Double-extraction-hole one-feeding and one-extraction stepping type crack deflagration fracturing extraction method

Abstract

The invention aims to provide a double-extraction-hole one-feeding and one-extraction stepping type fracture deflagration fracturing extraction method, and belongs to the technical field of reservoir exploitation, the method comprises the following steps: firstly, carrying out vertical drilling construction on a to-be-exploited area to obtain extraction wells A and B, using a perforating gun to break through a sleeve, and then carrying out hydraulic fracturing to preliminarily form a fracture, so that the two extraction holes are communicated through the fracture; after the fracturing fluid is discharged, preliminary extraction is carried out; after the concentration of the methane is reduced, a combustion improver is efficiently introduced into a gap through circulation of the gap of the two holes, methane is exploded, cracks are expanded, extraction is continued, and repeated explosion can be carried out; and after extraction of the two extraction hole areas is completed, an extraction hole C is drilled in the extraction direction and is combined with the extraction well B to form a new'one-feeding and one-extraction 'mode, and the like, so that stepping type extraction is formed. And step-by-step mining is carried out, the previous combustion improver input hole serves as a methane extraction hole of the next stage, drilled wells are fully utilized, and a working area is reasonably planned and mined.

Description

Technical Field

[0001] The present invention belongs to the technical field of reservoir exploitation, and in particular relates to a double-extraction hole "one delivery and one extraction" step-by-step fissure deflagration-induced fracturing extraction method. Background Art

[0002] With the rapid development of my country's economy, people are consuming more and more resources in all walks of life. Among them, the proportion of clean energy consumption such as natural gas, coalbed methane and shale gas is increasing, which has led to the increasing development of exploration and development of such resources. Conventional natural gas currently has a complete drilling and completion method and is at a high level of development.

[0003] Shale gas is an unconventional natural gas, and the amount required in natural gas is increasing year by year. The efficient development of this type of natural gas will greatly alleviate the severe situation of tight national energy supply. From the development history of shale gas exploitation, there are mainly five types of exploitation methods: vertical well development method, vertical well fracturing development method, horizontal well and horizontal well fracturing development method, synchronous fracturing development method and "factory-based" horizontal well fracturing development method.

[0004] From the above, we can see that fracturing technology is a core technology for shale gas exploitation. Different fracturing fluid processes are used to transform shale gas reservoirs. Through fracturing, the main fractures and multi-level secondary fractures are intertwined to form a complex fracture network, or even the largest-scale three-dimensional fracture network system.

[0005] In order to achieve better fracturing effect, multiple hydraulic fracturing is generally required, which will greatly consume water resources and has great limitations in areas with scarce water resources. In addition, hydraulic fracturing is not very effective for reservoirs with high density. Therefore, it is necessary to study more efficient, convenient and fast ways to effectively transform reservoirs, so that natural fractures or initial fractures of hydraulic fracturing can be effectively expanded, and fractures or communication between fractures can be achieved, thereby increasing the gas production of shale gas development.

[0006] With the adjustment of the structure of my country's energy and coal industries, the number of coal mine closures has increased. On the one hand, some coal mines have not met the safety production requirements, and more importantly, there is a need to alleviate environmental problems. However, with the closure of coal mines, more than 50% of the coal remains underground, and these abandoned mines contain huge gas resources and are also closed. The extraction and utilization of residual gas in abandoned coal mines may become a new growth point for the coalbed methane industry. China has a large number of abandoned coal mines, most of which are high-gas mines, so the development of abandoned coal mine gas resources has broad application prospects. If this enriched gas can be developed and utilized, it will further alleviate my country's resource shortage.

[0007] Abandoned mine gas is mainly produced by various types of residual coal in the space of the working face goaf, left coal pillars, adjacent unloaded coal seams affected by mining above and below the working face goaf, overlying rocks above and below the working face goaf, and biological causes. It mainly exists in free and adsorbed states, and some of it is stored in dissolved states in stable water systems or accumulated water.

[0008] Abandoned coal mine gas extraction plays an important role in the development and utilization of abandoned coal mine gas resources. At present, abandoned coal mine gas extraction technologies mainly include ground extraction (including shaft extraction), underground closed extraction and reserved special pipeline extraction. Domestic scholars' research on abandoned coal mine gas extraction mainly focuses on well layout optimization.

[0009] The main technical problems encountered in actual projects are: 1) The cracks and fissures of the original coal seams in abandoned coal mines are not fully developed, and it is impossible to achieve safe explosion in the goaf of abandoned mines using existing technologies. The migration of gas in the goaf is blocked, and the drainage rate is low. 2) The sensors and other equipment in the casing of the drainage mine are precise, and there is a lack of efficient and safe detonation devices to protect the sensors from the impact of the explosion and ensure their work efficiency and data accuracy. 3) There is a lack of reasonable planning, layout and mining of the work area. Abandoned coal mine gas extraction wells are expensive, have low utilization rates, and have low cost-effectiveness. Summary of the invention

[0010] In view of the problems of large water consumption, insignificant hydraulic fracturing effect, few cracks in abandoned mines, insufficient gas migration, and lack of safe and efficient detonation devices in existing fracturing technologies, the present invention provides a double-extraction hole "one-delivery and one-extraction" step-by-step fissure deflagration fracturing extraction method.

[0011] In order to solve the above problems, the present invention firstly performs vertical drilling construction on the area to be mined to obtain two extraction wells A and B with appropriate distances, then uses a perforating gun to drill through the casing, and then hydraulic fracturing is performed to initially create cracks so that the two extraction holes are connected through the cracks; preliminary extraction is carried out after the fracturing fluid is discharged; after the methane concentration is reduced, the combustion aid is efficiently introduced into the cracks by utilizing the flow of the two-hole gap, and the methane is combusted and exploded to expand the cracks and then continued to be extracted, and repeated explosions can be performed; after the extraction of the two extraction hole areas is completed, a new extraction hole C is drilled at an appropriate distance along the mining direction, and combined with the extraction well B into a new "one-delivery and one-extraction" mode, and so on, to form a step-by-step mining.

[0012] The specific steps are as follows: S1. Drilling work First, the mining area is detected to determine the mining depth and rock hardness parameters. Then, a drill rod is used to drill two vertical shafts A and B from one end of the mining area. After reaching the pre-fracturing position, the drill rod is removed, and casings are lowered to form casing strings. Then, cement is transported into the casing strings to fill the space between the casing strings and the well wall to form a cement ring to fully prevent leakage. At the same time, a delivery pipeline and a methane extraction pipeline with a methane concentration sensor 1 are set up to extend into the vertical shafts A and B. The delivery pipeline is provided with a valve 1, and the methane extraction pipeline is provided with a valve 2 and a pipeline connector. Storage tanks, methane collection tanks, and a ground intelligent controller for controlling the detonation device in the wellbore are arranged on the ground. The storage tank is connected to the delivery pipeline, and the methane collection tank is connected to the methane extraction pipeline; S2, perforating gun seam making Lower the perforating guns into the vertical shafts A and B to the same horizontal position, use the perforating bullets to penetrate the casing string, cement ring and target rock, form the perforating channel, and then recover the perforating guns; S3. Hydraulic fracturing The vertical shafts A and B simultaneously transport fracturing fluid to the casing string through the storage tank and the delivery pipeline. The fracturing fluid reaches the perforation holes of the casing string for hydraulic fracturing to form fractures for methane extraction. When the pumping pressure drops to 30%, the injection of fracturing fluid is stopped. After the hydraulic fracturing is completed, the fracturing fluid is returned. S4. Methane extraction After the backflow is completed, the cracks of the vertical shafts A and B are connected, and the desorption amount of methane gas increases. At this time, the delivery pipeline and the methane extraction pipeline of the vertical shaft B are temporarily closed, and the vertical shaft A is used as the extraction tube. The delivery pipeline in the vertical shaft A is closed, the methane extraction pipeline is opened, and the methane extraction pump of the vertical shaft A is started for extraction. The methane gas is monitored in real time using a methane concentration sensor set on the methane extraction pipeline. If the concentration of the extracted methane gas is stable and remains above the preset value, it is judged that this is the stable extraction stage; S5. Cracks caused by explosion When the methane concentration in the extraction process monitored by the methane concentration sensor 1 is lower than the preset value in real time, the methane extraction pipeline of wellbore A is disconnected from the methane collection tank on the ground through the pipeline connector. The methane extraction pipeline is temporarily used as an underground gas extraction and emptying pipeline. The detonator with the methane concentration sensor 2 and the oxygen concentration sensor is lowered to the original perforating gun position. Oxygen is introduced into the casing string of wellbore B along the delivery pipeline. The negative pressure condition in the casing string quickly draws oxygen into wellbore B, and enters wellbore A through the crack between the two wellbores. The sensor reading on the detonator in wellbore A is observed. When the explosion limit of methane gas is reached, the intelligent controller on the ground controls the detonator to seal the perforation channel. After completion, the intelligent controller on the ground ignites the methane in the crack to induce combustion and explosion. S6. Continue extraction after explosion After the explosion, the original cracks become larger and form crack intersections, forks, and even more complex crack networks, causing methane to continue to overflow, thereby increasing the methane gas concentration in the shaft. At this time, the methane extraction pipeline and the methane collection tank of the wellbore A are reconnected through the pipeline connector to continue gas extraction. When the methane gas concentration decreases again, step S5 is repeated to perform methane explosion fracturing again. The above steps are repeated to achieve hydraulic fracturing and deflagration fracturing, expand and increase the cracks in the reservoir, so that more methane in the reservoir is desorbed and collected in the casing string, and transported to the well through the methane extraction pipeline until the methane extraction increase rate is less than 10%, and the fracturing and extraction operation of the layer section is terminated; S7, step-by-step drilling and extraction Seal wellbore A and drill wellbore C along the mining direction from wellbore B. If wellbore C is provided with casing, the casing in wellbore C is perforated with a perforating gun and hydraulically fractured. If wellbore C is not provided with casing, hydraulic fracture is directly performed on wellbore C to connect wellbores B and C through the cracks. Wellbore B is used as the extraction tube and C is used as the combustion-aid delivery tube. The above steps S4-S6 are repeated, and so on, to carry out the double extraction hole "one delivery and one extraction" step-by-step extraction method.

[0013] Furthermore, the distance between one side of the wellbore A and the edge of the mining area is the effective radius of hydraulic fracturing, and the distance between the other side and the wellbore B is twice the effective radius of hydraulic fracturing.

[0014] Furthermore, the distance between the wellbore C and the wellbore B is twice the effective radius of hydraulic fracturing.

[0015] Furthermore, a sealing cover is provided at the wellhead of the vertical shaft.

[0016] Furthermore, the delivery pipeline is used to deliver fracturing fluid or combustion aid.

[0017] Furthermore, the storage tank is used to store fracturing fluid or combustion aid.

[0018] Furthermore, the detonating device includes a shell and two telescopic rods, the telescopic rods are located on both sides of the bottom of the shell, and the side walls of the shell are provided with openings matching the telescopic rods. A motor is provided in the shell, and the output end of the motor is connected to gear one, the bottom of gear one is meshed with gear two, and the bottom two sides of gear two are respectively meshed with gear three, one end of the telescopic rod is connected to gear three through a screw, a nut is provided at one end of the screw close to the telescopic rod, a brake is provided on the other side of the screw, gear three is connected through a connecting rod, a clutch is provided on the side of the connecting rod close to gear three, an electric spark igniter is provided on the other end of the telescopic rod, and a magnetic locator is provided on the side wall of the shell.

[0019] The beneficial effects of the present invention are as follows: 1. The present invention realizes deflagration in shale reservoirs or abandoned mine goafs by setting up a detonation device. On the one hand, it effectively expands cracks to form crack intersections, bifurcations, or even more complex crack networks, thereby achieving effective connection between two wellbores; on the other hand, it protects sensors and other equipment in the casing from the impact of the explosion, thereby ensuring their working efficiency and data accuracy.

[0020] 2. The setting of double extraction holes, after extracting methane, uses the extraction negative pressure of the extraction holes to extract the combustion aid into the fissures, and the two holes are connected. When the extraction hole end is pumping gas, the combustion aid in the other hole section can be effectively distributed in the fissures, which is helpful for mixing with the combustion aid.

[0021] 3. Step-by-step mining, the previous combustion-supporting agent input hole is used as the methane extraction hole in the next stage, which makes full use of the drilled wells and also rationally plans and mines the working area. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the double extraction hole "one delivery and one extraction" step-by-step fissure deflagration fracturing extraction method of the present invention; Figure 2 This is a global schematic diagram of embodiment 1 of the present invention for shale reservoir extraction; Figure 3 This is a schematic diagram of embodiment 2 of the present invention for use in a part of the goaf of an abandoned mine and ground drilling; Figure 4 It is a structural schematic diagram of the detonating device of the present invention; Figure 5 This is a schematic diagram of the internal structure of the detonator; Among them: 1-storage tank; 2-valve one; 3-transmission pipeline; 4-methane concentration sensor one; 5-methane extraction pipeline; 6-valve two; 7-pipeline connector; 8-methane collection tank; 9-ground intelligent controller; 10-cable pipeline; 11-vertical shaft; 12-sealing cover; 13-casing string; 14-cement ring; 15-crack; 16-perforation channel; 17-methane concentration sensor two; 18-oxygen concentration sensor; 19-housing; 20-telescopic rod; 21-spark igniter; 22-gear one; 23-motor; 24-nut; 25-screw; 26-clutch; 27-brake; 28-magnetic positioner; 29-gear two; 30-gear three; 31-connecting rod. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Example 1 The present invention is used for extraction of shale gas S1. Drilling work First, the mining area is detected to determine the mining depth, rock hardness and other parameters. Then, two vertical shafts A and B are drilled from one end of the mining area to reach the pre-fracturing position. The distance between one side of the vertical shaft A and the edge of the mining area is about the effective radius of hydraulic fracturing, and the distance between the other side and the shaft B is twice the effective radius of hydraulic fracturing. After reaching a certain depth, the drill rod is removed, and the casing is lowered to form a casing column 13. Then, cement is transported to the casing column 13 so that it fills between the casing column 13 and the well wall to form a cement ring 14 to fully prevent leakage. At the same time, a delivery pipeline 3 is set up to transport fracturing fluid and a methane extraction pipeline 5 with a methane concentration sensor 4. The methane extraction pipeline 5 is provided with a valve 2 6 and a pipeline connector 7. A valve 2 is also set on the delivery pipeline 3. A storage tank 1 is arranged on the ground to store fracturing fluid, a methane collection tank 8 and a ground intelligent controller 9 to control the detonation device in the wellbore. S2, perforating gun seam making The perforating guns are lowered into the two wellbores A and B to the same horizontal position, and the perforating bullets are used to penetrate the casing string 13, cement ring 14 and target rock to create a perforating channel 16 several feet long. The perforating guns are then retrieved, and in order to effectively connect and overlap the hydraulic fracturing cracks of the two wellbores in the later stage, the perforating channels of the two wellbores are on the same plane; S3. Hydraulic fracturing The fracturing fluid is injected from the storage tank 1 into the casing string 13 through the delivery pipeline 3. The two wellbores A and B can be injected at the same time. The fracturing fluid reaches the perforation holes of the casing string 13 and enters the perforation channel 16 to hydraulically fracture the shale reservoir to form the fracture 15 for methane extraction. When the pumping pressure drops to 30%, the injection of the fracturing fluid is stopped, and the fracturing fluid is returned after the hydraulic fracturing is completed. S4. Methane extraction After the return flow is completed, the fracturing fissures 15 of wellbore A and B are connected, and the amount of methane gas desorption in the shale reservoir increases. At this time, the delivery pipeline 3 and the methane extraction pipeline 5 of wellbore B are temporarily blocked, and wellbore A is used as the extraction pipe. The delivery pipeline 3 of wellbore A is closed through the valve 3 of wellbore A, the methane extraction pipeline 5 is opened, and the methane extraction pump of wellbore A is started for extraction. The methane gas concentration is monitored in real time using the methane concentration sensor 4 set on the methane extraction pipeline 5; if the extracted methane gas concentration is stable and remains above the preset value, it is judged that this is the stable extraction stage; S5. Cracks caused by explosion When the methane concentration sensor 14 monitors the methane concentration in the extraction process in real time and is lower than the preset value, the extraction pipeline 5 of the wellbore A is disconnected from the methane collection tank 8 on the ground through the pipeline connector 7, and the extraction pipeline 5 is temporarily used as an underground gas extraction and emptying pipeline, and then the detonator with the methane concentration sensor 217 and the oxygen concentration sensor 18 is lowered to the original perforating gun position. A magnetic locator 28 is installed in the detonator, and its position from the perforating channel 16 is the same as the position of the locator in the original perforating gun from the perforating channel 16, so as to better locate. Then, the delivery pipeline 3 of wellbore B is disconnected from the storage tank 1 through the pipeline connector 7, and the oxygen tank is connected. Oxygen is introduced into the casing string 13 along the delivery pipeline 3. The negative pressure condition in the casing string 13 quickly sucks oxygen into wellbore B, and enters wellbore A through the crack between the two wellbores. The readings of the two sensors on the detonation device of wellbore A are observed. When the explosion limit of methane gas is reached, the ground intelligent controller 9 controls the motor 23 in the detonation device to work, driving the gear 1 22 to rotate, so that the telescopic rod 20 is synchronously extended to both sides, partially enters the perforation channel 16, and blocks the perforation channel. After completion, the ground intelligent controller 9 ignites the methane in the crack to induce combustion and explosion; S6. Continue extraction after explosion After the deflagration, the original cracks become larger and form a crack network with intersections, forks and even more complex cracks, causing methane to continue to overflow, thereby increasing the methane gas concentration in the shaft. At this time, the methane extraction pipeline 5 and the methane collection tank 8 of the wellbore A are reconnected through the pipeline connector 7 to continue gas extraction. When the methane gas concentration decreases again, step S5 is repeated to perform methane explosion fracturing again. The above steps are repeated to achieve hydraulic fracturing and explosion-induced fracturing of the shale reservoir, expand and increase the cracks in the reservoir, so that more methane in the reservoir is desorbed and collected in the casing string 13, and transported to the well through the methane extraction pipeline 5 until the methane extraction increase rate is less than 10%, and the fracturing and extraction operation of the layer section is terminated.

[0025] S7, step-by-step drilling and extraction Seal wellbore A, drill wellbore C along the mining direction at a distance twice the effective radius of the hydraulic fracturing on the other side of wellbore B, hydraulically fracture wellbore C, connect wellbores B and C through the fractured fissures, use wellbore B as the extraction tube and C as the combustion aid delivery tube, repeat steps S4 to S6, and so on, to carry out double extraction hole "one delivery and one extraction" step-by-step extraction of shale reservoirs.

[0026] Example 2 The present invention is used for extracting gas from abandoned mines S1. Drilling work First, the mining area is detected to determine the mining depth, rock hardness and other parameters. Then, two vertical shafts A and B are drilled from one end of the mining area by a drill pipe to reach the pre-fracturing position. The drill pipe is removed, and casings are lowered to form a casing column 13. Then, cement is transported to the casing column 13 so that it is filled between the casing column 13 and the well wall to form a cement ring 14 to fully prevent leakage. At the same time, a delivery pipeline 3 is set to transport combustion aids and a methane extraction pipeline 5 with a methane concentration sensor 4. The methane extraction pipeline 5 is provided with a valve 2 6 and a pipeline connector 7. A valve 2 is also provided on the delivery pipeline 3. A storage tank 1, a methane collection tank 8 and a ground intelligent controller 9 for controlling the detonation device in the wellbore are arranged on the ground. S2, perforating gun seam making The perforating guns are lowered into the two wellbores A and B to the same horizontal position, and the perforating bullets are used to penetrate the casing string 13, cement ring 14 and target rock to create a perforating channel 16 several feet long. The perforating guns are then retrieved, and in order to effectively connect and overlap the hydraulic fracturing cracks of the two wellbores in the later stage, the perforating channels of the two wellbores are on the same plane; S3. Hydraulic fracturing The fracturing fluid is injected from the storage tank 1 into the casing string 13 through the delivery pipeline 3. The two wellbores A and B can be injected at the same time. The fracturing fluid reaches the perforation holes of the casing string 13 and enters the perforation channel 16 to hydraulically fracture the shale reservoir to form the fracture 15 for methane extraction. When the pumping pressure drops to 30%, the injection of the fracturing fluid is stopped, and the fracturing fluid is returned after the hydraulic fracturing is completed. S4. Methane extraction The fracturing fissures 15 of wellbore A and B are connected, and the amount of methane gas overflowing from the abandoned mine increases. At this time, the delivery pipeline 3 and the methane extraction pipeline 5 of wellbore B are temporarily blocked, and wellbore A is used as the extraction pipe. The delivery pipeline 3 of A is closed through the valve 3 of wellbore A, the methane extraction pipeline 5 is opened, and the methane extraction pump of wellbore A is started for extraction. The methane gas concentration is monitored in real time using the methane concentration sensor 4 set on the extraction pipeline; if the extracted methane gas concentration is stable and remains above the preset value, it is judged that this is the stable extraction stage; S5. Cracks caused by explosion When the methane concentration sensor 14 monitors the methane concentration in the extraction process in real time and is lower than the preset value, the extraction pipeline 5 of the wellbore A is disconnected from the methane collection tank 8 on the ground through the pipeline connector 7, and the extraction pipeline 5 is temporarily used as an underground gas extraction and emptying pipeline, and then the detonator with the methane concentration sensor 217 and the oxygen concentration sensor 18 is lowered to the original perforating gun position. A magnetic locator 28 is installed in the detonator, and its position from the perforating channel 16 is the same as the position of the locator in the original perforating gun from the perforating channel 16, so as to better locate. Then, the delivery pipeline 3 of wellbore B is opened to introduce oxygen into the casing string 13. The negative pressure condition in the casing string 13 quickly draws oxygen into wellbore B, and enters wellbore A through the crack between the two wellbores. The readings of the two sensors on the detonation device of wellbore A are observed. When the explosion limit of methane gas is reached, the ground intelligent controller 9 controls the motor 23 in the detonation device to work, driving the gear 1 22 to rotate, so that the telescopic rod 20 extends to both sides synchronously, partially enters the perforation channel 16, and blocks the perforation channel. After completion, the ground intelligent controller 9 ignites the methane in the crack to induce combustion and explosion; S6. Continue extraction after explosion After the deflagration, the original cracks become larger and form crack intersections, forks, and even more complex crack networks, causing methane to continue to overflow, thereby increasing the methane gas concentration in the shaft. At this time, the methane extraction pipeline 5 and the methane collection tank 8 of the wellbore A are reconnected through the pipeline connector 7 to continue gas extraction. When the methane gas concentration decreases again, step S5 is repeated to perform methane explosion fracturing again. The above steps are repeated to achieve hydraulic fracturing and explosion-induced fracturing of the shale reservoir, expand and increase the cracks in the reservoir, so that more methane in the reservoir is desorbed and collected in the casing string 13, and transported to the well through the methane extraction pipeline 5 until the methane extraction increase rate is less than 10%, and the fracturing and extraction operation of the layer section is terminated.

[0027] S7, step-by-step drilling and extraction Seal wellbore A, drill wellbore C at an appropriate distance on the other side of wellbore B along the mining direction, perforate the casing in wellbore C and perform hydraulic fracturing to connect wellbores B and C through the cracks, use wellbore B as the extraction tube and C as the combustion aid delivery tube, repeat the above steps S4 to S6, and so on, to carry out the double extraction hole "one delivery and one extraction" extraction method for abandoned mines.

[0028] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A double extraction hole "one delivery and one extraction" step-by-step fissure deflagration extraction method, characterized in that: The steps include: S1. Drilling work First, the mining area is detected to determine the mining depth and rock hardness parameters. Then, a drill rod is used to drill two vertical shafts A and B from one end of the mining area. After reaching the pre-fracturing position, the drill rod is removed and casing is lowered to form a casing column (13). Then, cement is transported into the casing column (13) so that it fills between the casing column (13) and the well wall to form a cement ring (14) to fully prevent leakage. At the same time, a delivery pipeline (3) and a methane extraction pipeline (5) with a methane concentration sensor (4) are arranged to extend into the vertical shafts A and B. The delivery pipeline (3) is provided with a valve (2). The methane extraction pipeline (5) is provided with a valve (6) and a pipeline connector (7). A storage tank (1), a methane collection tank (8) and a ground intelligent controller (9) for controlling the detonation device in the wellbore are arranged on the ground. The storage tank (1) is connected to the delivery pipeline (3), and the methane collection tank (5) is connected to the methane extraction pipeline (5); S2, perforating gun seam making Lowering perforating guns into the vertical shafts A and B to the same horizontal position, using perforating bullets to penetrate the casing string (13), cement sheath (14) and target rock to form perforating channels (16), and then recovering the perforating guns; S3. Hydraulic fracturing The vertical shafts A and B simultaneously convey fracturing fluid through the storage tank (1) and the conveying pipeline (3) to the casing string (13). The fracturing fluid reaches the perforation channel (16) of the casing string (13) and is hydraulically fractured to form fractures (15) for methane extraction. When the pumping pressure drops to 30%, the injection of the fracturing fluid is stopped. After the hydraulic fracturing is completed, the fracturing fluid is returned. S4. Methane extraction After the backflow is completed, the fissures (15) of wellbore A and B are connected, and the amount of methane gas desorption increases. At this time, the delivery pipeline (3) and the methane extraction pipeline (5) of wellbore B are temporarily closed, and wellbore A is used as the extraction tube. The delivery pipeline (3) in wellbore A is closed, the methane extraction pipeline (5) is opened, and the methane extraction pump of wellbore A is started for extraction. The methane gas is monitored in real time using a methane concentration sensor (4) provided on the methane extraction pipeline (5). If the extracted methane gas concentration is stable and remains above a preset value, it is determined that this is the stable extraction stage. S5. Cracks caused by explosion When the methane concentration during the extraction process monitored in real time by the methane concentration sensor 1 (4) is lower than the preset value, the methane extraction pipeline (5) of the wellbore A is disconnected from the methane collection tank (8) on the ground through the pipeline connector (7), and the methane extraction pipeline (5) is temporarily used as an underground gas extraction and emptying pipeline. The detonator with the methane concentration sensor 2 (17) and the oxygen concentration sensor (18) is lowered to the original perforating gun position, and oxygen is introduced into the casing string (13) of the wellbore B along the conveying pipeline (3). The negative pressure condition in the casing string (13) quickly draws the oxygen into the wellbore B, and enters the wellbore A through the crack between the two wellbores. The sensor reading on the detonator in the wellbore A is observed. When the methane gas reaches the explosion limit range, the ground intelligent controller (9) controls the detonator to block the perforation channel (16). After completion, the ground intelligent controller (9) ignites the methane in the crack to induce combustion and explosion. S6. Continue extraction after explosion After the explosion, the original cracks become larger and form a crack network with intersections, forks, or even more complex cracks, so that methane continues to overflow, thereby increasing the methane gas concentration in the shaft. At this time, the methane extraction pipeline (5) and the methane collection tank (8) of the wellbore A are reconnected through the pipeline connector (7) to continue gas extraction. When the methane gas concentration decreases again, step S5 is repeated to perform methane explosion fracturing again. The above steps are repeated to achieve hydraulic fracturing and explosion fracturing, expand and increase the cracks in the reservoir, so that more methane in the reservoir is desorbed and collected in the casing string (13), and transported to the well through the methane extraction pipeline (5) until the methane extraction volume increase rate is less than 10%, and the fracturing and extraction operation is terminated; S7, step-by-step drilling and extraction Seal the wellbore A, and drill the wellbore C in the wellbore B along the mining direction. If there is a casing in the wellbore C, the casing in the wellbore C is perforated with a perforating gun and hydraulically fractured. If there is no casing in the wellbore C, hydraulically fracture the wellbore C directly to connect the wellbores B and C through the cracks. Use the wellbore B as the extraction tube and C as the combustion-aid delivery tube, repeat steps S4-S6, and so on, to carry out the double extraction hole "one delivery and one extraction" step-by-step extraction method.

2. A double extraction hole "one delivery and one extraction" step-by-step fissure deflagration extraction method according to claim 1, characterized in that: The distance between one side of the wellbore A and the edge of the mining area is the effective radius of hydraulic fracturing, and the distance between the other side and the wellbore B is twice the effective radius of hydraulic fracturing.

3. A double extraction hole "one delivery and one extraction" step-by-step fissure deflagration extraction method according to claim 1, characterized in that: The distance between the wellbore C and the wellbore B is twice the effective radius of hydraulic fracturing.

4. A double extraction hole "one delivery and one extraction" step-by-step fissure deflagration extraction method according to claim 1, characterized in that: A sealing cover (12) is provided at the wellhead of the vertical shaft.

5. A double extraction hole "one delivery and one extraction" step-by-step fissure deflagration extraction method according to claim 1, characterized in that: The delivery pipeline (3) is used to deliver fracturing fluid or combustion aid.

6. A double extraction hole "one delivery and one extraction" step-by-step fissure deflagration extraction method according to claim 1, characterized in that: The storage tank (1) is used to store fracturing fluid or combustion aid.

7. A double extraction hole "one delivery and one extraction" step-by-step fissure deflagration extraction method according to claim 1, characterized in that: The detonating device comprises a housing (19) and two telescopic rods (20), wherein the telescopic rods (20) are located at two sides of the bottom of the housing (19), and the side wall of the housing (19) is provided with openings matching the telescopic rods (20). A motor (23) is provided in the housing (19), and the output end of the motor (23) is connected to a gear 1 (22), the bottom of the gear 1 (22) is meshed with a gear 2 (29), and the two sides of the bottom of the gear 2 (29) are respectively meshed with gears 3 (30), and the telescopic rods (20) are provided with a plurality of openings matching the telescopic rods (20). One end of the telescopic rod (20) is connected to the gear three (30) by a screw (25), a nut (24) is provided at one end of the screw (25) close to the telescopic rod (20), a brake (27) is provided at the other side of the screw (25), the gear three (30) is connected by a connecting rod (31), a clutch (26) is provided at one side of the connecting rod (31) close to the gear three (30), an electric spark igniter (21) is provided at the other end of the telescopic rod (20), and a magnetic locator (28) is provided on the side wall of the housing (19).

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