A gas combined drainage system and process

Abstract

The present invention discloses a gas combined drainage system and process, which relates to the technical field of gas drainage. It includes a foam fracturing system, a blasting gasification system, a drainage system, a detection unit and a control system. The fracturing pipeline of the foam fracturing system is arranged in the middle coal seam. The drainage points of the drainage system and the blasting points of the blasting gasification system are both located in the upper and lower coal seams on both sides of the middle coal seam. The drainage system operates in situ after the blasting gasification system withdraws the boreholes. Detection units are arranged on the foam fracturing system, the blasting gasification system and the drainage system. The foam fracturing system, the blasting gasification system, the drainage system and the detection unit are all communicatively connected to the control system. Through blasting operations, the present invention forms a favorable pressure unloading zone in the upper and lower coal seams. This unloading zone can significantly improve the gas permeability of the middle coal seam, making it easier for gas to escape, thereby effectively improving the gas drainage efficiency and significantly reducing the risk of gas outburst.

Description

Technical Field

[0001] The present invention relates to the technical field of gas drainage, and particularly to a combined gas drainage system and process. Background Art

[0002] Gas outburst is a special term for a disaster, which refers to a geological disaster caused by the increase of coal mining depth and gas content, and the formation of a soft coal seam breaking through the resistance line under the action of in-situ stress and the gravitational action of gas release, instantaneously releasing a large amount of gas and coal. In the process of coalbed methane extraction, gas outburst is a problem that cannot be ignored, especially in coal seams with high gas content, this problem is particularly prominent.

[0003] Traditional gas control methods, such as pre-drainage of gas and water injection for pressure reduction, although can reduce gas content and outburst risk to a certain extent, but in the face of complex and changeable geological conditions, these methods are often difficult to implement and the effects are not satisfactory. Especially in some coal seams with hard strata and complex structures, traditional control methods often cannot achieve the expected effects. Therefore, there is an urgent need for a new gas drainage system and process to solve this problem. Summary of the Invention

[0004] The purpose of the present invention is to provide a combined gas drainage system and process to solve the problems existing in the above-mentioned prior art and optimize the treatment of gas outburst problems.

[0005] To achieve the above purpose, the present invention provides the following solutions:

[0006] The present invention provides a combined gas drainage system, including a foam fracturing system, a blasting gasification system, a drainage system, a detection unit and a control system. The fracturing pipeline of the foam fracturing system is arranged in the middle coal seam. The drainage points of the drainage system and the blasting points of the blasting gasification system are both located in the upper coal seam and the lower coal seam on both sides of the middle coal seam. The drainage system operates in situ after the blasting gasification system withdraws the boreholes. The detection unit is arranged on the foam fracturing system, the blasting gasification system and the drainage system. The foam fracturing system, the blasting gasification system, the drainage system and the detection unit are all communicatively connected with the control system.

[0007] Preferably, the foam fracturing system includes a foam generator, a fracturing fluid storage tank, a high-pressure pump and a fracturing pipeline. One end of the foam generator is respectively connected to a water tank and a carbon dioxide gas storage tank, and the other end is connected to the fracturing fluid storage tank. The fracturing fluid storage tank is connected to the fracturing pipeline through a high-pressure pump. The fracturing pipeline is in an L shape and a plurality of fracturing holes are evenly distributed at equal intervals along the axial direction at the end.

[0008] Preferably, a mixer is connected to the fracturing fluid storage tank. The mixer is respectively communicated with the foam generator and the proppant storage tank. Proppant is stored in the proppant storage tank, and the proppant includes resin-coated sand, quartz sand, walnut shell, glass bead, plastic ball or ceramsite.

[0009] Preferably, a flowmeter and a valve of the detection unit are sequentially arranged on the outlet pipe of the high-pressure pump. A pressure sensor is arranged on the fracturing pipeline, and the pressure sensor is located inside the fracturing hole at the innermost side of the fracturing pipeline.

[0010] Preferably, the aperture of the fracturing hole is 50 mm - 100 mm; the outlet flow rate of the high-pressure pump is 150 L / min - 250 L / min, and the outlet pressure of the fracturing pipeline is 10 MPa - 15 MPa.

[0011] Preferably, the blasting gasification system includes a microencapsulation device, an injection pump, a water tank, a spiral static mixer and a Venturi injector. The upper end of the microencapsulation device is respectively communicated with a chemical reagent tank and a wrapping material tank, and the lower end is communicated with the spiral static mixer. The spiral static mixer is communicated with a plurality of the injection pumps. A plurality of drill holes are arranged at equal intervals and staggered between the upper coal seam and the lower coal seam. Steel cylinders are arranged in each drill hole. Each injection pump is communicated with the Venturi injector through a blasting pipe.

[0012] Preferably, the chemical reagent tank includes a hydrogen peroxide solution tank and a potassium perchlorate solution tank; the spacing between the drill holes is 2 m - 5 m; a temperature sensor of the detection unit is arranged on the plate heat exchanger of the microencapsulation device, and the temperature sensor is connected with a temperature controller; a pressure sensor of the detection unit is arranged on each injection pump, and the injection pressure of the injection pump is 5 MPa - 10 MPa.

[0013] Preferably, the gas drainage system includes a gas drainage pump, a separator and a gas storage tank. One end of the separator is communicated with the gas storage tank, and the other end is communicated with a plurality of the gas drainage pumps. Each gas drainage pump corresponds to one drill hole, and the gas drainage pump passes through the drill hole through a gas drainage pipe; a sampling port, a flowmeter of the detection unit and a gas concentration sensor are arranged on the outlet pipe of the gas drainage pump.

[0014] The present invention discloses a gas combined drainage process. According to the above-mentioned gas combined drainage system, the specific steps are as follows:

[0015] S1. Turn on the foam fracturing system and continuously inject the foam fracturing fluid. As the pressure gradually increases until it reaches the fracture point of the coal seam, the coal seam cracks and forms fractures. Further increase the flow rate of the foam fracturing fluid until the values of the flow meter and pressure sensor reach stability. Then gradually add proppants to the foam fracturing fluid. When the flow rate and pressure of the fracturing pipeline reach a stable state and the opening degree of the fracturing cracks remains at a predetermined standard, stop adding proppants.

[0016] S2. Turn on the blasting gasification system. Use a microencapsulation device to atomize the dissolved chemical reagent solution into tiny droplets through a spray head and make microcapsules. Turn on the injection pump and adjust the injection pressure of the injection pump to 5 MPa - 10 MPa. Inject the microcapsule mixture into the coal seam by means of pressure spraying. After the injection pressure of the microencapsulation device is stable and the values of the pressure sensor and flow meter reach stability, the injection pump stops injecting. After the injection is completed, utilize geothermal energy to catalyze the reaction of hydrogen peroxide and potassium perchlorate to generate a large amount of oxygen, increase the pressure in the coal seam, and cause the coal seam to fracture.

[0017] S3. Install the extraction system. When the gas concentration reaches more than 20% and the gas flow rate is stable, and at the same time meets the pressure standard of the negative pressure extraction system, it reaches the extraction standard. Turn on the extraction pump of the extraction system to conduct negative pressure extraction of coalbed methane. The coalbed methane is transported to the gas storage tank through a separator.

[0018] Preferably, in step S2, the operating temperature of the microencapsulation device is controlled at 15°C - 20°C, and the pressure at each location is monitored in real time; in step S3, a sample is taken before the coalbed methane enters the separator, and the gas sample is analyzed.

[0019] The present invention has achieved the following technical effects compared with the prior art:

[0020] Through blasting operations, the present invention forms a favorable pressure unloading zone in the upper and lower coal seams. This unloading zone can significantly improve the gas permeability of the middle coal seam, making it easier for gas to escape, thereby effectively improving the gas extraction efficiency and significantly reducing the risk of gas outburst. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 It is a schematic connection structure diagram of the fracturing and blasting system in the embodiment of the present invention;

[0023] Figure 2 Schematic diagram of the connection structure of the extraction system in the embodiment of the present invention;

[0024] Figure 3 Partial structure schematic diagram of the combined gas extraction system in the embodiment of the present invention;

[0025] In the figure: 1 - ground, 2 - rock stratum, 3 - roof, 4 - upper coal seam, 5 - middle coal seam, 6 - lower coal seam, 7 - floor, 8 - fracturing pipeline, 9 - foam fracturing crack, 10 - skip mining gasification coal seam, 11 - extraction pump, 12 - gas concentration sensor, 13 - pressure sensor, 14 - water tank, 15 - flowmeter, 16 - valve, 17 - high-pressure pump, 18 - fracturing fluid storage tank, 19 - mixer, 20 - proppant storage tank, 21 - foam generator, 22 - carbon dioxide gas storage tank, 23 - borehole, 24 - steel cylinder, 25 - injection pump, 26 - Venturi ejector, 27 - coalbed methane gas storage tank, 28 - pressure monitoring unit, 29 - temperature sensor, 30 - mixed microcapsule storage tank, 31 - temperature controller, 32 - plate heat exchanger, 33 - spiral static mixer, 34 - microencapsulation equipment, 35 - hydrogen peroxide solution tank, 36 - potassium perchlorate solution tank, 37 - coalbed methane analyzer, 38 - separator. Detailed implementation manners

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] The purpose of the present invention is to provide a combined gas extraction system and process to solve the problems existing in the prior art and optimize the treatment of gas outburst problems.

[0028] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0029] Embodiment 1

[0030] As Figures 1 to 3As shown in the figure, in this embodiment, a gas combined drainage system is provided, which includes a foam fracturing system, a blasting gasification system, a drainage system, a detection unit and a control system. The fracturing pipeline 8 of the foam fracturing system is arranged in the middle coal seam 5. The drainage points of the drainage system and the blasting points of the blasting gasification system are both located in the upper coal seam 4 and the lower coal seam 6 on both sides of the middle coal seam 5. The drainage system operates in situ after the blasting gasification system withdraws the borehole 23. Detection units are provided on the foam fracturing system, the blasting gasification system and the drainage system. The foam fracturing system, the blasting gasification system, the drainage system and the detection unit are all communicatively connected to the control system. In this embodiment, the middle coal seam 5 is the main area where gas accumulates. By blasting and gasifying on both sides of it, the channels can be effectively opened, which helps to accelerate the flow of gas towards the drainage points, making the negative pressure effect of the drainage system more significant and improving the drainage efficiency. By arranging the blasting points in the upper coal seam 4 and the lower coal seam 6 on both sides of the middle coal seam 5, the blasting operation can form a pressure unloading zone at these positions. The unloading zone helps to reduce the in-situ stress of the middle coal seam 5, making the gas in the middle coal seam 5 easier to escape and reducing the risk of gas outburst.

[0031] Specifically, the ground 1 is located at the top layer of the system, bearing the rock stratum 2 and the coal seam structure. The rock stratum 2 covers above the roof 3 and the coal seam, constituting an upper structure that cannot be ignored in the coal mining process. It provides support for the underground coal seam and affects the coal mining conditions. The roof 3 is a hard rock layer above the upper coal seam 4. The roof 3 is usually hard rock, which plays a role in protecting the coal seam and also affects the stability of the coal seam. The floor 7 is located below the coal seam and plays a role in supporting the coal seam and the whole structure. It is usually also a relatively hard rock stratum 2. Among them, the roof 3 and the floor 7 are key structural layers, which have an important impact on the stability and pressure conduction of the coal seam. The skip-mining gasified coal seams 10 are staggered and evenly distributed in the upper coal seam 4 and the lower coal seam 6.

[0032] As an alternative solution, in this embodiment, the foam fracturing system includes a foam generator 21, a fracturing fluid storage tank 18, a high-pressure pump 17 and a fracturing pipeline 8. One end of the foam generator 21 is respectively connected to the water tank 14 and the carbon dioxide gas storage tank 22, and the other end is connected to the fracturing fluid storage tank 18. The fracturing fluid storage tank 18 is connected to the fracturing pipeline 8 through the high-pressure pump 17. The fracturing pipeline 8 is in an L shape, and a number of fracturing holes are evenly distributed at equal intervals along the axial direction at the end. After the fracturing pipeline 8 is fractured, a number of foam fracturing fissures 9 will appear around the fracturing holes. In this embodiment, there is only one horizontal well in the middle coal seam 5, and one fracturing pipeline 8 is configured. After the fracturing pipeline 8 is fractured, it does not need to be withdrawn.

[0033] As an alternative, in this embodiment, a mixer 19 is connected to the fracturing fluid storage tank 18. The mixer 19 is respectively connected to the foam generator 21 and the proppant storage tank 20. Proppant is stored in the proppant storage tank 20. The proppant includes resin-coated sand, quartz sand, walnut shell, glass beads, plastic balls or ceramsite. In this embodiment, the selected proppant is resin-coated sand, whose base material is high-purity natural quartz sand, the resin type is phenolic resin, the resin coating ratio is 7%, and the proppant particle size is selected to be 0.6 mm - 1.18 mm.

[0034] As an alternative, in this embodiment, a flowmeter 15 and a valve 16 of the detection unit are sequentially arranged on the outlet pipe of the high-pressure pump 17, and a pressure sensor 13 is arranged on the fracturing pipeline 8. The pressure sensor 13 is located inside the fracturing hole at the innermost side of the fracturing pipeline 8. In this embodiment, each pressure sensor 13 is connected to a pressure monitoring unit 28 (digital display instrument), and the pressure on the fracturing pipeline 8 can be monitored in real time.

[0035] As an alternative, in this embodiment, the aperture of the fracturing hole is 50 mm - 100 mm; the outlet flow rate of the high-pressure pump 17 is 150 L / min - 250 L / min, and the outlet pressure of the fracturing pipeline 8 is 10 MPa - 15 MPa. In this embodiment, when dealing with deep coal seams, due to the high gas content and large stress in deep coal seams, gas outburst is likely to occur, so a higher fracturing pressure is required; when dealing with shallow coal seams, since the in-situ stress of shallow coal seams is relatively low, the fracturing pressure can be 12 MPa, and the scale of blasting gasification is also relatively small. The main purpose is to increase the gas flow channels in the shallow fractures and optimize the drainage efficiency.

[0036] As an alternative, in this embodiment, the blasting gasification system includes a microencapsulation device 34, an injection pump 25, a spiral static mixer 33 and a Venturi ejector 26. The upper end of the microencapsulation device 34 is respectively connected to a chemical reagent tank and a wrapping material tank, and the lower end is connected to the spiral static mixer 33. The spiral static mixer 33 is connected to a plurality of injection pumps 25. A plurality of drill holes 23 are arranged at equal intervals and staggered between the upper coal seam 4 and the lower coal seam 6. Steel cylinders 24 are arranged in the drill holes 23. Each injection pump 25 is connected to the Venturi ejector 26 through a blasting pipe. In this embodiment, the blasting gasification system can not only improve the gas drainage efficiency of the middle coal seam 5, but also improve the efficiency and safety of coal mining. It has higher flexibility and adaptability, is not limited by the formation structure and geological conditions, and can be effectively implemented in various complex coal seam environments. Using blasting technology to gasify the upper and lower coal seams 6 is an innovative and practical gas control method.

[0037] As an alternative, in this embodiment, the chemical reagent tank includes a hydrogen peroxide solution tank 35 and a potassium perchlorate solution tank 36; hydrogen peroxide and potassium perchlorate are prepared and mixed according to a mass ratio of 0.491. A spiral static mixer 33 is used to dissolve hydrogen peroxide and potassium perchlorate in a suitable solvent and mix with the wrapping material. Then, a microencapsulation device 34 is used to atomize the dissolved hydrogen peroxide and potassium perchlorate solution into tiny droplets through a spray head, and the solvent is removed by drying to improve the stability of the microcapsules. The spacing of the drill holes 23 is 2 m - 5 m, preferably 3 m. A temperature sensor 29 of the detection unit is provided on the plate heat exchanger 32 of the microencapsulation device 34, and the temperature sensor 29 is connected to a temperature controller 31. In this embodiment, a plate heat exchanger 32 is arranged in the mixed microcapsule storage tank 30, and a temperature sensor 29 is arranged in the plate heat exchanger 32. The temperature sensor 29 collects the liquid temperature data in real time and transmits it to the temperature controller 31. The temperature controller 31 compares the current temperature value in the plate heat exchanger 32 with the set value. If there is a deviation, the flow rate or power of the plate heat exchanger 32 is adjusted. The plate heat exchanger 32 adjusts the liquid temperature in the tank through a medium (cooling or heating), and this process is repeated until the temperature is maintained within a constant temperature range of 15°C - 20°C. A pressure sensor 13 of the detection unit is provided on each injection pump 25, and each pressure sensor 13 is connected to a pressure monitoring unit 28. The injection pressure of the injection pump 25 is 5 MPa - 10 MPa.

[0038] As an alternative, in this embodiment, the gas drainage system includes a drainage pump 11, a separator 38 and a gas storage tank 27. One end of the separator 38 communicates with the gas storage tank 27, and the other end communicates with a plurality of drainage pumps 11. Each drainage pump 11 corresponds to a drill hole 23, and the drainage pump 11 penetrates through the drill hole 23 through a drainage pipe; a sampling port, a flow meter 15 of the detection unit and a gas concentration sensor 12 are arranged on the air outlet pipe of the drainage pump 11.

[0039] Embodiment Two

[0040] In this embodiment, a gas combined drainage process is provided. According to the above gas combined drainage system, it specifically includes the following steps:

[0041] S1, start the foam fracturing system, and continue to inject foam fracturing fluid. As the pressure gradually increases until it reaches the rupture point of the coal seam, the coal seam cracks and forms cracks. The flow rate of the foam fracturing fluid is further increased until the values ​​of the flow meter 15 and the pressure sensor 13 are stable. Then, proppant is gradually added to the foam fracturing fluid. When the flow rate and pressure of the fracturing pipeline 8 reach a stable state and the openness of the fracturing gap is maintained at a predetermined standard, stop adding proppant. In this embodiment, the predetermined standards include a crack width of more than 5 mm, a crack length of more than 50 m, a crack closure capacity within the range of 10 MPa to 30 MPa, and a crack conductivity, i.e., a coal seam permeability increase of more than 5 times.

[0042] S2, start the blasting gasification system, use the microencapsulation device 34 to atomize the dissolved chemical reagent solution into tiny droplets through the spray head, and make microcapsules, start the injection pump 25, adjust the injection pressure of the injection pump 25 to 5MPa-10MPa, and inject the microcapsule mixture into the coal seam by pressure injection. After the injection pressure of the microencapsulation device 34 is stable and the values ​​of the pressure sensor 13 and the flow meter 15 are stable, the injection pump 25 stops injecting. After the injection is completed, the geothermal energy is used to catalyze the reaction of hydrogen peroxide and potassium perchlorate: , producing a large amount of oxygen, increasing the pressure in the coal seam and causing the coal seam to rupture;

[0043] S3, install the extraction system. When the gas concentration reaches more than 20% and the gas flow is stable, and the pressure standard of the negative pressure extraction system is met, the extraction standard is reached, and the extraction pump 11 of the extraction system is turned on to extract the coalbed methane under negative pressure. The coalbed methane is transported to the gas storage tank through the separator 38.

[0044] Preferably, in step S2, the operating temperature of the microencapsulation equipment 34 is controlled at 15°C-20°C, and the pressure at various locations is monitored in real time; in step S3, the coalbed methane is sampled before entering the separator 38, and the gas sample is analyzed.

[0045] Embodiment 3

[0046] A coal mine is located in an area with rich deep coal resources. The upper coal seam 4 of the coal mine is 3.0 meters thick, the lower coal seam 6 is 3.5 meters thick, and the coal seam depth is about 1,200 meters.

[0047] First, liquid water and carbon dioxide are transported to the foam generator 21. By adjusting the foam generator 21, a stable foam fracturing fluid is formed. The foam fracturing fluid can effectively penetrate the coal seam under high pressure conditions, generate cracks, and increase the permeability of the coal seam.

[0048] The prepared foam fracturing fluid is injected into the wellbore through a high-pressure pump 17. In this example, the coal seam is located deeper, with a higher gas content. Deep coal seams usually bear greater in-situ stresses and are prone to gas outbursts. Therefore, during the injection of the foam fracturing fluid, a relatively high fracturing pressure is required to ensure the generation of fractures and maintain the permeability of the coal seam. According to the size of the fractures and the characteristics of the coal seam, the injection pressure is adjusted to 13 MPa. This embodiment deals with deep coal seams with a high gas content. Deep coal seams have greater in-situ stresses and are prone to gas outbursts, so a higher fracturing pressure is needed. During the injection process, as the fracturing fluid is continuously injected, the pressure gradually increases. When the pressure reaches the fracture point of the coal seam (about 12 MPa), the coal seam begins to crack and form fractures. At this time, the flow rate and pressure reach a stable state, and then proppants are gradually added to the foam fracturing fluid to keep the fractures open.

[0049] First, prepare hydrogen peroxide and potassium perchlorate and mix them according to a mass ratio of 0.491. Use a spiral static mixer 33 to dissolve hydrogen peroxide and potassium perchlorate in a suitable solvent and mix them with the encapsulating material. Then, use a microencapsulation device 34 to atomize the dissolved hydrogen peroxide and potassium perchlorate solution into tiny droplets through a spray head, and remove the solvent through drying to improve the stability of the microcapsules. Control the temperature of the dried hydrogen peroxide and potassium perchlorate microcapsules at 15°C - 20°C through a thermostat 31 to inhibit the decomposition of both.

[0050] Turn on the pressure control system and adjust the injection pressure to 8 MPa. Then, turn on the injection pump 25 and inject the microcapsule mixture into the coal seam by means of pressure injection. After the injection pressure of the microencapsulation device 34 is stable and the values of the pressure sensor 13 and the flowmeter 15 reach stability, the injection pump 25 stops injecting. During the injection process, the control system monitors and controls the pressure changes during the injection process and maintains it between 5 MPa and 10 MPa. The temperature sensor 29 ensures that the temperature of the hydrogen peroxide microcapsules and the potassium perchlorate microcapsules is maintained between 25°C and 50°C to maintain the stability of the microcapsules and keep the reaction rate of hydrogen peroxide and potassium perchlorate relatively low.

[0051] Generally, the temperature of coal seams is between 130°C and 190°C. After injection, geothermal energy is used to catalyze the reaction of hydrogen peroxide and potassium perchlorate, generating a large amount of oxygen, increasing the pressure in the coal seams, causing the coal seams to rupture, and enhancing the gasification effect. A large amount of heat is released during the reaction, the temperature rises significantly, and the reaction rate is accelerated. The generated water is gasified into water vapor at high temperature, promoting the gasification reaction of the coal seams and converting the coal into usable synthesis gas. During the reaction process, coalbed methane samples are collected and sampled and detected by a coalbed methane analyzer 37 to analyze the composition and concentration of the gas samples. The specific quantification values of the collected coalbed methane samples are as follows: methane 25%, hydrogen 12%, carbon monoxide 28%, and carbon dioxide 35%. Among them, the ratio of carbon monoxide to carbon dioxide is 0.8, indicating that there is an appropriate combustion reaction during the gasification process.

[0052] After the coalbed methane samples meet the extraction standard, the extraction pump 11 is turned on to conduct negative-pressure extraction of the coalbed methane. The coalbed methane passes through the separator 38 to remove impurities and is finally transported to the gas storage tank 27.

[0053] Example 4

[0054] A certain coal mine has rich deep coal resources. The upper coal seam 4 of this coal mine has a thickness of 2.8 meters, and the lower coal seam 6 has a thickness of 3.2 meters. The depth of the coal seams is about 1000 meters.

[0055] First, liquid water and carbon dioxide are transported to the foam generator 21. By adjusting the foam generator 21, a stable foam fracturing fluid is formed. The foam fracturing fluid can effectively penetrate the coal seams under high-pressure conditions, generate fractures, and increase the permeability of the coal seams.

[0056] The prepared foam fracturing fluid is injected into the wellbore through the high-pressure pump 17. According to the size of the fractures and the characteristics of the coal seams, the injection pressure range is adjusted to 12 MPa. Since the in-situ stress of the shallow coal seams is relatively low, the fracturing pressure used is 12 MPa, and the scale of blasting gasification is also small. The main purpose is to increase the gas flow channels in the shallow fractures and optimize the extraction efficiency. During the injection process, as the fracturing fluid is continuously injected, the pressure gradually increases. When the pressure reaches the fracture point of the coal seam (about 11 MPa), the coal seam begins to crack and form fractures. At this time, the flow rate and pressure reach a stable state, and then proppants are gradually added to the foam fracturing fluid to keep the fractures open.

[0057] First, hydrogen peroxide and potassium perchlorate are prepared and mixed according to a mass ratio of 0.491. The hydrogen peroxide and potassium perchlorate are dissolved in a suitable solvent using a spiral static mixer 33 and mixed with the wrapping material. Then, a microencapsulation device 34 is used to atomize the dissolved hydrogen peroxide and potassium perchlorate solution into tiny droplets through a spray head, and the solvent is removed by drying to improve the stability of the microcapsules.

[0058] The temperature of the dried hydrogen peroxide and potassium perchlorate microcapsules is controlled between 15°C and 20°C by the thermostat 31 to inhibit the decomposition of both. During the injection process, the control system monitors and controls the pressure change during injection, maintaining it between 5 MPa and 10 MPa. Then, the injection pump 25 is turned on, and the microcapsule mixture is injected into the coal seam by means of pressure injection. During the injection process, the temperature sensor 29 ensures that the temperature of the hydrogen peroxide microcapsules and potassium perchlorate microcapsules is maintained between 25°C and 50°C.

[0059] Generally, the temperature of the coal seam is between 120°C and 180°C. After the injection is completed, geothermal energy is used to catalyze the reaction of hydrogen peroxide and potassium perchlorate, generating a large amount of oxygen, increasing the pressure in the coal seam, causing the coal seam to fracture, and improving the gasification effect. A large amount of heat is released during the reaction, the temperature rises significantly, and the reaction rate is accelerated. The generated water is gasified into water vapor at high temperature, promoting the gasification reaction of the coal seam and converting the coal into usable syngas. During the reaction process, coal seam gas samples are collected and the composition and concentration of the gas samples are analyzed. The specific quantification values of the collected coal seam gas samples are as follows: methane 30%, hydrogen 10%, carbon monoxide 25%, carbon dioxide 35%. The ratio of carbon monoxide to carbon dioxide is 0.71, indicating that there is an appropriate amount of oxidation reaction during the gasification process. In this case, it shows that the cracks have successfully expanded and the gas has been fully released.

[0060] After meeting the extraction standard, the extraction pump 11 is turned on to extract the coal seam gas under negative pressure. The coal seam gas passes through the separator 38 to remove impurities and is finally transported to the gas storage tank 27.

[0061] As can be seen from the above embodiments, the proportion of different gases in the gas composition can reflect the crack expansion situation after fracturing and gasification. For example, the ratio of methane to carbon dioxide can indicate whether the cracks have effectively expanded to the area with a high gas content; during the blasting gasification process, by monitoring the ratio of carbon monoxide to carbon dioxide in the gas composition, the chemical reaction efficiency of hydrogen peroxide and potassium perchlorate can be evaluated, and the temperature and gasification effect during the reaction process are crucial for gas escape.

[0062] In the present invention, specific examples are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A gas joint extraction system, characterized in that: It includes a foam fracturing system, an explosive gasification system, an extraction system, a detection unit and a control system. The fracturing pipeline of the foam fracturing system is arranged in the middle coal seam. The extraction point of the extraction system and the blasting point of the explosive gasification system are both located in the upper coal seam and the lower coal seam on both sides of the middle coal seam. The extraction system is operated in situ after the explosive gasification system is withdrawn from the borehole. The foam fracturing system, the explosive gasification system and the extraction system are all provided with the detection unit. The foam fracturing system, the explosive gasification system, the extraction system and the detection unit are all connected to the control system for communication. The blasting gasification system includes a microencapsulation device, an injection pump, a spiral static mixer and a venturi injector. The upper end of the microencapsulation device is respectively connected to a chemical reagent tank and a packaging material tank, and the lower end is connected to the spiral static mixer. The spiral static mixer is connected to a plurality of the injection pumps. The upper coal seam and the lower coal seam are staggered with a plurality of boreholes at equal intervals. Steel cylinders are arranged in the boreholes. Each of the injection pumps is connected to the venturi injector through a blasting tube. The chemical reagent tanks include a hydrogen peroxide solution tank and a potassium perchlorate solution tank; the spacing between the drill holes is 2m-5m; the plate heat exchanger of the microencapsulation equipment is provided with a temperature sensor of the detection unit, and the temperature sensor is connected to a temperature controller; each of the injection pumps is provided with a pressure sensor of the detection unit, and the injection pressure of the injection pump is 5MPa-10MPa.

2. The gas combined extraction system according to claim 1, characterized in that: The foam fracturing system includes a foam generator, a fracturing fluid storage tank, a high-pressure pump and a fracturing pipeline. One end of the foam generator is connected to a water tank and a carbon dioxide storage tank respectively, and the other end is connected to the fracturing fluid storage tank. The fracturing fluid storage tank is connected to the fracturing pipeline through a high-pressure pump. The fracturing pipeline is L-shaped and has a plurality of fracturing holes evenly distributed at equal intervals along the axial direction at the end.

3. The gas combined extraction system according to claim 2, characterized in that: The fracturing fluid storage tank is connected to a mixer, which is connected to the foam generator and the proppant reservoir respectively. The proppant reservoir stores proppant, which includes resin-coated sand, quartz sand, walnut shells, glass beads, plastic balls or ceramsite.

4. The gas combined extraction system according to claim 2, characterized in that: The flow meter and valve of the detection unit are arranged in sequence on the outlet pipe of the high-pressure pump, and a pressure sensor is arranged on the fracturing pipeline. The pressure sensor is located inside the innermost fracturing hole of the fracturing pipeline.

5. The gas combined extraction system according to claim 4, characterized in that: The aperture of the fracturing hole is 50mm-100mm; the outlet flow rate of the high-pressure pump is 150L / min-250L / min, and the outlet pressure of the fracturing pipeline is 10MPa-15MPa.

6. The gas combined extraction system according to claim 1, characterized in that: The extraction system includes an extraction pump, a separator and a gas storage tank. One end of the separator is connected to the gas storage tank, and the other end is connected to a plurality of the extraction pumps. Each extraction pump corresponds to a borehole, and the extraction pump passes through the borehole through an extraction pipe. A sampling port, a flow meter of the detection unit and a gas concentration sensor are provided on the outlet pipe of the extraction pump.

7. A gas joint extraction process, according to the gas joint extraction system according to any one of claims 1 to 6, characterized in that: The specific steps include: S1, start the foam fracturing system, continuously inject foam fracturing fluid, and as the pressure gradually increases until it reaches the breaking point of the coal seam, the coal seam will crack and form cracks, and further increase the flow rate of the foam fracturing fluid until the flow meter and pressure sensor values ​​are stable, and then gradually add proppant to the foam fracturing fluid. When the flow rate and pressure of the fracturing pipeline reach a stable state and the opening degree of the fracturing gap remains at a predetermined standard, stop adding proppant; S2, start the blasting gasification system, use the microencapsulation equipment to atomize the dissolved chemical reagent solution into tiny droplets through the spray head, and make microcapsules, start the injection pump, adjust the injection pressure of the injection pump to 5MPa-10MPa, and inject the microcapsule mixture into the coal seam by pressure injection. After the injection pressure of the microencapsulation equipment is stable and the values ​​of the pressure sensor and the flow meter are stable, the injection pump stops injecting. After the injection is completed, the geothermal energy is used to catalyze the reaction of hydrogen peroxide and potassium perchlorate to produce a large amount of oxygen, increase the pressure in the coal seam, and cause the coal seam to rupture; S3, install the extraction system. When the gas concentration reaches more than 20% and the gas flow is stable, and the pressure standard of the negative pressure extraction system is met, the extraction standard is reached, and the extraction pump of the extraction system is turned on to extract the coalbed methane under negative pressure. The coalbed methane is transported to the gas storage tank through the separator.

8. The gas combined extraction process according to claim 7, characterized in that: In step S2, the operating temperature of the microencapsulation equipment is controlled at 15°C-20°C, and the pressure at various locations is monitored in real time; in step S3, the coalbed methane is sampled before entering the separator, and the gas sample is analyzed.

Images