Coal seam active water pulse fracturing and moisture increasing experimental device and method

Abstract

The present application belongs to the technical field of dust prevention and control. In order to solve the problem that different stress, different types of active water and different water injection parameters of pulse active water cannot simulate the coal body fracturing wetting effect, a coal seam active water pulse fracturing and wetting experiment device and method are provided. The device prepares active water of different concentrations through an active water preparation device, the water pump and the second branch of the pulse water device are controlled to form a constant pressure water flow, and then the electric high pressure ball valve of the valve control system is debugged to form a pulse water flow of a specific waveform. After the pulse water flow is formed, it is introduced into the sample in the true triaxial loading device, and finally the acoustic emission monitoring device is used to monitor the fracturing of the sample under the simulated coal seam geological stress condition. The present application can simulate the pulse active water fracturing and wetting process of the coal body under the real coal seam stress condition, obtain the corresponding experimental data, and explore the influence of different active water and pulse parameters on the coal body fracturing and wetting effect.

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, resulting in immeasurable losses. Nowadays, the main methods for preventing and controlling dust in coal mines include ventilation and dust removal, coal seam water injection, spray dust reduction, chemical dust suppression, etc. 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 mine dust generation, 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 coal body pores, limiting the application effect of coal seam water injection technology.

[0003] To overcome these difficulties and improve coal seam water injection and dust reduction technology, researchers have proposed pulsed hydraulic fracturing. This technology applies periodic water pressure to the coal seam, causing gradual fatigue damage to the coal, prompting the formation and connection of cracks within the coal seam, increasing the coal's permeability and enhancing its wettability, thereby reducing dust generation. Another approach is to improve coal wettability by reducing contact or surface tension with the coal. Currently, pulsed activated water fracturing technology is still in its early stages of development and cannot simulate the wetting effects of pulsed activated water on coal fractures under varying ground stresses, different types of activated water, and different 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 that can simulate the pulse active water fracturing and wetting effect on coal body under different ground stresses, different types of active water and different water injection parameters.

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

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

[0007] The pulse hydraulic device provides pulse water flow for hydraulic fracturing of the sample, and comprises a water pump, a high-pressure electric ball valve and a water system, the input end of the water pump is connected with the active water preparation device, the output end of the water pump is connected with the water system, the water system comprises a main pipeline and first, second and third branches led out of the main pipeline, the high-pressure electric ball valve is arranged on the main pipeline and is located between the second branch and the third branch, the first branch is connected with the active water preparation device to form a first circulating water path, the second branch is used for storing energy to make the main pipeline form constant pressure water flow, and the third branch is connected with the active water preparation device to form a second circulating water path.

[0008] The valve control system is connected with the high-pressure electric ball valve to control the valve opening degree of the high-pressure electric ball valve, so that the constant pressure water flow forms a specific waveform pulse water flow.

[0009] The data collection system is connected with the pulse hydraulic device to monitor the pressure and flow in the pipeline.

[0010] The true triaxial loading device is used for applying different axial pressure and confining pressure to the sample to simulate the coal seam stress condition, and comprises a fracturing platform, a servo pump station, a fracturing pipe and a control system, the fracturing platform is internally provided with a box body, a plurality of oil cylinders are uniformly arranged on the outer surface of the box body, the control system is connected with the servo pump station to control the servo pump station to drive the plurality of oil cylinders to act on the sample, and the fracturing pipe is arranged in the sample and is connected with the main pipeline through a stop valve.

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

[0012] Optionally, the active water preparation device comprises a plurality of liquid storage tanks, a stirrer, a water tank, a first flow controller, a second flow controller and a third flow controller.

[0013] The plurality of liquid storage tanks are connected with the first flow controller, the second flow controller and the third flow controller respectively, the delivery pipelines of the plurality of liquid storage tanks all extend into the water tank, and the stirrer is arranged 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] A scale is arranged on the outer wall of the liquid storage tank.

[0015] Optionally, the delivery pipelines of the plurality of liquid storage tanks are converged to form a pipeline after passing through the first flow controller, the second flow controller and the third flow controller respectively 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 provided 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 the sample input through the first flow meter and the second flow meter, and measures pressure parameters of the 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 high-voltage electric ball valve lead-out line 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 its 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 their output ends 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] A second aspect of the present invention provides a coal seam active water pulse fracturing and wettability enhancement experimental method, which is based on any of the above-mentioned coal seam active water pulse fracturing and wettability enhancement experimental devices and includes the following steps:

[0029] S1. Preparation of active water: controlling the flow rate of the active agent stock solution in the active water preparation device according to predetermined parameters, obtaining a quantitative active agent stock solution, and stirring it uniformly to obtain an active aqueous solution;

[0030] S2. Processing of the sample: a sample of 300 mm × 300 mm × 300 mm was prepared according to the designed dimensions, 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. Load the sample, move the sample to a predetermined position in the fracturing platform, start the true triaxial loading device, set predetermined parameters, and inject hydraulic oil into the x-axis pipeline, y-axis pipeline, and z-axis pipeline connected to the plurality of cylinders through the servo pump station, controlling the pressure gradient to slowly and synchronously increase the pressure until the rated value is reached;

[0033] S5. Regulating the pulsed water flow: keeping all valves closed before activating the pulse device, starting the data collection system, starting the water pump and the first branch to form a first circulating water circuit, starting the second branch to form 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 simultaneously starting the third branch to form a pulsed water flow with a specific waveform at the constant-pressure water flow;

[0034] S6. Sample: Open the shut-off valve to allow a pulsed water flow to flow through the fracturing pipe into the sample until a drop occurs in the time-pressure curve of the injection pressure in the data collection system. Then, close the shut-off valve and the water pump in sequence, stop injecting water into the valve control system, stop collecting signals by the acoustic emission monitoring device, unload the sample, and remove it from the fracturing platform.

[0035] S7. Data processing: deriving flow rate time curves, pressure time curves, and acoustic emission time curves 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 effects of different loading parameters on the hydraulic fracture morphology and expansion.

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

[0037] The present invention provides an experimental device and method for pulsed fracturing and moistening of coal seams using active water. The device is equipped with an active water preparation device to prepare active water of different concentrations for the experiment, a pulsed hydraulic device to form a constant pressure water flow, and a valve control system to control a high-pressure electric ball valve to form a pulsed water flow with a specific waveform. By setting a true triaxial loading device, a servo pump station is used to push the oil cylinder and act on the sample. The pulsed water flows through the fracturing pipe and enters the sample, simulating the actual geological stress conditions of the coal seam. An acoustic emission monitoring device is connected to the true triaxial loading device to monitor the pulsed hydraulic fracturing sample and study the crack expansion law of the sample. By setting a data collection system, the pressure and flow of the input pulsed water flow can be monitored to explore the influence of different pulse parameters on the fracturing sample. The device can simulate the process of pulsed active water fracturing coal samples, obtain data from 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, providing 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 wettability enhancement experimental device according to an embodiment of the present invention;

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

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

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

[0044] Figure 5 Schematic diagram of the structure of the true triaxial loading device according to an embodiment of the present invention;

[0045] Figure 6 Schematic diagram of the structure of the acoustic emission monitoring device according to 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 flowmeter; 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, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[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 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, and 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 drawn 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 line 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 line; 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 provided inside the fracturing platform, and a plurality of oil cylinders 30 are evenly provided 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 provided 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 provided on the pipeline between the water tank 6 and the water pump 8, and a first one-way valve 9 is provided 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 provided on the first branch. The output end of the first branch is connected to the water tank 6, thereby forming 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 provided on the main line between the first branch and the second branch to control and measure the flow of the main line. A third ball valve 14 and an accumulator 15 are provided in sequence on the second branch to regulate the pressure in the pipeline so that the main line forms a constant-pressure water flow. A high-pressure electric ball valve 16 and a second one-way valve 21 are provided on the main line 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 one-way valve 21, the main line leads to the third branch and the water The third branch is connected to the water box 6 to form a second circulating water circuit. The second pressure transmitter 22, the second flow meter 23 and the needle valve 24 are sequentially arranged on the third branch. The needle valve 24 is used to fine-tune 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 sample through the stop valve 26. The formed pulse water flows through the fracturing pipe 33 into the interior of the sample. The sample has six faces. The true triaxial loading device includes six cylinders 30, six cylinders 30 are installed on the six sides of the sample. A servo pump station 34 is connected to the left and right cylinders, the front and rear cylinders, and the upper and lower cylinders via x-axis pipelines 27, y-axis pipelines 28, and z-axis pipelines 28, respectively. A control system 35 controls the servo pump station 34 to push the six cylinders 30 against the sample, automatically pressurizing or releasing the pressure. This applies different axial and confining pressures to the sample, simulating coal seam geostress conditions. The acoustic emission monitoring device then monitors the pulsed activated water fracturing of the sample under these simulated coal seam geostress conditions. This device can simulate the process of pulsed activated water fracturing coal samples, obtain data from different experimental conditions, and study the effects of different types of activated water and pulse parameters on the wetting and dust reduction effects 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, refer to 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. 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 stock 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 stock solution. A scale is set on the outer wall of the liquid storage tank 1 to clearly display the amount of the active agent stock 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 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. This not only reduces the internal space occupied by the water tank 6, but also makes it convenient to attach the merged pipeline to 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 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. 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 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, which wraps the sample. Specifically, the steel plate 29 can wrap all six sides of the sample, reducing the risk of sample breakage and lowering 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] A second aspect of this 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: controlling the flow rate of the active agent stock solution in the active water preparation device according to predetermined parameters, obtaining a quantitative active agent stock solution, and stirring it uniformly to obtain an active aqueous solution;

[0060] S2. Processing the sample: a 300mm×300mm×300mm sample was produced according to the designed dimensions. A cylinder with a diameter of 18mm and a depth of 165mm was drilled to form the fracturing section 31. The pre-processed fracturing tube 33 was placed into the fracturing section 31 and sealed with epoxy resin AB glue to form the sealing section 32.

[0061] S3. Connect the acoustic emission monitoring device to the sample, move the fixed sample to the front of the fracturing platform, connect the fracturing pipe 33 to the pulse generator through the fracturing line, and provide a total of 16 acoustic emission probes 36. Pass the 16 acoustic emission probes 36 through the reserved pores of the steel plate 29 and connect them to the sample at the predetermined position using vaseline coupling agent. After the connection is completed, fix the steel plate 29 and the sample together;

[0062] S4. Load the sample and move it to a predetermined position on the fracturing platform. Start the true triaxial loading device, set the predetermined parameters, and inject hydraulic oil into the x-axis pipeline 27, y-axis pipeline, and z-axis pipeline 28 connected to the multiple cylinders 30 through the servo pump station 34. Control the pressure gradient and slowly and synchronously increase the pressure until the rated value is reached.

[0063] S5. Adjust the pulsed water flow. Before the pulse device is activated, keep all valves closed, start the data collection system 39, start the water pump 8 and the first branch, that is, open the first ball valve 7. Start the water pump 8 and adjust the pressure relief valve 11 so that the first branch forms a first circulating water path. Start the second branch, that is, open the second ball valve 12 and the third ball valve 14, connect the accumulator 15, so that the water flow forms a stable constant-pressure water flow. Start the valve control system, input the predetermined parameters to control the valve opening of the high-pressure electric ball valve 16, and simultaneously start the third branch, that is, adjust the needle valve 24, so that the constant-pressure water flow forms a pulsed water flow with a specific waveform.

[0064] S6. Sample: Open the stop valve 26 to allow a pulsed water flow to flow through the fracturing pipe 33 into the sample until the time-pressure curve of the injection pressure in the data collection system 39 shows a drop. 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 remove it from the fracturing platform.

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

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

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

[0068] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily 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 is not intended to be limited to the embodiments described herein, but is to be construed in the widest possible manner consistent with the principles and novel features disclosed 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 provides 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 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 system, the water system comprising 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 (16) being arranged on the main line 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 line, the second branch being used to store energy so as to form a constant-pressure water flow in the main line, and the third branch being connected to the active water preparation device to form a second circulating water line; A valve control system is connected to the high-pressure electric ball valve (16) to control the valve opening thereof 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 provided inside the fracturing platform, and a plurality of oil cylinders (30) are evenly provided 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 provided in the sample and is connected to the main pipeline via 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 wettability experimental device according to claim 1, 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; A scale is provided on the outer wall of the liquid storage tank (1).

3. The coal seam active water pulse fracturing and moistening experimental device according to claim 2, 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 wettability experimental device according to claim 1, characterized in that: The first branch is provided with a first pressure transmitter (10) and a pressure relief valve (11); An accumulator (15) is provided on the second branch; 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 wettability experimental device according to claim 4, 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 wettability experimental device according to claim 1, characterized in that: 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 led to the high-voltage electric ball valve (16) to provide power for it. The high-voltage electric ball valve (16) leads the 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 wettability experimental device according to claim 1, characterized in that: The true triaxial loading device further comprises a steel plate (29), wherein the steel plate (29) wraps the specimen.

9. The coal seam active water pulse fracturing and wettability experimental device according to claim 1, characterized in that: The acoustic emission monitoring device includes 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 according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Preparation of active water: controlling the flow rate of the active agent stock solution in the active water preparation device according to predetermined parameters, obtaining a quantitative active agent stock solution, and stirring it uniformly to obtain an active aqueous solution; S2. Processing of the sample: a sample of 300 mm × 300 mm × 300 mm was prepared according to the designed dimensions, and a cylinder with a diameter of 18 mm and a depth of 165 mm was drilled as a fracturing section (31). The pre-processed fracturing tube (33) was 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 into 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 hydraulic 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 path, 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 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.

Images