A high-stress low-permeability coal seam permeability enhancement system and method

Abstract

The present invention discloses a high-stress, low-permeability coal seam permeability enhancement system and method, relating to the field of coalbed methane extraction. The system includes: a vibration subsystem for collecting stress values of the coal seam and, when the stress values of the coal seam reach a set condition, releasing stress in stress-concentrated areas of the coal seam to break the stress equilibrium state of the coal seam; a fracturing subsystem for hydraulically fracturing the coal seam after breaking the stress equilibrium state of the coal seam, thereby forming multiple cracks within the coal seam; and a heat injection subsystem for, after hydraulically fracturing the coal seam, using ferromagnetic oxide nanoparticles as a heat carrier to enhance the permeability of the coal seam based on the magnetothermal principle, thereby pyrolyzing the coal seam. The present invention combines vibration with hydraulic fracturing to effectively release stress and pre-induce cracks in the coal seam. It also uses ferromagnetic oxide nanoparticles as a heat carrier to enhance the permeability of the coal seam based on the magnetothermal principle, thereby reducing damage to the coal seam, improving the accuracy of the pyrolysis and permeability enhancement of the coal seam, and reducing the risk of environmental pollution.

Description

Technical Field

[0001] The present invention relates to the field of coalbed methane mining, and in particular to a high-stress low-permeability coalbed permeability enhancement system and method. Background Art

[0002] Deep coal seams are characterized by high pressure (high in-situ stress, high gas pressure, and high fissure water pressure), high temperature, and low permeability. These characteristics significantly increase the frequency and severity of rock bursts and coal and gas outbursts, posing safety risks to deep coal seam mining.

[0003] Current coal seam permeability enhancement technologies mainly include carbon dioxide fracturing, hydraulic fracturing and mechanical cavitation, but the use of any of the above methods alone is difficult to solve the low permeability problem of high-stress pulverized coal seams.

[0004] Specifically, (1) mechanical cavitation technology will cause stress redistribution and stress concentration in the surrounding coal body, thereby reducing the permeability of the coal seam. In addition, since the cross section of the borehole is a regular circle, the coal seam is not completely homogeneous and there are uncertain factors such as creep behavior, which seriously affect the implementation effect of mechanical cavitation. (2) Hydraulic fracturing has the disadvantages of short effective extraction time, single cracks formed, and damage to the coal seam. During fracturing operations in soft coal seams, the coal body is easy to break. When the water pressure is too high, the soft coal body around the borehole is prone to blockage and collapse under water pressure damage, blocking the gas migration channel and affecting subsequent fracturing work. (3) Due to the physical properties of carbon dioxide (such as heat of vaporization, pressure change with temperature, etc.), it is difficult to accurately control the carbon dioxide fracturing process. Compared with hydraulic fracturing technology, the application practice of carbon dioxide fracturing technology in coal seam permeability enhancement is relatively small, and there is a lack of sufficient experience accumulation and case analysis. In addition, carbon dioxide fracturing technology requires special equipment and materials, and is more expensive than traditional hydraulic fracturing technology.

[0005] Therefore, a new permeability enhancement scheme is needed to address the difficulty in enhancing the permeability of high-stress and low-permeability pulverized coal seams. Summary of the Invention

[0006] The purpose of the present invention is to provide a high-stress, low-permeability coal seam permeability enhancement system and method, which can effectively release stress and pre-cracks in the coal seam, reduce damage to the coal seam, improve the accuracy of coal seam pyrolysis permeability enhancement, and reduce the risk of environmental pollution.

[0007] To achieve the above objectives, the present invention provides a high-stress low-permeability coal seam permeability enhancement system, comprising:

[0008] a vibration subsystem for collecting stress values of the coal seam and, when the stress value of the coal seam reaches a set condition, releasing stress in a stress concentration area of the coal seam to break the stress equilibrium state of the coal seam;

[0009] a fracturing subsystem, configured to hydraulically fracture the coal seam after the vibration subsystem breaks the stress equilibrium state of the coal seam, thereby forming a plurality of cracks in the coal seam;

[0010] The heat injection subsystem is used to use ferromagnetic oxide nanoparticles as heat carriers to increase the permeability of the coal seam based on the magnetocaloric principle after the coal seam is hydraulically fractured by the fracturing subsystem, thereby pyrolyzing the coal seam.

[0011] To achieve the above-mentioned object, the present invention further provides a method for increasing the permeability of a high-stress, low-permeability coal seam, using the above-mentioned high-stress, low-permeability coal seam permeability increasing system. The method comprises:

[0012] Collect stress values of coal seams;

[0013] When the stress value of the coal seam reaches a set condition, releasing stress in the stress concentration area of the coal seam to break the stress equilibrium state of the coal seam;

[0014] After breaking the stress equilibrium state of the coal seam, hydraulically fracturing the coal seam;

[0015] After the coal seam is hydraulically fractured, ferromagnetic oxide nanoparticles are used as heat carriers to increase the permeability of the coal seam based on the magnetocaloric principle, thereby causing the coal seam to be pyrolyzed.

[0016] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: The present invention adopts a combination of vibration technology and hydraulic fracturing technology, which can effectively release stress and pre-cracks in coal seams. In addition, the magnetothermal principle is used to increase the permeability of coal seams, which can form more pores and promote coalbed methane analysis. The magnetic field has less damage to the coal seams, which is conducive to maintaining the integrity and stability of the coal seams. Further, ferromagnetic oxide nanoparticles are used as heat carriers, and the distribution and intensity of heat can be adjusted as needed to achieve precise control of the pyrolysis process. The iron oxide component in the ferromagnetic oxide nanoparticles can undergo an oxidation reaction with harmful gases, which can effectively reduce the amount of harmful gases generated, thereby reducing the risk of environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 Schematic diagram of the vibration subsystem and fracturing subsystem.

[0019] Figure 2 It is a three-dimensional well map.

[0020] Figure 3 Schematic diagram of the heat injection subsystem.

[0021] Figure 4 Schematic diagram of the extraction subsystem.

[0022] Figure 5 This is a flow chart of the high-stress low-permeability coal seam permeability enhancement method provided by the present invention.

[0023] Explanation of symbols: 1-ground, 2-rock layer No. 1, 3-rock layer No. 2, 4-rock layer No. 3, 5-roof, 6-coal seam, 7-floor, 8-horizontal well, 9-first borehole, 10-second borehole, 11-third borehole, 12-fourth borehole, 13-fifth borehole, 14-first steel cylinder, 15-second steel cylinder, 16-third steel cylinder, 17-fourth steel cylinder, 18-fifth steel cylinder, 19-stress sensor, 20-sensor chip, 21-vibration generator, 22-first control component, 23-hydraulic fracturing pipe, 24-mixing device, 25-fracturing fluid storage tank, 26-water tank, 27-first high-pressure pump, 28-first flowmeter, 29-dry nitrogen storage tank , 30-circulation pump, 31-first valve, 32-second valve, 33-pressure sensor, 34-second control component, 35-first crack, 36-second crack, 37-third crack, 38-fourth crack, 39-ferromagnetic oxide nanoparticle storage container, 40-second high-pressure pump, 41-third valve, 42-second flow meter, 43-frequency converter, 44-magnetic induction coil, 45-first temperature detector, 46-second temperature detector, 47-third control component, 48-first extraction pump, 49-second extraction pump, 50-third extraction pump, 51-fourth extraction pump, 52-fifth extraction pump, 53-separator, 54-coalbed methane storage tank. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] The purpose of the present invention is to provide a high-stress, low-permeability coal seam permeability enhancement system and method, which combines traditional hydraulic fracturing technology and uses the magnetothermal principle to pyrolyze the coal seam to achieve the permeability enhancement effect, thereby maximizing resource utilization and reducing the difficulty of coalbed methane extraction.

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] The high-stress low-permeability coal seam permeability enhancement system provided by the present invention comprises: a vibration subsystem, a fracturing subsystem and a heat injection subsystem. Furthermore, the high-stress low-permeability coal seam permeability enhancement system also comprises a drainage subsystem.

[0028] (1) The vibration subsystem is used to collect the stress value of the coal seam and release the stress in the stress concentration area of the coal seam when the stress value of the coal seam reaches the set condition to break the stress equilibrium state of the coal seam. Releasing the stress of the coal seam through the vibration subsystem can solve the problem of stress concentration.

[0029] Specifically, if Figure 1 As shown, the vibration subsystem includes: a steel cylinder, a stress sensor 19, a sensor chip 20, a vibration generator 21 and a first control component 22. The steel cylinder extends from the ground 1 to the coal seam 6. The stress sensor 19 and the vibration generator 21 are both set on the steel cylinder. Between the ground 1 and the coal seam 6, there are rock layer 1 2, rock layer 2 3, rock layer 3 4 and roof 5 in sequence. The bottom of the coal seam 6 is the bottom plate 7. Drilling from the ground 1 to the coal seam 6 forms a horizontal well 8, as shown in FIG. Figure 2 shown.

[0030] There are multiple steel cylinders, stress sensors 19, and vibration generators 21. In a specific embodiment, there are five steel cylinders: a first steel cylinder 14, a second steel cylinder 15, a third steel cylinder 16, a fourth steel cylinder 17, and a fifth steel cylinder 18. There are 20 stress sensors 19 and 50 vibration generators 21, meaning each steel cylinder is equipped with four stress sensors 19 and ten vibration generators 21. The steel cylinders secure and protect the stress sensors 19.

[0031] The stress sensor 19 is used to collect stress values in the coal seam 6. The sensor chip 20 is connected to the stress sensor 19 and is used to receive the stress values collected by the stress sensor 19. The first control component 22 is connected to the sensor chip 20 and the vibration generator 21 respectively. The first control component 22 is used to control the vibration generator 21 to activate when the stress value of the coal seam 6 reaches a set condition, thereby releasing stress in the stress-concentrated area of the coal seam 6 and breaking the stress equilibrium state of the coal seam 6.

[0032] The present invention first drills into the permeability enhancement zone coal seam 6, generating five boreholes: a first borehole 9, a second borehole 10, a third borehole 11, a fourth borehole 12, and a fifth borehole 13. A steel cylinder is placed in each borehole. A stress sensor 19 is installed in the coal seam 6 within the borehole to collect stress values. A sensor chip 20 converts the stress values collected by the stress sensor 19 into electrical signals. When the stress value in a soft coal seam reaches 50 MPa to 70 MPa, or when the stress value in a hard coal seam reaches 70 MPa to 90 MPa, a vibration generator 21 is activated to release stress in the stress-concentrated areas of the coal seam 6, thereby breaking the stress equilibrium in the permeability enhancement zone.

[0033] (2) The fracturing subsystem is used to hydraulically fracture the coal seam 6 after the vibration subsystem breaks the stress equilibrium state of the coal seam 6, so as to form multiple cracks in the coal seam 6.

[0034] Specifically, if Figure 1 As shown, the fracturing subsystem includes: a hydraulic fracturing pipe 23, a mixing device 24, a fracturing fluid storage tank 25, a water tank 26, a first high-pressure pump 27, a first flow meter 28, a dry nitrogen storage tank 29, a circulation pump 30, a first valve 31, a second valve 32, a pressure sensor 33 and a second control component 34.

[0035] The hydraulic fracturing pipe 23 extends from the ground surface 1 into the coal seam 6. The outlet of the mixing device 24 is connected to the inlet of the fracturing fluid storage tank 25. The outlet of the fracturing fluid storage tank 25 and the outlet of the water tank 26 are both connected to the inlet of the first high-pressure pump 27. The outlet of the first high-pressure pump 27 is connected to the inlet of the hydraulic fracturing pipe 23. The first flowmeter 28 is disposed between the outlet of the first high-pressure pump 27 and the inlet of the hydraulic fracturing pipe 23. The outlet of the dry nitrogen storage tank 29 is connected to the inlet of the circulation pump 30. The outlet of the circulation pump 30 is connected to the inlet of the hydraulic fracturing pipe 23. The first valve 31 is disposed between the outlet of the first high-pressure pump 27 and the first flowmeter 28. The second valve 32 is disposed between the outlet of the dry nitrogen storage tank 29 and the inlet of the circulation pump 30. The pressure sensor 33 is disposed within the hydraulic fracturing pipe 23.

[0036] The first flowmeter 28 is used to detect the flow rate of the liquid in the hydraulic fracturing pipe 23. The liquid in the hydraulic fracturing pipe 23 is fracturing fluid or water. The pressure sensor 33 is used to collect the pressure value in the hydraulic fracturing pipe 23. The second control component 34 is connected to the pressure sensor 33 and is used to control the states of the first valve 31 and the second valve 32 based on the flow rate of the liquid in the hydraulic fracturing pipe 23 and the pressure value in the hydraulic fracturing pipe 23, so as to hydraulically fracture the coal seam 6 using the fracturing fluid.

[0037] After breaking the stress equilibrium in the coal seam 6, the hydraulic fracturing pipe 23 is used to perform the first fracturing of the permeability-enhancing zone. Simultaneously, the vibration generator 21 is activated to accelerate the flow of fracturing fluid through the fissures in the coal seam 6. Quartz sand coated with a polymer material is used as a proppant. The proppant and fracturing fluid flow together through the hydraulic fracturing pipe 23 into the fissures. The proppant's coating polymer is epoxy resin, which is used to support the fractures. Figure 1 A total of four cracks are shown: a first crack 35 , a second crack 36 , a third crack 37 and a fourth crack 38 .

[0038] As the fracturing fluid is continuously injected, the pressure gradually increases. When the pressure reaches the breaking point of coal seam 6, coal seam 6 begins to crack, forming fissures. During this process, the flow rate increases accordingly due to the opening of the fissures. Once the fissures form and expand to a certain extent, the fracturing fluid flows more easily into the fissures, further increasing the flow rate and causing the pressure value to drop slightly. Observing the pressure sensor 33 and flowmeter, when the pressure and flow rate reach a relatively stable state, it indicates that the hydraulic fracturing effect has reached its limit.

[0039] The first high-pressure pump 27 then pumps water from the water tank 26 into the hydraulic fracturing pipe 23. The high-pressure water flow flushes out any remaining fracturing fluid within the pipe 23. The first valve 31 is closed. The second valve 32 is then opened, allowing flowing dry nitrogen to contact the remaining water within the pipe 23, evaporating it and allowing it to escape with the gas. Simultaneously, the nitrogen displaces gas from the coal seam 6.

[0040] (3) The heat injection subsystem is used to use ferromagnetic oxide nanoparticles as heat carriers to increase the permeability of the coal seam 6 based on the magnetocaloric principle after the coal seam 6 is hydraulically fractured by the fracturing subsystem, thereby causing the coal seam 6 to be pyrolyzed.

[0041] Specifically, if Figure 3 As shown, the heat injection subsystem includes: a ferromagnetic oxide nanoparticle storage container 39, a second high-pressure pump 40, a third valve 41, a second flow meter 42, a frequency converter 43, a magnetic induction coil 44, a temperature detector and a third control component 47.

[0042] The third control component 47 carries a power supply. There are multiple temperature detectors, preferably two: a first temperature detector 45 and a second temperature detector 46, which are respectively arranged in the first crack and the last crack.

[0043] The outlet of the ferromagnetic oxide nanoparticle storage container 39 is connected to the inlet of the second high-pressure pump 40. The outlet of the second high-pressure pump 40 is connected to the hydraulic fracturing pipe 23. The third valve 41 is disposed between the outlet of the second high-pressure pump 40 and the hydraulic fracturing pipe 23. The second flowmeter 42 is disposed between the third valve 41 and the hydraulic fracturing pipe 23. The temperature detector is disposed in the fracture of the coal seam 6. The magnetic induction coil 44 is disposed on the hydraulic fracturing pipe 23. The frequency converter 43 is connected to the magnetic induction coil 44. The third control component 47 is respectively connected to the frequency converter 43, the temperature detector, and the second flowmeter 42.

[0044] The third control component 47 is configured to heat the ferromagnetic oxide nanoparticles in the ferromagnetic oxide nanoparticle storage container 39 after the fracturing subsystem hydraulically fractures the coal seam 6, converting the ferromagnetic oxide nanoparticles into a nanomagnetic fluid, and control the state of the third valve 41 to allow the nanomagnetic fluid to flow into the fractures of the coal seam 6. Specifically, the third valve 41 is controlled to open to allow the nanomagnetic fluid to flow into the fractures of the coal seam 6.

[0045] The ferromagnetic oxide nanoparticle storage container 39 may also be directly a nanomagnetic fluid storage tank.

[0046] The temperature detector is used to detect the temperature of the nano-magnetic fluid in the fracture. The third control component 47 is further used to adjust the frequency converter 43 to change the alternating magnetic field intensity based on the temperature of the nano-magnetic fluid in the fracture, thereby increasing the temperature of the nano-magnetic fluid in the fracture to increase the permeability of the coal seam 6 and cause pyrolysis of the coal seam 6.

[0047] The present invention uses ferromagnetic oxide nanoparticles as a heat carrier, which exhibit strong magnetism under an applied magnetic field and have good thermal conductivity. The third valve 41 is opened to allow the nanomagnetic fluid to flow into the horizontal well 8. The magnetothermal heating switch within the third control component 47 is activated to initiate preheating, setting the temperature between 100°C and 120°C. The nanomagnetic fluid is heated, and the temperature detected by the temperature detector is monitored to ensure that the nanomagnetic fluid has reached the set temperature. During the magnetothermal anti-reflection process, the temperature and pressure of the coal seam 6 must be monitored and adjusted in real time, and the magnetic field strength must be adjusted promptly to achieve precise control and optimal heating of the coal seam 6.

[0048] The temperature of the coal seam 6 during the drying and degassing stage is below 200°C. The second high-pressure pump 40 is turned on to inject nano-magnetic fluid at 150°C to 180°C into the cracks of the coal seam 6. During this stage, the water in the coal seam 6 begins to evaporate, and the gas adsorbed on the coal surface (such as methane) begins to desorb. The temperature slowly rises and the pressure slightly decreases.

[0049] The temperature of coal seam 6 during the initial pyrolysis phase is between 200°C and 400°C. By adjusting the alternating magnetic field intensity via inverter 43, the nanomagnetic fluid gradually heats up. The temperature detected by the temperature detector indicates that when the temperature reaches between 380°C and 400°C, the coal begins to undergo thermochemical decomposition, producing light hydrocarbon gases. The structure of the coal also begins to change. The temperature detected by the temperature detector indicates that the temperature continues to rise, accelerating. As the gases produced by pyrolysis gradually accumulate, the pressure begins to increase significantly.

[0050] The temperature during the primary pyrolysis phase of coal seam 6 is between 400°C and 600°C. By adjusting the alternating magnetic field intensity of inverter 43, the nanomagnetic fluid gradually heats up to above 450°C. The pyrolysis reaction reaches its peak, generating a large amount of gaseous and liquid products. The coal's structure undergoes significant changes, forming semi-coke or coke. Observing the temperature detected by the temperature detector, the heat released by the pyrolysis reaction reaches equilibrium with the heating from the heat source, at which point the temperature reaches its peak and remains stable, and the pressure reaches its maximum and remains relatively stable.

[0051] During the pyrolysis process, the volatile matter in the coal is released, increasing the coal's porosity and specific surface area. After pyrolysis, hard or brittle minerals are formed in the coal seam 6, increasing its hardness and resistance to deformation. The magnetothermal heating switch and vibration generator 21 are then activated to promote the desorption of coalbed methane.

[0052] (4) The extraction subsystem is used to extract the coalbed methane under negative pressure after the heat injection subsystem pyrolyzes the coal seam 6.

[0053] Specifically, if Figure 4 As shown, the extraction subsystem includes an extraction pump, a separator 53, and a coalbed methane storage tank 54. The extraction pump is connected to a steel cylinder. The separator 53 is connected to the extraction pump and the coalbed methane storage tank 54, respectively. The number of extraction pumps is the same as the number of steel cylinders, and there are five extraction pumps: a first extraction pump 48, a second extraction pump 49, a third extraction pump 50, a fourth extraction pump 51, and a fifth extraction pump 52. The separator 53 is used to separate impurities from the coalbed methane.

[0054] After the coal seam 6 is pyrolyzed, the extraction pump is turned on to extract the coal seam gas under negative pressure. The extracted coal seam gas passes through the separator 53 to remove impurities in the coal seam gas, and is finally transported to the coal seam gas storage tank 54.

[0055] like Figure 5 As shown, the present invention is based on the above-mentioned high-stress and low-permeability coal seam permeability enhancement system and further provides a high-stress and low-permeability coal seam permeability enhancement method, including steps 1 to 4.

[0056] Step 1: Collect the stress value of coal seam 6.

[0057] Step 2: When the stress value of the coal seam 6 reaches a set condition, the stress is released in the stress concentration area of the coal seam 6 to break the stress equilibrium state of the coal seam 6 .

[0058] Specifically, when the stress value of the coal seam 6 reaches a set condition, the vibration generator 21 is activated to release stress in the stress-concentrated area of the coal seam 6, thereby breaking the stress equilibrium state of the coal seam 6. If the coal seam 6 is a soft coal seam, the set condition is a stress range of 50 MPa to 70 MPa. If the coal seam 6 is a hard coal seam, the set condition is a stress range of 70 MPa to 90 MPa.

[0059] Step 3: After breaking the stress equilibrium state of the coal seam 6, hydraulic fracturing is performed on the coal seam 6.

[0060] Specifically, after the stress equilibrium state of the coal seam 6 is broken, the first high-pressure pump 27 and the first valve 31 are started.

[0061] The fracturing fluid in the fracturing fluid storage tank 25 is injected into the hydraulic fracturing pipe 23 by the first high-pressure pump 27 to fracture the coal seam 6 , thereby forming a plurality of cracks in the coal seam 6 .

[0062] The flow rate of the fracturing fluid in the hydraulic fracturing pipe 23 is detected in real time, and the pressure value in the hydraulic fracturing pipe 23 is collected in real time.

[0063] When the flow rate of the fracturing fluid in the hydraulic fracturing pipe 23 and the pressure value in the hydraulic fracturing pipe 23 reach a stable state, the water in the water tank 26 is injected into the hydraulic fracturing pipe 23 through the first high-pressure pump 27 to flush the fracturing fluid in the hydraulic fracturing pipe 23.

[0064] The first valve 31 is closed, and the second valve 32 is opened. The dry nitrogen in the dry nitrogen storage tank 29 is injected into the hydraulic fracturing pipe 23 through the circulation pump 30 to evaporate the water in the hydraulic fracturing pipe 23. The second valve 32 is then closed.

[0065] Step 4: After hydraulic fracturing the coal seam 6, ferromagnetic oxide nanoparticles are used as heat carriers to increase the permeability of the coal seam 6 based on the magnetocaloric principle, thereby pyrolyzing the coal seam 6.

[0066] Specifically, after the coal seam 6 is hydraulically fractured, the ferromagnetic oxide nanoparticles in the ferromagnetic oxide nanoparticle storage container 39 are heated to convert the ferromagnetic oxide nanoparticles into nanomagnetic fluid, and the third valve 41 is opened.

[0067] The nano-magnetic fluid is injected into the hydraulic fracturing pipe 23 by a second high-pressure pump 40 , so that the nano-magnetic fluid flows into the cracks of the coal seam 6 .

[0068] The temperature of the nano magnetic fluid in the crack is detected in real time.

[0069] According to the temperature of the nano-magnetic fluid in the fracture, the frequency converter 43 is adjusted to change the alternating magnetic field intensity, so as to increase the temperature of the nano-magnetic fluid in the fracture, thereby increasing the permeability of the coal seam 6 and causing the coal seam 6 to be pyrolyzed.

[0070] Furthermore, the method for increasing the permeability of high-stress and low-permeability coal seams further includes step 5: after the coal seam 6 is pyrolyzed, the coalbed methane is extracted under negative pressure.

[0071] The present invention combines vibration technology with hydraulic fracturing technology to effectively release stress and pre-induce cracks in the coal seam 6. The use of magnetothermal principles for permeability enhancement can form more pores and promote coalbed methane analysis. The magnetic field has less damage to the coal seam 6, which is beneficial for maintaining the integrity and stability of the coal seam 6. Furthermore, the nanomagnetic fluid can adjust the distribution and intensity of heat as needed to achieve precise control of the pyrolysis process. The iron oxide component in the ferromagnetic oxide nanoparticles undergoes an oxidation reaction with harmful gases (such as carbon monoxide), which can effectively reduce the amount of harmful gases generated. Compared with traditional extraction methods, nanomagnetic fluids have a lower risk of environmental pollution.

[0072] In order to better understand the technical solution of the present invention, two specific examples are provided below to introduce the permeability enhancement process of high-stress and low-permeability coal seams.

[0073] Example 1: A hard coal seam with gas outburst was encountered with a depth of about 1030m and a thickness of about 6m.

[0074] 1. Preparation stage: Drill a hole at a predetermined location in the permeability enhancement zone coal seam 6. Install a stress sensor 19 and a sensor chip 20 to monitor the stress value.

[0075] 2. When the stress value reaches 70Mpa-90Mpa, the vibration generator 21 is turned on to release the stress in the stress concentration area and break the stress equilibrium state of the coal seam 6 in the permeability enhancement area.

[0076] 3. First Fracturing Stage: The hydraulic fracturing pipe 23 is used to perform the first fracturing of the permeability-enhancing zone coal seam 6. Simultaneously, the vibration generator 21 is activated to accelerate the flow of the fracturing fluid through the fissures. As the fracturing fluid is injected, cracks begin to form as pressure increases, and the flow rate increases accordingly. Once cracks form and expand, the fracturing fluid flows more easily into the cracks, further increasing the flow rate.

[0077] 4. Cleaning and gas displacement stage: First, use the first high-pressure pump 27 to inject water from the water tank 26 into the hydraulic fracturing pipe 23 to flush the residual fracturing fluid, and then use dry nitrogen to contact the residual water to evaporate the water and flow out with the gas. At the same time, the nitrogen also displaces the gas in the coal seam 6.

[0078] 5. Magnetothermal Reflectivity Enhancement Process: Open third valve 41 to allow the nano-magnetic fluid to flow into horizontal well 8. Turn on the magnetothermal heating switch to begin preheating, with the temperature set to 100°C. Real-time monitoring and adjustment of the temperature and pressure of coal seam 6 and the magnetic field intensity are performed to achieve precise control and optimal heating of coal seam 6.

[0079] 6. Coal seam 6 drying and degassing stage: adjust the frequency converter 43 to raise the temperature of the nano-magnetic fluid to 150°C, then start the second high-pressure pump 40 to inject the 150°C nano-magnetic fluid into the cracks of the coal seam 6. The water in the coal begins to evaporate, and the gas (such as methane) adsorbed on the coal surface begins to desorb.

[0080] 7. Coal Seam 6 Pyrolysis Reaction Stage: Adjust the frequency converter 43 to change the alternating magnetic field intensity, gradually heating the nano-magnetic fluid and observing the temperature detector to ensure that the temperature reaches 230°C. Observe the temperature detector and the pyrolysis temperature will gradually rise, the gas produced by the pyrolysis will gradually accumulate, and the pressure will begin to increase significantly.

[0081] 8. Coal Seam 6 Main Pyrolysis Stage: Adjusting inverter 43 to change the alternating magnetic field intensity gradually heats the nanomagnetic fluid to 450°C, reaching the temperature of the main pyrolysis stage. Observing the temperature detector, the pyrolysis reaction reaches its peak, with large amounts of gaseous and liquid products generated, and the coal structure undergoing significant changes.

[0082] 9. Gas extraction phase: Turn on the magnetic thermal heating switch to heat the gas to 80°C, and start the vibration generator 21 to promote the desorption of coalbed methane. Turn on the extraction pump to extract the coalbed methane under negative pressure to remove impurities in the coalbed methane, and finally transport it to the coalbed methane storage tank 54.

[0083] Example 2: A soft coal seam with gas outburst was encountered with a depth of about 980m and a thickness of about 5m.

[0084] 1. Preparation stage: Drill a hole at a set position in the coal seam 6 in the permeability enhancement zone, and install a pressure sensor 33 and a sensor chip 20 to monitor the stress value.

[0085] 2. When the stress value reaches 50 MPa to 70 MPa, the vibration generator 21 is turned on to release the stress in the stress concentration area and break the stress equilibrium state of the coal seam 6 in the permeability enhancement area.

[0086] 3. First Fracturing Stage: The hydraulic fracturing pipe 23 is used to perform the first fracturing of the permeability-enhancing zone coal seam 6. Simultaneously, the vibration generator 21 is activated to accelerate the flow of the fracturing fluid through the fissures. As the fracturing fluid is injected, cracks begin to form as pressure increases, and the flow rate increases accordingly. Once cracks form and expand, the fracturing fluid flows more easily into the cracks, further increasing the flow rate.

[0087] 4. Cleaning and gas displacement stage: First, use the first high-pressure pump 27 to inject water from the water tank 26 into the hydraulic fracturing pipe 23 to flush the residual fracturing fluid, and then use dry nitrogen to contact the residual water to evaporate the water and flow out with the gas. At the same time, the nitrogen also displaces the gas in the coal seam 6.

[0088] 5. During the magnetothermal enhancement process, open third valve 41 to allow the nano-magnetic fluid to flow into horizontal well 8. Turn on the magnetothermal heating switch to begin preheating, with the temperature set to 100°C. Real-time monitoring and adjustment of the temperature and pressure of coal seam 6 and the magnetic field intensity are performed to achieve precise control and optimal heating of coal seam 6.

[0089] 6. Coal seam 6 drying and degassing stage: adjust the frequency converter 43 to raise the temperature of the nano-magnetic fluid to 170°C, then start the second high-pressure pump 40 to inject the 170°C nano-magnetic fluid into the cracks of the coal seam 6. The water in the coal begins to evaporate, and the gas (such as methane) adsorbed on the coal surface begins to desorb.

[0090] 7. Coal Seam 6 Pyrolysis Reaction Stage: Adjust the frequency converter 43 to change the alternating magnetic field intensity, gradually heating the nano-magnetic fluid to 240°C. Observe the temperature detector to ensure that the temperature reaches the initial stage of the pyrolysis reaction. Observe the temperature detector and the pyrolysis temperature will gradually rise. As the pyrolysis gas gradually accumulates, the pressure begins to increase significantly.

[0091] 8. Coal Seam 6 Main Pyrolysis Stage: Adjusting inverter 43 to change the alternating magnetic field intensity gradually heats the nanomagnetic fluid to 450°C, reaching the temperature of the main pyrolysis stage. Observing the temperature detector, the pyrolysis reaction reaches its peak, with large amounts of gaseous and liquid products generated, and the coal structure undergoing significant changes.

[0092] 9. Gas extraction phase: Turn on the magnetic thermal heating switch to heat the gas to 80°C, and start the vibration generator 21 to promote the desorption of coalbed methane. Turn on the extraction pump to extract the coalbed methane under negative pressure, remove impurities in the coalbed methane, and then transfer it to the coalbed methane storage tank 54.

[0093] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0094] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A high stress low permeability coal seam permeability enhancement system, characterized in that: The high stress and low permeability coal seam permeability enhancement system comprises: a vibration subsystem for collecting stress values of the coal seam and, when the stress value of the coal seam reaches a set condition, releasing stress in a stress concentration area of the coal seam to break the stress equilibrium state of the coal seam; a fracturing subsystem, configured to hydraulically fracture the coal seam after the vibration subsystem breaks the stress equilibrium state of the coal seam, thereby forming a plurality of cracks in the coal seam; The fracturing subsystem includes: a hydraulic fracturing pipe, a mixing device, a fracturing fluid storage tank, a water tank, a first high-pressure pump, a first flow meter, a dry nitrogen storage tank, a circulation pump, a first valve, a second valve, a pressure sensor and a second control component; The hydraulic fracturing pipe extends from the ground into the coal seam; the outlet of the mixing device is communicated with the inlet of the fracturing fluid storage tank; the outlet of the fracturing fluid storage tank and the outlet of the water tank are both communicated with the inlet of the first high-pressure pump; the outlet of the first high-pressure pump is communicated with the inlet of the hydraulic fracturing pipe; the first flow meter is arranged between the outlet of the first high-pressure pump and the inlet of the hydraulic fracturing pipe; the outlet of the dry nitrogen storage tank is communicated with the inlet of the circulation pump; the outlet of the circulation pump is communicated with the inlet of the hydraulic fracturing pipe; the first valve is arranged between the outlet of the first high-pressure pump and the first flow meter; the second valve is arranged between the outlet of the dry nitrogen storage tank and the inlet of the circulation pump; the pressure sensor is arranged in the hydraulic fracturing pipe; The first flow meter is used to detect the flow rate of the liquid in the hydraulic fracturing pipe; the liquid in the hydraulic fracturing pipe is fracturing fluid or water; the pressure sensor is used to collect the pressure value in the hydraulic fracturing pipe; the second control component is connected to the pressure sensor, and the second control component is used to control the states of the first valve and the second valve according to the flow rate of the liquid in the hydraulic fracturing pipe and the pressure value in the hydraulic fracturing pipe, so as to hydraulically fracture the coal seam with the fracturing fluid; wherein, as the fracturing fluid is continuously injected, the pressure will gradually increase. When the pressure reaches the rupture point of the coal seam, the coal seam begins to crack, forming cracks, and quartz sand with a surface coated with a polymer material is used as a proppant, and the proppant and the fracturing fluid flow into the cracks through the hydraulic fracturing pipe together; The heat injection subsystem is used to use ferromagnetic oxide nanoparticles as heat carriers to increase the permeability of the coal seam based on the magnetocaloric principle after the coal seam is hydraulically fractured by the fracturing subsystem, thereby pyrolyzing the coal seam.

2. The high stress and low permeability coal seam anti-permeability system according to claim 1, characterized in that: The high stress and low permeability coal seam permeability enhancement system further comprises: The extraction subsystem is used to extract the coalbed methane under negative pressure after the coal seam is pyrolyzed by the heat injection subsystem.

3. The high stress and low permeability coal seam anti-permeability system according to claim 1, characterized in that: The vibration subsystem includes: a steel cylinder, a stress sensor, a sensor chip, a vibration generator and a first control component; the steel cylinder extends from the ground into the coal seam; the stress sensor and the vibration generator are both arranged on the steel cylinder; The stress sensor is used to collect the stress value of the coal seam; the sensor chip is connected to the stress sensor, and the sensor chip is used to receive the stress value collected by the stress sensor; the first control component is connected to the sensor chip and the vibration generator respectively, and the first control component is used to control the vibration generator to start when the stress value of the coal seam reaches a set condition, so as to release stress to the stress concentration area of the coal seam and break the stress equilibrium state of the coal seam.

4. The high stress and low permeability coal seam anti-permeability system according to claim 1, characterized in that: The heat injection subsystem includes: a ferromagnetic oxide nanoparticle storage container, a second high-pressure pump, a third valve, a second flow meter, a frequency converter, a magnetic induction coil, a temperature detector and a third control component; The outlet of the ferromagnetic oxide nanoparticle storage container is connected to the inlet of the second high-pressure pump; the outlet of the second high-pressure pump is connected to the hydraulic fracturing pipe; the third valve is arranged between the outlet of the second high-pressure pump and the hydraulic fracturing pipe; the second flow meter is arranged between the third valve and the hydraulic fracturing pipe; the temperature detector is arranged in the crack of the coal seam; the magnetic induction coil is arranged on the hydraulic fracturing pipe; the frequency converter is connected to the magnetic induction coil; and the third control component is respectively connected to the frequency converter, the temperature detector and the second flow meter; The third control component is used to heat the ferromagnetic oxide nanoparticles in the ferromagnetic oxide nanoparticle storage container after the fracturing subsystem hydraulically fractures the coal seam, so that the ferromagnetic oxide nanoparticles are converted into nanomagnetic fluid, and control the state of the third valve to allow the nanomagnetic fluid to flow into the fractures of the coal seam; The temperature detector is used to detect the temperature of the nano-magnetic fluid in the crack; the third control component is also used to adjust the frequency converter to change the alternating magnetic field intensity according to the temperature of the nano-magnetic fluid in the crack, so as to increase the temperature of the nano-magnetic fluid in the crack, thereby increasing the permeability of the coal seam and causing pyrolysis of the coal seam.

5. A method for increasing the permeability of a high-stress, low-permeability coal seam, using the high-stress, low-permeability coal seam increasing permeability system according to any one of claims 1 to 4, characterized in that: The high stress and low permeability coal seam permeability enhancement method comprises: Collect stress values of coal seams; When the stress value of the coal seam reaches a set condition, releasing stress in the stress concentration area of the coal seam to break the stress equilibrium state of the coal seam; After breaking the stress equilibrium state of the coal seam, hydraulically fracturing the coal seam; After the coal seam is hydraulically fractured, ferromagnetic oxide nanoparticles are used as heat carriers to increase the permeability of the coal seam based on the magnetocaloric principle, thereby causing the coal seam to be pyrolyzed.

6. The method for increasing permeability of high-stress low-permeability coal seams according to claim 5, characterized in that: The high stress and low permeability coal seam permeability enhancement method further comprises: After the coal seam is pyrolyzed, the coal seam gas is extracted under negative pressure.

7. The method for increasing permeability of high-stress low-permeability coal seams according to claim 5, characterized in that: When the stress value of the coal seam reaches a set condition, the stress is released in the stress concentration area of the coal seam to break the stress equilibrium state of the coal seam, specifically including: When the stress value of the coal seam reaches a set condition, the vibration generator is started to release the stress in the stress concentration area of the coal seam to break the stress equilibrium state of the coal seam.

8. The method for increasing permeability of high-stress low-permeability coal seams according to claim 5, characterized in that: After breaking the stress equilibrium state of the coal seam, hydraulic fracturing is performed on the coal seam, specifically comprising: After breaking the stress equilibrium state of the coal seam, starting the first high-pressure pump and the first valve; injecting the fracturing fluid in the fracturing fluid storage tank into the hydraulic fracturing pipe by the first high-pressure pump to fracture the coal seam, thereby forming a plurality of cracks in the coal seam; Real-time detection of the flow rate of the fracturing fluid in the hydraulic fracturing pipe and real-time collection of the pressure value in the hydraulic fracturing pipe; When the flow rate of the fracturing fluid in the hydraulic fracturing pipe and the pressure value in the hydraulic fracturing pipe reach a stable state, injecting water in the water tank into the hydraulic fracturing pipe through the first high-pressure pump to flush the fracturing fluid in the hydraulic fracturing pipe; The first valve is closed, and the second valve is opened. Dry nitrogen in the dry nitrogen storage tank is injected into the hydraulic fracturing pipe through a circulation pump to evaporate water in the hydraulic fracturing pipe, and the second valve is closed.

9. The method for increasing permeability of high-stress low-permeability coal seams according to claim 8, characterized in that: After hydraulic fracturing the coal seam, ferromagnetic oxide nanoparticles are used as heat carriers to increase the permeability of the coal seam based on the magnetocaloric principle, thereby pyrolyzing the coal seam, which specifically includes: After hydraulic fracturing the coal seam, heating the ferromagnetic oxide nanoparticles in the ferromagnetic oxide nanoparticle storage container to convert the ferromagnetic oxide nanoparticles into nanomagnetic fluid, and opening a third valve; injecting the nano-magnetic fluid into the hydraulic fracturing pipe through a second high-pressure pump, so that the nano-magnetic fluid flows into the cracks of the coal seam; Real-time detection of the temperature of the nano-magnetic fluid in the crack; According to the temperature of the nano-magnetic fluid in the crack, the frequency converter is adjusted to change the alternating magnetic field intensity to increase the temperature of the nano-magnetic fluid in the crack, thereby increasing the permeability of the coal seam and pyrolyzing the coal seam.

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