A method for co-production of deep multi-thin coalbed methane and coalbed gasification

Abstract

The present invention relates to a method for co-production of deep multi-thin coalbed methane and coalbed gasification, comprising: drilling three gas production wells and a gasification well, and penetrating each thin coal seam, the three gas production wells forming a triangle, and the gasification well being located in the middle of the triangle; drilling a branch well system on the side of the gas production well away from the gasification well, the branch well system comprising a main well and a plurality of branch wells at different heights, the ends of the branch wells all pointing to the gasification well; dividing thin coal seams with similar formation pressure into a mining section, with a branch well corresponding to the bottom of each mining section; the three gas production wells simultaneously fracturing each thin coal seam in the lowest mining section, and then simultaneously mining the coalbed methane in the lowest mining section; during gas mining, the lowest branch well of the three branch well systems serves as an injection well, and the gasification well serves as a production well, to perform coalbed gasification; after coalbed methane mining is completed, any one of the gas production wells serves as an injection well, and the gasification well serves as a production well, to gasify the lowest thin coal seam, and then the gasification well serves as an injection well, and the other two gas production wells serve as production wells, to continue gasifying the lowest coal seam.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane mining and underground gasification, and in particular relates to a method for co-producing deep multi-thin-layer coalbed methane and coalbed gasification. Background Art

[0002] In deep underground coalbed methane (CBM) development, a unique type of coal seam is multi-layered reservoirs. These reservoirs consist of multiple thin layers spaced one above the other, each ranging in thickness from 0.8 to 1.3 meters, much thinner than typical CBM reservoirs. Multi-layered reservoirs, characterized by their small thickness, numerous layers, and high heterogeneity, have long been a challenge in CBM development. Natural fractures in thin coal seams are poorly developed, resulting in generally low permeability, leading to inefficient gas desorption, diffusion, and seepage. This strong heterogeneity makes unified development difficult, and the resource abundance of individual layers is low. Currently, multi-layered development is commonly employed to achieve economic development. However, fracturing each layer through a vertically penetrating multi-layered reservoir is challenging. Environmental parameters (such as pressure and permeability) can vary significantly, particularly formation pressures, sometimes varying by orders of magnitude. This makes unified stimulation impossible and forces individual layer stimulation necessary. Furthermore, stimulation of adjacent layers can interfere with each other, making CBM development from these layers challenging. Summary of the Invention

[0003] In response to the above problems, the present invention provides a method for co-producing deep multi-thin coalbed methane and coalbed gasification, comprising:

[0004] S100: Drill three gas production wells and one gasification well, all penetrating all thin coal seams. The three gas production wells form a triangle, with the gasification well located in the middle of the triangle.

[0005] S200: Drilling a branch well system on a side of the gas production well away from the gasification well. The branch well system corresponds to each gas production well one-to-one. The branch well system includes a main well and several branch wells at different heights. The branch wells are horizontal wells, and the ends of the branch wells all point to the gasification well.

[0006] S300: Thin coal seams with the same or similar formation pressure are divided into a mining section, and a branch well corresponds to the bottom of each mining section;

[0007] S400: Three gas production wells simultaneously perforate and fracture each thin coal seam in the bottom mining section, and then simultaneously produce coalbed methane in the bottom mining section;

[0008] While producing gas, the bottommost branch wells of the three branch well systems are used as injection wells to inject gasifying agents. The gasification wells are used as production wells to gasify the coal seam and provide heat to the mining section above to promote coal seam gas production.

[0009] According to S400, coalbed methane and coalbed gasification are carried out in each mining section from bottom to top;

[0010] S500: After the coalbed methane extraction is completed, any one of the gas production wells is used as an injection well and the gasification well is used as a production well to gasify the thin coal seam at the bottom. Then, the gasification well is used as an injection well and the other two gas production wells are used as production wells to continue gasifying the thin coal seam at the bottom.

[0011] According to S500, several thin coal seams are gasified from bottom to top.

[0012] The properties of multiple thin-layer coalbed methane reservoirs vary significantly. The combined production of multiple thin-layer coalbed methane is primarily controlled by reservoir pressure and permeability. Permeability is related to geological structure, coal body structure, and formation pressure. Within the same area, coal reservoir pressure is the primary controlling factor for stratified coalbed methane combined production. Under normal pressure gradients, the deeper the coal seam, the greater the reservoir pressure. This invention selects the most representative reservoir pressure to classify multiple thin-layer reservoirs. All thin-layer reservoirs are divided into several mining sections from bottom to top. Each mining section includes several thin coal seams. The formation pressures of coal seams within the same mining section are the same or similar, facilitating centralized mining. Compared to mining a single thin coal seam individually, this invention can increase gas production from gas wells. Different mining sections with significantly different pressures require different perforating and fracturing operations (with different operating parameters and fracturing fluid composition).

[0013] In order to further increase gas production, the present invention combines coalbed methane mining with coalbed gasification. A branch well corresponds to the bottom of a mining section. When the branch well and the gasification well cooperate to gasify the coal seam, a large amount of heat is generated. The heat rises to the mining section above where coalbed methane is being mined. After the thin coal seam in the mining section is heated, it is conducive to the desorption of methane, thereby increasing coalbed methane production.

[0014] After coalbed methane extraction is complete in each mining section, underground gasification can be performed depending on coalbed conditions. In this scenario, gas production wells and gasification wells alternately serve as injection and extraction wells, gasifying the underground coal. The triangular arrangement of the three production wells maximizes coalbed methane extraction and underground gasification, fully utilizing both coalbed methane and coal resources.

[0015] Optionally, in step S100, the gas production well and the gasification well are all vertical wells, and the three gas production wells form an equilateral triangle. On the cross section of the equilateral triangle, the distance between the gasification well and each gas production well is equal; the bottom ends of the three gas production wells are the same depth, and the bottom end of the gasification well is lower than the bottom end of the gas production well.

[0016] Optionally, in step S200, the main well of the branch well system is a vertical well, and the side wall of the main well is connected to several branch wells, and the several branch wells are arranged in sequence from top to bottom. The branch wells are all horizontal wells, and the ends of the horizontal sections of the branch wells extend toward the corresponding gas production wells.

[0017] Optionally, in step S300, the horizontal section of the branch well is lower than the bottom of the corresponding production section;

[0018] The depth of the horizontal section of the bottommost branch well of the branch well system is greater than the depth of the bottom end of the gas production well. The bottom end of the gasification well is at the same depth as the horizontal sections of the three bottommost branch wells, which is convenient for receiving the coal gas produced by gasification of the branch wells.

[0019] Optionally, in step S400, taking a mining well as an example, the mining of coalbed methane is specifically as follows:

[0020] S401: perforating the sidewall of the thinnest coal seam at the bottom of the bottom mining section of the gas well, fracturing the thinnest coal seam without draining fluid, and then isolating the thinnest coal seam;

[0021] S402: perforating the sidewall of the sub-bottom thin coal seam in the bottom mining section of the gas well, fracturing the sub-bottom thin coal seam without draining the fluid, and then isolating the sub-bottom thin coal seam;

[0022] According to S401-402, the thin coal seams in the bottom mining section are perforated and fractured from bottom to top. After all the thin coal seams in the mining section are fractured, the fluid is drained uniformly.

[0023] S403: After drainage, use existing technology to uniformly mine coalbed methane from all thin coal seams in the bottom mining section.

[0024] Further optionally, if the distance between two adjacent thin coal seams is not more than 20 meters, a temporary plugging method of throwing balls is adopted, that is, at the end of the fracturing of the lower coal seam, soluble temporary plugging balls are thrown into the gas well. Under the pressure of the fracturing fluid, the temporary plugging balls block the perforations of the lower coal seam, thereby sealing the side wall of the gas well corresponding to the lower coal seam.

[0025] Further optionally, if the distance between two adjacent thin coal seams is greater than 20 meters, a soluble bridge plug is lowered into the gas production well to seal the cross section of the production well between the upper and lower thin coal seams.

[0026] Optionally, in step S401 or S402, perforation is performed on the sidewall of the bottommost branch well corresponding to the bottom of the gasification well, and the perforation direction is toward the three gas production wells.

[0027] Optionally, while implementing step S403, gas injection pipes are respectively introduced into the three branch well systems, with the bottom end of each gas injection pipe reaching the end of the corresponding bottommost branch well close to the gasification well; a production pipe is introduced into the gasification well, with the bottom end opening of the production pipe corresponding to the depth of the bottommost branch well, for collecting the mixed coal gas produced by gasification.

[0028] Optionally, step S500 is specifically as follows:

[0029] S501: In a clockwise direction, three gas production wells are designated as the first gas production well, the second gas production well, and the third gas production well, respectively. The first gas production well is used as the injection well, and the gasification well is used as the production well. The coal seam at the bottom of the first gas production well to the gasification well is gasified.

[0030] S502: When the high-temperature gasification zone between the first production well and the gasification well expands to the front of the gas cooling zone, the gasification well is used as an injection well, and the second and third gas production wells are used as production wells to continue gasifying the bottom coal seam between the gasification well and the second and third gas production wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the top view of the gas production well, gasification well and branch well system in the embodiment;

[0032] Figure 2 It is a side view structural diagram of gas production wells, gasification wells and branch well systems.

[0033] In the attached figure, 1-gas production well, 2-gasification well, 3-main well, 4-branch well, 5-branch well system. DETAILED DESCRIPTION

[0034] This embodiment provides a method for co-production of deep multi-thin coalbed methane and coalbed gasification, such as Figure 1-Figure 2 Shown, including:

[0035] S100: Drill three gas production wells 1 and one gasification well 2. The three gas production wells form a triangle, with the gasification well located in the middle of the triangle. Both the gas production wells and the gasification wells penetrate each thin coal seam.

[0036] S200: Drilling a branch well system 5 on the side of the gas production well away from the gasification well. The branch well system corresponds to each gas production well one-to-one. The branch well system includes a main well 3 and several branch wells 4 at different heights. The branch wells are horizontal wells, and the ends of the branch wells all point to the gasification well.

[0037] S300: Thin coal seams with the same or similar formation pressure are divided into a mining section, and the depth of each mining section corresponds to the depth of a branch well;

[0038] S400: Three gas production wells simultaneously perforate and fracture each thin coal seam in the bottom mining section, and then simultaneously produce coalbed methane in the bottom mining section;

[0039] While producing gas, the bottommost branch wells of the three branch well systems are used as injection wells to inject gasifying agents. The gasification wells are used as production wells to gasify the coal seam and provide heat to the mining section above to promote coal seam gas production.

[0040] According to S400, coalbed methane and coalbed gasification are carried out in each mining section from bottom to top;

[0041] S500: After the coalbed methane extraction is completed, any one of the gas production wells is used as an injection well and the gasification well is used as a production well to gasify the thin coal seam at the bottom. Then, the gasification well is used as an injection well and the other two gas production wells are used as production wells to continue gasifying the thin coal seam at the bottom.

[0042] According to S500, several thin coal seams are gasified from bottom to top.

[0043] Optionally, in step S100, based on geological exploration information, three gas production wells and one gasification well are drilled downward from the ground. The gas production wells and the gasification wells are both vertical wells, and both penetrate the thin coal seams stacked above and below. The three gas production wells form an equilateral triangle. On the cross section of the equilateral triangle, the distance between the gasification well and each gas production well is equal. The bottom ends of the three gas production wells are the same depth, and the bottom end of the gasification well is lower than the bottom end of the gas production well.

[0044] Casing is run into the gas production wells, and cementing and completion operations are performed according to existing technologies. Casing and / or screens are run into the gasification wells to ensure that the sidewalls of the gasification wells can connect to the various thin coal seams, and cementing and completion operations are performed according to existing technologies.

[0045] Optionally, in step S200, a group of mutually corresponding branch well systems, gas production wells, and gasification wells are sequentially arranged along a straight line. Three gas production wells correspond to three straight lines, and the three straight lines intersect at the gasification well.

[0046] The main well of the branch well system is a vertical well. The side wall of the main well is connected to several branch wells. The branch wells are arranged in sequence from top to bottom. The branch wells are all horizontal wells. The branch wells include an inclination section and a horizontal section. The top of each branch well is connected to the side wall of the main well, and then an inclination section is set, and then a horizontal section is drilled. The end of the horizontal section extends toward the corresponding gas well.

[0047] The various branch wells in the same branch well system can be parallel to each other and have corresponding upper and lower positions. The position of the branch well end is appropriately set based on the characteristics of the thin coal seam in which the branch well's horizontal section is located and the needs of coal seam gasification. Generally, the branch well end does not reach the corresponding gas production well, that is, the gas production well is located between the branch well end and the gasification well. During subsequent gasification, the coal seam between the branch well end and the gasification well is gasified and burned. The high-temperature zone of coal seam gasification is located just below the mining section where the corresponding gas production well is currently producing coal seam methane, facilitating the direct rise of heat and its transfer to the coal seam in the mining section being produced. The heating of the coal seam in the mining section is conducive to the desorption of methane, thereby increasing coal seam methane production.

[0048] Optionally, in step S300, the horizontal section of the branch well is deeper than the bottom of the corresponding mining section, meaning that the horizontal section of the branch well is lower than the bottom of the corresponding mining section. The vertical distance between the horizontal section and the bottom of the mining section is determined based on a comprehensive assessment of the safety requirements of coalbed methane extraction and underground gasification, as well as the efficiency of gasification heat transfer. Branch wells can be drilled, run, cemented, and completed using existing technologies. Screens are preferably used to provide reliable support and connect the branch well to the main well.

[0049] Further optionally, the depth of the horizontal section of the bottommost branch well of the branch well system is greater than the depth of the bottom end of the gas production well, and the bottom end of the gasification well is at the same depth as the horizontal sections of the three bottommost branch wells, so as to facilitate the corresponding reception of coal gas produced by gasification of the branch wells.

[0050] Optionally, in step S400, taking a mining well as an example, the mining of coalbed methane is specifically as follows:

[0051] S401: perforating the sidewall of the thinnest coal seam at the bottom of the bottom mining section of the gas well, fracturing the thinnest coal seam without draining fluid, and then isolating the thinnest coal seam;

[0052] S402: perforating the sidewall of the sub-bottom thin coal seam in the bottom mining section of the gas well, fracturing the sub-bottom thin coal seam without draining the fluid, and then isolating the sub-bottom thin coal seam;

[0053] According to S401-402, the thin coal seams in the bottom mining section are perforated and fractured from bottom to top. After all the thin coal seams in the mining section are fractured, the fluid is drained uniformly.

[0054] S403: After drainage, use existing technology to uniformly mine coalbed methane from all thin coal seams in the bottom mining section.

[0055] Further optionally, if the distance between two adjacent thin coal seams is not more than 20 meters, a temporary plugging method of throwing balls is adopted, that is, at the end of the fracturing of the lower coal seam, soluble temporary plugging balls are thrown into the gas well. Under the pressure of the fracturing fluid, the temporary plugging balls block the perforations of the lower coal seam, thereby sealing the side wall of the gas well corresponding to the lower coal seam.

[0056] Further optionally, if the distance between two adjacent thin coal seams is greater than 20 meters, a soluble bridge plug is lowered into the gas production well to seal the cross section of the production well between the upper and lower thin coal seams.

[0057] This method uses separate perforation and fracturing for each thin coal seam within the same mining section, followed by unified drainage. This method then allows for the combined extraction of coalbed methane from all coal seams within the mining section, significantly increasing gas production per unit time and reducing mining costs. Three gas production wells operate simultaneously in the same thin coal seam within the same mining section using this method.

[0058] Optionally, in step S401 or S402, perforations are performed on the sidewall of the bottommost branch well corresponding to the bottom of the gasification well, and the perforation direction is toward the three gas production wells, so that the gasification well can receive gasification gas from the three bottommost branch wells.

[0059] Optionally, while implementing step S403, gas injection pipes are respectively introduced into the three branch well systems, with the bottom end of each gas injection pipe reaching the end of the corresponding bottommost branch well close to the gasification well, and the top of the gas injection pipe is at the ground wellhead of the main well and is connected to the gasification agent supply device to provide gasification agent for the bottommost branch well of the three branch well systems and ignite it; a production pipe is introduced into the gasification well, with the bottom end opening of the production pipe corresponding to the depth of the bottommost branch well, for collecting the mixed coal gas produced by gasification.

[0060] According to steps S401-S403 and the operations on the branch wells and gasification wells in these three steps, the coalbed methane of each mining section is mined in sequence from bottom to top, and the coal seams below the corresponding mining sections are gasified in sequence from bottom to top.

[0061] For example, when mining the sub-bottom mining section, the depth of the branch well corresponding to the sub-bottom mining section is within the range of the bottom mining section. The branch well may correspond to any thin coal seam in the bottom mining section, as long as the gasification of the thin coal seam below and the mining of coalbed methane in the sub-bottom mining section above can be carried out safely.

[0062] Preferably, after each branch well completes gasification of the corresponding coal seam, cement is injected from the main well. The cement flows into the newly gasified branch well and then flows along the branch well into the coal seam, filling the cavity formed by the gasification of the coal seam. The cement flow rate is controlled (not too fast and flows down the sidewall of the main well that is not connected to the branch well). Alternatively, a pipeline is introduced into the main well, with the bottom of the pipeline corresponding to the branch well that has completed its gasification task, for separate cement injection. This ensures that cement flows only into the branch well that has completed its gasification task and does not flow into the ungasified branch wells above.

[0063] Optionally, step S500 is specifically as follows:

[0064] S501: In a clockwise direction, three gas production wells are designated as the first gas production well, the second gas production well, and the third gas production well, respectively. The first gas production well is used as the injection well, and the gasification well is used as the production well. The coal seam at the bottom of the first gas production well to the gasification well is gasified.

[0065] S502: When the high-temperature gasification zone between the first production well and the gasification well expands to the front of the gas cooling zone, the gasification well is used as an injection well, and the second and third gas production wells are used as production wells to continue gasifying the bottom coal seam between the gasification well and the second and third gas production wells.

[0066] Further optionally, in step S501, a gas injection pipe is introduced into the first gas production well, and the bottom end of the gas injection pipe reaches the bottommost coal seam corresponding to the first gas production well; a production pipe is introduced into the gasification well, and the opening at the bottom end of the production pipe corresponds to the depth of the bottom end of the gas injection pipe. The gasification agent is input into the gas injection pipe and ignited, and the mixed coal gas produced by gasification is discharged from the gasification well.

[0067] The bottommost coal seam in step S501 refers to the deepest coal seam reached by the bottom end of the production well, rather than the coal seam corresponding to the bottommost branch well. The bottommost branch well is lower than the bottom end of the production well.

[0068] The gasification high-temperature zone is a high-temperature zone for coal combustion. The coal gas (i.e., CH4, CO, H2) formed by the reaction of water vapor and coal flows to the production well through the dry distillation zone and is then produced through the production well.

[0069] The front edge of the gas cooling zone is 2 / 3 of the distance between adjacent injection wells and production wells; the gasification high-temperature zone gradually moves from the injection well to the production well. When the distance between the edge of the gasification high-temperature zone closest to the production well and the injection well reaches 2 / 3 of the distance between the adjacent injection well and the production well, the first gas production well is closed, and the gasification well is used as an injection well. The second and third gas production wells are both used as production wells to continue gasifying the bottom coal seam.

[0070] The gas cooling zone is roughly the retorting zone. Coal in this zone is heated, potentially undergoing chemical reactions, but it does not burn. The coal gas produced by coal combustion cools as it passes through the gas cooling zone, reducing the gas pressure at the production well and facilitating gas extraction. Therefore, a portion of the coal seam is always retained between the production well and the injection well as a gas cooling zone.

[0071] In step S502, the coal seams between the gasification well and the second gas production well, and between the gasification well and the third gas production well can be gasified simultaneously, thereby making fuller use of underground coal seam resources.

[0072] According to S500, coal seam gasification is carried out on several thin coal seams from bottom to top. This means that if the coal seam conditions are good, all thin coal seams can be gasified one by one in sequence, and the entire deep coal seam area will not collapse. If the coal seam conditions are not good, thin coal seams can be gasified at intervals to ensure that the entire deep coal seam area will not collapse.

[0073] Further optionally, in step S500, after the first gas production well gasifies a certain coal seam, a pipeline is lowered into the first gas production well for injecting cement to seal the internal space of the first gas production well corresponding to the coal seam that has just been gasified, thereby preventing the gasification agent from entering the lower coal seam when the upper coal seam is subsequently gasified;

[0074] Similarly, after the second and third gas production wells gasify a certain coal seam, pipelines are lowered into the second and third gas production wells respectively to input cement to seal the internal space of the coal seams that have just been gasified in the second and third gas production wells, so as to prevent the gasification agent from entering the lower coal seam when the upper coal seam is subsequently gasified.

Claims

1. A method for co-production of deep multi-thin coalbed methane and coalbed gasification, characterized in that: include: S100: Drill three gas production wells and one gasification well, all penetrating all thin coal seams. The three gas production wells form a triangle, with the gasification well located in the middle of the triangle. S200: Drilling a branch well system on a side of the gas production well away from the gasification well, the branch well system including a main well and several branch wells at different heights, with the ends of the branch wells all pointing to the gasification well; S300: Thin coal seams with the same or similar formation pressure are divided into a mining section, and a branch well corresponds to the bottom of each mining section; S400: Three gas production wells simultaneously perforate and fracture each thin coal seam in the bottom mining section, and then simultaneously produce coalbed methane in the bottom mining section; While producing gas, the bottommost branch wells of the three branch well systems are used as injection wells, and the gasification wells are used as production wells to gasify the coal seam and provide heat for the mining section above; According to S400, coalbed methane and coalbed gasification are carried out in each mining section from bottom to top; S500: After the coalbed methane extraction is completed, any one of the gas production wells is used as an injection well and the gasification well is used as a production well to gasify the thin coal seam at the bottom; then the gasification well is used as an injection well and the other two gas production wells are used as production wells to continue gasifying the thin coal seam at the bottom; According to S500, several thin coal seams are gasified from bottom to top; In step S400, the coalbed methane production steps of any production well are specifically as follows: S401: perforating the sidewall of the thinnest coal seam at the bottom of the bottom mining section of the gas well, fracturing the thinnest coal seam without draining fluid, and then isolating the thinnest coal seam; S402: perforating the sidewall of the sub-bottom thin coal seam in the bottom mining section of the gas well, fracturing the sub-bottom thin coal seam without draining the fluid, and then isolating the sub-bottom thin coal seam; According to S401-402, the thin coal seams in the bottom mining section are perforated and fractured from bottom to top. After all the thin coal seams in the mining section are fractured, the fluid is drained uniformly. The sidewall of the bottom branch well corresponding to the bottom of the gasification well is perforated, and the perforation direction is toward the three gas production wells. S403: After drainage, all thin coal seams in the bottom mining section are mined uniformly for coalbed methane; Gas injection pipes are introduced into the three branch well systems respectively. The bottom end of each gas injection pipe reaches the end of the corresponding lowest branch well close to the gasification well. The top of the gas injection pipe is at the surface wellhead of the main well and is connected to the gasification agent supply device to provide gasification agent to the lowest branch well of the three branch well systems and ignite it. A production pipe is introduced into the gasification well. The opening at the bottom of the production pipe corresponds to the depth of the bottom branch well and is used to collect the mixed coal gas produced by gasification.

2. The method for co-production of deep multi-thin coalbed methane and coalbed gasification according to claim 1, characterized in that: In step S100, the gas production well and the gasification well are all vertical wells, and the three gas production wells form an equilateral triangle. On the cross section of the equilateral triangle, the distance between the gasification well and each gas production well is equal; the bottom ends of the three gas production wells are the same depth, and the bottom end of the gasification well is lower than the bottom end of the gas production well.

3. The method for co-production of deep multi-thin coalbed methane and coalbed gasification according to claim 1, characterized in that: In step S200, the main well of the branch well system is a vertical well, and the side wall of the main well is connected to several branch wells, which are arranged in sequence from top to bottom. The branch wells are all horizontal wells, and the ends of the horizontal sections of the branch wells extend toward the corresponding gas production wells; the gas production wells are between the ends of the branch wells and the gasification wells.

4. The method for co-production of deep multi-thin coalbed methane and coalbed gasification according to claim 3, characterized in that: In step S300, the horizontal section of the branch well is lower than the bottom of the corresponding production section; the depth of the horizontal section of the bottommost branch well of the branch well system is greater than the depth of the bottom end of the gas production well, and the bottom end of the gasification well is at the same depth as the horizontal sections of the three bottommost branch wells, which is convenient for receiving the corresponding coal gas produced by gasification of the branch wells.

5. The method for co-production of deep multi-thin coalbed methane and coalbed gasification according to claim 3, characterized in that: If the distance between two adjacent thin coal seams is no more than 20 meters, the temporary plugging method of throwing balls is adopted. At the end of the fracturing of the lower coal seam, soluble temporary plugging balls are thrown into the gas well. Under the pressure of the fracturing fluid, the temporary plugging balls block the perforations of the lower coal seam, thereby sealing the side wall of the gas well corresponding to the lower coal seam.

6. The method for co-production of deep multi-thin coalbed methane and coalbed gasification according to claim 3, characterized in that: If the distance between two adjacent thin coal seams is greater than 20 meters, a soluble bridge plug will be lowered into the gas well to seal the cross section of the mining well between the upper and lower thin coal seams.

7. The method for co-production of deep multi-thin coalbed methane and coalbed gasification according to claim 1, characterized in that: Step S500 is specifically as follows: S501: In a clockwise direction, three gas production wells are designated as the first gas production well, the second gas production well, and the third gas production well, respectively. The first gas production well is used as the injection well, and the gasification well is used as the production well. The coal seam at the bottom of the first gas production well to the gasification well is gasified. S502: When the high-temperature gasification zone between the first production well and the gasification well expands to the front of the gas cooling zone, the gasification well is used as an injection well, and the second and third gas production wells are used as production wells to continue gasifying the bottom coal seam between the gasification well and the second and third gas production wells.

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