A low-permeability rock layer pulse type hydraulic fracturing device and a pulse fracturing method

Abstract

The application provides a low-permeability rock layer pulse type hydraulic fracturing device and a pulse fracturing method, relates to the technical field of fracturing devices, and discloses the following technical scheme: a fracturing rod is provided with a front end blocking air bag and a rear end blocking air bag at the front end and the rear end of the fracturing rod, respectively; a pair of auxiliary fracturing air bag sliding sleeves are further arranged on the rod body between the front end blocking air bag and the rear end blocking air bag; the fracturing hole comprises a front section fracturing hole, a middle section fracturing hole and a rear section fracturing hole; the displacement generated by the auxiliary fracturing air bag sliding sleeves is used for positioning the fracturing position; and the front section fracturing hole, the middle section fracturing hole and the rear section fracturing hole are used for partition fracturing. The power transmission is more efficient, so that the propelling rod no longer bears huge propelling pressure, and the risk of damage is reduced; low-amplitude pulse pressure and high-amplitude pulse fracturing are used for fracturing according to the rock fracture opening and the distribution range, a low-permeability rock layer pulse fracturing method is formed, accurate and efficient fracturing of the low-permeability rock layer is realized, and more uniform fracturing effect is ensured.

Description

Technical Field

[0001] This invention relates to the field of fracturing equipment technology, specifically to a pulsed hydraulic fracturing device and method for low-permeability rock formations. Background Technology

[0002] Hydraulic fracturing technology has been widely applied in engineering fields such as transportation, water conservancy, and energy. It uses high-pressure water to fracture rock strata, forming a fracture network that provides seepage channels for the diffusion of mixed solutions, significantly improving fracturing efficiency. It is a key technology in fracturing projects such as oil and gas extraction, grouting reinforcement, and gas extraction. Deep underground rock masses have complex environments, especially high-stress, low-permeability rock masses, which face even more complex technical challenges in fracturing. Conventional constant-pressure fracturing methods are difficult to use to form complex fracture networks in deep, low-permeability rock masses. Pulse fracturing can reduce the rock mass fracturing pressure, increase the fatigue damage range, and promote the formation of fracture networks. However, existing fracturing methods and pulse fracturing devices in low-permeability rock strata tend to result in uneven distribution of fracture networks during the pulse fracturing process. On the one hand, the distribution and aperture of fractures vary greatly at different distances from the excavation face, lacking a reasonable pulse fracturing method. On the other hand, existing fracturing devices have long pushing processes and high friction during staged fracturing, making it difficult to achieve autonomous pushing of the fracturing rod and precise positioning of the fracturing based on fracture distribution, thus hindering efficient fracturing of low-permeability rock strata.

[0003] The prior art, disclosed in CN102787833A, describes a method and system for hydraulic fracturing and increasing water supply in bedrock wells. This includes a set of surface equipment consisting of a fracturing pump, manifold, and high-pressure swivel, along with in-well fracturing tools. It features one or more packers that can be inserted into the well and distributed throughout the working section. Each packer is a cylindrical rubber elastomer with an annular chamber. A constant-pressure opening valve is installed between each set of packers. A ball-dropping unloading valve is installed above the upper packer. A bottom plug is installed at the bottom of the drill string. The surface equipment is connected to the in-well drill pipe of the in-well fracturing tools via a high-pressure pipeline. During operation, the mixed solution enters the annular cavity of each packer to expand and seal it. When the system pressure reaches a certain value, the pressure regulating valve opens, and the mixed solution enters the packer. As the system pressure continues to increase and exceeds the tensile strength of the rock itself, the rock cracks, forming new fractures that extend to the water storage structure, thereby increasing the water output of the well. At the same time, high-pressure mixed solution can also be used to flush and increase water in existing water-bearing fractures.

[0004] However, the aforementioned device still has significant drawbacks in its use: the fracturing rod of the device is a common form in existing technology. While it can effectively perform fracturing, its function is relatively limited, only capable of fracturing operations inside the borehole. In existing technologies, the fracturing rod is typically pushed from the outside of the borehole inwards via a connecting tube, a process affected by frictional resistance within the borehole. Furthermore, the long propulsion distance of the fracturing rod places a significant burden on the pushing rod, potentially causing damage during its advancement. Additionally, during fracturing, the mixed solution preferentially enters the rock mass or coal seam through the fracture fissures, but the distribution of these fissures cannot be controlled, leading to uneven fracturing. Existing pulse fracturing methods struggle to implement efficient fracturing techniques tailored to the specific fracture distribution characteristics of rock formations, thus hindering subsequent production operations. Summary of the Invention

[0005] The purpose of this invention is to provide a pulsed hydraulic fracturing device and method for low-permeability rock formations to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A pulsed hydraulic fracturing device for low-permeability rock formations includes:

[0008] A fracturing rod is connected to the end of a fracturing connecting pipe. A front-end sealing airbag and a rear-end sealing airbag are respectively installed at the front and rear ends of the fracturing rod. A pair of auxiliary fracturing airbag sleeves are telescopically installed on the rod body between the front and rear sealing airbags. The front-end sealing airbag, the rear-end sealing airbag, and the pair of auxiliary fracturing airbag sleeves are controlled by an externally installed pumping and releasing device. A fracturing hole is also provided on the rod body, through which the mixed solution transported inward through the fracturing connecting pipe is pumped outward, thereby performing the fracturing operation.

[0009] The fracturing holes include a front fracturing hole, a middle fracturing hole, and a rear fracturing hole. The auxiliary fracturing airbag sleeve is telescopically mounted on the rod between the front fracturing hole and the middle fracturing hole, and between the middle fracturing hole and the rear fracturing hole. In the traveling mode, the fracturing rod is driven to move forward by pumping the mixed solution into the front fracturing hole, and to move backward by pumping the mixed solution into the rear fracturing hole. In the fracturing mode, the fracturing position is located by the displacement generated by the auxiliary fracturing airbag sleeve, and the fracturing operation is carried out in sections through the front fracturing hole, the middle fracturing hole, and the rear fracturing hole.

[0010] Preferably, a pair of auxiliary fracturing airbag sleeves are connected to a telescopic slide rod. The telescopic slide rod is inserted into a slide rod hole corresponding to the fracturing rod. One end of the telescopic slide rod away from the auxiliary fracturing airbag sleeve is connected to a return spring, and the other end of the return spring is connected to the end of the slide rod hole. The return spring ensures that the auxiliary fracturing airbag sleeve is positioned at the midpoint between the front fracturing hole and the middle fracturing hole, or between the middle fracturing hole and the rear fracturing hole, without external force. In travel mode, it moves towards the front fracturing hole... Before pumping the mixed solution, it is necessary to ensure that the front-end plugging airbag and the auxiliary fracturing airbag sleeve located on one side are in a pumped expansion state. At this time, the outside of the rod of the front fracturing hole is generated by pumping water pressure, and the gas in the front-end plugging airbag is slowly released to loosen its tight contact with the inner wall. At this time, the water pressure pushes the front-end plugging airbag to move forward with the auxiliary fracturing airbag sleeve as a fulcrum. Similarly, by pumping the mixed solution into the rear fracturing hole, the fracturing rod is driven to move backward.

[0011] Preferably, the fracturing rod is also equipped with a capacitive grid sensor. The fixed grid of the capacitive grid sensor is located outside the slide rod hole, and the moving grid of the capacitive grid sensor is located on the telescopic slide rod. The mechanical displacement is converted into an electrical signal by the capacitive grid sensor, thereby obtaining the displacement data of a pair of auxiliary fracturing airbag slide sleeves.

[0012] Preferably, the front end of the fracturing rod is further provided with a cone-shaped body.

[0013] Preferably, the fracturing connecting tube is movably inserted into the pulse generator, and the pulse generator causes the mixed solution entering the fracturing connecting tube to generate a pulse frequency.

[0014] Preferably, the fracturing connecting pipe is connected to the pumping machine via a high-pressure pipeline. The pumping machine is equipped with a normal pumping zone and a high-pressure pumping zone. Both the normal pumping zone and the high-pressure pumping zone have two or more sets of pumping inlets and pumping outlets. The high-pressure pipeline is connected to the pumping outlet in the high-pressure pumping zone.

[0015] Preferably, the pump is also connected to a mixing pump, which uniformly mixes the solution input from the water storage tank and the slurry tank and sends it into the pump.

[0016] Preferably, the water storage tank and the slurry tank are respectively connected to two pumping inlets set on the ordinary pumping area through pipelines, and the mixed solution in the water storage tank and the slurry tank is pumped into the mixing pump by the pumping machine.

[0017] Preferably, a diversion pipe controlled by an electromagnetic valve is provided at the connection between the upper end of the pulse generator and the high-pressure pipeline. Three sets of pumping channels are respectively opened on the fracturing connecting pipe and connected to each diversion pipe. The three sets of pumping channels are respectively connected to the front fracturing hole, the middle fracturing hole and the rear fracturing hole, so as to perform forward movement, backward movement or zonal fracturing operation by conducting the corresponding electromagnetic valve.

[0018] A pulse fracturing method, employing the aforementioned pulsed hydraulic fracturing device for low-permeability rock formations, includes the following steps:

[0019] Step 1: Select a drill bit for drilling construction, advance the fracturing borehole into the coal roadway, and install a fracturing rod at the front end of the borehole;

[0020] Step 2: The fracturing rod is adjusted to the traveling mode. In this mode, the front sealing airbag and the auxiliary fracturing airbag sleeve set on one side are kept in an inflated state. The front fracturing hole is pumped with mixed solution to generate pump water pressure outside the rod body. The gas in the front sealing airbag is slowly released. The water pressure pushes the front sealing airbag to move forward with the auxiliary fracturing airbag sleeve as the fulcrum, thereby extending the fracturing rod 1 into the coal seam borehole depth.

[0021] Step 3: After reaching the fracturing depth, the fracturing rod is adjusted to fracturing mode. In this mode, a pair of auxiliary fracturing airbags extend and inflate according to the command, further dividing the sealing area into smaller sections such as the front section, middle section, and rear section, achieving precise zoning. Their expansion and contraction displacement is fed back in real time by the capacitive grid sensor. At this time, the mixed solution is pumped into the front section fracturing hole, the middle section fracturing hole, and the rear section fracturing hole through the pumping channel, and all auxiliary fracturing airbags, front sealing airbags, and rear sealing airbags are in an expanded and positioned state.

[0022] Step 4: When the water pressure reaches the threshold, the gas inside the auxiliary fracturing airbags on both sides is slowly released. At this time, the friction between the auxiliary fracturing airbags on both sides and the inner wall surface decreases, and the mixed solution preferentially moves towards the direction where fracturing has already taken place. Because the water flow has already flowed into the rock strata or coal seam at the fracturing location, the water pressure outside the fracturing rod at that location is reduced, thus determining that the location is a fracture zone, while the other locations are micro-fracture zones.

[0023] Step 5: Extract the gas from the auxiliary fracturing gasbag sleeve to redistribute the mixed solution outside the fracturing rod. The auxiliary fracturing gasbag sleeve is then reset by the reset spring connected to it. At this time, gas is supplied to the auxiliary fracturing gasbag sleeve again, so that it can once again fit tightly against the borehole wall. In the fracture development area, pulsed water pressure is used to increase the permeability of the rock mass and increase the fracturing amplitude in the micro-fracture area to ensure precise fracturing in each fracture fracturing area.

[0024] Step 6: After fracturing is completed, move the fracturing rod out of the borehole.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] The present invention utilizes an auxiliary fracturing airbag sliding sleeve telescopically mounted on the fracturing rod to perform forward and backward movement. This movement directly acts on the fracturing rod, making power transmission more efficient during its movement inside the mine compared to the method of advancing from the end. This also relieves the propulsion rod from bearing enormous propulsion pressure, greatly reducing the risk of damage.

[0027] This invention divides the fracturing rod into multiple fracturing sections and monitors the fracturing position using an auxiliary fracturing gasbag sliding sleeve with telescopic movement. By monitoring the slippage of the sliding sleeve, the rock strata are divided into fracture development zones and microfracture zones. A low-amplitude pulse pressure method is used in the fracture development zone, while a high-amplitude pulse pressure method is used in the microfracture zone to ensure precise fracturing in each fracture fracturing area. This provides data guidance for subsequent targeted fracturing and enables targeted fracturing operations in areas with insufficient fracturing, greatly ensuring the uniformity of fracturing. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0029] Figure 2 This is a schematic diagram of the overall structure of the fracturing rod of the present invention;

[0030] Figure 3 This is a cross-sectional schematic diagram of a partial connection structure of the fracturing rod according to the present invention;

[0031] Figure 4 This is an enlarged schematic diagram of a portion of the fracturing rod structure of the present invention;

[0032] Figure 5 This is a flowchart of the pulse fracturing method of the present invention.

[0033] In the diagram: 1. Fracturing rod, 2. Fracturing connecting pipe, 3. Front sealing airbag, 4. Rear sealing airbag, 5. Auxiliary fracturing airbag sliding sleeve, 6. Front fracturing hole, 7. Middle fracturing hole, 8. Rear fracturing hole, 9. Telescopic sliding rod, 10. Sliding rod hole, 11. Return spring, 12. Grid, 13. Cone body, 14. Pulse generator, 15. High-pressure pipeline, 16. Pump, 17. Ordinary pumping area, 18. High-pressure pumping area, 19. Mixing pump, 20. Water storage tank, 21. Slurry tank, 22. Diversion pipeline, 23. Pumping channel. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Please see Figures 1-5 The present invention provides a technical solution:

[0036] A pulsed hydraulic fracturing device for low-permeability rock formations mainly consists of core components such as a fracturing rod 1, a fracturing connecting pipe 2, a front-end sealing airbag 3, a rear-end sealing airbag 4, and a pair of auxiliary fracturing airbag sliding sleeves 5. The device has two main working modes: travel and fracturing. The airbags are controlled by an external pumping and air regulating device, and combined with pulsed pumping of mixed solution, it can realize directional drilling and segmented fracturing of rock formations.

[0037] Example 1:

[0038] In this embodiment, the fracturing rod 1 serves as the main body of the device, with its end connected to the fracturing connecting pipe 2. The fracturing rod 1 is provided with nozzles for fracturing, and a cone-shaped body 13 can be installed at its front end to assist in rock breaking and advancement.

[0039] The front sealing airbag 3 and the rear sealing airbag 4 are fixed to the front and rear ends of the fracturing rod 1, respectively. After inflation, they can expand and fit tightly against the inner wall of the borehole to seal the target section during fracturing.

[0040] The auxiliary fracturing airbag sleeve 5 consists of a pair of retractable sleeves located on the fracturing rod 1 between the front fracturing hole 6 and the middle fracturing hole 7, and between the middle fracturing hole 7 and the rear fracturing hole 8, respectively. They are connected to the telescopic sliding rod 9 and maintained in their initial position by a return spring 11. Their main functions are to assist in positioning in fracturing mode and to serve as a fulcrum for forward or backward movement in traveling mode.

[0041] There are three sets of fracturing holes distributed along the fracturing rod 1: front fracturing hole 6, middle fracturing hole 7 and rear fracturing hole 8. These holes are connected to the pumping system through the fracturing connecting pipe 2 and the internal pumping channel 23, and are used to spray high-pressure mixed solution.

[0042] The telescopic slide rod 9 is inserted into the slide rod hole 10 of the fracturing rod 1. It is equipped with a moving grid of the grating sensor, while the fixed grid 12 is located outside the slide rod hole 10. The sensor can convert the mechanical displacement of the slide sleeve into an electrical signal in real time, thereby accurately monitoring the position of the auxiliary fracturing airbag slide sleeve 5.

[0043] The hydraulic fracturing device composed of the above-mentioned apparatus has two working modes: traveling and fracturing. In traveling mode, the front sealing airbag 3 and the auxiliary fracturing airbag sleeve 5 set near its side are kept in an inflated state. The mixed solution is pumped into the front fracturing hole 6. At this time, the pumping water pressure is generated outside the rod of the front fracturing hole 6. At this time, the gas in the front sealing airbag 3 is slowly released, so that it is separated from the tight contact with the inner wall of the borehole. Since the friction between the front sealing airbag 3 and the inner wall of the borehole is reduced, the water pressure pushes the front sealing airbag 3 to move forward with the auxiliary fracturing airbag sleeve 5 as the fulcrum, realizing a worm-like crawling movement. Similarly, the fracturing rod 1 can be controlled to move backward in a corresponding way. However, considering that the backward movement can be achieved by directly pulling the fracturing connecting pipe 2 connected to the fracturing rod 1 outward, this movement method is more direct.

[0044] In fracturing mode, a pair of auxiliary fracturing airbag sleeves 5 can extend and inflate upon command, further dividing the sealing area into smaller segments such as the front, middle, and rear sections, achieving precise zoning. Their extension and retraction displacement is fed back in real time by a capacitive sensor. When fracturing location positioning and monitoring are required, a mixed solution is simultaneously pumped into the front fracturing hole 6, middle fracturing hole 7, and rear fracturing hole 8 through the pumping channel. At the same time, it ensures that the front sealing airbag 3, rear sealing airbag 4, and auxiliary fracturing airbag sleeves 5 are tightly pressed against each other. When the water pressure reaches a threshold on the inner wall of the borehole, the gas inside the auxiliary fracturing airbag sleeve 5 is slowly released through an externally installed pump-air control device. At this time, the friction between the auxiliary fracturing airbag sleeves 5 on both sides and the inner wall decreases, and the mixed solution preferentially moves towards the direction where fracturing has already occurred. Because the water flow has already entered the rock or coal seam at the fracturing location, the water pressure outside the fracturing rod 1 at that location decreases. Therefore, the mixed solution on the high water pressure side will push the auxiliary fracturing airbag sleeve 5 to shift towards the low water pressure side. The overcapacity sensor detects the expansion and contraction of the auxiliary fracturing gas bladder sleeve 5 in real time, thus detecting the location of uneven fracturing. By monitoring, the area where the mixed solution flows preferentially is identified as the fracture development zone, while the area where the mixed solution flows slowly is identified as the micro-fracture zone. After monitoring is completed, the gas in the front sealing gas bladder 3, the rear sealing gas bladder 4, and the auxiliary fracturing gas bladder sleeve 5 is released simultaneously, so that the mixed solution is evenly distributed outside the fracturing rod 1. At this time, according to the detected location of uneven fracturing, the expansion of the front sealing gas bladder 3 and the adjacent auxiliary fracturing gas bladder sleeve 5 can be controlled to perform targeted fracturing of the rock strata or coal seam outside the front fracturing hole 6. The expansion of the auxiliary fracturing gas bladder sleeves 5 on both sides can be controlled to fracturing the middle fracturing hole 7. The expansion of the auxiliary fracturing gas bladder sleeve 5 and the rear sealing gas bladder 4 can be controlled to perform targeted fracturing of the rear fracturing hole 8. During this process, the mixed solution only flows out through the corresponding fracturing hole, and with the coordination of pulse pressure of different amplitudes, the fracturing operation inside the borehole can be completed more accurately.

[0045] Example 2:

[0046] In this embodiment, to accurately monitor the position of the auxiliary fracturing airbag sleeve 5, the auxiliary fracturing airbag sleeve 5 is connected to the telescopic slide rod 9. The telescopic slide rod 9 is inserted into the slide rod hole 10 opened in the fracturing rod 1. One end of the telescopic slide rod 9 away from the auxiliary fracturing airbag sleeve 5 is connected to the return spring 11, and the other end of the return spring 11 is connected to the end of the slide rod hole 10. The return spring 11 ensures that the auxiliary fracturing airbag sleeve 5 is positioned at the midpoint of the line connecting the front fracturing hole 6 and the middle fracturing hole 7, and the middle fracturing hole 7 and the rear fracturing hole 8, without external force. Furthermore, a capacitive grating sensor is installed on the fracturing rod 1. The fixed grating 12 of the capacitive grating sensor is located outside the slide rod hole 10, and the moving grating of the capacitive grating sensor is located on the telescopic slide rod 9. The capacitive grating sensor converts the mechanical displacement of the telescopic slide rod 9 into an electrical signal, thereby obtaining the displacement data of a pair of auxiliary fracturing airbag sleeves 5.

[0047] Example 3:

[0048] The system also includes a pulse generator 14, with the fracturing connecting pipe 2 movably inserted into it. This allows the flowing mixed solution to generate a pulse frequency, enhancing the fracturing effect. The solution is modulated into a pulse wave as it passes through the pulse generator 14 and then ejected through a designated fracturing orifice. The pulse load can more effectively generate fatigue damage and extend fractures in the rock formation, improving fracturing efficiency. During fracturing, the pulse generator 14 can operate in two modes: pressurized pulse and static pulse. Pressurized pulse involves simultaneously pumping pulses and the mixed solution, while static pulse stops pumping the pulsed solution and uses the mixed solution already pumped outside the fracturing rod 1 for static pulse fracturing. These two operation processes can occur in both monolithic fracturing and staged fracturing operations.

[0049] Example 4:

[0050] At the upper end of the pulse generator 14, it is connected to the high-pressure pipeline 15 through the diversion pipeline 22 equipped with a solenoid valve. By controlling the opening and closing of different solenoid valves, the mixed solution can be directionally guided to achieve driving or zonal fracturing.

[0051] The mixed solution is stored in the water tank 20 and the slurry tank 21. The pump 16 is equipped with a normal pumping zone 17 and a high-pressure pumping zone 18. The normal pumping zone is responsible for pumping the mixed solution from the water tank 20 and the slurry tank 21 into the mixing pump 19 to uniformly mix the water and fracturing slurry. The high-pressure pumping zone outputs the mixed high-pressure solution through the high-pressure pipeline 15.

[0052] Pulse fracturing working method:

[0053] Taking the fracturing and permeability enhancement of a low-permeability coal seam as an example, the steps are as follows:

[0054] The drilling was carried out using a φ94mm drill bit. The fracturing borehole was 40m ahead of the coal roadway excavation face. The fracturing rod 1 was installed. In the traveling mode, the front sealing airbag 3 and the auxiliary fracturing airbag sleeve 5 set on one side of it were kept in an inflated state. The front fracturing hole 6 was pumped with mixed solution to generate pump water pressure on the outside of the rod body. The gas in the front sealing airbag 3 was slowly released. The water pressure pushed the front sealing airbag 3 forward with the auxiliary fracturing airbag sleeve 5 as the fulcrum, thereby extending the fracturing rod 1 into the depth of the coal seam borehole.

[0055] Upon reaching the drilling depth, a pair of auxiliary fracturing airbag sleeves 5 extend and inflate according to instructions, further dividing the sealing area into smaller segments such as the front, middle, and rear sections, achieving precise zoning. Their extension and retraction displacement is fed back in real-time by a grating sensor. Simultaneously, a mixed solution is pumped into the front fracturing hole 6, middle fracturing hole 7, and rear fracturing hole 8 through the pumping channel. At the same time, the front sealing airbag 3, rear sealing airbag 4, and auxiliary fracturing airbag sleeves 5 are kept tightly against the inner wall of the borehole. When the water pressure reaches the threshold, the gas inside the auxiliary fracturing airbag sleeves 5 on both sides is slowly released. At this point, the friction between the auxiliary fracturing airbag sleeves 5 and the inner wall decreases, and the mixed solution preferentially moves towards the direction where fracturing has already occurred, because the fracturing location has been pushed towards the rock strata by the water flow. Or, if the coal seam flows internally, the water pressure outside the fracturing rod 1 decreases, thus identifying that location as a fracture zone, while other locations are micro-fracture zones. At this time, the gas inside the auxiliary fracturing gas bag sleeve 5 is extracted, causing the mixed solution to redistribute outside the fracturing rod 1. The auxiliary fracturing gas bag sleeve 5 is then reset by the action of the reset spring 11 connected to it. At this time, air is supplied to the auxiliary fracturing gas bag sleeve 5 again, so that it can once again fit tightly against the borehole inner wall. In the fracture development zone, to increase the permeability of the rock mass, a pulse water pressure with an upper limit of 25 MPa, a lower limit of 15 MPa, and a fracturing amplitude of 10 MPa is used for fracturing. In the micro-fracture zone, the fracturing amplitude is increased, with a lower limit of 0 MPa and an upper limit of 25 MPa, to ensure precise fracturing in each fracture fracturing zone.

[0056] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A pulsed hydraulic fracturing device for low-permeability rock formations, characterized in that, include: A fracturing rod is connected to the end of a fracturing connecting pipe. A front-end sealing airbag and a rear-end sealing airbag are respectively installed at the front and rear ends of the fracturing rod. A pair of auxiliary fracturing airbag sleeves are telescopically installed on the rod body between the front and rear sealing airbags. The front-end sealing airbag, the rear-end sealing airbag, and the pair of auxiliary fracturing airbag sleeves are controlled by an externally installed pumping and releasing device. A fracturing hole is also provided on the rod body, through which the mixed solution transported inward through the fracturing connecting pipe is pumped outward, thereby performing the fracturing operation. The fracturing holes include front fracturing holes, middle fracturing holes, and rear fracturing holes. The auxiliary fracturing airbag sleeve is telescopically mounted on the rod between the front fracturing holes and the middle fracturing holes, and between the middle fracturing holes and the rear fracturing holes. In the traveling mode, the fracturing rod is driven to move forward by pumping the mixed solution into the front fracturing holes, and to move backward by pumping the mixed solution into the rear fracturing holes. In the fracturing mode, the fracturing position is located by the displacement generated by the auxiliary fracturing airbag sleeve, and the fracturing operation is carried out in sections through the front fracturing holes, the middle fracturing holes, and the rear fracturing holes. A pair of auxiliary fracturing airbag sleeves are connected to a telescopic slide rod. The telescopic slide rod is inserted into a slide rod hole corresponding to the fracturing rod. The end of the telescopic slide rod away from the auxiliary fracturing airbag sleeve is connected to a return spring, and the other end of the return spring is connected to the end of the slide rod hole. The return spring ensures that the auxiliary fracturing airbag sleeve is positioned at the midpoint between the front fracturing hole and the middle fracturing hole, or between the middle fracturing hole and the rear fracturing hole, when no external force is applied. In travel mode, it moves towards the front fracturing hole... Before pumping the mixed solution, it is necessary to ensure that the front-end plugging airbag and the auxiliary fracturing airbag sleeve located on one side are in a pumped expansion state. At this time, the outside of the rod of the front fracturing hole is generated by pumping water pressure, and the gas in the front-end plugging airbag is slowly released to loosen its tight contact with the inner wall. At this time, the water pressure pushes the front-end plugging airbag to move forward with the auxiliary fracturing airbag sleeve as a fulcrum. Similarly, by pumping the mixed solution into the rear fracturing hole, the fracturing rod is driven to move backward.

2. The pulsed hydraulic fracturing device for low-permeability rock formations according to claim 1, characterized in that: The fracturing rod is also equipped with a capacitive grid sensor. The fixed grid of the capacitive grid sensor is located outside the slide rod hole, and the moving grid of the capacitive grid sensor is located on the telescopic slide rod. The mechanical displacement is converted into an electrical signal by the capacitive grid sensor, thereby obtaining the displacement data of a pair of auxiliary fracturing airbag slide sleeves.

3. The pulsed hydraulic fracturing device for low-permeability rock formations according to claim 2, characterized in that: The front end of the fracturing rod is also provided with a cone-shaped body.

4. The pulsed hydraulic fracturing device for low-permeability rock formations according to claim 3, characterized in that: The fracturing connecting tube is movably inserted into the pulse generator, which causes the mixed solution entering the fracturing connecting tube to generate a pulse frequency.

5. The pulsed hydraulic fracturing device for low-permeability rock formations according to claim 4, characterized in that: The fracturing connecting pipe is connected to the pumping machine via a high-pressure pipeline. The pumping machine is equipped with a normal pumping zone and a high-pressure pumping zone. Both the normal pumping zone and the high-pressure pumping zone have two or more sets of pumping inlets and pumping outlets. The high-pressure pipeline is connected to the pumping outlet in the high-pressure pumping zone.

6. The pulsed hydraulic fracturing device for low-permeability rock formations according to claim 5, characterized in that: The pump is also connected to a mixing pump, which uniformly mixes the solution input from the water storage tank and the slurry tank and sends it into the pump.

7. A pulsed hydraulic fracturing device for low-permeability rock formations according to claim 6, characterized in that: The water storage tank and slurry tank are respectively connected to two pumping inlets set on the ordinary pumping area through pipelines. The mixed solution in the water storage tank and slurry tank is pumped into the mixing pump by the pumping machine.

8. The pulsed hydraulic fracturing device for low-permeability rock formations according to claim 7, characterized in that: The upper end of the pulse generator is connected to the high-pressure pipeline with a solenoid valve-controlled diversion pipe. The fracturing connecting pipe is provided with three sets of pumping channels that are connected to each diversion pipe. The three sets of pumping channels are connected to the front fracturing hole, the middle fracturing hole and the rear fracturing hole, respectively, so as to perform forward movement, backward movement or zonal fracturing operation by conducting the corresponding solenoid valve.

9. A pulse fracturing method, wherein the fracturing method employs the low-permeability rock formation pulse hydraulic fracturing device as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Select a drill bit for drilling construction, advance the fracturing borehole into the coal roadway, and install a fracturing rod at the front end of the borehole; Step 2: The fracturing rod is adjusted to the traveling mode. In this mode, the front sealing airbag and the auxiliary fracturing airbag sleeve set on one side are kept in an inflated state. The front fracturing hole is pumped with mixed solution to generate pump water pressure outside the rod body. The gas in the front sealing airbag is slowly released. The water pressure pushes the front sealing airbag forward with the auxiliary fracturing airbag sleeve as the fulcrum, thereby extending the fracturing rod into the depth of the coal seam borehole. Step 3: After reaching the fracturing depth, the fracturing rod is adjusted to fracturing mode. In this mode, a pair of auxiliary fracturing airbags extend and inflate according to the command, further dividing the sealing area into smaller sections such as the front section, middle section, and rear section, achieving precise zoning. Their expansion and contraction displacement is fed back in real time by the capacitive grid sensor. At this time, the mixed solution is pumped into the front section fracturing hole, the middle section fracturing hole, and the rear section fracturing hole through the pumping channel, and all auxiliary fracturing airbags, front sealing airbags, and rear sealing airbags are in an expanded and positioned state. Step 4: When the water pressure reaches the threshold, the gas inside the auxiliary fracturing airbags on both sides is slowly released. At this time, the friction between the auxiliary fracturing airbags on both sides and the inner wall surface decreases, and the mixed solution preferentially moves towards the direction where fracturing has already taken place. Because the water flow has already flowed into the rock strata or coal seam at the fracturing location, the water pressure outside the fracturing rod at that location is reduced, thus determining that the location is a fracture zone, while the other locations are micro-fracture zones. Step 5: Extract the gas from the auxiliary fracturing gasbag sleeve to redistribute the mixed solution outside the fracturing rod. The auxiliary fracturing gasbag sleeve is then reset by the reset spring connected to it. At this time, gas is supplied to the auxiliary fracturing gasbag sleeve again, so that it can once again fit tightly against the borehole wall. In order to increase the permeability of the rock mass, pulsed water pressure is used to fracturing the fractured areas. The fracturing amplitude is increased in the microfracture area to ensure precise fracturing in each fracture fracturing area. Step 6: After fracturing is completed, move the fracturing rod out of the borehole.

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