High-stress low-permeability coal seam anti-reflection system and method

Abstract

The invention discloses a high-stress low-permeability coal seam anti-reflection system and method, and relates to the field of coal bed gas exploitation, and the system comprises a vibration subsystem which is used for collecting a stress value of a coal seam, and releasing stress in a stress concentration area of the coal seam when the stress value of the coal seam reaches a set condition, so as to break the stress balance state of the coal seam; the fracturing subsystem is used for performing hydraulic fracturing on the coal seam after the stress balance state of the coal seam is broken, so that a plurality of cracks are formed in the coal seam; and the heat injection subsystem is used for performing permeability increasing on the coal seam based on the magnetocaloric principle by adopting ferromagnetic oxide nanoparticles as a heat carrier after the coal seam is subjected to hydraulic fracturing, so that the coal seam is pyrolyzed. According to the method, vibration and hydraulic fracturing are combined, stress release and pre-cracking are effectively conducted on the coal seam, ferromagnetic oxide nanoparticles are adopted as heat carriers, permeability increasing is conducted on the coal seam on the basis of the magnetocaloric principle, damage to the coal seam is reduced, the pyrolysis permeability increasing precision of the coal seam is improved, and the risk of environmental pollution is reduced.

Description

Technical Field

[0001] The 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 ground stress, high gas pressure and high fissure water pressure), high temperature and low permeability. The above characteristics will significantly increase the frequency and severity of rock bursts, coal and gas outburst accidents in deep coal seams, and bring safety hazards to deep coal seam mining.

[0003] The current coal seam permeability enhancement technologies mainly include: carbon dioxide fracturing, hydraulic fracturing and mechanical cavitation, but the use 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 fracture formation, and damage to the coal seam. When fracturing 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 the damage of water pressure, blocking the gas migration channel and affecting subsequent fracturing work. (3) Carbon dioxide fracturing technology has certain difficulties in accurately controlling the carbon dioxide fracturing process due to the physical properties of carbon dioxide (such as heat of vaporization, pressure changes with temperature, etc.). Compared with hydraulic fracturing technology, there are fewer applications of carbon dioxide fracturing technology in coal seam permeability enhancement, and there is a lack of sufficient experience accumulation and case analysis. In addition, carbon dioxide fracturing technology requires special equipment and materials, and its cost is higher than that of traditional hydraulic fracturing technology.

[0005] Therefore, it is necessary to propose a new permeability enhancement scheme 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 and 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 object, the present invention provides a high stress and low permeability coal seam permeability enhancement system, comprising: A vibration subsystem is used to collect the stress value of the coal seam, and when the stress value of the coal seam reaches a set condition, release the stress to the stress concentration area of ​​the coal seam to break the stress equilibrium state of the coal seam; A fracturing subsystem, used for hydraulically fracturing the coal seam after the vibration subsystem breaks the stress equilibrium state of the coal seam, so as to form a plurality of cracks in the coal seam; 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 magnetothermal principle after the fracturing subsystem has hydraulically fractured the coal seam, thereby pyrolyzing the coal seam.

[0008] To achieve the above object, the present invention also provides a high stress low permeability coal seam permeability enhancement method, using the above high stress low permeability coal seam permeability enhancement system, the high stress 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 pyrolyzing the coal seam.

[0009] 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-crack the coal seam. In addition, the magnetothermal principle is used to increase the permeability of the coal seam, which can form more pores and promote the analysis of coalbed methane. The magnetic field has less damage to the coal seam, which is beneficial to maintaining the integrity and stability of the coal seam. 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 oxidation reactions 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

[0010] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. 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 creative labor.

[0011] Figure 1 Schematic diagram of the vibration subsystem and the fracturing subsystem.

[0012] Figure 2 It is a three-dimensional well diagram.

[0013] Figure 3Schematic diagram of the heat injection subsystem.

[0014] Figure 4 Schematic diagram of the extraction subsystem.

[0015] Figure 5 A flow chart of the high stress and low permeability coal seam permeability enhancement method provided by the present invention.

[0016] 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-bottom plate, 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

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0018] 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 utilizes the magnetothermal principle to pyrolyze the coal seam to achieve a permeability enhancement effect, thereby maximizing resource utilization and reducing the difficulty of coalbed methane extraction.

[0019] 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.

[0020] 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.

[0021] (1) The vibration subsystem is used to collect the stress value of the coal seam, and when the stress value of the coal seam reaches the 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. Releasing the stress of the coal seam through the vibration subsystem can solve the problem of stress concentration.

[0022] Specifically, 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 arranged on the steel cylinder. There are rock layer 1 2, rock layer 2 3, rock layer 3 4 and roof 5 between the ground 1 and the coal seam 6, and the bottom of the coal seam 6 is the bottom plate 7. Drill a hole from the ground 1 to the coal seam 6 to form a horizontal well 8, as shown in FIG. Figure 2 shown.

[0023] Among them, the number of steel cylinders, stress sensors 19 and vibration generators 21 are all multiple. As a specific implementation, the number of steel cylinders is 5: the first steel cylinder 14, the second steel cylinder 15, the third steel cylinder 16, the fourth steel cylinder 17 and the fifth steel cylinder 18, the number of stress sensors 19 is 20, and the number of vibration generators 21 is 50, that is, 4 stress sensors 19 and 10 vibration generators 21 are set on each steel cylinder. The function of the steel cylinder is to fix and protect the stress sensor 19.

[0024] The stress sensor 19 is used to collect the stress value of the coal seam 6. The sensor chip 20 is connected to the stress sensor 19, and the sensor chip 20 is used to receive the stress value collected by the stress sensor 19. The first control component 22 is connected to the sensor chip 20 and the vibration generator 21 respectively, and the first control component 22 is used to control the vibration generator 21 to start when the stress value of the coal seam 6 reaches a set condition, so as to release stress in the stress concentration area of ​​the coal seam 6 to break the stress equilibrium state of the coal seam 6.

[0025] The present invention firstly drills the coal seam 6 in the permeability enhancement zone, that is, generates 5 boreholes: the first borehole 9, the second borehole 10, the third borehole 11, the fourth borehole 12 and the fifth borehole 13, and a steel cylinder is correspondingly arranged in each borehole. The stress sensor 19 is installed in the coal seam 6 in the borehole to collect the stress value of the coal seam 6, and the sensor chip 20 converts the stress value collected by the stress sensor 19 into an electrical signal. When the stress value of the soft coal seam reaches 50Mpa~70Mpa, or the stress value of the hard coal seam reaches 70Mpa~90Mpa, the vibration generator 21 is turned on to release the stress in the stress concentration area of ​​the coal seam 6, breaking the stress equilibrium state of the coal seam 6 in the permeability enhancement zone.

[0026] (2) The fracturing subsystem is used to hydraulically fractur the coal seam 6 after the vibration subsystem breaks the stress equilibrium state of the coal seam 6, so as to form a plurality of cracks in the coal seam 6.

[0027] Specifically, 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.

[0028] The hydraulic fracturing pipe 23 extends from the ground 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 flow meter 28 is arranged 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 gas 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 arranged between the outlet of the first high-pressure pump 27 and the first flow meter 28. The second valve 32 is arranged between the outlet of the dry nitrogen gas storage tank 29 and the inlet of the circulation pump 30. The pressure sensor 33 is arranged in the hydraulic fracturing pipe 23.

[0029] The first flow meter 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 the second control component 34 is used to control the state of the first valve 31 and the second valve 32 according to 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 through the fracturing fluid.

[0030] After breaking the stress equilibrium state of the coal seam 6, the hydraulic fracturing pipe 23 is used to perform the first fracturing on the permeability enhancement zone coal seam 6, and at the same time, the vibration generator 21 is turned on to accelerate the flow of fracturing fluid in the cracks of the coal seam 6. 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 23. The coating polymer of the proppant is selected from epoxy resin, which is used to support the cracks. 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 .

[0031] As the fracturing fluid is continuously injected, the pressure will gradually increase. When the pressure reaches the breaking point of the coal seam 6, the coal seam 6 begins to crack and form cracks. In this process, due to the opening of the cracks, the flow rate will increase accordingly. Once the cracks are formed and expanded to a certain extent, the fracturing fluid will flow into the cracks more easily, further increasing the flow rate and the pressure value will drop slightly. Observe the pressure sensor 33 and the flow meter. When the pressure value and flow rate reach a relatively stable state, it indicates that the hydraulic fracturing effect has reached its limit.

[0032] The first high-pressure pump 27 is further used to inject water from the water tank 26 into the hydraulic fracturing pipe 23, and the residual fracturing fluid in the hydraulic fracturing pipe 23 is washed clean by the force of the high-pressure water flow. The first valve 31 is closed. Then the second valve 32 is opened, and the flowing dry nitrogen is used to contact the residual water in the hydraulic fracturing pipe 23, so that the water evaporates and flows out with the gas. At the same time, the nitrogen can also displace the gas in the coal seam 6.

[0033] (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 fracturing subsystem has hydraulically fractured the coal seam 6, thereby causing pyrolysis of the coal seam 6.

[0034] Specifically, 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.

[0035] 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.

[0036] 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 arranged between the outlet of the second high-pressure pump 40 and the hydraulic fracturing pipe 23. The second flow meter 42 is arranged between the third valve 41 and the hydraulic fracturing pipe 23. The temperature detector is arranged in the crack of the coal seam 6. The magnetic induction coil 44 is arranged 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 flow meter 42.

[0037] The third control component 47 is used to heat the ferromagnetic oxide nanoparticles in the ferromagnetic oxide nanoparticle storage container 39 after the fracturing subsystem performs hydraulic fracturing on the coal seam 6, so that the ferromagnetic oxide nanoparticles become nanomagnetic fluids, and control the state of the third valve 41 so that the nanomagnetic fluid flows into the cracks of the coal seam 6. Specifically, the third valve 41 is controlled to be opened so that the nanomagnetic fluid flows into the cracks of the coal seam 6.

[0038] The ferromagnetic oxide nanoparticle storage container 39 can also directly adopt a nano magnetic fluid storage tank.

[0039] The temperature detector is used to detect the temperature of the nano magnetic fluid in the crack. The third control component 47 is also used to adjust the frequency converter 43 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 6 and causing the coal seam 6 to pyrolyze.

[0040] The present invention selects ferromagnetic oxide nanoparticles as heat carriers, which will show strong magnetism under an external 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, and the magnetothermal heating switch in the third control component 47 is turned on to start preheating. The temperature is set to 100°C~120°C, and the nanomagnetic fluid is heated. The temperature detected by the temperature detector is observed to ensure that the nanomagnetic fluid has reached the set temperature. During the magnetothermal permeability enhancement process, the temperature and pressure of the coal seam 6 need to be monitored and adjusted in real time, and the strength of the magnetic field is adjusted in time to achieve accurate control and optimization of the heating of the coal seam 6.

[0041] 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 the 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 (such as methane) adsorbed on the coal surface begins to desorb. The temperature rises slowly and the pressure drops slightly.

[0042] The temperature of the initial stage of the pyrolysis reaction of the coal seam 6 is in the range of 200°C to 400°C. The frequency converter 43 is adjusted to change the alternating magnetic field strength so that the nano magnetic fluid gradually heats up. The temperature detected by the temperature detector is observed. When the temperature reaches 380°C to 400°C, the coal begins to undergo thermochemical decomposition and produces light hydrocarbon gas. The structure of the coal also begins to change. Observe the temperature detected by the temperature detector. The temperature will continue to rise and the rising speed will accelerate. As the gas produced by pyrolysis gradually accumulates, the pressure begins to increase significantly.

[0043] The temperature of the main pyrolysis stage of the coal seam 6 is in the range of 400°C to 600°C. The frequency converter 43 is adjusted to change the alternating magnetic field strength, so that the nano magnetic fluid gradually heats up to above 450°C, the pyrolysis reaction reaches a peak, and a large amount of gas and liquid products are generated. The structure of the coal changes significantly, forming semi-coke or coke. Observe the temperature detected by the temperature detector. The heat released by the pyrolysis reaction reaches a balance with the heating of the heat source. At this time, the temperature reaches a peak and remains stable, and the pressure reaches a maximum value and remains relatively stable.

[0044] During the pyrolysis process, after the volatile matter in the coal is released, the porosity and specific surface area of ​​the coal increase. After pyrolysis, hard or brittle minerals will be formed in the coal seam 6, which increases the hardness of the coal seam 6 and enhances its anti-deformation ability. The magnetothermal heating switch and the vibration generator 21 are further turned on to promote the analysis of coalbed methane.

[0045] (4) The extraction subsystem is used to extract the coalbed methane under negative pressure after the heat injection subsystem pyrolyzes the coal seam 6.

[0046] Specifically, 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. Among them, the number of extraction pumps is the same as the number of steel cylinders, and the number of extraction pumps is 5: 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 coalbed methane.

[0047] 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.

[0048] 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 also provides a high stress and low permeability coal seam permeability enhancement method, including steps 1 to 4.

[0049] Step 1: Collect the stress value of coal seam 6.

[0050] 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.

[0051] Specifically, when the stress value of the coal seam 6 reaches the set condition, the vibration generator 21 is started to release the stress in the stress concentration area of ​​the coal seam 6 to break 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 50Mpa~70Mpa. If the coal seam 6 is a hard coal seam, the set condition is a stress range of 70Mpa~90Mpa.

[0052] Step 3: After breaking the stress equilibrium state of the coal seam 6, hydraulic fracturing is performed on the coal seam 6.

[0053] 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.

[0054] The first high-pressure pump 27 injects the fracturing fluid in the fracturing fluid storage tank 25 into the hydraulic fracturing pipe 23 to fracture the coal seam 6 , so that a plurality of cracks are formed in the coal seam 6 .

[0055] 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.

[0056] 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 .

[0057] 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, and the second valve 32 is closed.

[0058] 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, so as to pyrolyze the coal seam 6.

[0059] 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.

[0060] The nano magnetic fluid is injected into the hydraulic fracturing pipe 23 through the second high-pressure pump 40 , so that the nano magnetic fluid flows into the cracks of the coal seam 6 .

[0061] The temperature of the nano magnetic fluid in the crack is detected in real time.

[0062] 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 that the nano magnetic fluid in the fracture is heated up, so as to increase the permeability of the coal seam 6 and pyrolyze the coal seam 6 .

[0063] Furthermore, the high-stress low-permeability coal seam permeability enhancement method further includes step 5: after the coal seam 6 is pyrolyzed, the coal seam gas is extracted under negative pressure.

[0064] The present invention combines vibration technology with hydraulic fracturing technology, which can effectively release stress and pre-crack the coal seam 6. The use of magnetothermal principle to increase permeability can form more pores and promote coalbed methane analysis. The magnetic field has less damage to the coal seam 6, which is beneficial to maintaining the integrity and stability of the coal seam 6. Furthermore, the nano-magnetic 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, nano-magnetic fluids have a lower risk of environmental pollution.

[0065] 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.

[0066] Example 1: A hard coal seam with gas outbursts was encountered with a burial depth of about 1030m and a thickness of about 6m.

[0067] 1. Preparation stage: Drill holes at the set positions of the permeability enhancement zone coal seam 6. Install stress sensors 19 and sensor chips 20 to monitor stress values.

[0068] 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 balance state of the coal seam 6 in the permeability enhancement area.

[0069] 3. First fracturing stage: Use hydraulic fracturing pipe 23 to perform the first fracturing on the permeability enhancement zone coal seam 6, and turn on vibration generator 21 to accelerate the flow of fracturing fluid in the cracks. When the fracturing fluid is injected, as the pressure increases, cracks begin to form and the flow rate increases accordingly. Once the cracks are formed and expanded, the fracturing fluid flows into the cracks more easily, further increasing the flow rate.

[0070] 4. Cleaning and gas displacement stage: First, use the first high-pressure pump 27 to inject water in 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 make the water evaporate and flow out with the gas. At the same time, the nitrogen also displaces the gas in the coal seam 6.

[0071] 5. Magnetothermal permeability enhancement process: Open the third valve 41 to allow the nano-magnetic fluid to flow into the horizontal well 8, turn on the magnetothermal heating switch to start preheating, and set the temperature to 100° C. Monitor and adjust the temperature and pressure of the coal seam 6 in real time, adjust the magnetic field intensity, and achieve precise control and optimization of the heating effect of the coal seam 6.

[0072] 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.

[0073] 7. Coal seam 6 pyrolysis reaction stage: adjust the frequency converter 43, change the alternating magnetic field strength, make the nano magnetic fluid gradually heat up, and observe the temperature detector to ensure that the temperature reaches 230° C. Observe the temperature detector, the pyrolysis temperature will gradually rise, the gas produced by pyrolysis will gradually accumulate, and the pressure will begin to increase significantly.

[0074] 8. Main pyrolysis stage of coal seam 6: adjust the frequency converter 43, change the alternating magnetic field intensity, and gradually heat the nano magnetic fluid to 450°C, so that its temperature reaches the temperature of the main pyrolysis stage. Observe the temperature detector, the pyrolysis reaction reaches the peak, a large amount of gas and liquid products are generated, and the structure of the coal changes significantly.

[0075] 9. Gas extraction stage: Turn on the magnetic heat heating switch for heating, set the temperature to 80°C, turn on the vibration generator 21 to promote the analysis 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.

[0076] Example 2: A soft coal seam with gas outburst was encountered with a burial depth of about 980m and a thickness of about 5m.

[0077] 1. Preparation stage: drilling a hole at a set position of the coal seam 6 in the permeability enhancement zone, installing a pressure sensor 33 and a sensor chip 20 to monitor the stress value.

[0078] 2. When the stress value reaches 50Mpa~70Mpa, the vibration generator 21 is turned on to release the stress in the stress concentration area and break the stress balance state of the coal seam 6 in the permeability enhancement area.

[0079] 3. First fracturing stage: Use hydraulic fracturing pipe 23 to perform the first fracturing on the permeability enhancement zone coal seam 6, and turn on vibration generator 21 to accelerate the flow of fracturing fluid in the cracks. When the fracturing fluid is injected, as the pressure increases, cracks begin to form and the flow rate increases accordingly. Once the cracks are formed and expanded, the fracturing fluid flows into the cracks more easily, further increasing the flow rate.

[0080] 4. Cleaning and gas displacement stage: First, use the first high-pressure pump 27 to inject water in 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 make the water evaporate and flow out with the gas. At the same time, the nitrogen also displaces the gas in the coal seam 6.

[0081] 5. During the magnetothermal permeability enhancement process, the third valve 41 is opened to allow the nano-magnetic fluid to flow into the horizontal well 8, and the magnetothermal heating switch is turned on to start preheating, with the temperature set to 100° C. The temperature and pressure of the coal seam 6 are monitored and adjusted in real time, and the magnetic field strength is adjusted to achieve precise control and optimization of the heating effect of the coal seam 6.

[0082] 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.

[0083] 7. Coal seam 6 pyrolysis reaction stage: adjust the frequency converter 43, change the alternating magnetic field strength, make the nano magnetic fluid gradually heat up to 240°C, and observe the temperature detector to ensure that the temperature reaches the starting stage temperature of the pyrolysis reaction. Observe the temperature detector, the pyrolysis temperature will gradually rise, and the pressure will begin to increase significantly due to the gradual accumulation of gas produced by pyrolysis.

[0084] 8. Main pyrolysis stage of coal seam 6: adjust the frequency converter 43, change the alternating magnetic field intensity, and gradually heat the nano magnetic fluid to 450°C, so that its temperature reaches the temperature of the main pyrolysis stage. Observe the temperature detector, the pyrolysis reaction reaches the peak, a large amount of gas and liquid products are generated, and the structure of the coal changes significantly.

[0085] 9. Gas extraction stage: Turn on the magnetic heat heating switch for heating, set the temperature to 80°C, turn on the vibration generator 21 to promote the analysis of coalbed methane. Turn on the extraction pump to extract the coalbed methane under negative pressure, remove impurities in the coalbed methane, and then transport it to the coalbed methane storage tank 54.

[0086] The technical features of the above embodiments may 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.

[0087] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A high stress and 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 is used to collect the stress value of the coal seam, and when the stress value of the coal seam reaches a set condition, release the stress to the stress concentration area of ​​the coal seam to break the stress equilibrium state of the coal seam; A fracturing subsystem, used for hydraulically fracturing the coal seam after the vibration subsystem breaks the stress equilibrium state of the coal seam, so as to form a plurality of cracks in the coal seam; 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 magnetothermal principle after the fracturing subsystem has hydraulically fractured the coal seam, thereby pyrolyzing the coal seam.

2. The high stress and low permeability coal seam permeability enhancement system according to claim 1 is 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 heat injection subsystem pyrolyzes the coal seam.

3. The high stress and low permeability coal seam permeability enhancement system according to claim 1 is 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 to 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 respectively connected to the sensor chip and the vibration generator, 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 to break the stress equilibrium state of the coal seam.

4. The high stress and low permeability coal seam permeability enhancement system according to claim 1, characterized in that: 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 gas 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 gas 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 gas 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 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 state of the first valve and the second valve according to the flow rate of liquid in the hydraulic fracturing pipe and the pressure value in the hydraulic fracturing pipe, so as to hydraulically fracture the coal seam through fracturing fluid.

5. The high stress and low permeability coal seam permeability enhancement system according to claim 4, 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; 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 performs hydraulic fracturing on the coal seam, so that the ferromagnetic oxide nanoparticles are converted into nanomagnetic fluids, and control the state of the third valve so that the nanomagnetic fluids flow into the cracks of the coal seam; The temperature detector is used to detect the temperature of the nanomagnetic 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 nanomagnetic fluid in the crack, so as to increase the permeability of the coal seam and cause the coal seam to pyrolyze.

6. A high stress low permeability coal seam permeability enhancement method, using the high stress low permeability coal seam permeability enhancement system according to any one of claims 1 to 5, 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 pyrolyzing the coal seam.

7. The high stress and low permeability coal seam permeability enhancement method according to claim 6, 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.

8. The high stress and low permeability coal seam permeability enhancement method according to claim 6, characterized in that: 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, 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.

9. The high stress and low permeability coal seam permeability enhancement method according to claim 6, 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 through the first high-pressure pump to fracture the coal seam, so as to form 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, and the dry nitrogen in the dry nitrogen storage tank is injected into the hydraulic fracturing pipe through a circulation pump to evaporate the water in the hydraulic fracturing pipe, and the second valve is closed.

10. The high stress and low permeability coal seam permeability enhancement method according to claim 9, 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 magnetothermal principle, so as to pyrolyze 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, so that the nano magnetic fluid in the crack is heated up, so as to increase the permeability of the coal seam and pyrolyze the coal seam.

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