Deep multi-thin-layer coal bed gas and coal bed gas gasification co-production method

Abstract

The invention relates to a deep multi-thin-layer coal bed gas and coal bed gas gasification co-production method which comprises the steps that three gas recovery wells and a gasification well are drilled and penetrate through all thin coal beds, the three gas recovery wells define a triangle, and the gasification well is located in the middle of the triangle; a multilateral well system is drilled on the side, away from the gasification well, of the gas recovery well, the multilateral well system comprises a main well and a plurality of multilateral wells with different heights, and the tail ends of the multilateral wells all point to the gasification well; thin coal seams with similar formation pressure are divided into mining sections, and the lower portion of each mining section corresponds to one branch well; the three gas recovery wells are used for fracturing the thin coal seams of the lowest exploitation section at the same time, and coal bed gas of the lowest exploitation section is exploited at the same time; during gas production, the lowest branch well of the three branch well systems is an injection well, the gasification well is a production well, and coal bed gasification is carried out; after coal bed gas production is finished, any one gas production well serves as an injection well, the gasification well serves as a production well, the lowest thin coal bed is gasified, then the gasification well serves as the injection well, the other two gas production wells serve as production wells, and the lowest coal bed continues to be gasified.

Description

Technical Field

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

[0002] In the field of deep underground coalbed methane development, there is a special type of coal seam, which is a multi-thin layer reservoir, that is, there are multiple thin reservoirs with upper and lower intervals. The thickness of each reservoir is between 0.8 and 1.3 meters, which is much smaller than that of ordinary coalbed methane reservoirs. The multi-thin layer reservoir has small thickness, many layers and strong heterogeneity, and its exploitation has always been a difficult problem in the field of coalbed methane development. The natural fractures of thin coal seams are poorly developed and the permeability is generally low, resulting in low gas desorption-diffusion-seepage efficiency. The heterogeneity of thin coal seams is strong, making it difficult to develop them uniformly, and the resource abundance of a single layer is low. At present, the form of multi-layer superposition development is generally adopted to achieve economic development. However, it is difficult to vertically penetrate multiple thin layer reservoirs through one well and fracture and transform each thin layer, because the environmental parameters (such as pressure, permeability, etc.) of each thin layer sometimes vary greatly, especially the formation pressure difference is significant, sometimes differing by several orders of magnitude, resulting in the inability to transform uniformly and only being able to transform single layers. Moreover, there will also be mutual interference during the transformation of adjacent layers, making the development of multi-thin layer coalbed methane always difficult. Summary of the Invention

[0003] In view of the above problems, the present invention provides a method for co-producing deep multi-thin coalbed methane and coalbed gasification, including: S100: Drill three gas production wells and one gasification well, all of which penetrate through each thin coal seam. The three gas production wells form a triangle, and the gasification well is in the middle of the triangle; S200: Drill a branch well system on the side of the gas production well far from the gasification well. The branch well system corresponds to the gas production well one by 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; S300: Divide the thin coal seams with the same or similar formation pressure into one production section, and one branch well corresponds to the lower part of each production section; S400: The three gas production wells simultaneously perforate and fracture each thin coal seam in the bottommost production section, and then simultaneously extract the coalbed methane in the bottommost production section; While extracting gas, the bottommost branch wells of the three branch well systems all serve as injection wells to inject gasifying agents, and the gasification well serves as a production well for coalbed gasification, and at the same time provides heat for the upper production section to promote the increase of coalbed methane production; According to S400, extract coalbed methane and carry out coalbed gasification for each production section from bottom to top in sequence; S500: After the coalbed methane extraction is completed, using any one of the gas production wells as the injection well and the gasification well as the production well, conduct coalbed gasification on the thinnest coal seam at the bottom. Then, using the gasification well as the injection well and the other two gas production wells as the production wells, continue the coalbed gasification on the thinnest coal seam at the bottom; According to S500, conduct coalbed gasification on several thin coal seams from bottom to top.

[0004] The properties of each layer in the multi-thin-layer coalbed methane reservoir vary significantly. The co-production of coalbed methane from multi-thin-layers is mainly controlled by reservoir pressure and reservoir permeability. Permeability is related to geological structure, coal body structure, formation pressure, etc. For the same plot area, the coal reservoir pressure is the main controlling factor for the stratified co-production of coalbed methane. Under normal pressure gradient, the greater the coal seam burial depth, the greater the coal reservoir pressure. The present invention selects the most representative reservoir pressure to divide the multi-thin-layer reservoir, divides all thin-layer reservoirs into several production sections in the order from bottom to top, each production section includes several thin coal seams, and the formation pressures of the coal seams within the same production section are the same or similar, which is convenient for centralized production. Compared with the single production of a single thin coal seam, the present invention can increase the gas production volume of the gas production well. For different production sections with large pressure differences, different perforation and fracturing operations (different operation parameters and fracturing fluid compositions) are implemented.

[0005] To further increase the gas production volume, the present invention combines coalbed methane extraction with coalbed gasification. One branch well corresponds to the lower part of one production 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 production section where coalbed methane is being extracted above. After the thin coal seams in the production section are heated, it is beneficial to the desorption of methane, thereby increasing the coalbed methane production volume.

[0006] When the coalbed methane extraction in each production section is completed, underground gasification can also be carried out according to the coal seam conditions. At this time, the gas production well and the gasification well take turns acting as the injection well and the production well to gasify the underground coal. Coupled with the triangular arrangement of the three gas production wells, it is convenient to maximize the extraction of coalbed methane and underground gasification, and make full use of coalbed methane and coal resources.

[0007] Optionally, in step S100, both the gas production well and the gasification well are vertical wells. 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 at the same depth, and the bottom end of the gasification well is lower than the bottom ends of the gas production wells.

[0008] Optionally, in step S200, the main well of the branch well system is a vertical well. The side wall of the main well is connected with several branch wells. The several branch wells are arranged in sequence from top to bottom. The branch wells are all horizontal wells, and the end of the horizontal section of the branch well extends towards the corresponding gas production well.

[0009] Optionally, 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 in 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, facilitating the corresponding reception of the coal gas produced by the gasification of the branch wells.

[0010] Optionally, in step S400, taking one production well as an example, the specific process of extracting coalbed methane is as follows: S401: Perforate the sidewall of the bottommost thin coal seam corresponding to the bottommost production section of the gas production well, then fracture the bottommost thin coal seam, temporarily do not drain the liquid, and then seal off the bottommost thin coal seam. S402: Perforate the sidewall of the second bottommost thin coal seam corresponding to the bottommost production section of the gas production well, then fracture the second bottommost thin coal seam, also temporarily do not drain the liquid, and then seal off the second bottommost thin coal seam. According to S401 - 402, perforate and fracture each thin coal seam of the bottommost production section from bottom to top in sequence. After all the thin coal seams in this production section are fractured, drain the liquid uniformly. S403: After draining the liquid, use the existing technology to uniformly extract coalbed methane from all the thin coal seams in the bottommost production section.

[0011] Further optionally, if the distance between two adjacent thin coal seams is not greater than 20 meters, the form of ball plugging temporarily is adopted, that is, at the end stage of fracturing the lower coal seam, soluble temporary plugging balls are thrown into the gas production well. Under the pressure of the fracturing fluid, the temporary plugging balls block the perforation holes of the lower coal seam, thereby sealing the sidewall of the gas production well corresponding to the lower coal seam.

[0012] 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.

[0013] Optionally, in step S401 or S402, perforate the sidewall of the gasification well bottom corresponding to the bottommost branch well, and the perforation direction is towards the three gas production wells.

[0014] Optionally, while implementing step S403, injection pipes are respectively introduced into the three branch well systems. The bottom end of each injection pipe reaches one end of the corresponding bottommost branch well close to the gasification well; a production pipe is introduced into the gasification well, and the bottom end opening of the production pipe corresponds to the depth of the bottommost branch well, for collecting the mixed coal gas produced by gasification.

[0015] Optionally, step S500 is specifically as follows: S501: In a clockwise direction, denote the three gas production wells as the first gas production well, the second gas production well, and the third gas production well respectively. Take the first gas production well as the injection well and the gasification well as the production well, and gasify the bottommost coal seam from the first gas production well to the gasification well; S502: When the gasification high-temperature zone between the first production well and the gasification well expands to the front of the gas cooling zone, take the gasification well as the injection well, and both the second gas production well and the third gas production well as production wells, and continue to gasify the bottommost coal seam between the gasification well and the second gas production well and the third gas production well. Description of the Drawings

[0016] Figure 1 It is a top-view structural schematic diagram of the gas production well, gasification well and branch well system in the embodiment; Figure 2 It is a side-view structural schematic diagram of the gas production well, gasification well and branch well system.

[0017] In the drawings, 1 - gas production well, 2 - gasification well, 3 - main well, 4 - branch well, 5 - branch well system. Detailed Embodiment

[0018] This embodiment provides a method for co-producing deep multi-thin coalbed methane and coal gasification, as Figure 1 - Figure 2 shown, including: S100: Drill three gas production wells 1 and one gasification well 2. The three gas production wells form a triangle, and the gasification well is in the middle of the triangle. Both the gas production wells and the gasification well penetrate through each thin coal seam; S200: Drill a branch well system 5 on the side of the gas production well away from the gasification well. The branch well system corresponds to the gas production well one by 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; S300: Divide the thin coal seams with the same or similar formation pressure into one mining section, and the depth of each mining section corresponds to the depth of one branch well; S400: The three gas production wells simultaneously perforate and fracture each thin coal seam in the bottommost mining section, and then simultaneously produce the coalbed methane in the bottommost mining section; While producing gas, the bottommost branch wells of the three branch well systems are used as injection wells to inject the gasification agent, and the gasification well is used as the production well for coal gasification, and at the same time provides heat for the upper mining section to promote the increase in coalbed methane production; According to S400, produce coalbed methane and coal gasification for each mining section from bottom to top in turn; S500: After the coalbed methane production is completed, take any one of the gas production wells as the injection well and the gasification well as the production well to gasify the bottommost thin coal seam, and then take the gasification well as the injection well and the other two gas production wells as the production wells to continue gasifying the bottommost thin coal seam; According to S500, coal seam gasification is carried out on several thin coal seams from bottom to top.

[0019] Optionally, in step S100, according to the geological exploration information, three gas production wells and one gasification well are drilled vertically downward from the ground. Both the gas production wells and the gasification well are vertical wells and penetrate through each thin coal seam stacked up and down. 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 have the same depth, and the bottom end of the gasification well is lower than the bottom ends of the gas production wells.

[0020] Casing pipes are respectively lowered into the gas production wells, and cementing and well completion operations are carried out according to the existing technology. Casing pipes and / or screen pipes are lowered into the gasification well to ensure that the side wall of the gasification well can communicate with each thin coal seam, and then cementing and well completion operations are carried out according to the existing technology.

[0021] Optionally, in step S200, a set of corresponding branch well systems, gas production wells, and gasification wells are arranged in sequence along a straight line. The three gas production wells correspond to three straight lines, and these three straight lines intersect at the gasification well. The main well of the branch well system is a vertical well. The side wall of the main well is connected with several branch wells. The several branch wells are arranged in sequence from top to bottom. The branch wells are all horizontal wells. The branch wells include a deflecting section and a horizontal section. The top of each branch well is connected to the side wall of the main well, then a deflecting section is set, and then the horizontal section is drilled. The end of the horizontal section extends towards the corresponding gas production well.

[0022] The branch wells of the same branch well system can be parallel to each other and their vertical positions can correspond. According to the characteristics of the thin coal seam where the horizontal section of the branch well is located and the requirements for coal seam gasification at this coal seam, the position of the end of the branch well is reasonably set. Generally, the end of the branch well does not reach the position of the corresponding gas production well, that is, the gas production well is between the end of the branch well and the gasification well. During subsequent gasification, the coal seam between the end of the branch well and the gasification well is gasified by combustion. The high-temperature area of coal seam gasification is just below the production section of the coal seam gas being mined by the corresponding gas production well, which is convenient for heat to directly rise and be transferred to the coal seam in the production section being mined. After the coal seam in the production section is heated, it is beneficial to the desorption of methane, thereby increasing the output of coal seam gas.

[0023] Optionally, in step S300, the depth of the horizontal section of the branch well is greater than the bottom of the corresponding production section, that is, the horizontal section of the branch well is lower than the bottom of the corresponding production section. The distance between the horizontal section and the bottom of the production section in the vertical direction is comprehensively evaluated according to the safety requirements of coal seam gas production and underground gasification, as well as the heat transfer efficiency of gasification heat, and a reasonable distance is determined. The branch well system can be drilled, cased, cemented, and completed using existing technology. It is preferred to use screen pipes to facilitate providing reliable support and the connection between the branch well and the main well.

[0024] Further optionally, the depth of the horizontal section of the bottommost branch well in 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, facilitating the corresponding reception of the coal gas produced by the gasification of the branch wells.

[0025] Optionally, in step S400, taking one production well as an example, the specific process of extracting coalbed methane is as follows: S401: Perforate the sidewall of the bottommost thin coal seam corresponding to the bottommost production section of the gas production well, then fracture the bottommost thin coal seam, temporarily do not drain the liquid, and then seal off the bottommost thin coal seam; S402: Perforate the sidewall of the second bottommost thin coal seam corresponding to the bottommost production section of the gas production well, then fracture the second bottommost thin coal seam, also temporarily do not drain the liquid, and then seal off the second bottommost thin coal seam; According to S401 - 402, perforate and fracture each thin coal seam in the bottommost production section from bottom to top in sequence. After all the thin coal seams in this production section are fractured, drain the liquid uniformly; S403: After draining the liquid, use the existing technology to uniformly extract coalbed methane from all the thin coal seams in the bottommost production section.

[0026] Further optionally, if the distance between two adjacent thin coal seams is not greater than 20 meters, the form of ball plugging is adopted, that is, at the end of the fracturing of the lower coal seam, soluble plugging balls are thrown into the gas production well. Under the pressure of the fracturing fluid, the plugging balls block the perforation holes of the lower coal seam, thereby sealing the sidewall of the gas production well corresponding to the lower coal seam.

[0027] 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.

[0028] The present invention adopts the form of separate perforation and fracturing for each thin coal seam in the same production section, then drains the liquid uniformly, and then jointly extracts the coalbed methane from all the coal seams in this production section, which can greatly increase the gas production per unit time and reduce the production cost. Three gas production wells operate on the same thin coal seam in the same production section simultaneously according to the above method.

[0029] Optionally, in step S401 or S402, perforate the sidewall of the gasification well corresponding to the bottommost branch well at the bottom, and the perforation direction is towards the three gas production wells, so that the gasification well can receive the coal gas obtained from the gasification of the three bottommost branch wells.

[0030] Optionally, while implementing step S403, injection pipes are respectively introduced into the three branch well systems. The bottom end of each injection pipe reaches one end close to the gasification well of the corresponding bottommost branch well. The top of the injection pipe is at the ground wellhead of the main well and is connected to the gasifying agent supply device to supply the gasifying agent to the bottommost branch wells of the three branch well systems and ignite it; a production pipe is introduced into the gasification well. The bottom end opening of the production pipe corresponds to the depth of the bottommost branch well for collecting the mixed coal gas produced by gasification.

[0031] According to steps S401 - S403 and the operations on the branch wells and the gasification well in these three steps, the coalbed methane in each mining section is mined successively from bottom to top, and the coal seam below the corresponding mining section is gasified successively from bottom to top.

[0032] 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 bottommost mining section. This branch well may correspond to any thin coal seam in the bottommost mining section, as long as the gasification of the thin coal seam below and the mining of the coalbed methane in the upper sub-bottom mining section can be carried out safely.

[0033] Preferably, after each branch well completes the gasification of the corresponding coal seam, cement is poured from the main well. The cement flows into the branch well that has just completed gasification and flows along this branch well into the coal seam to fill the cavity formed after the coal seam is gasified. Control the flow rate of the cement (the flow rate is not too fast and flows down along the side wall of the main well that is not connected to the branch well), or introduce a pipeline into the main well. The bottom of the pipeline corresponds to the branch well that has completed the gasification task at the bottom, for injecting cement separately, so that the cement can only flow into the branch well that has completed the gasification task at the bottom and will not flow into the ungasified branch wells above.

[0034] Optionally, step S500 is specifically as follows: S501: In a clockwise direction, the three gas production wells are respectively denoted as the first gas production well, the second gas production well, and the third gas production well. Taking the first gas production well as the injection well and the gasification well as the production well, gasify the bottommost coal seam from the first gas production well to the gasification well; S502: When the gasification high-temperature zone between the first production well and the gasification well expands to the front of the gas cooling zone, take the gasification well as the injection well, and both the second gas production well and the third gas production well as production wells, and continue to gasify the bottommost coal seam between the gasification well and the second gas production well and the third gas production well.

[0035] Further optionally, in step S501, an injection pipe is introduced into the first gas production well. The bottom end of the injection pipe reaches the bottommost coal seam corresponding to the first gas production well; a production pipe is introduced into the gasification well. The bottom end opening of the production pipe corresponds to the depth of the bottom end of the injection pipe. The injection pipe inputs the gasifying agent and ignites it, and the produced mixed coal gas is discharged from the gasification well.

[0036] The bottommost coal seam in step S501 refers to the coal seam with the deepest depth reached by the bottom end of the production well, rather than the coal seam corresponding to the bottommost branch well, and the bottommost branch well is lower than the bottom end of the production well.

[0037] The gasification high-temperature zone is the high-temperature zone where coal burns. The coal gas (i.e., CH4, CO, H2) formed by the reaction of water vapor and coal flows through the dry distillation zone to the production well and is then produced through the production well.

[0038] The front 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 adjacent injection wells and production wells, the first gas production well is closed, the gasification well is used as the injection well, and the second and third gas production wells are used as production wells to continue gasifying the bottommost coal seam.

[0039] The gas cooling zone is roughly the dry distillation zone. The coal in this area is heated and may undergo chemical reactions but does not burn. The coal gas produced after coal combustion will cool down during the process of passing through the gas cooling zone, reducing the gas pressure in the production well and facilitating the production of coal gas. Therefore, a part of the coal seam is always reserved between the production well and the injection well as the gas cooling zone.

[0040] 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, making more full use of the underground coal seam resources.

[0041] According to S500, gasifying several thin coal seams from bottom to top means that if the coal seam conditions are good, all thin coal seams can be gasified one by one in sequence while the entire deep coal seam area does not collapse; if the coal seam conditions are not good, the thin coal seams can be gasified at intervals to ensure that the entire deep coal seam area does not collapse.

[0042] 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 block the internal space of the coal seam corresponding to the first gas production well that has just been gasified, preventing the gasification agent from entering the lower coal seam when gasifying the upper coal seam later; Similarly, after the second and third gas production wells gasify a certain coal seam, pipelines are respectively lowered into the second and third gas production wells for injecting cement to block the internal spaces of the coal seams corresponding to the second and third gas production wells that have just been gasified, preventing the gasification agent from entering the lower coal seam when gasifying the upper coal seam later.

Claims

1. A method for co-producing coalbed methane and coalbed gasification in deep multi-thin coal seams, characterized in that, Including: S100: Drilling three gas production wells and one gasification well, all of which penetrate through each thin coal seam. The three gas production wells form a triangle, and the gasification well is located in the middle of the triangle; S200: Drilling a branch well system on the side of the gas production well far from the gasification well. The branch well system includes a main well and several branch wells at different heights, and the ends of the branch wells all point to the gasification well; S300: Dividing the thin coal seams with the same or similar formation pressure into one mining section, and corresponding to each mining section below there is a branch well; S400: The three gas production wells simultaneously perforate and fracture each thin coal seam in the bottommost mining section, and then simultaneously extract the coalbed methane in the bottommost mining section; While extracting gas, the bottommost branch wells of the three branch well systems all serve as injection wells, and the gasification well serves as a production well to carry out coal seam gasification and provide heat for the upper mining section; According to S400, extract coalbed methane and carry out coal seam gasification for each mining section from bottom to top in turn; S500: After the coalbed methane extraction is completed, using any one of the gas production wells as an injection well and the gasification well as a production well, carry out coal seam gasification on the bottommost thin coal seam; then using the gasification well as an injection well and the other two gas production wells as production wells, continue to gasify the bottommost thin coal seam; According to S500, carry out coal seam gasification on several thin coal seams from bottom to top.

2. The method for co-producing deep multi-thin-layer coalbed methane and coal gasification according to claim 1, characterized in that, In step S100, the gas production wells and the gasification well are both vertical wells. 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 have the same depth, and the bottom end of the gasification well is lower than the bottom ends of the gas production wells.

3. The method for co-producing deep multi-thin-layer coalbed methane and coal gasification according to claim 1, characterized in that, In step S200, the main well of the branch well system is a vertical well. The side wall of the main well is connected with 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 end of the horizontal section of the branch well extends towards the corresponding gas production well; the gas production well is located between the end of the branch well and the gasification well.

4. The method for co-producing deep multi-thin-layer coalbed methane and coal 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 mining 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 and the horizontal sections of the three bottommost branch wells are at the same depth, which is convenient for correspondingly receiving the coal gas produced by the gasification of the branch well.

5. The method for co-production of deep multi-thin-layer coalbed methane and coalbed gasification according to claim 3, characterized in that, In step S400, the specific steps for extracting coalbed methane from any one production well are as follows: S401: Perforate on the side wall of the bottommost thin coal seam of the bottommost mining section corresponding to the gas production well, then fracture the bottommost thin coal seam, temporarily do not drain the liquid, and then seal off the bottommost thin coal seam; S402: Perforate on the side wall of the second-bottom thin coal seam of the bottommost mining section corresponding to the gas production well, then fracture the second-bottom thin coal seam, also temporarily do not drain the liquid, and then seal off the second-bottom thin coal seam; According to S401 - 402, perforate and fracture each thin coal seam in the bottommost mining section from bottom to top in turn. After all the thin coal seams in this mining section are fractured, then drain the liquid uniformly; S403: After draining the liquid, uniformly extract coalbed methane from all the thin coal seams in the bottommost mining section.

6. The method for co-producing deep multi-thin coalbed methane and coalbed gasification according to claim 5, wherein If the distance between two adjacent thin coal seams is no more than 20 meters, the form of throwing soluble temporary plugs is adopted. At the end of the fracturing of the lower coal seam, soluble temporary plugs are thrown into the gas production well. Under the pressure of the fracturing fluid, the temporary plugs block the perforation holes of the lower coal seam, thereby sealing the side wall of the gas production well corresponding to the lower coal seam.

7. The method for co-producing deep multi-thin-layer coalbed methane and coalbed gasification according to claim 5, characterized in that If the distance between two adjacent thin coal seams is greater than 20 meters, soluble bridge plugs are lowered into the gas production well to seal the cross-section of the production well between the upper and lower thin coal seams.

8. The method for co-production of deep multi-thin-layer coalbed methane and coalbed gasification according to claim 5, characterized in that, In step S401 or S402, perforations are made on the side wall of the bottom of the gasification well corresponding to the bottommost branch well, and the perforation direction is towards the three gas production wells.

9. The method for co-producing deep multi-thin-layer coalbed methane and coalbed gasification according to claim 8, characterized in that, While implementing step S403, injection pipes are respectively introduced into the three branch well systems, and the bottom end of each injection pipe reaches one end of the corresponding bottommost branch well close to the gasification well; a production pipe is introduced into the gasification well, and the bottom end opening of the production pipe corresponds to the depth of the bottommost branch well for collecting the mixed coal gas produced by gasification.

10. The method for co-producing deep multi-thin-layer coalbed methane and coalbed gasification according to claim 1, characterized in that Step S500 is specifically as follows: S501: In a clockwise direction, the three gas production wells are respectively denoted as the first gas production well, the second gas production well, and the third gas production well. Taking the first gas production well as the injection well and the gasification well as the production well, gasify the bottommost coal seam from the first gas production well to the gasification well. 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, take the gasification well as the injection well, and both the second gas production well and the third gas production well as production wells, and continue to gasify the bottommost coal seam between the gasification well and the second gas production well and the third gas production well.

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