A method for collaborative development of coalbed methane and underground coal gasification

Abstract

The present invention relates to a method for the coordinated development of coalbed methane and underground coal gasification, comprising: drilling a vertical shaft one, drilling a plurality of horizontal wells one from the side of the vertical shaft one to the surrounding area for mining coalbed methane and gasifying coal; drilling a plurality of vertical shafts two from the horizontal well one between two adjacent main horizontal wells one, the positions of the vertical shafts two and the main horizontal wells one corresponding one to one, and the ends of the main horizontal wells one pointing to the vertical shaft two; a horizontal section between two adjacent main horizontal wells one from the ends of the horizontal well one pointing to the horizontal well two; drilling a horizontal well two from the side of the vertical shaft one, the ends of the horizontal well two pointing to the bottom of the adjacent vertical shaft one; mining coalbed methane through the vertical shaft one and the horizontal well one; performing coalbed gasification by using the vertical shaft one as an injection well and the horizontal well one as a production well; then filling the gasified stratum part with concrete to prevent collapse; performing coalbed gasification by using each horizontal well one as an injection well and the vertical shaft two and the horizontal well two as production wells.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane and coal mining, and in particular relates to a method for the coordinated development of coalbed methane and underground coal gasification. Background Art

[0002] my country is rich in coal resources. Direct mining of coal mostly occurs in shallow coal seams, while development of deeper coal seams focuses on extracting coalbed methane (CBM). Direct mining of deep coal resources requires a high level of technical expertise. Transporting deep coal to the surface is challenging, energy-intensive, and uneconomical. Underground coal combustion and gasification produce large quantities of gas, which contains combustible components such as carbon monoxide, methane, and hydrogen, and can be collected and utilized as resource gas. Currently, underground coal gasification is still in the research phase, with limited industrial applications. Underground coal gasification requires the drilling of corresponding injection and extraction wells, while coalbed methane extraction requires the drilling of extraction wells. Furthermore, for deeper strata, drilling is both economically and time-consuming, and resource extraction is limited to the perimeter of the well. Utilizing drilling to maximize deep stratum resource extraction is the best way to reduce extraction costs, but those skilled in the art have explored this area relatively little. Summary of the Invention

[0003] In response to the above problems, the present invention provides a method for the coordinated development of coalbed methane and underground coal gasification, comprising:

[0004] S1: A vertical shaft 1 is drilled downward from the ground, and several horizontal wells 1 are drilled in parallel from the side of the vertical shaft 1 to the surrounding area. The horizontal sections of the horizontal wells 1 and the bottom of the vertical shaft 1 are located in the same stratum at the same depth, for extracting coalbed methane and gasifying coal in the stratum;

[0005] S2: A plurality of horizontal wells 1 are divided into main horizontal wells 1 and slave horizontal wells 1, and at least one slave horizontal well 1 is provided between two adjacent main horizontal wells 1;

[0006] Several vertical shafts 2 are drilled downward from the ground, and the positions of the vertical shafts 2 correspond to the positions of the main horizontal wells 1, and the ends of the main horizontal wells 1 point to the vertical shafts 2;

[0007] S3: A horizontal section between two adjacent main horizontal wells 1, from the end of horizontal well 1 to horizontal well 2; horizontal well 2 is drilled from the side of vertical well 1, with the end of horizontal well 2 pointing to the bottom of the adjacent vertical well 1;

[0008] S4: CBM extraction through vertical well 1 and horizontal well 1;

[0009] S5: Using vertical shaft 1 as the injection well, inject gasification agent, and using horizontal well 1 as the production well, gasify the coal seam between the bottom of vertical shaft 1 and each horizontal well 1; then, fill the gasified stratum with concrete to prevent collapse;

[0010] S6: Use each horizontal well 1 as an injection well, input gasification agent respectively, use vertical well 2 and horizontal well 2 as production wells, and gasify the coal seam between horizontal well 1 and vertical well 2 and horizontal well 2.

[0011] The present invention considers the development of coalbed methane and coal gasification within a deep stratum as a whole. A conventional vertical shaft 1 and several horizontal wells 2 are first drilled to enable coalbed methane extraction in step S4. When drilling vertical shaft 1, taking into account the need for later coal gasification, vertical shaft 1 is drilled all the way to the stratum where the horizontal section of horizontal well 1 is located (i.e., the target stratum). After the coalbed methane in the target stratum is extracted, the coal in that stratum is gasified. In step S5, vertical shaft 1 serves as the injection well, and several horizontal wells 1 serve as extraction wells. Starting from the center (vertical shaft 1), the coal is gradually gasified and burned outward (toward the several horizontal wells 1). The generated coal gas enters horizontal well 1 and is then discharged to the surface along horizontal well 1 and vertical shaft 1.

[0012] Furthermore, the present invention utilizes several horizontal wells 1 as injection wells, and drills several vertical shafts 2 and horizontal well 2 around horizontal well 2 as production wells. The coal between horizontal well 1, vertical shaft 2, and horizontal well 2 is gasified, and the generated coal gas is discharged to the surface through horizontal well 2 and vertical shaft 2, maximizing the utilization of coal and coalbed methane in deep strata. After gasification, vertical shaft 1 can also be used in step S5 to fill the cavity formed after gasification with concrete to prevent stratum collapse. Thus, according to the method provided by the present invention, the coalbed methane and coal resources in the strata surrounding horizontal well 1 can be fully utilized. Both vertical shaft 1 and vertical shaft 2 are substantially vertical.

[0013] Optionally, in step S1, several horizontal wells are evenly arranged radially with vertical well 1 as the center, and horizontal well 1 has an inclined section and a horizontal section connected in sequence. The top of the inclined section of horizontal well 1 is the starting end and is connected to the side of vertical well 1. The horizontal section of horizontal well 1 is inside the target formation, and the end of the horizontal section away from vertical well 1 is the end.

[0014] Further optionally, step S1 is specifically as follows:

[0015] (1) Drill a vertical shaft 1 from the ground downward, and drill several horizontal wells 1 from the side of the vertical shaft 1 to the surrounding areas, so that the bottom of the vertical shaft 1 reaches the middle and lower part of the target formation;

[0016] (2) Lower the screen pipe to the bottom of the vertical well 1, then place the well pipe on top of the screen pipe and perform cementing; place the well pipe in each horizontal well 1 to form the well wall and perform cementing;

[0017] (3) Perforate the horizontal section of each horizontal well 1; then, seal the lower part of the vertical shaft 1 corresponding to each horizontal well 1; and then perform fracturing and drainage operations on the horizontal section of each horizontal well 1.

[0018] Optionally, in step S2, the structure of the master horizontal well 1 is the same as that of the slave horizontal well 1, and they are divided into master and slave, in order to locate the vertical well 2 and the horizontal well 2;

[0019] The bottom of vertical shaft 2 reaches the lower-middle portion of the target formation. The portion of vertical shaft 2 within the target formation serves as a screen to facilitate the delivery of gasification agent. A gap exists between the bottom of vertical shaft 2 and the end of main horizontal well 1, facilitating gasification of the coal seam between them in step S6. Each vertical shaft 2 is spaced identically from vertical shaft 1. The distance between the bottom of vertical shaft 2 and the end of main horizontal well 1 is determined based on actual coal seam gasification needs, ensuring that vertical shaft 2 can collect the gas produced by coal seam gasification.

[0020] Optionally, in step S3, horizontal well 2 has an inclined section and a horizontal section connected in sequence, the top of the inclined section of horizontal well 2 is the starting end and is connected to the side of vertical well 2, the horizontal section of horizontal well 2 is inside the target formation, and the end of the horizontal section of horizontal well 2 away from vertical well 2 is the end.

[0021] Further optionally, steps S2 and S3 are specifically as follows:

[0022] (4) Drill a vertical shaft 2 downward from the ground, and drill a horizontal well 2 obliquely downward from the side of the vertical shaft 2. The bottom of the vertical shaft 2 reaches the middle and lower part of the target formation, and the vertical shaft 2 corresponds to the main horizontal well 1 one to one;

[0023] (5) Lower the screen pipe to the bottom of the second vertical shaft, then place the well pipe on top of the screen pipe and perform cementing; place the well pipe into the second horizontal well to form the well wall and perform cementing;

[0024] (6) Complete the docking of the top of horizontal well 2 and the side of vertical well 2 according to existing technology; then complete the installation of well pipes in other parts of vertical well 2 and the cementing and completion work;

[0025] (7) Perforate the horizontal section of each horizontal well.

[0026] Optionally, in step S5, an injection pipe is lowered into vertical shaft 1, and the bottom of the injection pipe reaches the bottom of vertical shaft 1 for injecting gasifying agent and ignition; an exhaust pipe 1 is introduced into each horizontal well 1, and the top of each exhaust pipe 1 is directly connected to the wellhead on the ground to output the coal gas discharged from each horizontal well 1.

[0027] Further optionally, the outer side of the part of the exhaust pipe 1 in the vertical shaft 1 has an interlayer 1, which wraps the outer side surface of the corresponding part of the exhaust pipe. The interlayer 1 is connected to its own water inlet pipe and water outlet pipe, which can input and output cooling water for the interlayer 1, cool the coal gas in the exhaust pipe 1, and avoid affecting the gasification agent in the injection pipe.

[0028] Further optionally, the portion of the injection pipe above the top of each horizontal well is provided with interlayer 2, which wraps the outer side surface of the corresponding injection pipe portion. Interlayer 2 is connected to its own water inlet pipe and water outlet pipe, and can input and output cooling water for interlayer 2.

[0029] Optionally, in step S6, a conventional injection pipe is introduced into each horizontal well 1 respectively, and the bottom end of each injection pipe first stays at the edge of the corresponding coal seam after gasification in step S5, and then as the gasified coal seam in horizontal well 1 continues to expand toward vertical well 2 and horizontal well 2, the bottom end of the injection pipe advances toward the end of horizontal well 1 inside the corresponding horizontal well 1; exhaust pipe 2 is introduced into both vertical well 2 and horizontal well 2. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of vertical shaft 1, horizontal well 1, and vertical shaft 2 in the embodiment;

[0031] Figure 2 Schematic diagram of vertical well 2, horizontal well 2 and horizontal well 1;

[0032] Figure 3 Schematic diagram of vertical well 2 and horizontal well 2.

[0033] In the attached figure, 1-vertical well 1, 2-horizontal well 1, 3-vertical well 2, 4-horizontal well 2, 5-main horizontal well 1, 6-injection pipe, 7-slave horizontal well 1, 8-exhaust pipe 1. DETAILED DESCRIPTION

[0034] This embodiment provides a method for the coordinated development of coalbed methane and underground coal gasification, such as Figure 1-Figure 3 Shown, including:

[0035] S1: A vertical shaft 1 is drilled downward from the ground, and several horizontal wells 2 are drilled in parallel from the side of the vertical shaft 1. The horizontal sections of the horizontal wells 2 and the bottom of the vertical shaft 1 are located in the same stratum at the same depth, for extracting coalbed methane and gasifying coal in the stratum.

[0036] S2: Several horizontal wells 2 are divided into main horizontal wells 5 and slave horizontal wells 7, and at least one slave horizontal well 7 is provided between two adjacent main horizontal wells 5;

[0037] Several vertical shafts 2 3 are drilled downward from the ground. The positions of the vertical shafts 2 3 correspond to the positions of the main horizontal well 1 5 one by one. The ends of the main horizontal well 1 5 point to the vertical shaft 2 3.

[0038] S3: A horizontal section between two adjacent main horizontal wells 5, from the end of horizontal well 1 7 to horizontal well 2 4; horizontal well 2 4 is drilled from the side of vertical well 1 1, with the end of horizontal well 2 4 pointing to the bottom of the adjacent vertical well 1;

[0039] S4: CBM extraction through vertical well 1 and horizontal well 2;

[0040] S5: Using vertical shaft 1 as the injection well, inject gasification agent, and using horizontal well 2 as the production well, gasify the coal seam between the bottom of vertical shaft 1 and each horizontal well 2; then, fill the gasified stratum with concrete to prevent collapse;

[0041] S6: Use each horizontal well 1 2 as an injection well, input gasification agent respectively, use vertical well 2 3 and horizontal well 2 4 as production wells, and gasify the coal seam between horizontal well 1 2 and vertical well 2 3 and horizontal well 2 4.

[0042] Before step S1, the following steps are also included: using existing geological exploration methods and technologies to explore deep strata, selecting strata suitable for both coalbed methane mining and coal gasification as target strata, conducting reasonable geological planning, and selecting suitable locations as well platforms.

[0043] Optionally, in step S1, the bottom of the vertical well 1 reaches the middle and lower part of the target formation; a plurality of horizontal wells 2 are evenly arranged in a radial pattern with the vertical well 1 as the center, and the horizontal well 2 has a build-up section and a horizontal section connected in sequence. The top of the build-up section of the horizontal well 2 is the starting end and is connected to the side of the vertical well 1. The horizontal section of the horizontal well 2 is located inside the target formation, and the end of the horizontal section away from the vertical well 1 is the end. The angles between the starting ends of two adjacent horizontal wells 2 are the same.

[0044] The portion of the vertical shaft 1 located in the target formation is a screen pipe, which is convenient for outputting the gasification agent.

[0045] Further optionally, step S1 is specifically as follows:

[0046] (1) Drill a vertical shaft 1 from the ground downward, and drill several horizontal wells 2 from the side of the vertical shaft 1 to the surrounding areas, so that the bottom of the vertical shaft 1 reaches the middle and lower part of the target formation;

[0047] (2) Lower the screen pipe to the bottom of the vertical well 1, then place the well pipe on top of the screen pipe and perform cementing; place the well pipe in each horizontal well 2 to form the well wall and perform cementing;

[0048] (3) Perforate the horizontal section of each horizontal well-2; then, seal the pressure below the position corresponding to each horizontal well-1 in the vertical well-1; and then perform fracturing and drainage operations on the horizontal section of each horizontal well-2.

[0049] The drilling, setting of wellbore screens, cementing, completion, perforation, fracturing, and drainage operations in steps (1) to (3) above can all be performed using existing technologies in the art. The wellbore is a hollow cylindrical pipe with a solid sidewall and no through-holes.

[0050] At the location where the vertical shaft 1 and the horizontal shaft 2 are connected, a well pipe with several connecting openings is installed. The connecting openings are connected to the top of the horizontal shaft 2 in a one-to-one correspondence. Concrete is poured outside the connecting openings to seal the outside of the connecting openings. Then, the installation of the part above the connecting opening of the vertical shaft 1 and the well cementing and completion work are completed.

[0051] Alternatively, the existing five-stage completion technology can be used. All wellbore tubing (i.e., casing) is lowered into vertical shaft 1 (main wellbore), and the connection with horizontal well 1 is hydraulically isolated. Side drilling can be performed from both vertical shaft 1 and horizontal well 1. Auxiliary packers, sleeves, and other completion devices can be used in vertical shaft 1 to cross-connect horizontal well 1 to achieve hydraulic isolation.

[0052] Further optionally, in step (3), a soluble bridge plug is lowered into the vertical shaft 1 to block the cross-sectional area of ​​the vertical shaft 1. The soluble bridge plug is located below the position where all horizontal wells 1 connect to the vertical shaft 1 to prevent fracturing fluid and coalbed methane from entering the lower space of the vertical shaft, because this part does not play a role in coalbed methane extraction and only plays a role in subsequent coalbed gasification and filling.

[0053] During CBM extraction, new bridge plugs are lowered promptly based on the estimated time it takes for the bridge plug to dissolve, continuing until CBM extraction is complete. After the last bridge plug dissolves, the entire interior of Shaft 1 is connected, facilitating the subsequent introduction of gasifying agents through Shaft 1.

[0054] Optionally, in step S2, the structure of the master horizontal well 1 5 and the slave horizontal well 1 7 are the same, with master and slave distinctions, in order to locate the vertical well 2 3 and the horizontal well 2 4;

[0055] The bottom of vertical shaft 2 (3) reaches the lower-middle portion of the target formation. The portion of vertical shaft 2 (3) within the target formation serves as a screen to facilitate the delivery of gasification agent. A gap exists between the bottom of vertical shaft 2 (3) and the end of main horizontal well 1 (2) to facilitate gasification of the coal seam between them in step S6. Each vertical shaft 2 (3) is spaced the same distance from vertical shaft 1 (1). The distance between the bottom of vertical shaft 2 (3) and the end of main horizontal well 1 (2) is determined based on actual coal seam gasification needs, ensuring that vertical shaft 2 (3) can collect the coal gas produced by coal seam gasification.

[0056] Optionally, in step S3, horizontal well 2 4 has an inclined section and a horizontal section connected in sequence, the top of the inclined section of horizontal well 2 4 is the starting end and is connected to the side of vertical well 2 3, the horizontal section of horizontal well 2 4 is inside the target formation, and the end of the horizontal section away from vertical well 2 3 is the end; there is a spacing between each end of horizontal well 1 2 and the horizontal section of horizontal well 2 4, and the spacing is equal, which is smaller than the spacing from the end of horizontal well 1 2 to the bottom of vertical well 2 3.

[0057] Further optionally, the horizontal wells 2 4 are distributed in sequence in a clockwise or counterclockwise direction, and the end of each horizontal well 2 4 points to the bottom of the next adjacent vertical well 2 3 .

[0058] Further optionally, steps S2 and S3 are specifically as follows:

[0059] (4) Drill a vertical shaft 23 downward from the ground, and drill a horizontal well 24 obliquely downward from the side of the vertical shaft 23. The bottom of the vertical shaft 23 reaches the middle and lower part of the target formation. The vertical shaft 23 can correspond to the main horizontal well 12 one to one.

[0060] (5) Lower the screen pipe to the bottom of the vertical well 2 (3), then place the well pipe on top of the screen pipe and perform cementing; place the well pipe into the horizontal well 2 (4) to form the well wall and perform cementing;

[0061] (6) Complete the docking of the top of the horizontal well 2 4 and the side of the vertical well 2 3 according to existing technology; then, complete the installation of the well pipes in the other parts of the vertical well 2 3 and the cementing and completion work;

[0062] (7) The horizontal sections of each horizontal well 24 are perforated to connect the horizontal well 24 with the external formation environment so that the coal gas produced by coal gasification can enter the horizontal well 24.

[0063] In step (6), a section of screen pipe can be set at the top of horizontal well 2, and a section of screen pipe can also be set at the side wall of vertical well 2 corresponding to the position of the top of horizontal well 2. A hole can be opened on the side of the screen pipe of vertical well 2 facing horizontal well 2, and the top of horizontal well 2 is connected to the side wall of vertical well 2, so that horizontal well 2 and vertical well 2 can be connected to each other.

[0064] Optionally, in step S4, a soluble bridge plug is set in the vertical well 1, and then the existing technology is used to mine coalbed methane in the target formation through the vertical well 1 and the horizontal well 2.

[0065] Through the fracturing transformation of the formation and coalbed methane extraction by horizontal well 1-2, the cracks and pores in the target formation are fully opened and expanded, the permeability of the formation is improved, and good environmental conditions are provided for the subsequent diffusion of the gasification agent input from vertical well 1 or horizontal well 2 in the formation, which is conducive to more complete gasification of the coal seam between vertical well 1 and horizontal well 2, and between horizontal well 2 and vertical well 3.

[0066] Optionally, in step S5, an injection pipe 6 is lowered into vertical shaft 1, with the bottom of the injection pipe reaching the bottom of vertical shaft 1, for injecting gasifying agent and igniting the gas. An exhaust pipe 8 is introduced into each horizontal well 2, with the top of each exhaust pipe 8 directly connected to the surface wellhead to discharge the coal gas discharged from each horizontal well 2. Exhaust pipe 8 is a conventional exhaust pipe in the field of coalbed gasification.

[0067] Further optionally, the outer side of the exhaust pipe 8 in the vertical shaft 1 includes an interlayer 1, which wraps the outer side surface of the corresponding exhaust pipe 8. The interlayer 1 is connected to its own water inlet pipe and water outlet pipe, which can input and output cooling water for the interlayer 1, cool the coal gas in the exhaust pipe 8, and avoid affecting the gasification agent in the injection pipe.

[0068] Further optionally, the portion of the injection pipe above the top of each horizontal well 1 is provided with interlayer 2, which wraps the outer side of the corresponding injection pipe portion. Interlayer 2 is connected to its own water inlet pipe and water outlet pipe, which can input and output cooling water for interlayer 2; preferably, the outside of interlayer 2 is also covered with a thermal insulation layer, which effectively isolates the heat emitted by the exhaust pipe 18 and effectively retains the cooling brought by interlayer 2, so that the gasification agent in the injection pipe is affected as little as possible by the exhaust gas, thereby making the portion above the docking opening of the vertical well 1 have both injection and production functions, saving drilling costs.

[0069] In step S5, an injection pipe is introduced into the vertical shaft 1 to introduce a gasifying agent into the target formation. Conventional ignition techniques are then used to begin gasifying and burning the coal within the target formation. Since horizontal wells 2 are radially and evenly arranged around shaft 1, forming a circular area centered at the bottom of shaft 1 and radiating outward, gasification also originates from this center and diffuses into the surrounding coal seams. The generated coal gas enters the nearby horizontal well 2 and is then discharged to the surface through exhaust pipe 8. This process also completes pre-cooling through interlayer 1. Because the horizontal section of horizontal well 2 is of a certain length and is perforated throughout the horizontal section from the initial perforation, the gasification area around the bottom of shaft 1 can expand along the length of the horizontal section of horizontal well 2. The generated coal gas enters horizontal well 2 through certain perforations in the nearby horizontal section and is then discharged. This expands the coal seam area that can be gasified between vertical well 1 and horizontal well 2, and the high-temperature gasification zone expands outward along the horizontal section of horizontal well 2 until the gasification agent can no longer reach it and the maximum gasification area is reached. At this time, the edge of the distillation zone may not have reached the end of horizontal well 2.

[0070] Then, the injection pipe and exhaust pipe 8 are removed, and concrete is injected into the interior of vertical shaft 1. The concrete reaches the target stratum, filling the voids left by gasification and preventing collapse. If the coal seam corresponding to the horizontal section of horizontal shaft 2 remains partially ungasified, the concrete will stop at the edge of the ungasified coal seam, leaving it unaffected. Ultra-fine cement-based grouting material (particle size <0.08mm) can be used; under high-pressure injection conditions, it can penetrate the screen at the bottom of vertical shaft 1 and enter the stratum.

[0071] Optionally, in step S6, a conventional injection pipe is introduced into each horizontal well 1 2, with the bottom end of each injection pipe initially positioned at the edge of the corresponding coal seam gasified in step S5. As the coal seam gasified in horizontal well 1 2 continuously expands toward vertical well 2 3 and horizontal well 2 4, the bottom end of the injection pipe is advanced within the corresponding horizontal well 1 2 toward the end of horizontal well 2.

[0072] The interiors of both vertical shaft 2 3 and horizontal well 2 4 are led into exhaust pipe 2. The coal gas obtained by coalbed gasification in step S6 enters the horizontal sections of vertical shaft 2 3 and horizontal well 2 4 and is finally discharged to the ground through vertical shaft 2 3 .

[0073] Further optionally, the bottom of the exhaust pipe 2 in the vertical shaft 2 3 reaches the bottom of the vertical shaft 2 3, and the exhaust pipe 2 in the horizontal well 2 4 extends to the end of the horizontal well 2 4; in the upper half of the vertical shaft 2 3, the two exhaust pipes 2 are side by side and extend along the vertical shaft 2 3 to the ground.

[0074] In step S6, gasification begins at the edge of the remaining coal seam after gasification in step S5. Horizontal Well 1 serves as an injection well, injecting a gasifying agent and igniting it. This combustion of the coal seam surrounding Horizontal Well 1 is then gradually advanced toward Vertical Well 2 3 and Horizontal Well 2 4. If a small amount of coal gas enters Horizontal Well 1 through other through-holes in Horizontal Well 1, it will also be burned. Alternatively, the wellhead of Vertical Well 1 can be sealed in advance, allowing only the injection pipe to flow, thus preventing even minimal coal gas from being discharged from Vertical Well 1.

Claims

1. A method for the coordinated development of coalbed methane and underground coal gasification, characterized in that: include: S1: Drilling a vertical shaft 1, and drilling several horizontal wells 1 in parallel from the side of the vertical shaft 1 to the surrounding areas. The horizontal sections of the horizontal wells 1 and the bottom of the vertical shaft 1 are located in the same stratum at the same depth, for extracting coalbed methane and gasifying coal in the stratum; S2: A plurality of horizontal wells 1 are divided into main horizontal wells 1 and slave horizontal wells 1, and at least one slave horizontal well 1 is provided between two adjacent main horizontal wells 1; Drill several vertical shafts 2, with the positions of the vertical shafts 2 corresponding to the main horizontal wells 1, and the ends of the main horizontal wells 1 pointing to the vertical shafts 2; S3: A horizontal section between two adjacent main horizontal wells 1, from the end of horizontal well 1 to horizontal well 2; horizontal well 2 is drilled from the side of vertical well 2, with the end of horizontal well 2 pointing to the bottom of the adjacent vertical well 2; S4: CBM extraction through vertical well 1 and horizontal well 1; S5: Using vertical shaft 1 as the injection well and horizontal shaft 1 as the production well, the coal seam between the bottom of vertical shaft 1 and each horizontal shaft 1 is gasified; then, concrete is filled into the gasified stratum; S6: Using each horizontal well 1 as an injection well and vertical well 2 and horizontal well 2 as production wells, gasify the coal seam between horizontal well 1, vertical well 2 and horizontal well 2; In step S1, a plurality of horizontal wells 1 are evenly arranged in a radial pattern with vertical well 1 as the center. Horizontal well 1 comprises a buildup section and a horizontal section connected in sequence. The top of the buildup section of horizontal well 1 is the starting point and is connected to the side of vertical well 1. The horizontal section of horizontal well 1 is located within the target formation, and the end of the horizontal section away from vertical well 1 is the end point. The part of the shaft 1 that is inside the target formation is a screen pipe, which is convenient for outputting the gasification agent; In step S5, an injection pipe is lowered into the first vertical shaft, with the bottom of the injection pipe reaching the bottom of the first vertical shaft for injecting gasifying agent and igniting the gas. An exhaust pipe is introduced into each first horizontal shaft, with the top of each exhaust pipe directly connected to the surface wellhead to discharge the gas discharged from each first horizontal shaft. The outer side of the exhaust pipe 1 located in the vertical shaft 1 is provided with an interlayer 1, which is connected to its own water inlet pipe and water outlet pipe, and can input and output cooling water to the interlayer 1 to cool the gas in the exhaust pipe 1; The injection pipe is provided with a second interlayer at the portion above the top of each horizontal well. The second interlayer is connected to its own water inlet pipe and water outlet pipe, which can input and output cooling water for the second interlayer. In step S6, an injection pipe is introduced into each horizontal well 1. The bottom end of each injection pipe initially rests at the edge of the corresponding coal seam gasified in step S5. Then, as the coal seam gasified in horizontal well 1 continues to expand toward vertical well 2 and horizontal well 2, the bottom end of the injection pipe advances within the corresponding horizontal well 1 toward the end of the horizontal well 1. Exhaust pipe 2 is introduced into the interior of vertical shaft 2 and horizontal well 2.

2. The method for the coordinated development of coalbed methane and underground coal gasification according to claim 1, characterized in that: Step S1 is specifically as follows: (1) Drill a vertical shaft 1 downward from the ground, and drill several horizontal wells 1 from the side of the vertical shaft 1 to the surrounding areas, so that the bottom of the vertical shaft 1 reaches the middle and lower part of the target formation; (2) Lower the screen pipe to the bottom of the vertical well 1, then place the well pipe on top of the screen pipe and perform cementing; place the well pipe in each horizontal well 1 to form the well wall and perform cementing; (3) Perforate the horizontal section of each horizontal well 1; then, seal the lower part of the vertical shaft 1 corresponding to each horizontal well 1; and then perform fracturing and drainage operations on the horizontal section of each horizontal well 1.

3. The method for coordinated development of coalbed methane and underground coal gasification according to claim 1, characterized in that: In step S2, the main horizontal well 1 and the slave horizontal well 1 have the same structure; there is a distance between the bottom of the vertical well 2 and the end of the main horizontal well 1.

4. The method for the coordinated development of coalbed methane and underground coal gasification according to claim 3, characterized in that: In step S3, horizontal well 2 has an inclined section and a horizontal section connected in sequence. The top of the inclined section of horizontal well 2 is the starting end and is connected to the side of vertical well 2. The horizontal section of horizontal well 2 is inside the target formation, and the end of the horizontal section of horizontal well 2 away from vertical well 2 is the end.

5. The method for coordinated development of coalbed methane and underground coal gasification according to claim 4, characterized in that: Steps S2 and S3 are specifically as follows: (4) Drill a vertical shaft 2 downward from the ground, and drill a horizontal well 2 obliquely downward from the side of the vertical shaft 2. The bottom of the vertical shaft 2 reaches the middle and lower part of the target formation, and the vertical shaft 2 corresponds to the main horizontal well 1 one to one; (5) Lower the screen pipe to the bottom of the second vertical shaft, then place the well pipe on top of the screen pipe and perform cementing; place the well pipe into the second horizontal well to form the well wall and perform cementing; (6) Complete the docking of the top of horizontal well 2 and the side of vertical well 2 according to existing technology; then complete the installation of well pipes in other parts of vertical well 2 and the cementing and completion work; (7) Perforate the horizontal section of each horizontal well.

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