High-voltage electric pulse cracking coal rock stress shock wave monitoring device

Abstract

The invention discloses a high-voltage electric pulse cracking coal rock stress shock wave monitoring device which comprises a high-voltage pulse capacitor, a voltage divider, a high-voltage pulse switch, a high-voltage pulse cracking generation chamber, a high-voltage probe, a Rogowski coil and an oscilloscope. A test piece is fixed in the high-pressure pulse cracking generation chamber, a circle of test piece clamping assembly corresponding to the test piece is arranged in the high-pressure pulse cracking generation chamber, needle-shaped electrodes are arranged on the two sides, not provided with the test piece clamping assembly, of the test piece, and a piezoelectric pressure sensor is arranged on the high-pressure pulse cracking generation chamber. The detection signal output ends of all the piezoelectric pressure sensors are connected with the pressure detection signal input end of the stress wave signal collector, and a Faraday cage used for covering the piezoelectric pressure sensors is arranged in the high-pressure pulse fracturing generation chamber. The propagation characteristics of the high-voltage electric pulse stress shock waves in the coal rock mass can be accurately and directly captured in real time, and accurate and reliable data support is provided for deep research on a high-voltage pulse electric crushing mechanism.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mining, and particularly relates to a monitoring device for stress shock waves generated by high-voltage electric pulses for fracturing coal and rock. Background Art

[0002] Coalbed methane (CBM), as an important unconventional natural gas resource, is characterized by being clean, efficient, and low-carbon. With the gradual extension of coal mining in China to deeper depths, the occurrence environment of CBM presents the characteristics of "three highs and one low". Among them, the low coal seam permeability has become the core factor restricting the efficient exploitation of CBM. Therefore, developing efficient coal seam permeability enhancement technologies has become the key breakthrough direction for improving the development and utilization level of CBM.

[0003] At present, conventional coal seam permeability enhancement methods include hydraulic fracturing permeability enhancement technology, water jet permeability enhancement technology, deep blasting pre-fracturing permeability enhancement technology, and high-voltage pulse discharge technology, etc. These methods have achieved certain results in coal seam permeability enhancement. However, these methods themselves also have some defects. For example, the hydraulic fracturing permeability enhancement technology has problems such as a small fracturing range, easy closure of the generated fractures, and insignificant permeability enhancement effect for soft coal seams; the water jet permeability enhancement technology is limited by the influence of the jet structure, and its permeability enhancement range is limited; the implementation of the deep blasting pre-fracturing permeability enhancement technology may have misfires and is prone to safety hazards, so its popularization is restricted. The high-voltage pulse discharge technology has advantages such as strong fracturing ability, green and controllable, significant fracturing effect, and simple operation, and is particularly suitable for the field of coal seam permeability enhancement.

[0004] At present, there are mainly two ways to apply the high-voltage pulse discharge technology to the field of coal seam permeability enhancement: liquid-electric effect crushing and electro-fracturing. Among them, the liquid-electric effect uses a liquid as the impact medium, and utilizes the stress shock wave front generated by it to act on the solid surface, thereby causing local fracture; while electro-fracturing directly converts electrical energy into a plasma channel to act on the solid medium, and superimposes with the expansion stress generated by it to generate a greater stress shock wave inside the solid material, and the fracture effect is more obvious, and the energy utilization efficiency is significantly higher than that of the liquid-electric effect. Therefore, in-depth study of the propagation mechanism and fracturing characteristics of the electro-fracturing shock wave helps to reveal the action mechanism of the stress shock wave on the crack propagation and stress release of coal and rock, so as to provide theoretical support for optimizing the permeability enhancement effect. And stress shock wave monitoring is the core means to achieve this research goal. By quantitatively analyzing the intensity, propagation path, and energy attenuation law of the shock wave, it provides key data support for studying the shock wave action mechanism, and then optimizes the electro-fracturing parameters to improve the fracturing efficiency.

[0005] Existing high-voltage pulse discharge technologies employ a variety of monitoring means, providing certain support for obtaining experimental data on the fracturing of coal and rock masses by high-voltage electrical pulses. However, the existing research on stress shock wave monitoring methods mainly focuses on the field of hydroelectric fragmentation, while there are relatively few monitoring methods for stress shock waves during the electro-fragmentation process. In addition, due to the strong electric field interference during the electro-fragmentation process, sensors cannot be directly attached to the surface of the specimen for monitoring, further increasing the difficulty of signal acquisition. At the same time, the current monitoring methods for stress shock waves in electro-pulse fragmentation mainly rely on dynamic strain gauges, fiber Bragg grating sensors, and high-speed cameras. Although these methods can capture some signals, they can only obtain indirect data on the responses caused by stress shock waves and cannot achieve real-time, accurate, and direct measurement of stress shock waves. Summary of the Invention

[0006] The present invention aims to solve the technical problems existing in the prior art and particularly innovatively proposes a monitoring device for stress shock waves generated by high-voltage electrical pulses in coal and rock, which can capture the propagation characteristics of high-voltage electrical pulse stress shock waves in coal and rock masses in real time, accurately, and directly, providing accurate and reliable data support for in-depth research on the mechanism of high-voltage pulse electro-fragmentation.

[0007] To achieve the above object, the present invention provides a monitoring device for stress shock waves generated by high-voltage electrical pulses in coal and rock, including a high-voltage pulse capacitor, a voltage divider, a high-voltage pulse switch, and a high-voltage pulse fracturing chamber connected in sequence to form a closed loop. A high-voltage probe and a Rogowski coil are provided on the wire connecting the high-voltage pulse fracturing chamber and the high-voltage pulse capacitor, and the signal output ends of the high-voltage probe and the Rogowski coil are both connected to an oscilloscope; a specimen is fixed in the high-voltage pulse fracturing chamber, and a circle of specimen clamping assemblies is provided in the high-voltage pulse fracturing chamber corresponding to the specimen. Needle electrodes are provided on both sides of the specimen where the specimen clamping assemblies are not provided, and the needle electrodes are in contact with the specimen and release high-voltage pulses.

[0008] A piezoelectric pressure sensor is equipped on the high-voltage pulse fracturing chamber corresponding to each specimen clamping assembly. The detection signal output ends of all piezoelectric pressure sensors are connected to the pressure detection signal input end of a stress wave signal collector. A Faraday cage for covering the piezoelectric pressure sensor is provided in the high-voltage pulse fracturing chamber corresponding to each piezoelectric pressure sensor, and each Faraday cage is connected to the power ground through a wire.

[0009] Each specimen clamping assembly includes a fixed base and a transmission rod slidably connected to the fixed base. One end of the transmission rod faces the specimen and is provided with a clamping plate for pressing against the specimen, and a clamp is formed by combining all the clamping plates. The other end of the transmission rod extends into the Faraday cage and abuts against the piezoelectric pressure sensor. A jack for the transmission rod to pass through is provided on the fixed base, and a linear bearing is provided in the jack.

[0010] In the above solution: A fixing sleeve is arranged outside the needle-shaped electrode, and the needle-shaped electrode is fixed on the side wall of the high-voltage pulse fracturing chamber through the fixing sleeve. A clamping plate is also arranged at one end of the fixing sleeve close to the test piece, and the ends of the two needle-shaped electrodes both pass through the clamping plate and abut against the test piece.

[0011] In the above solution: Threads are arranged on the outer side wall of the fixing sleeve, and two nuts are threadedly connected to the fixing sleeve. The two nuts are respectively located inside and outside the high-voltage pulse fracturing chamber, and the fixing sleeve is fixed by abutting against both sides of the side wall of the high-voltage pulse fracturing chamber through the inner and outer nuts respectively.

[0012] In the above solution: The fixed base includes a fixed panel, and a pair of fixing bolts are fixed on the fixed panel, and the fixed base is fixed on the side wall of the high-voltage pulse fracturing chamber through the fixing bolts. The structure is simple and the fixing is stable.

[0013] In the above solution: The transmission rod and the fixing sleeve are both of an integral structure with the clamping plate, which can improve the structural rigidity.

[0014] In the above solution: The high-voltage pulse capacitor is equipped with a high-voltage pulse power supply and a centralized control computer. The control output end of the centralized control computer is connected to the control signal input end of the high-voltage pulse power supply, and the power supply end of the high-voltage pulse power supply is connected to the power input end of the high-voltage pulse capacitor. The provided centralized control computer can adjust the power supply amount and power supply voltage of the high-voltage pulse power supply, and can charge the high-voltage pulse capacitor with the required amount of electricity for the pulse through the high-voltage pulse power supply gap.

[0015] In the above solution: The installation distance between the needle-shaped electrode and the piezoelectric pressure sensor is greater than 50 mm, which can ensure the safe operation of the equipment.

[0016] In the above solution: There are four test piece clamping assemblies, which are respectively arranged on the front, rear, upper and lower sides of the test piece. It can detect impacts in the vertical and horizontal directions.

[0017] In the above solution: The transmission rod, the fixing sleeve, the clamping plate, the nut, the linear bearing and the fixed base are all made of peek material.

[0018] In summary, the beneficial effects of the present invention are as follows: The needle-shaped electrode is provided to release high-voltage pulses to the test piece, thereby electrically fragmenting the test piece. The provided test piece clamping assembly can fix the test piece and also serves as a conduction medium for the shock wave of electrical fragmentation. In combination with the piezoelectric pressure sensor, it is ensured that the impact force during the high-voltage pulse fracturing process can be stably obtained, and the data is transmitted to the stress wave signal collector for dynamic analysis. The provided Faraday cage can reduce the electromagnetic interference to the piezoelectric pressure sensor during the high-voltage pulse discharge process, form a closed electromagnetic shielding environment, effectively block high-frequency electromagnetic waves, and improve the data accuracy. The structure is simple, it can capture the propagation characteristics of the high-voltage pulse stress shock wave in the coal and rock mass in real time, accurately and directly, provide accurate and reliable data support for the in-depth study of the mechanism of high-voltage pulse electrical fragmentation, the equipment input cost is low, it can achieve faster and more accurate real-time signal feedback, and effectively avoid the limitations of conventional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the system schematic diagram of the present invention.

[0020] Figure 2 is the cross-section of the high-voltage pulse fracturing chamber of the present invention Figure 1 .

[0021] Figure 3 is the cross-section of the high-voltage pulse fracturing chamber of the present invention Figure 2 . DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The present invention will be further described below through embodiments in combination with the drawings:

[0023] As Figures 1 to 3 shown, a high-voltage pulse fracturing coal and rock stress shock wave monitoring device includes a high-voltage pulse capacitor 3, a voltage divider 4, a high-voltage pulse switch 5, and a high-voltage pulse fracturing chamber 6 that are sequentially connected to form a closed loop. A high-voltage probe 16 and a Rogowski coil 17 are provided on the wire connecting the high-voltage pulse fracturing chamber 6 and the high-voltage pulse capacitor 3, and the signal output ends of the high-voltage probe 16 and the Rogowski coil 17 are both connected to an oscilloscope 19.

[0024] The high-voltage pulse capacitor 3 is equipped with a high-voltage pulse power supply 2 and a centralized control computer 1. The control output end of the centralized control computer 1 is connected to the control signal input end of the high-voltage pulse power supply 2, and the power supply end of the high-voltage pulse power supply 2 is connected to the power input end of the high-voltage pulse capacitor 3. The provided centralized control computer 1 can adjust the power supply amount and power supply voltage of the high-voltage pulse power supply 2, and can charge the high-voltage pulse capacitor 3 with the required pulse power through the high-voltage pulse power supply 2 at intervals. The pulse release signal output end of the centralized control computer 1 is connected to the pulse release signal input end of the high-voltage pulse switch 5.

[0025] A specimen is fixed inside the high-voltage pulse fracturing chamber 6. Four specimen clamping assemblies are arranged corresponding to the specimen inside the high-voltage pulse fracturing chamber 6, which are respectively arranged on the front and rear sides and the upper and lower sides of the specimen.

[0026] A piezoelectric pressure sensor 14 is equipped corresponding to each specimen clamping assembly on the high-voltage pulse fracturing chamber 6. Combining with the piezoelectric pressure sensor 14, the impact stress in the vertical and horizontal directions can be detected. The detection signal output ends of all the piezoelectric pressure sensors 14 are connected to the pressure detection signal input end of the stress wave signal collector 18. A Faraday cage 15 for covering the piezoelectric pressure sensor 14 is arranged corresponding to each piezoelectric pressure sensor 14 inside the high-voltage pulse fracturing chamber 6, and each Faraday cage 15 is connected to the power ground through a wire. Figure 1 In order to better show the fixing panel 11 and the fixing bolts 12, only one side is drawn with the Faraday cage 15, and the Faraday cages 15 on the other three sides are omitted.

[0027] Each specimen clamping assembly includes a fixed base and a transmission rod 10 slidably connected to the fixed base. The fixed base includes a fixing panel 11, on which a pair of fixing bolts 12 are fixed and fixed to the side wall of the high-voltage pulse fracturing chamber 6 through the fixing bolts 12. The structure is simple and the fixing is stable. One end of the transmission rod 10 faces the specimen and is provided with a clamping plate 9 for abutting against the specimen, and a gripper is formed by combining all the clamping plates 9. Among them, the transmission rod 10 and the clamping plate 9 are of an integral structure, which can improve the structural rigidity. The other end of the transmission rod 10 extends into the Faraday cage 15 through the gap of the Faraday cage 15 and abuts against the piezoelectric pressure sensor 14. A jack for the transmission rod 10 to pass through is arranged on the fixing panel 11, and a linear bearing 13 sleeved on the transmission rod 10 is arranged in the jack.

[0028] Needle electrodes 7 are arranged on both sides of the specimen where no specimen clamping assembly is provided. The ends of the two needle electrodes 7 both extend outside the high-voltage pulse fracturing chamber 6 and serve as the wire connection terminals of the high-voltage pulse fracturing chamber 6, and the needle electrodes 7 are both abutted against the specimen and release high-voltage pulses. The needle electrodes 7 are equipped with fixing sleeves and fixed to the side wall of the high-voltage pulse fracturing chamber 6 through the fixing sleeves. A through hole for accommodating the needle electrode 7 is arranged on the fixing sleeve, and a clamping plate 9 is also arranged at one end of the fixing sleeve close to the specimen, and the two ends of the needle electrode 7 are respectively located outside the fixing sleeve and outside the clamping plate 9. The installation distance between the needle electrode 7 and the piezoelectric pressure sensor 14 is greater than 50 mm, which can ensure the safe operation of the equipment.

[0029] The outer sidewall of the fixed sleeve is provided with threads, and two nuts 8 are threadedly connected to the fixed sleeve. The two nuts 8 are respectively located inside and outside the high-voltage pulse fracturing chamber 6, and the fixed sleeve is fixed by pressing against both sides of the sidewall of the high-voltage pulse fracturing chamber 6 through the inner and outer nuts 8 respectively. The fixed sleeve and the clamping plate 9 are also of an integrated structure.

[0030] Components inside the high-voltage pulse fracturing chamber 6, such as the transmission rod 10, the fixed sleeve, the clamping plate 9, the nuts, the linear bearing 13, the fixed panel 11, and the fixing bolts 12, are all made of high-voltage insulating, high-temperature resistant, and high-strength peek material to meet the experimental requirements of the equipment in high-voltage and high-temperature environments.

[0031] During use, the centralized control computer 1 controls the high-voltage charging power supply 2 to determine the charging voltage and charging speed of the high-voltage pulse capacitor 3. When the voltage across the high-voltage pulse capacitor 3 reaches the set threshold, the centralized control computer 1 triggers the high-voltage pulse switch 5 to close, and discharges from the tip of the needle-shaped electrode 7 to the specimen inside the gripper 9. During the discharge process, the waveform signals on the stress wave signal receiver 18 and the oscilloscope 19 should be monitored in real time to determine whether the specimen has been broken down.

[0032] If the specimen has not been broken down, only weak noise signals will be displayed on the stress wave signal receiver 18, and there will be no obvious changes in the breakdown voltage and current on the oscilloscope 19. When the specimen is broken down, its rupture will cause extrusion of the clamping plate 9 in all directions. Subsequently, the stress on the clamping plate 9 is transmitted to the piezoelectric pressure sensor 14 through the transmission rod 10, and the stress waveform signal of the specimen breakdown process within the μs time scale is dynamically displayed on the stress wave signal receiver 18. At the same time, the voltage and current signals when the specimen is broken down will be clearly presented on the oscilloscope 19.

[0033] During the test process, it is necessary to collect the stress waveform data of the stress wave signal receiver 18 and synchronously collect the current and voltage signals on the oscilloscope 19. After the test, the negative electrode of the high-voltage pulse capacitor 3 should be grounded to release its remaining voltage to ensure the safety of the test.

Claims

1. A monitoring device for stress shock waves caused by high-voltage electric pulses in coal and rock, comprising a high-voltage pulse capacitor (3), a voltage divider (4), a high-voltage pulse switch (5), and a high-voltage pulse fracturing chamber (6) that are connected in sequence to form a closed loop, and characterized in that: A high-voltage probe (16) and a Rogowski coil (17) are provided on the wire connecting the high-voltage pulse fracturing chamber (6) and the high-voltage pulse capacitor (3). The signal output ends of the high-voltage probe (16) and the Rogowski coil (17) are both connected to an oscilloscope (19). A specimen is fixed inside the high-voltage pulse fracturing chamber (6). A circle of specimen clamping assemblies is provided corresponding to the specimen inside the high-voltage pulse fracturing chamber (6). Needle electrodes (7) are provided on both sides of the specimen where the specimen clamping assemblies are not provided, and the needle electrodes (7) are both in contact with the specimen and release high-voltage pulses. A piezoelectric pressure sensor (14) is equipped corresponding to each specimen clamping assembly on the high-voltage pulse fracturing chamber (6). The detection signal output ends of all the piezoelectric pressure sensors (14) are connected to the pressure detection signal input end of a stress wave signal collector (18). A Faraday cage (15) for covering the piezoelectric pressure sensor (14) is provided corresponding to each piezoelectric pressure sensor (14) inside the high-voltage pulse fracturing chamber (6). Each Faraday cage (15) is connected to the power ground through a wire. Each specimen clamping assembly includes a fixed base and a transmission rod (10) slidably connected to the fixed base. One end of the transmission rod (10) faces the specimen and is provided with a clamping plate (9) for abutting against the specimen, and a clamp is formed by combining all the clamping plates (9). The other end of the transmission rod (10) extends into the Faraday cage (15) and abuts against the piezoelectric pressure sensor (14). A jack for the transmission rod (10) to pass through is provided on the fixed base, and a linear bearing (13) is provided in the jack.

2. The high-voltage electric pulse-induced coal and rock stress shock wave monitoring device according to claim 1, characterized in that: A fixing sleeve is provided outside the needle electrode (7), and the fixing sleeve is fixed on the side wall of the high-voltage pulse fracturing chamber (6) through the fixing sleeve. A clamping plate (9) is also provided at the end of the fixing sleeve close to the specimen, and the ends of the two needle electrodes (7) both pass through the clamping plate (9) and abut against the specimen.

3. The stress shock wave monitoring device for coal and rock fractured by high-voltage electric pulse according to claim 2, characterized in that: Threads are provided on the outer side wall of the fixing sleeve, and two nuts (8) are threadedly connected to the fixing sleeve. The two nuts (8) are respectively located inside and outside the high-voltage pulse fracturing chamber (6), and the fixing sleeve is fixed by the inner and outer nuts (8) respectively abutting against both sides of the side wall of the high-voltage pulse fracturing chamber (6).

4. The high-voltage electric pulse-induced coal and rock stress shock wave monitoring device according to claim 3, characterized in that: The transmission rod (10) and the fixing sleeve are both of an integral structure with the clamping plate (9).

5. The stress shock wave monitoring device for coal and rock fractured by high-voltage electric pulse according to claim 1, wherein: The fixed base includes a fixed panel (11), and a pair of fixing bolts (12) are provided on the fixed panel (11), and the fixed panel (11) is fixed on the side wall of the high-voltage pulse fracturing chamber (6) through the fixing bolts (12).

6. The stress shock wave monitoring device for coal and rock fractured by high-voltage electric pulse according to claim 1, wherein: The high-voltage pulse capacitor (3) is equipped with a high-voltage pulse power supply (2) and a centralized control computer (1). The control output end of the centralized control computer (1) is connected to the control signal input end of the high-voltage pulse power supply (2). The power supply end of the high-voltage pulse power supply (2) is connected to the power input end of the high-voltage pulse capacitor (3).

7. The stress shock wave monitoring device for coal and rock fractured by high-voltage electric pulse according to claim 1, characterized in that: The installation distance between the needle electrode (7) and the piezoelectric pressure sensor (14) is greater than 50 mm.

8. A high-voltage electric pulse-induced coal and rock stress shock wave monitoring device according to claim 1, characterized in that: There are four specimen clamping assemblies, which are respectively arranged on the front and rear sides and the upper and lower sides of the specimen.

9. The high-voltage electric pulse-induced coal and rock stress shock wave monitoring device according to claim 3, characterized in that: The transmission rod (10), fixed sleeve, clamping plate (9), nut, linear bearing (13) and fixed base are all made of peek material.

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