True triaxial hydrofracture multi-scale monitoring system fusing acoustic emission, ultrasonic wave and strain linkage

Abstract

The invention discloses a true triaxial hydraulic fracturing multi-scale monitoring system fusing acoustic emission, ultrasonic wave and strain linkage, and relates to the technical field of true triaxial hydraulic fracturing, which comprises a device main body, a horizontal stress loading system, a hydraulic servo pump pressure module, an acoustic emission monitoring system, a crack strain monitoring system and an ultrasonic monitoring system, according to the true triaxial hydrofracture multi-scale monitoring system integrating acoustic emission, ultrasonic wave and strain linkage, the hydrofracture process is comprehensively monitored through the acoustic emission monitoring module, the ultrasonic wave monitoring module and the strain gauge array monitoring module in an experiment, and the three monitoring means are matched with one another; and a data support with high temporal-spatial resolution is provided for the whole crack evolution process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of true triaxial hydraulic fracturing, in particular to a true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic wave and strain linkage. BACKGROUND

[0002] In shale gas / oil exploitation, hydraulic fracturing is an engineering technology for fracturing rock layers by high-pressure fluid to enhance resource exploitation efficiency. In the laboratory, true triaxial conditions can effectively simulate field fracturing, which has guiding significance for field design and construction. The true triaxial hydraulic fracturing device, as a laboratory test equipment in the field of oil and gas exploitation, can simulate the stress state under actual engineering conditions, that is, different stress components are applied to three directions (X, Y and Z directions) of a cubic specimen of different sizes. direction, direction, direction) respectively. By combining the three stress components, the law of fracture pressure and the fracture mechanism under different stress states are studied. Compared with the conventional triaxial hydraulic fracturing test, the true triaxial hydraulic fracturing device can better simulate the stress state and fracture law of field hydraulic fracturing, thereby having wide application. In the 1960s, true triaxial hydraulic fracturing experimental technology gradually emerged. In the 1970s, Hubbert and Willis built the first true triaxial fracturing experimental system in the University of Minnesota, USA, focusing on the regulation mechanism of stress state on crack propagation path. With the continuous improvement of such devices, researchers gradually introduced acoustic emission, strain gauge array and other monitoring methods to deeply analyze the rock mechanics behavior in the process of hydraulic fracturing from different scales and angles. Today, the study of the fracture mechanism and crack propagation law of rock under true triaxial hydraulic fracturing conditions is still a core problem that needs to be broken through in this field. The existing true triaxial hydraulic fracturing device generally uses acoustic emission, strain gauge array and other monitoring methods, which has achieved certain results in the study of crack fracture mechanism, but still has problems such as not fully considering the scale effect and lack of coordination between monitoring systems, which limits the reproduction ability of the real fracture mechanism of underground cracks. Therefore, it is necessary to provide a true triaxial hydraulic fracturing device with multi-scale adaptability and multi-source monitoring coordination mechanism. SUMMARY

[0003] The present application provides a true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic wave and strain linkage, which can effectively solve the problems raised in the background technology.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves and strain linkage, comprising a main body, a horizontal stress loading system, a hydraulic servo pump pressure module, an acoustic emission monitoring system, a fracture strain monitoring system and an ultrasonic monitoring system.

[0005] According to the above technical solution, the applicable dimensions of the device body and the horizontal stress loading system upper pressure plate with a side length of 300mm include the lower pressure plate and the side pressure plate, which include dimensions of 300mm, 250mm, 200mm, 150mm, and 100mm. The horizontal stress loading system includes a two-way integrated reaction frame, an ultra-thin hydraulic jack, an ultra-thin hydraulic jack pad, and a manual pressure pump. The manual pressure pump is used to apply circumferential stress to the sample.

[0006] According to the above technical solution, the hydraulic servo pump pressure module includes an air compressor, a control box, and a hydraulic servo pump pressure control system.

[0007] According to the above technical solution, the acoustic emission monitoring system includes a full-information acoustic emission signal analyzer, an acoustic emission signal amplifier, and eight acoustic emission ceramic probes, wherein two of the acoustic emission probes are arranged on the rock being tested. First surface of the direction; Two acoustic emission probes are placed on the rock being tested. Second measuring surface in the direction; Two acoustic emission probes are placed on the rock being tested. First surface of the direction; Two acoustic emission probes are placed on the rock being tested. Second measuring surface in the direction; The eight acoustic emission ceramic probes are connected to the acoustic emission signal amplifier via wires; The acoustic emission signal amplifier is connected to the full-information acoustic emission signal acquisition instrument and the computer via wires.

[0008] According to the above technical solution, the crack strain monitoring system includes n strain gauges, a strain acquisition instrument and a strain acquisition computer, and the strain gauges are fixedly installed on the sample surface in a preset direction in which cracks may form. Among them A patch is placed at 25mm intervals along the direction in which cracks may form on the surface, in two... Each strain gauge is placed at 25mm intervals on the directional plane. The strain gauges are connected to the strain acquisition instrument via wires through the strain gauge wire grooves preset on the upper pressure plate and the pressure measuring plates of each size. The data is then transmitted to the strain acquisition computer via a network cable.

[0009] According to the above technical solution, the ultrasonic monitoring system consists of m ultrasonic array probes, a regulated power supply and a digital oscilloscope. A total of m ultrasonic array probes are deployed, arranged using the flat measurement method, symmetrically distributed at a distance of 30mm from the water injection hole, with the arrangement direction parallel to the expected crack propagation direction, one side being the transmitting probe and the other side being the receiving probe. m sets of paired ultrasonic probes are arranged on the side of the rock sample along the direction of minimum principal stress. The center of the probe is 30 mm away from the geometric center of the sample. The direction of the measurement line is perpendicular to the vertical principal stress plane. One side is set as the transmitting end and the other side is set as the receiving end. The spacing between adjacent probes in the same row is 35 mm. All ultrasonic probes are connected to a regulated power supply and a digital oscilloscope via connecting cables to achieve stable excitation and high-precision acquisition of ultrasonic signals. The test is performed using the flat test method, in which the transmitting and receiving transducers are placed on the same surface of the sample and effectively coupled by a coupling agent.

[0010] According to the above technical solution, a true triaxial hydraulic fracturing device and a multi-scale hydraulic fracturing fracture mechanism monitoring method are proposed. The experiment comprehensively monitors the hydraulic fracturing process through an acoustic emission monitoring module, an ultrasonic monitoring module, and a strain gauge array monitoring module. Among them, the acoustic emission system can realize the spatial location of cracks; ultrasonic monitoring is highly sensitive to changes in crack depth and can quantitatively analyze the changes in crack width during crack propagation; the strain gauge array has a fast response speed and is relatively sensitive to the crack initiation time sequence, and can capture the strain change at the moment of crack initiation, so as to realize the quantitative identification and time sequence judgment of crack initiation and propagation behavior in rock mass. The three monitoring methods work together to provide high spatiotemporal resolution data support for the entire process of crack evolution.

[0011] According to the above technical solution, the test method for a large-size triaxial hydraulic fracturing test device includes the following steps: Step 1: Sample Preparation and Loading The design dimension of this device is 300mm. 3 250mm 3 200mm 3 150mm 3 100mm 3 To accommodate multiple sizes, a pre-fabricated wellbore is constructed at the center of the prepared sample. A water injection pipe is pre-embedded at the simulated wellbore location. Epoxy resin is used to fill and fix the gap between the end cap and the wellbore. Finally, the sample is dried and cured for 24 hours, and the sample surface is polished to ensure a proper fit between the pressure head and the water injection pipe head. An appropriate amount of ink is injected into the water injection pipe head to observe the crack direction after the test. The sample is placed in the loading chamber, and four cylindrical pressure pads are placed on the upper pressure plate using positioning pins. One end of the fracturing fluid delivery pipeline is connected to and fixed to the circular water injection port of the upper pressure plate; an acoustic emission probe is installed and connected to the acoustic emission monitoring module; According to the experimental design, samples were set up on both the TAW-2000 and horizontal stress loading systems. , , Load parameters in three directions; to ensure uniform stress on all surfaces of the specimen, the triaxial stress is slowly applied sequentially to the corresponding values ​​of the minimum horizontal principal stress, the maximum horizontal principal stress, and the vertical stress during the loading process. To prevent eccentric failure of the specimen, the loading process is divided into three stress loading gradients to ensure uniform application of the triaxial stress. The vertical stress first reaches the minimum principal stress value, and then the triaxial stress is applied sequentially to the corresponding values ​​to reach the target pressure. The pressure is kept stable for hydraulic fracturing test. Step 2: Conduct triaxial hydraulic fracturing tests The air compressor delivers the fracturing fluid from the hydraulic servo pump module to the main body of the device, and connects it through the circular water inlet on the upper pressure plate; Set the fracturing fluid discharge rate using the hydraulic servo pump pressure module; set the sample size, longitudinal wave velocity, and acoustic emission probe coordinates according to the acoustic emission monitoring system to monitor the acoustic emission positioning information in real time during the hydraulic fracturing test; enable the water pressure start option and start the data logger, and simultaneously start the full-information acoustic emission analyzer to start collecting acoustic emission signals through the acoustic emission computer control system; monitor the water pressure in real time through the water pressure-time curve displayed by the hydraulic servo pump pressure module; after the water pressure reaches its peak and drops for a period of time, stop the pump pressure and close the recording after the water pressure stabilizes, and the hydraulic fracturing indoor test ends. Step 3: Depressurize and change samples After the triaxial hydraulic fracturing test is completed, data acquisition is stopped and saved. The full-information acoustic emission analyzer, strain acquisition instrument, and oscilloscope are turned off. The water pressure is unloaded to the lower limit, at which point the yellow light on the control box illuminates. The control box is then turned off. The vertical stress, maximum horizontal principal stress, and minimum horizontal principal stress are unloaded in sequence. The connection between the fracturing fluid delivery pipe and the circular water injection port of the upper pressure plate is disconnected. The fracturing fluid in the loading chamber (i.e., the surrounding area) is processed, and the next sample is used for the next test.

[0012] Compared with existing technologies, the beneficial effects of this invention are: the invention has a scientifically sound and reasonable structure, is safe and convenient to use, and proposes a true triaxial hydraulic fracturing multi-scale monitoring system that integrates acoustic emission, ultrasonic waves, and strain linkage. This device can apply pressure in three directions to a cubic rock sample. direction, direction, Independent loading (direction) enables hydraulic fracturing tests under various stress states.

[0013] This invention proposes a true triaxial hydraulic fracturing multi-scale monitoring system that integrates acoustic emission, ultrasonic waves, and strain linkage. The experimental device is a multi-size hydraulic fracturing platform that can perform hydraulic fracturing tests on cubic rock samples with side lengths of 300mm, 250mm, 200mm, 150mm, and 100mm by changing the cover plates of different specifications. This device is helpful for systematically studying the response law of rocks of different sizes during the hydraulic fracturing process and has important experimental and engineering application value.

[0014] This invention proposes a true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic wave, and strain linkage. Experiments were conducted to comprehensively monitor the hydraulic fracturing process using an acoustic emission monitoring module, an ultrasonic wave monitoring module, and a strain gauge array monitoring module. The acoustic emission system enables spatial localization of cracks; ultrasonic wave monitoring is highly sensitive to changes in crack depth, allowing for quantitative analysis of crack width changes during crack propagation; and the strain gauge array has a fast response speed and is sensitive to crack initiation timing, capturing sudden strain changes at the moment of crack initiation. This enables quantitative identification and temporal judgment of crack initiation and propagation behavior in rock masses. The three monitoring methods work together to provide high spatiotemporal resolution data support for the entire crack evolution process.

[0015] This invention proposes a true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage. This hydraulic fracturing testing device is compatible with equipment such as the MTS-815 rigid rock mechanics hydraulic servo system and the TAW-2000 electro-hydraulic servo rock triaxial testing instrument. By structurally modifying the triaxial loading chamber based on a conventional loading frame, true triaxial loading functionality can be achieved, thereby improving the assembly versatility and adaptability of this true triaxial hydraulic fracturing testing device. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0017] In the attached diagram: Figure 1 This is a schematic diagram of the external structure of a true triaxial hydraulic fracturing multi-scale monitoring system that integrates acoustic emission, ultrasonic waves and strain linkage according to the present invention. Figure 2 This is a schematic diagram of the overall structure of a cross section of a true triaxial hydraulic fracturing multi-scale monitoring system that integrates acoustic emission, ultrasonic waves and strain linkage according to the present invention. Figure 3 This is a top view of a true triaxial hydraulic fracturing multi-scale monitoring system that integrates acoustic emission, ultrasonic waves and strain linkage according to the present invention. Figure 4This is a schematic diagram of the upper pressure plate of a true triaxial hydraulic fracturing multi-scale monitoring system that integrates acoustic emission, ultrasonic waves and strain linkage according to the present invention. Figure 5 This is a schematic diagram of the pressure plate of a true triaxial hydraulic fracturing multi-scale monitoring system that integrates acoustic emission, ultrasonic waves and strain linkage according to the present invention. Figure 6 This is a schematic diagram of the structure of an ultrasonic array probe, strain gauge and acoustic emission probe arranged on a rock to be tested according to the present invention; Labels in the diagram: 1. Main body of the device; 2. Horizontal stress loading system; 3. Hydraulic servo pump pressure module; 4. Acoustic emission monitoring system; 5. Crack strain monitoring system; 6. Ultrasonic monitoring system; 7. Manual pressurization pump; 8. Control box; 9. Air compressor; 10. Hydraulic servo pump pressure control system; 11. Acoustic emission signal amplifier; 12. Full-information acoustic emission analyzer; 13. Acoustic emission computer; 14. Strain acquisition instrument; 15. Strain acquisition computer; 16. Ultrasonic emission plate; 17. Oscilloscope; 18. Upper pressure plate; 19. Ultra-thin hydraulic jack; 20. Ultra-thin hydraulic jack pad; 21. 100mm cube side pressure plate; 22. 150mm cube side pressure plate; 23. 200mm... Legislative body side pressure plate; 24, 250mm cube side pressure plate; 25, 300mm cube side pressure plate; 26, 100mm cube pad; 27, 150mm cube pad; 28, 200mm cube pad; 29, 250mm cube pad; 30, 300mm cube pad; 31, bidirectional integrated reaction frame; 32, positioning pin; 33, upper pressure plate circular water inlet; 34, side pressure block lifting hole; 35, device main body lifting hole; 36, water inlet pipe hole; 37, ultrasonic wire guide groove; 38, strain gauge wire guide groove; 39, lateral strain gauge wire guide groove; 40, acoustic emission flange; 41, water inlet pipe; 42, strain gauge; 43, ultrasonic array probe; 44, acoustic emission probe device. Detailed Implementation

[0018] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0019] Example: The present invention provides a technical solution, such as... Figures 1-6 As shown, a true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage is provided. This system can apply different principal stress conditions to rocks in three directions, thereby simulating the actual geostress environment. The device utilizes multiple sensing methods, including an ultrasonic array probe 43, strain gauges 42, and an acoustic emission probe device 44, to achieve full-process monitoring of the rock fracturing mechanism. For a clearer explanation of this invention, the relevant terms are defined as follows: axial pressure correspondence... Directional stress; of the two horizontal stresses, the one with the larger value is called the maximum horizontal principal stress, denoted as . The smaller value is called the minimum horizontal principal stress, denoted as . During the loading process, the following should be met: The relationship.

[0020] A true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage includes a main body 1; a horizontal stress loading system 2; a hydraulic servo pump pressure module 3; an acoustic emission monitoring system 4; a fracture strain monitoring system 5; and an ultrasonic monitoring system 6.

[0021] The main body of the device 1 includes a bidirectional integrated reaction frame 31, an upper pressure plate 18, a 300mm cube side pressure plate 25 and a 300mm cube pad 30, a 250mm cube side pressure plate 24 and a 250mm cube pad 29, a 200mm cube side pressure plate 23 and a 200mm cube pad 28, a 150mm cube side pressure plate 22 and a 150mm cube pad 27, and a 100mm cube side pressure plate 21 and a 100mm cube pad 26.

[0022] The horizontal stress loading system 2 includes a two-way integrated reaction frame 31, an ultra-thin hydraulic jack 19, an ultra-thin hydraulic jack pad 20, and a manual pressure pump 7.

[0023] The hydraulic servo pump pressure module 3 includes an air compressor 9, a control box 8, and a hydraulic servo pump pressure control system 10. Fracturing fluid is fed into the control box 8 via a water supply pipe, and the air compressor 9 supplies high-pressure gas to the control box 8 to pressurize the fracturing fluid. The control box 8 is connected to the hydraulic servo pump pressure control system 10 via wires. The fracturing fluid delivery pipeline is connected to the circular water injection port 33 on the upper pressure plate.

[0024] The acoustic emission monitoring module 4 includes a full-information acoustic emission analyzer 12, an acoustic emission computer 13, an acoustic emission signal amplifier 11, and an acoustic emission probe device 44. The ceramic surface of the acoustic emission probe device 44 is in contact with and fixed to the sample surface and installed on the acoustic emission flange 40. It is connected to the acoustic emission signal amplifier 11 through a wire. The acoustic emission signal amplifier 11 is connected to the full-information acoustic emission analyzer 12 through a wire and is controlled and monitored in real time by the acoustic emission computer 13. There are a total of 8 acoustic emission ceramic probes in the hydraulic fracturing test, and the probe numbers are S1, S2, S3, S4, S5, S6, S7, and S8. The two acoustic emission probes S1 and S2 are installed on the first measuring surface of the sample in the X direction, the two acoustic emission probes S5 and S6 are installed on the second measuring surface of the sample in the X direction, the two acoustic emission probes S7 and S8 are installed on the first measuring surface of the sample in the Y direction, and the two acoustic emission probes S3 and S4 are installed on the second measuring surface of the sample in the Y direction. The acoustic emission probes on the first and second sides in the X and Y directions are arranged using a staggered positioning method.

[0025] The crack strain monitoring system 5 includes strain gauges 42, a strain acquisition instrument 14, and a strain acquisition computer 15. For example... Figure 5 As shown, strain gauge 42 is fixedly installed on the surface of the specimen in a predetermined direction in which cracks may form (this direction extends along the water injection hole and is perpendicular to the minimum principal stress). (Direction) Around the water injection pipe 41, four strain gauges 42 are arranged at the four corners of a rectangle with a side length of 50 mm parallel to the sample. Simultaneously, a strain gauge 42 is arranged at 25 mm intervals along the extended sides of two rectangles parallel to the crack. Different numbers of strain gauges 42 are used for samples of different sizes. The strain gauges 42 are connected to the strain acquisition instrument 14 via wires through pre-set strain gauge wire grooves 38 and lateral strain gauge wire grooves 39 on the upper pressure plate 18 and the side pressure plates of each size. Data is then transmitted to the strain acquisition computer 15 via a network cable.

[0026] The ultrasonic monitoring system 6 consists of an ultrasonic array probe 43, an ultrasonic transmitting plate 16, and an oscilloscope 17. Based on the principle of the planar measurement method in ultrasonic measurement, the ultrasonic array probes 43 are arranged in pairs at 30 mm intervals at both ends of the expected crack. Each pair of probes consists of one ultrasonic transmitting probe and one ultrasonic receiving probe. The probes are connected to the ultrasonic transmitting plate 16 via pre-set ultrasonic wire grooves 37 in the upper pressure plate 18, and then the transmitting plate is connected to the oscilloscope 17 to realize the transmission and reception of ultrasonic signals.

[0027] The following is a large-scale triaxial hydraulic fracturing simulation test on a cubic test sample. The test sample is 250mm×250mm×250mm in size. The upper pressure plate 18 and the 250mm cubic pad 29 are both 250mm×250mm in size. The size of the four surrounding pressure plates is slightly smaller than the size of the test sample.

[0028] The main body 1 of the device is placed on the press through the device body lifting hole 35. A pre-fabricated well shaft is then placed at the center of the prepared sample. A water injection pipe 41 is pre-embedded at the simulated well shaft location. Epoxy resin is used to fill and fix the gap between the main water pipe end cap and the well shaft. The sample is then dried and cured for 24 hours, and the sample surface is polished to ensure the bottom surface of the upper pressure plate 18 aligns with the head of the water injection pipe 41. An appropriate amount of ink is injected into the head of the water injection pipe 41 to observe the crack direction after the test. The sample is placed on a 250mm cube pad 29, and the 250mm cube side pressure plate is installed onto the main body 1 through the side pressure block lifting hole 34. The main body 1 is connected to the TAW-2000 via the positioning pin 32 to provide vertical stress. The acoustic emission probe device 44 is installed and connected to the acoustic emission monitoring system 4.

[0029] Align the water injection pipe 41 with the water injection pipe hole 36 and install the upper pressure plate 18 on the top surface of the sample. Strain gauges 42 are fixedly installed on the sample surface in the direction where cracks are likely to form. The strain gauges 42 are connected to the strain acquisition instrument 14 via wires through the upper pressure plate 18 and the pre-set strain gauge 42 wire grooves 38 on each size pressure plate, and then connected to the strain acquisition computer 15 via a network cable. Ultrasonic array probes 43 are arranged in pairs at 30 mm from both ends of the expected crack. The probes are connected to the ultrasonic transmitting plate 16 via the pre-set ultrasonic wire grooves 37 in the upper pressure plate 18, and then connected to the oscilloscope 17 via the transmitting plate to achieve ultrasonic signal transmission and reception. The acoustic emission probe device 44 has its ceramic surface in contact with and fixed to the sample surface, and is connected to the acoustic emission signal amplifier 11 via wires. The acoustic emission signal amplifier 11 is connected to the full-information acoustic emission analyzer 12 via wires and to the acoustic emission computer 13.

[0030] According to the experimental design, samples were set on either the TAW-2000 or MTS-815 and the horizontal stress loading system 2, respectively. direction, direction, Load parameters in three directions; to ensure uniform stress distribution on all surfaces of the specimen, the triaxial stresses are applied sequentially and slowly until the minimum horizontal principal stress is reached during loading. Maximum horizontal principal stress Vertical stress The corresponding values. To prevent eccentric failure of the specimen, the loading process is divided into three stress loading gradients to ensure uniform application of triaxial stress. The vertical stress first reaches the minimum principal stress value, and then the triaxial stress is loaded to the corresponding values ​​in sequence to reach the target pressure. The pressure is then kept stable for hydraulic fracturing test.

[0031] The air compressor 9 delivers the fracturing fluid from the hydraulic servo pump module 3 to the main body 1 of the device, and connects it through the circular water inlet 33 of the upper pressure plate 18.

[0032] The fracturing fluid discharge rate is set using the hydraulic servo pump pressure module 3. The sample size, longitudinal wave velocity, and acoustic emission probe coordinates are set according to the acoustic emission monitoring system 4 to monitor acoustic emission positioning information in real time during the hydraulic fracturing test. The water pressure start option is activated, and the data logger is turned on. Simultaneously, the full-information acoustic emission analyzer 12 is activated, and the acoustic emission signal acquisition is controlled by the acoustic emission computer 13. The water pressure is monitored in real time using the water pressure-time curve displayed by the hydraulic servo pump pressure module 3. After the water pressure reaches its peak and drops for a period of time, the pump pressure is stopped and the recording is turned off, thus ending the hydraulic fracturing indoor test.

[0033] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves and strain linkage, comprising a main body, a horizontal stress loading system, a hydraulic servo pump pressure module, an acoustic emission monitoring system, a fracture strain monitoring system and an ultrasonic monitoring system.

2. The true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage as described in claim 1, characterized in that: The main body of the device and the horizontal stress loading system have an upper pressure plate with a side length of 300mm. Applicable sizes include five types of lower pressure plates and side pressure plates, with dimensions of 300mm, 250mm, 200mm, 150mm, and 100mm. The horizontal stress loading system includes a two-way integrated reaction frame, an ultra-thin hydraulic jack, an ultra-thin hydraulic jack pad, and a manual pressure pump. The manual pressure pump is used to apply circumferential stress to the sample.

3. The true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage as described in claim 1, characterized in that: The hydraulic servo pump pressure module includes an air compressor, a control box, and a hydraulic servo pump pressure control system.

4. The true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage as described in claim 1, characterized in that: The acoustic emission monitoring system includes a full-information acoustic emission signal analyzer, an acoustic emission signal amplifier, and eight acoustic emission ceramic probes, of which two acoustic emission probes are positioned on the rock being tested. First surface of the direction; Two acoustic emission probes are placed on the rock being tested. Second measuring surface in the direction; Two acoustic emission probes are placed on the rock being tested. First surface of the direction; Two acoustic emission probes are placed on the rock being tested. Second measuring surface in the direction; The eight acoustic emission ceramic probes are connected to the acoustic emission signal amplifier via wires; The acoustic emission signal amplifier is connected to the full-information acoustic emission signal acquisition instrument and the computer via wires.

5. The true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage as described in claim 1, characterized in that: The crack strain monitoring system includes n strain gauges, a strain acquisition instrument, and a strain acquisition computer. The strain gauges are fixedly installed on the surface of the sample in a preset direction in which cracks may form. Among them A patch is placed at 25mm intervals along the direction in which cracks may form on the surface, in two... Each strain gauge is placed at 25mm intervals on the directional plane. The strain gauges are connected to the strain acquisition instrument via wires through the strain gauge wire grooves preset on the upper pressure plate and the pressure measuring plates of each size. The data is then transmitted to the strain acquisition computer via a network cable.

6. The true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage as described in claim 1, characterized in that: The ultrasonic monitoring system consists of m ultrasonic array probes, a regulated power supply, and a digital oscilloscope. A total of m ultrasonic array probes are deployed using the planar method, symmetrically distributed at a distance of 30mm from the water injection hole, with the arrangement direction parallel to the expected crack propagation direction. One side is the transmitting probe, and the other side is the receiving probe. m sets of paired ultrasonic probes are arranged on the side of the rock sample along the direction of minimum principal stress. The center of the probe is 30 mm away from the geometric center of the sample. The direction of the measurement line is perpendicular to the vertical principal stress plane. One side is set as the transmitting end and the other side is set as the receiving end. The spacing between adjacent probes in the same row is 35 mm. All ultrasonic probes are connected to a regulated power supply and a digital oscilloscope via connecting cables to achieve stable excitation and high-precision acquisition of ultrasonic signals. The test is performed using the flat test method, in which the transmitting and receiving transducers are placed on the same surface of the sample and effectively coupled by a coupling agent.

7. The true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage as described in claim 1, characterized in that: A true triaxial hydraulic fracturing device and a multi-scale hydraulic fracturing fracture mechanism monitoring method are proposed. The experiment comprehensively monitors the hydraulic fracturing process through an acoustic emission monitoring module, an ultrasonic monitoring module, and a strain gauge array monitoring module. Among them, the acoustic emission system can realize the spatial location of cracks; ultrasonic monitoring is highly sensitive to changes in crack depth and can quantitatively analyze the changes in crack width during crack propagation; the strain gauge array has a fast response speed and is relatively sensitive to the crack initiation time sequence, and can capture the strain change at the moment of crack initiation, so as to realize the quantitative identification and time sequence judgment of crack initiation and propagation behavior in rock mass. The three monitoring methods work together to provide high spatiotemporal resolution data support for the entire process of crack evolution.

8. The true triaxial hydraulic fracturing multi-scale monitoring system integrating acoustic emission, ultrasonic waves, and strain linkage as described in claim 1, characterized in that: The test method for a large-scale triaxial hydraulic fracturing test apparatus includes the following steps: Step 1: Sample Preparation and Loading The design dimension of this device is 300mm. 3 250mm 3 200mm 3 150mm 3 100mm 3 To accommodate multiple sizes, a pre-fabricated wellbore is constructed at the center of the prepared sample. A water injection pipe is pre-embedded at the simulated wellbore location. Epoxy resin is used to fill and fix the gap between the end cap and the wellbore. Finally, the sample is dried and cured for 24 hours, and the sample surface is polished to ensure a proper fit between the pressure head and the water injection pipe head. An appropriate amount of ink is injected into the water injection pipe head to observe the crack direction after the test. The sample is placed in the loading chamber, and four cylindrical pressure pads are placed on the upper pressure plate using positioning pins. One end of the fracturing fluid delivery pipeline is connected to and fixed to the circular water injection port of the upper pressure plate; an acoustic emission probe is installed and connected to the acoustic emission monitoring module; According to the experimental design, samples were set up on both the TAW-2000 and horizontal stress loading systems. , , Load parameters in three directions; to ensure uniform stress on all surfaces of the specimen, the triaxial stress is slowly applied sequentially to the corresponding values ​​of the minimum horizontal principal stress, the maximum horizontal principal stress, and the vertical stress during the loading process. To prevent eccentric failure of the specimen, the loading process is divided into three stress loading gradients to ensure uniform application of the triaxial stress. The vertical stress first reaches the minimum principal stress value, and then the triaxial stress is applied sequentially to the corresponding values ​​to reach the target pressure. The pressure is kept stable for hydraulic fracturing test. Step 2: Conduct triaxial hydraulic fracturing tests An air compressor delivers fracturing fluid from the hydraulic servo pump module to the main body of the device, and connects it through the circular water inlet on the upper pressure plate. The fracturing fluid discharge rate is set through the hydraulic servo pump module. The sample size, longitudinal wave velocity, and acoustic emission probe coordinates are set according to the acoustic emission monitoring system to monitor the acoustic emission positioning information in real time during the hydraulic fracturing test. The water pressure start option is activated and the data logger is turned on. At the same time, the full-information acoustic emission analyzer is turned on to start collecting acoustic emission signals through the acoustic emission computer control system. The water pressure is monitored in real time through the water pressure-time curve displayed by the hydraulic servo pump module. After the water pressure reaches its peak and drops for a period of time, the pump pressure is stopped and the recording is turned off, and the hydraulic fracturing indoor test ends. Step 3: Depressurize and change samples After the triaxial hydraulic fracturing test is completed, data acquisition is stopped and saved. The full-information acoustic emission analyzer, strain acquisition instrument, and oscilloscope are turned off. The water pressure is unloaded to the lower limit, at which point the yellow light on the control box illuminates. The control box is then turned off. The vertical stress, maximum horizontal principal stress, and minimum horizontal principal stress are unloaded in sequence. The connection between the fracturing fluid delivery pipe and the circular water injection port of the upper pressure plate is disconnected. The fracturing fluid in the loading chamber (i.e., the surrounding area) is processed, and the next sample is used for the next test.

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