Collaborative development method for coal bed gas and coal underground gasification

Abstract

The invention relates to a coal bed gas and coal underground gasification collaborative development method, which comprises the following steps of: drilling a vertical shaft I, and drilling a plurality of horizontal wells I from the side surface of the vertical shaft I to the periphery for exploiting coal bed gas and gasified coal; a plurality of second vertical shafts are drilled between every two adjacent first main horizontal wells, the second vertical shafts correspond to the first main horizontal wells one to one in position, and the tail ends of the first main horizontal wells point to the second vertical shafts. A horizontal section, pointing from the tail end of the horizontal well I to the horizontal well II, between the two adjacent main horizontal wells I; a second horizontal well is drilled from the side face of the first vertical shaft, and the tail end of the second horizontal well points to the bottom of the adjacent first vertical shaft; coal bed gas exploitation is conducted through the first vertical well and the first horizontal well; the first vertical well serves as an injection well, the first horizontal well serves as a production well, and coal bed gasification is conducted; then, the gasified stratum part is filled with concrete, and collapse is avoided; and coal bed gasification is carried out by taking each horizontal well I as an injection well and taking the vertical well II and the horizontal well II as production wells.

Description

Technical Field

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

[0002] China is rich in coal resources. Most of the direct coal mining is carried out in shallow coal seams, and the development of deep coal seams focuses on the extraction of coalbed methane. The direct mining of deep coal resources requires a high level of technology. It is difficult to transport deep coal to the ground, with high energy consumption and low economy. Underground coal combustion gasification generates a large amount of gas, which contains combustible gas 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 stage, and there are not many industrial application cases. Underground coal gasification requires drilling corresponding injection wells and production wells, and coalbed methane extraction requires drilling production wells. For deep buried strata, the economic cost and time cost of drilling are relatively high, and the scope of resource extraction is around the drilling wells. Making the best use of the drilling wells to extract deep strata resources to the greatest extent is the best way to reduce the extraction cost, and there has been little exploration in this regard by those skilled in the art. Summary of the Invention

[0003] In view of the above problems, the present invention provides a method for the collaborative development of coalbed methane and underground coal gasification, including: S1: Drill a vertical well 1 downward from the ground, and horizontally drill several horizontal wells 1 in parallel around from the side of the vertical well 1. The horizontal sections of the horizontal wells 1 and the bottom of the vertical well 1 are in the strata at the same depth, and are used to extract the coalbed methane in this strata and gasify the coal in this strata; S2: Divide several horizontal wells 1 into main horizontal wells 1 and secondary horizontal wells 1, and there is at least one secondary horizontal well 1 between two adjacent main horizontal wells 1; Drill several vertical wells 2 downward from the ground. The vertical wells 2 correspond to the positions of the main horizontal wells 1 one by one, and the end of the main horizontal well 1 points to the vertical well 2; S3: The end of the secondary horizontal well 1 between two adjacent main horizontal wells 1 points to the horizontal section of the horizontal well 2; Drill a horizontal well 2 from the side of the vertical well 1, and the end of the horizontal well 2 points to the bottom of the adjacent vertical well 1; S4: Extract coalbed methane through the vertical well 1 and the horizontal wells 1; S5: Take the vertical well 1 as the injection well, input the gasifying agent, take the horizontal wells 1 as the production wells, and gasify the coal seams between the bottom of the vertical well 1 and each horizontal well 1; Then, fill the gasified strata part with concrete to avoid collapse; S6: Take each horizontal well 1 as the injection well, input the gasifying agent respectively, take the vertical well 2 and the horizontal well 2 as the production wells, and gasify the coal seams between the horizontal well 1 and the vertical well 2, and between the horizontal wells 2.

[0004] The present invention considers the coalbed methane and coal gasification development in a certain deep formation as a whole. First, a conventional vertical shaft 1 and several horizontal wells 2 are drilled, enabling the extraction of coalbed methane in step S4. When drilling the vertical shaft 1, considering the later demand for coal gasification, the vertical shaft 1 is drilled all the way into the formation where the horizontal section of the horizontal well 1 is located (i.e., the target formation). After the coalbed methane in the target formation is extracted, the coal in this formation is then gasified. In step S5, taking the vertical shaft 1 as the injection well and several horizontal wells 1 as the production wells, starting from the center (vertical shaft 1) and gradually gasifying and burning outward (towards the direction of several horizontal wells 1), the generated coal gas enters the horizontal wells 1 and then is discharged to the ground along the horizontal wells 1 and the vertical shaft 1.

[0005] Moreover, the present invention also uses several horizontal wells 1 as injection wells, drills several vertical shafts 2 and horizontal wells 2 around the horizontal wells 2 as production wells, gasifies the coal between the horizontal wells 1, vertical shafts 2, and horizontal wells 2, and the generated coal gas is discharged to the ground through the horizontal wells 2 and the vertical shafts 2, maximizing the utilization of the coal and coalbed methane in the deep formation. After gasification, in step S5, the vertical shaft 1 can also be used to fill the cavity formed after gasification with concrete to avoid formation collapse. Thus, according to the method provided by the present invention, the coalbed methane and coal resources in the formation around the horizontal well 1 can be fully utilized. Both the vertical shaft 1 and the vertical shaft 2 are basically vertical.

[0006] Optionally, in step S1, several horizontal wells 1 are uniformly arranged radially with the vertical shaft 1 as the center. The horizontal wells 1 have an inclined section and a horizontal section connected in sequence. The top of the inclined section of the horizontal well 1 is the starting end and is connected to the side of the vertical shaft 1. The horizontal section of the horizontal well 1 is inside the target formation, and the end of the horizontal section far from the vertical shaft 1 is the end.

[0007] Further optionally, step S1 is specifically: (1) Drill a vertical shaft 1 from the ground downward, and drill several horizontal wells 1 from the side of the vertical shaft 1 in all directions. The bottom of the vertical shaft 1 reaches the middle and lower part of the target formation; (2) Lower a screen pipe to the bottom of the vertical shaft 1, then set a well pipe above the screen pipe and perform well cementing; place well pipes in each horizontal well 1 to form a wellbore and perform well cementing; (3) Perforate the horizontal section of each horizontal well 1; then, seal and press the position below the corresponding horizontal well 1 in the vertical shaft 1; and then perform fracturing and fluid drainage operations on the horizontal section of each horizontal well 1.

[0008] Optionally, in step S2, the main horizontal well 1 and the secondary horizontal well 1 have the same structure. The distinction between the main and secondary is for positioning the vertical shaft 2 and the horizontal well 2; The bottom of the second vertical shaft reaches the middle and lower part of the target formation. The part of the second vertical shaft within the target formation is a screen pipe, which is convenient for outputting the gasifying agent. There is a spacing between the bottom of the second vertical shaft and the end of the first main horizontal well, which is convenient for gasifying the coal seam between them in step S6. The spacing between each second vertical shaft and the first vertical shaft is the same. The distance between the bottom of the second vertical shaft and the end of the first main horizontal well is determined according to the actual needs of coal seam gasification, so that the second vertical shaft can collect the coal gas produced by coal seam gasification.

[0009] Optionally, in step S3, the second horizontal well has an inclined section and a horizontal section connected in sequence. The top of the inclined section of the second horizontal well is the starting end and is connected to the side of the second vertical shaft. The horizontal section of the second horizontal well is inside the target formation, and the end of the horizontal section of the second horizontal well far from the second vertical shaft is the end.

[0010] Further optionally, steps S2 and S3 are specifically as follows: (4) Drill the second vertical shaft downward from the ground, and drill the second horizontal well obliquely downward from the side of the second vertical shaft. The bottom of the second vertical shaft reaches the middle and lower part of the target formation, and the second vertical shaft and the first main horizontal well can correspond one by one; (5) Lower the screen pipe to the bottom of the second vertical shaft, then set the well pipe above the screen pipe and perform well cementing; place the well pipe in the second horizontal well to form the wellbore wall and perform well cementing; (6) Complete the docking between the top of the second horizontal well and the side of the second vertical shaft according to the existing technology; then, complete the installation of the well pipes in other parts of the second vertical shaft and well cementing and well completion work; (7) Perforate the horizontal sections of each second horizontal well.

[0011] Optionally, in step S5, lower the injection pipe into the first vertical shaft. The bottom of the injection pipe reaches the bottom of the first vertical shaft, which is used for injecting the gasifying agent and ignition; introduce the first exhaust pipe into each first horizontal well. The top ends of the respective first exhaust pipes lead directly to the ground wellhead to discharge the coal gas discharged from each first horizontal well.

[0012] Further optionally, the outer side of the part of the first exhaust pipe within the first vertical shaft has a first interlayer. The first interlayer wraps the outer side of the corresponding part of the first exhaust pipe. The first interlayer is connected with its own water inlet pipe and water outlet pipe, which can input and output cooling water for the first interlayer to cool the coal gas in the first exhaust pipe and avoid affecting the gasifying agent in the injection pipe.

[0013] Further optionally, the part of the injection pipe above the top of each first horizontal well is provided with a second interlayer. The second interlayer wraps the outer side of the corresponding part of the injection pipe. The second interlayer is connected with its own water inlet pipe and water outlet pipe, which can input and output cooling water for the second interlayer.

[0014] Optionally, in step S6, conventional injection pipes are respectively introduced into each horizontal well 1. The bottom end of each injection pipe first stays at the position of the edge of the gasified coal seam corresponding to step S5, and then, as the gasified coal seam in horizontal well 1 expands continuously towards vertical well 2 and horizontal well 2, the bottom end of the injection pipe advances towards the end of horizontal well 1 inside the corresponding horizontal well 1; exhaust pipes 2 are introduced into both vertical well 2 and horizontal well 2. Description of the Drawings

[0015] Figure 1 It is a schematic diagram of vertical well 1, horizontal well 1 and vertical well 2 in the embodiment; Figure 2 It is a schematic diagram of vertical well 2, horizontal well 2 and horizontal well 1; Figure 3 It is a schematic diagram of vertical well 2 and horizontal well 2.

[0016] In the drawings, 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 - secondary horizontal well 1, 8 - exhaust pipe 1. Detailed Embodiment

[0017] This embodiment provides a method for collaborative development of coalbed methane and underground coal gasification, as Figures 1-3 shown, including: S1: Drill a vertical well 1 downward from the ground, and drill a number of horizontal wells 2 in parallel around from the side of the vertical well 1. The horizontal sections of the horizontal wells 2 and the bottom of the vertical well 1 are in the strata at the same depth, for extracting coalbed methane from this strata and gasifying the coal in this strata; S2: Divide the number of horizontal wells 2 into main horizontal wells 5 and secondary horizontal wells 7, and at least one secondary horizontal well 7 is provided between two adjacent main horizontal wells 5; Drill a number of vertical wells 3 downward from the ground, and the positions of the vertical wells 3 correspond one by one to those of the main horizontal wells 5, and the end of the main horizontal well 5 points to the vertical well 3; S3: The end of the secondary horizontal well 7 between two adjacent main horizontal wells 5 points to the horizontal section of the horizontal well 4; drill a horizontal well 4 from the side of the vertical well 1, and the end of the horizontal well 4 points to the bottom of the adjacent vertical well 1; S4: Extract coalbed methane through the vertical well 1 and the horizontal wells 2; S5: Use the vertical well 1 as the injection well to input the gasifying agent, and use the horizontal wells 2 as the production wells to gasify the coal seam between the bottom of the vertical well 1 and each horizontal well 2; then, fill the gasified strata part with concrete to avoid collapse; S6: Use each horizontal well 2 as the injection well to respectively input the gasifying agent, and use the vertical well 3 and the horizontal well 4 as the production wells to gasify the coal seam between the horizontal well 2 and the vertical well 3 and the horizontal well 4.

[0018] Before step S1, the following steps are also included: Using existing geological exploration methods and technologies, explore the deep strata, select the strata that are suitable for both coalbed methane extraction and coal gasification as the target strata, conduct reasonable geological planning, and select a suitable location as the well platform.

[0019] Optionally, in step S1, the bottom of the first vertical well 1 reaches the middle and lower part of the target strata; a plurality of first horizontal wells 2 are radially and evenly arranged with the first vertical well 1 as the center. The first horizontal well 2 has an inclined section and a horizontal section connected in sequence. The top of the inclined section of the first horizontal well 2 is the starting end and is connected to the side of the first vertical well 1. The horizontal section of the first horizontal well 2 is inside the target strata, and the end far from the first vertical well 1 of the horizontal section is the end; the included angle between the starting ends of two adjacent first horizontal wells 2 is the same; The part of the first vertical well 1 inside the target strata is a screen pipe, which is convenient for outputting the gasifying agent.

[0020] Further optionally, step S1 is specifically: (1) Drill the first vertical well 1 downward from the ground, and drill a plurality of first horizontal wells 2 respectively around from the side of the first vertical well 1. The bottom of the first vertical well 1 reaches the middle and lower part of the target strata; (2) Lower the screen pipe to the bottom of the first vertical well 1, then set the well pipe above the screen pipe and conduct cementing; place the well pipe into each first horizontal well 2 to form a wellbore and conduct cementing; (3) Perforate the horizontal section of each first horizontal well 2; then, seal and press the position below the corresponding position of each first horizontal well in the first vertical well 1; then conduct fracturing and liquid drainage operations on the horizontal section of each first horizontal well 2.

[0021] For each operation such as drilling, setting the well pipe and screen pipe, cementing, well completion, perforating, fracturing, and liquid drainage in the above steps (1)-(3), the existing technologies in the field can be used. The well pipe is a hollow cylindrical pipe, and the side wall is solid without through holes.

[0022] At the position where the first vertical well 1 is docked with the first horizontal well 2, set a well pipe with a plurality of docking openings. The docking openings are respectively docked with the top ends of the first horizontal wells 2 one by one. Pour concrete outside the docking openings to seal the outside of the docking openings; then, complete the installation, cementing, and well completion work of the part above the docking openings of the first vertical well 1; The existing five-stage well completion technology can also be used. The first vertical well (main wellbore) is fully lowered with the well pipe (i.e., casing), and the connection with the first horizontal well is hydraulically isolated. Sidetracking can be carried out from both the first vertical well and the first horizontal well. By using auxiliary packers, sleeves and other well completion devices in the first vertical well, a straddle connection can be made to the first horizontal well to achieve hydraulic isolation.

[0023] Further optionally, in step (3), a soluble bridge plug is lowered into the first vertical shaft 1 to block the cross-sectional area of the first vertical shaft. The soluble bridge plug is located below the positions where all the first horizontal wells are connected to the first vertical shaft, so as to prevent fracturing fluid and coalbed methane from entering the lower space of the first vertical shaft, because this part does not play a role in the extraction of coalbed methane and only plays a role in subsequent coal gasification and filling.

[0024] During the process of extracting coalbed methane, according to the estimated dissolution time of the bridge plug, a new bridge plug is lowered in a timely manner until the extraction of coalbed methane is completed. After the last bridge plug dissolves, the entire space inside the first vertical shaft 1 is connected, which is convenient for subsequent input of gasifying agent through the first vertical shaft 1.

[0025] Optionally, in step S2, the main first horizontal well 5 and the secondary first horizontal well 7 have the same structure. The distinction between the main and secondary is for the positioning of the second vertical shaft 3 and the second horizontal well 4. The bottom of the second vertical shaft 3 reaches the middle and lower part of the target formation. The part of the second vertical shaft 3 within the target formation is a screen pipe, which is convenient for outputting the gasifying agent. There is a spacing between the bottom of the second vertical shaft 3 and the end of the main first horizontal well 2, which is convenient for gasifying the coal seam between them in step S6. The spacing between each second vertical shaft 3 and the first vertical shaft 1 is the same. The distance between the bottom of the second vertical shaft 3 and the end of the main first horizontal well 2 is determined according to the actual needs of coal gasification, so that the second vertical shaft 3 can collect the coal gas produced by coal gasification.

[0026] Optionally, in step S3, the second horizontal well 4 has an inclined section and a horizontal section connected in sequence. The top of the inclined section of the second horizontal well 4 is the starting end and is connected to the side of the second vertical shaft 3. The horizontal section of the second horizontal well 4 is inside the target formation, and the end away from the second vertical shaft 3 is the end; there is a spacing between the end of each secondary first horizontal well 2 and the horizontal section of the second horizontal well 4, and the spacing is equal. This spacing is smaller than the spacing between the end of the first horizontal well 2 and the bottom of the second vertical shaft 3.

[0027] Further optionally, the second horizontal wells 4 are distributed in sequence in a clockwise or counterclockwise direction, and the end of each second horizontal well 4 points to the bottom of the adjacent next second vertical shaft 3.

[0028] Further optionally, steps S2 and S3 are specifically as follows: (4) Drill the second vertical shaft 3 from the ground downward, and drill the second horizontal well 4 obliquely downward from the side of the second vertical shaft 3. The bottom of the second vertical shaft 3 reaches the middle and lower part of the target formation, and the second vertical shaft 3 and the main first horizontal well 2 can correspond one by one; (5) Lower a screen pipe to the bottom of the second vertical shaft 3, then set a well pipe above the screen pipe and perform cementing; place a well pipe in the second horizontal well 4 to form a wellbore and perform cementing; (6) Complete the docking of the top of the second horizontal well 4 with the side of the second vertical well 3 according to the existing technology level; then, complete the installation of the well pipes of other parts of the second vertical well 3, as well as the cementing and well completion work. (7) Perforate the horizontal sections of each second horizontal well 4 to connect the second horizontal well 4 with the external formation environment, so that the gas produced by coal gasification can enter the second horizontal well 4.

[0029] In step (6), a section of screen pipe can be set at the top of the second horizontal well, and a section of screen pipe is also set at the position of the side wall of the second vertical well corresponding to the top of the second horizontal well. Holes can be opened on the side of the screen pipe of the second vertical well facing the side of the second horizontal well. When the top of the second horizontal well is docked with the side wall of the second vertical well, the second horizontal well and the second vertical well can be interconnected.

[0030] Optionally, in step S4, a soluble bridge plug is set in the first vertical well 1, and then, according to the existing technology, coalbed methane is extracted from the target formation through the first vertical well 1 and the first horizontal well 2.

[0031] Through the fracturing transformation of the formation and the extraction of coalbed methane by the first horizontal well 2, the fissures and pores in the target formation are fully opened and expanded, improving the permeability of the formation, providing good environmental conditions for the diffusion of the gasifying agent input from the first vertical well 1 or the first horizontal well 2 in the formation, and facilitating the more complete gasification of the coal seam between the first vertical well 1 and the first horizontal well 2 and the coal seam between the first horizontal well 2 and the second vertical well 3.

[0032] Optionally, in step S5, an injection pipe 6 is lowered into the first vertical well 1, and the bottom of the injection pipe reaches the bottom of the first vertical well 1 for injecting the gasifying agent and ignition; an exhaust pipe 8 is introduced into each first horizontal well 2, and the top ends of the exhaust pipes 8 lead directly to the ground wellhead to discharge the gas discharged from each first horizontal well 2. The exhaust pipe 8 is a conventional discharge pipe in the field of coal seam gasification.

[0033] Further optionally, the outer side of the part of the exhaust pipe 8 in the first vertical well has a first sandwich layer. The first sandwich layer wraps the outer side of the corresponding part of the exhaust pipe 8. The first sandwich layer is connected with its own water inlet pipe and water outlet pipe, and can input and output cooling water to the first sandwich layer to cool the gas in the exhaust pipe 8 and avoid affecting the gasifying agent in the injection pipe.

[0034] Further optionally, the part of the injection pipe above the top of each first horizontal well is provided with a second sandwich layer. The second sandwich layer wraps the outer side of the corresponding part of the injection pipe. The second sandwich layer is connected with its own water inlet pipe and water outlet pipe, and can input and output cooling water to the second sandwich layer; preferably, a heat insulation layer is further coated on the outer side of the second sandwich layer to effectively isolate the heat dissipated by the exhaust pipe 8 and effectively retain the cold quantity brought by the second sandwich layer, so that the gasifying agent in the injection pipe is less affected by the discharged gas, and further the part above the docking opening of the first vertical well 1 has both the functions of injection and extraction, saving the drilling cost.

[0035] In step S5, an injection pipe is introduced into the vertical shaft 1, and the gasifying agent is input into the target formation. Using conventional ignition technology, the coal in the target formation starts to gasify and burn. Since the horizontal well 1 uniformly surrounds the shaft 1 in a radial manner, that is, a circular area is formed. This area radiates from the bottom of the shaft 1 to the surroundings. Therefore, during gasification, it also starts from this center and spreads to the surrounding coal seams. The generated coal gas enters the nearby horizontal well 1 and then is discharged to the ground along the exhaust pipe 1. Moreover, pre-cooling treatment is completed through the interlayer 1. Since the horizontal section of the horizontal well 1 has a certain length and through holes left during initial perforation are provided along the horizontal section, the gasification area around the bottom of the shaft 1 can extend along the length of the horizontal section of the horizontal well 1. The generated coal gas enters the horizontal well 1 from some through holes in the nearby horizontal section and then is discharged. In this way, the coal seam area that can be gasified between the shaft 1 and the horizontal well 1 is expanded. The high-temperature gasification area extends outward along the horizontal section of the horizontal well 1 until the gasifying agent cannot reach, reaching the maximum limit of the gasification area. At this time, the edge of the dry distillation area may not have reached the end of the horizontal well 1.

[0036] Then, the injection pipe and the exhaust pipe 1 are withdrawn, and concrete is injected into the shaft 1. The concrete reaches the target formation and fills the formation that has become empty due to gasification, preventing the formation from collapsing. If there is still some part of the coal seam corresponding to the horizontal section of the horizontal well 1 that has not been gasified, the concrete stops spreading when it reaches the edge of the un-gasified coal seam, without affecting the un-gasified coal seam. Ultra-fine cement-based grouting materials (particle size < 0.08 mm) can be used, which can penetrate the screen pipe at the bottom of the shaft 1 and enter the formation under high-pressure injection conditions.

[0037] Optionally, in step S6, conventional injection pipes are respectively introduced into each horizontal well 1. The bottom end of each injection pipe first stays at the position of the edge of the coal seam gasified in the corresponding step S5, and then as the coal seam gasified in the horizontal well 1 continuously expands towards the shaft 2 and the horizontal well 2, the bottom end of the injection pipe advances towards the end of the horizontal well 1 inside the corresponding horizontal well 1; Exhaust pipes 2 are introduced into both the shaft 2 and the horizontal well 2. The coal gas obtained from coal seam gasification in step S6 enters the horizontal sections of the shaft 2 and the horizontal well 2, and finally is discharged to the ground from the shaft 2.

[0038] Further optionally, the bottom of the exhaust pipe 2 in the shaft 2 reaches the bottom of the shaft 2, and the exhaust pipe 2 in the horizontal well 2 extends to the end of the horizontal well 2; in the upper half of the shaft 2, the two exhaust pipes 2 are arranged side by side and extend to the ground along the shaft 2.

[0039] In step S6, gasification starts from the edge of the coal seam remaining after gasification in step S5. Horizontal well 1-2 serves as the injection well, where the gasification agent is input and ignited to burn the coal seam around horizontal well 1-2 and gradually advance in the direction of vertical shaft 2-3 and horizontal well 2-4. If a small amount of coal gas enters horizontal well 1-2 through other through-holes of horizontal well 1-2, it will also be burned. The wellhead of vertical shaft 1-1 can also be blocked in advance, allowing only the injection pipe to enter, to avoid the discharge of an extremely small amount of coal gas from vertical shaft 1-1.

Claims

1. A method for the collaborative development of coalbed methane and underground coal gasification, characterized in that, Including: S1: Drill a first vertical shaft, and drill a number of first horizontal wells in parallel around from the side of the first vertical shaft. The horizontal sections of the first horizontal wells and the bottom of the first vertical shaft are in the strata at the same depth, for extracting coalbed methane from this strata and gasifying the coal in this strata; S2: Divide the number of first horizontal wells into main first horizontal wells and secondary first horizontal wells. There is at least one secondary first horizontal well between two adjacent main first horizontal wells; Drill a number of second vertical shafts, and the second vertical shafts correspond to the positions of the main first horizontal wells one by one. The end of the main first horizontal well points to the second vertical shaft; S3: The ends of the secondary first horizontal wells between two adjacent main first horizontal wells point to the horizontal section of the second horizontal well; Drill the second horizontal well from the side of the first vertical shaft, and the end of the second horizontal well points to the bottom of the adjacent first vertical shaft; S4: Extract coalbed methane through the first vertical shaft and the first horizontal wells; S5: Use the first vertical shaft as the injection well and the first horizontal wells as the production wells to gasify the coal seams between the bottom of the first vertical shaft and each first horizontal well; Then, fill the gasified strata with concrete; S6: Use each first horizontal well as the injection well and the second vertical shafts and the second horizontal wells as the production wells to gasify the coal seams between the first horizontal wells and the second vertical shafts and the second horizontal wells.

2. The method for the collaborative development of coalbed methane and underground coal gasification according to claim 1, characterized in that, In step S1, the number of first horizontal wells is evenly arranged radially around the first vertical shaft; The first horizontal well has an inclined section and a horizontal section connected in sequence. The top of the inclined section of the first horizontal well is the starting end and is connected to the side of the first vertical shaft. The horizontal section of the first horizontal well is inside the target strata, and the end of the horizontal section away from the first vertical shaft is the end.

3. The method for co-developing coalbed methane and underground coal gasification according to claim 2, characterized in that Step S1 is specifically: (1) Drill the first vertical shaft downward from the ground, and drill a number of first horizontal wells around from the side of the first vertical shaft. The bottom of the first vertical shaft reaches the middle and lower part of the target strata; (2) Lower a screen pipe to the bottom of the first vertical shaft, then set a casing pipe above the screen pipe and perform cementing; Place casing pipes in each first horizontal well to form a wellbore and perform cementing; (3) Perforate the horizontal sections of each first horizontal well; Then, seal and press the area below the corresponding positions of each first horizontal well in the first vertical shaft; Then, perform fracturing and liquid drainage operations on the horizontal sections of each first horizontal well.

4. The method for co - development of coalbed methane and underground coal gasification according to claim 2, characterized in that, In step S2, the structures of the main first horizontal wells and the secondary first horizontal wells are the same; There is a spacing between the bottom of the second vertical shaft and the end of the main first horizontal well.

5. The method for co-developing coalbed methane and underground coal gasification according to claim 4, characterized in that, In step S3, the second horizontal well has an inclined section and a horizontal section connected in sequence. The top of the inclined section of the second horizontal well is the starting end and is connected to the side of the second vertical shaft. The horizontal section of the second horizontal well is inside the target strata, and the end of the horizontal section of the second horizontal well away from the second vertical shaft is the end.

6. The method for co - development of coalbed methane and underground coal gasification according to claim 5, wherein, Steps S2 and S3 are specifically: (4) Drill the second vertical shaft downward from the ground, and drill the second horizontal well obliquely downward from the side of the second vertical shaft. The bottom of the second vertical shaft reaches the middle and lower part of the target strata, and the second vertical shaft and the main first horizontal well can correspond one by one; (5) Lower a screen pipe to the bottom of the second vertical shaft, then set a casing pipe above the screen pipe and perform cementing; Place casing pipes in the second horizontal well to form a wellbore and perform cementing; (6) Complete the docking between the top of the second horizontal well and the side of the second vertical shaft according to the existing technology; Then, complete the installation of the casing pipes in other parts of the second vertical shaft and the cementing and well completion work. (7) Perforate the horizontal sections of each horizontal well two.

7. The method for collaborative development of coalbed methane and underground coal gasification according to claim 1, wherein In step S5, lower the injection pipe into the first vertical shaft. The bottom of the injection pipe reaches the bottom of the first vertical shaft and is used for injecting the gasifying agent and ignition. Introduce the first exhaust pipe into each horizontal well one. The top ends of the respective first exhaust pipes lead directly to the surface wellhead to discharge the gas discharged from each horizontal well one.

8. The method for co-developing coalbed methane and underground coal gasification according to claim 7, wherein The outer side of the part of the first exhaust pipe located in the first vertical shaft has a first interlayer. The first interlayer is connected with its own water inlet pipe and water outlet pipe, and can input and output cooling water to the first interlayer to cool the gas in the first exhaust pipe. The part of the injection pipe above the top of each horizontal well one is provided with a second interlayer. The second interlayer is connected with its own water inlet pipe and water outlet pipe, and can input and output cooling water to the second interlayer.

9. The method for co-developing coalbed methane and underground coal gasification according to claim 8, characterized in that, In step S6, introduce the injection pipe into each horizontal well one respectively. The bottom end of each injection pipe first stays at the position of the edge of the coal seam gasified in the corresponding step S5, and then as the gasified coal seam in the horizontal well one continuously expands towards the second vertical shaft and the horizontal well two, the bottom end of the injection pipe advances towards the end of the horizontal well one inside the corresponding horizontal well one. The second exhaust pipe is introduced into both the second vertical shaft and the horizontal well two.

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