Coal bed gasification auxiliary fracturing method

Abstract

The coal bed gasification auxiliary fracturing method comprises the steps that drilling parameters are designed; selecting a well spacing interval, and constructing a main shaft and a horizontal well; a gasification operation tool is put into the horizontal well through the gasification pipe column; injecting a combustion improver and water vapor into the horizontal well, igniting or detonating a methane-air mixture in the complex crack in the target coal seam, and realizing gasification transformation operation of the coal seam; carbon dioxide is used for displacing gasification products to form a CO and H2 enrichment area at the end, close to the well, of the coal seam; potassium permanganate particles are pressed into pores of the CO and H2 enrichment area of the coal seam to form an ignition zone; the internal space of the coal seam is ignited through microwave ignition; potassium permanganate particles are thermally decomposed to continuously supply oxygen as a newly added combustion improver; and the operations of gasification transformation, product displacement and ignition blast are alternately carried out. The method is low in implementation cost and simple in implementation process, the continuous burning and explosion effect of the internal space of the coal seam can be effectively improved, gasification anti-reflection and large-range burning and explosion fracturing yield increasing transformation of the coal seam can be achieved, and the yield and mining benefits of the coal seam gas can be greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of unconventional natural gas exploitation, and in particular relates to a coalbed gasification assisted fracturing method. Background Art

[0002] Although my country has abundant reserves of coalbed methane, its mining efficiency and difficulty are very high due to the low permeability of its reservoirs. It is often necessary to carry out fracturing and permeability enhancement operations before subsequent mining operations can be carried out. At present, hydraulic fracturing technology is mainly used to enhance the permeability of reservoirs. Although hydraulic fracturing technology has accelerated the development of unconventional natural gas, it also has many problems such as large water resource consumption, reservoir clay expansion, groundwater pollution, and difficulty in handling return fluids. In addition, conventional hydraulic fracturing has a series of problems in shale gas development, such as insufficient reservoir fracture degree and single fracture extension direction. In order to overcome the problems of conventional hydraulic fracturing, a method of in-situ explosion fracturing of reservoir methane has emerged. Explosion fracturing technology is a new type of coalbed methane mining technology that aims to increase the permeability and recovery rate of coalbed methane by inducing controlled explosion reactions in coal seams to form a complex fracture network. This technology utilizes the explosion characteristics of methane and oxygen mixed gas and achieves efficient fracturing of coal seams by precisely controlling the explosion conditions. The combustion and explosion reaction can produce a large amount of high-temperature and high-pressure gas in a short period of time, which is conducive to the rapid formation of a complex fracture network, thereby significantly improving the permeability of coalbed methane.

[0003] In order to improve the effect of explosive fracturing, it is necessary to achieve precise control of ignition conditions. The conventional ignition head ignition method currently used has a small ignition range, so it has high requirements on the concentration of methane and combustion-supporting agent mixed gas in the ignition area, which greatly reduces the success rate of ignition. In addition, the ignition area is near the well end, and it is also difficult to achieve ignition and explosion operations inside the coal seam during implementation. For this reason, it is urgent to provide a fracturing method with a larger ignition range, a higher ignition success rate, and the ability to significantly improve the range and effect of coal seam production increase transformation. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a coalbed gasification assisted fracturing method. The method has low implementation cost and simple implementation process. It can effectively improve the continuous combustion and explosion effect of the internal space of the coal seam, and can achieve gasification permeability enhancement and large-scale combustion and explosion fracturing to increase production of the coal seam, which can greatly improve the production and mining efficiency of coalbed methane.

[0005] In order to achieve the above object, the present invention provides a coalbed gasification assisted fracturing method, comprising the following steps:

[0006] Step 1: Preparation;

[0007] Collect geological parameters and exploration data of the target coal seam, and analyze the structure and density of the coal seam based on the geological parameters and exploration data; at the same time, analyze the well logging data to determine the structure and geological conditions of the coal seam, and design the coal seam drilling parameters based on the structure and geological conditions of the coal seam;

[0008] Step 2: Arrangement of main wellbore and horizontal wells;

[0009] S21: Based on the analysis results of the logging data, the structure and density of the coal seam are evaluated and the well layout interval is selected;

[0010] S22: After determining the well layout interval, vertically drill the main wellbore to the middle section of the target coal seam, and extend a horizontal well parallel to the target coal seam from the end of the main wellbore. At the same time, ensure that the horizontal well penetrates the target coal seam to be fractured;

[0011] Step 3: Arrangement of ground fracturing equipment and lowering of tools;

[0012] A bridge plug is lowered into the end of the horizontal well of the target coal seam, and a surface fracturing device is arranged on the ground. The surface fracturing device and the gasification operation tool are then connected through a gasification pipe string, and the gasification operation tool is lowered into the horizontal well using the gasification pipe string; wherein the gasification pipe string comprises a continuous oil pipe and a high-pressure hose, the high-pressure hose is coaxially inserted into the interior of the continuous oil pipe, and a pipe annulus is formed between the high-pressure hose and the continuous oil pipe, the gasification operation tool comprises a centralizer, a packer, a delivery nozzle and an ignition electrode, the centralizer and the packer are sequentially mounted on the outside of the end of the gasification pipe string from the head end to the end end, and the delivery nozzle and the ignition electrode are both installed at the end of the high-pressure hose;

[0013] Step 4: Gasification transformation of coal seams;

[0014] S41: Setting the packer by means of annular pressure;

[0015] S42: Using the surface fracturing equipment to provide injection pressure, injecting a combustion aid into the target well section through the tubing annulus, and injecting water vapor into the target well section through the high-pressure hose;

[0016] S43: Ignition electrodes are used to ignite or detonate the methane-air mixture in the complex fractures of the target coal seam. The high temperature conditions formed are used to cause the coal to react chemically with the continuously supplied water vapor to produce gasification products. At the same time, the gasification products and coal continue to react chemically under high temperature conditions to produce methane, thereby achieving the gasification transformation of the coal seam. The porosity of the target coal seam is increased through the gasification transformation operation, forming a larger coal seam gasification transformation area. At the same time, the gasification products produced by the gasification transformation operation will diffuse and fill the target well section.

[0017] Step 5: Using carbon dioxide to displace gasification products to form a CO and H2 enrichment zone;

[0018] After the gasification reformation operation is completed, a large amount of carbon dioxide is injected into the horizontal well using a high-pressure hose. Under the displacement effect of carbon dioxide, the gasification products enter the coal seam near the well through the pores generated by the gasification reformation operation, forming a CO and H2 enriched area in the coal seam near the well;

[0019] Step 6: Press potassium permanganate particles into the pores in the coal seam to form an ignition zone;

[0020] S61: Replace the delivery nozzle and ignition electrode at the end of the high-pressure hose with a fracturing delivery tool and a microwave transmitter; two microwave transmitters are installed at the end of the fracturing delivery tool and are arranged symmetrically on both sides;

[0021] S62: Use liquid nitrogen to carry potassium permanganate particles as fracturing fluid to perform fracturing operations on the coal seam near the wellbore. While expanding the original pore size and range, the potassium permanganate particles are pressed into the pores and cracks of the coal seam near the wellbore, and the potassium permanganate particles are mixed with CO and H2 in the near-wellbore area to form an ignition zone containing potassium permanganate-gasification products; at the same time, an explosion zone containing methane gas is formed in the far-wellbore area;

[0022] Step 7: Microwave ignition operation;

[0023] Control the microwave transmitter to start working, use microwave ignition to ignite the inside of the coal seam, so that the high manganese acid in the near-wellbore area decomposes oxygen when heated, and the oxygen is mixed with the gasification product to cause combustion and explosion, thereby triggering combustion and explosion inside the coal seam; at the same time, the oxygen produced by the thermal decomposition of high manganese acid is used as a new combustion aid to further promote continuous combustion and explosion operations inside the coal seam;

[0024] Step 8: Alternately perform gasification reform-product displacement-ignition and explosion operations;

[0025] Repeat steps 4 to 7 multiple times, alternately performing gasification transformation-product displacement-ignition and explosion operations, so as to cause the coal seam to loosen continuously and the pore range of the coal seam to extend and expand continuously, thereby forming a new coal seam gasification transformation zone with a gradually expanding range. At the same time, the release distance between the gasification product and the combustion aid is continuously increased, forming a new ignition zone and a new explosion zone, thereby expanding the production increase transformation effect and scope through continuous explosion and fracturing.

[0026] Furthermore, in order to ensure the fracturing effect, in step one, the structure and geological conditions of the coal seam include the thickness and distribution of the coal seam, the physical properties of the coal seam, and the gas and water content of the coal seam.

[0027] Furthermore, in order to ensure the fracturing effect, in step 2 S21, an area with thick coal seams and rich gas content is selected as a well-laying layer section, and at the same time, it is ensured that the well-laying layer section avoids the development area of ​​fault and fold geological structures.

[0028] Preferably, the gasification products include CO and H2.

[0029] As a preference, in step three, the bridge plug is a drillable bridge plug.

[0030] The present invention adopts a technical method combining coalbed gasification operation with continuous explosion fracturing. First, the target coalbed horizontal well is drilled to build a basic framework, and then the coalbed gasification transformation method is used to preliminarily increase the porosity of the coalbed, and the CO and H2 enrichment zone is formed near the well end by injecting carbon dioxide to displace the gasification product. On this basis, liquid nitrogen fracturing technology is used to carry potassium permanganate particles into the pores to mix with CO and H2 in the near-well zone to form a potassium permanganate-gasification product ignition zone; a methane gas explosion zone is formed in the far-well zone. Finally, in order to improve the explosion fracturing effect, precise control of ignition conditions is achieved. The conventional ignition head ignition method currently used has a small ignition range, so the concentration of methane and combustion-supporting agent mixed gas in the ignition area and other explosion characteristics are required to be high, which greatly reduces the ignition success rate. And because the ignition area is near the well end, it is difficult to achieve ignition and explosion operations inside the coal seam. The present invention combines coalbed gasification technology on the basis of conventional explosion fracturing. Coalbed gasification technology is a technology that converts coal resources in coal seams into gaseous fuels, aiming to improve the utilization rate of coal resources and reduce environmental pollution. This technology converts coal into gaseous fuels such as H2 and CO through gasification reactions in coal seams. Gasification operations can increase the porosity of coal seams, and gasification products such as H2 and CO have lower ignition energy. Introducing them into the pores of coal seams, in this way, the internal heating and ignition operations of the coal seams using microwave heating can effectively improve the success rate and efficiency of ignition. While initiating the explosion zone inside the coal seam, the high-temperature decomposition of potassium permanganate is used to continuously supply oxygen, which not only improves the ignition efficiency, but also effectively improves the continuous explosion effect of the internal space of the coal seam, thereby realizing the gasification permeability enhancement and large-scale production increase and transformation operations of the coal seam.

[0031] This method has low implementation cost and simple implementation process. It can effectively improve the continuous combustion and explosion effect of the internal space of the coal seam, realize the gasification and permeability enhancement of the coal seam and large-scale combustion and explosion fracturing to increase production, which can greatly improve the production and mining efficiency of coalbed methane. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of well arrangement in the present invention;

[0033] Figure 2 It is a schematic diagram of the layout of the ground fracturing equipment and the lowering state of the tools in the present invention;

[0034] Figure 3 It is a schematic diagram of the coal seam gasification transformation operation state in the present invention;

[0035] Figure 4 Schematic diagram of the state of carbon dioxide displacing gasification products in the present invention;

[0036] Figure 5 This is a schematic diagram of the state in which potassium permanganate particles are pressed into the pores of a coal seam in the present invention;

[0037] Figure 6 It is a schematic diagram of the operating state of microwave ignition in the present invention;

[0038] Figure 7 It is a schematic diagram of the state of alternating gasification reform-product displacement-ignition and explosion operations in the present invention.

[0039] In the figure: 1. main wellbore, 2. coal seam, 3. drillable bridge plug, 4. horizontal well, 5. ground fracturing equipment, 6. continuous oil pipe, 7. high-pressure hose, 8. oil pipe annulus, 9. centralizer, 10. packer, 11. release nozzle, 12. water vapor, 13. ignition electrode, 14. coal seam gasification transformation zone, 15. carbon dioxide, 16. gasification products, 17. CO, H2 enrichment zone, 18. fracturing fluid, 19. fracturing release tool, 20. potassium permanganate particles, 21. ignition zone, 22. combustion zone, 23. microwave ignition, 24. oxygen, 25. microwave transmitter, 26. new coal seam gasification transformation zone, 27. new ignition zone, 28. new combustion zone, 29. combustion aid. DETAILED DESCRIPTION

[0040] The present invention will be further described below.

[0041] like Figures 1 to 7 As shown, the present invention proposes a coal seam gasification assisted fracturing method, which uses a method of directional drilling of horizontal wells, improves the coal seam porosity by gasification operations on the coal seam, and uses the near-well ignition zone formed by the gasification operation products to improve the ignition efficiency of the internal coal seam explosion fracturing. At the same time, combined with microwave ignition and potassium permanganate decomposition oxygen supply technology, it can effectively realize the ignition and continuous explosion of the internal space of the coal seam; alternating gasification transformation-product displacement-ignition and explosion operations can promote the continuous expansion of the coal seam porosity range, and at the same time, the distance between the gasification product and the combustion aid is continuously increased, which greatly improves the range of production increase transformation. Specifically, it includes the following steps:

[0042] Step 1: Preparation;

[0043] Collect geological parameters and exploration data of the target coal seam, and analyze the structure and density of coal seam 2 based on the geological parameters and exploration data; at the same time, analyze the well logging data to determine the structure and geological conditions of coal seam 2, and design reasonable drilling parameters for coal seam 2 based on the structure and geological conditions of coal seam 2;

[0044] Step 2: Arrangement of the main wellbore 1 and the horizontal well 4;

[0045] S21: Based on the analysis results of the well logging data, combined with the structure and density of the coal seam 2, an assessment is made to select the well layout interval;

[0046] S22: After determining the well layout interval, vertically drill the main wellbore 1 to the middle section of the target coal seam 2, and extend a horizontal well 4 parallel to the target coal seam 2 from the end of the main wellbore 1. At the same time, ensure that the horizontal well 4 penetrates the target coal seam 2 to be fractured, thereby creating favorable conditions for subsequent coalbed methane mining;

[0047] Step 3: Arrangement of ground fracturing equipment and lowering of tools;

[0048] A bridge plug 3 is lowered into the end of a horizontal well 4 of a target coal seam 2, and a surface fracturing device 5 is arranged on the ground. The surface fracturing device 5 and a gasification operation tool are then connected via a gasification string, and the gasification operation tool is lowered into the horizontal well 4 using the gasification string; wherein the gasification string comprises a continuous tubing 6 and a high-pressure hose 7, wherein the high-pressure hose 7 is coaxially inserted into the interior of the continuous tubing 6, and a tubing annulus 8 is formed between the high-pressure hose 7 and the continuous tubing 6, and the gasification operation tool comprises a centralizer 9, a packer 10, a delivery nozzle 11, and an ignition electrode 13, wherein the centralizer 9 and the packer 10 are sequentially mounted on the outside of the end of the gasification string from the head end to the end end, and the delivery nozzle 11 and the ignition electrode 13 are both installed at the end of the high-pressure hose 7;

[0049] Step 4: Gasification transformation of coal seam 2;

[0050] S41: Setting the packer 10 by means of annular pressure;

[0051] S42: Using the surface fracturing equipment 5 to provide injection pressure, injecting a combustion aid 29 into the target well section through the oil pipe annulus 8, and injecting water vapor 12 into the target well section through the high-pressure hose 7;

[0052] S43: The methane-air mixture in the complex fractures of the target coal seam 2 is ignited or detonated by means of the ignition electrode 13, and the high temperature condition is used to make the coal react chemically with the continuously supplied water vapor 12 to produce the gasification product 16. At the same time, the gasification product 16 and the coal continue to react chemically under the high temperature condition to produce methane, thereby realizing the gasification transformation operation of the coal seam 2; the porosity of the target coal seam 2 is increased by the gasification transformation operation, and a larger coal seam gasification transformation area 14 is formed. At the same time, the gasification product 16 produced by the gasification transformation operation will diffuse and fill the target well section, thereby making the ignition energy of the target well section lower, so as to create more favorable conditions for the exploitation of coalbed methane;

[0053] Step 5: Using carbon dioxide 15 to displace gasification product 16 to form CO and H2 enrichment zone 17;

[0054] After the gasification reformation operation is completed, a large amount of carbon dioxide 15 is injected into the horizontal well 4 using a high-pressure hose 7. Under the displacement effect of the carbon dioxide 15, the gasification product 16 enters the coal seam 2 near the well end through the pores generated by the gasification reformation operation, forming a CO and H2 enrichment zone 17 in the coal seam 2 near the well end;

[0055] Step 6: Pressing potassium permanganate particles 20 into the pores in the coal seam 2 to form an ignition zone 21;

[0056] S61: Replace the delivery nozzle 11 and the ignition electrode 13 at the end of the high-pressure hose 7 with a fracturing delivery tool 19 and a microwave transmitter 25; two microwave transmitters are installed at the end of the fracturing delivery tool and are arranged symmetrically on both sides;

[0057] S62: Using liquid nitrogen to carry potassium permanganate particles 20 as a fracturing fluid 18, the coal seam 2 near the wellbore is subjected to fracturing operations. While expanding the original pore size and range, the potassium permanganate particles 20 are pressed into the pores and cracks of the coal seam 2 near the wellbore, and the potassium permanganate particles 20 are mixed with CO and H2 in the near-wellbore zone to form an ignition zone 21 containing potassium permanganate-gasification products; at the same time, an explosion zone 22 containing methane gas is formed in the far-wellbore zone, thereby making full preparations for subsequent ignition operations and helping to reduce the difficulty of subsequent ignition;

[0058] Step 7: Microwave ignition operation;

[0059] The microwave transmitter 25 is controlled to start working, and the inside of the coal seam 2 is ignited by microwave ignition 23, so that the high manganese acid in the near-well area decomposes into oxygen 24 when heated, and the oxygen 24 is mixed with gasification products 16 such as CO and H2 to cause combustion and explosion, thereby triggering combustion and explosion inside the coal seam 2; the microwave heating ignition method inside the coal seam effectively improves the ignition efficiency and strongly promotes the combustion and explosion effect of methane gas at the far end of the well;

[0060] At the same time, the oxygen 24 produced by the thermal decomposition of high manganese acid is used as a new combustion aid to further promote the continuous combustion and explosion operation inside the coal seam 2, further improving the transformation efficiency of the coal seam 2;

[0061] Step 8: Alternately perform gasification reform-product displacement-ignition and explosion operations;

[0062] Repeat steps 4 to 7 several times, alternately performing gasification reform-product displacement-ignition and explosion operations, so as to cause the coal seam 2 to be continuously loosened and the pore range of the coal seam 2 to be continuously extended and expanded, thereby forming a new coal seam gasification reform zone 26 with a gradually expanding range. At the same time, the release distance between the gasification product 16 and the combustion aid 29 is continuously increased, thereby forming a new ignition zone 27 and a new explosion zone 28, thereby expanding the production increase reform effect and range through continuous explosion and fracturing, thereby improving the output and mining efficiency of coalbed methane.

[0063] In order to ensure the fracturing effect, in step one, the structure and geological conditions of the coal seam 2 include the thickness and distribution of the coal seam 2, the physical properties of the coal seam 2, and the gas and water content of the coal seam 2.

[0064] In order to ensure the fracturing effect, in step 2 S21, the area with thick coal seam 2 and rich gas content is selected as the well layout section. At the same time, it is ensured that the well layout section avoids the area with developed fault and fold geological structures.

[0065] As a preference, the gasification product 16 includes CO and H2, etc.

[0066] As a preference, in step three, the bridge plug 3 is a drillable bridge plug.

[0067] The present invention adopts a technical method combining coalbed gasification operation with continuous explosion fracturing. First, the target coalbed horizontal well is drilled to build a basic framework, and then the coalbed gasification transformation method is used to preliminarily increase the porosity of the coalbed, and the CO and H2 enrichment zone is formed near the well end by injecting carbon dioxide to displace the gasification product. On this basis, liquid nitrogen fracturing technology is used to carry potassium permanganate particles into the pores to mix with CO and H2 in the near-well zone to form a potassium permanganate-gasification product ignition zone; a methane gas explosion zone is formed in the far-well zone. Finally, in order to improve the explosion fracturing effect, precise control of ignition conditions is achieved. The conventional ignition head ignition method currently used has a small ignition range, so the concentration of methane and combustion-supporting agent mixed gas in the ignition area and other explosion characteristics are required to be high, which greatly reduces the ignition success rate. And because the ignition area is near the well end, it is difficult to achieve ignition and explosion operations inside the coal seam. The present invention combines coalbed gasification technology on the basis of conventional explosion fracturing. Coalbed gasification technology is a technology that converts coal resources in coal seams into gaseous fuels, aiming to improve the utilization rate of coal resources and reduce environmental pollution. This technology converts coal into gaseous fuels such as H2 and CO through gasification reactions in coal seams. Gasification operations can increase the porosity of coal seams, and gasification products such as H2 and CO have lower ignition energy. Introducing them into the pores of coal seams, in this way, the internal heating and ignition operations of the coal seams using microwave heating can effectively improve the success rate and efficiency of ignition. While initiating the explosion zone inside the coal seam, the high-temperature decomposition of potassium permanganate is used to continuously supply oxygen, which not only improves the ignition efficiency, but also effectively improves the continuous explosion effect of the internal space of the coal seam, thereby realizing the gasification permeability enhancement and large-scale production increase and transformation operations of the coal seam.

[0068] This method has low implementation cost and simple implementation process. It can effectively improve the continuous combustion and explosion effect of the internal space of the coal seam, realize the gasification and permeability enhancement of the coal seam and large-scale combustion and explosion fracturing to increase production, which can greatly improve the production and mining efficiency of coalbed methane.

Claims

1. A coalbed gasification assisted fracturing method, characterized in that: The steps include: Step 1: Preparation; Collecting geological parameters and exploration data of the target coal seam, and analyzing the structure and density of the coal seam (2) based on the geological parameters and exploration data; at the same time, analyzing the well logging data to determine the structure and geological conditions of the coal seam (2), and designing the drilling parameters of the coal seam (2) based on the structure and geological conditions of the coal seam (2); Step 2: Arrangement of the main wellbore (1) and the horizontal well (4); S21: Based on the analysis results of the well logging data, combined with the structure and density of the coal seam (2), an assessment is made to select a well layout interval; S22: After determining the well layout interval, vertically drill the main wellbore (1) to the middle section of the target coal seam (2), and extend a horizontal well (4) parallel to the target coal seam (2) from the end of the main wellbore (1), while ensuring that the horizontal well (4) penetrates the target coal seam (2) to be fractured; Step 3: Arrangement of ground fracturing equipment and lowering of tools; A bridge plug (3) is lowered into the end of a horizontal well (4) of a target coal seam (2), and a surface fracturing device (5) is arranged on the ground. The surface fracturing device (5) and a gasification operation tool are then connected via a gasification pipe string, and the gasification operation tool is lowered into the horizontal well (4) using the gasification pipe string. The gasification pipe string comprises a continuous oil pipe (6) and a high-pressure hose (7). The high-pressure hose (7) is coaxially inserted into the interior of the continuous oil pipe (6), and a pipe annulus (8) is formed between the high-pressure hose (7) and the continuous oil pipe (6). The gasification operation tool comprises a centralizer (9), a packer (10), a delivery nozzle (11), and an ignition electrode (13). The centralizer (9) and the packer (10) are sequentially mounted on the outside of the end of the gasification pipe string from the head end to the tail end. The delivery nozzle (11) and the ignition electrode (13) are both installed at the end of the high-pressure hose (7). Step 4: Gasification transformation of coal seam (2); S41: Setting the packer (10) by means of annular pressure; S42: Using the surface fracturing equipment (5) to provide injection pressure, injecting a combustion aid (29) into the target well section through the oil pipe annulus (8), and injecting water vapor (12) into the target well section through the high-pressure hose (7); S43: using an ignition electrode (13) to ignite or detonate the methane-air mixture in the complex fractures of the target coal seam (2), and utilizing the high temperature conditions to cause the coal to react chemically with the continuously supplied water vapor (12) to produce a gasification product (16). At the same time, the gasification product (16) and the coal continue to react chemically under high temperature conditions to produce methane, thereby achieving a gasification transformation operation on the coal seam (2); the porosity of the target coal seam (2) is increased through the gasification transformation operation, forming a coal seam gasification transformation zone (14) of a larger scope, and at the same time, the gasification product (16) produced by the gasification transformation operation diffuses and fills the target well section; Step 5: Using carbon dioxide (15) to displace the gasification product (16) to form a CO and H2 enrichment zone (17); After the gasification reformation operation is completed, a large amount of carbon dioxide (15) is injected into the horizontal well (4) using a high-pressure hose (7). Under the displacement effect of the carbon dioxide (15), the gasification product (16) enters the coal seam (2) near the well end through the pores generated by the gasification reformation operation, forming a CO and H2 enrichment zone (17) in the coal seam (2) near the well end; Step 6: Pressing potassium permanganate particles (20) into the pores in the coal seam (2) to form an ignition zone (21); S61: replacing the delivery nozzle (11) and the ignition electrode (13) at the end of the high-pressure hose (7) with a fracturing delivery tool (19) and a microwave transmitter (25); two microwave transmitters (25) are installed at the end of the fracturing delivery tool (19) and are arranged symmetrically on both sides; S62: Using liquid nitrogen to carry potassium permanganate particles (20) as a fracturing fluid (18), a fracturing operation is performed on the coal seam (2) near the wellbore end, and while expanding the original pore size and range, the potassium permanganate particles (20) are pressed into the pores and cracks of the coal seam (2) near the wellbore end, and the potassium permanganate particles (20) are mixed with CO and H2 in the near-wellbore area to form an ignition zone (21) containing potassium permanganate-gasification products; at the same time, an explosion zone (22) containing methane gas is formed in the far-wellbore area; Step 7: Microwave ignition operation; The microwave transmitter (25) is controlled to start working, and the inside of the coal seam (2) is ignited by means of microwave ignition (23), so that the high manganese acid in the vicinity of the wellbore is decomposed into oxygen (24) when it is heated, and the oxygen (24) is mixed with the gasification product (16) to cause combustion and explosion, thereby triggering combustion and explosion inside the coal seam (2); at the same time, the oxygen (24) produced by the high manganese acid decomposition when it is heated is used as a new combustion aid to further promote the continuous combustion and explosion operation inside the coal seam (2); Step 8: Alternately perform gasification reform-product displacement-ignition and explosion operations; Steps 4 to 7 are repeatedly performed multiple times, and gasification reform-product displacement-ignition and explosion operations are performed alternately, so that the coal seam (2) is continuously loosened and the pore range of the coal seam (2) is continuously extended and expanded, thereby forming a new coal seam gasification reform zone (26) with a gradually expanding range. At the same time, the distance between the gasification product (16) and the combustion aid (29) is continuously increased, forming a new ignition zone (27) and a new explosion zone (28), thereby expanding the production increase reform effect and range through continuous explosion fracturing.

2. A coalbed gasification assisted fracturing method according to claim 1, characterized in that: In step one, the structure and geological conditions of the coal seam (2) include the thickness and distribution of the coal seam (2), the physical properties of the coal seam (2), and the gas and water content of the coal seam (2).

3. A coalbed gasification assisted fracturing method according to claim 1, characterized in that: In step 2 S21, an area with thick coal seam (2) and rich gas content is selected as a well-laying layer section, and at the same time, it is ensured that the well-laying layer section avoids the area with developed fault and fold geological structures.

4. A coalbed gasification assisted fracturing method according to claim 1, characterized in that: In step 4 S43, the gasification product (16) includes CO and H2.

5. The coalbed gasification assisted fracturing method according to claim 1, characterized in that: In step 4 S43, in step 3, the bridge plug (3) is a drillable bridge plug.

Images