Experimental equipment and method for coal extraction and pressure relief of horizontal well

Abstract

The invention discloses experimental equipment for coal extraction and pressure relief of a horizontal well, which comprises a carbon dioxide storage tank, a water-based storage tank, a ball valve I, a ball valve II, an air pump system, a liquid pump system, an experimental seat and a plurality of experimental loading cylinders, the experimental loading cylinders are arranged and distributed, the experimental loading cylinders are horizontally mounted on the experimental seat, and coal rock sample columns are stored in the experimental loading cylinders; a horizontal channel is formed in the center of the coal rock sample column, and a coal taking pipe is horizontally and slidably arranged in the experiment loading cylinder; delivery pipes are arranged outside the experiment loading cylinders, the exhaust end of the carbon dioxide storage tank is connected with a sealing pipe, and an air pump system is arranged between the delivery pipes and the sealing pipe; the liquid discharging end of the water-based storage tank is connected with a liquid feeding pipe, and the other end of the liquid feeding pipe is communicated with the conveying pipe through a tee joint; according to the experimental device, various complex stress states of the coal seam in the actual mining process can be simulated, and the mechanical behavior of the coal seam can be evaluated more comprehensively.

Description

Technical Field

[0001] The invention belongs to the technical field of coal seam horizontal well pressure relief experimental equipment, in particular to experimental equipment and method for horizontal well coal excavation pressure relief. Background Art

[0002] In the process of coal mining, efficient extraction of coalbed methane (methane) is crucial to ensure mine safety and improve resource utilization. Traditional vertical well mining methods have many limitations, such as low extraction efficiency and limited impact range; while horizontal well segmented coal excavation pressure relief and permeability enhancement technology can effectively improve the extraction efficiency of coalbed methane, reduce mine gas concentration, reduce the risk of gas explosion, and improve the permeability of coal seams, creating favorable conditions for subsequent coal mining; At present, the research on the mechanism of horizontal well segmented coal excavation pressure relief and permeability enhancement involves multiple disciplines such as coal mining, rock mechanics, and fluid mechanics. Although there have been certain experimental and numerical simulation studies, the specific mechanism of stress redistribution and crack expansion in coal seams after coal excavation is still not clear enough, and further in-depth research is needed; In the prior art, such as the invention patent with patent number CN109632625B, the high-pressure pulsating fluid injection module mainly used can effectively improve the impact strength and control accuracy of the experimental simulation, and simulate the pressure pulsation excitation and stress release of the tectonic coal coalbed methane horizontal well; but it lacks environmental control of the coal seam and cannot effectively simulate the porosity and stress changes near the coal seam horizontal well, resulting in significant differences in the experimental results, making it impossible to conduct a comparative reference for the experiment, affecting the reliability and scientificity of the research.

[0003] Therefore, it is necessary to provide experimental equipment and methods for decompression of coal mining in horizontal wells to solve the problems raised in the above-mentioned background technology. Summary of the invention

[0004] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: experimental equipment for decompression of coal mining in horizontal wells, including a carbon dioxide storage tank, a water-based storage tank, a ball valve 1, a ball valve 2, an air pump system, a liquid pump system, an experimental seat and an experimental carrier tube, wherein the experimental carrier tubes are arranged and distributed in a plurality, each of which is horizontally installed on the experimental seat, and a coal rock sample column is stored therein, a horizontal channel is opened in the center of the coal rock sample column, a coal extraction pipe is horizontally slidably arranged in the experimental carrier tube, a threaded blade is rotatably arranged in the coal extraction pipe, and the threaded blade transports the coal body at the horizontal channel to the outside through the coal extraction pipe; A delivery pipe is arranged outside the experimental carrier tube, a fracturing channel is opened on the pipe wall of the coal extraction pipe, and one end of the delivery pipe is sealed and connected to the fracturing channel; The exhaust end of the carbon dioxide storage tank is connected to a sealing pipe, the other end of the sealing pipe is connected to the delivery pipe, a ball valve is installed on the sealing pipe, and an air pump system is arranged between the delivery pipe and the sealing pipe; The discharge end of the water-based storage tank is connected to a liquid delivery pipe, the other end of the liquid delivery pipe is connected to the delivery pipe through a tee, the second ball valve is installed on the liquid delivery pipe, and a liquid pump system is also provided on the liquid delivery pipe; The delivery pipe is also provided with a pressure gauge and a flow meter; The experimental carrier tube is provided with an extraction system outside.

[0005] Furthermore, as a preference, each of the experimental carrier tubes is provided with a plurality of stress loading units axially distributed therein, and each of the stress loading units performs different torsional stress loading at each position of the coal rock sample column; and a plurality of expansion units are also circumferentially distributed therein, and the expansion units are all inserted and buried in the coal rock sample column, and the expansion units expand the coal rock sample column at multiple points during the gas pressure loading process.

[0006] Furthermore, as a preference, stress monitoring sensors are distributed in the experimental carrier tube, a central control system is provided outside the experimental seat, and the central control system is electrically connected to each of the stress monitoring sensors through a data acquisition instrument.

[0007] Further, as a preference, the stress loading unit comprises an outer ring sleeve, which is fixed concentrically in the test carrier tube, and a swivel is rotatably connected in the outer ring sleeve; The coal-rock sample column is covered with an annular protective mesh sleeve, a steel ring is arranged outside the protective mesh sleeve, and the rotating ring is arranged coaxially with the steel ring; An arc-shaped liquid channel is provided in the outer ring sleeve, and a liquid inlet and a liquid outlet are distributed up and down on the side wall of the outer ring sleeve. The liquid inlet is connected to a circulation pipe outside, and the liquid outlet is connected to a return pipe outside. Guide oil is transported in the circulation pipe and the return pipe; a liquid storage cylinder is provided outside the return pipe, and the other end of the circulation pipe is connected to the output port of the liquid storage cylinder.

[0008] Further, as a preference, a plurality of shaft plates are distributed on the circumference of the inner wall of the steel ring, and a notch is provided on the protective mesh sleeve, and each of the shaft plates is embedded in the coal rock sample column through the notch; A plurality of inner springs are distributed between the rotating ring and the steel ring; and a plurality of baffles are arranged on the outer wall of the rotating ring, and the baffles push the rotating ring to deflect when the guide oil continues to flow, and at this time, the inner springs are gradually compressed; A plurality of partition liners cooperating with the spoiler are distributed on the inner wall of the outer ring sleeve, each of the partition liners can be in sealing contact with the spoiler, and when the guide oil is pumped at different pressures, the gap between the partition liners and the spoiler increases or decreases accordingly.

[0009] Furthermore, as a preference, a liquid conducting groove is also provided on the inner wall of the rotating ring, the cross section of the liquid conducting groove is an arc-shaped structure, and a plurality of leaf plates are distributed on the inner side wall of the liquid conducting groove; Among them, steel balls are mixed in the guide oil, and the steel balls form an unstable impact on the leaf plate as the guide oil flows along the guide groove.

[0010] Further, as a preference, the expansion unit comprises a protective tube, on which a plurality of high-pressure airbags are distributed axially, a plurality of air tubes of different lengths are distributed in the protective tube, one end of each of the air tubes is respectively connected to the air inlet of the high-pressure airbag; a sealing disk is fixed at the end of the protective tube, and an air channel corresponding to the air tube is arranged on the circumference of the sealing disk; A through pipe is coaxially and sealingly arranged on one side of the protective tube close to the sealing disk, one end of the through pipe is in sealing contact with the sealing disk, and oblique holes are arranged in the through pipe, which are sealed and connected with each airway during the rotation and adjustment of the through pipe.

[0011] Further, as a preference, a mounting sleeve is provided on the sliding sleeve of the through-tube, a support spring is connected to one side of the mounting sleeve, and the support spring sleeve is arranged outside the through-tube.

[0012] Further, as a preferred method, a horizontal well coal excavation pressure relief and permeability enhancement extraction experimental method for crushed soft low permeability coal seams is provided. It includes the following steps: Step 1. In the preparation stage, the equipment is connected and operated, and a number of experimental carriers are selected for the experiment. The crushed, soft, and low-permeability coal sample columns obtained in the early stage are placed in each experimental carrier, and each coal sample column is ultrasonically scanned by an ultrasonic detector to detect the distribution of cracks in each coal sample column; Step 2. Loading simulation: for each experimental carrier tube, the coal-rock sample column in each experimental carrier tube is preferentially subjected to multi-point expansion pressure by using an expansion unit, and the stress changes of the coal-rock sample column at different positions are monitored by a stress sensor to ensure that the stress loading of each experimental carrier tube meets the experimental requirements; then, according to the experimental restoration simulation requirements, the coal-rock sample column is subjected to torsional stress loading at different positions by using each stress loading unit, wherein during torsional stress loading, the diversion oil can be continuously transported through the circulation pipe, so that the swivel forms an uninterrupted dynamic loading on the coal-rock sample column under the deflection action; Step 3. Coal is removed to relieve pressure, and the threaded blades in the coal extraction pipe are started. The coal extraction pipe is gradually pushed deeper into the coal sample column, thereby forming a horizontal channel in the coal sample column; at the same time, the air pump system or the liquid pump system is started to deliver the carbon dioxide in the carbon dioxide storage tank and the water-based liquid in the water-based storage tank into the fracturing channel of the coal extraction pipe through the delivery pipe, so as to perform internal fracturing on the coal sample column; Step 4. Extraction test: extract coalbed methane from the coal sample column through the extraction system installed outside the experimental carrier tube, and record the relevant parameters of the extraction volume and pressure; Step 5. Data collation and comparison: collate the data recorded during the experiment, including stress, air pressure, flow rate, and extraction volume. Compare the crack expansion and permeability changes of the coal rock sample column in each experimental carrier tube, so as to evaluate the impact of different coal excavation and pressure relief on the permeability of the broken, soft, and low-permeability coal seams.

[0013] Compared with the prior art, the present invention has the following beneficial effects: Coal rock sample columns can be placed in the multiple experimental carrier tubes used in the present invention so as to conduct control experiments, thereby more accurately evaluating the migration of coalbed methane during coal excavation and pressure relief in broken, soft and low-permeability coal seams with different porosities and stress distributions, thereby improving the experimental credibility and restoring authenticity; The expansion unit mainly used in the present invention can preferentially perform internal expansion pressure on the coal rock sample column, thereby adjusting the porosity distribution of the coal rock sample column, and then the stress loading unit used can perform different torsional stress loading at various positions of the coal rock sample column, simulating various complex stress states existing in the coal seam during the actual mining process, increasing the flexibility of the experiment, and more comprehensively evaluating the mechanical behavior of the coal seam. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the system flow of the present invention; Figure 2 It is a schematic diagram of the structure of the experimental carrier tube in the present invention; Figure 3 is a cross-sectional view of an experimental carrier tube in the present invention; Figure 4 It is a structural schematic diagram of the stress loading unit in the present invention; Figure 5 is a cross-sectional view of the stress loading unit in the present invention; Figure 6 It is a structural schematic diagram of the liquid guiding groove in the present invention; Figure 7 is a cross-sectional view of the swivel ring of the present invention; Figure 8 It is a structural schematic diagram of the expansion unit in the present invention; In the figure: 1. Experimental carrier; 11. Experimental seat; 12. Delivery pipe; 13. Flow meter; 14. Pressure gauge; 15. Threaded blade; 16. Coal extraction pipe; 2. Central control system; 21. Carbon dioxide storage tank; 22. Water-based storage tank; 23. Sealing pipe; 24. Ball valve 1; 25. Air pump system; 26. Liquid pump system; 27. Liquid delivery pipe; 28. Data acquisition instrument; 3. Stress loading unit; 31. Outer ring sleeve; 32 , swivel; 33, protective mesh; 34, steel ring; 35, liquid inlet; 36, circulation pipe; 37, return pipe; 38, shaft plate; 39, inner spring; 310, baffle; 311, partition lining; 4, expansion unit; 41, protective tube; 42, high-pressure airbag; 43, air pipe; 44, air inlet; 45, airway; 46, through pipe; 47, oblique holes; 48, installation sleeve; 5, liquid guide groove; 51, leaf plate. DETAILED DESCRIPTION

[0015] See also Figure 1-Figure 8 In an embodiment of the present invention, an experimental device for decompression of coal mining in a horizontal well comprises a carbon dioxide storage tank 21, a water-based storage tank 22, a ball valve 1 24, a ball valve 2, an air pump system 25, a liquid pump system 26, an experimental seat 11 and an experimental carrier 1, wherein the experimental carrier 1 is arranged in a plurality of distributed arrangements, each of which is horizontally mounted on the experimental seat 11, and a coal sample column is stored therein, a horizontal channel is opened in the center of the coal sample column, a coal extraction pipe 16 is horizontally slidably arranged in the experimental carrier 1, a threaded blade 15 is rotatably arranged in the coal extraction pipe 16, and the threaded blade 15 transports the coal body at the horizontal channel to the outside through the coal extraction pipe 16; A delivery pipe 12 is disposed outside the experimental carrier tube 1, a fracturing channel is opened on the pipe wall of the coal extraction pipe 16, and one end of the delivery pipe 12 is sealed and connected to the fracturing channel; The exhaust end of the carbon dioxide storage tank 21 is connected to a sealing pipe 23, the other end of the sealing pipe 23 is connected to the delivery pipe 12, a ball valve 24 is installed on the sealing pipe 23, and an air pump system 25 is arranged between the delivery pipe 12 and the sealing pipe 23; The discharge end of the water-based storage tank 22 is connected to a liquid delivery pipe 27, the other end of the liquid delivery pipe 27 is connected to the delivery pipe 12 through a tee, the ball valve 2 is installed on the liquid delivery pipe 27, and a liquid pump system 26 is also provided on the liquid delivery pipe 27; that is, in the present invention, carbon dioxide gas can be injected into the fracturing channel through the air pump system 25 to perform pneumatic fracturing on the coal rock sample column, and water-based liquid (fracturing fluid) can be injected into the fracturing channel through the liquid pump system 26 to perform hydraulic fracturing on the coal rock sample column, so that different fracturing methods can be selected according to experimental requirements, and pneumatic fracturing or hydraulic fracturing can be used alone, or they can be used in combination to simulate complex fracturing processes.

[0016] The delivery pipe 12 is also provided with a pressure gauge 14 and a flow meter 13; The experimental carrier tube 1 is provided with an extraction system outside, and the extraction system can extract the coalbed methane in the coal rock sample column in the experimental simulation and monitor the coalbed methane extraction flow change data in real time.

[0017] In this embodiment, each of the experimental carrier tubes 1 is provided with a plurality of stress loading units 3 distributed axially, and each of the stress loading units 3 performs different torsional stress loading at each position of the coal rock sample column; and a plurality of expansion units 4 are also distributed circumferentially in the experimental carrier tube 1, and the expansion units 4 are all inserted and buried in the coal rock sample column. During the gas pressure loading process, the expansion units 4 expand the coal rock sample column at multiple points so as to geologically restore the coal rock sample column to make it closer to the actual geological conditions, and at the same time simulate the stress state of the actual coal seam underground.

[0018] As a preferred embodiment, stress monitoring sensors (not shown in the figure) are also distributed in the experimental carrier tube 1, and a central control system 2 is provided outside the experimental seat 11. The central control system 2 is electrically connected to each of the stress monitoring sensors through a data acquisition device 28.

[0019] In this embodiment, the stress loading unit 3 includes an outer ring sleeve 31, which is fixed concentrically in the test carrier tube 1, and a rotating ring 32 is rotatably connected in the outer ring sleeve 31; The coal rock sample column is covered with an annular protective mesh sleeve 33, and a steel ring 34 is arranged outside the protective mesh sleeve 33, and the rotating ring 32 is arranged coaxially with the steel ring 34; An arc-shaped liquid channel is provided in the outer ring sleeve 31, and a liquid inlet 35 and a liquid outlet are distributed on the upper and lower sides of the side wall of the outer ring sleeve 31. The liquid inlet 35 is connected to a circulation pipe 36, and the liquid outlet is connected to a return pipe 37. Guide oil is transported in the circulation pipe 36 and the return pipe 37. A liquid storage cylinder is provided outside the return pipe 37, and the other end of the circulation pipe 36 is connected to the output port of the liquid storage cylinder.

[0020] In this embodiment, a plurality of shaft plates 38 are distributed on the inner wall circumference of the steel ring 34, and a notch is provided on the protective mesh sleeve 33, and each shaft plate 38 is embedded in the coal rock sample column through the notch; A plurality of inner springs 39 are distributed between the swivel 32 and the steel ring 34; and a plurality of baffles 310 are arranged on the outer wall of the swivel 32, and the baffles 310 push the swivel 32 to perform a deflection movement in the continuous flow of the guide oil, at which time the inner springs 39 are gradually compressed; that is, the guide oil in the liquid storage cylinder can enter the arc-shaped liquid channel in the outer ring sleeve 31 through the circulation pipe 36, so that the swivel 32 is pushed to perform a deflection movement through the baffles 310 in the continuous flow, and at this time, the inner springs 39 can form a torsional effect on the steel ring 34, so that torsional stress is generated in the coal rock sample column; A plurality of partition linings 311 cooperating with the spoiler 310 are distributed on the inner wall of the outer ring sleeve 31, and each of the partition linings 311 can be sealed and contacted with the spoiler 310, and when the guide oil is pumped at different pressures, the gap between the partition lining 311 and the spoiler 310 increases or decreases accordingly; and because the guide oil flows continuously and can be pumped at variable pressure, the swivel 32 can form corresponding dynamic stress loading, on the one hand, it can continuously and accurately control the size of the torsional moment, compared with the hydraulic cylinder used in traditional technology, it often needs to be changed by mechanical or manual adjustment to change the torque output, the adjustment range is limited, and the adjustment process is not fine enough; on the other hand, the torsional effect produced by the swivel 32 on the steel ring 34 in the present invention is continuous and variable, and the response speed is fast during adjustment, and almost zero delay can be achieved, and the instantaneous change of loading stress can be quickly simulated to realize real-time control of the loading force output.

[0021] In this embodiment, the inner wall of the rotating ring 32 is further provided with a liquid conducting groove 5, the cross section of the liquid conducting groove 5 is an arc-shaped structure, and a plurality of leaf plates 51 are distributed on the inner side wall of the liquid conducting groove 5; Among them, steel balls are mixed in the diversion oil. The steel balls form an unstable impact on the leaf plate 51 as the diversion oil flows along the liquid guide groove 5, realizing a dynamically variable torsional stress loading effect, thereby effectively simulating the unstable ground pressure changes in the underground broken soft low-permeability coal seam.

[0022] As a preferred embodiment, the expansion unit 4 includes a protective tube 41, on which a plurality of high-pressure airbags 42 are distributed axially, and a plurality of air pipes 43 of different lengths are distributed in the protective tube 41, and one end of each of the air pipes 43 is respectively connected to the air inlet 44 of the high-pressure airbag 42; a sealing disk is fixed at the end of the protective tube 41, and an air channel 45 corresponding to the air pipe is arranged on the circumference of the sealing disk; A through tube 46 is coaxially and sealably rotatably provided on one side of the protective tube 41 close to the sealing disk, one end of the through tube 46 is in sealing contact with the sealing disk, and oblique holes 47 are provided in the through tube 46. The oblique holes 47 are sealably connected with each air passage 45 during the rotation adjustment of the through tube 46. That is to say, the through tube 46 can inject air and pressurize the high-pressure airbag 42 through each air passage 45 during the rotation adjustment, so as to be able to flexibly control various points of the coal rock sample column and effectively adjust the internal pore distribution changes of the coal rock sample column.

[0023] In this embodiment, a mounting sleeve 48 is provided on the sliding sleeve of the through-tube 46 , and a support spring is connected to one side of the mounting sleeve 48 . The support spring sleeve is provided outside the through-tube 46 , so as to facilitate the connection of the air supply hose to the outside through the mounting sleeve 48 .

[0024] In this embodiment, the experimental method of coal digging, pressure relief and permeability enhancement in horizontal wells in broken soft and low permeability coal seams is as follows: It includes the following steps: Step 1. In the preparation stage, the equipment is connected and operated, and a number of experimental carrier tubes 1 are selected for the experiment. The crushed, soft, and low-permeability coal sample columns obtained in the early stage are placed in each experimental carrier tube 1, and each coal sample column is ultrasonically scanned by an ultrasonic detector to detect the distribution of cracks in each coal sample column; Step 2. Loading simulation: for each experimental carrier tube 1, the coal-rock sample column is preferentially subjected to multi-point expansion pressure using the expansion unit 4, and the stress changes of the coal-rock sample column at different positions are monitored by the stress sensor to ensure that the stress loading of each experimental carrier tube 1 meets the experimental requirements; and then, according to the experimental restoration simulation requirements, the coal-rock sample column is subjected to torsional stress loading at different positions through each stress loading unit 3, wherein the diversion oil can be continuously transported through the circulation pipe during torsional stress loading, so that the swivel 32 forms an uninterrupted dynamic loading on the coal-rock sample column under the deflection action; Step 3. Coal is removed to relieve pressure, and the threaded blades 15 in the coal extraction pipe 16 are started. The coal extraction pipe 16 gradually advances into the coal sample column, thereby forming a horizontal channel in the coal sample column; at the same time, the air pump system 25 or the liquid pump system 26 is started to deliver the carbon dioxide in the carbon dioxide storage tank 21 and the water-based liquid in the water-based storage tank 22 into the fracturing channel of the coal extraction pipe 16 through the delivery pipe 12, so as to perform internal fracturing on the coal sample column; Step 4. Extraction test: extract coalbed methane from the coal sample column through the extraction system arranged outside the experimental carrier tube 1, and record the relevant parameters of the extraction volume and pressure; Step 5. Data collation and comparison: collate the data recorded during the experiment, including stress, air pressure, flow rate, and extraction volume. Compare the crack expansion and permeability changes of the coal rock sample column in each experimental carrier tube 1, so as to evaluate the impact of different coal excavation and pressure relief on the permeability of the broken soft and low-permeability coal seam.

[0025] What is described above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An experimental device for decompression of coal mining in a horizontal well, comprising a carbon dioxide storage tank (21), a water-based storage tank (22), a first ball valve (24), a second ball valve, an air pump system (25), a liquid pump system (26), an experimental seat (11) and an experimental carrier tube (1), characterized in that: The experimental carrier tubes (1) are arranged in a plurality and distributed, each of the experimental carrier tubes (1) is horizontally mounted on an experimental seat (11), and a coal rock sample column is stored therein, a horizontal channel is opened in the center of the coal rock sample column, a coal extraction pipe (16) is horizontally slidably arranged in the experimental carrier tube (1), a threaded blade (15) is rotatably arranged in the coal extraction pipe (16), and the threaded blade (15) transports the coal body in the horizontal channel to the outside through the coal extraction pipe (16); A delivery pipe (12) is arranged outside the experimental carrier tube (1), a fracturing channel is opened on the pipe wall of the coal extraction pipe (16), and one end of the delivery pipe (12) is sealed and connected to the fracturing channel; The exhaust end of the carbon dioxide storage tank (21) is connected to a sealing pipe (23), the other end of the sealing pipe (23) is connected to the delivery pipe (12), a ball valve (24) is installed on the sealing pipe (23), and an air pump system (25) is arranged between the delivery pipe (12) and the sealing pipe (23); The discharge end of the water-based storage tank (22) is connected to a liquid delivery pipe (27), the other end of the liquid delivery pipe (27) is connected to the delivery pipe (12) via a tee, the second ball valve is installed on the liquid delivery pipe (27), and a liquid pump system (26) is also provided on the liquid delivery pipe (27); The delivery pipe (12) is also provided with a pressure gauge (14) and a flow meter (13); The experimental carrier tube (1) is provided with an extraction system outside.

2. The experimental equipment for decompression of horizontal well coal mining according to claim 1 is characterized by: A plurality of stress loading units (3) are axially distributed in each of the experimental carrier tubes (1), and each of the stress loading units (3) performs different torsional stress loading at various positions of the coal rock sample column; and a plurality of expansion units (4) are circumferentially distributed in the experimental carrier tube (1), and each of the expansion units (4) is inserted and embedded in the coal rock sample column, and the expansion units (4) expand the coal rock sample column at multiple points during the gas pressure loading process.

3. The experimental equipment for decompression of horizontal well coal mining according to claim 2 is characterized by: Stress monitoring sensors are also distributed in the experimental carrier tube (1), and a central control system (2) is provided outside the experimental seat (11). The central control system (2) is electrically connected to each of the stress monitoring sensors via a data acquisition device (28).

4. The experimental equipment for decompression of horizontal well coal mining according to claim 2 is characterized by: The stress loading unit (3) comprises an outer ring sleeve (31) which is fixed coaxially in the test carrier tube (1), and a rotating ring (32) is rotatably connected in the outer ring sleeve (31); The coal rock sample column is covered with an annular protective mesh sleeve (33), the protective mesh sleeve (33) is provided with a steel ring (34) on its outer surface, and the rotating ring (32) is coaxially arranged with the steel ring (34); An arc-shaped liquid channel is provided inside the outer ring sleeve (31), and a liquid inlet (35) and a liquid outlet are distributed on the side wall of the outer ring sleeve (31) in an upper and lower manner. The liquid inlet (35) is externally connected to a circulation pipe (36), and the liquid outlet is externally connected to a return pipe (37). Guide oil is transported in the circulation pipe (36) and the return pipe (37); a liquid storage cylinder is provided outside the return pipe (37), and the other end of the circulation pipe (36) is connected to the output port of the liquid storage cylinder.

5. The experimental equipment for decompression of horizontal well coal mining according to claim 4 is characterized by: A plurality of shaft plates (38) are distributed around the inner wall of the steel ring (34), and a notch is provided on the protective mesh sleeve (33), and each shaft plate (38) is embedded in the coal rock sample column through the notch; A plurality of inner springs (39) are arranged between the rotating ring (32) and the steel ring (34); and a plurality of baffles (310) are arranged on the outer wall of the rotating ring (32), wherein the baffles (310) push the rotating ring (32) to perform a deflection movement when the guide oil continues to flow, and at this time, the inner springs (39) are gradually compressed; A plurality of partition liners (311) matching with the spoiler (310) are distributed on the inner wall of the outer ring sleeve (31), and each of the partition liners (311) can be in sealing contact with the spoiler (310), and when the guide oil is pumped at different pressures, the gap between the partition liners (311) and the spoiler (310) increases or decreases accordingly.

6. The experimental equipment for decompression of coal mining in horizontal wells according to claim 5 is characterized by: The inner wall of the rotating ring (32) is also provided with a liquid conducting groove (5), the cross section of the liquid conducting groove (5) is an arc-shaped structure, and a plurality of leaf plates (51) are distributed on the inner side wall of the liquid conducting groove (5); The guide oil contains steel balls, which flow along the guide groove (5) with the guide oil and cause unstable impacts on the leaf plate (51).

7. The experimental equipment for decompression of horizontal well coal mining according to claim 2, characterized in that: The expansion unit (4) comprises a protective tube (41) on which a plurality of high-pressure air bags (42) are distributed axially, and a plurality of air pipes (43) of different lengths are distributed inside the protective tube (41), and one end of each of the air pipes (43) is respectively connected to an air inlet (44) of the high-pressure air bag (42); a sealing disk is fixed to the end of the protective tube (41), and an air channel (45) corresponding to the air pipe is arranged on the circumference of the sealing disk; A through pipe (46) is coaxially and sealingly rotatably provided on one side of the protective tube (41) close to the sealing disk, one end of the through pipe (46) is in sealing contact with the sealing disk, and oblique holes (47) are provided in the through pipe (46). The oblique holes (47) are in sealing connection with each air passage (45) during the rotation adjustment of the through pipe (46).

8. The experimental equipment for decompression of horizontal well coal mining according to claim 7, characterized in that: The through-tube (46) is slidably sleeved with a mounting sleeve (48), one side of the mounting sleeve (48) is connected to a support spring, and the support spring sleeve is sleeved outside the through-tube (46).

9. An experimental method for depressurizing and permeability-enhancing extraction of horizontal wells in crushed, soft and low-permeability coal seams, which uses the experimental equipment for depressurizing horizontal wells as described in any one of claims 1 to 8, characterized in that: It includes the following steps: Step 1. In the preparation stage, the equipment is connected and operated, a number of experimental carrier tubes (1) are selected for the experiment, the crushed soft low-permeability coal rock sample columns obtained in the early stage are placed in each experimental carrier tube (1), and each coal rock sample column is ultrasonically scanned by an ultrasonic detector to detect the distribution of cracks in each coal rock sample column; Step 2. Loading simulation: for each experimental carrier tube (1), the coal rock sample column is preferentially subjected to multi-point expansion pressure using an expansion unit (4), and the stress changes of the coal rock sample column at different positions are monitored by a stress sensor to ensure that the stress loading of each experimental carrier tube (1) meets the experimental requirements; and then, according to the experimental restoration simulation requirements, the coal rock sample column is subjected to torsional stress loading at different positions through each stress loading unit (3), wherein during torsional stress loading, the diversion oil can be continuously transported through the circulation pipe, so that the swivel (32) forms an uninterrupted dynamic loading on the coal rock sample column under the deflection action; Step 3. Coal is removed to relieve pressure, and the threaded blades (15) in the coal extraction pipe (16) are started, and the coal extraction pipe (16) is gradually advanced into the coal sample column, thereby forming a horizontal channel in the coal sample column; at the same time, the air pump system (25) or the liquid pump system (26) is started to deliver the carbon dioxide in the carbon dioxide storage tank (21) and the water-based liquid in the water-based storage tank (22) into the fracturing channel of the coal extraction pipe (16) through the delivery pipe (12), so as to perform internal fracturing on the coal sample column; Step 4. Extraction test: extract coalbed methane from the coal sample column through an extraction system arranged outside the experimental carrier tube (1), and record the extraction volume and pressure related parameters; Step 5. Data collation and comparison: collate the data recorded during the experiment, including relevant data on stress, air pressure, flow rate, and extraction volume, and compare the crack expansion and permeability changes of the coal sample column in each experimental carrier tube (1), so as to evaluate the impact of different coal excavation and pressure relief on the permeability of the crushed, soft, and low-permeability coal seam.

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