Rock-coal-rock combination fracturing anti-reflection experiment system and method under true triaxial condition

Abstract

The invention provides a rock-coal-rock combination fracturing anti-reflection experiment system and method under a true triaxial condition, and relates to the technical field of anhydrous fracturing, and the system is characterized in that a liquid CO2 storage tank is connected with a true triaxial holder through a booster pump and a first flowmeter in sequence; the vacuum pump is connected with the first gas concentration detector; the true triaxial holder is connected with the second valve and the sixth valve; the temperature control system is connected with the true triaxial holder; the first CH4 gas storage bottle is connected with the true triaxial holder through a first valve; the true triaxial clamp holder is of a hexahedral hollow structure; the servo systems are connected with different side surfaces of the true triaxial holder; the second gas concentration detector is connected with the true triaxial holder through a fourth flowmeter; the third gas concentration detector is connected with the true triaxial holder through a second flowmeter; the second CH4 gas storage bottle is connected with the true triaxial holder through a fifth valve; and the third CH4 gas storage bottle is connected with the true triaxial holder through a fourth valve. And the experimental data accuracy can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of waterless fracturing, and in particular to a rock-coal-rock combination fracturing and permeability enhancement experimental system and method under true triaxial conditions. Background Art

[0002] A rock-coal-rock complex is a composite geological structure formed by the natural cementation of coal seams with their roof and floor rock layers. It typically appears as a layered combination of "rock layer-coal layer-rock layer" (e.g., sandstone-coal-mudstone). This structure is widely found in coal mine strata, and its mechanical properties and seepage behavior are significantly influenced by the strength of the coal-rock interface, lithologic differences, and the distribution of in-situ stresses.

[0003] The necessity of conducting fracturing and permeability enhancement experiments on rock-coal-rock combinations is that deep soft coal seams have low permeability and are difficult to extract gas. Direct fracturing can easily cause plastic deformation of the coal body and lead to crack closure. However, by fracturing high-strength rock layers (such as sandstone) on the top and bottom plates, cracks can be induced to extend along the coal-rock interface and penetrate the original fracture network of the coal seam, achieving indirect permeability enhancement, which is beneficial for efficient deep coalbed methane extraction, gas disaster prevention and control, and Geological storage provides key parameters and theoretical support, while verifying the adaptability of indirect fracturing technology to complex geological conditions.

[0004] However, in the existing technology, during the fracturing and permeability enhancement experiment on the rock-coal-rock combination, it is often placed directly in a closed cavity for direct permeability enhancement experiment, which cannot simulate the actual three-dimensional stress state of the coal rock underground. The experimental conditions are inconsistent with reality, and accurate and reliable rock-coal-rock combination permeability enhancement data cannot be obtained. Summary of the Invention

[0005] In order to solve the technical problems in the prior art that during the fracturing and permeability enhancement experiment on the rock-coal-rock combination, the rock-coal-rock combination is often directly placed in a closed cavity for direct permeability enhancement experiment, which cannot simulate the actual three-dimensional stress state of the coal rock in the underground, the experimental conditions are inconsistent with the actual situation, and it is impossible to obtain accurate and reliable rock-coal-rock combination permeability enhancement data, the present invention provides a rock-coal-rock combination fracturing and permeability enhancement experiment system and method under true triaxial conditions.

[0006] The technical solutions provided by the embodiments of the present invention are as follows:

[0007] First aspect

[0008] An embodiment of the present invention provides a rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions, the system comprising:

[0009] liquid Storage tank, booster pump, vacuum pump, temperature control system, first valve, first flow meter, first servo system, second servo system, third servo system, second valve, third valve, fourth valve, second flow meter, third flow meter, fourth flow meter, first Gas cylinder, second Gas cylinder, third Gas cylinder, fifth valve, first gas concentration detector, second gas concentration detector, third gas concentration detector, sixth valve and true three-axis clamp;

[0010] liquid The storage tank is connected to the true three-axis gripper through the booster pump and the first flow meter in sequence;

[0011] The vacuum pump is connected to the first gas concentration detector through the second valve, the sixth valve and the third flow meter in sequence, and the true three-axis clamp is connected to the second valve and the sixth valve respectively;

[0012] The temperature control system is connected to the true three-axis gripper;

[0013] First The gas cylinder is connected to the true three-axis gripper through a first valve;

[0014] The true triaxial gripper is a hexahedral hollow structure, wherein the interior of the true triaxial gripper is used to place the rock-coal-rock combination;

[0015] The first servo system, the second servo system and the third servo system are respectively connected to the movable side view surface, the movable top view surface and the movable front view surface of the true three-axis clamp;

[0016] The second gas concentration detector is connected to the true triaxial holder via the fourth flow meter; the third gas concentration detector is connected to the true triaxial holder via the second flow meter;

[0017] second The gas cylinder is connected to the true three-axis gripper through the fifth valve; the third The gas cylinder is connected to the true three-axis gripper through the fourth valve.

[0018] Second aspect

[0019] An embodiment of the present invention provides a rock-coal-rock combination fracture permeability enhancement test method under true triaxial conditions, which is applied to the fracture permeability enhancement test system of the first aspect. The method includes:

[0020] S1: preparing a rock-coal-rock assembly by a groove carving method, and placing a fracturing pipe in the rock-coal-rock assembly;

[0021] S2: placing the rock-coal-rock assembly with the fracturing tube arranged in a true triaxial gripper;

[0022] S3: adjusting the movable side view surface, the movable top view surface, and the movable front view surface so that the pressures of the rock-coal-rock assembly on the movable side view surface, the movable top view surface, and the movable front view surface reach a first preset pressure, a second preset pressure, and a third preset pressure, respectively;

[0023] S4: vacuum the true three-axis gripper;

[0024] S5: Conduct rock-coal-rock combination Adsorption treatment;

[0025] S6: injecting test gas into the true triaxial holder to obtain initial permeability data of the rock-coal-rock combination;

[0026] S7: Fracturing the rock-coal-rock combination;

[0027] S8: Experimental permeability of the rock-coal-rock combination after testing fracture;

[0028] S9: Injecting gas into the true three-axis gripper ,test Displacement data;

[0029] S10: Output initial permeability, experimental permeability and Displacement data was collected to complete the rock-coal-rock combination fracturing and permeability enhancement experiment.

[0030] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0031] In the present invention, the rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions uses a true triaxial clamp as the core device, and through three independent servo systems, acts on the front view, top view and side view of the sample respectively to achieve non-equistress loading in the X, Y and Z directions, thereby accurately reproducing the stress state of underground coal and rock at depth, and improving the accuracy and reliability of the rock-coal-rock combination fracturing and permeability enhancement experimental data. The system is equipped with liquid Storage tanks and booster pumps can transfer liquid High pressure injection is performed on the rock-coal-rock combination sample to implement indirect fracturing operations, forming a fracture network to enhance permeability. At the same time, the system is connected with three directions of Gas cylinders can be used to inject methane gas into the sample to achieve multi-directional saturation treatment. In order to achieve a comprehensive evaluation of permeability and displacement effect, the system is equipped with high-precision flow meters and gas concentration detectors on each flow channel, which can monitor and record the flow in each direction before and after fracturing in real time. Flow rate changes and concentration fluctuations, thereby quantitatively analyzing liquid This multi-dimensional monitoring and acquisition method has a significant effect on the crack expansion and gas displacement process, further improving the reliability of the anti-permeability experiment and the accuracy of the experimental data. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 A schematic structural diagram of a rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions provided by an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of the structure of a data processing system provided by an embodiment of the present invention;

[0035] Figure 3 An exploded schematic diagram of the structure of a true three-axis gripper provided by an embodiment of the present invention;

[0036] Figure 4 A schematic flow chart of a method for fracturing and permeability enhancement of a rock-coal-rock combination under true triaxial conditions provided in an embodiment of the present invention.

[0037] Reference numerals:

[0038] 1. Liquid Storage tank; 2. Booster pump; 3. Vacuum pump; 4. Temperature control system; 5. First valve; 6. First flow meter; 7. First servo system; 8. Second servo system; 9. Third servo system; 10. Second valve; 11. Third valve; 12. Fourth valve; 13. Second flow meter; 14. Third flow meter; 15. Fourth flow meter; 16. Data processing system; 17. First Gas cylinder; 18, second Gas cylinder; 19, third Gas cylinder; 20. Fifth valve; 21. First gas concentration detector; 22. Second gas concentration detector; 23. Third gas concentration detector; 24. Sixth valve; 25. True three-axis clamp; 26. Fracturing pipe. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0040] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as an "exemplary" in the present invention should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of the word "exemplary" is intended to present concepts in a concrete manner. Furthermore, in the embodiments of the present invention, "and / or" can mean both or either of the two.

[0041] In the embodiments of the present invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, when the distinction is not emphasized, the meanings they convey are the same. The terms "of," "corresponding," and "corresponding" may sometimes be used interchangeably. It should be noted that, when the distinction is not emphasized, the meanings they convey are the same.

[0042] In the embodiments of the present invention, sometimes a subscript such as W1 may be mistakenly written as a non-subscript form such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0043] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0044] Reference Manual Figure 1 , showing a structural schematic diagram of a rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions provided by an embodiment of the present invention.

[0045] Reference Manual Figure 2 , which shows a structural diagram of a data processing system provided by an embodiment of the present invention.

[0046] Reference Manual Figure 3 , showing a structural explosion diagram of a true three-axis clamp provided by an embodiment of the present invention.

[0047] An embodiment of the present invention provides a rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions, the system comprising:

[0048] liquid Storage tank 1, booster pump 2, vacuum pump 3, temperature control system 4, first valve 5, first flow meter 6, first servo system 7, second servo system 8, third servo system 9, second valve 10, third valve 11, fourth valve 12, second flow meter 13, third flow meter 14, fourth flow meter 15, first Gas cylinder 17, second Gas cylinder 18, third Gas cylinder 19 , fifth valve 20 , first gas concentration detector 21 , second gas concentration detector 22 , third gas concentration detector 23 , sixth valve 24 and true three-axis clamp 25 .

[0049] liquid The storage tank 1 is connected to the true three-axis clamp 25 through the booster pump 2 and the first flow meter 6 in sequence.

[0050] The vacuum pump 3 is connected to the first gas concentration detector 21 through the second valve 10, the sixth valve 24 and the third flow meter 14 in sequence, and the true three-axis clamper 25 is connected to the second valve 10 and the sixth valve 24 respectively.

[0051] The temperature control system 4 is connected to the true three-axis clamp 25 .

[0052] First The gas cylinder 17 is connected to the true three-axis clamp 25 through the first valve 5 .

[0053] The true triaxial clamp 25 is a hexahedral hollow structure, wherein the interior of the true triaxial clamp 25 is used to place the rock-coal-rock combination.

[0054] The first servo system 7 , the second servo system 8 and the third servo system 9 are respectively connected to the movable side view surface, the movable top view surface and the movable front view surface of the true three-axis clamper 25 .

[0055] The second gas concentration detector 22 is connected to the true three-axis clamp 25 via the fourth flow meter 15. The third gas concentration detector 23 is connected to the true three-axis clamp 25 via the second flow meter 13.

[0056] The second CH4 gas cylinder 18 is connected to the true three-axis clamp 25 through the fifth valve 20. The gas cylinder 19 is connected to the true three-axis gripper 25 through the fourth valve 12 .

[0057] Among them, liquid The storage tank 1 and the booster pump 2 are used to store liquid carbon dioxide, which is then pressurized by the booster pump and injected into the rock-coal-rock combination sample to achieve indirect fracturing operation, induce crack formation and improve permeability. The vacuum pump 3 is used to evacuate the internal environment of the true triaxial gripper before the experiment to simulate the underground low-pressure environment and provide Saturation treatment creates conditions. The temperature control system 4 adjusts the temperature in the experimental chamber to ensure that the experimental process is carried out under the proposed thermal conditions, reflecting the underground thermal-mechanical-gas coupling environment. Various valves (5, 10-12, 20, 24 control different gases ( ) and the on-off flow of liquids, enabling process switching and safe isolation between experimental stages. Flow meters (6,13-15) accurately measure the volumetric flow rate of injected or outflowing gas, providing basic data for permeability and displacement efficiency assessments. Gas cylinders (17-19) inject methane into the sample from three directions to perform multi-directional saturation treatment to simulate the gas occurrence state in the coal seam. Gas concentration detectors (21-23) are placed on three opposite sides of the true triaxial clamp to monitor the gas concentration in different directions in real time. The concentration changes of displacement The first, second, and third servo systems (7-9) independently apply stress to the three active surfaces of the true triaxial gripper, achieving non-isotropic stress loading in the X, Y, and Z directions, simulating the actual underground stress field. The true triaxial gripper 25 is a hexahedral hollow structure used to hold rock, coal, and rock combination specimens, serving as the core platform for loading and fluid injection.

[0058] The connection surfaces of the first, second, and third gas concentration detectors 21, 22, and 23 connected to the true triaxial clamp 25 are located on opposite sides of the movable top-view surface, movable side-view surface, and movable front-view surface, respectively. In other words, the connection surface between the first gas concentration detector 21 and the true triaxial clamp 25 is opposite the movable top-view surface. The connection surface between the second gas concentration detector 22 and the true triaxial clamp 25 is opposite the movable side-view surface. The connection surface between the third gas concentration detector 23 and the true triaxial clamp 25 is opposite the movable front-view surface.

[0059] The experimental system is based on the principle of "true triaxial loading + multi-source gas injection + multi-point detection". It uses a true triaxial clamp to achieve three-dimensional unequal stress loading on the sample and truly restore the physical behavior of coal rock in the complex stress environment underground. Indirect fracturing technology and three-way The saturation treatment system simulates the entire coalbed methane extraction process. Equipped with flow and concentration monitoring modules, it provides real-time, quantitative assessment of fracture expansion and gas displacement efficiency. The highly integrated and automated overall structure delivers more accurate and reliable experimental results, making it suitable for complex coalbed methane recovery and carbon sequestration testing.

[0060] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0061] In the present invention, the rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions uses a true triaxial clamp as the core device, and through three independent servo systems, acts on the front view, top view and side view of the sample respectively to achieve non-equistress loading in the X, Y and Z directions, thereby accurately reproducing the stress state of underground coal and rock at depth, and improving the accuracy and reliability of the rock-coal-rock combination fracturing and permeability enhancement experimental data. The system is equipped with liquid Storage tanks and booster pumps can transfer liquid High pressure injection is performed on the rock-coal-rock combination sample to implement indirect fracturing operations, forming a fracture network to enhance permeability. At the same time, the system is connected with three directions of Gas cylinders can be used to inject methane gas into the sample to achieve multi-directional saturation treatment. In order to achieve a comprehensive evaluation of permeability and displacement effect, the system is equipped with high-precision flow meters and gas concentration detectors on each flow channel, which can monitor and record the flow in each direction before and after fracturing in real time. Flow rate changes and concentration fluctuations, thereby quantitatively analyzing liquid This multi-dimensional monitoring and acquisition method has a significant effect on the crack expansion and gas displacement process, further improving the reliability of the anti-permeability experiment and the accuracy of the experimental data.

[0062] In a possible implementation, the rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions further includes: a data processing system 16 .

[0063] The first gas concentration detector 21 , the second gas concentration detector 22 , and the third gas concentration detector 23 are all connected to the data processing system 16 .

[0064] It should be noted that this structure connects three sets of gas concentration detectors with the data processing system to achieve centralized collection, automatic recording and real-time analysis of multi-directional data, significantly improving the intelligence level of the experiment and data processing efficiency, and facilitating a comprehensive and accurate evaluation of the fracturing and permeability enhancement effect.

[0065] In a possible implementation, the rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions further includes: a fracturing pipe 26 .

[0066] The fracturing pipe 26 is connected to the booster pump 2 .

[0067] It should be noted that the structure directly connects the booster pump to the interior of the sample by setting a fracturing pipe, so that the liquid It can be efficiently and directionally injected into the rock-coal-rock combination, improving the control accuracy of the fracturing process and the effectiveness of fracture induction, and helping to form an ideal fracture network structure.

[0068] The present invention also provides a rock-coal-rock combination fracture and permeability enhancement test method under true triaxial conditions, which is applied to the rock-coal-rock combination fracture and permeability enhancement test system under true triaxial conditions. The method includes:

[0069] S1: Prepare a rock-coal-rock assembly by a groove carving method, and arrange a fracturing pipe 26 in the rock-coal-rock assembly.

[0070] It should be noted that obtaining a coal-rock assembly with a natural interface through the grooving method and arranging fracturing pipes can retain the original structural characteristics and crack distribution to the greatest extent, which helps to truly reflect the crack evolution and fluid permeation behavior of coal rock under actual geological conditions, and improve the representativeness of the experiment and the credibility of the results.

[0071] In a possible implementation, S1 specifically includes:

[0072] The sampling line is arranged along the coal seam dip angle of the coal seam sampling point.

[0073] The coal seam is cut along the sampling line to obtain coal rock blocks.

[0074] The coal rock block is cut to obtain a coal rock combination sample with a coal rock interface.

[0075] A fracturing hole is opened on the coal-rock combination sample, wherein the fracturing hole is located on one side of the coal-rock interface.

[0076] Place the fracturing pipe in the fracturing hole.

[0077] It should be noted that this process preserves the original geological appearance and fracture structure characteristics to the greatest extent by arranging sampling lines along the dip of the coal seam and obtaining samples with natural coal-rock interfaces. At the same time, fracturing holes and fracturing pipes are arranged on one side of the interface, which helps the fractures to expand preferentially on the weak structural surface, thereby improving the fracture conductivity efficiency and the authenticity of the experimental simulation.

[0078] S2: The rock-coal-rock assembly with the fracturing tube 26 arranged therein is placed in the true triaxial clamp 25 .

[0079] S3: Adjust the movable side view surface, the movable top view surface and the movable front view surface so that the pressure of the rock-coal-rock combination on the movable side view surface, the movable top view surface and the movable front view surface reaches the first preset pressure, the second preset pressure and the third preset pressure respectively.

[0080] It should be noted that by adjusting the three movable surfaces of the true triaxial clamp and applying preset pressures in different directions, the loading of the rock-coal-rock combination under a three-dimensional non-isostress state can be achieved, which is closer to the actual underground stress environment, helps to comprehensively study the influence of different stress conditions on crack propagation and permeability characteristics, and improves the authenticity and scientific nature of the experimental simulation.

[0081] It should be noted that those skilled in the art can set the first preset pressure, the second preset pressure and the third preset pressure according to actual needs, and the present invention does not limit this.

[0082] In a possible implementation, S3 is specifically:

[0083] By adjusting the first servo system 7, the second servo system 8 and the third servo system 9, the pressure of the rock-coal-rock combination on the movable side view surface, the movable top view surface and the movable front view surface reaches the first preset pressure, the second preset pressure and the third preset pressure respectively.

[0084] It can be understood that by precisely controlling the stress state of the rock-coal-rock combination in three directions through three sets of independent servo systems, independent loading of non-equivalent stresses on the X, Y, and Z axes can be achieved, which can simulate the complex and realistic three-dimensional stress field of deep formations and improve the accuracy of fracturing experiments and the authenticity of mechanical response simulations.

[0085] S4: The true three-axis gripper 25 is vacuumed.

[0086] S4 specifically includes:

[0087] Close the first valve 5 , the third valve 11 , the fourth valve 12 , the fifth valve 20 , the sixth valve 24 , and the second valve 10 .

[0088] The vacuum pump 3 is turned on to evacuate the interior of the true three-axis gripper 25 .

[0089] It should be noted that by vacuuming the interior of the true three-axis gripper, residual gas is effectively eliminated to avoid impurities interfering with subsequent Adsorption and permeability tests ensure the purity and repeatability of the initial state of the experiment, thereby improving the accuracy and reliability of the experimental data.

[0090] S5: Conduct rock-coal-rock combination Adsorption treatment.

[0091] S5 specifically includes:

[0092] Close the second valve 10 , the third valve 11 , and the sixth valve 24 .

[0093] Open the first valve 5 , the fourth valve 12 , and the fifth valve 20 .

[0094] Open the first Gas cylinder 17, second CH4 gas cylinder 18 and third The gas cylinder 19 is injected into the true three-axis gripper 25 in three directions. , the rock-coal-rock combination Adsorption treatment.

[0095] It should be noted that by injecting from three directions simultaneously The gas is adsorbed to achieve uniform and sufficient methane saturation of the rock-coal-rock combination under multi-dimensional stress conditions, effectively simulating the gas storage environment in underground coal seams, and providing a basis for subsequent permeability testing and Displacement experiments provide a realistic and reliable basis for initial gas distribution.

[0096] S6: Injecting test gas into the true triaxial holder 25 to obtain initial permeability data of the rock-coal-rock combination.

[0097] It should be noted that by injecting test gas into the true triaxial clamp and measuring its flow characteristics, the initial permeability data of the rock-coal-rock combination before fracturing can be accurately obtained, providing a benchmark comparison for subsequent fracturing effect evaluation and ensuring that the quantitative analysis of permeability enhancement efficiency has a scientific basis and data support.

[0098] In a possible implementation, S6 specifically includes:

[0099] The temperature control system 4 is turned on to adjust the interior of the true three-axis gripper 25 to a preset temperature.

[0100] It should be noted that those skilled in the art can set the preset temperature according to actual needs, and the present invention does not limit this.

[0101] Close the first valve 5, the second valve 10, the third valve 11, and the fifth valve 20. Open the fourth valve 12 and the sixth valve 24, and inject CH4 gas from the third CH4 gas cylinder 19 into the true triaxial clamp 25. Observe the third flowmeter 14 and record the gas flow rate per unit time.

[0102] Close the second valve 10, the third valve 11, the fourth valve 12, the fifth valve 20, and the sixth valve 24, open the first valve 5, and inject CH4 gas from the first CH4 gas cylinder 17 into the true three-axis clamp 25. Observe the fourth flowmeter 15 and record the gas flow rate per second unit time.

[0103] Close the first valve 5, the second valve 10, the third valve 11, the fourth valve 12, and the sixth valve 24, open the fifth valve 20, and inject CH4 gas from the second CH4 gas cylinder 18 into the true three-axis clamp 25. Observe the second flowmeter 13 and record the gas flow rate per unit time.

[0104] The first unit time gas flow rate, the second unit time gas flow rate and the second unit time gas flow rate are output as initial permeability data.

[0105] Specifically, the process is achieved by precisely controlling the Gas injection and flow meter measurement of gas flow in different directions can comprehensively assess the initial permeability of the rock-coal-rock complex under a three-dimensional stress environment. By recording multi-directional flow data, a more reliable permeability benchmark is provided, providing a scientific basis for subsequent experimental data comparison and effect evaluation, ensuring the accuracy and repeatability of experimental results.

[0106] S7: Fracturing the rock-coal-rock combination.

[0107] It should be noted that by applying liquid Fracturing can induce cracks to expand along the natural structural interface under simulated three-dimensional ground stress conditions, forming a complex fracture network and improving the permeability of coal seams. At the same time, it avoids the water-sensitive damage problem caused by hydraulic fracturing, realizes a green and efficient fracture transformation method, and improves the authenticity and practical value of permeability enhancement experiments.

[0108] In a possible implementation, S7 specifically includes:

[0109] The third valve 11 is opened, and the first valve 5 , the second valve 10 , the fourth valve 12 , the fifth valve 20 and the sixth valve 24 are closed.

[0110] Turn on booster pump 2, the liquid Tank 1 injects liquid into booster pump 2 , continuing for a preset time to complete the fracturing of the rock-coal-rock combination.

[0111] It should be noted that those skilled in the art can set the preset duration according to actual needs, and the present invention does not limit this.

[0112] Close the third valve 11.

[0113] It should be noted that the liquid is injected by precisely controlling the booster pump Continuously applying pressure to rock-coal-rock assemblages for fracturing effectively triggers fracture propagation under simulated three-dimensional stress conditions, forming enhanced permeability pathways. By adjusting the injection duration, the fracturing intensity can be controlled according to experimental requirements, ensuring the adjustability and repeatability of experimental results, and ensuring that the fracturing effect is highly consistent with the geological environment.

[0114] S8: Experimental permeability of the rock-coal-rock combination after testing fracture.

[0115] It should be noted that the permeability test of the rock-coal-rock combination after fracturing can directly reflect the changes in fluid migration capacity after the formation of cracks. By comparing and analyzing the data before fracturing, the fracturing transformation effect can be quantitatively evaluated to verify the The practical application value and permeability enhancement efficiency of fracturing in improving coal seam permeability.

[0116] In a possible implementation, S8 specifically includes:

[0117] The rock-coal combination fracturing and permeability enhancement experimental system under true triaxial conditions was adjusted in the same way as the initial permeability data testing process to obtain the experimental permeability.

[0118] It can be understood that this process ensures the consistency and comparability of the experimental permeability data with the initial data by adopting the same method as the initial permeability test, so that the permeability changes of the rock-coal-rock combination after fracturing can be accurately evaluated, and a reliable basis for analyzing the permeability enhancement effect can be provided, which helps to verify the actual effect of the fracturing transformation and the efficiency of improving the permeability.

[0119] S9: Inject gas into the true three-axis gripper 25 , test CH4 displacement data.

[0120] It should be noted that by injecting gas into the true three-axis gripper , using its The strong adsorption and diffusivity of The effective displacement of Its migration and substitution capabilities in fractures can also verify its dual potential in improving coalbed methane recovery and carbon sequestration.

[0121] In a possible implementation, S9 specifically includes:

[0122] Open the third valve 11 and the sixth valve 24.

[0123] Close the first valve 5 , the second valve 10 , the fourth valve 12 , and the fifth valve 20 .

[0124] Open liquid Tank 1, turn off the booster pump 2 to inject gas into the true three-axis gripper 25 , for the coal-rock combination Carry out displacement.

[0125] According to the first gas concentration detector 21, the second gas concentration detector 22, and the third gas concentration detector 23, the rock-coal-rock combination is recorded. The content is reduced to the preset rock-coal combination The displacement time of the content.

[0126] It should be noted that by injecting gaseous In the coal-rock combination Carry out displacement and use multiple gas concentration detectors to monitor in real time Concentration changes can be accurately assessed displacement By recording the displacement time, we can quantify It plays an important role in coalbed methane recovery and carbon storage, providing important experimental data support and optimizing the fracturing and displacement process parameters in actual engineering.

[0127] It should be noted that those skilled in the art can set the preset The present invention does not limit the content of the gas. Optionally, the readings of the gas concentration detector in three directions can be observed simultaneously to monitor the content of the gas in real time. Concentration changes, record The time required for the content to drop from the initial value to 10% is the displacement time.

[0128] S10: Output initial permeability, experimental permeability and Displacement data was collected to complete the rock-coal-rock combination fracturing and permeability enhancement experiment.

[0129] Finally, all valves, temperature control system, booster pump and vacuum pump were closed, the triaxial pressure was removed, the sample was taken out, and the collected data was processed.

[0130] In actual application, the provided rock-coal-rock combination fracturing permeability enhancement experimental method under true triaxial conditions obtains the original structure sample and arranges the fracturing pipe by the groove method, and uses the true triaxial clamp to apply non-uniform stress in the X, Y, and Z directions to simulate the three-dimensional real stress environment underground. After saturation treatment, the initial permeability data was obtained by testing the gas, and then the liquid Fracturing is carried out to induce cracks to expand along the natural structure and form high permeability channels. Injection Displacement experiments collect three-dimensional gas concentration and flow changes, which can achieve accurate evaluation of permeability changes and displacement efficiency.

[0131] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0132] In the present invention, the rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions uses a true triaxial clamp as the core device, and through three independent servo systems, acts on the front view, top view and side view of the sample respectively to achieve non-equistress loading in the X, Y and Z directions, thereby accurately reproducing the stress state of underground coal and rock at depth, and improving the accuracy and reliability of the rock-coal-rock combination fracturing and permeability enhancement experimental data. The system is equipped with liquid Storage tanks and booster pumps can transfer liquid High pressure injection is performed on the rock-coal-rock combination sample to implement indirect fracturing operations, forming a fracture network to enhance permeability. At the same time, the system is connected with three directions of Gas cylinders can be used to inject methane gas into the sample to achieve multi-directional saturation treatment. In order to achieve a comprehensive evaluation of permeability and displacement effect, the system is equipped with high-precision flow meters and gas concentration detectors on each flow channel, which can monitor and record the flow in each direction before and after fracturing in real time. Flow rate changes and concentration fluctuations, thereby quantitatively analyzing liquid This multi-dimensional monitoring and acquisition method has a significant effect on the crack expansion and gas displacement process, further improving the reliability of the anti-permeability experiment and the accuracy of the experimental data.

[0133] The above embodiments can be implemented in whole or in part via software, hardware (e.g., circuits), firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented in whole or in part in the form of a computer program product. The computer program product comprises one or more computer instructions or computer programs. When loaded or executed on a computer, the processes or functions described in accordance with the embodiments of the present invention are fully or partially performed. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible by a computer, or a data storage system such as a server or data center that contains a collection of one or more available media. The available medium can be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media. The semiconductor media can be a solid-state drive.

[0134] It should be understood that the term "and / or" as used herein simply describes a relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. A and B can be singular or plural. Furthermore, the character " / " as used herein generally indicates an "or" relationship between the associated objects, but it may also indicate an "and / or" relationship. For specific understanding, please refer to the context.

[0135] In this disclosure, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or plural.

[0136] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0137] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0138] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0139] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0140] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0141] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0142] If the functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or the portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for enabling a computer system (which can be a personal computer, server, or network system, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes various media that can store program code, such as USB flash drives, mobile hard drives, read-only memories (ROM), random access memories (RAM), magnetic disks, or optical disks.

[0143] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

[0144] There are a few points to note:

[0145] (1) The drawings of the embodiments of the present invention only relate to the structures related to the embodiments of the present invention. Other structures may refer to conventional designs.

[0146] (2) For the sake of clarity, the thickness of layers or regions in the drawings used to describe the embodiments of the present invention are exaggerated or reduced, that is, these drawings are not drawn to scale. It is understood that when an element such as a layer, film, region, or substrate is referred to as being "on" or "under" another element, the element may be "directly on" or "under" the other element or intervening elements may be present.

[0147] (3) In the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other to form new embodiments.

[0148] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions, characterized in that: include: Liquid CO2 storage tank, booster pump, vacuum pump, temperature control system, first valve, first flowmeter, first servo system, second servo system, third servo system, second valve, third valve, fourth valve, second flowmeter, third flowmeter, fourth flowmeter, first CH4 gas cylinder, second CH4 gas cylinder, third CH4 gas cylinder, fifth valve, first gas concentration detector, second gas concentration detector, third gas concentration detector, sixth valve, and true three-axis gripper; The liquid CO2 storage tank is connected to the true three-axis gripper via the booster pump and the first flow meter in sequence; The vacuum pump is connected to the first gas concentration detector through the second valve, the sixth valve and the third flow meter in sequence, and the true three-axis clamp is connected to the second valve and the sixth valve respectively; The temperature control system is connected to the true three-axis clamp; The first CH4 gas cylinder is connected to the true three-axis gripper via the first valve; The true triaxial clamp is a hexahedral hollow structure, wherein the interior of the true triaxial clamp is used to place the rock-coal-rock combination; The first servo system, the second servo system and the third servo system are respectively connected to the movable side view surface, the movable top view surface and the movable front view surface of the true three-axis clamp; The second gas concentration detector is connected to the true three-axis clamp via the fourth flow meter; the third gas concentration detector is connected to the true three-axis clamp via the second flow meter; The second CH4 gas cylinder is connected to the true three-axis clamp through the fifth valve; the third CH4 gas cylinder is connected to the true three-axis clamp through the fourth valve.

2. The rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions according to claim 1 is characterized in that: The rock-coal-rock combination fracture permeability enhancement experimental system under true triaxial conditions also includes: a data processing system; The first gas concentration detector, the second gas concentration detector and the third gas concentration detector are all connected to the data processing system.

3. The rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions according to claim 1 is characterized in that: The rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions further includes: a fracturing pipe; The fracturing pipe is connected to the booster pump.

4. A method for increasing the permeability of a rock-coal-rock combination by fracturing under true triaxial conditions, characterized in that: The fracturing and permeability enhancement experimental system applied to any one of claims 1 to 3, the method comprising: S1: preparing the rock-coal-rock assembly by a groove carving method, and arranging the fracturing pipe in the rock-coal-rock assembly; S2: placing the rock-coal-rock assembly with the fracturing tube arranged thereon into the true triaxial clamp; S3: adjusting the movable side view surface, the movable top view surface, and the movable front view surface so that the pressures of the rock-coal-rock assembly on the movable side view surface, the movable top view surface, and the movable front view surface reach a first preset pressure, a second preset pressure, and a third preset pressure, respectively; S4: vacuuming the true three-axis gripper; S5: performing CH4 adsorption treatment on the rock-coal-rock combination; S6: injecting a test gas into the true triaxial holder to obtain initial permeability data of the rock-coal-rock combination; S7: fracturing the rock-coal-rock combination; S8: Experimental permeability of the rock-coal-rock combination after testing fracture; S9: injecting gaseous CO2 into the true triaxial holder to test CH4 displacement data; S10: Outputting the initial permeability, the experimental permeability and the CH4 displacement data to complete the rock-coal-rock combination fracturing and permeability enhancement experiment.

5. The rock-coal-rock combination fracture permeability enhancement experimental method under true triaxial conditions according to claim 4, characterized in that: Said S1 specifically includes: Arrange sampling lines along the coal seam dip angle at the coal seam sampling point; Cutting the coal seam along the sampling line to obtain coal rock blocks; Cutting the coal rock block to obtain a sample of the coal rock assembly having a coal rock interface; Opening a fracturing hole on the coal-rock combination sample, wherein the fracturing hole is located on one side of the coal-rock interface; The fracturing pipe is arranged in the fracturing hole.

6. The rock-coal-rock combination fracture permeability enhancement experimental method under true triaxial conditions according to claim 4, characterized in that: The S3 is specifically: By adjusting the first servo system, the second servo system and the third servo system, the pressure of the rock-coal-rock combination on the movable side view surface, the movable top view surface and the movable front view surface reaches the first preset pressure, the second preset pressure and the third preset pressure respectively.

7. The rock-coal-rock combination fracture permeability enhancement experimental method under true triaxial conditions according to claim 4, characterized in that: The S6 specifically includes: Turning on the temperature control system to adjust the interior of the true three-axis gripper to a preset temperature; closing the first valve, the second valve, the third valve, and the fifth valve; Open the fourth valve and the sixth valve, inject CH4 gas into the true triaxial gripper from the third CH4 gas cylinder, observe the third flowmeter 14, and record the gas flow rate per unit time; Close the second valve, the third valve, the fourth valve, the fifth valve, and the sixth valve, open the first valve, inject CH4 gas into the true triaxial gripper from the first CH4 gas cylinder, observe the fourth flowmeter, and record the gas flow rate per second unit time; Close the first valve, the second valve, the third valve, the fourth valve, and the sixth valve, open the fifth valve, inject CH4 gas into the true triaxial gripper from the second CH4 gas cylinder, observe the second flowmeter, and record the gas flow rate per unit time for a third unit time; The first unit time gas flow rate, the second unit time gas flow rate, and the second unit time gas flow rate are output as the initial permeability data.

8. The rock-coal-rock combination fracture permeability enhancement experimental method under true triaxial conditions according to claim 4, characterized in that: The S7 specifically includes: opening the third valve, and closing the first valve, the second valve, the fourth valve, the fifth valve, and the sixth valve; Turning on the booster pump, and injecting liquid CO2 from the liquid CO2 storage tank into the booster pump for a preset time to complete the fracturing of the rock-coal-rock combination; Close the third valve.

9. The rock-coal-rock combination fracture permeability enhancement experimental method under true triaxial conditions according to claim 4, characterized in that: The S8 is specifically: The rock-coal-rock combination fracturing and permeability enhancement experimental system under true triaxial conditions is adjusted in the same manner as the initial permeability data testing process to obtain the experimental permeability.

10. The rock-coal-rock combination fracture permeability enhancement experimental method under true triaxial conditions according to claim 4, characterized in that: The S9 specifically includes: opening the third valve and the sixth valve; closing the first valve, the second valve, the fourth valve, and the fifth valve; Open the liquid CO2 storage tank and close the booster pump to inject gaseous CO2 into the true triaxial gripper to displace CH4 in the rock-coal-rock combination; According to the first gas concentration detector, the second gas concentration detector and the third gas concentration detector, the displacement time required for the CH4 content of the rock-coal-rock combination to drop to the preset rock-coal-rock combination CH4 content is recorded.

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