Deep coal seam CO2 composite fracturing test device and test method

Abstract

The invention relates to a deep coal seam CO2 composite fracturing test device and test method, and belongs to the technical field of deep coal seam fracturing tests. Comprising a sample storage container, an inner cylinder, a cover cylinder, an opening and closing assembly and an outer cylinder, a cover plate covers the top of the sample storage container, a cover cylinder is arranged on the cover plate, the upper end of the inner cylinder is inserted into the cover cylinder, the lower end of the inner cylinder extends downwards to the bottom of the sample storage container, and first through holes are uniformly formed in the side wall of the inner cylinder; a spark plug for converting liquid carbon dioxide into gas is arranged in the inner cylinder; an outer cylinder is arranged at the inner bottom of the sample storage container, second through holes in one-to-one correspondence with the first through holes are formed in the side wall of the outer cylinder, high-pressure gas is injected into the pressurization cylinder through the pressurization system, and the high-pressure gas is guided into the sample storage container through the communication hole, so that the pressure conditions of the coal seam at different underground depths are simulated; key parameters and influence rules thereof in the CO2 composite fracturing process can be researched in a mode closer to the actual situation, and powerful technical support is provided for optimizing CO2 composite fracturing process parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of deep coal seam fracturing tests, and in particular to a deep coal seam CO2 composite fracturing test device and a test method. Background Art

[0002] With the continued growth in energy demand and the increasing difficulty in extracting traditional oil and gas resources, the development of unconventional energy sources such as deep coal seams and natural gas has become increasingly important. In the extraction of these unconventional energy sources, fracturing technology is widely used to increase reservoir permeability and recovery rates. While traditional hydraulic fracturing is effective, in some cases it poses significant challenges such as high water consumption and a high risk of environmental pollution. In recent years, CO2 composite fracturing, as a new and environmentally friendly technology, has demonstrated great potential in deep coalbed methane development. This technology utilizes liquid or supercritical carbon dioxide as a fracturing medium, which not only reduces the demand for water resources but also improves the pore structure of coal seams through its unique physical and chemical properties, further increasing gas production efficiency.

[0003] However, in actual applications, it has been found that the effectiveness of CO2 composite fracturing varies significantly under different geological conditions. This is mainly due to the complex and variable underground environment, where factors such as temperature and pressure affect the state of CO2 and its interaction with rock. Therefore, how to accurately simulate real underground conditions, especially how to reflect the impact of pressure changes at different depths on the effectiveness of CO2 composite fracturing, has become a key focus of current research. Existing laboratory testing equipment is difficult to fully simulate the complex working conditions in the field, especially when it comes to precise control and data acquisition in high-pressure environments. Summary of the Invention

[0004] In order to solve or partially solve the problems existing in the related technologies, the present invention provides a deep coal seam CO2 composite fracturing test device and test method, which aims to study the key parameters and their influencing laws in the CO2 composite fracturing process in a manner closer to the actual situation by constructing an experimental platform that can flexibly adjust the internal pressure; this device can simulate the pressure variation range from the surface to a depth of several thousand meters, and on this basis carry out a systematic burst performance evaluation, providing strong technical support for optimizing CO2 composite fracturing process parameters and improving deep coalbed methane extraction efficiency; in addition, the device also has high safety and easy operation, and is suitable for wide application in scientific research institutions and industry.

[0005] The above-mentioned deep coal seam CO2 composite fracturing test device includes a sample storage container, an inner cylinder, a cover cylinder, an opening and closing assembly, and an outer cylinder; The top cover of the sample storage container is provided with a cover plate, the side wall of the sample storage container is evenly provided with communication holes, the outer cover of the sample storage container is provided with a pressure cylinder, and the pressure cylinder is connected to the pressure system through a pipeline; The cover plate is provided with a cover cylinder, which is connected to an injection pipe, and the injection pipe is connected to the liquid carbon dioxide supply system through a pipeline; the upper end of the inner cylinder is inserted into the cover cylinder and is rotatably connected to the cover cylinder, and the lower end extends downward to the bottom of the sample storage container. First through holes are evenly opened on the side wall of the inner cylinder; an opening and closing assembly for driving the inner cylinder to rotate is provided above the cover cylinder; a spark plug for converting liquid carbon dioxide into gas is provided in the inner cylinder; An outer cylinder is provided at the inner bottom of the sample storage container, the top end of the outer cylinder is sealed with the cover plate, the outer cylinder and the cover cylinder are coaxially arranged, and the inner side wall of the outer cylinder is in contact with the outer side wall of the inner cylinder; a second through hole is provided on the side wall of the outer cylinder, which corresponds to the first through hole one by one, and by rotating the inner cylinder, the positions of the first through hole and the second through hole can be in a state of relative connection or staggered sealing.

[0006] In some embodiments, a hydraulic rod is provided on one side of the sample storage container, and the upper end of the hydraulic rod is fixedly connected to the mounting plate.

[0007] The opening and closing assembly includes a special-shaped block, a torsion spring, an extrusion block, and an electric push rod; The inner cylinder is provided with a rotating shaft, and the upper end of the rotating shaft passes through the cover cylinder and is installed with a special-shaped block, and the upper side surface of the special-shaped block is provided with a first inclined surface; a torsion spring is connected between the special-shaped block and the cover cylinder; An extrusion block is provided above the special-shaped block, and a second inclined surface is provided on the lower side of the extrusion block to match the first inclined surface; an electric push rod is provided on the mounting plate, and a telescopic rod of the electric push rod is fixedly connected to the extrusion block; The electric push rod drives the extrusion block to press the special-shaped block downward, so that the second inclined surface slides along the first inclined surface, thereby driving the special-shaped block to rotate.

[0008] In some embodiments, the liquid carbon dioxide supply system includes a CO2 storage tank and a valve. The CO2 storage tank is connected to the injection pipe via a docking pipe, and the docking pipe is provided with a valve.

[0009] In some programs, A rotating ring is rotatably mounted on the cover cylinder, and a gear ring is provided on the rotating ring; A motor is provided above the rotating ring, and a gear is provided on the output shaft of the motor, and the gear is meshed with the ring gear; A crack detector is fixedly connected to the rotating ring.

[0010] In some embodiments, a fitting sheet is provided at the bottom of the cover plate, and a sealing ring is provided at the top of the sample storage container, and the fitting sheet is in contact with the sealing ring.

[0011] In some embodiments, the sample storage container is provided with a first pressure sensor for detecting the internal pressure thereof; A second pressure sensor is provided in the cover tube for detecting the internal pressure thereof; The signal input end of the controller is respectively connected to the first pressure sensor, and the signal output end of the controller is respectively electrically connected to the pressurizing system and the opening and closing component.

[0012] In some embodiments, the sample storage container is disposed in a box body, and a box door is provided on one side of the box body.

[0013] Based on the above-mentioned deep coal seam CO2 composite fracturing test device, the present application also provides an experimental method for the deep coal seam CO2 composite fracturing test device, which specifically includes the following steps: S1: Place the coal sample into the sample container and compact it, then inject liquid carbon dioxide into the inner cylinder and adjust the internal pressure of the sample container; S2: Gasifying the liquid carbon dioxide in the inner cylinder. When the gas pressure in the inner cylinder reaches a critical point, the inner cylinder rotates to connect the first through hole and the second through hole. The carbon dioxide gas in the inner cylinder is ejected outward through the first through hole and the second through hole. The generated high-pressure gas energy fractures the coal seam in the sample storage container. S3: Scan and evaluate the crack conditions of the coal seam inside the sample container.

[0014] The technical solution provided by the present invention can have the following beneficial effects: This application uses a pressurizing system to inject high-pressure gas into the pressurizing cylinder, and the high-pressure gas is introduced into the sample storage container through the connecting hole to simulate the pressure conditions of coal seams at different underground depths. The key parameters and their influencing laws in the CO2 composite fracturing process can be studied in a way that is closer to the actual situation, providing strong technical support for optimizing CO2 composite fracturing process parameters and improving the efficiency of deep coalbed methane extraction.

[0015] The technical solution provided by the present invention may also include the following beneficial effects: 1. Energy is released through multiple first through holes and second through holes, which realizes rapid and efficient release of gas energy, avoids the energy concentration problem of single-point injection, and ensures faster and more uniform gas release; at the same time, it effectively avoids the technical problem of local blockage. Furthermore, it ensures that CO2 gas is ejected from multiple places. This multi-directional injection simulates the expansion of multiple fractures in underground coal seams, and the gas energy is distributed more widely, avoiding local overpressure or unfractured areas, and enhancing the uniformity and coverage of the fracturing effect.

[0016] 2. The rotation of the inner cylinder is precisely controlled by the opening and closing components, which effectively improves the accuracy and convenience of energy release control and makes the control more reliable.

[0017] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0019] Figure 1 This is a schematic diagram of the assembly structure of the cover plate, hydraulic cylinder, cover barrel and other components of the present invention; Figure 2 for Figure 1 Schematic diagram of the cross-sectional structure; Figure 3 Schematic diagram of the matching structure of the outer cylinder and the inner cylinder of the present invention; Figure 4 Schematic diagram of the matching structure of the inner cylinder and the spark plug of the present invention; Figure 5 Schematic diagram of the coordination structure of the inner cylinder, telescopic rod and mounting plate of the present invention; Figure 6 It is a structural schematic diagram of the opening and closing assembly of the present invention; Figure 7 This is a schematic diagram of the assembly of the special-shaped block and the cover tube of the opening and closing assembly of the present invention; Figure 8 This is a schematic structural diagram of the liquid carbon dioxide supply system of the present invention; Figure 9 This is a schematic diagram of the installation of the crack detector of the present invention; Figure 10 Schematic diagram of the assembly of the bonding sheet and the sealing ring with the cover plate and the sample storage container respectively; Figure 11 This is a schematic diagram of the assembly of the bonding sheet and the sealing ring of the present invention; Figure 12 This is a schematic diagram of the assembly of the box and the sample storage container of the present invention; Figure 13 Schematic diagram of the external structure of the box body of the present invention; Figure 14 This is a control block diagram of the present invention; The markings of the components in the accompanying drawings are as follows: 1. Sample container; 101. Connecting hole; 2. Inner cylinder; 201. First through hole; 3. Cover cylinder; 4. Opening and closing assembly; 401. Special-shaped block; 4011. First inclined surface; 402. Torsion spring; 403. Extrusion block; 4031. Second inclined surface; 404. Electric push rod; 405. Rotating shaft; 5. Outer cylinder; 501. Second through hole; 6. Cover plate; 7. Pressurizing cylinder; 8. Pressurizing system; 801. Pressure pump; 802. Air pump Bottle; 9. Injection pipe; 10. Liquid carbon dioxide supply system; 1001. CO2 storage tank; 1002. Valve; 11. Spark plug; 12. Mounting plate; 13. Connecting plate; 14. Hydraulic rod; 15. Rotating ring; 16. Ring gear; 17. Motor; 18. Crack detector; 19. Laminating sheet; 20. Sealing ring; 21. First pressure sensor; 22. Second pressure sensor; 23. Box body; 2301. Box door. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0021] Example 1: like Figure 1-Figure 5 As shown, the present application provides a deep coal seam CO2 composite fracturing test device, including a sample storage container 1, an inner tube 2, a cover tube 3, an opening and closing assembly 4, and an outer tube 5.

[0022] The sample storage container 1 is roughly hollow cylindrical with an open top. The top cover of the sample storage container 1 is provided with a cover plate 6, which closes the top of the sample storage container 1 and forms a closed cavity inside. The side wall of the sample storage container 1 is evenly distributed with connecting holes 101. The sample storage container 1 is outer-mounted with a pressurizing cylinder 7, and a gap is left between the inner wall of the pressurizing cylinder 7 and the outer wall of the sample storage container 1. The pressurizing cylinder 7 is connected to the pressurizing system 8 through a pipeline; when working, the pressurizing system 8 introduces pressurized gas into the pressurizing cylinder 7 through the pipeline, and then the pressurized gas is introduced into the sample storage container 1 through the connecting hole 101, thereby achieving the purpose of adjusting the internal pressure of the sample storage container 1, thereby simulating different pressure changes.

[0023] The cover plate 6 is provided with a cover tube 3, which is in the shape of a hollow tube with a closed upper end and a lower end fixedly connected to the cover plate 6 and communicated with the internal cavity of the sample storage container 1; the cover tube 3 is provided with an injection pipe 9, which is arranged near the upper end of the cover tube 3, and the injection pipe 9 is connected to the liquid carbon dioxide supply system 10 through a pipeline; the upper end of the inner tube 2 is inserted into the cover tube 3 and is rotatably connected to the cover tube 3, and the lower end extends downward to the bottom of the sample storage container 1, and the side wall of the inner tube 2 is evenly provided with first through holes 201; an opening and closing component 4 for driving the inner tube 2 to rotate is provided above the cover tube 3; a spark plug 11 for converting liquid carbon dioxide into gas is provided in the inner tube 2.

[0024] The inner bottom of the sample storage container 1 is provided with an outer cylinder 5, the top end of the outer cylinder 5 is sealed with the cover plate 6, the outer cylinder 5 is coaxially arranged with the cover cylinder 3, and the inner side wall of the outer cylinder 5 is in contact with the outer side wall of the inner cylinder 2, thereby sealing the gap between the outer cylinder 5 and the inner cylinder 2; the side wall of the outer cylinder 5 is provided with a second through hole 501 which is arranged in a one-to-one correspondence with the first through hole 201, and by rotating the inner cylinder 2, the positions of the first through hole 201 and the second through hole 501 can be relatively connected or dislocated. The blocked state, wherein relative communication means that the first through hole 201 and the second through hole 501 are positioned relative to each other, thereby forming conduction, so that the internal space of the inner cylinder 2 and the external space of the outer cylinder 5 are connected through the first through hole 201 and the second through hole 501; staggered blocking means that the first through hole 201 and the second through hole 501 are staggered with each other, the first through hole 201 is facing the closed area of ​​the side wall of the outer cylinder 5, and the second through hole 501 is facing the closed area of ​​the side wall of the inner cylinder 2, so that the first through hole 201 and the second through hole 501 are both in a blocked state.

[0025] When conducting a fracturing test, the coal sample is placed in the sample container 1 and compacted. After the coal sample is placed, the cover plate 6 is put on to close the sample container 1. When the cover plate 6 is put on, the inner cylinder 2 is inserted into the outer cylinder 5 from above. In the initial state, the second through hole 501 on the outer cylinder 5 and the first through hole 201 on the inner cylinder 2 are in a misaligned state, and the second through hole 501 and the first through hole 201 are both blocked. Then the pressurizing system 8 injects high-pressure gas into the pressurizing cylinder 7, and the high-pressure gas is introduced into the sample container 1 through the connecting hole 101, thereby adjusting the internal pressure of the sample container 1 to simulate the pressure changes of coal seams at different depths underground. After the pressure is adjusted, the liquid carbon dioxide supply system 10 is used to supply the liquid carbon dioxide. Liquid carbon dioxide is injected into the cover tube 3. After the liquid carbon dioxide is injected, the spark plug 11 operates to gasify the liquid carbon dioxide. When the air pressure in the inner tube 2 reaches the critical point, the opening and closing component 4 is activated to drive the inner tube 2 to rotate until the first through hole 201 and the second through hole 501 are in a relatively connected state. The gaseous carbon dioxide in the inner tube 2 is released outward after passing through the first through hole 201 and the second through hole 501 in turn. The high-pressure gas energy generated will fracture the coal seam in the sample container. After fracturing, the opening and closing component 4 is activated to drive the inner tube 2 to rotate again until the first through hole 201 and the second through hole 501 are in a dislocated and blocked state, so that they can be filled with liquid carbon dioxide for fracturing next time.

[0026] This embodiment releases energy through multiple first through holes and second through holes, thereby achieving rapid and efficient release of gas energy, avoiding the energy concentration problem of single-point injection, and ensuring faster and more uniform gas release; at the same time, it effectively avoids the technical problem of local blockage, and furthermore, ensures that CO2 gas is ejected from multiple places. This multi-directional injection simulates the expansion of multiple cracks in underground coal seams, and the gas energy is distributed more widely, avoiding local overpressure or unfractured areas, and enhancing the uniformity and coverage of the fracturing effect.

[0027] This embodiment accurately controls the rotation of the inner cylinder through the opening and closing assembly, effectively improving the accuracy and convenience of energy release control and making the control more reliable.

[0028] In some embodiments, Figure 1 As shown, a mounting plate 12 is provided above the cover plate 6, and the cover plate 6 and the mounting plate 12 are connected as a whole through a connecting plate 13. Specifically, the connecting plates 13 are evenly spaced around the circumference of the cover plate 6 to strengthen the connection strength between the cover plate 6 and the mounting plate 12; a hydraulic rod 14 is provided on one side of the sample storage container 1, and the upper end of the hydraulic rod 14 is fixedly connected to the mounting plate 12.

[0029] When the hydraulic rod 14 is extended, it drives the mounting plate 12 to move upward, and the mounting plate 12 drives the cover plate 6 to move upward through the connecting plate 13 to open the cover plate 6. When the hydraulic rod 14 is shortened, it drives the cover plate 6 to move downward to close the cover plate 6. This design effectively reduces the labor intensity of the staff when opening or closing the cover plate 6. At the same time, the hydraulic rod 14 can provide downward positive pressure for the cover plate 6, effectively ensuring that the cover plate 6 can be firmly covered on the sample storage container 1.

[0030] In this embodiment, if Figure 6 and Figure 7 As shown, the opening and closing assembly 4 includes a special-shaped block 401, a torsion spring 402, an extrusion block 403, and an electric push rod 404; a rotating shaft 405 is provided on the inner cylinder 2, and the upper end of the rotating shaft 405 is installed with the special-shaped block 401 after passing through the cover cylinder 3, and the upper side surface of the special-shaped block 401 is provided with a first inclined surface 4011; a torsion spring 402 is connected between the special-shaped block 401 and the cover cylinder 3; an extrusion block 403 is provided above the special-shaped block 401, and the lower side surface of the extrusion block 403 is provided with a second inclined surface 4031 that matches the first inclined surface 4011; an electric push rod 404 is provided on the mounting plate 12, and the telescopic rod of the electric push rod 404 is fixedly connected to the extrusion block 403.

[0031] In the initial state, the first inclined surface 4011 and the second inclined surface 4031 are partially fitted together, and the torsion spring 402 is in a natural state. When the electric push rod 404 is extended, the extrusion block 403 is driven to squeeze the special-shaped block 401 downward. Since the extrusion block 403 is fixedly connected to the electric push rod 404 and cannot rotate, the first inclined surface 4011 slides along the second inclined surface 4031, thereby driving the special-shaped block 401 to rotate, and then driving the inner cylinder 2 to rotate through the rotating shaft 405, and driving the torsion spring 402 to rotate, and the torsion spring 402 accumulates force; when the electric push rod 404 is shortened, the extrusion block 403 is driven to move upward, the extrusion block 403 is separated from the special-shaped block 401, the special-shaped block 401 is separated, and the torsion spring 402 releases the torque, thereby driving the inner cylinder 2 to rotate and reset.

[0032] In some embodiments, Figure 5 As shown, the liquid carbon dioxide supply system 10 includes a CO2 storage tank 1001 and a valve 1002. The CO2 storage tank 1001 is connected to the injection pipe 9 via a connecting pipe, on which the valve 1002 is installed. During operation, the valve 1002 controls the opening and closing of the CO2 connecting pipe to control the amount of liquid CO2 injected into the inner cylinder 2.

[0033] In some embodiments, Figure 8-Figure 9 As shown, a rotating ring 15 is rotatably mounted on the cover tube 3, and a gear ring 16 is provided on the rotating ring 15; a motor 17 is provided above the rotating ring 15, and a gear is provided on the output shaft of the motor 17, and the gear is engaged with the gear ring 16; a crack detector 18 is fixedly connected to the rotating ring 15.

[0034] When the coal sample is fracturing, the motor 17 and the crack detector 18 start to operate. The output shaft of the motor 17 rotates to drive the gear to rotate, the gear rotation drives the ring gear 16 to rotate, the ring gear 16 rotates to drive the rotating ring 15 to rotate, and the rotating ring 15 rotates to drive the crack detector 18 to rotate one circle, thereby scanning and evaluating the crack conditions of the coal seam inside the sample container 1.

[0035] In some embodiments, Figure 10 and Figure 11 As shown, a fitting piece 19 is provided at the bottom of the cover plate 6 (the fitting piece 19 is in a circular shape, and is not completely drawn in the figure in order to express the sealing ring 20), and a sealing ring 20 is provided at the top of the sample storage container 1. When the cover plate 6 moves downward to cover the sample storage container 1, the fitting piece 19 will also move downward to fit the sealing ring 20. The cooperation between the fitting piece 19 and the sealing ring 20 ensures the sealing between the cover plate 6 and the sample storage container 1.

[0036] In some specific embodiments, the pressurizing system 8 (conventional technical means, not shown in the figure) includes a pressure pump 801 and a gas cylinder 802; the gas cylinder 802 contains carbon dioxide gas, the gas cylinder 802 is connected to the air inlet end of the pressure pump 801, and the air outlet end of the pressure pump 801 is connected to the internal cavity of the pressure cylinder 7. When pressurization is required, the pressure pump 801 introduces the carbon dioxide gas in the gas cylinder 802 into the pressure cylinder 7, and then the carbon dioxide gas is introduced into the inner cylinder 2 through the connecting hole 101 on the inner cylinder 2, thereby adjusting the pressure in the inner cylinder 2, thereby simulating the pressure conditions of coal seams at different depths.

[0037] In some embodiments, Figure 14 As shown, the sample storage container 1 is provided with a first pressure sensor 21 for detecting the size of its internal pressure; the cover tube 3 is provided with a second pressure sensor 22 for detecting the size of its internal pressure; the signal input end of the controller is respectively connected to the first pressure sensor 21, and the signal output end of the controller is respectively electrically connected to the pressurizing system 8 and the opening and closing component 4. Specifically, the signal output end of the controller is electrically connected to the electric push rod 404 and the pressure pump 801.

[0038] During operation, the first pressure sensor 21 detects the internal pressure of the sample container 1 and transmits it to the controller. When the pressure in the sample container 1 reaches the set pressure, the controller controls the pressure pump 801 to close to adjust the pressure in the sample container 1.

[0039] The second pressure sensor 22 detects the pressure inside the cover tube 3 and transmits it to the controller. When the air pressure in the inner tube 2 reaches the critical point, the controller controls the electric push rod 404 to move, and the inner tube 2 rotates, so that the first through hole 201 and the second through hole 501 are relatively connected, and the carbon dioxide gas in the inner tube 2 is ejected outward through the first through hole 201 and the second through hole 501. The generated high-pressure gas energy will fracture the coal seam in the sample container 1.

[0040] Thus, the automatic control of the electric push rod 404 is achieved, which is beneficial to the automation of the experimental process and is easy to use.

[0041] In some embodiments, Figure 12 and Figure 13 As shown, the sample storage container 1 is arranged in a box body 23, which is conducive to the safe conduct of the experimental process. A box door 2301 is provided on one side of the box body 23.

[0042] Example 2: Based on Example 1, the present application provides an experimental method for a deep coal seam CO2 composite fracturing test device, which specifically includes the following steps: S1: Place the coal sample into the sample container 1 and compact it. Then, a certain amount of liquid carbon dioxide is injected into the inner cylinder 2 through the liquid carbon dioxide supply system 10. The pressure inside the sample container 1 is adjusted by the pressurizing system 8 to simulate the pressure changes at different depths underground. S2: The spark plug 11 gasifies the liquid carbon dioxide. When the gas pressure in the inner tube 2 reaches a critical point, the opening and closing assembly 4 drives the inner tube 2 to rotate, so that the first through hole 201 and the second through hole 501 are relatively connected. The carbon dioxide gas in the inner tube 2 is ejected outward through the first through hole 201 and the second through hole 501. The generated high-pressure gas energy fractures the coal seam in the sample storage container 1. S3: The motor 17 is activated to drive the crack detector 18 to rotate around the cover tube 3. The crack detector 18 uses ultrasonic detection or computer tomography technology to scan and evaluate the crack conditions of the coal seam inside the sample container 1.

[0043] While various embodiments of the present invention have been described above, the foregoing description is intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to existing technologies, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A deep coal seam CO2 composite fracturing test device, characterized by: It comprises a sample storage container (1), an inner tube (2), a cover tube (3), an opening and closing assembly (4), and an outer tube (5); The top cover of the sample storage container (1) is provided with a cover plate (6), the side wall of the sample storage container (1) is evenly provided with communication holes (101), the outer shell of the sample storage container (1) is provided with a pressurizing cylinder (7), and the pressurizing cylinder (7) is connected to the pressurizing system (8) through a pipeline; The cover plate (6) is provided with a cover barrel (3), and the cover barrel (3) is provided with an injection pipe (9), and the injection pipe (9) is connected to the liquid carbon dioxide supply system (10) through a pipeline; the upper end of the inner barrel (2) is inserted into the cover barrel (3) and is rotatably connected to the cover barrel (3), and the lower end extends downward to the bottom of the sample storage container (1), and the side wall of the inner barrel (2) is evenly provided with first through holes (201); an opening and closing assembly (4) for driving the inner barrel (2) to rotate is provided above the cover barrel (3); a spark plug (11) for converting liquid carbon dioxide into gas is provided in the inner barrel (2); An outer cylinder (5) is provided at the inner bottom of the sample storage container (1), the top end of the outer cylinder (5) is sealed with the cover plate (6), the outer cylinder (5) is coaxially arranged with the cover cylinder (3), and the inner side wall of the outer cylinder (5) is in contact with the outer side wall of the inner cylinder (2); a second through hole (501) is provided on the side wall of the outer cylinder (5) and is arranged in a one-to-one correspondence with the first through hole (201), and by rotating the inner cylinder (2), the positions of the first through hole (201) and the second through hole (501) can be in a state of relative communication or misalignment and blocking.

2. A deep coal seam CO2 composite fracturing test device according to claim 1, characterized in that: A mounting plate (12) is provided above the cover plate (6), and the cover plate (6) and the mounting plate (12) are connected as one body via a connecting plate (13); A hydraulic rod (14) is provided on one side of the sample storage container (1), and the upper end of the hydraulic rod (14) is fixedly connected to the mounting plate (12).

3. The deep coal seam CO2 composite fracturing test device according to claim 2, characterized in that: The opening and closing assembly (4) comprises a special-shaped block (401), a torsion spring (402), an extrusion block (403), and an electric push rod (404); The inner cylinder (2) is provided with a rotating shaft (405), and the upper end of the rotating shaft passes through the cover cylinder (3), and is then installed with a special-shaped block (401), and the upper side surface of the special-shaped block (401) is provided with a first inclined surface (4011); a torsion spring (402) is connected between the special-shaped block (401) and the cover cylinder (3); An extrusion block (403) is provided above the special-shaped block (401), and a second inclined surface (4031) is provided on the lower side of the extrusion block (403) to match the first inclined surface (4011); an electric push rod (404) is provided on the mounting plate (12), and a telescopic rod of the electric push rod (404) is fixedly connected to the extrusion block (403); The electric push rod (404) drives the extrusion block (403) to press the special-shaped block (401) downward, causing the first inclined surface (4011) to slide along the second inclined surface (4031), thereby driving the special-shaped block (401) to rotate.

4. The deep coal seam CO2 composite fracturing test device according to claim 1, characterized in that: The liquid carbon dioxide supply system (10) comprises a CO2 storage tank (1001), a valve (1002), The CO2 storage tank (1001) is connected to the injection pipe (9) via a butt joint, and a valve (1002) is provided on the butt joint.

5. The deep coal seam CO2 composite fracturing test device according to claim 1, characterized in that: A rotating ring (15) is rotatably mounted on the cover cylinder (3), and a gear ring (16) is provided on the rotating ring (15); A motor (17) is provided above the rotating ring (15), and a gear is provided on the output shaft of the motor (17), and the gear is meshed with the ring gear (16); A crack detector (18) is fixedly connected to the rotating ring (15).

6. The deep coal seam CO2 composite fracturing test device according to claim 1, characterized in that: A fitting sheet (19) is provided at the bottom of the cover plate (6), and a sealing ring (20) is provided at the top of the sample storage container (1), and the fitting sheet (19) and the sealing ring (20) are in contact with each other.

7. The deep coal seam CO2 composite fracturing test device according to claim 1, characterized in that: The sample storage container (1) is provided with a first pressure sensor (21) for detecting the internal pressure thereof; A second pressure sensor (22) is provided in the cover tube (3) for detecting the internal pressure thereof; The signal input end of the controller is connected to the first pressure sensor (21) and the second pressure sensor (22) respectively. The signal output end of the controller is electrically connected to the pressurizing system (8) and the opening and closing component (4) respectively.

8. The deep coal seam CO2 composite fracturing test device according to claim 1, characterized in that: The sample storage container (1) is arranged in a box body (23), and a box door (2301) is provided on one side of the box body (23).

9. The experimental method of a deep coal seam CO2 composite fracturing test device according to any one of claims 1 to 8, characterized in that: The specific steps include: S1: Place the coal sample into the sample container (1) and compact it, then inject liquid carbon dioxide into the inner cylinder (2), and adjust the internal pressure of the sample container (1); S2: The liquid carbon dioxide in the inner cylinder (2) is gasified. When the gas pressure in the inner cylinder (2) reaches a critical point, the inner cylinder (2) rotates so that the first through hole (201) and the second through hole (501) are relatively connected. The carbon dioxide gas in the inner cylinder (2) is ejected outward through the first through hole (201) and the second through hole (501). The generated high-pressure gas energy fractures the coal seam in the sample storage container (1); S3: Scan and evaluate the crack conditions of the coal seam inside the sample container (1).

Images