Remote controllable shock wave combined with hydraulic fracturing for large-scale seam fracture prevention

Abstract

The application discloses a coal rock anti-burst method of large-range seam forming by remote controllable shock wave and hydraulic fracturing, and comprises the following steps: step one, detecting and recording the stress concentration degree of target coal seam or rock stratum; step two, drilling; step three, withdrawing the hollow drill rod, arranging the discharge electrode connected with the cable at the front end of the hollow drill rod, and sending the discharge electrode into the drill hole through the hollow drill rod; step four, sealing the hole by using a hole sealer and performing hydraulic fracturing; steps five to seven, completing multiple repeated electric pulse discharge operations; and step eight, testing the pressure relief effect of the coal seam or rock stratum. The method uses the drilling cuttings method, high-pressure hydraulic fracturing and high-voltage electric pulse to perform large-range cracking and pressure relief on the coal rock stratum, changes the stress state of the coal rock stratum, and reduces the stress concentration degree, so that the anti-burst purpose is achieved. The method is mainly applied to deep coal rock body tunneling roadways and coal mining working faces containing coal rock body impact tendency.

Description

Technical Field

[0001] This invention relates to the field of safe and efficient mining technology of coal and rock strata, specifically to a method for preventing coal and rock erosion by remotely controllable shock wave combined with hydraulic fracturing to create large-scale fractures, which can effectively reduce the risk of rockburst in coal and rock strata. Background Technology

[0002] In my country, coal mines prone to rock bursts account for 3.78% of the total number of coal mines nationwide, and their production capacity accounts for 8.99% of the total national coal production capacity. The risk of rock bursts seriously threatens the safe production of coal mines. Rock bursts are a dynamic phenomenon caused by excessive stress concentration, where the elastic strain energy accumulated in the coal or rock mass is suddenly released under certain conditions, causing the coal or rock mass to undergo rapid brittle failure and be thrown into the mining space.

[0003] In recent years, with the continuous increase in mining depth, the mining environment and geological conditions have become increasingly harsh, and the high stress concentration in deep mines has led to a growing problem of rockbursts. During coal mining, the energy accumulated in the coal seam cannot be released slowly and in a timely manner, resulting in frequent mine tremors. When the elastic potential energy accumulated in the coal or rock mass is suddenly released, it can cause instantaneous failure of the coal or rock mass, inducing rockbursts. This not only affects coal mining efficiency but also causes casualties and equipment damage, resulting in huge economic losses and adverse social impacts. Therefore, it is currently necessary and urgent to prevent and control rockbursts in mines.

[0004] Coal seam impact tendency is an intrinsic cause of rockbursts, essentially stemming from the coal seam's accumulated deformation energy and high stress concentration, which can lead to impact damage. According to the "Classification and Determination Method of Coal Impact Tendency," laboratory tests using field samples indicate that a coal seam exhibits impact tendency when its uniaxial compressive strength exceeds 7 MPa, its elastic energy index and impact energy index exceed 2 and 1.5 respectively, and its dynamic failure time exceeds 50 ms. However, current comprehensive rockburst prevention methods for deep, high-pressure coal and rock strata mainly rely on drill cuttings combined with online stress monitoring systems, a simplistic approach with unsatisfactory rockburst prevention effects. Summary of the Invention

[0005] This invention aims to provide a method for preventing coal and rock erosion by remotely controllable shock wave combined with hydraulic fracturing to create large-scale fractures, thereby changing the stress state of the coal seam and reducing the degree of stress concentration, so as to achieve the purpose of efficient and rapid erosion prevention.

[0006] Therefore, the technical solution adopted in this invention is: a method for preventing coal and rock erosion by remotely controllable shock wave-assisted hydraulic fracturing for large-scale fracture creation, comprising the following steps:

[0007] Step 1: Select the target coal seam or rock stratum, and use the drill cuttings method combined with an online stress monitoring system to detect the stress concentration of the target coal seam or rock stratum, and record the amount of drill cuttings and stress value at this time;

[0008] Step 2: Use a drilling rig to drill a borehole in the target coal seam or rock stratum;

[0009] Step 3: After drilling is completed, remove the hollow drill rod, unscrew the drill bit at the front end of the hollow drill rod, place the discharge electrode of the connecting cable at the front end of the hollow drill rod, and insert the discharge electrode into the borehole through the hollow drill rod; a pressure sensor is installed in the middle of the hollow drill rod, and the pressure sensor is used to monitor and record the pressure changes in the borehole in real time.

[0010] Step 4: Use a hole sealer to seal the hole, and then operate the controller to continuously inject high-pressure water into the borehole through the hollow drill rod to perform hydraulic fracturing.

[0011] Step 5: After hydraulic fracturing is completed, the charging voltage is set remotely using a computer, and a charging command is sent. The high-voltage charging power supply begins to charge the capacitor. When the voltage reaches the predetermined voltage, charging stops.

[0012] Step 6: After charging is complete, a discharge command is sent via fiber optic cable using a computer. The high-voltage discharge circuit switches the capacitor and discharge electrodes, and the electrical pulse generation system is remotely started to complete one discharge. The discharge electrodes discharge in the water, and the electrical energy is converted into mechanical energy, forming a shock wave that propagates outward in a spherical shape. This shock wave acts on the coal or rock mass, causing it to generate new fractures, while further expanding and extending the large-scale fractures generated by hydraulic fracturing.

[0013] Step 7: After repeating the electrical pulse discharge operation multiple times, disconnect the high-voltage discharge switch and stop the discharge; after the discharge is completed, remove the hollow drill rod and discharge electrode.

[0014] Step 8: Using the drill cuttings method combined with an online stress monitoring system, the stress concentration of the target coal seam or rock stratum after electrical pulse discharge is detected. The amount of drill cuttings and the stress value before electrical pulse discharge are compared to verify the stress relief effect of this technology on the coal seam or rock stratum.

[0015] As a preferred embodiment of the above scheme, in step two, a visual monitor capable of real-time monitoring of the shock wave pulse signal and crack propagation is installed inside the borehole; in step six, the visual monitor is used to monitor and detect the shock wave pulse signal and microseismic information of crack propagation in real time.

[0016] More preferably, in step seven, the number of electrical pulse discharges is 6-8 times.

[0017] Further preferably, the hollow drill rod adopts a double drill rod and can achieve multi-section docking. Each drill rod section includes an inner drill rod, an outer drill rod, a nut, and a screw ring. The inner drill rod and the outer drill rod are nested together to form an inner channel and an outer channel. The inner drill rod adopts a spiral drill rod, and the spiral structure combined with the outer channel is used for chip removal. The inner channel is used for water injection. The upper end of the inner drill rod has threads on both the inner and outer sides, and the lower end has threads on both the outer and inner sides, for achieving drill rod docking. The upper end of the outer drill rod has threads on both the inner and outer sides, for achieving nesting of the inner drill rod and outer drill rod, and for protecting the hole wall from damage during drilling. The outer surface of the outer drill rod has a row of grooves for placing and fixing cables, and the cables are constrained by the tightening of the screw ring and the outer thread at the lower end of the outer drill rod. Each drill rod section has at least two nuts, and the nuts have threads on both the inner and outer sides for nesting connection of the inner drill rod and outer drill rod, and are connected and fixed by a spiral blade in the middle. The blades of the spiral blade are hollowed out for chip removal. Hollow drill rods are not limited by distance; multiple rods can be joined together to achieve long-distance drilling, offering great flexibility. The drill rod has a simple structure, high stability, and is easy to assemble. It facilitates slag removal and protects the borehole wall from damage. The inner and outer drill rods are detachable and hollow, both suitable for water injection. The inner drill rod can be removed depending on the required water volume; if a large volume is needed, removing the inner rod increases the unit water injection capacity of the outer drill rod. A row of grooves on the outer side of the drill rod can be used to place and secure cables, facilitating the delivery of discharge electrodes into the borehole. The drill rod's hollow interior allows for the installation of pressure sensors as needed. The entire anti-fracturing process can be completed using a single hollow drill rod, including drilling, high-pressure hydraulic fracturing, and high-pressure electrical pulses, significantly reducing costs and offering simplicity and efficiency.

[0018] A further preferred embodiment is that the outer diameter of the upper and lower ends of the outer drill rod is larger than the outer diameter at the middle position, and the groove is opened at both ends.

[0019] More preferably, the drill bit is detachably coaxially mounted on the front end of the hollow drill rod.

[0020] A further preferred embodiment is that each section of the drill pipe has two nuts, located at both ends of the drill pipe.

[0021] A further preferred embodiment is that the high-voltage charging power supply, capacitor, high-voltage discharge switch, and controller are integrated into the all-terrain mobile platform.

[0022] More preferably, the all-terrain mobile platform is also equipped with a charging protection device.

[0023] The beneficial effects of this invention are as follows: First, this invention utilizes high-pressure hydraulic fracturing technology to fracture the coal and rock mass, thereby generating a large-scale fracture around the borehole. Then, a high-pressure electric pulse system is used to expand and connect the large-scale fractures through the electrohydraulic effect, further expanding the fracture range and forming a more complex fracture network. This can effectively change the stress state of the coal seam, reduce the stress concentration of the coal seam, and achieve the purpose of relieving pressure on the coal seam.

[0024] This method uses a combination of drill cuttings fracturing, high-pressure hydraulic fracturing, and high-pressure electrical pulses to induce fracturing and decompression in coal and rock strata, thereby changing the stress state of the coal seam and reducing the degree of stress concentration, thus achieving the purpose of preventing rock erosion. It is mainly applied to deep coal and rock mass tunneling roadways and longwall mining faces containing coal and rock mass with rock erosion tendency. Attached Figure Description

[0025] Figure 1 The steps of this invention are shown in the diagram.

[0026] Figure 2 A schematic diagram of the device structure of the present invention.

[0027] Figure 3 A schematic diagram of the drilling process of the drill bit of this invention.

[0028] Figure 4 This is a block diagram of a high-voltage electric pulse system.

[0029] Figure 5 This is a schematic diagram of the system.

[0030] Figure 6 This is a schematic diagram of the disassembled section of a drill pipe.

[0031] Figure 7 This is a schematic diagram of the hollow drill rod after the two sections are joined together. Detailed Implementation

[0032] The present invention will be further described below with reference to the embodiments and accompanying drawings:

[0033] like Figure 1 — Figure 5 As shown, a method for preventing coal and rock erosion by remotely controlled shock wave combined with hydraulic fracturing to create large-scale fractures includes the following steps:

[0034] Step 1: Select the target coal seam or rock stratum, and use the drill cuttings method combined with an online stress monitoring system to detect the stress concentration of the target coal seam or rock stratum, and record the amount of drill cuttings and stress value at this time.

[0035] Step 2: Use drilling rig 7 to drill a borehole 1 in the target coal seam or rock stratum. Drill bit 2 is detachably coaxially mounted on the front end of hollow drill rod 5.

[0036] Step 3: After drilling hole 1 is completed, remove the hollow drill rod 5, unscrew the drill bit 2 at the front end of the hollow drill rod 5, place the discharge electrode 17 of the connecting cable 16 at the front end of the hollow drill rod 5, and insert the discharge electrode 17 into the drill hole 1 through the hollow drill rod 5. A pressure sensor 18 is installed in the middle of the hollow drill rod 5, which is used to monitor and record the pressure changes inside the drill hole 1 in real time.

[0037] Step 4: Use the sealing device 4 to seal the borehole. Then, operate the controller 9 to continuously inject high-pressure water into the borehole 1 through the hollow drill rod 5 to perform hydraulic fracturing. The rear end of the drilling rig 7 is connected to the high-pressure water injection pump 10 through the water pipe 8.

[0038] Step 5: After hydraulic fracturing is completed, the charging voltage is remotely set using computer 15 and a charging command is sent. The high-voltage charging power supply 14 starts charging capacitor 13. When the voltage reaches the predetermined voltage, charging stops.

[0039] Step Six: After charging is complete, the computer 15 sends a discharge command via optical fiber, and the high-voltage discharge switch 6 connects the capacitor 13 and the discharge electrode 17 to remotely start the electrical pulse generation system, completing one discharge. The discharge electrode 17 discharges in the water, converting electrical energy into mechanical energy, forming a shock wave that propagates outward in a spherical shape. This shock wave acts on the coal or rock mass, causing new fractures and further expanding and extending the large-scale fractures generated by hydraulic fracturing.

[0040] Step 7: After repeating the electrical pulse discharge operation multiple times, disconnect the high-voltage discharge switch 6 to stop the discharge; after the discharge is completed, remove the hollow drill rod 5 and the discharge electrode 17. The number of electrical pulse discharges is best 3-5 times.

[0041] Step 8: Using the drill cuttings method combined with an online stress monitoring system, the stress concentration of the target coal seam or rock stratum after electrical pulse discharge is detected. The amount of drill cuttings and the stress value before electrical pulse discharge are compared to verify the stress relief effect of this technology on the coal seam or rock stratum.

[0042] Ideally, in step two, a visual monitor 3 capable of real-time monitoring of the shock wave pulse signal and crack propagation is installed inside borehole 1; in step six, the visual monitor 3 is used to monitor and detect the shock wave pulse signal and microseismic information of crack propagation in real time.

[0043] Combination Figure 6 — Figure 7 As shown, the hollow drill rod 5 adopts a double drill rod configuration and can achieve multi-section connection. Each drill rod section mainly consists of an inner drill rod 51, an outer drill rod 52, a nut 53, and a threaded ring 54.

[0044] The inner drill pipe 51 and the outer drill pipe 52 are nested together to form an inner channel 55 and an outer channel 56. The inner drill pipe 51 is a spiral drill pipe, and the spiral structure combined with the outer channel 56 is used for removing cuttings and slag, while the inner channel 55 is used for water injection.

[0045] The inner drill rod 51 has threads on its upper inner and outer ends and lower outer ends for connecting the drill rods. The outer drill rod 52 has threads on its upper inner end and lower inner and outer ends for nesting the inner drill rod 51 and the outer drill rod 52, and can protect the hole wall from damage during drilling.

[0046] The outer surface of the outer drill rod 52 has a row of grooves 52a for placing and fixing cables, and the cables are constrained by the tightening of the screw ring 54 with the external thread at the lower end of the outer drill rod 52. Preferably, the outer diameter at the upper and lower ends of the outer drill rod 52 is larger than the outer diameter at the middle position.

[0047] Each drill rod section has at least two nuts 53, both internally and externally threaded, for nesting connection between the inner drill rod 51 and the outer drill rod 52, and fixed by a central helical blade 53a. The blades of the helical blade 53a have open spaces between them for chip removal. Preferably, each drill rod section has two nuts 53, located at both ends of the drill rod.

[0048] Ideally, such as Figure 4 , Figure 5 As shown, the high-voltage charging power supply 14, capacitor 13, high-voltage discharge switch 6, and controller 9 are integrated on the all-terrain mobile platform 11. A charging protection device 12 is also equipped on the all-terrain mobile platform.

[0049] Hydraulic fracturing is a technique that uses high-pressure water injected into stress concentration zones through boreholes to transfer or release stress and energy in the surrounding rock. This technique can increase the pore water pressure in coal and rock masses, reduce the effective stress in the coal and rock masses, and promote the propagation of fractures in the coal and rock masses.

[0050] High-voltage electric pulse (HEP) is a technology that uses electrodes to discharge high-voltage, high-energy energy, converting electrical energy into mechanical energy. This technology is based on the principle of nuclear explosion shock waves. This invention applies HEP to coal seams or rock strata with high-power discharge, generating shock waves that cause fracturing. It offers advantages such as high power, strong environmental adaptability, and environmental friendliness. The HEP system uses a remote control terminal, allowing for parameter setting and monitoring via a remote computer. The charging and discharging operations can be completed remotely via fiber optic commands, keeping operators away from the field and further improving operator safety. The system's control module, while receiving remote control commands, can also send feedback on the equipment's operating status to the remote computer, achieving real-time remote monitoring of the equipment's operation.

[0051] The electrode material selected for discharge electrode 17 is preferably a high-strength alloy that is resistant to high pressure and corrosion. The electrode support is made of stainless steel and high-strength insulating material, which is long-lasting, corrosion-resistant, impact-resistant, easy to maintain, and easy to replace. The starting voltage of the electric pulse generation system is 15kV, and the electric pulse generation frequency is 50Hz. The high-voltage discharge switch 6 adopts an independent switching circuit, which has high discharge efficiency, strong environmental adaptability, long discharge life, and good maintainability. The control of high-voltage electric pulse charging and discharging is divided into two working modes: local control and remote control. It can receive remote control commands and send equipment status signals to a remote computer. The hydraulic shock wave propagates outward in a spherical shape, and its instantaneous shock wave pressure can reach tens to hundreds of megapascals, thereby converting electrical energy into mechanical energy. Drilling is carried out using a drilling rig, which can control the drilling direction in a directional manner, and the construction cycle is short with high work efficiency. A visual monitor 3 is used to monitor the pulse signal and micro-vibration information of crack propagation in real time, and a pressure sensor 18 is used to monitor the pressure change in the hole in real time. The operation is simple and the safety is high. Water can be injected directly into the borehole through the hollow drill rod, eliminating the need for additional water injection pipelines inside the borehole, reducing manual operation steps, and saving time and effort. Placing the discharge electrode 17 at the front end of the hollow drill rod of the drilling rig facilitates its insertion into the borehole, reduces the difficulty of manual operation, and improves work efficiency.

[0052] This invention employs a remote control system to charge and discharge capacitors, while simultaneously utilizing a computer to remotely monitor equipment operation. This allows workers to operate remotely from the construction site, improving equipment safety. By combining hydraulic fracturing and high-voltage electric pulse technology, this invention creates large-scale fractures and relieves pressure in coal seams. Building upon hydraulic fracturing, a high-voltage electric pulse system discharges water, generating a strong shock wave that propagates spherically and acts on the coal or rock mass. This causes numerous internal fractures to form, expanding and extending the original fractures. This effectively increases the number of fractures in the coal or rock mass, altering the stress state of the coal or rock strata, reducing stress concentration, and achieving pressure relief. Furthermore, the large-scale fractures generated by hydraulic fracturing, after being subjected to high-voltage electric pulses, achieve even greater directional expansion and penetration, expanding the effective influence range of the large-scale fractures. The stress concentration in the coal or rock strata is significantly reduced, providing a solid foundation for the prevention and control of rockbursts.

Claims

1. A method for preventing coal and rock erosion by remotely controllable shock wave combined with hydraulic fracturing to create large-scale fractures, characterized in that, Includes the following steps: Step 1: Select the target coal seam or rock stratum, and use the drill cuttings method combined with an online stress monitoring system to detect the stress concentration of the target coal seam or rock stratum, and record the amount of drill cuttings and stress value at this time; Step 2: Use a drilling rig (7) to drill a borehole (1) in the target coal seam or rock stratum; Step 3: After the drilling (1) is completed, remove the hollow drill rod (5), unscrew the drill bit (2) at the front end of the hollow drill rod (5), place the discharge electrode (17) of the connecting cable (16) at the front end of the hollow drill rod (5), and send the discharge electrode (17) into the borehole (1) through the hollow drill rod (5); the hollow drill rod (5) is equipped with a pressure sensor (18) in the middle, and the pressure sensor (18) is used to monitor and record the pressure changes in the borehole (1) in real time; Step 4: Use the sealing device (4) to seal the hole, and then operate the controller (9) to continuously inject high-pressure water into the borehole (1) through the hollow drill rod (5) to perform hydraulic fracturing; Step 5: After hydraulic fracturing is completed, the charging voltage is set remotely using a computer (15), and a charging command is sent. The high-voltage charging power supply (14) starts charging the capacitor (13). When the voltage reaches the predetermined voltage, the charging stops. Step 6: After charging is completed, use computer (15) to send a discharge command through optical fiber, use high voltage discharge switch (6) to connect capacitor (13) and discharge electrode (17), remotely start the electric pulse generation system, and complete one discharge; discharge electrode (17) discharges in water, electrical energy is converted into mechanical energy, forming a shock wave that propagates outward in a spherical shape, which acts on the coal body or rock body, causing it to generate new cracks, and at the same time further expands and extends the large-scale cracks generated by hydraulic fracturing; Step 7: After repeating the electrical pulse discharge operation multiple times, disconnect the high-voltage discharge switch (6) and stop the discharge; after the discharge is completed, remove the hollow drill rod (5) and the discharge electrode (17). Step 8: Using the drill cuttings method combined with an online stress monitoring system, the stress concentration of the target coal seam or rock stratum after electrical pulse discharge is detected. The amount of drill cuttings and the stress value before electrical pulse discharge are compared to verify the stress relief effect of this technology on the coal seam or rock stratum. The hollow drill rod (5) adopts a double drill rod and can realize multi-section docking. Each drill rod section includes an inner drill rod (51), an outer drill rod (52), a nut (53), and a screw ring (54). The inner drill rod (51) and the outer drill rod (52) are nested together to form an inner channel (55) and an outer channel (56). The inner drill rod (51) adopts a spiral drill rod, and the spiral structure combined with the outer channel (56) is used for chip removal. The inner channel (55) is used for water injection. The inner drill rod (51) has threads on the inner and outer sides of the upper end and the outer side of the lower end for drilling rod docking. The outer drill rod (52) has threads on the inner side of the upper end and the inner and outer sides of the lower end for drilling rod docking. To achieve the nesting of the inner drill rod (51) and the outer drill rod (52), and to protect the hole wall from damage during the drilling process; the outer surface of the outer drill rod (52) is provided with a row of grooves (52a) for placing and fixing the cable, and the cable is constrained by the fastening of the screw ring (54) and the external thread at the lower end of the outer drill rod (52); there are at least two nuts (53) on each section of the drill rod, and the nuts (53) are threaded inside and outside, for the nesting connection of the inner drill rod (51) and the outer drill rod (52), and are connected and fixed by the middle spiral blade (53a), and the blades of the spiral blade (53a) are hollowed out for chip removal.

2. The method for preventing coal and rock erosion by remotely controllable shock wave combined with hydraulic fracturing for large-scale fracture creation according to claim 1, characterized in that: In step two, a visual monitor (3) capable of real-time monitoring of the shock wave pulse signal and crack propagation is installed in the borehole (1); in step six, the visual monitor (3) is used to monitor and detect the shock wave pulse signal and crack propagation microseismic information in real time.

3. The method for preventing coal and rock erosion by remotely controllable shock wave combined with hydraulic fracturing for large-scale fracture creation according to claim 1, characterized in that: In step seven, the electrical pulse discharge is performed 6 to 8 times.

4. The method for preventing coal and rock erosion by remotely controllable shock wave combined with hydraulic fracturing for large-scale fracture creation as described in claim 1, characterized in that: The outer diameter of the upper and lower ends of the external drill rod (52) is greater than the outer diameter at the middle position, and the groove (52a) is opened at both ends.

5. The method for preventing coal and rock erosion by remotely controllable shock wave combined with hydraulic fracturing for large-scale fracture creation according to claim 1, characterized in that: The drill bit (2) is detachably coaxially mounted on the front end of the hollow drill rod (5).

6. The method for preventing coal and rock erosion by remotely controllable shock wave combined with hydraulic fracturing for large-scale fracture creation according to claim 1, characterized in that: There are two nuts (53) on each section of the drill pipe, located at both ends of the drill pipe.

7. The method for preventing coal and rock erosion by remotely controllable shock wave combined with hydraulic fracturing for large-scale fracture creation according to claim 1, characterized in that: The high-voltage charging power supply (14), capacitor (13), high-voltage discharge switch (6), and controller (9) are integrated on the all-terrain mobile platform (11).

8. The method for preventing coal and rock erosion by remotely controllable shock wave-assisted hydraulic fracturing for large-scale fracture creation according to claim 7, characterized in that: The all-terrain mobile platform is also equipped with a charging protection device (12).

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