Vertical separate layer fracturing extraction method for coal-bed gas well

Abstract

The invention discloses a coal-bed gas well vertical layering fracturing extraction method. The method comprises the following steps that S1, a vertical shaft is constructed in a mining area; s2, a plurality of layers of radial extraction sections are constructed in the coal reservoir in the vertical shaft; s3, a casing pipe is put into the vertical shaft for well cementation, and meanwhile an extraction screen pipe is arranged in the radial extraction section; s4, fracturing anti-reflection operation is conducted on the multiple layers of radial extraction sections; and S5, coal bed gas extraction operation is conducted on the multiple layers of radial extraction sections from top to bottom, and meanwhile water gathered into the bottom of the vertical shaft and deposited coal powder are extracted upwards. According to the method, the principle is scientific, the multiple layers of radial extraction sections are evenly arranged in the circumferential direction of the vertical shaft, the method is particularly suitable for a thick coal reservoir, meanwhile, the extraction range of the vertical shaft in the radial direction is extended, the single-well extraction yield is increased, and therefore economy, high efficiency, safety and stability of coal bed gas extraction are guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane development, and particularly relates to a vertical layered fracturing and extraction method for coalbed methane wells. Background Art

[0002] Coalbed Methane (CBM), commonly known as "gas", is an unconventional natural gas mainly composed of methane (CH4), adsorbed on the surface of coal matrix particles or free in coal pores, and is an associated mineral resource of coal.

[0003] For high-gas coal reservoirs, it is necessary to extract gas before coal mining, which not only improves the safety of coal mining operations, but also can concentrate and extract high-purity gas. At present, vertical wells (shaft wells) in the gas extraction of high-gas coal reservoirs are the earliest and most widely used well types in coalbed methane development, with low costs. Although vertical wells can be applied to the gas extraction of relatively thick coal reservoirs, the single-well output is generally low (only the extraction can be carried out within a small radius centered on the vertical well). Therefore, simple vertical wells are suitable for medium-high permeability coal seams. Therefore, in order to increase the single-well output and for relatively thick coal reservoirs, it is necessary to optimize and improve the gas extraction of existing vertical wells. Summary of the Invention

[0004] The purpose of the present invention is to provide a vertical layered fracturing and extraction method for coalbed methane wells with a large extraction range, good extraction effect, and suitable for relatively thick coal reservoirs.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions: A vertical layered fracturing and extraction method for coalbed methane wells, comprising the following steps: S1. Construct a vertical well in the mining area, the vertical well vertically penetrates the coal reservoir downward, and the lower end of the vertical well extends into the rock layer below the coal reservoir; S2. Construct several radial extraction sections in the vertical well towards the coal reservoir; S3. Lower a casing into the vertical well for cementing, and at the same time, arrange extraction screen pipes inside the radial extraction sections. Through holes corresponding to each layer of radial extraction sections are opened on the casing, the inner end of the extraction screen pipe is fixedly connected to the outer circle of the casing, and each extraction screen pipe is communicated with the inside of the casing through one of the through holes; S4. Conduct fracturing and permeability enhancement operations on several layers of radial extraction sections respectively; S5. Conduct coalbed methane extraction operations on several layers of radial extraction sections from top to bottom respectively, and at the same time, pump the water and deposited coal powder flowing into the bottom of the vertical well upward.

[0006] In step S2, several radial drainage sections are evenly arranged in the height direction. Each radial drainage section includes four drainage holes arranged in a circular array around the central line of the shaft. The drainage holes are inclined from high to low along the central line direction; when the vertical projections of any two adjacent radial drainage sections are on the same plane, the included angle between two adjacent drainage holes is 45°; A drainage screen pipe as described above is provided in each drainage hole. A filter hole plate is provided at the outer port of the drainage screen pipe. The inner diameter of the drainage screen pipe is smaller than the diameter of the through hole; the lowest position of the inner port of the drainage screen pipe is lower than the lowest position of the through hole; A number of water guide pipes are evenly provided on the circumferential direction of the casing wall at the interface between the coal reservoir and the rock layer. The outer end of the water guide pipe extends into the coal reservoir. A stainless steel filter screen is provided at the outer port of the water guide pipe. The inner end of the water guide pipe passes through the casing and is flush with the inner circle of the casing.

[0007] During the fracturing and permeability enhancement operation in step S4, a sealed diversion and gas distribution device is arranged in the casing. An air injection pump is used on the ground to extract fracturing gas (nitrogen or carbon dioxide) and inject the fracturing gas into the sealed diversion and gas distribution device through a fracturing gas transmission pipe. The sealed diversion and gas distribution device then simultaneously introduces the fracturing gas into each drainage screen pipe of the same layer of radial drainage section. The fracturing gas fractures the coal body through the screen holes, increases the pores and fractures of the coal body, and improves the permeability of the coal seam; The sealed diversion and gas distribution device includes a fracturing cylinder with its central line coinciding with the central line of the casing. An upper cover plate and a lower cover plate are respectively fixed at the upper and lower ends of the fracturing cylinder. An upper fracturing annular sealing bag and a lower fracturing annular sealing bag are respectively fixed on the upper and lower parts of the outer circle of the fracturing cylinder. An upper partition plate and a lower partition plate are horizontally arranged in the fracturing cylinder. The upper partition plate and the lower partition plate divide the interior of the fracturing cylinder into an upper cavity, a middle cavity, and a lower cavity. An air injection hole is opened on the fracturing cylinder between the upper partition plate and the lower partition plate. A main air injection pipe connected to the fracturing gas transmission pipe is provided at the center of the upper cover plate. The lower end of the main air injection pipe passes through the upper cavity and is fixedly connected to the upper partition plate. The interior of the main air injection pipe is communicated with the interior of the middle cavity. An upper air supply device connected to the upper fracturing annular sealing bag is arranged in the upper cavity, and a lower air supply device connected to the lower fracturing annular sealing bag is arranged in the lower cavity.

[0008] The upper air supply device and the lower air supply device have the same structure. Both include a first air pump. The air outlet of the first air pump is connected to a first air charging pipe. The outlet end of the first air charging pipe passes through the fracturing cylinder and is connected to the fracturing annular sealing bag. A first pressure sensor and a first air charging solenoid valve are sequentially installed on the first air charging pipe along the air flow direction. A first exhaust pipe joint is connected to the first air charging pipe between the first air charging solenoid valve and the fracturing annular sealing bag. A first exhaust solenoid valve is provided on the first exhaust pipe joint; A number of rollers rollingly connected to the inner circle of the casing are provided on both the upper cover plate and the lower cover plate. At least three lifting rings are evenly arranged on the upper cover plate along the circumferential direction; A water permeable pipe is vertically arranged between the upper cover plate and the lower cover plate. The water permeable pipe passes through the upper partition plate and the lower partition plate, and the center line of the water permeable pipe is parallel to the center line of the fracturing cylinder. An upper wire passing pipe parallel to and in contact with the main gas injection pipe is connected to the upper cover plate. The lower port of the upper wire passing pipe communicates with the inside of the upper cavity. A lower wire passing pipe passing through the hollow cavity is arranged between the upper partition plate and the lower partition plate.

[0009] During the coalbed methane extraction operation in step S5, a sealed gas gathering and extraction device that is simultaneously connected to the inner ports of the extraction screen pipes in the same radial extraction section is arranged in the casing. An extraction pump is arranged on the ground. The extraction pump is connected to the top of the sealed gas gathering and extraction device through an extraction main pipe. Under the suction of the extraction pump, the coalbed methane inside the coal reservoir is pumped to the underground gas storage or LNG plant for storage through the sealed gas gathering and extraction device. The sealed gas gathering and extraction device includes an extraction cylinder whose center line coincides with the center line of the casing. An upper sealing plate and a lower sealing plate are respectively fixedly arranged at the upper end and the lower end of the extraction cylinder. An extraction annular sealing bag is respectively fixedly arranged at the upper part and the lower part of the outer circle of the extraction cylinder. An upper flat plate and a lower flat plate are horizontally arranged in the extraction cylinder. The upper flat plate and the lower flat plate divide the inside of the extraction cylinder into an upper chamber, a middle chamber and a lower chamber. Extraction holes are opened on the extraction cylinder between the upper flat plate and the lower flat plate. An extraction connection pipe connected to the extraction main pipe is arranged at the center of the upper sealing plate. The lower end of the extraction connection pipe passes through the upper chamber and is fixedly connected to the upper flat plate. The inside of the extraction connection pipe communicates with the inside of the middle chamber. A first air supply device connected to the upper extraction annular sealing bag is arranged in the upper chamber, and a second air supply device connected to the lower extraction annular sealing bag is arranged in the lower chamber.

[0010] The first air supply device and the second air supply device have the same structure. Both include a second air pump. The air outlet of the second air pump is connected to a second air charging pipe. The outlet end of the second air charging pipe passes through the extraction cylinder and is connected to the extraction annular sealing bag. A second pressure sensor and a second air charging solenoid valve are installed on the second air charging pipe. A second exhaust pipe joint is connected to the second air charging pipe between the second air charging solenoid valve and the extraction annular sealing bag. A second exhaust solenoid valve is arranged on the second exhaust pipe joint. A number of guide wheels rollingly connected to the inner circle of the casing are arranged on both the upper sealing plate and the lower sealing plate. At least three hanging rings are evenly arranged along the circumferential direction on the upper cover plate. A vertically penetrating water pipe is arranged between the upper sealing plate and the lower sealing plate. The water pipe passes through the upper sealing plate and the lower sealing plate, and the center line of the water pipe is parallel to the center line of the extraction cylinder. A first wire passing pipe parallel to and in contact with the extraction connection pipe is connected to the upper sealing plate. The lower port of the first wire passing pipe communicates with the inside of the upper chamber. A second wire passing pipe passing through the middle chamber is arranged between the upper sealing plate and the lower sealing plate. A wire passing hole corresponding to the second wire passing pipe up and down is opened on the lower sealing plate.

[0011] In step S5, the water and sedimented pulverized coal flowing into the bottom of the shaft are pumped upward by arranging a submersible pump and an anti-sediment agitation device in a casing at the bottom of the shaft; The anti-sediment agitation device includes a support ring, a motor reducer, an installation box, a stirring shaft, an upper support and a lower support. The outer diameter of the support ring is equal to the inner diameter of the casing. The support ring is coaxially and fixedly arranged on the inner wall of the casing. The installation box is fixedly arranged on the support ring. The motor reducer is arranged in the installation box. The stirring shaft is arranged vertically. Both the upper support and the lower support are fixedly connected to the inner wall of the casing. The upper and lower parts of the stirring shaft are respectively rotationally connected to the upper support and the lower support through waterproof bearings. A number of stirring rods are fixedly arranged on the stirring shaft. The upper end of the stirring shaft passes through the bottom of the installation box and extends into the installation box. A positioning bearing is arranged in the installation box and is rotationally connected to the stirring shaft. A main gear is installed on the main shaft of the motor reducer. A driven gear meshing with the main gear is installed on the stirring shaft. A downcomer vertically passing through the installation box is arranged in the installation box. A water collecting hopper with a large upper part and a small lower part and communicating with the upper port of the downcomer is arranged at the top of the installation box. The upper edge of the water collecting hopper is connected to the inner wall of the casing; An installation frame is arranged on the inner wall of the casing. The submersible pump is arranged on the installation frame. The outlet of the submersible pump extends to the ground through a vertically arranged drain pipe. The lower part of the drain pipe is fixedly connected to the inner wall of the casing through a connecting plate. The drain pipe is parallel to the center line of the casing in the casing. The outer diameter of the drain pipe is smaller than the inner diameters of the water passing pipe and the downcomer. The drain pipe passes through the downcomer and the water passing pipe.

[0012] The specific process of the fracturing and permeability enhancement operation in step S4 is as follows: At the shaft wellhead, a hoisting device (winch) is used to hook and connect the lifting ring at the top of the sealed diversion gas distribution device, connect the gas injection pump, the fracturing gas storage tank, the fracturing gas transmission pipe and the gas injection main pipe. According to the distance between each radial extraction section and the shaft wellhead recorded during construction, the hoisting device lowers the sealed diversion gas distribution device along the casing to the uppermost radial extraction section. At this time, the inner ports of the four extraction screen pipes are both located between the upper and lower fracturing annular sealing capsules. The hoisting device is closed, and then two first air pumps are started. The first air pumps fill the fracturing annular sealing capsules with air through the first air filling pipes. The fracturing annular sealing capsules expand radially. The pressure signals monitored in real time by the first pressure sensors are transmitted to the PLC controller on the ground. When the inflation pressure reaches the set pressure value, the PLC controller issues a closing command to the first air pumps and the first air filling solenoid valves. The fracturing annular sealing capsules seal the annular gap between the outer circle of the fracturing cylinder and the inner circle of the casing. Then, the valve of the fracturing gas storage tank is opened, and the gas injection pump is started. The gas injection pump extracts the fracturing gas in the fracturing gas storage tank and injects it into the extraction screen pipes in sequence through the fracturing gas transmission pipe, the gas injection main pipe, the hollow cavity, the gas injection holes, and the through holes. The high-pressure fracturing gas is injected into the coal reservoir through the screen holes on the extraction screen pipes to fracture the coal body, increase the pores and fractures of the coal body, and enhance the permeability of the coal seam; The pressure of the injected high-pressure fracturing gas is controlled between 50 - 70 MPa, and the injection speed should be controlled at 2 - 3 m3 Inject high-pressure fracturing gas for 3 - 10 days at [X] / min. After the fracturing of the uppermost layer of the radial extraction section is completed, turn off the gas injection pump, and the PLC controller sends a command to open the first exhaust solenoid valve. The high-pressure gas in the fracturing annular seal bladder is discharged through the first charging pipe and the first exhaust pipe joint, and the outer circle of the fracturing annular seal bladder no longer contacts the inner wall of the casing. Then, start the lifting device, lower the sealed diversion gas distribution device to the second layer of the radial extraction section, and perform gas injection fracturing on the second layer of the radial extraction section in the same operation mode as the fracturing process of the uppermost layer of the radial extraction section. After the fracturing is completed, move downward in turn to perform gas injection fracturing on other layers of the radial extraction section until all layers of the radial extraction section are fractured. Then, the lifting device lifts the sealed diversion gas distribution device to the ground to complete the fracturing permeability enhancement operation.

[0013] The specific process of coalbed methane extraction operation in step S5 is as follows: After the fracturing permeability enhancement operation is completed, remove the sealed diversion gas distribution device from the steel wire rope of the lifting device, and then hang the hanging ring at the top of the sealed gas-gathering extraction device on the steel wire rope hook of the lifting device. Connect the extraction pump, the extraction gas storage tank, the extraction main pipe, and the extraction connecting pipe, according to the distance between each layer of the radial extraction section and the shaft wellhead recorded during the construction; The hoisting device lowers the sealed gas gathering and extraction device downward along the casing to the uppermost radial extraction section. At this time, the inner ports of the four extraction screen pipes are all located between the upper and lower extraction annular sealing sacs. The hoisting device is closed, and then two second air pumps are started. The second air pumps fill the extraction annular sealing sac with air through the second charging pipe. The extraction annular sealing sac expands radially. The pressure signal monitored in real time by the second pressure sensor is transmitted to the PLC controller on the ground. When the inflation pressure reaches the set pressure value, the PLC controller issues a closing command to the second air pump and the second inflation solenoid valve. The extraction annular sealing sac seals the annular gap between the outer circumference of the extraction cylinder and the inner circumference of the casing. Then, the extraction pump is turned on. The extraction pump extracts coalbed methane inside the extraction screen pipes through the extraction main pipe, the extraction connecting pipe, the middle chamber, the extraction holes, and the through holes. The coalbed methane in the coal reservoir overflows through the fractures formed by hydraulic fracturing and enters the extraction screen pipes through the screen holes and is pumped by the extraction pump to the underground gas storage or the LNG plant for storage; a flow meter is arranged on the extraction main pipe to monitor the flow rate of the extracted coalbed methane. When the flow rate is less than 0.04 m³ / min, it indicates that the extraction operation of the uppermost radial extraction section is completed. The extraction pump is closed, and the PLC controller issues an opening command to the second exhaust solenoid valve. The high-pressure gas in the extraction annular sealing sac is discharged through the second charging pipe and the second exhaust pipe joint. The outer circumference of the extraction annular sealing sac no longer contacts the inner wall of the casing. Then, the hoisting device is started, and the sealed gas gathering and extraction device is lowered to the second radial extraction section. According to the operation mode of the coalbed methane extraction process for the uppermost radial extraction section, the coalbed methane extraction operation is carried out for the second radial extraction section. After the extraction is completed, it is moved downward to sequentially carry out the coalbed methane extraction for other radial extraction sections until the extraction operations for all radial extraction sections are completed. The hoisting device lifts the sealed gas gathering and extraction device to the ground to complete the coalbed methane extraction operation.

[0014] The submersible pump and the anti-sediment agitation device are installed after the casing cementing in step (3). Since each extraction screen pipe in each radial extraction section is arranged with an inner high and outer low inclination, and a number of extraction screen holes are provided on the extraction screen pipe, the water that infiltrates into the extraction screen pipe from the coal reservoir above the extraction holes will continue to seep downward, and the water will not be discharged into the casing from the inner port of the extraction screen pipe. The water in the coal reservoir deposits on the rock formation and finally flows into and gathers in the lower space of the casing through the water guide pipe, carrying coal powder. The specific process of pumping the water and the deposited coal powder that have gathered at the bottom of the shaft upward is as follows: The motor reducer drives the stirring shaft to rotate through the meshing main gear and driven gear. The stirring rods on the stirring shaft stir up the coal powder deposited at the bottom of the casing. The submersible pump pumps the coal powder mixed water through the drain pipe to the ground.

[0015] Adopting the above technical solution, compared with the prior art, the present invention has the following technical effects: (1) In the present invention, multiple radial drainage sections are evenly arranged from top to bottom in the coal reservoir. Each radial drainage section includes drainage holes with an included angle of 90°. In this way, a farther drainage range can be radiated radially through the vertical shaft, thereby increasing the single-well drainage volume. When the vertical projections of any two adjacent radial drainage sections are on a plane, the included angle between two adjacent drainage holes is 45°. Such a structural arrangement can minimize the number of drainage holes opened, and at the same time, make the drainage radiation range of each drainage hole as uniform as possible. The cylindrical area with the vertical shaft as the center line is more balanced during the operations of hydraulic fracturing for permeability enhancement and coalbed methane drainage, with basically no dead corners.

[0016] (2) A drainage screen pipe is arranged in the drainage hole. It can not only support the drainage hole to prevent cave-ins, but also has a number of evenly distributed screen holes. When injecting fracturing gas, it can be injected into the coal reservoir through the screen holes. When draining coalbed methane, the gas in the coal reservoir can enter the drainage screen pipe through the screen holes and be pumped out. The setting of the filter hole plate improves the permeability between the drainage screen pipe and the coal reservoir, and at the same time blocks the coal body from entering the drainage screen pipe.

[0017] (3) A number of water guide pipes are evenly arranged in the circumferential direction at the lower part of the casing. The water in the coal reservoir seeps down to the top of the rock formation and no longer seeps down along the rock formation, but converges into the inside of the casing through the water guide pipes. At the same time, coal powder will also flow into the casing through the water guide pipes. Therefore, a submersible pump and an anti-sediment stirring device are arranged in the water storage space at the bottom of the casing. The anti-sediment stirring device stirs up the coal powder that is insoluble in water, and the submersible pump pumps the coal powder mixed water to the ground.

[0018] (4) Each drainage screen pipe is arranged in an inclined manner with the outer part lower and the inner part higher, to prevent the water seeping into the drainage screen pipe from flowing towards the inner port of the drainage screen pipe. Since the inner diameter of the drainage screen pipe is smaller than the diameter of the through hole and the lowest position of the inner port of the drainage screen pipe is lower than the lowest position of the through hole, this structure further prevents the water in the drainage screen pipe from entering the through hole on the casing through the inner port of the drainage screen pipe. To prevent the coal body from entering the drainage screen pipe through the screen holes, a number of hemispherical support ventilation nets can be fixedly welded on the outer circumference of the drainage screen pipe, and each hemispherical support ventilation net covers a screen hole. In this way, it can not only support the coal body, but also not reduce the ventilation area between the screen hole and the coal body. The sum of the outer diameter of the drainage screen pipe and the diameter of the hemispherical support ventilation net should be slightly smaller than the inner diameter of the drainage hole. In this way, it is not only convenient to install the drainage screen pipe into the drainage hole. According to the principle of borehole pressure relief, there is an annular space between the outer circumference of the drainage screen pipe inserted into the drainage hole and the inner circumference of the drainage hole, providing a larger pressure relief space for the coal body, thereby improving the safety during the process of coalbed methane drainage. The drainage screen pipe is provided with several sections, and adjacent sections are connected by threads.

[0019] (5) The two fracturing annular sealing capsules of the sealed diversion gas distribution device are made of rubber. Annular shallow grooves are respectively formed in the upper and lower parts of the outer circumference of the fracturing cylinder. The inner diameter of the fracturing annular sealing rubber capsule is equal to the bottom diameter of the annular shallow groove. The fracturing annular sealing rubber capsule is sleeved in the annular shallow groove and has good stability in the axial direction. After the fracturing annular sealing rubber capsule is inflated and expanded, its inner circle and outer circle are respectively tightly pressed against the annular shallow groove and the inner circle of the casing, having a good sealing effect. The upper wire pipe is used to thread the cables for supplying power and transmitting signals to the upper gas supply device and the lower gas supply device. The lower wire pipe is used to thread the cables for supplying power and transmitting signals to the lower gas supply device. The rollers are used to play a good guiding role when the sealed diversion gas distribution device moves up and down in the casing, avoiding abrasion of the fracturing annular sealing rubber capsule. The main function of the water permeable pipe is to pass through the drain pipe that pumps the water stored at the bottom of the casing upward. The outer diameter of the drain pipe is smaller than the inner diameter of the water permeable pipe. Therefore, the gap between the drain pipe and the water permeable pipe can pass the flowing water.

[0020] (6) The overall structure of the sealed gas gathering and extraction device is the same as that of the sealed diversion gas distribution device. In terms of function, one is for injection fracturing and the other is for extracting coalbed methane. The two extraction annular sealing capsules of the sealed gas gathering and extraction device are made of rubber. Annular shallow grooves are respectively formed in the upper and lower parts of the outer circumference of the extraction cylinder. The inner diameter of the extraction annular sealing rubber capsule is equal to the bottom diameter of the annular shallow groove. The extraction annular sealing rubber capsule is sleeved in the annular shallow groove and has good stability in the axial direction. After the extraction annular sealing rubber capsule is inflated and expanded, its inner circle and outer circle are respectively tightly pressed against the annular shallow groove and the inner circle of the casing, having a good sealing effect. The first wire pipe is used to thread the cables for supplying power and transmitting signals to the first gas supply device and the second gas supply device. The second wire pipe is used to thread the cables for supplying power and transmitting signals to the second gas supply device. The guide wheels are used to play a good guiding role when the sealed gas gathering and extraction device moves up and down in the casing, avoiding abrasion of the extraction annular sealing rubber capsule. The main function of the water passing pipe is to pass through the drain pipe that pumps the water stored at the bottom of the casing upward. The outer diameter of the drain pipe is smaller than the inner diameter of the water passing pipe. Therefore, the gap between the drain pipe and the water passing pipe can pass the flowing water.

[0021] (7) The setting of the anti-precipitation agitation device avoids the precipitation of pulverized coal at the bottom of the casing. The anti-precipitation agitation device uses a motor reducer to drive the stirring shaft and the stirring rod to rotate. The stirring rod stirs up the pulverized coal in the water, and the pulverized coal mixed water is pumped to the ground together by a high-lift submersible pump, and then the pulverized coal is filtered out after precipitation. The center lines of the submersible pump and the stirring shaft are both arranged deviating from the center line of the casing, rather than being arranged vertically up and down, so that the stirred pulverized coal can be quickly pumped away by the submersible pump. For energy conservation, the motor reducer can operate intermittently. The setting of the downcomer enables the water above to flow into the water storage position at the lower part of the casing through the downcomer when it falls on the water collecting hopper.

[0022] In summary, the present invention uses a construction shaft. In the coal reservoir section within the shaft, it is evenly divided into several radial extraction sections along the height direction according to the thickness. Taking the shaft as the center line, each radial extraction section includes four extraction holes with an included angle of 90°. The adjacent extraction holes in the upper and lower layers are staggered. Then, a casing is lowered into the shaft and cemented. An extraction screen pipe is lowered into the extraction hole. Next, carbon dioxide or nitrogen is injected into the four extraction screen pipes in each radial extraction section to fracture and enhance the permeability of the coal reservoir (multiple sealed diversion and gas distribution devices can also be used to fracture and enhance the permeability of multiple radial extraction sections simultaneously). Of course, high-pressure water injection can also be used for hydraulic fracturing (without gas injection to improve the purity of the extracted coalbed methane). Then, the coalbed methane in each radial extraction section is extracted (multiple sealed gas gathering and extraction devices can also be used to extract multiple radial extraction sections simultaneously). At the same time, the temporarily stored water and pulverized coal at the bottom of the shaft are pumped to the ground.

[0023] The principle of the present invention is scientific. By evenly arranging several radial extraction sections in the circumferential direction of the shaft, it is particularly suitable for relatively thick coal reservoirs, while extending the extraction range of the shaft in the radial direction and increasing the single-well extraction output, thus ensuring the economic, efficient, safe, and stable exploitation of coalbed methane. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic elevational sectional structure view of the present invention; Figure 2 is Figure 1 the A-A sectional view in Figure 3 is Figure 1 the B-B sectional view in Figure 4 is Figure 1 the enlarged view of part C in Figure 5 is Figure 1 the enlarged view of part D in Figure 6 is Figure 1 the partial enlarged view of the extraction screen pipe in Figure 7 is the structural schematic view of the sealed diversion and gas distribution device; Figure 8 is the cross-sectional schematic view of the semi-circular pipe arranged outside the casing. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following further describes in detail the embodiments of the present invention in conjunction with the drawings and embodiments.

[0026] As Figures 1-7 shown, the method for vertical layered fracturing and extraction of coalbed methane wells of the present invention includes the following steps: S1. Construct a vertical shaft in the mining area. The vertical shaft vertically penetrates the coal reservoir 1 downward, and the lower end of the vertical shaft extends into the rock layer 2 below the coal reservoir 1. S2. Construct several radial extraction sections in the vertical shaft towards the coal reservoir 1. S3. Lower a casing 3 into the vertical shaft for cementing. At the same time, set extraction screen pipes 4 inside the radial extraction sections. Through holes 5 corresponding to and penetrating each layer of radial extraction sections are opened on the casing 3. The inner end of the extraction screen pipe 4 is fixedly connected to the outer circle of the casing 3. Each extraction screen pipe 4 is communicated with the inside of the casing 3 through one of the through holes 5. S4. Conduct fracturing and permeability enhancement operations on several layers of radial extraction sections respectively. S5. Conduct coalbed methane extraction operations on several layers of radial extraction sections from top to bottom respectively. At the same time, pump the water and deposited coal powder that flow into the bottom of the vertical shaft upward.

[0027] In step S2, several layers of radial extraction sections are evenly arranged in the height direction. Each layer of radial extraction section includes four extraction holes 6 arranged in a circular array around the central axis of the vertical shaft. The extraction holes 6 are inclined with the inner part higher and the outer part lower along the central axis direction. When the vertical projections of any two adjacent layers of radial extraction sections are on the same plane, the included angle between two adjacent extraction holes 6 is 45°. One of the extraction screen pipes 4 is arranged in each extraction hole 6. A filter hole plate is arranged at the outer port of the extraction screen pipe 4. The inner diameter of the extraction screen pipe 4 is smaller than the diameter of the through hole 5. The lowest position of the inner port of the extraction screen pipe 4 is lower than the lowest position of the through hole 5. A number of circular screen holes 71 are evenly opened on the extraction screen pipe 4. In order to prevent coal bodies from entering the extraction screen pipe 4 through the screen holes 71, several hemispherical support and ventilation meshes 72 can be fixedly welded on the outer circle of the extraction screen pipe 4. Each hemispherical support and ventilation mesh 72 covers one screen hole 71. In this way, it can not only support the coal bodies, but also not reduce the ventilation area between the screen holes 71 and the coal bodies.

[0028] A number of water conduits 7 are evenly arranged along the circumferential direction at the interface between the coal reservoir 1 and the rock layer on the pipe wall of the casing 3. The water conduits 7 are inclined with the outer part higher and the inner part lower. The outer end of the water conduit 7 extends into the coal reservoir 1. A stainless steel filter screen is arranged at the outer port of the water conduit 7. The inner end of the water conduit 7 passes through the casing 3 and is flush with the inner circle of the casing 3.

[0029] During the fracturing and permeability enhancement operation in step S4, a sealed diversion and gas distribution device is arranged in the casing 3. On the ground, an air injection pump is used to extract fracturing gas (nitrogen or carbon dioxide) and inject the fracturing gas into the sealed diversion and gas distribution device through a fracturing gas pipeline. The sealed diversion and gas distribution device then simultaneously passes the fracturing gas into each extraction screen pipe 4 of the same layer of radial extraction section. The fracturing gas fractures the coal bodies through the screen holes 71, increases the pores and fractures of the coal bodies, and improves the permeability of the coal seam. The sealed diversion gas distribution device includes a fracturing cylinder 9 whose center line coincides with the center line of the casing 3. An upper cover plate 10 and a lower cover plate 11 are respectively fixed at the upper and lower ends of the fracturing cylinder 9. An upper and a lower fracturing annular sealing bladder 12 are respectively fixed on the upper and lower parts of the outer circle of the fracturing cylinder 9. An upper partition plate 13 and a lower partition plate 14 are horizontally arranged inside the fracturing cylinder 9. The upper partition plate 13 and the lower partition plate 14 divide the inside of the fracturing cylinder 9 into an upper cavity 15, a middle cavity 16 and a lower cavity 17. An air injection hole 18 is opened on the fracturing cylinder 9 between the upper partition plate 13 and the lower partition plate 14. At the center of the upper cover plate 10, an air injection main pipe 19 connected to the fracturing gas transmission pipe is provided. The lower end of the air injection main pipe 19 passes through the upper cavity 15 and is fixedly connected to the upper partition plate 13. The inside of the air injection main pipe 19 is communicated with the inside of the middle cavity 16. An upper air supply device connected to the upper fracturing annular sealing bladder 12 is arranged in the upper cavity 15, and a lower air supply device connected to the lower fracturing annular sealing bladder 12 is arranged in the lower cavity 17.

[0030] The upper air supply device and the lower air supply device have the same structure, and both include a first air pump 20. The air outlet of the first air pump 20 is connected with a first air charging pipe 21. The outlet end of the first air charging pipe 21 passes through the fracturing cylinder 9 and is connected to the fracturing annular sealing bladder 12. A first pressure sensor 22 and a first air charging solenoid valve 23 are sequentially installed on the first air charging pipe 21 along the air flow direction. A first exhaust pipe joint 24 is connected between the first air charging solenoid valve 23 and the fracturing annular sealing bladder 12 on the first air charging pipe 21, and a first exhaust solenoid valve 25 is provided on the first exhaust pipe joint 24; A number of rollers 26 that are in rolling connection with the inner circle of the casing 3 are provided on both the upper cover plate 10 and the lower cover plate 11. At least three lifting rings 27 are evenly arranged on the upper cover plate 10 along the circumferential direction; A water permeable pipe 28 is vertically arranged between the upper cover plate 10 and the lower cover plate 11. The water permeable pipe 28 passes through the upper partition plate 13 and the lower partition plate 14, and the center line of the water permeable pipe 28 is parallel to the center line of the fracturing cylinder 9; An upper wire passing pipe 29 that is parallel and in contact with the air injection main pipe 19 is connected to the upper cover plate 10. The lower port of the upper wire passing pipe 29 is communicated with the inside of the upper cavity 15. A lower wire passing pipe 30 passing through the middle cavity 16 is provided between the upper partition plate 13 and the lower partition plate 14.

[0031] When carrying out the coalbed methane extraction operation in step S5, a sealed gas gathering extraction device that is simultaneously communicated with the inner ports of the extraction screen pipes 4 in the same radial extraction section is arranged in the casing 3. An extraction pump is arranged on the ground. The extraction pump is connected to the top of the sealed gas gathering extraction device through an extraction main pipe. Under the suction of the extraction pump, the coalbed methane inside the coal reservoir 1 is drawn to the underground gas storage or LNG plant for storage through the sealed gas gathering extraction device; The sealed gas collection and extraction device includes an extraction tube 31 whose center line coincides with the center line of the casing 3. An upper sealing plate 32 and a lower sealing plate 33 are fixed to the upper and lower ends of the extraction tube 31 respectively. An extraction annular sealing bag 34 is fixed to the upper and lower parts of the outer circle of the extraction tube 31 respectively. An upper flat plate 35 and a lower flat plate 36 are horizontally arranged in the extraction tube 31. The upper flat plate 35 and the lower flat plate 36 divide the interior of the extraction tube 31 into an upper chamber 37, a middle chamber 38 and a lower chamber 39. An exhaust hole 40 is provided between the upper plate 35 and the lower plate 36. An exhaust connecting pipe 41 connected to the exhaust main pipe is provided at the center of the upper sealing plate 32. The lower end of the exhaust connecting pipe 41 passes through the upper chamber 37 and is fixedly connected to the upper plate 35. The interior of the exhaust connecting pipe 41 is communicated with the interior of the middle chamber 38. A first air supply device connected to the upper exhaust annular sealing bag 34 is provided in the upper chamber 37, and a second air supply device connected to the lower exhaust annular sealing bag 34 is provided in the lower chamber 39.

[0032] The first air supply device and the second air supply device have the same structure and both include a second air pump 43. The air outlet of the second air pump 43 is connected to a second air filling pipe 44. The outlet end of the second air filling pipe 44 passes through the extraction cylinder 31 and is connected to the extraction annular sealing bag 34. A second pressure sensor 45 and a second air filling solenoid valve 46 are installed on the second air filling pipe 44. A second exhaust pipe joint 47 is connected to the second air filling pipe 44 between the second air filling solenoid valve 46 and the extraction annular sealing bag 34. A second exhaust solenoid valve 48 is provided on the second exhaust pipe joint 47. The upper sealing plate 32 and the lower sealing plate 33 are both provided with a plurality of guide wheels 49 that are in rolling connection with the inner circle of the casing 3, and the upper cover plate 10 is evenly provided with at least three hanging rings 50 along the circumferential direction; A vertically transparent water pipe 51 is provided between the upper sealing plate 32 and the lower sealing plate 33. The water pipe 51 passes through the upper sealing plate 32 and the lower sealing plate 33. The center line of the water pipe 51 is parallel to the center line of the extraction tube 31. A first threading tube 52 is connected to the upper sealing plate 32 and is parallel to and in contact with the extraction connecting tube 41. The lower end of the first threading tube 52 is connected to the interior of the upper chamber 37. A second threading tube 53 is provided between the upper sealing plate 32 and the lower sealing plate 33, passing through the middle chamber 38. The lower sealing plate 33 is provided with threading holes 54 corresponding to the upper and lower parts of the second threading tube 53.

[0033] In step S5, the water and the deposited coal powder collected at the bottom of the shaft are pumped upwards by installing a submersible pump 55 and an anti-sedimentation stirring device in the casing 3 at the bottom of the shaft; The anti-settling agitation device includes a support ring 56, a motor reducer 57, an installation box 58, a stirring shaft 59, an upper support 60 and a lower support 61. The outer diameter of the support ring 56 is equal to the inner diameter of the sleeve 3. The support ring 56 is coaxially and fixedly arranged on the inner wall of the sleeve 3. The installation box 58 is fixedly arranged on the support ring 56. The motor reducer 57 is arranged in the installation box 58. The stirring shaft 59 is arranged vertically. Both the upper support 60 and the lower support 61 are fixedly connected to the inner wall of the sleeve 3. The upper and lower parts of the stirring shaft 59 are respectively rotatably connected to the upper support 60 and the lower support 61 through waterproof bearings 62. A number of stirring rods 63 are fixedly arranged on the stirring shaft 59. The upper end of the stirring shaft 59 passes through the bottom of the installation box 58 and extends into the installation box 58. A positioning bearing is arranged in the installation box 58 and is rotatably connected to the stirring shaft 59. The main shaft of the motor reducer 57 is equipped with a main gear 64, and a driven gear 65 meshing with the main gear 64 is installed on the stirring shaft 59. A downcomer 66 vertically passing through the installation box 58 is arranged in the installation box 58. A water collecting hopper 67 with a large upper part and a small lower part and communicating with the upper port of the downcomer 66 is arranged at the top of the installation box 58. The upper edge of the water collecting hopper 67 is connected to the inner wall of the sleeve 3; An installation frame 68 is arranged on the inner wall of the sleeve 3. The submersible pump 55 is arranged on the installation frame 68. The outlet of the submersible pump 55 extends to the ground through a vertically arranged drain pipe 69. The lower part of the drain pipe 69 is fixedly connected to the inner wall of the sleeve 3 through a connecting plate 70. The drain pipe 69 is parallel to the center line of the sleeve 3 inside the sleeve 3. The outer diameter of the drain pipe 69 is smaller than the inner diameters of the water passing pipe 51 and the downcomer 66. The drain pipe 69 passes through the downcomer 66 and the water passing pipe 51.

[0034] The specific process of the hydraulic fracturing and permeability enhancement operation in step S4 is as follows: At the shaft wellhead, use a hoisting device (winch) to hook and connect the lifting ring 27 at the top of the sealed diversion and gas distribution device, connect the gas injection pump, the fracturing gas storage tank (or fracturing truck), the fracturing gas transmission pipe, and the gas injection main pipe 19. According to the distance between each radial extraction section and the shaft wellhead recorded during construction, the hoisting device lowers the sealed diversion and gas distribution device along the casing 3 to the uppermost radial extraction section. At this time, the inner ports of the four extraction screen pipes 4 are all located between the upper and lower fracturing annular sealing capsules 12. Close the hoisting device, and then start two first air pumps 20. The first air pumps 20 fill the fracturing annular sealing capsule 12 with air through the first air filling pipe 21. The fracturing annular sealing capsule 12 expands radially. The pressure signal real-time monitored by the first pressure sensor 22 is transmitted to the PLC controller on the ground. When the inflation pressure reaches the set pressure value, the PLC controller sends a closing command to the first air pump 20 and the first air filling solenoid valve 23. The fracturing annular sealing capsule 12 seals the annular gap between the outer circle of the fracturing cylinder 9 and the inner circle of the casing 3. Then, open the valve of the fracturing gas storage tank and start the gas injection pump. The gas injection pump extracts the fracturing gas in the fracturing gas storage tank and injects it into the extraction screen pipe 4 through the fracturing gas transmission pipe, the gas injection main pipe 19, the hollow cavity 16, the gas injection hole 18, and the through hole 5 in sequence. The high-pressure fracturing gas is injected into the coal reservoir 1 through the screen holes 71 on the extraction screen pipe 4 to fracture the coal body, increase the pores and fractures of the coal body, and enhance the permeability of the coal seam; The pressure of the injected high-pressure fracturing gas is controlled between 50 - 70 MPa, and the injection speed should be controlled between 2 - 3 m 3 / min, and the injection of the high-pressure fracturing gas lasts for 3 - 10 days. After the fracturing of the uppermost radial extraction section is completed, close the gas injection pump. The PLC controller sends an opening command to the first exhaust solenoid valve 25. The high-pressure gas in the fracturing annular sealing capsule 12 is discharged through the first air filling pipe 21 and the first exhaust pipe joint 24. The outer circle of the fracturing annular sealing capsule 12 no longer contacts the inner wall of the casing 3. Then, start the hoisting device and lower the sealed diversion and gas distribution device to the second radial extraction section. According to the operation method of the fracturing process of the uppermost radial extraction section, perform gas injection fracturing on the second radial extraction section. After the fracturing is completed, move downward and perform gas injection fracturing on other radial extraction sections in sequence until all radial extraction sections are fractured. Then, the hoisting device lifts the sealed diversion and gas distribution device to the ground to complete the hydraulic fracturing and permeability enhancement operation.

[0035] The specific process of the coalbed methane extraction operation in step S5 is as follows: After the hydraulic fracturing and permeability enhancement operation is completed, remove the sealed diversion and gas distribution device from the steel wire rope of the hoisting device, and then hang the hanging ring 50 at the top of the sealed gas gathering and extraction device on the steel wire rope hook of the hoisting device, connect the extraction pump, the extraction gas storage tank, the extraction main pipe, and the extraction connecting pipe 41. According to the distance between each radial extraction section and the shaft wellhead recorded during construction; The hoisting device lowers the sealed gas-gathering extraction device downward along the casing 3 to the uppermost radial extraction section. At this time, the inner ports of the four extraction screen pipes 4 are all located between the upper and lower extraction annular sealing sacs 34. The hoisting device is closed, and then two second air pumps 43 are started. The second air pumps 43 fill the extraction annular sealing sac 34 with air through the second charging pipes 44. The extraction annular sealing sac 34 expands radially. The pressure signal monitored in real time by the second pressure sensor 45 is transmitted to the PLC controller on the ground. When the inflation pressure reaches the set pressure value, the PLC controller issues a closing command to the second air pumps 43 and the second charging solenoid valve 46. The extraction annular sealing sac 34 seals the annular gap between the outer circle of the extraction cylinder 31 and the inner circle of the casing 3. Then the extraction pump is started. The extraction pump extracts coalbed methane inside the extraction screen pipe 4 through the extraction main pipe, the extraction connecting pipe 41, the middle chamber 38, the extraction holes 40, and the through holes 5. The coalbed methane in the coal reservoir 1 overflows through the fractures formed by hydraulic fracturing and enters the extraction screen pipe 4 through the screen holes 71 and is pumped by the extraction pump to the underground gas storage or LNG plant for storage; a flowmeter is provided on the extraction main pipe to monitor the flow rate of the extracted coalbed methane. When the flow rate is less than 0.04 m³ / min, it indicates that the extraction operation of the uppermost radial extraction section is completed. The extraction pump is closed, and the PLC controller issues an opening command to the second exhaust solenoid valve 48. The high-pressure gas in the extraction annular sealing sac 34 is discharged through the second charging pipes 44 and the second exhaust pipe joint 47. The outer circle of the extraction annular sealing sac 34 no longer contacts the inner wall of the casing 3. Then the hoisting device is started to lower the sealed gas-gathering extraction device to the second radial extraction section. According to the operation method of the coalbed methane extraction process for the uppermost radial extraction section, the coalbed methane extraction operation is carried out on the second radial extraction section. After the extraction is completed, it is moved downward to carry out the coalbed methane extraction on other radial extraction sections in turn until the extraction operations of all radial extraction sections are completed. The hoisting device lifts the sealed gas-gathering extraction device to the ground to complete the coalbed methane extraction operation.

[0036] The submersible pump 55 and the anti-sediment agitation device are installed after the casing 3 is cemented in step (3). Since each extraction screen pipe 4 of each radial extraction section is arranged with an inner high and outer low inclination, the inner end of the extraction screen pipe 4 is fixedly connected to the outer circle of the casing 3. The extraction screen pipe 4 does not have screen holes in a section near the casing (such as 0.5 - 1 m), and a number of extraction screen holes 71 are provided on the extraction screen pipe 4. The water that infiltrates into the extraction screen pipe 4 from the coal reservoir 1 above the extraction holes 6 will continue to seep downward, and the water will not be discharged into the casing 3 from the inner port of the extraction screen pipe 4. The water in the coal reservoir 1 deposits on the rock formation 2 and finally flows and gathers into the lower space of the casing 3 through the water conduit 7 together with the coal powder; The specific process of pumping the water and deposited pulverized coal into the bottom of the vertical shaft upward is as follows: The motor reducer 57 drives the stirring shaft 59 to rotate through the meshing main gear 64 and driven gear 65. The stirring rod 63 on the stirring shaft 59 stirs up the pulverized coal deposited at the bottom of the casing 3. The submersible pump 55 pumps the pulverized coal-carrying mixed water to the ground through the drain pipe 69.

[0037] Since the casing 3 is cemented in the vertical shaft in the present invention, the water in the coal reservoir 1 and the rock stratum above the coal reservoir 1 cannot flow downward through the shaft wall. This will increase the water content in the coal reservoir 1 and affect the production of coalbed methane. Therefore, the following methods can be used to solve the problem of rapid drainage of water in the coal reservoir 1: As Figure 8 shown, at least three semi-circular pipes 73 are welded to the outer circumference of the casing 3. The center line of the semi-circular pipe 73 is parallel to the center line of the casing 3. All the semi-circular pipes 73 are arranged in a circumferential array along the center line of the casing. The upper port of the semi-circular pipe 73 is not lower than the ground and is provided with a breathable cover plate. The lower port of the semi-circular pipe 73 is connected to the water guide pipe 7. A number of drain holes 74 are evenly opened along the length direction on the semi-circular pipe 73. A stainless steel filter screen covering the drain holes 74 is welded to the outer circumference of the semi-circular pipe 73. In this case, when cementing the well, it is ensured that the radius of the vertical shaft is slightly larger than the radial dimension from the outer circumference of all the semi-circular pipes 73 to the center line of the casing. The stainless steel filter screen is close to the shaft wall. Between the adjacent two semi-circular pipe casings in the vertical shaft, cementing materials are filled (filling gravel and compacting layer by layer. The gravel also has good water permeability). The water in the upper rock stratum and the coal reservoir 1 can flow into the semi-circular pipe 73 through the drain holes 74 and flow downward through the water guide pipe 7 into the water storage part at the bottom of the casing 3, and at the same time infiltrate through the filled gravel. The semi-circular pipe 73 also has the function of improving the strength of the casing 3.

[0038] The hoisting device, gas injection pump, extraction pump, underground gas storage and other components in the present invention are all prior arts, and their specific structures will not be elaborated and are not shown in the figure. In addition, in order to improve the fracturing effect, a fracturing booster pump can be arranged in the hollow cavity 16 in the fracturing cylinder 9; in order to improve the extraction effect, an extraction booster pump is arranged in the middle chamber 38 in the extraction cylinder 31.

[0039] The above embodiments illustrate the basic principles and characteristics of the present invention. However, the above only illustrates the preferred embodiments of the present invention and is not limited by the described embodiments. Under the inspiration of this patent, those of ordinary skill in the art can also make many forms of deformation and improvement without departing from the purpose of the present invention and the scope protected by the claims. These all belong to the protection scope of the present invention. Therefore, the scope of the present invention patent and protection should be subject to the appended claims.

Claims

1. Vertical layered fracturing and drainage method for coalbed methane wells, characterized in that: It includes the following steps: S1. Construct a vertical shaft in the mining area. The vertical shaft vertically penetrates the coal reservoir and the lower end of the vertical shaft extends into the rock formation below the coal reservoir. S2. Construct several radial extraction sections in the vertical shaft towards the coal reservoir. S3. Lower a casing pipe into the vertical shaft for cementing. Meanwhile, set extraction screen pipes inside the radial extraction sections. Through holes corresponding to each layer of the radial extraction sections are opened on the casing pipe. The inner end of the extraction screen pipe is fixedly connected to the outer circumference of the casing pipe, and each extraction screen pipe communicates with the inside of the casing pipe through one of the through holes. S4. Conduct fracturing and permeability enhancement operations on several layers of radial extraction sections respectively. S5. Conduct coalbed methane extraction operations on several layers of radial extraction sections from top to bottom. Meanwhile, pump the water and deposited coal powder flowing into the bottom of the vertical shaft upwards.

2. The vertical layered fracturing and drainage method for coalbed methane wells according to claim 1, wherein: In step S2, several layers of radial extraction sections are evenly arranged in the height direction. Each layer of the radial extraction section includes four extraction holes arranged in a circular array around the center line of the vertical shaft. The extraction holes are inclined from high to low along the center line direction; when the vertical projections of any two adjacent layers of radial extraction sections are on the same plane, the included angle between two adjacent extraction holes is 45°. One of the extraction screen pipes is arranged in each extraction hole. A filter hole plate is arranged at the outer port of the extraction screen pipe. The inner diameter of the extraction screen pipe is smaller than the diameter of the through hole; the lowest position of the inner port of the extraction screen pipe is lower than the lowest position of the through hole. A number of water conduits are evenly arranged along the circumferential direction at the interface between the bottom of the coal reservoir and the rock formation on the casing pipe wall. The outer end of the water conduit extends into the coal reservoir. A stainless steel filter screen is arranged at the outer port of the water conduit. The inner end of the water conduit passes through the casing pipe and is flush with the inner circumference of the casing pipe.

3. The vertical layered fracturing and drainage method for coalbed methane wells according to claim 2, characterized in that: During the fracturing and permeability enhancement operation in step S4, a sealed diversion and gas distribution device is arranged inside the casing pipe. On the ground, an air injection pump is used to extract fracturing gas (nitrogen or carbon dioxide) and inject the fracturing gas into the sealed diversion and gas distribution device through a fracturing gas transmission pipe. The sealed diversion and gas distribution device then simultaneously passes the fracturing gas into each extraction screen pipe of the same layer of the radial extraction section. The fracturing gas fractures the coal body through the screen holes, increases the pores and fractures of the coal body, and improves the permeability of the coal seam. The sealed diversion and gas distribution device includes a fracturing cylinder with its center line coinciding with the center line of the casing pipe. An upper cover plate and a lower cover plate are respectively fixedly arranged at the upper and lower ends of the fracturing cylinder. An upper fracturing annular seal bag and a lower fracturing annular seal bag are respectively fixedly arranged at the upper and lower parts of the outer circumference of the fracturing cylinder. An upper partition plate and a lower partition plate are horizontally arranged inside the fracturing cylinder. The upper partition plate and the lower partition plate divide the inside of the fracturing cylinder into an upper cavity, a middle cavity, and a lower cavity. Injection holes are opened on the fracturing cylinder between the upper partition plate and the lower partition plate. A main injection pipe connected to the fracturing gas transmission pipe is arranged at the center of the upper cover plate. The lower end of the main injection pipe passes through the upper cavity and is fixedly connected to the upper partition plate. The inside of the main injection pipe communicates with the inside of the middle cavity. An upper gas supply device connected to the upper fracturing annular seal bag is arranged in the upper cavity, and a lower gas supply device connected to the lower fracturing annular seal bag is arranged in the lower cavity.

4. The vertical layered fracturing and drainage method for coalbed methane wells according to claim 3, characterized in that: The upper air supply device and the lower air supply device have the same structure and both include a first air pump. The air outlet of the first air pump is connected to a first inflation pipe. The outlet end of the first inflation pipe passes through the fracturing cylinder and is connected to the fracturing annular sealing bag. A first pressure sensor and a first inflation solenoid valve are installed on the first inflation pipe in sequence along the airflow direction. A first exhaust pipe joint is connected to the first inflation pipe between the first inflation solenoid valve and the fracturing annular sealing bag. The first exhaust pipe joint is provided with a first exhaust solenoid valve. The upper cover plate and the lower cover plate are both provided with a plurality of rollers that are in rolling connection with the inner circle of the casing, and the upper cover plate is evenly provided with at least three lifting rings along the circumferential direction; A water permeable pipe is vertically provided between the upper cover plate and the lower cover plate, the water permeable pipe passes through the upper partition plate and the lower partition plate, and the center line of the water permeable pipe is parallel to the center line of the fracturing tube; An upper threading pipe parallel to and in contact with the gas injection main pipe is connected to the upper cover plate, and the lower end of the upper threading pipe is communicated with the interior of the upper cavity. A lower threading pipe passing through the hollow cavity is provided between the upper and lower partitions.

5. The vertical layered fracturing and drainage method for coalbed methane wells according to claim 2, characterized in that: During the coalbed methane extraction operation in step S5, a sealed gas collection extraction device is provided in the casing and is simultaneously connected to the inner port of the extraction screen of the same radial extraction section. A extraction pump is provided on the ground and is connected to the top of the sealed gas collection extraction device through an extraction main pipe. Under the suction action of the extraction pump, the coalbed methane inside the coal reservoir is extracted through the sealed gas collection extraction device to an underground gas storage reservoir or an LNG plant for storage. The sealed gas gathering and extraction device includes an extraction tube whose center line coincides with the center line of the casing, and an upper sealing plate and a lower sealing plate are fixedly provided at the upper and lower ends of the extraction tube respectively, and an extraction annular sealing bag is fixedly provided at the upper and lower parts of the outer circle of the extraction tube respectively, and an upper flat plate and a lower flat plate are horizontally provided in the extraction tube, and the upper flat plate and the lower flat plate divide the interior of the extraction tube into an upper chamber, a middle chamber and a lower chamber, and an extraction hole is opened on the extraction tube between the upper flat plate and the lower flat plate, and an extraction connecting pipe connected to the extraction main pipe is provided at the center of the upper sealing plate, and the lower end of the extraction connecting pipe passes through the upper chamber and is fixedly connected to the upper plate, and the interior of the extraction connecting pipe is communicated with the interior of the middle chamber, a first air supply device connected to the upper extraction annular sealing bag is provided in the upper chamber, and a second air supply device connected to the lower extraction annular sealing bag is provided in the lower chamber.

6. The vertical layered fracturing and drainage method for coalbed methane wells according to claim 5, characterized in that: The first air supply device and the second air supply device have the same structure, and both include a second air pump, the air outlet of the second air pump is connected to a second air filling pipe, the outlet end of the second air filling pipe passes through the extraction tube and is connected to the extraction annular sealing bag, a second pressure sensor and a second air filling solenoid valve are installed on the second air filling pipe, a second exhaust pipe joint is connected to the second air filling solenoid valve and the extraction annular sealing bag on the second air filling pipe, and a second exhaust solenoid valve is provided on the second exhaust pipe joint; The upper and lower sealing plates are both provided with a number of guide wheels that are in rolling connection with the inner circle of the casing, and the upper cover plate is evenly provided with at least three hanging rings along the circumferential direction; A vertically transparent water pipe is provided between the upper sealing plate and the lower sealing plate. The water pipe passes through the upper sealing plate and the lower sealing plate, and the center line of the water pipe is parallel to the center line of the extraction tube. A first wire threading pipe parallel to and in contact with the extraction connecting pipe is connected to the upper sealing plate. The lower port of the first wire threading pipe communicates with the inside of the upper chamber. A second wire threading pipe passing through the middle chamber is provided between the upper sealing plate and the lower sealing plate. A wire threading hole corresponding to the second wire threading pipe up and down is opened on the lower sealing plate.

7. The vertical layered fracturing and drainage method for coalbed methane wells according to claim 6, characterized in that: In step S5, the water and deposited pulverized coal flowing into the bottom of the vertical shaft are pumped upward by arranging a submersible pump and an anti-sediment agitation device in the casing at the bottom of the vertical shaft. The anti-sediment agitation device includes a support ring, a motor reducer, an installation box, a stirring shaft, an upper support and a lower support. The outer diameter of the support ring is equal to the inner diameter of the casing. The support ring is coaxially and fixedly arranged on the inner wall of the casing. The installation box is fixedly arranged on the support ring. The motor reducer is arranged in the installation box. The stirring shaft is arranged vertically. The upper support and the lower support are both fixedly connected to the inner wall of the casing. The upper and lower parts of the stirring shaft are respectively rotatably connected to the upper support and the lower support through waterproof bearings. A number of stirring rods are fixedly arranged on the stirring shaft. The upper end of the stirring shaft passes through the bottom of the installation box and extends into the installation box. A positioning bearing is arranged in the installation box and is rotatably connected to the stirring shaft. The main shaft of the motor reducer is provided with a main gear. A driven gear meshing with the main gear is arranged on the stirring shaft. A downcomer vertically passing through the installation box is arranged in the installation box. A water collecting hopper with a large upper part and a small lower part communicating with the upper port of the downcomer is arranged at the top of the installation box. The upper edge of the water collecting hopper is connected to the inner wall of the casing. An installation frame is arranged on the inner wall of the casing. The submersible pump is arranged on the installation frame. The outlet of the submersible pump extends to the ground through a vertically arranged drain pipe. The lower part of the drain pipe is fixedly connected to the inner wall of the casing through a connecting plate. The drain pipe is parallel to the center line of the casing in the casing. The outer diameter of the drain pipe is smaller than the inner diameters of the water passing pipe and the downcomer. The drain pipe passes through the downcomer and the water passing pipe.

8. The vertical layered fracturing and drainage method for coalbed methane wells according to claim 7, characterized in that: The specific process of the fracturing and permeability enhancement operation in step S4 is as follows: At the wellhead of the vertical shaft, a hoisting device (winch) is used to hook the lifting ring at the top of the sealed diversion gas distribution device, connect the injection air pump, the fracturing gas storage tank, the fracturing gas transmission pipe and the injection main pipe. According to the distance between each radial extraction section and the wellhead of the vertical shaft recorded during construction, the hoisting device lowers the sealed diversion gas distribution device along the casing to the uppermost radial extraction section. At this time, the inner ports of the four extraction screen pipes are all located between the upper and lower fracturing annular sealing sacs. The hoisting device is closed, and then two first air pumps are started. The first air pumps fill the fracturing annular sealing sac with air through the first charging pipes. The fracturing annular sealing sac expands radially. The pressure signals monitored in real time by the first pressure sensors are transmitted to the PLC controller on the ground. When the inflation pressure reaches the set pressure value, the PLC controller issues a closing command to the first air pumps and the first charging solenoid valves. The fracturing annular sealing sac seals the annular gap between the outer circle of the fracturing cylinder and the inner circle of the casing. Then, the valve of the fracturing gas storage tank is opened, and the injection air pump is started. The injection air pump extracts the fracturing gas in the fracturing gas storage tank and injects it into the extraction screen pipe through the fracturing gas transmission pipe, the injection main pipe, the extraction connecting pipe, the hollow cavity, the injection holes and the through holes in sequence. The high-pressure fracturing gas is injected into the coal reservoir through the screen holes on the extraction screen pipe to fracture the coal body, increase the pores and fractures of the coal body, and improve the permeability of the coal seam. The pressure of the injected high-pressure fracturing gas is controlled between 50 and 70 MPa, and the injection speed should be controlled between 2 and 3 m 3 / min, and the injection of the high-pressure fracturing gas lasts for 3 to 10 days; after the fracturing of the uppermost radial extraction section is completed, the gas injection pump is closed, and the PLC controller sends a command to open the first exhaust solenoid valve, and the high-pressure gas in the fracturing annular seal bag is discharged through the first charging pipe and the first exhaust pipe joint. The outer circle of the fracturing annular seal bag no longer contacts the inner wall of the casing. Then, the lifting device is started, and the sealed diversion gas distribution device is lowered to the second radial extraction section. According to the operation method of the fracturing process of the uppermost radial extraction section, the second radial extraction section is subjected to injection pressure fracturing. After the fracturing is completed, it is moved downward in turn to perform injection pressure fracturing on other radial extraction sections until all the radial extraction sections are fractured. Then, the lifting device lifts the sealed diversion gas distribution device to the ground to complete the fracturing and permeability enhancement operation.

9. The vertical layered fracturing and drainage method for coalbed methane wells according to claim 8, characterized in that: The specific process of coalbed methane extraction operation in step S5 is as follows: After the fracturing and permeability enhancement operation is completed, the sealed diversion and gas separation device is removed from the steel wire rope of the lifting device, and then the hanging ring at the top of the sealed gas gathering and extraction device is hung on the steel wire rope hook of the lifting device. Connect the extraction pump, the extracted gas storage tank, the extraction main pipe, and the extraction connecting pipe. According to the distance between each radial extraction section and the shaft wellhead recorded during construction; The lifting device lowers the sealed gas gathering and extraction device along the casing to the uppermost radial extraction section. At this time, the inner ports of the four extraction screen pipes are all located between the upper and lower extraction annular seals. The lifting device is closed, and then two second air pumps are started. The second air pumps fill the extraction annular seal with air through the second charging pipe. The extraction annular seal expands radially. The pressure signal monitored by the second pressure sensor is transmitted to the PLC controller on the ground. When the inflation pressure reaches the set pressure value, the PLC controller sends a closing command to the second air pumps and the second charging solenoid valve. The extraction annular seal seals the annular gap between the outer circle of the extraction cylinder and the inner circle of the casing. Then, the extraction pump is started. The extraction pump extracts coalbed methane inside the extraction screen pipe through the extraction main pipe, the extraction connecting pipe, the middle chamber, the extraction holes, and the through holes. The coalbed methane in the coal reservoir overflows through the fractures enhanced by fracturing and enters the extraction screen pipe through the screen holes and is pumped by the extraction pump to the underground gas storage or LNG plant for storage; A flow meter is provided on the extraction main pipe to monitor the flow rate of the extracted coalbed methane. When the flow rate is less than 0.04 m³ / min, it indicates that the extraction operation of the uppermost radial extraction section is completed. The extraction pump is closed, and the PLC controller sends an opening command to the second exhaust solenoid valve. The high-pressure gas in the extraction annular seal is discharged through the second charging pipe and the second exhaust pipe joint. The outer circle of the extraction annular seal no longer contacts the inner wall of the casing. Then, the lifting device is started, and the sealed gas gathering and extraction device is lowered to the second radial extraction section. According to the operation method of the coalbed methane extraction process for the uppermost radial extraction section, the coalbed methane extraction operation is carried out on the second radial extraction section. After the extraction is completed, it is moved downward in turn to carry out the coalbed methane extraction on other radial extraction sections until the extraction operations of all radial extraction sections are completed. Then, the lifting device lifts the sealed gas gathering and extraction device to the ground to complete the coalbed methane extraction operation.

10. The vertical layered fracturing and drainage method for coalbed methane wells according to claim 9, characterized in that: The submersible pump and the anti-sediment agitation device are set after the casing cementing in step (3). Since each extraction screen pipe of each radial extraction section is arranged with an inner high and outer low inclination, and a number of extraction screen holes are provided on the extraction screen pipe, the water that seeps into the extraction screen pipe from the coal reservoir above the extraction holes will continue to seep downward, and the water will not be discharged into the casing from the inner port of the extraction screen pipe. The water in the coal reservoir deposits on the rock layer and finally flows into and accumulates in the lower space of the casing through the water conduit, carrying coal powder; The specific process of pumping the water flowing into the bottom of the shaft and the deposited pulverized coal upward is as follows: The motor reducer drives the stirring shaft to rotate through the meshing of the main gear and the driven gear. The stirring rod on the stirring shaft stirs up the pulverized coal deposited at the bottom of the casing, and the submersible pump pumps the pulverized coal-carrying mixed water to the ground through the drain pipe.

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