated device arranged on the ground outside the injection well and the gas production wellhead. The dedicated device includes an injection subsystem, a downhole acoustic wave excitation subsystem, a gas production and processing subsystem, a separation and recovery subsystem, and an intelligent monitoring subsystem. The injection subsystem includes a carbon dioxide storage tank, a carbon dioxide heating device, a booster injection pump, a nitrogen cylinder group, a copper oxide powder storage tank, a three-component solid-liquid mixing tank equipped with an ultrasonic dispersion device, an isopropyl alcohol-based carrier liquid stirring tank, an open-air aluminum particle storage area, and a permeation agent injection pump. The carbon dioxide storage tank is connected to the carbon dioxide heating device via a carbon dioxide anti-high pressure switch. The carbon dioxide heating device is connected to the booster injection pump, which is connected to the injection well via a pipeline. The outlet of the permeation agent injection pump is connected to the injection well via a pipeline. The inlet of the permeation agent injection pump is connected to the bottom of the three-component solid-liquid mixing tank equipped with an ultrasonic dispersion device via a multi-parameter A transmitter. The nitrogen cylinder group is connected to one inlet of the copper oxide powder storage tank and the three-component solid-liquid mixing tank equipped with an ultrasonic dispersion device via pipelines. The isopropyl alcohol-based carrier liquid stirring tank and the open-air aluminum particle storage area are respectively connected to the two inlets of the three-component solid-liquid mixing tank equipped with an ultrasonic dispersion device via pipelines. The downhole acoustic excitation subsystem includes a piezoelectric ceramic vibrator installed in the injection well, an acoustic frequency stabilizing generator connected to the piezoelectric ceramic vibrator via a piezoelectric accelerometer, and the acoustic frequency stabilizing generator being connected to a signal processing control console. The gas production and processing subsystem includes a pump connected to the gas production well, a primary cyclone separator, a secondary cyclone separator, a gas collection tower, a waste liquid discharge pool, and a gas condensation and dehydration device; the pump is connected to the primary cyclone separator, the secondary cyclone separator, the gas collection tower, and the gas condensation and dehydration device in sequence via pipelines, and the bottom of the gas condensation and dehydration device is connected to the waste liquid pool. The separation and recovery subsystem includes a polyimide hollow fiber membrane gas separator, a separated carbon dioxide storage tank, a steam turbine, a post-combustion impurity gas storage tank, a self-priming diaphragm compressor, a CH4 self-pressurized gas storage tank, a spiral-wound DD3R carbon dioxide molecular sieve membrane, a spiral-wound compressor, and a supercritical carbon dioxide temperature control device after pressure reduction and cooling. The lower side of the polyimide hollow fiber membrane gas separator is connected to a gas condensation and dehydration device via a pipeline; the other lower side is connected to the steam turbine and the post-combustion impurity gas storage tank via pipelines; the middle section is connected to the separated carbon dioxide storage tank, the spiral-wound DD3R carbon dioxide molecular sieve membrane, the spiral-wound compressor, and the supercritical carbon dioxide temperature control device after pressure reduction and cooling connected to the carbon dioxide storage tank via pipelines; the upper section is connected to the self-priming diaphragm compressor and the CH4 self-pressurized gas storage tank via pipelines. The intelligent monitoring subsystem includes an infrared thermal sensor, a piezoelectric accelerometer, a signal processing console, an injection well signal processing system, a TDLAS laser spectrometer, a primary laser scattering sensor, a secondary laser scattering sensor, an infrared temperature sensor integrated with the spectrometer, and a gas well anomaly detection switch. The temperature signal collected by the infrared thermal sensor is transmitted to the injection well signal processing system. Vibration, gas composition, fluid impurities, and temperature and spectral composite signals collected by the piezoelectric accelerometer, TDLAS laser spectrometer, primary laser scattering sensor, secondary laser scattering sensor, and infrared temperature sensor integrated with the spectrometer are all transmitted to the signal processing console. The signal processing console transmits the analysis results to the injection well signal processing system and simultaneously outputs anomaly control commands to the gas well anomaly detection switch. The injection well signal processing system outputs control commands to the relevant actuators of the injection well based on the received temperature data and linkage analysis results.

[0016] Beneficial Effects: By adopting the above-mentioned technical solution, this invention overcomes the problems of low permeability, insufficient separation efficiency, low carbon dioxide utilization, and uneven fracture development in traditional coalbed methane extraction. Through the synergistic effect of supercritical carbon dioxide and nano-nitrogen combined with acoustic diffusion technology, it achieves efficient extraction and recycling of coalbed methane. This invention first stores supercritical CO2 in a high-pressure storage tank, and simultaneously configures a composite chemical system containing a carrier liquid, copper oxide, and aluminum powder. Utilizing the characteristic of the permeation enhancer to reduce methane adsorption, it improves fluid permeability and gas desorption efficiency. The mixture of supercritical CO2, nitrogen, and composite chemical agents is injected into the coal seam via a manifold injection system. Simultaneously, a multi-frequency acoustic wave device is used to emit multi-band acoustic waves. The low-frequency band excites micro-fractures in the coal seam, while the mid-to-high-frequency band enhances fracture connectivity and displacement, forming a synergistic mechanism of "chemical permeation enhancement - acoustic fracturing - supercritical displacement." After two-stage solid-liquid separation, amine desulfurization, and deep dehydration pretreatment at the gas extraction end, a separation technology coupling polyimide hollow fiber membrane and spiral-wound DD3R carbon dioxide molecular sieve membrane precisely separates the extracted gas into high-purity methane, recyclable CO2, and low-calorific-value miscellaneous gases. The methane is pressurized and stored, then directly utilized as clean energy. The purified CO2 is injected into the coal seam in a closed loop for reuse. The miscellaneous gases are used to generate electricity via a steam turbine for energy recovery. This achieves full-process optimization of efficient coalbed methane extraction, precise separation, and cascaded resource utilization, significantly improving the efficiency, purity, and low-carbon benefits of coalbed methane development. By utilizing the high permeability of supercritical carbon dioxide and the synergistic displacement effect of nitrogen, combined with acoustic vibration to improve coal seam fracture development, the desorption efficiency of coalbed methane is significantly improved. Furthermore, through multi-stage purification and high-precision membrane separation technology, efficient separation of methane and carbon dioxide and recycling of carbon dioxide are achieved, reducing carbon emissions while improving resource utilization. The main advantages compared to existing technologies are: ① The synergistic effect of supercritical carbon dioxide and nano nitrogen combined with acoustic diffusion technology can increase coal seam permeability by more than 30%, significantly improving coalbed methane extraction efficiency. ② The separation system with integrated molecular sieve membranes achieves methane purity ≥98% and carbon dioxide recovery rate ≥90%, significantly improving resource utilization; ③ The carbon dioxide recycling injection model reduces greenhouse gas emissions by more than 80%, which is in line with the concept of low-carbon development; ④ The full-process intelligent monitoring and automatic control system ensures the safety of system operation, extends the service cycle of a single well by 2-3 years, and increases the cumulative gas production efficiency by more than 40%. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the arrangement of the CO2 coalbed methane-driving device assisted by frequency conversion acoustic wave according to the present invention.

[0018] Figure 2 This is a general technical route diagram for the variable frequency acoustic wave-assisted CO2-driven coalbed methane treatment of the present invention.

[0019] Figure 3 This is a schematic diagram of the process of CO2-assisted coalbed methane extraction using frequency conversion acoustic wave assisted by the present invention.

[0020] In the diagram: 1-Ground surface; 2-Carbon dioxide storage tank; 3-Carbon dioxide high-pressure anti-abnormal switch; 4-Carbon dioxide heating equipment; 5-Boost injection pump; 6-Temperature and pressure control switch; 7-Lithium iron phosphate battery pack; 8-Injection well; 9-Injection well distributed fiber optic sensor; 10-Piezoelectric ceramic vibrator; 11-Infrared thermal sensor; 12-Injection well signal cabinet; 13-Injection well signal processing system; 14-Nitrogen cylinder group; 15-Nitrogen cylinder group high-pressure anti-abnormal switch; 16-Nitrogen mass flow meter; 17-Copper oxide powder storage tank; 18-Nitrogen-copper oxide mixed fluid mass flow meter; 19-Isopropanol-based carrier liquid mass flow meter; 20-Aluminum powder mass flow meter; 21-Three-component solid-liquid mixing tank equipped with ultrasonic dispersion device; 22-A multi-parameter transmitter; 23-Piezoelectric accelerometer; 24-Acoustic wave frequency stabilizer generator; 25-Signal processing control console; 26-Gas well signal cabinet; 27-TDLAS laser spectrum. Instrument; 28-Gas well; 29-First-stage cyclone separator; 30-Second-stage cyclone separator; 31-First-stage laser scattering sensor; 32-Second-stage laser scattering sensor; 33-B multi-parameter transmitter; 34-Gas trapping tower; 35-Waste liquid tank; 36-Gas condensation and dehydration equipment; 37-Polyimide hollow fiber membrane gas separator; 38-Infrared temperature sensor of integrated spectrometer; 39-Separated carbon dioxide storage tank; 40-Steam turbine; 41- 42-Post-combustion impurity gas storage tank; 43-Self-priming diaphragm compressor; 44-CH4 self-pressurized gas storage tank; 45-Separated carbon dioxide high-pressure switch; 46-Roll-wound DD3R carbon dioxide molecular sieve membrane; 47-Isopropanol-based carrier liquid stirring tank; 48-Roll-wound compressor; 49-Supercritical carbon dioxide temperature control equipment after pressure reduction and cooling; 50-Battery pack; 51-Gas well anti-abnormality switch; 52-Aluminum particle open-pit storage yard; 53-Permeability enhancement agent injection pump; 54-Drawdown pump. Detailed Implementation

[0021] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings: The method for coalbed methane extraction and separation based on frequency conversion acoustic wave assistance of the present invention comprises the following specific steps: (a) Based on the coal seam geological structure map, coalbed methane reservoir distribution characteristics and development plan, after determining the spatial location of injection well 8 and gas production well 28 on the surface 1, drilling will be carried out. The horizontal distance between the two wells will be controlled at 30-80m according to the coal seam permeability classification, and the vertical depth difference will not exceed 12m. The drilling area will be selected in a flat area with a topographic slope of <12°, avoiding fault fracture zones, groundwater bodies and geological disaster hazard areas, and ensuring that the well site area is ≥1800m². The foundation bearing capacity is ≥300kPa to meet the equipment layout and long-term operation and maintenance needs of the five major systems of gas injection, gas production, separation, circulation and monitoring. The distance between the injection well 8 and the gas production well 28 is adjusted according to the coal seam permeability. The distance between areas with a permeability lower than 0.08mD is reduced to 30-50m, and the distance between areas with a permeability of 0.08-0.5mD is set to 60-80m. A fire lane with a width of ≥5m must be set up at the well site and equipped with a foam fire extinguishing system. Flammable, explosive and corrosive materials are prohibited from being piled up within 80m of the well site.

[0022] (b) Dedicated equipment is installed on the ground 1 surrounding injection well 8 and gas production well 28; raw material CO2 is stored in carbon dioxide storage tank 2 in the dedicated equipment, and the temperature is adjusted to 31.1-75℃, preferably 45℃, by carbon dioxide heating equipment 4, and then pressurized to 8.2MPa supercritical state by booster injection pump 5. The temperature and pressure control switch 6 ensures that the temperature and pressure of the gas output by booster injection pump 5 meet the conditions; lithium iron phosphate battery pack 7 is used to provide separate power to carbon dioxide heating equipment 4 and booster injection pump 5; carbon dioxide heating equipment 4 has high-precision temperature control capability and can be calibrated in real time, operating at 30-80℃. The temperature error within the operating range is ≤ ±0.2℃; the design pressure of the carbon dioxide storage tank 2 is ≥30MPa, and the volume is determined to be 200m³ based on the daily injection volume. It is equipped with a pressure warning device, and the pressure relief program is automatically activated when the pressure exceeds 5%; the carbon dioxide storage tank 2 is made of 316L stainless steel, and the inner wall is polished with a polishing degree Ra≤0.6μm; the injection well 8 is equipped with a P110 grade casing with a casing wall thickness ≥14.5mm. The cement in the injection well 8 is returned to a height of 60m below the surface, the cement slurry density is controlled at 1.90-2.00g / cm³, and the setting time is ≥72h to ensure the wellbore sealing.

[0023] (c) Open the nitrogen cylinder group 14 in the special equipment, and simultaneously start the three-component solid-liquid mixing tank 21 equipped with an ultrasonic dispersion device. Mix the isopropanol-based carrier liquid with the isopropanol-based carrier liquid mass flow meter 19, the surface-oxidized and passivated aluminum powder particles with the aluminum powder mass flow meter 20, and the CuO powder coated with an 80nm silane film with the nitrogen-copper oxide mixed fluid mass flow meter 18 at a molar ratio of 1:1.5:1. The stirring speed is controlled at 300-500 r / min, and the mixing time is ≥30 min. Ensure a mixing uniformity ≥98%; control the nitrogen volume fraction ratio to 2-4% using dedicated equipment such as nitrogen mass flow meter 16, nitrogen-copper oxide mixed fluid mass flow meter 18, and isopropanol-based carrier liquid mass flow meter 19, ensuring full integration with supercritical CO2 and mixed reagents in the static mixing section; install 12-18 spiral static mixers in the mixing pipe section to ensure a three-phase mixing uniformity ≥98%; install a two-stage pressure reducing and stabilizing valve at the outlet of nitrogen cylinder group 14, stabilizing the output pressure at 0.8-1.2MPa. The three-component solid-liquid mixing tank 21 equipped with an ultrasonic dispersion device is equipped with a CS-3000 ultrasonic dispersion device with a dispersion power of 1500-3000W, ensuring the suspension stability of aluminum powder and CuO powder in the carrier liquid ≥96h; the outlet of nitrogen cylinder group 14 is equipped with a pressure reducing and stabilizing valve, stabilizing the output pressure at 0.8-1.2MPa, and the nitrogen mass flow meter 16 has a measurement accuracy of ±0.3%, accurately controlling the proportion of each medium.

[0024] (d) The fully mixed fluid from the static mixing section in step (c) is pressurized to 10-18 MPa by the permeation enhancer injection pump 52 in a special device. The parameters are monitored in real time by the injection fluid temperature and pressure monitoring device. The pressure is 10-18 MPa and the temperature is 45-60℃. The fluid is injected into injection well 8 at a rate of 1-4 m³ / h. Simultaneously, the acoustic wave frequency generator 24 is started to drive the piezoelectric ceramic vibrator 10 to emit variable frequency acoustic waves in 10 stages: the first stage is a low-frequency acoustic wave of 38-42 Hz with an amplitude of 1.8-2.2 MPa. The first stage involves 8 minutes of continuous sound waves to stimulate the original micro-fractures in the coal seam; the second stage uses 58-62Hz mid-frequency sound waves with an amplitude of 1.0-1.2MPa for 25 minutes to promote fracture expansion and connectivity; during the injection process, the third stage uses 75-80Hz high-frequency sound waves with an amplitude of 0.4-0.6MPa to promote the penetration of the agent into the fractures, with the high-frequency band continuing until the end of the injection process. The sound wave power is controlled at 8-12kW throughout the injection process, and the vibration expands the coal seam fractures to enhance the fluid displacement and agent penetration effects.

[0025] (e) Coalbed methane is displaced by supercritical carbon dioxide at 8.2 MPa and introduced into production well 28. The mixed gas produced from production well 28 is extracted by extraction pump 53 and first enters a primary cyclone separator 29 to remove solid particles with a diameter >20 μm. Then it is deeply filtered by a secondary cyclone separator 30 with a filtration accuracy of 2 μm. Subsequently, it enters a gas capture tower 34, where MDEA amine liquid adsorption is used for desulfurization and impurity removal. The MDEA amine liquid concentration is 25-30%, and the liquid-to-gas ratio is controlled at 20-25 L / m³. The waste liquid generated from filtration is... The waste liquid is discharged into the waste liquid pool 35 for centralized treatment; a multi-parameter transmitter 33 is installed on the pipeline from the secondary cyclone separator 30 to the gas capture tower 34 to transmit parameters such as filtration accuracy, gas composition, temperature, and pressure to the gas well signal cabinet 26 in real time; the amine concentration is controlled at 25-30%, the liquid-to-gas ratio is adjusted to 20-25 L / m³, and the gas-liquid countercurrent contact time is ≥4s; the coal dust-containing waste liquid generated by filtration is discharged into a dedicated waste liquid pool 35 for centralized treatment, with the bottom slag hopper tilted at an angle of 15°-20° to facilitate the settling and recovery of waste residue. The primary cyclone separator 29 and the secondary cyclone separator 30 both adopt a tangential inlet design, with a separation efficiency of ≥98%; the gas capture tower 34 is equipped with a multi-layer spray device, and the gas-liquid contact time is ≥4s.

[0026] (f) The desulfurized and impurity-removed gas enters the gas condensation and dehydration equipment 36, where the temperature is reduced to 3-6℃ to achieve condensation and dehydration. The dew point of the dehydrated gas is ≤-40℃. The dried gas enters the polyimide hollow fiber membrane gas separation tower 37, where the gas is separated into upper, middle, and lower parts. A composite separation system of spiral wound SAPO-34 membrane and hollow fiber ZIF-8 membrane is adopted, with an operating pressure of 3-5MPa and a temperature of 35-45℃. The precise separation and purification of CO2 and methane are achieved through two-stage membrane separation, taking advantage of the excellent properties of polyimide materials. The gas separation characteristics allow for the separation of methane and carbon dioxide with a purity ≥98% under operating tower conditions of 3-5 MPa pressure and 35-45℃. The gas condensation and dehydration equipment 36 adopts a vortex refrigeration unit with a cooling capacity of 80-120 kW and a cooling rate ≥5℃ / min. The polyimide hollow fiber membrane has a single membrane area ≥60 m², and is backwashed with dry nitrogen once a month during operation at a pressure of 0.6-0.9 MPa for 15-20 min each time.

[0027] (g) Real-time control of the entire process is achieved through the signal processing console 25 in the dedicated equipment. The distributed fiber optic sensors 9 in the injection well are spirally laid along the well wall with a spacing of ≤4m to monitor the injection temperature (accuracy ±0.1℃), pressure (accuracy ±0.08%FS) and coal seam fracture response in real time; monitor the temperature and pressure stability of the injected fluid and the coal seam fracture response, and connect the carbon dioxide anti-high pressure stop switch 3 and the nitrogen cylinder group anti-high pressure stop switch 15 in series. The data is transmitted to the injection well signal cabinet 12 and the signal processing console 25 and backed up and processed by the injection well signal processing system 13. The proportion of produced gas components is detected in real time by the TDLAS laser spectrometer 27 on the gas production well side (measurement accuracy ≤±0.1%). A primary laser scattering sensor 31 and a secondary laser scattering sensor 32 monitor particle residue. An infrared temperature sensor 38 integrated with a spectrometer and a piezoelectric accelerometer 23 collect equipment operating parameters, and the data is transmitted to the gas well signal cabinet 26 for backup storage. All data is transmitted to the signal processing console 25 and the injection well signal processing system 13. When parameters are abnormal, the gas well stop switch 50 is triggered to ensure safe system operation. All monitoring data is transmitted to the signal processing console 25 in real time. When parameters exceed the set threshold, the carbon dioxide anti-high pressure stop switch 3, the nitrogen cylinder group anti-high pressure stop switch 15, and the gas well stop switch 50 automatically activate within 0.3 seconds to achieve emergency cut-off and pressure relief, ensuring safe system operation. The bending radius of the injection well distributed fiber optic sensor 9 is ≥35mm, and the attenuation rate is ≤0.15dB / km when the signal transmission distance is ≤15km. The TDLAS laser spectrometer 27 has a measurement accuracy of ≤±0.1%, and can monitor CH4 and CO2 component concentration changes in real time, with a wireless data transmission delay of ≤0.5s.

[0028] (h) The methane separated in step f is pressurized to 2-4 MPa by a self-priming diaphragm compressor 42 in a dedicated device. The pressure is adjusted according to storage or transportation requirements, and the methane is stored in a high-strength methane storage tank 43 with a design pressure of 5 MPa and an airtightness level meeting GB50341 Class I standard. It is then transported to a CH4 self-pressurized storage tank 43 for later use. The separated carbon dioxide enters a post-separation carbon dioxide storage tank 39 for buffering. A post-separation carbon dioxide anti-high-pressure switch 44 allows selection of whether the separated carbon dioxide can be reused. If purified using a spiral-wound DD3R carbon dioxide molecular sieve membrane 45, with a CO2 purity ≥99%, the separated CO2 enters the post-separation carbon dioxide storage tank 39 for pressure stabilization. The gas is pressurized to the supercritical injection pressure by the spiral wound compressor 47, then depressurized and cooled, and then adjusted to the set temperature by the supercritical carbon dioxide temperature control device 48 before returning to the carbon dioxide storage tank 2 to rejoin the gas injection cycle; the gas is pressurized to the injection pressure by the spiral wound compressor 47, then depressurized and cooled, and then adjusted to the temperature by the supercritical carbon dioxide temperature control device 48 before returning to the carbon dioxide storage tank 2 for recycling; the low-calorific-value impurity gas generated by separation is introduced into the steam turbine 40 for catalytic combustion, with an inlet steam pressure of 4-6 MPa and a power generation efficiency of ≥32%, which drives the battery pack 49 for energy storage; the exhaust gas (CO2+H2O) after combustion is stored in the after-combustion impurity gas storage tank 41, and after purification, it can be reinjected into the circulation system; finally, it is reinjected into the goaf. The spiral-wound DD3R carbon dioxide molecular sieve membrane 45 adopts a three-layer composite structure, with a honeycomb-shaped flow guide mesh between each layer to improve the gas permeation rate. The spiral-wound compressor 47 performs four-stage compression, with an exhaust temperature ≤90℃ and a lubricating oil flash point ≥220℃. The filter element is replaced every 800 hours of operation to ensure that the oil content of the compressed gas is ≤3ppm. Methane is collected in a CH4 self-pressurized storage tank, carbon dioxide is recirculated after being pressurized by a diaphragm compressor, and impurities are converted by a steam turbine catalytic combustion device, thereby realizing the extraction and resource utilization of coalbed methane.

[0029] The present invention relates to a device for coalbed methane extraction and separation based on variable frequency acoustic wave assistance, comprising a special device arranged on the ground around injection well 8 and gas production well 28. The special device includes an injection subsystem, a downhole acoustic wave excitation subsystem, a gas production and processing subsystem, a separation and recovery subsystem, and an intelligent monitoring subsystem. The injection subsystem includes a carbon dioxide storage tank 2, a carbon dioxide heating device 4, a booster injection pump 5, a nitrogen cylinder group 14, a copper oxide powder storage tank 17, a three-component solid-liquid mixing tank 21 equipped with an ultrasonic dispersion device, an isopropanol-based carrier liquid stirring tank 46, an open-air aluminum particle storage area 51, and a permeation enhancer injection pump 52. The carbon dioxide storage tank 2 is connected to the carbon dioxide heating device 4 via a carbon dioxide anti-high pressure switch 3. The carbon dioxide heating device 4 is connected to the booster injection pump 5, which is connected to the injection well 8 via a pipeline. The permeation enhancer... The outlet of the permeation enhancer injection pump 52 is connected to the injection well 8 via a pipeline. The inlet of the permeation enhancer injection pump 52 is connected to the bottom of the three-component solid-liquid mixing tank 21 equipped with an ultrasonic dispersion device via a multi-parameter transmitter A 22. The nitrogen gas cylinder group 14 is connected to one inlet of the copper oxide powder storage tank 17 and the three-component solid-liquid mixing tank 21 equipped with an ultrasonic dispersion device via pipelines. The isopropanol-based carrying liquid stirring tank 46 and the aluminum particle open-air storage field 51 are respectively connected to the two inlets of the three-component solid-liquid mixing tank 21 equipped with an ultrasonic dispersion device via pipelines. The downhole acoustic excitation subsystem includes a piezoelectric ceramic vibrator 10 installed in the injection well 8, an acoustic frequency stabilizing generator 24 connected to the piezoelectric ceramic vibrator 10 via a piezoelectric accelerometer 23, and the acoustic frequency stabilizing generator 24 is connected to a signal processing control console. The gas production and processing subsystem includes a pump 53 connected to the gas production well 28, a primary cyclone separator 29, a secondary cyclone separator 30, a gas collection tower 34, a waste liquid discharge tank 35, and a gas condensation and dehydration device 36; the pump 53 is connected in sequence to the primary cyclone separator 29, the secondary cyclone separator 30, the gas collection tower 34, and the gas condensation and dehydration device 36 via pipelines, and the bottom of the gas condensation and dehydration device 36 is connected to the waste liquid tank 35; The separation and recovery subsystem includes a polyimide hollow fiber membrane gas separator 37, a separated carbon dioxide storage tank 39, a steam turbine 40, a post-combustion impurity gas storage tank 41, a self-priming diaphragm compressor 42, a CH4 self-pressurized storage tank 43, a spiral wound DD3R carbon dioxide molecular sieve membrane 45, a spiral wound compressor 47, and a supercritical carbon dioxide temperature control device 48 after pressure reduction and cooling. The lower side of the polyimide hollow fiber membrane gas separator 37 is connected to a gas condensation and dehydration device 36 via a pipeline; the other lower side is connected to the steam turbine 40 and the post-combustion impurity gas storage tank 41 via pipelines; the middle section is connected to the separated carbon dioxide storage tank 39, the spiral wound DD3R carbon dioxide molecular sieve membrane 45, the spiral wound compressor 47, and the supercritical carbon dioxide temperature control device 48 after pressure reduction and cooling connected to the carbon dioxide storage tank 2 via pipelines; the upper section is connected to the self-priming diaphragm compressor 42 and the CH4 self-pressurized storage tank 43 via pipelines. The intelligent monitoring subsystem includes an infrared thermal sensor 11, a piezoelectric accelerometer 23, a signal processing console 25, an injection well signal processing system 13, a TDLAS laser spectrometer 27, a primary laser scattering sensor 31, a secondary laser scattering sensor 32, an infrared temperature sensor 38 integrated with the spectrometer, and a gas well anomaly detection switch 50. The temperature signal collected by the infrared thermal sensor 11 is transmitted to the injection well signal processing system 13. The vibration, gas composition, fluid impurities, and temperature and spectral composite signals collected by the piezoelectric accelerometer 23, the TDLAS laser spectrometer 27, the primary laser scattering sensor 31, the secondary laser scattering sensor 32, and the infrared temperature sensor 38 integrated with the spectrometer are all transmitted to the signal processing console 25. The signal processing console 25 transmits the analysis results to the injection well signal processing system 13 and simultaneously outputs anomaly control commands to the gas well anomaly detection switch 50. The injection well signal processing system 13 outputs control commands to the relevant actuators of the injection well 8 based on the received temperature data and the linkage analysis results.

[0030] In the injection subsystem, the carbon dioxide storage tank 2 is connected to the injection well 8 via the carbon dioxide heating device 4 and the booster injection pump 5. Simultaneously, the nitrogen cylinder group 14 and the three-component solid-liquid mixing tank 21, equipped with a CS-3000 ultrasonic dispersion device and containing isopropanol-based carrier liquid, aluminum powder particles, and CuO powder, are connected in parallel to the injection well 8 via the nitrogen-copper oxide mixed fluid mass flow meter 18, the isopropanol-based carrier liquid mass flow meter 19, and the permeation enhancer injection pump 52. In the downhole acoustic excitation subsystem, the piezoelectric ceramic vibrator 10 located in the injection well 8 is driven by the configured acoustic frequency generator 24. Coalbed methane is displaced to the gas production well 28 via 8.2 MPa supercritical carbon dioxide. The extraction pump 53 connected to the gas production well 28 in the gas production treatment subsystem is sequentially connected to… The primary cyclone separator 29, the secondary cyclone separator 30, the gas collection tower 34, and the gas condensation and dehydration equipment 36 are connected to the polyimide hollow fiber membrane gas separation tower 37 of the separation and recovery subsystem. The polyimide hollow fiber membrane gas separation tower 37 is connected to the CH4 self-pressurized gas storage tank 43 and the separated carbon dioxide storage tank 39, respectively. The separated carbon dioxide is returned to the carbon dioxide storage tank 2 through the spiral wound DD3R carbon dioxide molecular sieve membrane 45, the spiral wound compressor 47, and the supercritical carbon dioxide temperature control equipment 48 after pressure reduction and cooling. The steam turbine 40 is connected to the afterburning impurity gas storage tank 41 and the battery pack 49. The intelligent monitoring subsystem realizes full-process parameter monitoring through the injection well distributed fiber optic sensor 9, the laser scattering sensor, and the TDLAS laser spectrometer 27.

Claims

1. A method for coalbed methane extraction and separation utilization based on variable frequency acoustic wave assistance, characterized in that... Includes the following steps: (a) Based on the geological structure map of the coal seam, the distribution characteristics of the coalbed methane reservoir and the development plan, after determining the spatial location of the injection well (8) and the gas production well (28) on the ground, drilling should be carried out in a flat area with a topographic slope of <12°, avoiding fault fracture zones, groundwater bodies and areas with potential geological hazards, and ensuring that the well site covers an area of ​​≥1800m². (b) Dedicated equipment is arranged on the ground outside the injection well (8) and the gas production well (28); raw material CO2 is stored in the carbon dioxide storage tank (2) in the dedicated equipment, and the temperature is adjusted to 31.1-75℃, preferably 45℃, by the carbon dioxide heating equipment (4), and then pressurized to 8.2MPa supercritical state by the booster injection pump (5); the carbon dioxide storage tank is designed with a pressure ≥30MPa, and the volume is determined to be 200m³ according to the daily injection volume. It is equipped with a pressure warning device, and the pressure relief program is automatically started when the pressure exceeds 5%. (c) Open the nitrogen cylinder group (14) in the special equipment, and at the same time start the three-component solid-liquid mixing tank (21) equipped with an ultrasonic dispersion device. Mix the isopropanol-based carrier liquid, surface-oxidized and passivated aluminum powder particles, and CuO powder coated with an 80nm silane film in a molar ratio of 1:1.5:

1. The stirring speed is controlled at 300-500r / min, the mixing time is ≥30min, and the mixing uniformity is ensured to be ≥98%. The nitrogen mixing ratio is controlled to be 2-4% by the nitrogen mass flow meter (16), the nitrogen-copper oxide mixed fluid mass flow meter (18), and the isopropanol-based carrier liquid mass flow meter (19) in the special equipment, so that it can be fully integrated with supercritical CO2 and mixed agents in the static mixing section. (d) The mixed fluid that has been fully integrated in the static mixing section of step (c) is pressurized to 10-18MPa by the permeation agent injection pump (52) in the special equipment, and the parameters are monitored in real time by the injection fluid temperature and pressure monitoring device, and injected into the injection well (8) at a discharge rate of 1-4m³ / h. Synchronously start the acoustic wave frequency generator (24) to drive the piezoelectric ceramic vibrator (10) to emit segmented frequency-converting acoustic waves: 38-42Hz low frequency band for 8 minutes, 58-62Hz mid frequency band for 25 minutes, 75-80Hz high frequency band for continuous operation until the injection ends, and control the acoustic wave power at 8-12kW. Vibration expands the coal seam fractures and promotes the penetration of the agent. (e) The mixed gas produced by the gas well (28) is extracted by the extraction pump (53) and first enters the first-stage cyclone separator (29) to remove solid particles with a particle size >20μm. Then it is deeply filtered by the second-stage cyclone separator (30) with a filtration accuracy of 2μm. Then it enters the gas capture tower (34) and is desulfurized and impurities removed by MDEA amine liquid adsorption method. The concentration of MDEA amine liquid is 25-30%, and the liquid-to-gas ratio is controlled at 20-25L / m³. The waste liquid generated by filtration is discharged into the waste liquid pool (35) for centralized treatment. (f) The gas after desulfurization and impurity removal enters the gas condensation and dehydration equipment (36), and the temperature is reduced to 3-6℃ to achieve condensation and dehydration. The dew point of the gas after dehydration is ≤-40℃. The dried gas enters the polyimide hollow fiber membrane gas separation tower (37). Utilizing the excellent gas separation characteristics of polyimide material, the separation of methane and carbon dioxide with a purity ≥98% is completed under the conditions of pressure of 3-5MPa and temperature of 35-45℃ in the operating tower. (g) Real-time control of the entire process is achieved through the signal processing console (25) in the dedicated equipment. The distributed fiber optic sensor (9) of the injection well in the dedicated equipment is spirally laid along the well wall with a spacing of ≤4m to monitor the temperature and pressure stability of the injected fluid and the response of the coal seam fracture. The carbon dioxide anti-high pressure stop switch (3) and the nitrogen gas cylinder group anti-high pressure stop switch (15) are connected in series. The proportion of the produced gas components is detected in real time by the TDLAS laser spectrometer (27) on the gas production well side. The first-level laser scattering sensor (31) and the second-level laser scattering sensor (32) monitor the particle residue. The infrared temperature sensor (38) of the integrated spectrometer and the piezoelectric accelerometer (23) collect the equipment operating parameters. All data are transmitted to the signal processing console (25) and the injection well signal processing system (13). When the parameters are abnormal, the gas production well stop switch (50) is triggered to ensure the safe operation of the system. (h) The methane separated in step (f) is pressurized to 2-4 MPa by a self-priming diaphragm compressor (42) in a special equipment and transported to a CH4 self-pressurized gas storage tank (43) for storage and use. The separated carbon dioxide enters the carbon dioxide storage tank (39) after separation and is then purified by a spiral wound DD3R carbon dioxide molecular sieve membrane (45) with a CO2 purity ≥99%. It is then pressurized to the injection pressure by a spiral wound compressor (47), and after depressurization and cooling, the temperature is adjusted by a supercritical carbon dioxide temperature control device (48) and returned to the carbon dioxide storage tank (2) for recycling. The low-calorific-value impurity gas generated by separation is introduced into a steam turbine (40) for catalytic combustion with an inlet steam pressure of 4-6 MPa and a power generation efficiency ≥32%. This drives the battery pack (49) for energy storage. The exhaust gas (CO2+H2O) after combustion is stored in the impurity gas storage tank (41) after combustion and is finally reinjected into the goaf.

2. The method for coalbed methane extraction and separation based on variable frequency acoustic wave assistance according to claim 1, characterized in that: In step (a), the distance between the injection well (8) and the gas production well (28) is adjusted according to the coal seam permeability. The distance between areas with permeability below 0.08mD is reduced to 30-50m, and the distance between areas with permeability of 0.08-0.5mD is set to 60-80m. A fire passage with a width of ≥5m must be set up at the well site and equipped with a foam fire extinguishing system. Flammable, explosive and corrosive materials are prohibited from being piled up within 80m of the well site.

3. The method for coalbed methane extraction and separation based on variable frequency acoustic wave assistance according to claim 1, characterized in that: In step (b), the carbon dioxide storage tank (2) is made of 316L stainless steel and the inner wall is polished with a polishing degree Ra≤0.6μm; the injection well (8) is equipped with a P110 steel grade casing with a casing wall thickness ≥14.5mm. The cement in the injection well (8) is returned to a height of 60m below the surface, the cement slurry density is controlled at 1.90-2.00g / cm³, and the setting time is ≥72h to ensure the well casing is sealed.

4. The method for coalbed methane extraction and separation based on variable frequency acoustic wave assistance according to claim 1, characterized in that: In step (c), the three-component solid-liquid mixing tank (21) equipped with an ultrasonic dispersion device is equipped with a CS-3000 ultrasonic dispersion device with a dispersion power of 1500-3000W, ensuring that the aluminum powder and CuO powder are suspended in the carrier liquid with a stability of ≥96h; the outlet of the nitrogen cylinder group (14) is equipped with a pressure reducing and stabilizing valve, and the output pressure is stable at 0.8-1.2MPa; the nitrogen mass flow meter (16) has a measurement accuracy of ±0.3%, accurately controlling the proportion of each medium.

5. The method for coalbed methane extraction and separation based on variable frequency acoustic wave assistance according to claim 1, characterized in that: In step (e), the primary cyclone separator (29) and the secondary cyclone separator (30) both adopt a tangential inlet design with a separation efficiency of ≥98%; the gas collection tower (34) is equipped with a multi-layer spray device with a gas-liquid contact time of ≥4s.

6. The method for coalbed methane extraction and separation based on variable frequency acoustic wave assistance according to claim 1, characterized in that: In step (f), the gas condensation dehydration equipment (36) adopts a vortex refrigeration unit with a cooling capacity of 80-120kW and a cooling rate of ≥5℃ / min; the single-strand polyimide hollow fiber membrane has an area of ​​≥60m², and is backwashed with dry nitrogen once a month during operation, with a backwashing pressure of 0.6-0.9MPa and a backwashing time of 15-20min each time.

7. The method for efficient extraction and separation of coalbed methane according to claim 1, characterized in that: In step (g), the bending radius of the injection well distributed optical fiber sensor (9) is ≥35mm, and the attenuation rate is ≤0.15dB / km when the signal transmission distance is ≤15km; the measurement accuracy of the TDLAS laser spectrometer (27) is ≤±0.1%, and it can monitor the changes in CH4 and CO2 component concentrations in real time, with a data wireless transmission delay of ≤0.5s.

8. The method for coalbed methane extraction and separation based on variable frequency acoustic wave assistance according to claim 1, characterized in that: In step (h), the spiral wound DD3R carbon dioxide molecular sieve membrane (45) adopts a three-layer composite structure, with a honeycomb guide net between each layer of membrane to improve the gas permeation rate; the spiral wound compressor (47) is divided into four stages of compression, with an exhaust temperature ≤90℃, a lubricating oil flash point ≥220℃, and the filter element is replaced every 800 hours of operation to ensure that the oil content of the compressed gas is ≤3ppm.

9. A system for implementing the method for coalbed methane extraction and separation based on frequency conversion acoustic wave assistance as described in any one of claims 1-8, characterized in that: This includes the installation of specialized equipment on the ground outside the injection well (8) and the gas production well (28). The specialized equipment includes an injection subsystem, a downhole acoustic excitation subsystem, a gas production and processing subsystem, a separation and recovery subsystem, and an intelligent monitoring subsystem. The injection subsystem includes a carbon dioxide storage tank (2), a carbon dioxide heating device (4), a booster injection pump (5), a nitrogen cylinder group (14), a copper oxide powder storage tank (17), a three-component solid-liquid mixing tank (21) equipped with an ultrasonic dispersion device, an isopropanol-based carrier liquid stirring tank (46), an aluminum particle open-air storage field (51), and a permeation enhancer injection pump (52). The carbon dioxide storage tank (2) is connected to the carbon dioxide heating device (4) via a carbon dioxide anti-high pressure switch (3), and the carbon dioxide heating device (4) is connected to the booster injection pump (5) which is connected to the injection well (8) via a pipeline. The outlet of the permeation enhancer injection pump (52) is connected to the injection well (8) via a pipeline. The inlet of the permeation enhancer injection pump (52) is connected to the bottom of the three-component solid-liquid mixing tank (21) equipped with an ultrasonic dispersion device via a multi-parameter transmitter (22). The nitrogen gas cylinder group (14) is connected to one inlet of the copper oxide powder storage tank (17) and the three-component solid-liquid mixing tank (21) equipped with an ultrasonic dispersion device via a pipeline. The isopropanol-based carrying liquid stirring tank (46) and the aluminum particle open-air storage field (51) are respectively connected to the two inlets of the three-component solid-liquid mixing tank (21) equipped with an ultrasonic dispersion device via pipelines. The downhole acoustic excitation subsystem includes a piezoelectric ceramic vibrator (10) installed in the injection well (8), an acoustic frequency generator (24) connected to the piezoelectric ceramic vibrator (10) via a piezoelectric accelerometer (23), and the acoustic frequency generator (24) is connected to the signal processing control console. The gas production and processing subsystem includes a pump (53) connected to the gas production well (28), a primary cyclone separator (29), a secondary cyclone separator (30), a gas collection tower (34), a waste liquid discharge pool (35), and a gas condensation and dehydration device (36); the pump (53) is connected in sequence to the primary cyclone separator (29), the secondary cyclone separator (30), the gas collection tower (34), and the gas condensation and dehydration device (36) via pipelines, and the bottom of the gas condensation and dehydration device (36) is connected to the waste liquid pool (35); The separation and recovery subsystem includes a polyimide hollow fiber membrane gas separator (37), a carbon dioxide storage tank (39) after separation, a steam turbine (40), a waste gas storage tank (41) after combustion, a self-priming diaphragm compressor (42), a CH4 self-pressurized storage tank (43), a spiral wound DD3R carbon dioxide molecular sieve membrane (45), a spiral wound compressor (47), and a supercritical carbon dioxide temperature control device (48) after pressure reduction and cooling; the pipeline on one side of the lower part of the polyimide hollow fiber membrane gas separator (37) is connected to the gas... The lower part is connected to the condensation and dehydration equipment (36); the other side of the lower part is connected to the steam turbine (40) and the combustion waste gas storage tank (41) in sequence via pipelines; the middle part is connected to the separated carbon dioxide storage tank (39), the spiral wound DD3R carbon dioxide molecular sieve membrane (45), the spiral wound compressor (47), and the supercritical carbon dioxide temperature control equipment (48) connected to the carbon dioxide storage tank (2) via pressure reduction and cooling; the upper part is connected to the self-priming diaphragm compressor (42) and the CH4 self-pressurized gas storage tank (43) in sequence via pipelines. The intelligent monitoring subsystem includes an infrared thermal sensor (11), a piezoelectric accelerometer (23), a signal processing control console (25), an injection well signal processing system (13), a TDLAS laser spectrometer (27), a primary laser scattering sensor (31), a secondary laser scattering sensor (32), an infrared temperature sensor integrated with the spectrometer (38), and a gas well anti-abnormality switch (50); the temperature signal collected by the infrared thermal sensor (11) is transmitted to the injection well signal processing system (13); the piezoelectric accelerometer (23) and the TDLAS laser spectrometer (27) Vibration, gas composition, fluid impurities, temperature and spectral composite signals collected by the primary laser scattering sensor (31), the secondary laser scattering sensor (32) and the infrared temperature sensor (38) of the integrated spectrometer are all transmitted to the signal processing console (25). The signal processing console (25) transmits the analysis results to the injection well signal processing system (13) and outputs abnormal control commands to the gas well stop switch (50). The injection well signal processing system (13) outputs control commands to the relevant actuators of the injection well (8) based on the received temperature data and linkage analysis results.

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