A method for in-situ gasification mining of coal seams by drilling

Abstract

The present invention discloses a drilling-type coal seam in-situ gasification mining method, which belongs to the technical field of coal in-situ gasification and coalbed methane mining. Two vertical boreholes are constructed from the ground through the rock layer to the coal seam, and then horizontal boreholes are constructed at the bottom of the two vertical boreholes to communicate with each other. A combustion system is set in one borehole, and an extraction system is arranged in the other borehole; the combustion system includes a combustion pipe with multiple flame nozzles at the end. After the combustion pipe enters the end of the horizontal borehole, it is ignited and sprays fire into the coal seam, and the extraction system is started for extraction. At the same time, the combustion pipe moves along the horizontal borehole while burning until it reaches the other end of the horizontal borehole. The combustion pipe rotates slowly horizontally with the entrance end of the horizontal borehole as the center of the circle while continuously telescoping back and forth, forming a gasification goaf that is fan-shaped when viewed from the horizontal plane, and mining is stopped until the gasification goaf is close to forming a circle. Coal mining is directly changed to gas and water gas mining, achieving unmanned underground mining, reducing mining costs, and reducing waste ground emissions.

Description

Technical Field

[0001] The present invention relates to the technical field of coalbed methane mining, and in particular to a drilling-type coalbed in-situ gasification mining method. Background Art

[0002] After shallow coal seams are mined, coal mining gradually extends to deeper depths. However, deep solid resource mining leads to an increase in sudden engineering disasters and major accidents, and deteriorates the working environment. Based on existing mining methods, the level of mining technology development, and the understanding and prevention of mine hazards, the mining depth of solid minerals cannot be extended indefinitely. Traditional mining methods and current technology are no longer sufficient to support deep solid resource mining. Instead, there is a limit to the mining depth. Xie Heping et al. proposed a method for determining the limit mining depth based on several factors, including ambient temperature at the coal face, roadway deformation control, and the catastrophic accumulation of energy in the mining rock mass. They clearly stated that under current technological conditions, the limit for underground coal mining is 1500 meters, making mining deeper into coal seams a challenge. Currently, there is no unmanned in-situ coalbed methane gasification method. In existing experiments, the challenge is how to guide large-scale, directional combustion and gasification in coal seams. Although gasification processes based on horizontal wells and retreating injection points have achieved breakthroughs in directional combustion, large-scale coalbed gasification requires numerous wells, resulting in high drilling costs and poor economic viability. Summary of the Invention

[0003] To address the difficulties in deep coal mining, this patent directly conducts controlled combustion gasification of coal seams underground, converting coal into a mixed gas mainly composed of H2, CO, CH4, CO2 and other gases, achieving the green and environmentally friendly mining goal of "no coal on the ground and no people underground" in the development of deep coal resources.

[0004] In order to solve the above technical problems, the present invention provides a drilling type coal seam in-situ gasification mining method, which constructs two vertical boreholes from the ground through the rock layer to the coal seam, and then constructs horizontal boreholes at the bottom of the two vertical boreholes to communicate with each other, thereby forming a U-shaped long borehole; then a combustion system is set in one of the vertical boreholes, and an extraction system is arranged in the other vertical borehole; the combustion system includes a combustion pipe, and a plurality of flame nozzles are provided at the end of the combustion pipe. After the combustion of the flame nozzle is stable, the combustion pipe is ignited and sprays fire into the coal seam. After the combustion of the flame nozzle is stable, the extraction system is started for extraction, and at the same time, the combustion pipe moves along the horizontal borehole while burning until it reaches the other end of the horizontal borehole. Then, the combustion pipe slowly rotates horizontally with the entry end of the horizontal borehole as the center of the circle and continues to move back and forth, thereby forming a fan-shaped gasification goaf area in the coal seam when viewed from the horizontal plane. When the gasification goaf in the coal seam is close to forming a circular area, mining is stopped, and the combustion system is recovered to complete the drilling type coal seam in-situ gasification mining at that location.

[0005] The specific steps include:

[0006] S1. Arrange a vertical borehole and an L-shaped long borehole into the coal seam from two locations on the surface, and penetrate the end of the vertical borehole through the L-shaped long borehole in the coal seam to form a U-shaped borehole in the coal seam; then, run casing into the wellbore of the vertical borehole and the L-shaped long borehole for reinforcement;

[0007] Use vertical drilling to drain the water in the horizontal section of the L-shaped long borehole;

[0008] An extraction system is installed in a vertical borehole. A extraction pipeline is installed at the end of the vertical borehole using a sealed section, with a length of no less than 3 meters. One end of the pipeline extends into the wellbore and reaches the coal seam, while the other end is connected to a heat exchanger and a gas-liquid separator via a sequential pipeline from an extraction pump station. The gas-liquid separator is equipped with outlets for removing wastewater and mixed gas, respectively. The mixed gas is then transported to the factory through the pipeline for further separation according to product requirements.

[0009] The drill rod and drill bit used for drilling are withdrawn, and a fuel efficiency system is installed at the surface wellhead of the L-shaped long borehole: a drilling platform is set up, and a special drill rod is lowered into the L-shaped long borehole using the drilling platform until it reaches the coal seam. A fire tube is provided inside the special drill rod, and the fire tube includes pipes for conveying oxidants and reducing agents and cables. The pipes for conveying oxidants and reducing agents and the cables are wrapped with flexible high-temperature resistant casing on the outside. A flame drill head connected to the end of the fire tube is provided at the end of the special drill rod, and the tail of the fire tube extends to the surface through the drilling platform. The oxidant conveying pipe of the fire tube is connected to the gas tank filled with oxidant set on the surface, and the pipe conveying reducing agent is connected to the gas tank filled with reducing agent set on the surface. A backfire preventer is provided at the connection between the gas tank and the pipe. The end of the cable in the fire tube is connected to the ignition device in the flame drill head, and the tail is connected to an igniter for ignition by a remote-controlled ignition device.

[0010] S2. Inject nitrogen into the L-shaped long borehole to check for air tightness and start the extraction pump station. When the odor of nitrogen is detected from the mixer outlet of the gas-liquid separator and no nitrogen odor is detected in other lines, joints, and inlets, it indicates that the U-shaped borehole gas path is unobstructed and there is no gas leakage on the surface. The air tightness test is considered to be qualified.

[0011] S3. Start the drilling platform and use a special drill pipe to move the jet drill bit to the horizontal end of the L-shaped long borehole in the coal seam. Then, inject oxidant and reducing agent gases into the fire pipe through two gas cylinders, so that the oxidant and reducing agent gases flow along the fire pipe to the jet drill bit. At the same time, use the igniter to continuously control the jet drill bit to continuously ignite until the igniter obtains a temperature of the jet drill bit that is continuously stable at above 500°C, indicating that the ignition is successful. Then stop ignition. At this time, the jet drill bit performs in-situ gasification and combustion of the coal seam. Continuously monitor the temperature of the jet drill bit to control the direction of the jet drill bit flame and prevent explosion. Start the extraction pump station to extract the gas discharged from the vertical borehole.

[0012] S4, the flame drill bit continues to burn and moves along the horizontal section of the L-shaped long drill hole as the burning time increases, thereby driving the flame to move, and the movement speed of the flame drill bit is adjusted according to the composition of the mixed gas discharged from the gas-liquid separator;

[0013] S5. When the igniter indicates that the drill bit temperature is stable above 1000°C, and combined with the analysis of the composition of the mixed gas extracted from the vertical borehole by the extraction pump station, the supply of the reducing agent is reduced and water vapor is transported through the reducing agent pipeline to replace it. The water vapor is used to react with carbon under high temperature conditions to produce water gas. The carbon, methane and other gases in the coal seam react with the oxidant to support combustion, and the coal reacts with the water vapor to produce water gas;

[0014] S6. In the coal seam, a special drill pipe follows the horizontal section of the L-shaped long borehole as its starting point. With the starting point of the horizontal section of the L-shaped long borehole as the center of the circle, it rotates while driving the flame drill bit to continuously extend and retract back and forth. The fire continuously burns the coal, thus forming a fan-shaped combustion goaf with a continuously expanding angle in the coal seam. The flame drill bit and special drill pipe always move along one side of the coal wall, extending and retracting back and forth under the protection of the unburned coal seam, thereby preventing the flame drill bit and special drill pipe from being damaged by roof collapse.

[0015] When the fan-shaped goaf in the coal seam is close to forming a circular area, that is, when the width of the unmined area at the edge of the circle formed by gasification is less than 5m, mining is stopped, the flame drill bit and special drill rod are recovered, and the drilling-type coal seam in-situ gasification mining is completed.

[0016] Furthermore, the tail end portion of the fire tube is arranged in a winch, and its length is adjusted by the winch arranged at the wellhead.

[0017] Furthermore, the special drill pipe is composed of two semi-cylindrical shells, which are installed in the fire tube and are tightly buckled, thereby achieving the requirement of sending the soft fire tube into an ultra-long horizontal section and moving it back and forth.

[0018] Furthermore, the flame drill bit is firmly connected to a section of the fire pipe and guides the spray direction of the flame, with a spray distance of more than 3m.

[0019] Furthermore, the drilling route is centered on the well where the drilling platform is located, and it always drills and burns back and forth on one side, forming a fan-shaped structure with an increasing angle, and finally nearly forming a circular structure on a plane.

[0020] Furthermore, the specially made drill rod and flame drill bit always move back and forth along one side of the coal wall.

[0021] Furthermore, the number of vertical drill holes is greater than or equal to one. When the number is greater than one, the vertical drill holes used for extraction are evenly distributed on the boundary of the formed mining circle, thereby forming a circular distribution, thereby reducing the gas extraction path in the fan-shaped goaf and improving the gas extraction efficiency.

[0022] Furthermore, the nozzle of the flame drill bit always sprays toward one side of the coal wall during the coal seam gasification process.

[0023] The beneficial effects of the present invention are as follows: this method is applied to in-situ coal gasification mining and is suitable for various coal mines, especially deep coal mines and extremely thin coal seams that are difficult to mine using traditional mining methods. This method transforms the traditional "underground coal excavation to the surface" into "underground gasification gas extraction." At the same time, in the expanded area of drilling and combustion formed in the goaf, the flame-jet drill bit and special drill rod always move along the side of the coal wall, drilling under the cover of the coal seam, thereby preventing the flame-jet drill bit and special drill rod from being damaged by roof collapse. This method achieves the goal of no one underground and no coal and gangue aboveground, significantly reducing the risks of personnel operations, lowering mining costs, and reducing waste emissions to the surface. It is a way to achieve green coal mining.

[0024] The same borehole can achieve large-scale gasification of the coal seam, directly changing coal mining to gas and water gas mining, realizing unmanned mining underground and no waste rock coming out of the mine above ground, significantly reducing the risks of personnel in the operation process, reducing mining costs, and at the same time reducing waste emissions to the ground. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 A diagram showing the connection of various devices in a drilling-type coal seam in-situ gasification mining method provided by an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of the mining process provided by an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of the end of mining provided by an embodiment of the present invention.

[0029] Description of reference numerals:

[0030] 1. Wellbore; 2. Sealing section; 3. Pipeline; 4. Pumping station; 5. Flow meter; 6. Heat exchanger; 7. Valve; 8. Gas-liquid separator; 9. Gas tank; 10. Backfire arrester; 11. Cable; 12. Ignitor; 13. Winch; 14. Fire pipe; 15. Drilling platform; 16. Special drill pipe; 17. Flame drill bit; 18. L-shaped long borehole; 19. Vertical borehole; 20. Combustion zone; 21. Fly ash; 22. Coal seam; 23. Rock stratum; 24. High-temperature resistant casing. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] like Figure 1 As shown, a drilling-type coal seam in-situ gasification mining method of the present invention constructs two vertical boreholes from the ground through the rock layer 23 to the coal seam 22, and then constructs horizontal boreholes at the bottom of the two vertical boreholes to communicate with each other, thereby forming a U-shaped long borehole; thereafter, a combustion system is set in one of the vertical boreholes, and an extraction system is arranged in the other vertical borehole; the combustion system includes a combustion pipe, and a plurality of flame nozzles are provided at the end of the combustion pipe. After the combustion of the flame nozzle is stable, the combustion pipe is ignited and sprays fire into the coal seam 22. After the combustion of the flame nozzle is stable, the extraction system is started for extraction, and at the same time, the combustion pipe moves along the horizontal borehole while burning until it reaches the other end of the horizontal borehole, and then the combustion pipe slowly rotates horizontally with the entrance end of the horizontal borehole as the center of the circle and continues to move back and forth, thereby forming a fan-shaped gasification goaf area in the coal seam 22 when viewed from the horizontal plane. When the gasification goaf in the coal seam 22 is close to forming a circular area, mining is stopped, and the combustion system is recovered to complete the drilling-type coal seam in-situ gasification mining there.

[0033] The specific steps are as follows:

[0034] S1. Arrange a vertical borehole 19 and an L-shaped long borehole 18 into the coal seam 22 from two locations on the ground, and penetrate the end of the vertical borehole 19 through the L-shaped long borehole 18 in the coal seam 22 to form a U-shaped borehole in the coal seam 22; then, reinforce the wellbore 1 by running casing in the vertical borehole 19 and the L-shaped long borehole 18;

[0035] Use vertical borehole 19 to drain the water in the horizontal section of L-shaped long borehole 18;

[0036] A drainage system is installed in a vertical borehole 19. A drainage pipeline 3 is installed at the end of the vertical borehole 19 using a sealing section 2, which is no less than 3 meters long. One end of the pipeline 3 extends into the wellbore 1 and reaches the coal seam 22. The other end is connected to a heat exchanger 6 and a gas-liquid separator 8 via a sequential pipeline of a drainage pump station 4. The gas-liquid separator 8 is provided with pipeline outlets for removing wastewater and mixed gas, respectively. The mixed gas is transported to the factory through the pipeline for further separation according to product requirements.

[0037] Withdraw the drill rod and drill bit used for drilling, and install the fuel efficiency system at the surface wellhead of the L-shaped long borehole 18: set up a drilling platform 15, and use the drilling platform 15 to lower the special drill rod 16 into the L-shaped long borehole 18 until the coal seam 22. The special drill rod 16 is composed of two semi-cylindrical shells spliced together, and the fire tube 14 is installed and fastened tightly, so as to achieve the requirement of sending the soft fire tube 14 into the ultra-long horizontal section and moving back and forth; the special drill rod 16 is provided with a fire tube 14 inside, and the fire tube 14 includes a pipe for conveying an oxidant and a reducing agent and a cable 11. The outside of the pipe for conveying an oxidant and a reducing agent and the cable 11 are wrapped with a flexible high-temperature resistant casing 24. The end of the special drill rod 16 is provided with a flame drill bit 17 connected to the end of the fire tube 14. The tail of the fire tube 14 is drilled through The well platform 15 extends to the surface. The oxidant delivery pipeline of the fire tube 14 is connected to the gas tank 9 filled with oxidant set on the surface, and the reductant delivery pipeline is connected to the reductant gas tank 9 set on the surface. The connection between the gas tank 9 and the pipeline is provided with a backfire preventer 10 and a valve 7. The end of the cable 11 in the fire tube 14 is connected to the ignition device in the flame drill 17. The flame drill 17 is firmly connected to a section of the fire tube 14 and pulls the spray direction of the flame. The spray distance exceeds 3m. The tail of the cable 11 is connected to an igniter 12 for ignition by a remote-controlled ignition device; the oxidant delivery pipeline and the reductant delivery pipeline are both provided with a flow meter 5; the tail end of the fire tube 14 is arranged in the winch 13, and its length is adjusted by the winch 13 arranged at the wellhead. The special drill rod 16 is composed of two semi-cylindrical shells, which are installed in the fire tube 14 and are tightly buckled, so as to achieve the requirement of sending the flexible fire tube 14 into the horizontal section of ultra-long distance and moving it back and forth.

[0038] S2. Inject nitrogen into the L-shaped long borehole 18 to check for air tightness, start the extraction pump station 4, and when the odor of nitrogen is detected from the mixer outlet of the gas-liquid separator 8, and no nitrogen odor is detected in other lines, joints, and inlets, it indicates that the U-shaped borehole gas path is unobstructed and there is no gas leakage on the surface, and the air tightness test is judged to be qualified;

[0039] S3. Start the drilling platform 15 and use the special drill pipe 16 to move the jet drill bit 17 to the horizontal end of the L-shaped long borehole 18 in the coal seam 22. Then, inject oxidant and reducing agent gases into the fire tube 14 through two gas cylinders 9 respectively, so that the oxidant and reducing agent gases flow along the fire tube 14 to reach the jet drill bit 17. At the same time, use the igniter 12 to continuously control the jet drill bit 17 to continuously ignite until the igniter 12 obtains that the temperature of the jet drill bit 17 is continuously stable at above 500°C, indicating that the ignition is successful. Then stop ignition. At this time, the jet drill bit 17 performs in-situ gasification and combustion on the coal seam 22. The temperature of the jet drill bit 17 is continuously monitored to control the flame trend of the jet drill bit 17 to prevent explosion. Start the extraction pump station 4 to extract the gas discharged from the vertical borehole 19.

[0040] S4, the flame drill bit 17 continues to burn and moves along the horizontal section of the L-shaped long drill hole 18 as the burning time increases, thereby driving the flame to move, and the moving speed of the flame drill bit 17 is adjusted according to the composition of the mixed gas discharged from the gas-liquid separator 8;

[0041] S5. When the igniter 12 shows that the drill temperature is stable at above 1000°C, combined with the analysis of the mixed gas components extracted from the vertical borehole by the extraction pump station 4, the supply of the reducing agent is reduced and water vapor is transported through the reducing agent pipeline to replace it. Water vapor is used to react with carbon under high temperature conditions to produce water gas. The carbon, methane and other gases in the coal seam react with the oxidant to support the combustion. The coal reacts with water vapor to obtain water gas. During the combustion process, the fly ash (21) that has been collected and falls on the bottom plate of the combustion zone 20 is checked.

[0042] S6. In the coal seam 22, the special drill rod 16 takes the horizontal pipe section of the L-shaped long borehole 18 as the starting position, and rotates with the starting point of the horizontal pipe section of the L-shaped long borehole 18 as the center of the circle, driving the flame drill bit 17 to continuously extend and retract back and forth, and the fire power continuously burns the coal body, thereby forming a combustion void area 20 with a continuously expanding angle in the coal seam 22. The combustion void area 20 is specifically a horizontal fan-shaped combustion void area; the flame drill bit 17 and the special drill rod 16 always move along one side of the coal wall, and extend and retract back and forth under the cover of the unburned coal seam, thereby preventing the collapse of the roof from damaging the flame drill bit 17 and the special drill rod 16; the nozzle of the flame drill bit 17 always sprays toward one side of the coal wall during the coal seam gasification process, such as Figure 2 and Figure 3 As shown;

[0043] When the fan-shaped goaf in the coal seam 22 is close to forming a circular area, that is, when the width of the unmined area at the edge of the circle formed by gasification is less than 5m, mining is stopped, the flame drill bit 17 and the special drill rod 16 are recovered, and the drilling-type coal seam in-situ gasification mining is completed.

[0044] The drilling route is centered on the well where the drilling platform 15 is located, drilling and burning back and forth on one side, forming a fan-shaped structure with an increasing angle, and finally forming a circular structure on a flat surface. The special drill rod 16 and the flame drill bit 17 continuously move back and forth along one side of the coal wall. The number of vertical drill holes 19 is greater than or equal to one. When there is more than one vertical drill hole 19, the vertical drill holes 19 used are evenly distributed along the boundary of the formed stope circle, forming a circular distribution. This reduces the number of gas extraction paths in the fan-shaped goaf and improves gas extraction efficiency.

[0045] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A drilling-type coal seam in-situ gasification mining method, characterized in that: The specific steps are as follows: S1. Arranging a vertical borehole (19) and an L-shaped long borehole (18) in a coal seam (22) from two locations on the ground, and penetrating the end of the vertical borehole (19) through the L-shaped long borehole (18) in the coal seam (22) to form a U-shaped borehole in the coal seam (22); then, casing is respectively installed in the wellbore (1) of the vertical borehole (19) and the L-shaped long borehole (18) for reinforcement; Draining the water in the horizontal section of the L-shaped long borehole (18) by using a vertical borehole (19); A drainage system is installed in a vertical borehole (19), and a drainage pipe (3) is installed at the end of the vertical borehole (19) using a sealing section (2), and the sealing section (2) is not less than 3 meters; one end of the pipe (3) extends into the wellbore (1) to the coal seam (22), and the other end is connected to a heat exchanger (6) and a gas-liquid separator (8) through a sequential pipeline of a drainage pump station (4), and the gas-liquid separator (8) is provided with a pipeline outlet for removing waste water and mixed gas respectively, and the mixed gas is transported to the factory through the pipeline for further separation according to product requirements; The drill rod and drill bit used for drilling are withdrawn, and a fuel efficiency system is installed at the surface wellhead of the L-shaped long borehole (18): a drilling platform (15) is set up, and a special drill rod (16) is lowered into the L-shaped long borehole (18) by using the drilling platform (15) until the coal seam (22). A fire pipe (14) is provided inside the special drill rod (16), and the fire pipe (14) includes a pipe for conveying an oxidant and a reducing agent and a cable (11). The pipe for conveying an oxidant and a reducing agent and the cable (11) are wrapped with a flexible high-temperature resistant casing (24) on the outside. The end of the special drill rod (16) is provided with a fire pipe (14) The end of the fire tube (14) is connected to a flame drill head (17), the tail of the fire tube (14) extends to the surface through the drilling platform (15), the oxidant delivery pipeline of the fire tube (14) is connected to the gas tank (9) filled with oxidant set on the surface, the pipeline for delivering the reducing agent is connected to the gas tank (9) of the reducing agent set on the surface, and the connection between the gas tank (9) and the pipeline is provided with a backfire preventer (10), the end of the cable (11) in the fire tube (14) is connected to the ignition device in the flame drill head (17), and the tail is connected to an igniter (12) for igniting the remote control ignition device; S2. Inject nitrogen into the L-shaped long borehole (18) to check the air tightness, start the extraction pump station (4), and when the odor of nitrogen is detected from the mixer outlet of the gas-liquid separator (8), and the odor of nitrogen is not detected in other lines, joints and inlets, it indicates that the U-shaped borehole gas path is unobstructed and there is no gas leakage on the surface, and the air tightness test is judged to be qualified; S3, start the drilling platform (15) and use the special drill pipe (16) to move the jet drill bit (17) to the horizontal end of the L-shaped long borehole (18) in the coal seam (22), and then inject the oxidant and reducing agent gases into the fire pipe (14) through two gas tanks (9), so that the oxidant and reducing agent gases flow along the fire pipe (14) to reach the jet drill bit (17), and at the same time use the igniter (12) to continuously control the jet drill bit (17) to continuously ignite until the igniter (12) obtains the temperature of the jet drill bit (17) and continuously stabilizes at above 500°C, indicating that the ignition is successful, and stops ignition. At this time, the jet drill bit (17) performs in-situ gasification combustion on the coal seam (22), and continuously monitors the temperature of the jet drill bit (17) to control the trend of the flame of the jet drill bit (17) to prevent explosion; start the extraction pump station (4) to extract the gas discharged from the vertical borehole (19); S4, the flame drill bit (17) continues to burn and moves along the horizontal section of the L-shaped long drill hole (18) as the burning time increases, thereby driving the flame to move, and adjusting the moving speed of the flame drill bit (17) according to the composition of the mixed gas discharged from the gas-liquid separator (8); S5. When the igniter (12) indicates that the drill bit temperature is stable at above 1000°C, and combined with the analysis of the composition of the mixed gas extracted from the vertical borehole by the extraction pump station (4), the supply of the reducing agent is reduced and water vapor is transported through the reducing agent pipeline to replace it, and water gas is produced by reacting water vapor with carbon under high temperature conditions. The carbon, methane and other gases in the coal seam react with the oxidant to support the combustion, and the coal reacts with the water vapor to produce water gas; S6. In the coal seam (22), the special drill rod (16) is positioned along the horizontal pipe section of the L-shaped long borehole (18) as the starting position, and rotates with the starting point of the horizontal pipe section of the L-shaped long borehole (18) as the center of the circle, driving the jet drill bit (17) to continuously extend and retract back and forth, and the fire power continuously burns the coal body, thereby forming a fan-shaped combustion goaf with a continuously expanding angle in the coal seam (22); the jet drill bit (17) and the special drill rod (16) always move along one side of the coal wall, and extend and retract back and forth under the protection of the unburned coal seam, thereby preventing the jet drill bit (17) and the special drill rod (16) from being damaged by the collapse of the roof; When the fan-shaped goaf in the coal seam (22) approaches to forming a circular area, that is, when the width of the unmined area at the edge of the circle formed by gasification is less than 5m, mining is stopped, the flame drill bit (17) and the special drill rod (16) are recovered, and the drilling-type coal seam in-situ gasification mining at that location is completed.

2. The drilling type coal seam in-situ gasification mining method according to claim 1, characterized in that The tail end portion of the fire tube (14) is arranged in a hoist (13), and its length is adjusted by the hoist (13) arranged at the wellhead.

3. The drilling type coal seam in-situ gasification mining method according to claim 1, characterized in that: The special drill rod (16) is composed of two semi-cylindrical shells, which are installed in the fire tube (14) and are tightly buckled, thereby achieving the requirement of sending the soft fire tube (14) into the horizontal section of an ultra-long distance and moving it back and forth.

4. The drilling type coal seam in-situ gasification mining method according to claim 1, characterized in that: The flame drill bit (17) is firmly connected to a section of the fire tube (14) and guides the spray direction of the flame, with a spray distance exceeding 3m.

5. The drilling type coal seam in-situ gasification mining method according to claim 1, characterized in that: The drilling route of the drilling-type coal seam in-situ gasification mining method is centered on the well where the drilling platform (15) is located, and the drilling and burning are always carried out back and forth on one side to form a fan-shaped structure with an increasing angle, and finally close to forming a circular structure on a plane.

6. The drilling type coal seam in-situ gasification mining method according to claim 1, characterized in that: The special drill rod (16) and the flame-jet drill bit (17) always move back and forth along one side of the coal wall.

7. The drilling type coal seam in-situ gasification mining method according to claim 1, characterized in that: The number of vertical drill holes (19) is greater than or equal to one. When the number of vertical drill holes (19) is greater than one, the vertical drill holes (19) used for extraction are evenly distributed on the boundary of the formed mining field circle, thereby forming a circular distribution, thereby reducing the gas extraction path of the fan-shaped goaf and improving the gas extraction efficiency.

8. The drilling type coal seam in-situ gasification mining method according to claim 1, characterized in that: The nozzle of the flame-jet drill bit (17) always sprays toward one side of the coal wall during the coal seam gasification process.

Images