System and method for producing methane by in-situ plasma conversion of coal seams

Abstract

A system and method for producing methane by in-situ plasma conversion of coal seams, in which a plasma generator is movably arranged in a coal seam channel, and receives working medium and cooling medium from a working medium pipeline, and ionizes the working medium with high pressure to produce high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles, and the high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, and the high-temperature and high-activity hydrogen particles undergo a methanogenic reaction in situ in a reaction chamber to produce methane, and the methane is output from the vertical well. The system simplifies the process of producing methane from coal gasification, has low production costs, and high conversion efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of coal seam gasification, and in particular to a system and method for producing methane through in-situ plasma conversion of coal seams. Background Art

[0002] Coal seam in-situ gasification technology can convert underground coal seams into methane, hydrogen, carbon monoxide and other products on site. However, the methane in the coal seam in-situ gasification gas mainly comes from the pyrolysis reaction of the coal seam. Therefore, the methane content in the coal gas is generally about 10%, and the remaining 40-50% is hydrogen and carbon monoxide, accompanied by the production of about 40% carbon dioxide. On the one hand, this leads to great carbon emission pressure in the production process of coal seam gasification to methane. On the other hand, the remaining hydrogen and carbon monoxide need to be purified, separated, converted and methanated on the ground to further synthesize natural gas. The process is long and the system is complex, which increases investment and production costs. In addition, the traditional coal seam in-situ gasification method is the spontaneous reaction of underground dense coal seams with oxidants or gasifiers, which is semi-natural force controlled, with low conversion efficiency and low production intensity. Due to the complex environment of underground coal seams, coal seam interlayers, underground water gushing and the expansion of the reaction chamber all have a serious impact on the conversion reaction, making it difficult to ensure the efficient and stable supply of natural gas.

[0003] Therefore, the current coal seam in-situ gasification technology is expected to become an important supplement to my country's natural gas supply, but it has problems such as long process flow, large carbon emissions, high production costs, low conversion efficiency, and low production intensity. In order to ensure the efficient and stable supply of natural gas, a more optimized coal seam gasification method is urgently needed to efficiently and stably convert underground coal seams into natural gas products.

[0004] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0005] The purpose of the present invention is to provide a system and method for producing methane by in-situ plasma conversion of coal seams. In view of the current problems of long process flow, large carbon emissions, high production costs, low conversion efficiency, and low production intensity, a plasma generator that can simultaneously produce hydrogen and water vapor active particles is constructed in the coal seam. The high-temperature and highly active water vapor particles generated by high-voltage ionization of the plasma generator undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, and then further undergo a methanation reaction in situ with the high-temperature and highly active hydrogen particles generated by high-voltage ionization of the plasma generator in the reaction chamber to produce methane gas, which is discharged to the ground through a vertical well and can be used as a natural gas product after purification and separation. The transformation and methanogenic stages of coal seam gasification on the ground are eliminated, the process flow is shortened, and the production cost is reduced; only a small amount of by-products such as carbon dioxide are produced, which is environmentally friendly; due to the action of high-temperature and highly active particles, the underground in-situ conversion reaction is strengthened, the conversion effect is high, and the production intensity is large. In order to achieve the above-mentioned purpose, the present invention provides the following technical solutions:

[0006] A coal seam in-situ plasma conversion methane production system of the present invention comprises:

[0007] At least one directional drilling well, which vertically penetrates the overburden and the upper edge of the coal seam from the ground to form a vertical channel, and gradually deflects to the horizontal direction to form a non-vertical channel in the coal seam,

[0008] The vertical well uses the coordinates at the end of the non-vertical channel as the target point and passes vertically from the ground through the overburden and coal seam to connect with the non-vertical channel. The non-vertical channel between the directional drilling well and the vertical well is the coal seam channel. The vertical well is located in the pipeline of the coal seam and the sieve holes are arranged.

[0009] The gas injection pipe has one end connected to a gas injection pipe moving device located on the ground for moving the gas injection pipe, and the other end connected to a plasma generator. The gas injection pipe includes a power cable, a working medium pipeline and a cooling medium pipe.

[0010] A plasma generator is movably arranged in a coal seam channel. The plasma generator receives working medium and cooling medium from a working medium pipeline and ionizes the working medium at high pressure to generate high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles. The high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, which undergo a methanation reaction with the high-temperature and high-activity hydrogen particles in situ in the reaction chamber to generate methane, which is output from the vertical well.

[0011] In the in-situ plasma conversion system for producing methane from coal seams, the terminal coordinates of the non-vertical channel of the directional drilling are the target point, and the directional drilling also vertically passes through the overburden and the upper edge of the coal seam from the ground, and gradually deflects from the coal seam to the target point until it penetrates to form a directional drilling II. The non-vertical channel connecting the directional drilling and the directional drilling in the coal seam is the coal seam channel; between the directional drilling and the directional drilling II, a vertical channel is formed by vertically passing through the overburden and the coal seam from the ground as a vertical well, the directional drilling is provided with the gas injection pipe and the plasma generator, the directional drilling II is provided with the gas injection pipe II and the plasma generator II connected to the gas injection pipe II, the plasma generator II receives the working medium and the cooling medium from the working medium pipeline, and ionizes the working medium with high pressure to generate high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles, the high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, and the high-temperature and high-activity hydrogen particles undergo a methanogenic reaction in situ in the reaction chamber to produce methane.

[0012] In the coal seam in-situ plasma conversion methane production system, the plasma generator and plasma generator II are arranged on the same side of the vertical well and are arranged opposite to each other.

[0013] In the coal seam in-situ plasma conversion system for producing methane, the plasma generator and plasma generator II are arranged on both sides of the vertical well and are arranged opposite to each other.

[0014] In the coal seam in-situ plasma conversion methane production system, the gas injection pipe and the gas injection pipe II are both made of high temperature resistant, corrosion resistant and hydrogen embrittlement resistant steel, alloy material, carbon fiber material or composite material.

[0015] In the coal seam in-situ plasma conversion methane production system, the horizontal angle of the vertical channel is between 75° and 105°, and the horizontal angle of the non-vertical channel is between 0° and 20°.

[0016] In the coal seam in-situ plasma conversion system for producing methane, the coal seam channel length is 100 to 3000 m.

[0017] In the coal seam in-situ plasma conversion methane production system, a test device for detecting the gas flow rate and components of the gas is arranged at the wellhead of the vertical well located on the ground.

[0018] In the coal seam in-situ plasma conversion system for producing methane, the working medium includes hydrogen, water or carbon dioxide.

[0019] The production method of the coal seam in-situ plasma conversion methane production system includes:

[0020] After vertically passing through the overburden and the upper edge of the coal seam from the ground, it gradually deflects to the horizontal direction, forming a non-vertical channel in the coal seam. The non-vertical channel extends a certain distance in the coal seam to form a directional drilling well; with the coordinates of the end of the non-vertical channel of the directional drilling well as the target point, the vertical well vertically passes through the overburden and the coal seam from the ground and is connected to the non-vertical channel. The non-vertical channel between the directional drilling well and the vertical well is the coal seam channel. The vertical well is located in the pipeline of the coal seam and screen holes are arranged.

[0021] The gas injection pipe is connected to the plasma generator and then lowered to the directional drilling well. It is controlled by the ground and moved to the target area of ​​the coal seam channel. The plasma generator is debugged on the ground to test the inflow and outflow of the reaction medium and the inflow and outflow of the cooling medium. The power is turned on to test the start-up and reaction medium flow and power adjustment to be normal. The plasma generator is moved to the target area of ​​the coal seam channel and the horizontal distance between the plasma generator and the vertical well in the coal seam channel is 10-100 m.

[0022] The plasma generator is injected with a working medium of water and hydrogen in a molar ratio of 0.5 and a cooling medium by an injection device, and the plasma generator is started. The plasma generator receives the working medium and the cooling medium from the working medium pipeline and ionizes the working medium with high pressure to generate high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles. The high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, which undergo a methanogenic reaction with the high-temperature and high-activity hydrogen particles in situ in the reaction chamber to generate methane.

[0023] When the volume percentage of CH4 in the gas at the vertical well outlet is higher than 10%, it indicates that the coal seam has started to convert. The water and hydrogen flow and power of the plasma generator are gradually adjusted to maintain the production load between 10% and 50%, and the coal seam conversion methane production begins.

[0024] If the vertical well feedback shows that the volume ratio of carbon dioxide in the export gas exceeds 5%, keep the water injection volume unchanged and slowly increase the plasma generator hydrogen injection flow rate until the volume ratio of carbon dioxide in the export gas is lower than 5%; if the feedback shows that the volume ratio of hydrogen in the export gas exceeds 5%, slowly increase the plasma generator water injection flow rate until the volume ratio of hydrogen in the export gas is close to 0 and the volume ratio of carbon dioxide is 5%; the gas injection pipe injection device controls the water and hydrogen injection flow rates to make the molar ratio of water and hydrogen injected into the plasma generator between 0.5 and 0.6. When the export gas is normal, keep the ratio of water to hydrogen injected into the plasma generator unchanged, slowly adjust the water and hydrogen injection flow rates and the plasma generator power to stabilize the production load at 50%.

[0025] When the vertical well test device feedback shows that the outlet gas flow rate continues to decrease, the water and hydrogen injection flow rate and power of the plasma generator are increased to increase the conversion reaction load to 60%~100%. When the outlet gas flow rate of the vertical well feedback further decreases, it indicates that the conversion of the coal seam covered by the plasma generator and the vertical well is completed. The plasma generator is kept started, and the ground gas injection pipe moving device withdraws the plasma generator 10~100 m to continue the coal seam conversion production. The production is adjusted in this cycle. When the moving distance of the plasma generator is close to the non-vertical section distance of the coal seam, the power supply of the plasma generator is turned off, the injection of the reaction medium is stopped, the injection of the cooling medium is maintained, and the gas injection pipe and the plasma generator are withdrawn to the ground respectively.

[0026] In the above technical scheme, the present invention provides a coal seam in-situ plasma conversion methane production system and method, which has the following beneficial effects: by constructing a plasma generator that can simultaneously produce hydrogen and water vapor active particles in the coal seam, the high-temperature and high-activity water vapor particles generated by the high-voltage ionization of the plasma generator undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, and further react with the high-temperature and high-activity hydrogen particles generated by the high-voltage ionization of the plasma generator to undergo a methanogenic reaction in situ in the reaction chamber, and produce methane gas that is discharged to the ground through a vertical well, and can be used as a natural gas product after purification and separation. The present invention eliminates the transformation and methanogenic stages of coal seam gasification on the ground, shortens the process flow, and reduces production costs; only a small amount of byproducts such as carbon dioxide are produced, which is environmentally friendly; due to the action of high-temperature and high-activity particles, the underground reaction is strengthened, the conversion effect is high, and the production intensity is large, and it can be used for the development and utilization of carbon-based energy such as coal, peat, oil sands, coal gangue, oil shale, and heavy oil layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application 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 recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0028] Figure 1 A schematic structural diagram of a coal seam in-situ plasma conversion system for producing methane is provided in accordance with an embodiment of the present invention.

[0029] Figure 2 A schematic structural diagram of a coal seam in-situ plasma conversion system for producing methane is provided in accordance with an embodiment of the present invention.

[0030] Figure 3 A schematic structural diagram of a coal seam in-situ plasma conversion system for producing methane is provided in accordance with an embodiment of the present invention.

[0031] Description of reference numerals:

[0032] 1. Coal seam; 2. Coal seam channel; 3. Overburden; 4. Ground; 5. Directional drilling; 6. Gas injection pipe; 7. Plasma generator; 8. Vertical well; 9. Reaction chamber; 10. Plasma generator II; 11. Directional drilling II; 12. Gas injection pipe II. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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.

[0034] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0035] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0037] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0038] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0040] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] See also Figure 1-3 As shown, in one embodiment, a coal seam in-situ plasma conversion methane production system of the present invention comprises:

[0042] At least one directional drilling well 5, which vertically penetrates the overburden 3 and the upper edge of the coal seam 1 from the ground 4 to form a vertical channel, and gradually deflects to the horizontal direction to form a non-vertical channel in the coal seam,

[0043] The vertical well 8 is connected to the non-vertical channel by vertically passing through the overburden 3 and the coal seam 1 from the ground 4 with the coordinates at the end of the non-vertical channel as the target point. The non-vertical channel between the directional drilling well 5 and the vertical well 8 is the coal seam channel 2. The vertical well 8 is located in the pipeline of the coal seam and the sieve holes are arranged.

[0044] The gas injection pipe 6 has one end connected to a gas injection pipe moving device located on the ground 4 for moving the gas injection pipe 6, and the other end connected to a plasma generator. The gas injection pipe 6 includes a power cable, a working medium pipeline and a cooling medium pipe.

[0045] The plasma generator 7 is movably arranged in the coal seam channel 2. The plasma generator 7 receives the working medium and the cooling medium from the working medium pipeline and ionizes the working medium with high pressure to generate high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles. The high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam and are converted into hydrogen and carbon monoxide. The high-temperature and high-activity water vapor particles undergo a methanation reaction with the high-temperature and high-activity hydrogen particles in the reaction chamber 9 to generate methane. The methane is output from the vertical well 8.

[0046] In the in-situ plasma conversion system for producing methane from coal seams, the end coordinates of the non-vertical channel of the directional drilling 5 are the target point. Similarly, the ground 4 vertically passes through the overburden 3 and the upper edge of the coal seam 1, and the coal seam gradually deflects toward the target point until it penetrates to form a directional drilling II11. The non-vertical channel connecting the directional drilling 5 and the directional drilling in the coal seam is the coal seam channel 2; between the directional drilling 5 and the directional drilling II11, the ground 4 vertically passes through the overburden 3 and the coal seam to form a vertical channel as a vertical well 8. The directional drilling 5 is provided with the gas injection pipe 6 and the plasma generator 7. The directional drilling II11 is provided with a gas injection pipe II12 and a plasma generator II10 connected to the gas injection pipe II12. The plasma generator II10 receives the working medium and the cooling medium from the working medium pipeline and ionizes the working medium with high pressure to generate high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles. The high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, which undergo a methanogenic reaction with the high-temperature and high-activity hydrogen particles in situ in the reaction chamber 9 to produce methane.

[0047] In the coal seam in-situ plasma conversion system for producing methane, the plasma generator 7 and the plasma generator II 10 are arranged on the same side of the vertical well 8 and are arranged opposite to each other.

[0048] In the coal seam in-situ plasma conversion system for producing methane, the plasma generator 7 and the plasma generator II 10 are arranged on both sides of the vertical well 8 and are arranged opposite to each other.

[0049] In the coal seam in-situ plasma conversion methane production system, the gas injection pipe 6 and the gas injection pipe II 12 are both made of high temperature resistant, corrosion resistant and hydrogen embrittlement resistant steel, alloy material, carbon fiber material or composite material.

[0050] In the coal seam in-situ plasma conversion methane production system, the horizontal angle of the vertical channel is between 75° and 105°, and the horizontal angle of the non-vertical channel is between 0° and 20°.

[0051] In the coal seam in-situ plasma conversion system for producing methane, the length of the coal seam channel 2 is 100 to 3000 m.

[0052] In the coal seam in-situ plasma conversion methane production system, a test device for detecting the gas flow rate and components of the gas is arranged at the wellhead of the vertical well 8 located on the ground 4.

[0053] In the coal seam in-situ plasma conversion system for producing methane, the working medium includes hydrogen, water or carbon dioxide.

[0054] The production method of the coal seam in-situ plasma conversion methane production system includes:

[0055] After vertically passing through the overburden 3 and the upper edge of the coal seam from the ground 4, it gradually deflects to the horizontal direction to form a non-vertical channel in the coal seam. The non-vertical channel extends a certain distance in the coal seam to form a directional drilling 5; with the coordinates of the end of the non-vertical channel of the directional drilling 5 as the target point, the vertical well 8 vertically passes through the overburden 3 and the coal seam from the ground 4 and is connected with the non-vertical channel. The non-vertical channel between the directional drilling 5 and the vertical well 8 is the coal seam channel 2. The vertical well 8 is located in the pipeline of the coal seam and screen holes are arranged.

[0056] The gas injection pipe 6 is connected to the plasma generator and then lowered to the directional drilling well 5, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The plasma generator 7 is debugged on the ground 4 to test the inflow and outflow of the reaction medium and the inflow and outflow of the cooling medium. The power is turned on to test whether the start-up and reaction medium flow and power adjustment are normal. The plasma generator 7 is moved to the target area of ​​the coal seam channel 2, and the horizontal distance between the plasma generator 7 and the vertical well 8 in the coal seam channel 2 is 10-100 m.

[0057] The plasma generator 7 is injected with a working medium of water and hydrogen in a molar ratio of 0.5 and a cooling medium by an injection device, and the plasma generator 7 is started. The plasma generator 7 receives the working medium and the cooling medium from the working medium pipeline and ionizes the working medium with high pressure to generate high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles. The high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, which undergo a methanogenic reaction with the high-temperature and high-activity hydrogen particles in situ in the reaction chamber 9 to generate methane.

[0058] When the volume percentage of CH4 in the gas at the outlet of the vertical well 8 is higher than 10%, it indicates that the coal seam has started to convert. The water and hydrogen flow and power of the plasma generator 7 are gradually adjusted to keep the production load between 10% and 50%, and the coal seam conversion methane production begins.

[0059] If the vertical well 8 feedback shows that the volume ratio of carbon dioxide in the outlet gas exceeds 5%, the water injection amount is kept unchanged, and the hydrogen injection flow rate of the plasma generator 7 is slowly increased until the volume ratio of carbon dioxide in the outlet gas is lower than 5%; if the feedback shows that the volume ratio of hydrogen in the outlet gas exceeds 5%, the water injection flow rate of the plasma generator 7 is slowly increased until the volume ratio of hydrogen in the outlet gas is close to 0 and the volume ratio of carbon dioxide is 5%; the water and hydrogen injection flow rates are controlled by the injection device of the gas injection pipe 6, so that the molar ratio of water and hydrogen injected into the plasma generator 7 is between 0.5 and 0.6. When the outlet gas is normal, the ratio of water to hydrogen injected into the plasma generator 7 is kept unchanged, and the water and hydrogen injection flow rates and the power of the plasma generator 7 are slowly adjusted to stabilize the production load at 50%.

[0060] When the test device of vertical well 8 feeds back that the outlet gas flow rate continues to decrease, the water and hydrogen injection flow rate and power of plasma generator 7 are increased to increase the conversion reaction load to 60%~100%. When the outlet gas flow rate of vertical well 8 feeds back that it further decreases, it indicates that the conversion of the coal seam covered between plasma generator 7 and vertical well 8 is completed. The plasma generator 7 is kept started, and the gas injection pipe moving device 4 on the ground is used to withdraw the plasma generator 7 by 10~100 m to continue the coal seam conversion production. The production is adjusted in this way. When the moving distance of plasma generator 7 is close to the non-vertical section distance of the coal seam, the power supply of plasma generator 7 is turned off, the injection of reaction medium is stopped, the injection of cooling medium is maintained, and the gas injection pipe 6 and plasma generator 7 are withdrawn to the ground 4 respectively.

[0061] In one embodiment, the system includes at least two directional drilling wells 5 and one vertical well 8, and two gas injection pipes 6 are respectively lowered into the directional drilling wells 5, and the gas injection pipes 6 are respectively connected to plasma generators 7, and the plasma generators 7 use water vapor and hydrogen as working media respectively; or, a coal seam in-situ plasma conversion methane production system constructs a group of production wells and production wells in the coal seam, including at least one directional drilling well 5 and one vertical well 8, and a gas injection pipe 6 is lowered into the directional drilling well 5, and the gas injection pipe 6 is connected to a plasma generator 7 that can simultaneously inject hydrogen and water as working media. The method for producing methane by in-situ plasma conversion of coal seams is to construct a plasma generator 7 in the coal seam that can simultaneously produce hydrogen and water vapor active particles. The high-temperature and high-activity water vapor particles generated by the high-voltage ionization of the plasma generator 7 undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, and further undergo a methanation reaction in situ with the high-temperature and high-activity hydrogen particles generated by the high-voltage ionization of the plasma generator 7 in the reaction chamber 9, and the produced methane gas is discharged to the ground 4 through a vertical well 8, and can be used as a natural gas product after purification and separation.

[0062] In one embodiment, the coal seam in-situ plasma conversion methane production system includes at least one directional drilling well 5 and one vertical well 8. The directional drilling well 5 is lowered with a gas injection pipe 6. The gas injection pipe 6 is connected to a plasma generator 7 that can use hydrogen and water as working media at the same time. A series of conversion reactions occur in the coal seam to produce methane-rich gas. The coal seam in-situ plasma conversion methane production system includes a coal seam channel 2, a directional drilling well 5, a gas injection pipe 6, a plasma generator 7 and a vertical well 8. After vertically passing through the overburden 3 and the upper edge of the coal seam from the ground 4, it gradually deflects to the horizontal direction to form a non-vertical channel in the coal seam. The non-vertical channel extends a certain distance in the coal seam to form a directional drilling well 5; with the coordinates of the end of the non-vertical channel of the directional drilling well 5 as the target point, the ground 4 vertically passes through the overburden 3 and the coal seam and is connected to the non-vertical channel. The non-vertical channel between the directional drilling well 5 and the vertical well 8 is the coal seam channel 2. At least one directional drilling well 5 and one vertical well 8 constitute a coal seam gasification unit. The horizontal angle of the non-vertical channel is between 0° and 20°, and the horizontal angle of the vertical channel is between 75° and 105°.

[0063] The directional drilling 5 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe 6 is located on the ground 4, and the other end is connected to the plasma generator. The gas injection pipe 6 is connected to the plasma generator and then lowered to the directional drilling 5, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The gas injection pipe 6 can be made of steel, alloy, carbon fiber or composite material with high temperature resistance, corrosion resistance and hydrogen embrittlement resistance, and the inside can be covered with power cables, working medium pipelines, cooling medium pipelines, etc. that are matched with the plasma generator 7. The matched power cables, working medium pipelines, and cooling medium pipelines are connected to the injection device and control device on the ground 4 at one end, and connected to the plasma generator 7 at the other end. The plasma generator 7 has the function of working with hydrogen and water or hydrogen and carbon dioxide as media at the same time.

[0064] The coal seam channel 2 may have a length of 100 to 3000 m according to the process design.

[0065] The bottom of the vertical well 8 is close to the bottom of the coal seam, and the pipeline part located in the coal seam is arranged with sieve holes to facilitate the discharge of product gas. The product gas flow rate, component and other parameter testing devices are arranged at the wellhead position of the vertical well 8 located on the ground 4 to feedback the coal seam reaction situation and provide a control basis for the method of in-situ production of methane in the coal seam.

[0066] The present invention discloses a method for producing methane by in-situ plasma conversion of coal seams. The coal seam plasma generator 7 can excite and dissociate working media such as hydrogen and water into high-temperature and high-activity particles such as hydrogen free radicals and hydroxyl free radicals through high-voltage ionization. The high-temperature and high-activity particles react with the coal seam with high efficiency, and the conversion reaction includes but is not limited to:

[0067]

[0068] From the above reaction, it can be seen that the high temperature and high activity particles such as hydrogen free radicals and hydroxyl free radicals formed by the dissociation of hydrogen and water after the action of the plasma generator 7 react with the carbon of the coal seam in a series of reactions and are converted into hydrogen, carbon monoxide and methane. As the conversion reaction of the coal seam proceeds, several groups of reaction chambers 9 are gradually formed, and the maximum height of a single reaction chamber 9 is close to the coal seam, and the maximum width is greater than 34 m.

[0069] The hydrogen, carbon monoxide, methane, etc. converted by the reaction of the high-temperature and high-activity particles with the carbon in the coal seam flow in the reaction chamber 9 and the coal seam channel 2. During the flow, the hydrogen, carbon monoxide, etc. are further subjected to the following conversion reactions under the active action of hydrogen-containing free radicals and the catalytic action of the silicon-aluminum-iron-calcium-magnesium ash in the reaction chamber 9, including but not limited to:

[0070]

[0071] From the above reaction, it can be seen that hydrogen, carbon monoxide, etc. continue to undergo conversion reactions in the coal seam channel 2 and the reaction chamber 9 under the active action of hydrogen-containing free radicals and the catalytic action of silicon-aluminum-iron-calcium-magnesium ash in the reaction chamber 9, and finally generate a gas mainly composed of methane.

[0072] The production method includes,

[0073] 1) Installation

[0074] After vertically passing through the overburden 3 and the upper edge of the coal seam from the ground 4, it gradually deflects to the horizontal direction, forming a non-vertical channel in the coal seam, and the non-vertical channel extends a certain distance in the coal seam to form a directional drilling 5; with the coordinates of the end of the non-vertical channel of the directional drilling 5 as the target point, the ground 4 vertically passes through the overburden 3 and the coal seam and is connected to the non-vertical channel, and the non-vertical channel between the directional drilling 5 and the vertical well 8 is the coal seam channel 2. At least one directional drilling 5 and one vertical well 8 constitute a coal seam gasification unit. The horizontal angle of the non-vertical channel is between 0 and 20 degrees, and the horizontal angle of the vertical channel is between 75 degrees and 105 degrees.

[0075] The directional drilling 5 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe 6 is located on the ground 4, and the other end is connected to the plasma generator. The gas injection pipe 6 is connected to the plasma generator and then lowered to the directional drilling 5, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The gas injection pipe 6 can be made of steel, alloy, carbon fiber or composite material with high temperature resistance, corrosion resistance and hydrogen embrittlement resistance, and the inside can be covered with power cables, working medium pipelines, cooling medium pipelines, etc. that are matched with the plasma generator 7. The matched power cables, working medium pipelines, and cooling medium pipelines are connected to the injection device and control device on the ground 4 at one end, and connected to the plasma generator 7 at the other end. The plasma generator 7 has the function of working with hydrogen and water or hydrogen and carbon dioxide as media at the same time.

[0076] The coal seam channel 2 may have a length of 100 to 3000 m according to the process design.

[0077] The bottom of the vertical well 8 is close to the bottom of the coal seam, and the pipeline part located in the coal seam is arranged with sieve holes to facilitate the discharge of product gas. The wellhead of the vertical well 8 located on the ground 4 is arranged with product gas flow rate, component and other parameter testing devices.

[0078] According to the construction and installation method, the coal seam gasification unit is processed and all devices are installed. The plasma generator 7 is debugged on the ground 4, and the reaction medium in and out and the cooling medium in and out circulation are tested. The power is turned on to test the start-up and reaction medium flow and power adjustment. The plasma generator 7 is moved to the target area of ​​the coal seam channel 2 by the ground 4 control device, and the horizontal distance between the plasma generator 7 and the vertical well 8 in the coal seam channel 2 is 10~100 m.

[0079] 2) Production start-up

[0080] The injection device injects a certain flow of hydrogen into the plasma generator 7, and the flow data of the vertical well 8 test device is used to test whether the coal seam channel 2 and the vertical well 8 are unobstructed. After confirming that the conversion channel and the recovery pipe are unobstructed, the injection device injects a working medium of water and hydrogen with a molar ratio of about 0.5 and a cooling medium into the plasma generator 7, and turns on the power start switch to start the plasma generator 7.

[0081] According to the feedback from the test device components of the vertical well 8, when the volume percentage of CH4 in the gas at the outlet of the vertical well 8 is higher than 10%, it indicates that the coal seam has started to convert. The water and hydrogen flow and power of the plasma generator 7 are gradually adjusted to maintain the production load between 10% and 50%, and the coal seam conversion methane production is started.

[0082] 3) Main operations of production control

[0083] Judging from the outlet gas composition feedback from the test device of the vertical well 8, if the volume ratio of carbon dioxide in the outlet gas exceeds 5%, it indicates that the coal seam contains too much water and the molar ratio of water to hydrogen is too high. The water injection amount is kept unchanged, and the hydrogen injection flow rate of the plasma generator 7 is slowly increased until the volume ratio of carbon dioxide in the outlet gas is lower than 5%. If the volume ratio of hydrogen in the outlet gas exceeds 5%, it indicates that the molar ratio of water to hydrogen is too low and the injected hydrogen cannot be completely consumed. The water injection flow rate of the plasma generator 7 is slowly increased until the volume ratio of hydrogen in the outlet gas is close to 0 and the volume ratio of carbon dioxide is about 5%.

[0084] The injection device of the gas injection pipe 6 controls the injection flow of water and hydrogen, so that the molar ratio of water and hydrogen injected into the plasma generator 7 is between 0.5 and 0.6. At this time, the gas components produced mainly include methane, water vapor and a very small amount of carbon dioxide, which is a normal production situation. When the outlet gas is normal, the ratio of water and hydrogen injected into the plasma generator 7 is kept unchanged, and the injection flow of water and hydrogen and the power of the plasma generator 7 are slowly adjusted to stabilize the production load at about 50%, so as to stabilize the coalbed gasification methane production process.

[0085] For example, after a period of normal production, when the test device of the vertical well 8 feeds back that the outlet gas flow rate continues to decrease, it indicates that as the reaction cavity of the coal seam increases, the intensity of the conversion reaction decreases. At this time, it is necessary to increase the water and hydrogen injection flow and power of the plasma generator 7 to increase the conversion reaction load to 60%~100% to continue production.

[0086] After a period of time, the outlet gas flow rate of vertical well 8 testing device feedback further decreased, indicating that the coal seam between plasma generator 7 and vertical well 8 was completely converted. Keeping plasma generator 7 started, the surface 4 gas injection pipe moving device retreated plasma generator 7 10-100 m to continue coal seam conversion production.

[0087] 4) Production end operation

[0088] The production is adjusted in this way. According to the statistics of the moving distance of the gas injection pipe moving device on the ground 4, if the moving distance of the plasma generator 7 is close to the non-vertical section distance of the coal seam, it indicates that the coal seam covered by the unit has been converted. Turn off the power supply of the plasma generator 7, stop the injection of the reaction medium, maintain the injection of the cooling medium, and withdraw the gas injection pipe 6 and the plasma generator 7 to the ground 4 respectively. Perform the well closing operation. According to the above method, construction, installation and conversion production are carried out in another target coal seam block.

[0089] Example 1: (a directional drilling well 5, a vertical well 8, and a plasma generator 7 that can use water and hydrogen as working media at the same time)

[0090] The coal seam gasification method for producing methane proposed in the embodiment of the present invention has a buried depth of about 1360 m, an average thickness of 6 m, anthracite as the coal type, and a conversion unit is designed to cover a horizontal distance of 1000 m of the coal seam.

[0091] After vertically passing through the overburden 3 and the upper edge of the coal seam from the ground 4, it gradually deflects to the horizontal direction, forming a non-vertical channel in the coal seam, and the non-vertical channel extends about 1000 m in the coal seam to form a directional drilling 5; with the coordinates of the end of the non-vertical channel of the directional drilling 5 as the target point, it vertically passes through the overburden 3 and the coal seam from the ground 4 and connects with the non-vertical channel. The horizontal angle of the non-vertical channel is 3°, and the horizontal angle of the vertical channel is 91°.

[0092] Directional drilling 5 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe 6 is located on the ground 4, and the other end is connected to the plasma generator. The gas injection pipe 6 is connected to the plasma generator and then lowered to the directional drilling 5, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The gas injection pipe 6 can be made of steel, alloy, carbon fiber or composite material with high temperature resistance, corrosion resistance and hydrogen embrittlement resistance, and the inside can be covered with power cables, working medium pipelines, cooling medium pipelines, etc. that are matched with the plasma generator 7. The matched power cables, working medium pipelines, and cooling medium pipelines are connected to the injection device and control device on the ground 4 at one end, and connected to the plasma generator 7 at the other end. The plasma generator 7 has the function of working with hydrogen and water or hydrogen and carbon dioxide as the medium at the same time.

[0093] The bottom of the vertical well 8 is close to the bottom of the coal seam, wherein the pipeline part located in the coal seam is arranged with sieve holes. The wellhead position of the vertical well 8 located on the ground 4 is arranged with a parameter testing device such as product gas flow rate and composition.

[0094] According to the construction and installation method, the coalbed gasification unit is processed and all devices are installed. The plasma generator 7 is debugged on the ground 4, and the reaction medium in and out and cooling medium in and out circulation are tested. The power is turned on to test the start-up and reaction medium flow and power adjustment to be normal. The plasma generator 7 is moved by the ground 4 control device to a distance of about 30 m from the vertical well 8.

[0095] The injection device injects 100 Nm into the plasma generator 7. 3 / h of hydrogen, and the flow data of the vertical well 8 testing device is used to test whether the coal seam channel 2 and the vertical well 8 are unobstructed.

[0096] After confirming that the conversion channel and the recovery pipe are unobstructed, the injection device injects hydrogen into the plasma generator 7 at a flow rate of 200Nm 3 / h, inject water flow rate of about 80 kg / h, and cooling medium, turn on the power start switch, adjust the power of plasma generator 7 to about 500 kW, keep the load of plasma generator 7 between 10% and 50%, and start plasma generator 7. According to the feedback of the test device components of vertical well 8, when the volume percentage of CH4 in the outlet gas of vertical well 8 is higher than 10%, it indicates that the coal seam has started to convert. Gradually adjust the water and hydrogen flow and power of plasma generator 7, keep the production load between 10% and 50%, and make the molar ratio of water and hydrogen injected by plasma generator 7 and plasma generator II 10 between 0.5 and 0.6. At this time, the coal gas components produced mainly include methane, water vapor and a very small amount of carbon dioxide, and start coal seam conversion methane production.

[0097] After three days of continuous normal production, the test device of vertical well 8 reported that the volume ratio of carbon dioxide in the outlet gas exceeded 5%, indicating that the coal seam contained too much water and the molar ratio of water to hydrogen was too high. The hydrogen injection flow rate of plasma generator 7 was slowly increased until the volume ratio of carbon dioxide in the outlet gas was lower than 5%.

[0098] After 7 days of continuous production, the test device of vertical well 8 reported that the outlet gas flow rate continued to decrease, indicating that the conversion reaction intensity of the coal seam decreased with the increase of the reaction cavity. At this time, the hydrogen flow rate injected by plasma generator 7 was increased to 400 Nm 3 / h, the water injection flow rate is about 160 kg / h, the plasma generator 7 reaches about 1000 kW, the conversion reaction load is increased to 60%~100%, and production continues.

[0099] Six days later, the test device of vertical well 8 reported that the outlet gas flow rate further decreased, indicating that the conversion of the coal seam between plasma generator 7 and vertical well 8 was complete. Plasma generator 7 was kept started, and the surface 4 gas injection pipe moving device was used to withdraw plasma generator 7 by about 30 m to continue coal seam conversion production.

[0100] The production was adjusted in this way. According to the statistics of the moving distance of the gas injection pipe moving device 4 on the ground, when the plasma was generated and the retreat distance was close to 970 m, it indicated that the coal seam covered by the unit had been transformed. The power supply of the plasma generator 7 was turned off, the injection of the reaction medium was stopped, the injection of the cooling medium was maintained, and the plasma generator 7 was withdrawn to the ground 4. The well was shut in. According to the above method, construction, installation and gasification production were carried out in another target coal seam block.

[0101] In one embodiment, Figure 2As shown, the coal seam in-situ plasma conversion methane production system includes at least two directional drilling wells 5 and one vertical well 8. Two gas injection pipes are respectively lowered into the directional drilling wells 5. The gas injection pipes are respectively connected to plasma generators. The plasma generators use water and hydrogen as working media, respectively, and a series of conversion reactions occur in the coal seam to produce methane-rich gas.

[0102] The coal seam in-situ plasma conversion methane production system comprises a coal seam channel 2, a directional drilling well 5, a gas injection pipe 6, a plasma generator 7 and a vertical well 8. After vertically passing through the overburden 3 and the upper edge of the coal seam from the ground 4, it gradually deflects to the horizontal direction to form a non-vertical channel in the coal seam, and the non-vertical channel extends a certain distance in the coal seam to form a directional drilling well 5; with the coordinates of the end of the non-vertical channel of the directional drilling well 5 as the target point, the ground 4 also vertically passes through the overburden 3 and the upper edge of the coal seam, and the coal seam gradually deflects to the target point until it penetrates, forming a directional drilling well II 11, and the non-vertical channel connecting the directional drilling well 5 and the directional drilling II 11 in the coal seam is the coal seam channel 2; between the directional drilling well 5 and the directional drilling II 11, the ground 4 vertically passes through the overburden 3 and the coal seam to form a vertical channel, that is, a vertical well 8, and at least two directional drilling wells and one vertical well 8 constitute a coal seam gasification unit. The horizontal angle of the non-vertical channel is between 0° and 20°, and the horizontal angle of the vertical channel is between 75° and 105°.

[0103] The directional drilling 5 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe 6 is located on the ground 4, and the other end is connected to the plasma generator. The gas injection pipe 6 is connected to the plasma generator and then lowered to the directional drilling 5, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The gas injection pipe 6 can be made of steel, alloy, carbon fiber or composite material with high temperature resistance, corrosion resistance and hydrogen embrittlement resistance, and the inside can be covered with power cables, working medium pipelines, cooling medium pipelines, etc. that are matched with the plasma generator 7. The matched power cables, working medium pipelines, and cooling medium pipelines are connected to the injection device and control device on the ground 4 at one end, and connected to the plasma generator 7 at the other end. The plasma generator 7 has the function of working with media such as hydrogen, water, and carbon dioxide.

[0104] The directional drilling well II11 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe II12 is located on the ground 4, and the other end is connected to the plasma generator II10. The gas injection pipe II12 is connected to the plasma generator II and then lowered to the directional drilling well II11, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The gas injection pipe II12 can be made of steel, alloy, carbon fiber or composite material with high temperature resistance, corrosion resistance and hydrogen embrittlement resistance, and the inside can be covered with power cables, working medium pipelines, cooling medium pipelines, etc. that are matched with the plasma generator II10. One end of the matched power cables, working medium pipelines, and cooling medium pipelines are connected to the injection device and control device on the ground 4, and the other end is connected to the plasma generator II10. The plasma generator II10 has the function of working with hydrogen, water, carbon dioxide and other media.

[0105] The coal seam channel 2 may have a length of 100 to 3000 m according to process design.

[0106] The bottom of the vertical well 8 is close to the bottom of the coal seam, and the pipeline part located in the coal seam is arranged with sieve holes to facilitate the discharge of product gas. The product gas flow rate, component and other parameter testing devices are arranged at the wellhead position of the vertical well 8 located on the ground 4 to feedback the coal seam reaction situation and provide a control basis for the method of in-situ production of methane in the coal seam.

[0107] The production method includes,

[0108] 1) Installation

[0109] After vertically passing through the overburden 3 and the upper edge of the coal seam from the ground 4, it gradually deflects to the horizontal direction to form a non-vertical channel in the coal seam, and the non-vertical channel extends a certain distance in the coal seam to form a directional drilling 5; with the coordinates of the end of the non-vertical channel of the directional drilling 5 as the target point, the ground 4 also vertically passes through the overburden 3 and the upper edge of the coal seam, and gradually deflects from the coal seam to the target point until it penetrates, forming a directional drilling II 11, and the non-vertical channel connecting the directional drilling 5 and the directional drilling II 11 in the coal seam is the coal seam channel 2; between the directional drilling 5 and the directional drilling II 11, the ground 4 vertically passes through the overburden 3 and the coal seam to form a vertical channel, that is, a vertical well 8, and at least two directional drilling wells 5 and one vertical well 8 constitute a coal seam gasification unit. The horizontal angle of the non-vertical channel is 0-20°, and the horizontal angle of the vertical channel is between 75° and 105°.

[0110] The directional drilling 5 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe 6 is located on the ground 4, and the other end is connected to the plasma generator. The gas injection pipe 6 is connected to the plasma generator and then lowered to the directional drilling 5, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The gas injection pipe 6 is internally covered with power cables, working medium pipelines, cooling medium pipelines, etc. that are matched with the plasma generator 7. One end of the matched power cables, working medium pipelines, and cooling medium pipelines are connected to the injection device and control device on the ground 4, and the other end is connected to the plasma generator 7. The plasma generator 7 has the function of working with media such as hydrogen, water, and carbon dioxide.

[0111] The directional drilling well II11 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe II12 is located on the ground 4, and the other end is connected to the plasma generator II. The gas injection pipe II12 is connected to the plasma generator II and then lowered to the directional drilling well II11, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The inside of the gas injection pipe II12 can be covered with the power cable, working medium pipeline, cooling medium pipeline, etc. of the plasma generator II10. The power cable, working medium pipeline, and cooling medium pipeline are connected to the injection device and control device of the ground 4 at one end, and connected to the plasma generator II10 at the other end. The plasma generator II10 has the function of working with media such as hydrogen, water, and carbon dioxide. The distance between the plasma generator 7 and the plasma generator II10 in the coal seam channel 2 is 10~100 m.

[0112] The coal seam channel 2 may have a length of 100 to 3000 m according to the process design.

[0113] The bottom of the vertical well 8 is close to the bottom of the coal seam, and the pipeline part located in the coal seam is arranged with sieve holes to facilitate the discharge of product gas. The wellhead of the vertical well 8 located on the ground 4 is arranged with product gas flow rate, component and other parameter testing devices.

[0114] According to the construction and installation methods, the coal seam gasification unit is processed and all devices are installed. Debug the plasma generator 7 and plasma generator II 10 on the ground 4, test the reaction medium in and out, and the cooling medium in and out circulation, turn on the power, and test the startup and reaction medium flow and power adjustment to be normal. The ground 4 control device moves the plasma generator 7 and plasma generator II 10 to the target area of ​​the coal seam channel 2 respectively, and makes the distance between the plasma generator 7 and plasma generator II 10 in the coal seam channel 2 10~100 m. There are two types of positions of the plasma generator 7 and plasma generator II 10 in the coal seam channel 2, the plasma generator 7 and plasma generator II 10 are located on both sides of the vertical well 8 respectively, and the plasma generator 7 and plasma generator II 10 are located on one side of the vertical well 8 at the same time.

[0115] 2) Production start-up

[0116] The injection device sequentially injects a certain flow rate of reaction medium into the plasma generator 7 and the plasma generator II 10, and the flow data of the vertical well 8 test device is used to test whether the coal seam channel 2 and the vertical well 8 are unobstructed. After confirming that the conversion channel and the recovery pipe are unobstructed, the injection device injects the reaction medium and the cooling medium into the plasma generator 7 and the plasma generator II 10 respectively, turns on the power start switch, and starts the plasma generator 7 and the plasma generator II 10.

[0117] According to the feedback from the test device components of vertical well 8, when the volume percentage of CH4 in the gas at the outlet of vertical well 8 is higher than 10%, it indicates that the coal seam has started to convert. The reaction medium flow and power of plasma generator 7 and plasma generator II 10 are gradually adjusted to maintain the production load between 10% and 50%, and the coal seam conversion methane production is started.

[0118] 3) Main operations of production control

[0119] The methanogenic reaction of hydrogen and carbon monoxide is in accordance with the stoichiometric ratio of 3:1. In addition, a water-gas shift reaction will also occur in the coal seam channel 2. Part of the carbon monoxide reacts with water vapor in a stoichiometric ratio of 1:1 to generate hydrogen and carbon dioxide. However, the stoichiometric ratio of hydrogen and carbon dioxide for methanogenic reaction is 4:1. Combining the water-gas shift reaction with the carbon dioxide methanogenic reaction, the final stoichiometric ratio of hydrogen and carbon monoxide is still 3:1. Therefore, in combination with the coal seam gasification reaction, the molar ratio of water and hydrogen injected by the plasma generator 7 and the plasma generator II 10 needs to be controlled to be 1:2 to meet the conditions. In order to ensure the complete reaction of the injected hydrogen, the molar ratio of the injected water and hydrogen can be controlled to be slightly higher than 1:2, that is, the molar ratio is preferably between 0.5 and 0.6. Since the coal seam contains an indefinite amount of water, the molar ratio of water and hydrogen in the coal seam channel 2 may fluctuate, thereby affecting the progress of the methanogenic reaction. The composition of the outlet gas can be judged based on the feedback from the test device of the vertical well 8. If the volume ratio of carbon dioxide in the outlet gas exceeds 5%, it means that the coal seam contains too much water, the molar ratio of water to hydrogen is too high, and the carbon dioxide produced after the conversion in the coal seam cannot be completely consumed. It is necessary to slowly increase the hydrogen injection flow rate of plasma generator 7 and plasma generator II 10 until the volume ratio of carbon dioxide in the outlet gas is lower than 5%. If the volume ratio of hydrogen in the outlet gas exceeds 5%, it means that the molar ratio of water to hydrogen is too low, and the injected hydrogen cannot be completely consumed, resulting in hydrogen waste and the separation pressure of methane and hydrogen on the ground 4. It is necessary to slowly increase the injection flow rate of water of plasma generator 7 and plasma generator II 10 until the volume ratio of hydrogen in the outlet gas is close to 0 and the volume ratio of carbon dioxide is about 5%.

[0120] The water and hydrogen injection flows are controlled by the gas injection pipe 6 and the gas injection pipe II 12 injection devices respectively, so that the total molar ratio of water and hydrogen injected by the plasma generator 7 and the plasma generator II 10 is between 0.5 and 0.6. At this time, the gas components produced mainly include methane, water vapor and a very small amount of carbon dioxide, which is a normal production situation. When the outlet gas is normal, the ratio of water and hydrogen injected by the plasma generator 7 and the plasma generator II 10 is kept unchanged, and the water and hydrogen injection flows and the power of the plasma generator 7 are slowly adjusted to stabilize the production load at about 50%, and the process of producing methane by stable coalbed gasification is carried out.

[0121] For example, after a period of normal production, when the test device of vertical well 8 feeds back that the outlet gas flow rate continues to decrease, it indicates that as the reaction cavity of the coal seam increases, the intensity of the conversion reaction decreases. At this time, it is necessary to increase the water and hydrogen injection flow and power of plasma generator 7 and plasma generator II 10 to increase the conversion reaction load to 60%~100% and continue production.

[0122] After a period of time, the test device of vertical well 8 fed back that the outlet gas flow rate further decreased, indicating that the coal seam covered between plasma generator 7 and plasma generator II 10 was converted. The moving plan was determined according to the arrangement of plasma generator 7 and plasma generator II 10. If plasma generator 7 and plasma generator II 10 were located on both sides of vertical well 8, plasma generator 7 was kept started, and the 4 gas injection pipe moving devices on the ground were withdrawn 10-100m respectively; if plasma generator 7 and plasma generator II 10 were located on one side of vertical well 8 at the same time, plasma generator 7 was kept started, and the 4 gas injection pipe moving devices on the ground were withdrawn or extended the same distance between plasma generator 7 and plasma generator II 10, so that the distance between plasma generator 7 and plasma generator II 10 was 10-100m in the fresh coal seam, and coal seam conversion production continued.

[0123] 4) Production end operation

[0124] In this way, the production is adjusted in a cycle. According to the moving distance statistics of the gas injection pipe 6 and the gas injection pipe II 12 moving device, if the plasma generator 7 and the plasma generator II 10 are both located on one side of the vertical well 8, and the moving distance of the plasma generator 7 or the plasma generator II 10 is close to the non-vertical section distance of the coal seam, it indicates that the coal seam covered by the unit has been completely transformed; if the plasma generator 7 and the plasma generator II 10 are respectively located on both sides of the vertical well 8, and the sum of the moving distances of the plasma generator 7 and the plasma generator II 10 is close to the non-vertical section distance of the coal seam, it indicates that the coal seam covered by the unit has been completely transformed. Turn off the power supply of the plasma generator 7 or the plasma generator II 10, stop the injection of the reaction medium, maintain the injection of the cooling medium, and withdraw the gas injection pipe 6 and the gas injection pipe II 12 to the ground 4 respectively. Perform the well closure operation. According to the above method, construction, installation and conversion production are carried out in another target coal seam block.

[0125] Embodiment 2: (Two directional drilling wells 5, one vertical well 8, two plasma generators 7, using hydrogen and water as working media respectively, and the two plasma generators 7 are located on the same side of the vertical well 8)

[0126] The coal seam gasification method for producing methane proposed in the embodiment of the present invention has a coal seam resource buried at a depth of about 1200 m, an average thickness of 10 m, and non-caking coal. A conversion unit is designed to cover a coal seam horizontal distance of 1000 m.

[0127] After vertically passing through the overburden 3 and the upper edge of the coal seam from the ground 4, it gradually deflects to the horizontal direction, forming a non-vertical channel in the coal seam, and the non-vertical channel extends a certain distance in the coal seam to form a directional drilling 5; with the coordinates of the end of the non-vertical channel of the directional drilling 5 as the target point, the ground 4 also vertically passes through the overburden 3 and the upper edge of the coal seam, and gradually deflects from the coal seam to the target point until it penetrates, forming a directional drilling II 11, and the non-vertical channel connecting the directional drilling 5 and the directional drilling II 11 in the coal seam is the coal seam channel 2, and the length of the coal seam channel 2 is about 1000 m; between the directional drilling 5 and the directional drilling II 11, the ground 4 vertically passes through the overburden 3 and the coal seam to form a vertical channel, that is, a vertical well 8, and two directional drilling wells 5 and one vertical well 8 constitute a coal seam gasification unit. The horizontal angle of the non-vertical channel is about 5°, and the horizontal angle of the vertical channel is about 85°.

[0128] The directional drilling 5 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe 6 is located on the ground 4, and the other end is connected to the plasma generator. The gas injection pipe 6 is connected to the plasma generator and then lowered to the directional drilling 5, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The gas injection pipe 6 is internally covered with power cables, working medium pipelines, cooling medium pipelines, etc. that are matched with the plasma generator 7. One end of the matched power cables, working medium pipelines, and cooling medium pipelines are connected to the injection device and control device on the ground 4, and the other end is connected to the plasma generator 7. The plasma generator 7 has the function of working with hydrogen as the medium.

[0129] The directional drilling well II11 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe II12 is located on the ground 4, and the other end is connected to the plasma generator II. The gas injection pipe II12 is connected to the plasma generator II and then lowered to the directional drilling well II11, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The inside of the gas injection pipe II12 can be covered with the power cable, working medium pipeline, cooling medium pipeline, etc. of the plasma generator II10. The power cable, working medium pipeline, and cooling medium pipeline are connected to the injection device and control device on the ground 4 at one end, and connected to the plasma generator II10 at the other end. The plasma generator II10 has the function of working with water as the medium. The vertical well 8 is located at the center between the directional drilling well 5 and the directional drilling well II11. The vertical well 8 and the two directional drilling wells 5 are both located at about 500 m. The bottom of the vertical well 8 is close to the bottom of the coal seam, and the pipeline part located in the coal seam is arranged with sieve holes. The product gas flow rate, component and other parameter testing devices are arranged at the wellhead position of the vertical well 8 located on the ground 4.

[0130] According to the construction and installation methods, the coalbed gasification unit is processed and all devices are installed. Debug the plasma generator 7 and plasma generator II 10 on the ground 4, test the reaction medium in and out, cooling medium in and out circulation, turn on the power, test the start-up and reaction medium flow and power adjustment are normal. The ground 4 control device moves the plasma generator 7 and plasma generator II 10 respectively, so that the plasma generator 7 and plasma generator II 10 are both located on the right side of the vertical well 8, the plasma generator 7 is about 50 m away from the directional drilling II 11 vertical channel, and the plasma generator II 10 is about 0.5 m away from the directional drilling II 11 vertical channel.

[0131] The injection device injects 100 Nm into the plasma generator 7. 3 / h of hydrogen, and the flow data of the vertical well 8 test device is used to test whether the coal seam channel 2 and the vertical well 8 are unobstructed. After confirming that the conversion channel and the recovery pipe are unobstructed, the injection device injects hydrogen flow rate 300 Nm into the plasma generator 7 respectively. 3 / h, inject water flow of about 120 kg / h and cooling medium into plasma generator II 10, turn on the power start switch, adjust the power of plasma generator 7 and plasma generator II 10 to about 500 kW, keep the load of plasma generator 7 between 10% and 50%, and start plasma generator 7. According to the feedback of the component of the vertical well 8 test device, when the volume percentage of CH4 in the outlet gas of vertical well 8 is higher than 10%, it indicates that the coal seam has started to convert. Gradually adjust the water and hydrogen flow and power of plasma generator 7, keep the production load between 10% and 50%, and make the molar ratio of water and hydrogen injected by plasma generator 7 and plasma generator II 10 between 0.5 and 0.6. At this time, the coal gas components produced mainly include methane, water vapor and a very small amount of carbon dioxide, and start coal seam conversion methane production.

[0132] After 5 days of continuous normal production, the test device of vertical well 8 reported that the volume ratio of carbon dioxide in the outlet gas exceeded 5%, indicating that the coal seam contained too much water and the molar ratio of water to hydrogen was too high. The hydrogen injection flow rate of plasma generator 7 was slowly increased until the volume ratio of carbon dioxide in the outlet gas was lower than 5%.

[0133] After 6 days of continuous production, the test device of vertical well 8 reported that the outlet gas flow rate continued to decrease, indicating that the conversion reaction intensity of the coal seam decreased with the increase of the reaction cavity. At this time, the hydrogen injection flow rate of plasma generator 7 was increased to 600 Nm 3 / h, and the water flow rate of about 240 kg / h is injected into plasma generator II10. The power of plasma generator 7 and plasma generator II10 both reaches about 1000 kW, which increases the conversion reaction load to 60%~100% and continues production.

[0134] Four days later, the test device of vertical well 8 reported that the outlet gas flow rate further decreased, indicating that the coal seam between plasma generator 7 and plasma generator II 10 had been converted. Plasma generator 7 was kept started, and the surface gas injection pipe moving device 4 was used to withdraw the plasma generator by about 750 m and extend the plasma generator II by about 1050 m to continue coal seam conversion production.

[0135] The production was adjusted in this way. According to the statistics of the moving distance of the gas injection pipe moving device on the ground 4, when the plasma generator 7 retreated to a distance of nearly 950 m, it indicated that the coal seam covered by the unit had been completely transformed. The power supply of the plasma generator 7 was turned off, the injection of the reaction medium was stopped, the injection of the cooling medium was maintained, and the plasma generator 7 was withdrawn to the ground 4. The well was shut in. According to the above method, construction, installation and gasification production were carried out in another target coal seam block.

[0136] Example 3: (2 directional drilling wells, 1 vertical well 8, 2 plasma generators, using hydrogen and water as working media respectively, and the 2 plasma generators are located on both sides of the vertical well 8)

[0137] The coal seam gasification method for producing methane proposed in the embodiment of the present invention has a buried depth of about 800 m, an average thickness of 9 m, and lignite as the coal type. A conversion unit is designed to cover a horizontal distance of 1200 m of the coal seam.

[0138] After vertically passing through the overburden 3 and the upper edge of the coal seam from the ground 4, it gradually deflects to the horizontal direction, forming a non-vertical channel in the coal seam, and the non-vertical channel extends a certain distance in the coal seam to form a directional drilling 5; with the coordinates of the end of the non-vertical channel of the directional drilling 5 as the target point, the ground 4 also vertically passes through the overburden 3 and the upper edge of the coal seam, and gradually deflects from the coal seam to the target point until it penetrates, forming a directional drilling II 11. The non-vertical channel connecting the directional drilling 5 and the directional drilling II 11 in the coal seam is the coal seam channel 2, and the length of the coal seam channel 2 is about 1200 m; between the directional drilling 5 and the directional drilling II 11, the ground 4 vertically passes through the overburden 3 and the coal seam to form a vertical channel, that is, a vertical well 8. Two directional drilling wells and one vertical well 8 constitute a coal seam gasification unit. The horizontal angle of the non-vertical channel is about 5°, and the horizontal angle of the vertical channel is about 85°.

[0139] The directional drilling 5 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe 6 is located on the ground 4, and the other end is connected to the plasma generator. The gas injection pipe 6 is connected to the plasma generator and then lowered to the directional drilling 5, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The gas injection pipe 6 is internally covered with power cables, working medium pipelines, cooling medium pipelines, etc. that are matched with the plasma generator 7. One end of the matched power cables, working medium pipelines, and cooling medium pipelines are connected to the injection device and control device on the ground 4, and the other end is connected to the plasma generator 7. The plasma generator 7 has the function of working with hydrogen as the medium.

[0140] The directional drilling well II11 is provided with a gas injection pipe moving device, an injection device and a control device on the ground 4. One end of the gas injection pipe II12 is located on the ground 4, and the other end is connected to the plasma generator II. The gas injection pipe II12 is connected to the plasma generator II and then lowered to the directional drilling well II11, and is controlled by the ground 4 to move to the target area of ​​the coal seam channel 2. The inside of the gas injection pipe II12 can be covered with the power cable, working medium pipeline, cooling medium pipeline, etc. of the plasma generator II10. The power cable, working medium pipeline, and cooling medium pipeline are connected to the injection device and control device on the ground 4 at one end, and connected to the plasma generator II10 at the other end. The plasma generator II10 has the function of working with water as the medium. The vertical well 8 is located at the center between the directional drilling well 5 and the directional drilling well II11. The vertical well 8 and the two directional drilling wells 5 are both located at about 500 m. The bottom of the vertical well 8 is close to the bottom of the coal seam, and the pipeline part located in the coal seam is arranged with sieve holes. The product gas flow rate, component and other parameter testing devices are arranged at the wellhead position of the vertical well 8 located on the ground 4.

[0141] According to the construction and installation methods, the coalbed gasification unit is processed and all devices are installed. Debug the plasma generator 7 and plasma generator II 10 on the ground 4, test the reaction medium in and out, cooling medium in and out circulation, turn on the power, test the start-up and reaction medium flow and power adjustment to be normal. The ground 4 control device moves the plasma generator 7 and plasma generator II 10 respectively, so that the plasma generator 7 and plasma generator II 10 are located on both sides of the vertical well 8, respectively, the plasma generator 7 is about 825 m away from the vertical well, and the plasma generator II 10 is about 825 m away from the vertical well.

[0142] The injection device injects 100 Nm into the plasma generator 7. 3 / h of hydrogen, and the flow data of the vertical well 8 test device is used to test whether the coal seam channel 2 and the vertical well 8 are unobstructed. After confirming that the conversion channel and the recovery pipe are unobstructed, the injection device injects hydrogen flow rate 300 Nm into the plasma generator 7 respectively. 3 / h, inject water flow of about 120 kg / h and cooling medium into plasma generator II 10, turn on the power start switch, adjust the power of plasma generator 7 and plasma generator II 10 to about 500 kW, keep the load of plasma generator 7 between 10% and 50%, and start plasma generator 7. According to the feedback of the component of the vertical well 8 test device, when the volume percentage of CH4 in the outlet gas of vertical well 8 is higher than 10%, it indicates that the coal seam has started to convert. Gradually adjust the water and hydrogen flow and power of plasma generator 7, keep the production load between 10% and 50%, and make the molar ratio of water and hydrogen injected by plasma generator 7 and plasma generator II 10 between 0.5 and 0.6. At this time, the coal gas components produced mainly include methane, water vapor and a very small amount of carbon dioxide, and start coal seam conversion methane production.

[0143] After 3 days of continuous normal production, the test device of vertical well 8 reported that the volume ratio of hydrogen in the outlet gas exceeded 5%, indicating that the molar ratio of water to hydrogen was too low. The injection flow rate of water in plasma generator II 10 was slowly increased until the volume ratio of hydrogen in the outlet gas was close to 0 and the volume ratio of carbon dioxide was around 5%.

[0144] After 7 days of continuous production, the test device of vertical well 8 reported that the outlet gas flow rate continued to decrease, indicating that the conversion reaction intensity of the coal seam decreased with the increase of the reaction cavity. At this time, the hydrogen injection flow rate of plasma generator 7 was increased to 600 Nm 3 / h, and the water flow rate of about 240 kg / h is injected into plasma generator II10. The power of plasma generator 7 and plasma generator II10 both reaches about 1000 kW, which increases the conversion reaction load to 60%~100% and continues production.

[0145] Five days later, the test device of vertical well 8 reported that the outlet gas flow rate further decreased, indicating that the coal seam covered by plasma generator 7 and plasma generator II 10 had been converted. Plasma generator 7 was kept started, and the surface 4 gas injection pipe moving device respectively retreated plasma generator 7 and plasma generator II 10 by about 25 m to continue coal seam conversion production.

[0146] The production was adjusted in this way. According to the statistics of the moving distance of the gas injection pipe moving device on the ground 4, when the plasma generator 7 retreated to a distance of nearly 575 m, it indicated that the coal seam covered by the unit had been completely transformed. The power supply of the plasma generator 7 was turned off, the injection of the reaction medium was stopped, the injection of the cooling medium was maintained, and the plasma generator 7 was withdrawn to the ground 4. The well was shut in. According to the above method, construction, installation and gasification production were carried out in another target coal seam block.

[0147] Finally, it should be noted that the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making any creative work are within the scope of protection of the present application.

[0148] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A production method of a methane production system using coal seam in-situ plasma conversion, characterized in that: The coal seam in-situ plasma conversion methane production system comprises: At least one directional drilling well, which vertically penetrates the overburden and the upper edge of the coal seam from the ground to form a vertical channel, and gradually deflects to the horizontal direction to form a non-vertical channel in the coal seam, The vertical well uses the coordinates at the end of the non-vertical channel as the target point and passes vertically from the ground through the overburden and coal seam to connect with the non-vertical channel. The non-vertical channel between the directional drilling well and the vertical well is the coal seam channel. The vertical well is located in the pipeline of the coal seam and the sieve holes are arranged. The gas injection pipe has one end connected to a gas injection pipe moving device located on the ground for moving the gas injection pipe, and the other end connected to a plasma generator. The gas injection pipe includes a power cable, a working medium pipeline and a cooling medium pipe. A plasma generator is movably arranged in the coal seam passage. The plasma generator receives working medium and cooling medium from the working medium pipeline and ionizes the working medium with high pressure to generate high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles. The high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide. The high-temperature and high-activity water vapor particles undergo a methanogenic reaction with the high-temperature and high-activity hydrogen particles in the reaction chamber to generate methane. The methane is output from the vertical well. The production method comprises: After vertically passing through the overburden and the upper edge of the coal seam from the ground, it gradually deflects to the horizontal direction, forming a non-vertical channel in the coal seam. The non-vertical channel extends a certain distance in the coal seam to form a directional drilling well; with the coordinates of the end of the non-vertical channel of the directional drilling well as the target point, the vertical well vertically passes through the overburden and the coal seam from the ground and is connected to the non-vertical channel. The non-vertical channel between the directional drilling well and the vertical well is the coal seam channel. The vertical well is located in the pipeline of the coal seam and screen holes are arranged. The gas injection pipe is connected to the plasma generator and lowered to the directional drilling well. It is moved to the target area of ​​the coal seam channel by ground control. The plasma generator is debugged on the ground to test the inflow and outflow of the reaction medium and the inflow and outflow of the cooling medium. The power is turned on to test the start-up and reaction medium flow and power adjustment to be normal. The plasma generator is moved to the target area of ​​the coal seam channel and the horizontal distance between the plasma generator and the vertical well in the coal seam channel is 10-100m. The plasma generator is injected with a working medium of water and hydrogen in a molar ratio of 0.5 and a cooling medium by an injection device, and the plasma generator is started. The plasma generator receives the working medium and the cooling medium from the working medium pipeline and ionizes the working medium with high pressure to generate high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles. The high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, which undergo a methanogenic reaction with the high-temperature and high-activity hydrogen particles in situ in the reaction chamber to generate methane. When the volume percentage of CH4 in the gas at the vertical well outlet is higher than 10%, it indicates that the coal seam has started to convert. The water and hydrogen flow and power of the plasma generator are gradually adjusted to maintain the production load between 10% and 50%, and the coal seam conversion methane production begins. If the vertical well feedback shows that the volume ratio of carbon dioxide in the export gas exceeds 5%, keep the water injection volume unchanged and slowly increase the plasma generator hydrogen injection flow rate until the volume ratio of carbon dioxide in the export gas is lower than 5%; if the feedback shows that the volume ratio of hydrogen in the export gas exceeds 5%, slowly increase the plasma generator water injection flow rate until the volume ratio of hydrogen in the export gas is close to 0 and the volume ratio of carbon dioxide is 5%; the gas injection pipe injection device controls the water and hydrogen injection flow rates to make the molar ratio of water and hydrogen injected into the plasma generator between 0.5-0.

6. When the export gas is normal, keep the ratio of water to hydrogen injected into the plasma generator unchanged, slowly adjust the water and hydrogen injection flow rates and the plasma generator power to stabilize the production load at 50%. When the vertical well test device feedback shows that the outlet gas flow rate continues to decline, increase the water and hydrogen injection flow and power of the plasma generator to increase the conversion reaction load to 60%-100%. When the vertical well feedback shows that the outlet gas flow rate further decreases, it indicates that the conversion of the coal seam covered by the plasma generator and the vertical well is complete. Keep the plasma generator started, and withdraw the plasma generator 10-100m by the ground gas injection pipe moving device to continue the coal seam conversion production. Adjust the production in this cycle. When the moving distance of the plasma generator is close to the non-vertical section distance of the coal seam, turn off the power of the plasma generator, stop the injection of the reaction medium, maintain the injection of the cooling medium, and withdraw the gas injection pipe and the plasma generator to the ground respectively.

2. The method for producing methane by in-situ plasma conversion of coal seams according to claim 1, characterized in that: The end coordinates of the non-vertical channel of the directional drilling are the target point. The directional drilling well also vertically passes through the overburden and the upper edge of the coal seam from the ground, and gradually deflects from the coal seam to the target point until it penetrates to form a directional drilling well II. The non-vertical channel connecting the directional drilling well and the directional drilling well II in the coal seam is the coal seam channel; between the directional drilling well and the directional drilling well II, a vertical channel is formed by vertically passing through the overburden and the coal seam from the ground as a vertical well. The directional drilling well is provided with the gas injection pipe and the plasma generator. The directional drilling well II is provided with a gas injection pipe II and a plasma generator II connected to the gas injection pipe II. The plasma generator II receives the working medium and the cooling medium from the working medium pipeline and ionizes the working medium with high pressure to generate high-temperature and high-activity water vapor particles and high-temperature and high-activity hydrogen particles. The high-temperature and high-activity water vapor particles undergo a reduction reaction with the coal seam to be converted into hydrogen and carbon monoxide, which undergo a methanogenic reaction with the high-temperature and high-activity hydrogen particles in situ in the reaction chamber to produce methane.

3. The method for producing methane by in-situ plasma conversion of coal seams according to claim 2, characterized in that: The plasma generator and the plasma generator II are arranged on the same side of the vertical well and are arranged opposite to each other.

4. The method for producing methane by in-situ plasma conversion of coal seams according to claim 2, characterized in that: The plasma generator and plasma generator II are arranged on both sides of the vertical well and are arranged opposite to each other.

5. The method for producing methane by in-situ plasma conversion of coal seams according to claim 1, characterized in that: The gas injection pipe and the gas injection pipe II are both made of high temperature resistant, corrosion resistant and hydrogen embrittlement resistant alloy or composite material.

6. The method for producing methane by in-situ plasma conversion of coal seams according to claim 1, characterized in that: The horizontal angle of the vertical channel is between 75° and 105°, and the horizontal angle of the non-vertical channel is between 0° and 20°.

7. The method for producing methane by in-situ plasma conversion of coal seams according to claim 1, characterized in that: The length of the coal seam channel is 100-3000m.

8. The method for producing methane by in-situ plasma conversion of coal seams according to claim 1, characterized in that: A test device for detecting the gas flow rate and components of the gas is arranged at the wellhead of the vertical well on the ground.

9. The method for producing methane by in-situ plasma conversion of coal seams according to claim 1, characterized in that: The working medium includes hydrogen, water or carbon dioxide.

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