Experimental device and method for active water pulse fracturing and moistening enhancement of coal seam

Abstract

The invention belongs to the technical field of dust control. In order to solve the problem that the wetting effect of pulse active water with different ground stresses, different types of active water and different water injection parameters on coal body fracturing cannot be simulated, the invention provides a coal seam active water pulse fracturing and moistening experiment device and a coal seam active water pulse fracturing and moistening experiment method. A water pump and a second branch of the pulse hydraulic device are regulated and controlled to form constant-pressure water flow, then pulse water flow with a specific waveform is formed through an electric high-pressure ball valve debugged by the valve control system, and the pulse water flow is introduced into a sample in the true triaxial loading device after being formed; and finally, monitoring the fracturing condition of the pulsed active water on the sample under the condition of simulating the geological stress of the coal seam through an acoustic emission monitoring device. According to the invention, the process of fracturing and wetting the coal body by pulse active water under the real coal seam ground stress condition can be simulated, corresponding experimental data can be obtained, and the influence of different active water and pulse parameters on the fracturing and wetting effect of the coal body can be explored.

Description

Technical Field

[0001] The invention belongs to the technical field of dust prevention and control, and in particular relates to a coal seam active water pulse fracturing and moistening experimental device and method. Background Art

[0002] As a major energy country, my country consumes about 60% of its coal resources. The large-scale mining of coal resources is bound to cause many hidden dangers and disasters in mines. Among them, dust hazards, as one of the major threats to mine safety production, not only damage the health of underground personnel, but also may cause coal dust explosion accidents and cause immeasurable losses. Nowadays, there are mainly ventilation and dust removal, coal seam water injection, spray dust reduction, chemical dust suppression and other methods for underground dust prevention and control in coal mines. Among them, coal seam water injection technology is a method of active dust reduction at the source compared with other technologies. Therefore, coal seam water injection technology is the most commonly used dust suppression method in the coal industry. Although coal seam water injection technology plays an important role in reducing the generation of mine dust, factors such as the hydrophobicity of the coal body and the low permeability of the coal seam hinder the flow and wetting of water in the pores of the coal body, limiting the application effect of coal seam water injection technology.

[0003] In order to overcome the above difficulties and improve the technical level of coal seam water injection and dust reduction, researchers have proposed pulse hydraulic fracturing technology. Through the periodic change of water pressure acting on the coal seam, the coal body gradually suffers fatigue damage, prompting the formation and connection of cracks in the coal seam, improving the permeability of the coal body, enhancing the wetting ability and thus reducing dust generation. Another method is to use active water to reduce coal body contact or surface tension to improve the wettability of the coal body. At present, pulse active water fracturing technology is still in its initial development stage and cannot simulate the fracturing and wetting effects of pulse active water on coal bodies with different ground stresses, different types of active water and different water injection parameters. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a coal seam active water pulse fracturing and wetting experimental device and method which can simulate the pulse active water with different ground stresses, different types of active water and different water injection parameters on the coal body fracturing and wetting effect.

[0005] The first aspect of the present invention provides a coal seam active water pulse fracturing and moistening experimental device, comprising:

[0006] Active water preparation device, to prepare active water of different concentrations for experiments;

[0007] A pulse hydraulic device, which provides a pulse water flow for the hydraulic fracturing sample, and the pulse hydraulic device includes a water pump, a high-pressure electric ball valve and a water circuit system. The input end of the water pump is connected to the active water preparation device, and the output end of the water pump is connected to the water circuit system. The water circuit system includes a main line and a first branch, a second branch and a third branch drawn from the main line. The high-pressure electric ball valve is arranged on the main line and placed between the second branch and the third branch. The first branch is connected to the active water preparation device to form a first circulating water circuit. The second branch is used to store energy so that the main line forms a constant-pressure water flow. The third branch is connected to the active water preparation device to form a second circulating water circuit.

[0008] A valve control system is connected to the high-pressure electric ball valve to control the valve opening so that the constant-pressure water flow forms a pulse water flow with a specific waveform;

[0009] A data collection system, the data collection system is connected to the pulse hydraulic device to monitor the pressure and flow in the pipeline;

[0010] A true triaxial loading device is used to apply different axial pressures and confining pressures to the sample to simulate the ground stress conditions of the coal seam. The true triaxial loading device includes a fracturing platform, a servo pump station, a fracturing pipe and a control system. A box is arranged inside the fracturing platform, and a plurality of oil cylinders are evenly arranged on the outer surface of the box. The control system is connected to the servo pump station to control the servo pump station to drive the plurality of oil cylinders to act on the sample. The fracturing pipe is arranged in the sample and connected to the main pipeline through a stop valve.

[0011] The acoustic emission monitoring device is connected to the true triaxial loading device and is used to monitor the pulse hydraulic fracturing sample.

[0012] Optionally, the active water preparation device includes a plurality of liquid storage tanks, a mixer, a water tank, a first flow controller, a second flow controller and a third flow controller;

[0013] The plurality of liquid storage tanks are respectively connected to the first flow controller, the second flow controller and the third flow controller, the delivery pipelines of the plurality of liquid storage tanks are all extended into the water tank, and the stirrer is placed above the water tank so that the stirring blades of the stirrer extend into the water tank to stir the active agent stock solution;

[0014] The outer wall of the liquid storage tank is provided with scales.

[0015] Optionally, the delivery pipelines of the multiple liquid storage tanks are respectively merged into one pipeline after passing through the first flow controller, the second flow controller and the third flow controller, and extend into the water tank.

[0016] Optionally, a first pressure transmitter and a pressure relief valve are provided on the first branch;

[0017] An accumulator is provided on the second branch;

[0018] The third branch is provided with a second pressure transmitter, a second flow meter and a needle valve in sequence;

[0019] A third pressure transmitter is arranged between the main pipe and the true triaxial loading device.

[0020] Optionally, a first one-way valve is provided between the output end of the water pump and the first branch, a second ball valve and a first flow meter are provided between the first branch and the second branch, and a second one-way valve is provided between the high-pressure electric ball valve and the third branch.

[0021] Optionally, the first flow meter, the second flow meter, the first pressure transmitter, the second pressure transmitter and the third pressure transmitter are all connected to the data collection system;

[0022] The data collection system measures flow parameters of sample input through the first flow meter and the second flow meter, and measures pressure parameters of input water flow through the first pressure transmitter, the second pressure transmitter and the third pressure transmitter.

[0023] Optionally, the valve control system includes a computer, a switching power supply, a 485 module and a USB signal converter;

[0024] The switching power supply is connected to the power supply end of the 485 module, and a line is led to the high-voltage electric ball valve to provide power for it. The lead-out line of the high-voltage electric ball valve is connected to the analog port of the 485 module to convert the analog signal into a digital signal. The digital signal port of the 485 module is connected to the USB signal converter and the computer in sequence through the line, and the digital signal is converted so that it can control the opening of the high-voltage electric ball valve through specific programs and parameters on the computer, so that it changes in a specific range to generate a pulse waveform.

[0025] Optionally, the true triaxial loading device further includes a steel plate, which wraps the specimen.

[0026] Optionally, the acoustic emission monitoring device includes an acoustic emission collection and processing system, an acoustic signal amplifier and a plurality of acoustic emission probes;

[0027] The plurality of acoustic emission probes are arranged on the surface of the sample, and the output ends thereof are connected to the acoustic signal amplifier to obtain the original acoustic signal of the sample and amplify it. The acoustic emission collection and processing system is connected to the acoustic signal amplifier to convert and process the acoustic signal and monitor the crack expansion law of the sample.

[0028] The second aspect of the present invention provides a coal seam active water pulse fracturing and moisturizing experimental method, which is based on any of the above coal seam active water pulse fracturing and moisturizing experimental devices, and includes the following steps:

[0029] S1, preparation of active water, according to the predetermined parameters, control the flow rate of the active agent stock solution in the active water preparation device, obtain a quantitative active agent stock solution, and stir it evenly to obtain an active aqueous solution;

[0030] S2. Processing of the sample: a sample of 300 mm × 300 mm × 300 mm was made according to the designed size, and a cylinder with a diameter of 18 mm and a depth of 165 mm was drilled as the fracturing section. The pre-processed fracturing pipe was placed in the fracturing section and sealed with epoxy resin AB glue;

[0031] S3, connecting the acoustic emission monitoring device to the sample;

[0032] S4, loading the sample, moving the sample to a predetermined position in the fracturing platform, starting the true triaxial loading device, setting predetermined parameters, injecting hydraulic oil into the x-axis pipeline, y-axis pipeline and z-axis pipeline connected to the plurality of oil cylinders through the servo pump station, and controlling the pressure gradient to slowly and synchronously pressurize until the rated value is reached;

[0033] S5, regulating the pulse water flow, keeping all valves closed before starting the pulse device, starting the data collection system, starting the water pump and the first branch, so that the first branch forms a first circulating water circuit, starting the second branch, so that the water flow forms a stable constant pressure water flow, starting the valve control system, inputting predetermined parameters to control the valve opening of the high-pressure electric ball valve, and starting the third branch at the same time, so that the constant pressure water flow forms a pulse water flow with a specific waveform;

[0034] S6, sample, open the stop valve, let the pulse water flow into the sample through the fracturing pipe, until the time-pressure curve of the injection pressure in the data collection system drops, close the stop valve and the water pump in turn, stop injecting water into the valve control system, stop the acoustic emission monitoring device from collecting signals, unload the sample and move it out of the fracturing platform;

[0035] S7. Data processing: deriving flow rate time curve, pressure time curve and acoustic emission time curve through the data collection system and the acoustic emission monitoring device to analyze the hydraulic fracture morphology, the initiation and expansion mechanism of pulse hydraulic fractures and the influence of different loading parameters on the hydraulic fracture morphology and expansion.

[0036] Compared with the prior art, the technical solution provided by the embodiment of the present invention has the following beneficial effects:

[0037] The embodiment of the present invention provides a coal seam active water pulse fracturing and moistening experimental device and method. The device prepares active water of different concentrations for the experiment by setting an active water preparation device, sets a pulse hydraulic device to form a constant pressure water flow, controls the high-pressure electric ball valve through the valve control system, forms a pulse water flow with a specific waveform, sets a true triaxial loading device, uses a servo pump station to push the oil cylinder and act on the sample, and the pulse water flows through the fracturing pipe into the sample, simulating the real coal seam geological stress conditions. The acoustic emission monitoring device is connected to the true triaxial loading device, which can monitor the pulse hydraulic fracturing sample and study the crack expansion law of the sample. By setting a data collection system, it can monitor the pressure and flow of the input pulse water flow and explore the influence of different pulse parameters on the fracturing sample. The device can simulate the process of pulse active water fracturing coal samples, obtain data of different experimental conditions, study the influence of different types of active water and different pulse parameters on the wetting and dust reduction effect of coal samples, and provide support for subsequent research. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0040] Figure 1 This is a schematic structural diagram of a coal seam active water pulse fracturing and moistening experimental device according to an embodiment of the present invention;

[0041] Figure 2 It is a structural schematic diagram of the active water preparation device according to an embodiment of the present invention;

[0042] Figure 3 It is a structural schematic diagram of a pulse hydraulic device according to an embodiment of the present invention;

[0043] Figure 4 This is a schematic diagram of the structure of a valve control system according to an embodiment of the present invention;

[0044] Figure 5 It is a structural schematic diagram of a true triaxial loading device according to an embodiment of the present invention;

[0045] Figure 6 It is a schematic diagram of the structure of the acoustic emission monitoring device described in an embodiment of the present invention.

[0046] Among them, 1. liquid storage tank; 2. first flow controller; 3. second flow controller; 4. third flow controller; 5. mixer; 6. water tank; 7. first ball valve; 8. water pump; 9. first check valve; 10. first pressure transmitter; 11. pressure relief valve; 12. second ball valve; 13. first flow meter; 14. third ball valve; 15. accumulator; 16. high-voltage electric ball valve; 17. switching power supply; 18. 485 module; 19. USB signal converter; 20. meter Computer; 21. Second one-way valve; 22. Second pressure transmitter; 23. Second flow meter; 24. Needle valve; 25. Third pressure transmitter; 26. Stop valve; 27. X-axis pipeline; 28. Z-axis pipeline; 29. ​​Steel plate; 30. Oil cylinder; 31. Fracturing section; 32. Sealing section; 33. Fracturing pipe; 34. Servo pump station; 35. Control system; 36. Acoustic emission probe; 37. Acoustic signal amplifier; 38. Acoustic emission collection and processing system; 39. Data collection system. DETAILED DESCRIPTION

[0047] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0048] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0049] Reference Figures 1 to 6 As shown, the first aspect of this embodiment provides a coal seam active water pulse fracturing and wetting experimental device, including an active water preparation device, a pulse hydraulic device, a valve control system, a data collection system 39, a true triaxial loading device and an acoustic emission monitoring device.

[0050] Among them, the active water preparation device is used to prepare active water of different concentrations for the experiment; the pulse hydraulic device provides pulse water flow for the hydraulic fracturing sample, the pulse hydraulic device includes a water pump 8, a high-pressure electric ball valve 16 and a water system, the input end of the water pump 8 is connected to the active water preparation device, the output end of the water pump 8 is connected to the water system, the water system includes a main line and a first branch, a second branch and a third branch led out from the main line, the high-pressure electric ball valve 16 is arranged on the main line and placed between the second branch and the third branch, the first branch is connected to the active water preparation device to form a first circulating water circuit to ensure that the water pump 8 runs for a long time, the second branch is used to store energy to form a constant pressure water flow in the main line, and the third branch is connected to the active water preparation device to form a second circulating water circuit; the valve control system is connected to the high pressure The electric ball valve 16 is connected to control its valve opening so that the constant pressure water flow forms a pulse water flow with a specific waveform; the data collection system 39 is connected to the pulse hydraulic device to monitor the pressure and flow conditions in the pipeline; the true triaxial loading device is used to apply different axial pressures and confining pressures to the sample to simulate the ground stress conditions of the coal seam. The true triaxial loading device includes a fracturing platform, a servo pump station 34, a fracturing pipe 33 and a control system 35. A box is arranged inside the fracturing platform, and a plurality of oil cylinders 30 are evenly arranged on the outer surface of the box. The control system is connected to the servo pump station to control the servo pump station to drive the plurality of oil cylinders to act on the sample. The fracturing pipe 33 is arranged in the sample and is connected to the main pipeline through a stop valve 26; the acoustic emission monitoring device is connected to the true triaxial loading device to monitor the pulse hydraulic fracturing sample.

[0051] Specifically, refer to Figure 3As shown, a first installed ball valve 7 is arranged on the pipeline between the water tank 6 and the water pump 8, and a first non-return valve 9 is arranged between the output end of the water pump 8 and the first branch, so that the active water can only flow out along the water pump 8 to prevent the active water from flowing back into the water pump 8. A first pressure transmitter 10 and a pressure relief valve 11 are arranged on the first branch. The output end of the first branch is connected to the water tank 6, so as to form a first circulating water circuit, so that the water pump 8 can run for a long time. A second ball valve 12 and a first flow meter 13 are arranged on the main pipe between the first branch and the second branch to control and measure the flow of the main pipe. A third ball valve 14 and an accumulator 15 are arranged on the second branch in sequence to regulate the pressure in the pipeline so that the main pipe forms a constant-pressure water flow. A high-pressure electric ball valve 16 and a second non-return valve 21 are arranged on the main pipe between the second branch and the third branch. The high-pressure electric ball valve 16 is connected to the valve control system through a line, and its valve opening is controlled by the valve control system to change, so that the constant-pressure water flow forms a pulse water flow with a specific waveform. After the second non-return valve 21, the main pipe leads the third branch and the water The third branch is connected to the test box 6 to form a second circulating water circuit. The third branch is provided with a second pressure transmitter 22, a second flow meter 23 and a needle valve 24 in sequence. The needle valve 24 is used to slightly adjust the formation of the auxiliary water circuit waveform. The main line after the third branch is provided with a third pressure transmitter 25 and a stop valve 26 to monitor the input water pressure at all times, and to form a water circuit with the test sample through the stop valve 26. The formed pulse water flows into the inside of the test sample through the fracturing pipe 33. The test sample has six faces. The true triaxial loading device includes six oil cylinders 30, six oil cylinders 30 are respectively arranged on the six faces of the sample, the servo pump station 34 is respectively connected to the left and right cylinders, the front and rear cylinders and the upper and lower cylinders through the x-axis pipeline 27, the y-axis pipeline and the z-axis pipeline 28, and the control system 35 controls the servo pump station 34 to push the six cylinders 30 to act on the sample to complete the operation of automatic pressurization or pressure relief and emptying, thereby realizing the application of different axial pressures and confining pressures to the sample to simulate the geological stress conditions of the coal seam, and then the acoustic emission monitoring device is used to monitor the pulse active water fracturing of the sample under the simulated coal seam geological stress conditions. This device can simulate the process of pulse active water fracturing coal samples, obtain data of different experimental conditions, and study the influence of different types of active water and different pulse parameters on the wetting and dust reduction effect of coal samples.

[0052] Furthermore, the first flow meter 13, the second flow meter 23, the first pressure transmitter 10, the second pressure transmitter 22 and the third pressure transmitter 25 are all connected to the data collection system 39. The data collection system 39 measures the flow parameters of the sample input through the first flow meter 13 and the second flow meter 23, and measures the pressure parameters of the input water flow through the first pressure transmitter, the second pressure transmitter 22 and the third pressure transmitter 25.

[0053] Further, see Figure 2As shown, the active water preparation device includes multiple liquid storage tanks 1, a mixer 5, a water tank 6, a first flow controller 2, a second flow controller 3 and a third flow controller 4. The multiple liquid storage tanks 1 are respectively connected to the first flow controller 2, the second flow controller 3 and the third flow controller 4, and the delivery pipelines of the multiple liquid storage tanks 1 all extend into the water tank 6, so that the concentration of the active agent solution entering the water tank 6 is regulated by the first flow controller 2, the second flow controller 3 and the third flow controller 4 to form different types of active water, and the mixer 5 is placed above the water tank 6 so that the stirring blades of the mixer 5 extend into the water tank 6 to stir the active agent solution. A scale is set on the outer wall of the liquid storage tank 1 to clearly display the amount of the active agent solution, so as to better adjust the concentration of the active water.

[0054] In order not to affect the normal operation of the mixer 5, the delivery pipelines of multiple liquid storage tanks 1 are respectively merged into one pipeline after passing through the first flow controller 2, the second flow controller 3 and the third flow controller 4, and extend into the water tank 6, which not only reduces the internal space occupied by the water tank 6, but also facilitates the setting of the merged pipeline against the inner wall of the water tank 6 without affecting the operation of the blades of the mixer 5.

[0055] Reference Figure 4 As shown, the valve control system includes a computer 20, a switching power supply 17, a 485 module 18 and a USB signal converter 19. The switching power supply 17 is connected to the power supply end of the 485 module 18, and a line is connected to the high-voltage electric ball valve 16 to provide power for it. The high-voltage electric ball valve 16 leads out a line to connect to the analog port of the 485 module 18 to convert the analog signal into a digital signal. The digital signal port of the 485 module 18 is connected to the USB signal converter 19 and the computer 20 in sequence through the line, and the digital signal is converted so that it can control the opening of the high-voltage electric ball valve 16 through specific programs and parameters on the computer 20, so that it changes in a specific range to generate a pulse waveform, specifically generating a sine wave, a rectangular wave and a sawtooth wave.

[0056] Reference Figure 5 As shown, the true triaxial loading device further includes a steel plate 29, and the steel plate 29 wraps the sample. Specifically, the steel plate 29 can wrap all six sides of the sample, reducing the risk of sample breakage and safety risks.

[0057] Reference Figure 6 As shown, the acoustic emission monitoring device includes an acoustic emission collection and processing system 38, an acoustic signal amplifier 37 and multiple acoustic emission probes 36. The multiple acoustic emission probes 36 are all arranged on the surface of the sample, and their output ends are connected to the acoustic signal amplifier 37 to obtain the original acoustic signal of the sample and amplify it. The acoustic emission collection and processing system 38 is connected to the acoustic signal amplifier 37 to convert and process the acoustic signal to monitor the crack expansion law of the sample.

[0058] The second aspect of the present embodiment provides a coal seam active water pulse fracturing and moisturizing experimental method, which is based on the above-mentioned coal seam active water pulse fracturing and moisturizing experimental device and includes the following steps:

[0059] S1, preparation of active water, according to the predetermined parameters, control the flow rate of the active agent stock solution in the active water preparation device, obtain a quantitative active agent stock solution, and stir it evenly to obtain an active aqueous solution;

[0060] S2. Processing of the sample: a sample of 300 mm × 300 mm × 300 mm is made according to the designed size, and a cylinder with a diameter of 18 mm and a depth of 165 mm is drilled as the fracturing section 31. The pre-processed fracturing pipe 33 is placed in the fracturing section 31, and the hole is sealed with epoxy resin AB glue to form a sealing section 32;

[0061] S3, connecting the acoustic emission monitoring device with the sample, moving the fixed sample into the front of the fracturing platform, connecting the fracturing pipe 33 with the pulse generator through the fracturing pipeline, providing 16 acoustic emission probes 36, and passing the 16 acoustic emission probes 36 through the reserved pores of the steel plate 29, connecting them with the sample at a predetermined position with vaseline coupling agent, and fixing the steel plate 29 and the sample together after the connection;

[0062] S4, loading the sample, moving the sample to a predetermined position in the fracturing platform, starting the true triaxial loading device, setting predetermined parameters, injecting hydraulic oil into the x-axis pipeline 27, the y-axis pipeline and the z-axis pipeline 28 connected to the multiple cylinders 30 through the servo pump station 34, respectively, and controlling the pressure gradient to slowly and synchronously pressurize until the rated value is reached;

[0063] S5, regulating the pulse water flow, keeping all valves closed before the pulse device is started, turning on the data collection system 39, starting the water pump 8 and the first branch, that is, opening the first ball valve 7, starting the water pump 8 to adjust the pressure relief valve 11, so that the first branch forms a first circulation water path, starting the second branch, that is, opening the second ball valve 12 and the third ball valve 14, connecting the accumulator 15, so that the water flow forms a stable constant pressure water flow, starting the valve control system, inputting the predetermined parameters to control the valve opening of the high-pressure electric ball valve 16, and at the same time starting the third branch, that is, adjusting the needle valve 24, so that the constant pressure water flow forms a pulse water flow with a specific waveform;

[0064] S6, sample, open the stop valve 26, let the pulse water flow into the sample through the fracturing pipe 33, until the time-pressure curve of the injection pressure in the data collection system 39 drops, then close the stop valve 26 and the water pump 8 in sequence, stop injecting water into the valve control system, stop the acoustic emission monitoring device from collecting signals, unload the sample and move it out of the fracturing platform;

[0065] S7. Data processing: deriving flow rate time curve, pressure time curve and acoustic emission time curve through data collection system 39 and acoustic emission monitoring device, so as to analyze hydraulic fracture morphology, the initiation and expansion mechanism of pulse hydraulic fracture and the influence of different loading parameters on hydraulic fracture morphology and expansion.

[0066] This experimental method can simulate the pulse active water wetting process of coal fracturing under real coal seam ground stress conditions, obtain corresponding experimental data, and explore the influence of different active water and pulse parameters on the wetting effect of coal fracturing.

[0067] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0068] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments described herein, but should conform to the widest scope consistent with the principles and novel features invented herein.

Claims

1. A coal seam active water pulse fracturing and moistening experimental device, characterized in that: include: Active water preparation device, to prepare active water of different concentrations for experiments; A pulse hydraulic device, for providing a pulse water flow for a hydraulic fracturing sample, the pulse hydraulic device comprising a water pump (8), a high-pressure electric ball valve (16) and a water circuit system, the input end of the water pump (8) being connected to the active water preparation device, the output end of the water pump (8) being connected to the water circuit system, the water circuit system comprising a main circuit and a first branch, a second branch and a third branch drawn from the main circuit, the high-pressure electric ball valve (16) being arranged on the main circuit and placed between the second branch and the third branch, the first branch being connected to the active water preparation device to form a first circulating water circuit, the second branch being used to store energy so that the main circuit forms a constant-pressure water flow, and the third branch being connected to the active water preparation device to form a second circulating water circuit; A valve control system connected to the high-pressure electric ball valve (16) to control the valve opening so that the constant-pressure water flow forms a pulsed water flow with a specific waveform; A data collection system (39), the data collection system (39) is connected to the pulse hydraulic device to monitor the pressure and flow in the pipeline; A true triaxial loading device is used to apply different axial pressures and confining pressures to a sample to simulate the ground stress conditions of a coal seam. The true triaxial loading device comprises a fracturing platform, a servo pump station (34), a fracturing pipe (33) and a control system (35). A box is arranged inside the fracturing platform, and a plurality of oil cylinders (30) are evenly arranged on the outer surface of the box. The control system (35) is connected to the servo pump station (34) to control the servo pump station (34) to drive the plurality of oil cylinders (30) to act on the sample. The fracturing pipe (33) is arranged in the sample and connected to the main pipeline through a stop valve (26). The acoustic emission monitoring device is connected to the true triaxial loading device and is used to monitor the pulse hydraulic fracturing sample.

2. The coal seam active water pulse fracturing and wetting experimental device according to claim 1 is characterized in that: The active water preparation device comprises a plurality of liquid storage tanks (1), a mixer (5), a water tank (6), a first flow controller (2), a second flow controller (3) and a third flow controller (4); The plurality of liquid storage tanks (1) are respectively connected to the first flow controller (2), the second flow controller (3) and the third flow controller (4); the delivery pipelines of the plurality of liquid storage tanks (1) extend into the water tank (6); and the stirrer (5) is placed above the water tank (6) so that the stirring blades of the stirrer (5) extend into the water tank (6) to stir the active agent stock solution; The outer wall of the liquid storage tank (1) is provided with scales.

3. The coal seam active water pulse fracturing and moistening experimental device according to claim 2 is characterized in that: The delivery pipelines of the plurality of liquid storage tanks (1) are respectively combined to form a pipeline after passing through the first flow controller (2), the second flow controller (3) and the third flow controller (4), and extend into the water tank (6).

4. The coal seam active water pulse fracturing and moistening experimental device according to claim 1 is characterized in that: The first branch is provided with a first pressure transmitter (10) and a pressure relief valve (11); The second branch is provided with an accumulator (15); The third branch is provided with a second pressure transmitter (22), a second flow meter (23) and a needle valve (24) in sequence; A third pressure transmitter (25) is provided between the main pipe and the true triaxial loading device.

5. The coal seam active water pulse fracturing and moistening experimental device according to claim 4 is characterized in that: A first one-way valve (9) is provided between the output end of the water pump (8) and the first branch, a second ball valve (12) and a first flow meter (13) are provided between the first branch and the second branch, and a second one-way valve (21) is provided between the high-pressure electric ball valve (16) and the third branch.

6. The coal seam active water pulse fracturing and moistening experimental device according to claim 5, characterized in that: The first flow meter (13), the second flow meter (23), the first pressure transmitter (10), the second pressure transmitter (22) and the third pressure transmitter (25) are all connected to the data collection system (39); The data collection system (39) measures the flow parameters of the sample input through the first flow meter (13) and the second flow meter (23), and measures the pressure parameters of the input water flow through the first pressure transmitter (10), the second pressure transmitter (22) and the third pressure transmitter (25).

7. The coal seam active water pulse fracturing and moistening experimental device according to claim 1 is characterized in that: The valve control system comprises a computer (20), a switching power supply (17), a 485 module (18) and a USB signal converter (19); The switch power supply (17) is connected to the power supply end of the 485 module (18), and leads a line to the high-voltage electric ball valve (16) to provide power for it. The high-voltage electric ball valve (16) leads a line to the analog port of the 485 module (18) to convert the analog signal into a digital signal. The digital signal port of the 485 module (18) is connected to the USB signal converter (19) and the computer (20) in sequence through the line, and the digital signal is converted so that it can control the opening of the high-voltage electric ball valve (16) through specific programs and parameters on the computer (20), so that it changes in a specific range to generate a pulse waveform.

8. The coal seam active water pulse fracturing and wetting experimental device according to claim 1 is characterized in that: The true triaxial loading device also includes a steel plate (29), and the steel plate (29) wraps the sample.

9. The coal seam active water pulse fracturing and wetting experimental device according to claim 1, characterized in that: The acoustic emission monitoring device comprises an acoustic emission collection and processing system (38), an acoustic signal amplifier (37) and a plurality of acoustic emission probes (36); The plurality of acoustic emission probes (36) are arranged on the surface of the sample, and the output ends thereof are connected to the acoustic signal amplifier (37) to obtain the original acoustic signal of the sample and amplify it. The acoustic emission collection and processing system (38) is connected to the acoustic signal amplifier (37) to convert and process the acoustic signal and monitor the crack expansion law of the sample.

10. A coal seam active water pulse fracturing and moisturizing experimental method, based on a coal seam active water pulse fracturing and moisturizing experimental device as claimed in any one of claims 1 to 9, characterized in that: The following steps are involved: S1, preparation of active water, according to the predetermined parameters, control the flow rate of the active agent stock solution in the active water preparation device, obtain a quantitative active agent stock solution, and stir it evenly to obtain an active aqueous solution; S2. Processing of the sample: a sample of 300 mm×300 mm×300 mm is manufactured according to the designed size, and a cylinder with a diameter of 18 mm and a depth of 165 mm is drilled as a fracturing section (31). The pre-processed fracturing tube (33) is placed in the fracturing section (31) and sealed with epoxy resin AB glue; S3, connecting the acoustic emission monitoring device to the sample; S4, loading the sample, moving the sample to a predetermined position in the fracturing platform, starting the true triaxial loading device, setting predetermined parameters, and injecting hydraulic oil into the x-axis pipeline (27), y-axis pipeline and z-axis pipeline (28) connected to the plurality of oil cylinders (30) through the servo pump station (34), respectively, and controlling the pressure gradient to slowly and synchronously pressurize until the rated value is reached; S5, regulating the pulse water flow, keeping all valves closed before starting the pulse device, starting the data collection system (39), starting the water pump (8) and the first branch, so that the first branch forms a first circulating water circuit, starting the second branch, so that the water flow forms a stable constant pressure water flow, starting the valve control system, inputting predetermined parameters to control the valve opening of the high-pressure electric ball valve (16), and simultaneously starting the third branch, so that the constant pressure water flow forms a pulse water flow with a specific waveform; S6, sample, open the stop valve (26), allow the pulse water flow to enter the sample through the fracturing pipe (33), until the time-pressure curve of the injection pressure in the data collection system (39) drops, close the stop valve (26) and the water pump (8) in sequence, stop injecting water into the valve control system, stop the acoustic emission monitoring device from collecting signals, unload the sample and remove it from the fracturing platform; S7, data processing, obtaining a flow time curve, a pressure time curve and an acoustic emission time curve through the data collection system (39) and the acoustic emission monitoring device, so as to analyze the hydraulic fracture morphology, the initiation and expansion mechanism of the pulse hydraulic fracture and the influence of different loading parameters on the hydraulic fracture morphology and expansion.

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