Straight well layered extraction system for coal bed gas

Abstract

The utility model discloses a coal bed gas vertical well layered extraction system which comprises a vertical well vertically and downwards penetrating through a coal reservoir, and a plurality of layers of radial extraction sections are arranged in the coal reservoir. A casing pipe is arranged in the vertical shaft, a vertical drainage channel is arranged on the outer circle of the casing pipe, and an inner port of each layer of radial extraction section is communicated with the interior of the casing pipe. A derrick is arranged above the mouth of the vertical shaft on the ground, a lifting device is arranged on the derrick, and a steel wire rope of the lifting device is connected with a sealing gas gathering extraction device which can move up and down along the casing pipe and is communicated with an inner port of each layer of radial extraction section in a hanging mode. The plurality of layers of radial extraction sections are uniformly arranged in the circumferential direction of the vertical shaft, so that the vertical shaft is particularly suitable for thicker coal reservoirs, the extraction range of the vertical shaft in the radial direction is extended, the coal bed gas extraction process is simple and easy to implement, the single well extraction yield is improved, a smooth drainage channel is designed, water in the coal reservoirs is reduced, and the coal bed gas extraction efficiency is improved. Therefore, economy, high efficiency, safety and stability of coal bed gas exploitation are guaranteed.

Description

Technical Field

[0001] This utility model belongs to the field of coalbed methane development and utilization technology, specifically relating to a coalbed methane vertical well stratified extraction system. Background Technology

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

[0003] For high-gas coal reservoirs, gas extraction is necessary before mining. This not only improves the safety of mining operations but also allows for the concentrated extraction of high-purity gas. Currently, vertical wells are the earliest and most widely used well type for gas extraction in high-gas coal reservoirs due to their low cost. Although vertical wells can be used for gas extraction in thicker coal reservoirs, their single-well output is generally low (extraction can only be carried out within a small radius centered on the vertical well). Therefore, simple vertical wells are suitable for medium- to high-permeability coal seams. Thus, to increase single-well output and specifically for thicker coal reservoirs, it is necessary to optimize and improve the gas extraction capabilities of existing vertical wells. Utility Model Content

[0004] The purpose of this invention is to provide a coalbed methane vertical well stratified extraction system with a large extraction range, good extraction effect, and suitable for thicker coal reservoirs.

[0005] To solve the above-mentioned technical problems, this utility model adopts the following technical solution: a coalbed methane vertical well layered extraction system, including a vertical shaft that penetrates the coal reservoir vertically downwards, with the lower end of the shaft extending into the rock strata below the coal reservoir; several radial extraction sections are arranged vertically around the shaft within the coal reservoir; a casing is arranged coaxially within the shaft, with several vertical drainage channels between the outer circumference of the casing and the shaft wall; cementing gravel is filled between any two adjacent vertical drainage channels within the shaft; the inner end of each radial extraction section is connected to the inside of the casing; several water guide pipes are evenly arranged circumferentially on the casing wall at the interface between the bottom of the coal reservoir and the rock strata, with the outer end of the water guide pipe extending into the coal reservoir and the inner end of the water guide pipe passing through the casing and flush with the inner circumference of the casing;

[0006] On the ground, a derrick is installed above the shaft opening. A lifting device is installed on the derrick. The steel wire rope of the lifting device is connected to a sealed gas-gathering extraction device that can move up and down along the casing and communicate with the inner port of each radial extraction section.

[0007] Several radial extraction sections are evenly arranged along the vertical shaft. Each radial extraction section includes four extraction holes arranged in a circular array around the center line of the shaft. The extraction holes are inclined inward and outward along the center line. The angle between the center line of the extraction hole and the horizontal plane is 3-10°. When the vertical projections of any two adjacent radial extraction sections are on the same plane, the angle between the two adjacent extraction holes is 45°.

[0008] Each extraction hole is equipped with an extraction screen tube, and the outer end of the extraction screen tube is equipped with a filter plate. The casing has through holes that correspond to each radial extraction section. The inner diameter of the extraction screen tube is smaller than the diameter of the through hole. The inner end of the extraction screen tube is fixedly connected to the outer circle of the casing. Each extraction screen tube is connected to the inside of the casing through one of the aforementioned through holes. The lowest position of the inner end of the extraction screen tube is lower than the lowest position of the through hole.

[0009] The extraction screen pipe has several screen holes on the pipe wall between the casing and the filter plate at a distance of 0.5-1m. Several hemispherical support and ventilation nets are fixedly welded to the outer circle of the extraction screen pipe, and each hemispherical support and ventilation net covers one screen hole.

[0010] The vertical drainage channel uses a semi-circular pipe welded to the outer circumference of the casing. All the semi-circular pipes are arranged in a circumferential array along the center line of the casing. The upper end of the semi-circular pipe is higher than the ground and is equipped with a vent cover. The lower end of the semi-circular pipe is connected to the water guide pipe. Several drainage holes are evenly opened on the semi-circular pipe along its length. A stainless steel filter screen is welded to the outer circumference of the semi-circular pipe to cover the drainage holes.

[0011] The sealed gas extraction device includes an extraction cylinder whose centerline coincides with the centerline of the casing. An upper sealing plate and a lower sealing plate are fixedly installed at the upper and lower ends of the extraction cylinder, respectively. An extraction annular sealing bladder is fixedly installed at the upper and lower parts of the outer circumference of the extraction cylinder. An upper plate and a lower plate are horizontally arranged inside the extraction cylinder, dividing the interior into an upper chamber, a middle chamber, and a lower chamber. An extraction hole is opened between the upper and lower plates on the extraction cylinder. The lower end of the extraction connecting pipe passes through the upper chamber and is fixedly connected to the upper plate. The interior of the extraction connecting pipe communicates with the interior of the middle chamber. A first gas supply device connected to the upper extraction annular sealing bladder is located in the upper chamber, and a second gas supply device connected to the lower extraction annular sealing bladder is located in the lower chamber. An extraction connecting pipe is located at the center of the upper sealing plate, and an extraction pump is located on the ground. The upper end of the extraction connecting pipe is connected to the extraction pump via the extraction main pipe.

[0012] The first and second gas supply devices have the same structure, both including an air pump. The air pump outlet is connected to an inflation pipe. The outlet end of the inflation pipe passes through the extraction cylinder and is connected to the extraction annular sealing bladder. A pressure sensor and an inflation solenoid valve are installed on the inflation pipe. An exhaust pipe connector is connected between the inflation solenoid valve and the extraction annular sealing bladder on the inflation pipe. An exhaust solenoid valve is installed on the exhaust pipe connector.

[0013] Both the upper and lower sealing plates are provided with several guide wheels that are rolled and connected to the inner circle of the sleeve, and at least three hanging rings are evenly provided on the upper cover plate along the circumferential direction;

[0014] A vertical water pipe is installed between the upper and lower sealing plates, passing through both the upper and lower sealing plates, with the center line of the water pipe parallel to the center line of the extraction cylinder.

[0015] The upper sealing plate is connected to a first threaded pipe that is parallel to and in contact with the extraction connecting pipe. The lower end of the first threaded pipe is connected to the interior of the upper chamber. A second threaded pipe that passes through the middle chamber is provided between the upper sealing plate and the lower sealing plate. The lower sealing plate has threaded holes that correspond to the upper and lower ends of the second threaded pipe.

[0016] By adopting the above technical solution, compared with the prior art, this utility model has the following technical effects:

[0017] (1) This utility model opens a vertical shaft and evenly opens multiple radial extraction sections from top to bottom in the coal reservoir. Each radial extraction section includes extraction holes with an included angle of 90°. This allows for a wider extraction range through radial radiation from the vertical shaft, thereby increasing the extraction volume of a single well. When the vertical projections of any two adjacent radial extraction sections are on the same plane, the included angle between the two adjacent extraction holes is 45°. This structure can minimize the number of extraction holes and make the extraction radiation range of each extraction hole as uniform as possible. The cylindrical area with the vertical shaft as the center line is more balanced in fracturing and permeability enhancement and coalbed methane extraction operations, with basically no dead angles.

[0018] (2) An extraction screen is installed inside the extraction hole. This not only supports the extraction hole and prevents it from collapsing, but also has several screen holes evenly distributed on it. When fracturing gas is injected, it can be injected into the coal reservoir through the screen holes. When extracting coalbed methane, the gas in the coal reservoir can enter the extraction screen through the screen holes and be extracted. The filter plate improves the permeability between the extraction screen and the coal reservoir, while preventing coal from entering the extraction screen.

[0019] (3) Several water guide pipes are evenly installed in the circumferential direction at the lower part of the casing. Water in the coal reservoir seeps down to the top of the rock strata and no longer seeps down along the rock strata. Water in the upper rock strata and coal reservoir can flow into the semi-circular pipe through the drainage hole, and then flow down into the water storage part at the bottom of the casing through the water guide pipe. At the same time, it seeps down through the cementing crushed stones. Finally, it all flows into the casing through the water guide pipe. At the same time, coal dust will also flow into the casing through the water guide pipe. The submersible pump installed in the casing pumps the coal dust mixed with water to the surface. Since the water in the coal reservoir and the rock strata above the coal reservoir cannot flow down through the vertical shaft wall, the water content in the coal reservoir will increase, affecting the production of coalbed methane. Therefore, the several semi-circular pipes not only have the function of rapid water conduction, but also have the function of improving the strength of the casing.

[0020] (4) Each extraction screen is inclined with the outer side lower than the inner side to prevent water seeping into the extraction screen from flowing to the inner port of the extraction screen. Since the inner diameter of the extraction screen is smaller than the diameter of the through hole and the lowest position of the inner port of the extraction screen is lower than the lowest position of the through hole, this structure further prevents water in the extraction screen from entering the through hole on the casing through the inner port of the extraction screen. In order to prevent coal from entering the extraction screen through the screen hole, several hemispherical support and ventilation meshes can be fixedly welded to the outer circle of the extraction screen. Each hemispherical support and ventilation mesh covers one screen hole. This not only supports the coal but also does not reduce the ventilation area between the screen hole and the coal. The sum of the outer diameter of the extraction screen and the diameter of the hemispherical support ventilation mesh should be slightly smaller than the inner diameter of the extraction hole. This not only facilitates the installation of the extraction screen into the extraction hole, but also, based on the principle of borehole pressure relief, provides a larger pressure relief space for the coal seam by creating an annular space between the outer circle of the extraction screen inserted into the extraction hole and the inner circle of the extraction hole, thus improving the safety of the coalbed methane extraction process. The extraction screen consists of several sections, with adjacent sections connected by threads or welding.

[0021] (5) The specific process of the sealed gas extraction device for extracting coalbed methane is as follows: the hoisting device (winch) hooks and connects the hanging ring on the top of the sealed gas extraction device, and connects 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 opening recorded during construction.

[0022] The lifting device lowers the sealed gas distribution device along the casing to the uppermost radial extraction section. At this point, the inner ends of the four extraction screens are located between the upper and lower extraction annular sealing bladders. The lifting device is then closed, and two air pumps are started. The air pumps fill the extraction annular sealing bladders with air through the inflation pipes, causing the annular sealing bladders to expand radially. The pressure signal monitored in real time by the 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 air pumps and the inflation solenoid valve. The extraction annular sealing bladder 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 from the inside of the extraction screens through the extraction main pipe, extraction connecting pipe, central chamber, extraction hole, and through hole. The coalbed methane in the coal reservoir overflows through the fractures enhanced by fracturing and enters the extraction screens through the screen holes, where it is pumped into the underground reservoir by the extraction pump. The gas is stored in a gas storage facility or LNG plant. A flow meter is installed 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 shut down, and the PLC controller sends an opening command to the exhaust solenoid valve. The high-pressure gas in the extraction annular sealing bladder is discharged through the inflation pipe and exhaust pipe joint. The outer circle of the extraction annular sealing bladder is no longer in contact with the inner wall of the casing. Then, the lifting device is started to lower the sealed gas-gathering extraction device to the second radial extraction section. Following the operation method of the coalbed methane extraction process of the uppermost radial extraction section, the coalbed methane extraction operation is carried out in the second radial extraction section. After the extraction is completed, it is moved down to extract coalbed methane in other radial extraction sections in turn until the extraction operation of all radial extraction sections is completed. Then, the lifting device lifts the sealed gas-gathering extraction device to the ground, completing the coalbed methane extraction operation.

[0023] (6) The two extraction annular sealing bladders of the sealed gas-gathering extraction device are made of rubber. Shallow annular grooves are respectively provided on the upper and lower parts of the outer circumference of the extraction cylinder. The inner diameter of the extraction annular sealing rubber bladder is equal to the diameter of the bottom of the shallow annular groove. The extraction annular sealing rubber bladder has good stability in the axial direction when fitted inside the shallow annular groove. After the extraction annular sealing rubber bladder is inflated, its inner and outer circles are tightly pressed against the shallow annular groove and the inner circle of the casing, respectively, providing a good sealing effect. The first conduit is used to thread cables for power supply and signal transmission to the first and second gas supply devices. The second conduit is used to thread cables for power supply and signal transmission to the second gas supply device. The guide wheel provides good guidance when the sealed gas-gathering extraction device moves up and down inside the casing, preventing wear on the extraction annular sealing rubber bladder. The main function of the water pipe is to pass through the drain pipe that draws water stored at the bottom of the casing upwards. The outer diameter of the drain pipe is smaller than the inner diameter of the water pipe; therefore, the gap between the drain pipe and the water pipe allows the flowing water to pass through.

[0024] In summary, this utility model employs a vertical shaft for construction. Within the shaft, the coal reservoir is evenly divided into several radial extraction sections along its height, based on thickness. With the shaft as the center line, each radial extraction section includes four extraction holes with an included angle of 90°. Adjacent extraction holes in upper and lower layers are staggered. Then, casing is installed in the shaft and cemented. Extraction screens are installed in the extraction holes. Next, carbon dioxide or nitrogen is injected into the four extraction screens of each radial extraction section to perform fracturing and permeability enhancement on the coal reservoir (fracturing and permeability enhancement can be achieved using a sealed gas-gathering extraction device). Alternatively, high-pressure water injection can be used for hydraulic fracturing (without gas injection, improving the purity of the extracted coalbed methane). Then, coalbed methane is extracted from each radial extraction section (or multiple sealed gas-gathering extraction devices can be used simultaneously to extract from multiple radial extraction sections). By setting a vertical drainage channel on the outer circumference of the casing and installing a water guide pipe at the lower part of the casing (between the bottom of the coal reservoir and the top surface of the rock stratum), the water in the coal reservoir flows into the casing and is extracted by a high-lift submersible pump.

[0025] This invention is based on a scientific principle. By uniformly setting several layers of radial extraction sections in the circumference of the vertical shaft, it is particularly suitable for thicker coal reservoirs. At the same time, it extends the extraction range of the vertical shaft in the radial direction. The coalbed methane extraction process is simple and easy to implement, which increases the extraction output of a single well. It also designs a smooth drainage channel to reduce the moisture in the coal reservoir, thereby ensuring the economy, efficiency, safety and stability of coalbed methane extraction. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the elevation sectional structure of this utility model;

[0027] Figure 2 yes Figure 1 Sectional view of AA;

[0028] Figure 3 yes Figure 1 BB section view;

[0029] Figure 4 yes Figure 1 Enlarged view of section C;

[0030] Figure 5 yes Figure 1 Enlarged view of section D;

[0031] Figure 6 yes Figure 1 A partial enlarged view of the extraction screen tube;

[0032] Figure 7 This is a schematic diagram of the cross-section of a semi-circular tube installed outside the sleeve. Detailed Implementation

[0033] The embodiments of this utility model will be described in further detail below with reference to the accompanying drawings and examples.

[0034] like Figures 1-5 As shown, the coalbed methane vertical well layered extraction system of this utility model includes a vertical shaft that penetrates vertically downward through a coal reservoir 1, with its lower end extending into a rock stratum 2 below the coal reservoir 1. Several radial extraction sections are arranged vertically around the vertical shaft within the coal reservoir 1. A casing 3 is installed coaxially within the vertical shaft, and several vertical drainage channels 5 are provided on the outer circumference of the casing 3 between it and the shaft wall. Cementing gravel 7 is filled between any two adjacent vertical drainage channels 5 within the vertical shaft. Within each radial extraction section... All ports are connected to the inside of casing 3; several water guide pipes 8 are evenly arranged along the circumference at the interface between the bottom of coal reservoir 1 and the rock layer on the casing wall of casing 3. The outer end of the water guide pipe 8 extends into the coal reservoir 1, and the inner end of the water guide pipe 8 passes through casing 3 and is flush with the inner circle of casing 3; a derrick is provided above the shaft opening on the ground, and a hoisting device is provided on the derrick. The steel wire rope of the hoisting device is connected to a sealed gas-gathering extraction device that can move up and down along casing 3 and is connected to the port of each radial extraction section.

[0035] Several radial extraction sections are evenly arranged along the vertical shaft. Each radial extraction section includes four extraction holes 6 arranged in a circular array around the center line of the shaft. The extraction holes 6 are inclined inward and outward along the center line. The angle between the center line of the extraction holes 6 and the horizontal plane is 3-10°. When the vertical projections of any two adjacent radial extraction sections are on the same plane, the angle between the two adjacent extraction holes 6 is 45°.

[0036] Each extraction hole 6 is equipped with an extraction screen tube 4. The outer end of the extraction screen tube 4 is equipped with a filter plate. The sleeve 3 is provided with through holes 9 that correspond to each radial extraction section. The inner diameter of the extraction screen tube 4 is smaller than the diameter of the through hole 9. The inner end of the extraction screen tube 4 is fixedly connected to the outer circle of the sleeve 3. Each extraction screen tube 4 is connected to the inside of the sleeve 3 through one of the aforementioned through holes 9. The lowest position of the inner end of the extraction screen tube 4 is lower than the lowest position of the through hole 9.

[0037] The extraction screen pipe 4 has several screen holes 10 on the pipe wall between the casing and the filter plate at a distance of 0.5-1m. Several hemispherical support and ventilation nets 11 are fixedly welded to the outer circle of the extraction screen pipe 4, and each hemispherical support and ventilation net 11 covers one screen hole 10.

[0038] The vertical drainage channel 5 adopts a semi-circular pipe 12 welded to the outer circle of the sleeve 3. All the semi-circular pipes 12 are arranged in a circumferential array along the center line of the sleeve 3. The upper end of the semi-circular pipe 12 is higher than the ground and is equipped with a breathable cover plate. The lower end of the semi-circular pipe 12 is connected to the water guide pipe 8. Several drainage holes 13 are evenly opened on the semi-circular pipe 12 along the length direction. A stainless steel filter screen 14 covering the drainage holes 13 is welded to the outer circle of the semi-circular pipe 12.

[0039] The sealed gas extraction device includes an extraction cylinder 31 whose centerline coincides with the centerline of the casing 3. An upper sealing plate 32 and a lower sealing plate 33 are fixedly installed at the upper and lower ends of the extraction cylinder 31, respectively. An extraction annular sealing bladder 34 is fixedly installed at the upper and lower parts of the outer circumference of the extraction cylinder 31. An upper flat plate 35 and a lower flat plate 36 are horizontally arranged inside the extraction cylinder 31, dividing the interior of the extraction cylinder 31 into an upper chamber 37, a middle chamber 38, and a lower chamber 39. The extraction cylinder 31 is positioned between the upper flat plate 35 and the lower flat plate 36. An air extraction port 40 is provided intermittently. The lower end of the extraction connecting pipe 41 passes through the upper chamber 37 and is fixedly connected to the upper plate 35. The interior of the extraction connecting pipe 41 is connected to the interior of the middle chamber 38. The upper chamber 37 is provided with a first air supply device connected to the upper extraction annular sealing bladder 34. The lower chamber 39 is provided with a second air supply device connected to the lower extraction annular sealing bladder 34. An extraction connecting pipe 41 is provided at the center of the upper sealing plate 32. An extraction pump is provided on the ground. The upper end of the extraction connecting pipe 41 is connected to the extraction pump through the extraction main pipe.

[0040] The first and second gas supply devices have the same structure, both including an air pump 43. The air pump 43 has an air outlet connected to an air filling pipe 44. The outlet end of the air filling pipe 44 passes through the extraction cylinder 31 and is connected to the extraction annular sealing bladder 34. A pressure sensor 45 and an air filling solenoid valve 46 are installed on the air filling pipe 44. An exhaust pipe connector 47 is connected between the air filling solenoid valve 46 and the extraction annular sealing bladder 34 on the air filling pipe 44. An exhaust solenoid valve 48 is provided on the exhaust pipe connector 47.

[0041] Both the upper sealing plate 32 and the lower sealing plate 33 are provided with a number of guide wheels 49 that are rolled and connected to the inner circle of the sleeve 3, and at least three hanging rings 50 are evenly provided on the upper cover plate 10 along the circumferential direction.

[0042] A vertical 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, and the center line of the water pipe 51 is parallel to the center line of the extraction cylinder 31.

[0043] The upper sealing plate 32 is connected to a first threading pipe 52 that is parallel to and in contact with the extraction connecting pipe 41. The lower end of the first threading pipe 52 is connected to the interior of the upper chamber 37. A second threading pipe 53 that passes through the middle chamber 38 is provided between the upper sealing plate 32 and the lower sealing plate 33. The lower sealing plate 33 is provided with threading holes 54 that correspond to the upper and lower ends of the second threading pipe 53.

[0044] The working principle and technical effects of this utility model are as follows:

[0045] (1) This utility model opens a vertical shaft and evenly opens multiple radial extraction sections from top to bottom in the coal reservoir 1. Each radial extraction section includes extraction holes 6 with an included angle of 90°. This allows for a greater extraction range through radial radiation from the vertical shaft, thereby increasing the extraction volume of a single well. When the vertical projections of any two adjacent radial extraction sections are on the same plane, the included angle between the two adjacent extraction holes 6 is 45°. This structural setting can minimize the number of extraction holes 6 opened, and at the same time, it can make the extraction radiation range of each extraction hole 6 as uniform as possible. The cylindrical area with the vertical shaft as the center line is more balanced in fracturing and permeability enhancement and coalbed methane extraction operations, with basically no dead angles.

[0046] (2) An extraction screen 4 is installed inside the extraction hole 6. This not only supports the extraction hole 6 to prevent it from collapsing, but also has several screen holes 10 evenly distributed on it. When fracturing gas is injected, it can be injected into the coal reservoir 1 through the screen holes 10. When extracting coalbed methane, the gas in the coal reservoir 1 can enter the extraction screen 4 through the screen holes 10 and be extracted. The filter plate improves the permeability between the extraction screen 4 and the coal reservoir 1, while preventing coal from entering the extraction screen 4.

[0047] (3) Several water guide pipes 8 are evenly arranged in the lower circumferential direction of the casing 3. The water in the coal reservoir 1 seeps down to the top of the rock layer 2 and no longer seeps down along the rock layer 2. The water in the upper rock layer 2 and the coal reservoir 1 can flow into the semi-circular pipe 12 through the drainage hole 13, and then flow down into the water storage part at the bottom of the casing 3 through the water guide pipe 8. At the same time, it seeps down through the cementing crushed stone 7, and finally all flows into the inside of the casing 3 through the water guide pipe 8. At the same time, coal dust will also flow into the casing 3 through the water guide pipe 8. The submersible pump installed in the casing 3 pumps the coal dust mixed with water to the surface. Since the water in the coal reservoir 1 and the rock layer 2 above the coal reservoir 1 cannot flow down through the vertical shaft wall, the water content in the coal reservoir 1 will increase, affecting the production of coalbed methane. Therefore, the several semi-circular pipes 12 not only have the function of rapid water conduction, but also have the function of improving the strength of the casing 3.

[0048] (4) Each extraction screen 4 is inclined with the outer side lower than the inner side to prevent water seeping into the extraction screen 4 from flowing to the inner port of the extraction screen 4. Since the inner diameter of the extraction screen 4 is smaller than the diameter of the through hole 9 and the lowest position of the inner port of the extraction screen 4 is lower than the lowest position of the through hole 9, this structure further prevents water in the extraction screen 4 from entering the through hole 9 on the casing 3 through the inner port of the extraction screen 4. In order to prevent coal from entering the extraction screen 4 through the screen hole 10, several hemispherical support and ventilation nets 11 can be fixedly welded to the outer circle of the extraction screen 4. Each hemispherical support and ventilation net 11 covers one screen hole 10. This not only supports the coal but also does not reduce the ventilation area between the screen hole 10 and the coal. The sum of the outer diameter of the extraction screen pipe 4 and the diameter of the hemispherical support ventilation net 11 should be slightly smaller than the inner diameter of the extraction hole 6. This not only facilitates the installation of the extraction screen pipe 4 into the extraction hole 6, but also, based on the principle of borehole pressure relief, provides a larger pressure relief space for the coal seam by creating an annular space between the outer circle of the extraction screen pipe 4 inserted into the extraction hole 6 and the inner circle of the extraction hole 6, thereby improving the safety of the coalbed methane extraction process. The extraction screen pipe 4 consists of several sections, with adjacent sections connected by threads or welding.

[0049] (5) The specific process of the sealed gas extraction device for extracting coalbed methane is as follows: the hoisting device (winch) hooks and connects the top of the sealed gas extraction device to the hanging ring 50, and connects the extraction pump, the extracted 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 opening recorded during construction.

[0050] The lifting device lowers the sealed gas-gathering extraction device along the casing 3 to the uppermost radial extraction section. At this point, the inner ends of the four extraction screen pipes 4 are all located between the upper and lower extraction annular sealing bladders 34. The lifting device is then closed, and two air pumps 43 are started. The air pumps 43 inject air into the extraction annular sealing bladders 34 through the inflation pipes 44, causing the extraction annular sealing bladders 34 to expand radially. The pressure signal monitored in real time by the pressure sensor 45 is transmitted to the PLC controller on the ground. When the inflation pressure reaches a certain level... When the set pressure value is reached, the PLC controller sends a closing command to the air pump 43 and the inflation solenoid valve 46. The extraction annular sealing bladder 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 turned on. The extraction pump extracts coalbed methane from the inside of the extraction screen pipe 4 through the extraction main pipe, extraction connecting pipe 41, central chamber 38, extraction hole 40, and through hole 5. The coalbed methane in the coal reservoir 1 overflows through the fractures enhanced by fracturing and enters the extraction system through the screen hole 71. The coalbed methane is pumped into the underground gas storage facility or LNG plant by the extraction pump inside the screen pipe 4. A flow meter is installed 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 shut off, and the PLC controller sends an opening command to the exhaust solenoid valve 48. The high-pressure gas in the extraction annular sealing bladder 34 is discharged through the inflation pipe 44 and the exhaust pipe joint 47. The outer circle of the extraction annular sealing bladder 34 is no longer in contact with the inner wall of the casing 3. Then, the lifting device is started to lower the sealed gas-gathering extraction device to the second radial extraction section. Following the operation method of the coalbed methane extraction process of the uppermost radial extraction section, the coalbed methane extraction operation is carried out in the second radial extraction section. After the extraction is completed, it is moved down to extract coalbed methane in other radial extraction sections in turn until the extraction operation of all radial extraction sections is completed. Then, the lifting device lifts the sealed gas-gathering extraction device to the ground, completing the coalbed methane extraction operation.

[0051] (6) The two extraction annular sealing bladders 34 of the sealed gas extraction device are made of rubber. Shallow annular grooves are respectively provided on the upper and lower parts of the outer circumference of the extraction cylinder 31. The inner diameter of the extraction annular sealing rubber bladder 34 is equal to the diameter of the bottom of the shallow annular groove. The extraction annular sealing rubber bladder 34 has good stability in the axial direction when fitted inside the shallow annular groove. After the extraction annular sealing rubber bladder 34 is inflated, its inner and outer circumferences are tightly pressed against the shallow annular groove and the inner circumference of the sleeve 3, respectively, resulting in a good sealing effect. The first conduit 52 is used to thread cables for power supply and signal transmission to the first and second gas supply devices. The second conduit 53 is used to thread cables for power supply and signal transmission to the second gas supply device. The guide wheel 49 provides good guidance when the sealed gas extraction device moves up and down inside the sleeve 3, preventing wear on the extraction annular sealing rubber bladder 34. The main function of the water pipe 51 is to pass through the drain pipe 69, which draws water stored at the bottom of the sleeve 3 upwards. The outer diameter of the drain pipe 69 is smaller than the inner diameter of the water pipe 51. Therefore, the gap between the drain pipe 69 and the water pipe 51 can allow the flowing water to pass through.

[0052] The water and coal dust stored in the water storage section at the bottom of the vertical shaft in this utility model need to be pumped upwards. Therefore, a submersible pump 55 and an anti-sedimentation agitation device are installed in the casing 3 at the bottom of the vertical shaft.

[0053] The anti-sedimentation agitation device includes a support ring 56, a motor reducer 57, a mounting box 58, a stirring shaft 59, an upper bracket 60, and a lower bracket 61. The outer diameter of the support ring 56 is equal to the inner diameter of the sleeve 3, and the support ring 56 is coaxially fixed to the inner wall of the sleeve 3. The mounting box 58 is fixedly mounted on the support ring 56, and the motor reducer 57 is located inside the mounting box 58. The stirring shaft 59 is vertically arranged, and both the upper bracket 60 and the lower bracket 61 are fixedly connected to the inner wall of the sleeve 3. The upper and lower parts of the stirring shaft 59 are rotatably connected to the upper bracket 60 and the lower bracket 61 respectively via waterproof bearings 62. Several stirring rods 63 are fixedly installed on the stirring shaft 59. The upper end of the stirring shaft 59 passes through the bottom of the mounting box 58 and extends into the mounting box 58. The mounting box 58 is equipped with a positioning bearing that is rotatably connected to the stirring shaft 59. The main shaft of the motor reducer 57 is equipped with a main gear 64. The stirring shaft 59 is equipped with a driven gear 65 that meshes with the main gear 64. The mounting box 58 is equipped with a downpipe 66 that passes vertically through the mounting box 58. The top of the mounting box 58 is equipped with a water collecting hopper 67 that is connected to the upper end of the downpipe 66 and is larger at the top and smaller at the bottom. The upper edge of the water collecting hopper 67 is connected to the inner wall of the sleeve 3.

[0054] The inner wall of the sleeve 3 is provided with a mounting bracket 68, and the submersible pump 55 is mounted on the mounting bracket 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 diameter of the water pipe 51 and the downpipe 66. The drain pipe 69 passes through the downpipe 66 and the water pipe 51.

[0055] The specific process of pumping the water and coal dust that flow into the bottom of the 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 coal dust that has settled at the bottom of the casing 3. The submersible pump 55 pumps the coal dust mixed with water through the drain pipe 69 to the ground.

[0056] The derrick, lifting device, air injection pump, extraction pump, and underground gas storage tank in this utility model are all existing technologies, and their specific structures will not be described in detail, nor are they shown in the figures. In addition, to improve the extraction effect, an extraction booster pump is installed in the central chamber 38 within the extraction cylinder 31.

[0057] The above embodiments illustrate the basic principles and features of this utility model. However, the above descriptions are merely preferred embodiments and are not limited to these embodiments. Those skilled in the art, inspired by this patent, can make many modifications and improvements without departing from the spirit and scope of the claims, all of which fall within the protection scope of this utility model. Therefore, the patent and its scope of protection should be determined by the appended claims.

Claims

1. A coalbed methane vertical well stratified extraction system, characterized in that: This includes a vertical shaft that penetrates the coal reservoir vertically downwards, with its lower end extending into the rock strata below the coal reservoir; several radial extraction sections are arranged vertically around the shaft within the coal reservoir; a casing is installed coaxially inside the shaft, with several vertical drainage channels between the casing's outer circumference and the shaft wall; cementing gravel is filled between any two adjacent vertical drainage channels inside the shaft; the inner end of each radial extraction section is connected to the inside of the casing; several water guide pipes are evenly arranged circumferentially on the casing wall at the interface between the bottom of the coal reservoir and the rock strata, with the outer end of the water guide pipe extending into the coal reservoir and the inner end of the water guide pipe passing through the casing and flush with the inner circumference of the casing; On the ground, a derrick is installed above the shaft opening. A lifting device is installed on the derrick. The steel wire rope of the lifting device is connected to a sealed gas-gathering extraction device that can move up and down along the casing and communicate with the inner port of each radial extraction section.

2. The coalbed methane vertical well stratified extraction system according to claim 1, characterized in that: Several radial extraction sections are evenly arranged along the vertical shaft. Each radial extraction section includes four extraction holes arranged in a circular array around the center line of the shaft. The extraction holes are inclined inward and outward along the center line. The angle between the center line of the extraction hole and the horizontal plane is 3-10°. When the vertical projections of any two adjacent radial extraction sections are on the same plane, the angle between the two adjacent extraction holes is 45°.

3. The coalbed methane vertical well stratified extraction system according to claim 2, characterized in that: Each extraction hole is equipped with an extraction screen tube, and the outer end of the extraction screen tube is equipped with a filter plate. The casing has through holes that correspond to each radial extraction section. The inner diameter of the extraction screen tube is smaller than the diameter of the through hole. The inner end of the extraction screen tube is fixedly connected to the outer circle of the casing. Each extraction screen tube is connected to the inside of the casing through one of the aforementioned through holes. The lowest position of the inner end of the extraction screen tube is lower than the lowest position of the through hole. The extraction screen pipe has several screen holes on the pipe wall between the casing and the filter plate at a distance of 0.5-1m. Several hemispherical support and ventilation nets are fixedly welded to the outer circle of the extraction screen pipe, and each hemispherical support and ventilation net covers one screen hole.

4. The coalbed methane vertical well stratified extraction system according to any one of claims 1-3, characterized in that: The vertical drainage channel uses a semi-circular pipe welded to the outer circumference of the casing. All the semi-circular pipes are arranged in a circumferential array along the center line of the casing. The upper end of the semi-circular pipe is higher than the ground and is equipped with a vent cover. The lower end of the semi-circular pipe is connected to the water guide pipe. Several drainage holes are evenly opened on the semi-circular pipe along its length. A stainless steel filter screen is welded to the outer circumference of the semi-circular pipe to cover the drainage holes.

5. The coalbed methane vertical well stratified extraction system according to claim 3, characterized in that: The sealed gas extraction device includes an extraction cylinder whose centerline coincides with the centerline of the casing. An upper sealing plate and a lower sealing plate are fixedly installed at the upper and lower ends of the extraction cylinder, respectively. An extraction annular sealing bladder is fixedly installed at the upper and lower parts of the outer circumference of the extraction cylinder. An upper plate and a lower plate are horizontally arranged inside the extraction cylinder, dividing the interior into an upper chamber, a middle chamber, and a lower chamber. An extraction hole is opened between the upper and lower plates on the extraction cylinder. The lower end of the extraction connecting pipe passes through the upper chamber and is fixedly connected to the upper plate. The interior of the extraction connecting pipe communicates with the interior of the middle chamber. A first gas supply device connected to the upper extraction annular sealing bladder is located in the upper chamber, and a second gas supply device connected to the lower extraction annular sealing bladder is located in the lower chamber. An extraction connecting pipe is located at the center of the upper sealing plate, and an extraction pump is located on the ground. The upper end of the extraction connecting pipe is connected to the extraction pump via the extraction main pipe.

6. The coalbed methane vertical well stratified extraction system according to claim 5, characterized in that: The first and second gas supply devices have the same structure, both including an air pump. The air pump outlet is connected to an inflation pipe. The outlet end of the inflation pipe passes through the extraction cylinder and is connected to the extraction annular sealing bladder. A pressure sensor and an inflation solenoid valve are installed on the inflation pipe. An exhaust pipe connector is connected between the inflation solenoid valve and the extraction annular sealing bladder on the inflation pipe. An exhaust solenoid valve is installed on the exhaust pipe connector.

7. The coalbed methane vertical well stratified extraction system according to claim 6, characterized in that: Both the upper and lower sealing plates are provided with several guide wheels that are rolled and connected to the inner circle of the sleeve, and at least three hanging rings are evenly provided on the upper cover plate along the circumferential direction; A vertical water pipe is installed between the upper and lower sealing plates, passing through both the upper and lower sealing plates, with the center line of the water pipe parallel to the center line of the extraction cylinder. The upper sealing plate is connected to a first threaded pipe that is parallel to and in contact with the extraction connecting pipe. The lower end of the first threaded pipe is connected to the interior of the upper chamber. A second threaded pipe that passes through the middle chamber is provided between the upper sealing plate and the lower sealing plate. The lower sealing plate has threaded holes that correspond to the upper and lower ends of the second threaded pipe.

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