Visual experiment device, system and method for conventional triaxial hydraulic fracturing

Abstract

The invention discloses a visual experimental device, system and experimental method for conventional triaxial hydraulic fracturing, which can simulate and visualize the triaxial hydraulic fracturing process under controllable conditions by applying confining pressure and axial stress to an experimental sample and injecting fracturing fluid to simulate fracturing, thereby improving the predictability and efficiency of field operation. A radioisotope tracer detection imaging technology is used for monitoring the crack expansion process in real time, direct crack dynamic data are provided through comprehensive and real-time monitoring of a radioactivity detection probe and a detection imaging system, rock responses under different fracturing parameters can be predicted, and therefore a fracturing scheme with the highest cost benefit is selected; according to the invention, the formation and expansion of cracks in the experimental rock sample can be comprehensively observed in real time; the device is suitable for the industries of rock mechanics and petroleum engineering, and is used for simulating and monitoring the cracking and crack propagation process of experimental rock samples.

Description

Technical Field

[0001] This invention belongs to the field of rock hydraulic fracturing, specifically a visualization experimental device, system and experimental method for conventional triaxial hydraulic fracturing. Background Technology

[0002] Hydraulic fracturing is one of the key technologies for enhancing oil and gas production in unconventional reservoirs. Because hydraulic fracturing often operates at depths of several kilometers or more, directly observing the propagation of fracturing fractures during oil and gas extraction is extremely difficult. Existing hydraulic fracturing experimental grippers are made of opaque metallic materials, which affects the real-time observation and capture of the fracturing process and fracture propagation during experiments.

[0003] Utility model patent CN216247530U discloses a lightweight and visual hydraulic fracturing test demonstration device, including an upper and lower pressure plate made of acrylic material, as well as fastening bolts set at the edges. An acrylic rectangular frame is located inside, with T-bolt components on the front and left sides of the rectangular frame. A flat rock plate is placed inside the frame, and a fracturing tube is installed inside the rock plate. The fracturing tube protrudes from a through-hole in the upper pressure plate and is connected to a hand pump via a hose. A non-contact monitoring device is located above the rock plate and the upper pressure plate. In this patent, the upper and lower pressure plates and the rectangular frame are made of acrylic, allowing for real-time transparent observation of the hydraulic fracturing process of the experimental rock sample. However, the limitation of this device is that the sample itself is opaque, making it impossible to observe the propagation process of the hydraulic fractures inside the sample.

[0004] Chinese patent application CN111946318B discloses a multi-cluster synchronous fracturing visualization simulation device, system, and manufacturing method. The device includes: a transparent sample with blind holes drilled horizontally, and pre-fabricated initial fractures on the sample, with a preset distance between adjacent initial fractures; a camera fixedly installed inside the pre-drilled hole; and a simulated casing fixedly installed inside the blind holes, with injection holes on the simulated casing corresponding to the opening of each initial fracture. The first end of the simulated casing is a blind end, and the second end is used to connect to a hydraulic fracturing system. In this device, the sample is transparent and visible, and observation of the dynamic propagation of hydraulic fractures can be achieved simply by installing a camera to directly photograph the sample. However, the patent has the following problems: First, the sample support platform needs to apply confining pressure to the simulated rock sample, at which time the experimental sample will be completely covered, which limits the installation space of the camera device; Second, the components of the confining pressure loading system of the device are usually steel structures, which are prone to insufficient light after being covered, reducing the imaging quality; Third, when hydraulic cracks develop, they can extend in three-dimensional space, and the camera device cannot achieve full coverage of the shooting angle.

[0005] In summary, existing hydraulic fracturing experimental devices cannot provide real-time and comprehensive observation of the formation and propagation of hydraulic fracturing fractures in experimental rock samples. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a visualization experimental device, system, and method for conventional triaxial hydraulic fracturing, so as to achieve real-time and comprehensive observation of the formation and propagation of fractures within experimental rock samples.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A visualization experimental setup for conventional triaxial hydraulic fracturing includes: A transparent pressure chamber with a hollow interior. A fixed base is fixed at both the top and bottom of the transparent pressure chamber, and the fixed base is sealed to the transparent pressure chamber. The experimental specimen is placed inside a transparent pressure chamber. A base is fixed at both the top and bottom of the experimental specimen. A pressure plate is placed between the base and the fixed seat. A groove extending vertically is provided at the top of the experimental specimen, and a fracturing tube is placed in the groove. The tracer assembly, used to monitor fracture propagation, includes a fluid delivery component, a high-pressure pipeline, a fracturing fluid storage device, and a radioactive detection probe. The output end of the fluid delivery component is connected to the input end of the fracturing fluid storage device via a high-pressure pipeline, and the output end of the fracturing fluid storage device is connected to the fracturing pipe via a high-pressure pipeline. The fracturing fluid in the fracturing fluid storage device contains a radioactive tracer, and the radioactive detection probe is mounted on a transparent pressure chamber to track the fracturing fluid. The loading system includes a first loading part and a second loading part. The first loading part is a linear drive element, the output end of which is connected to a pressure plate at the bottom of the test specimen to apply axial stress to the test specimen. The second loading part includes a hydraulic oil storage device and an oil pipeline. The input end of the oil pipeline is connected to the hydraulic oil storage device, and the output end of the oil pipeline extends between the transparent pressure chamber and the test specimen to apply confining pressure to the test specimen.

[0008] As a limitation of the present invention, a plurality of radioactive detection probes are provided, which are spaced apart on the side wall of the transparent pressure chamber.

[0009] As a further limitation of the present invention: the bottom end of the transparent pressure chamber is sealed with a protective seat, and the protective seat and the fixed seat are in contact with the side inside the transparent pressure chamber.

[0010] As a further limitation of the present invention: an oil pipe clamp is provided on the fixed seat at the bottom of the transparent pressure chamber, corresponding to the position of the oil pipeline. The oil pipe clamp penetrates the protective seat vertically and is used to fix the output end of the oil pipeline.

[0011] As another limitation of the invention: the transparent pressure chamber is made of polycarbonate material.

[0012] As a further limitation of the present invention, it also includes a loading frame, with a transparent pressure chamber fixed inside the loading frame.

[0013] The present invention also provides a visualization experimental system for conventional triaxial hydraulic fracturing, including a computer control system, a detection and imaging system, a servo control hydraulic system, and a visualization experimental device for conventional triaxial hydraulic fracturing; The radioactive detection probe is electrically connected to the input of the detection imaging system, the output of the detection imaging system is electrically connected to the input of the computer control system, the output of the computer control system is electrically connected to the input of the servo control hydraulic system, the output of the servo control hydraulic system is electrically connected to the input of the hydraulic oil storage device, and the output of the computer control system is electrically connected to the input of the liquid delivery component.

[0014] This invention also provides a visualization experimental method for conventional triaxial hydraulic fracturing, which includes the following steps: S1. Start the servo-controlled hydraulic system. The servo-controlled hydraulic system drives the first loading part to work. The first loading part applies axial stress to the experimental sample, so that the pressure plate presses the experimental sample tightly. S2. Restart the servo-controlled hydraulic system. First, drive the second loading unit to work, so that the hydraulic oil in the hydraulic oil storage device enters the space between the transparent pressure chamber and the test sample through the oil pipeline, and applies confining pressure to the test sample until the confining pressure is loaded to the experimental design value. Second, drive the first loading unit to work, and apply axial stress to the test sample until the axial stress is also loaded to the experimental design value. S3. Activate the liquid delivery system to input the fracturing fluid containing the radioactive tracer from the fracturing fluid storage device into the test sample; S4. Activate the detection imaging system to display the flow spread data and three-dimensional image of the fracturing fluid transmitted in real time by the radioactive detection probe; and record the stress, strain and injection pressure data through the data acquisition system of the detection imaging system. S5. Inject fracturing fluid into the test specimen at a constant rate until the test specimen is fractured; after the test specimen is fractured, stop injecting fracturing fluid, release the confining pressure and axial stress, turn off the radioactivity detection probe, remove the test specimen, and the experiment ends. S6. Use a computer control system to process and analyze the data collected in step S4, observe the real-time stress-strain curves and crack propagation images during the fracturing process, and analyze the experimental results.

[0015] By adopting the above technical solution, the beneficial effects achieved by the present invention compared with the prior art are as follows: (1) This invention provides a visualization experimental device, system and experimental method for conventional triaxial hydraulic fracturing. By applying confining pressure and axial stress to the experimental sample and injecting fracturing fluid to simulate fracturing, the triaxial hydraulic fracturing process can be simulated and visualized under controllable conditions, thereby improving the predictability and efficiency of on-site operation. The radioactive isotope tracer detection imaging technology is used to monitor the crack propagation process in real time. The radioactive detection probe and detection imaging system provide direct dynamic data of cracks in a comprehensive and real-time manner, which helps the staff of actual engineering to better understand the formation and propagation of cracks, thereby better understanding the crack propagation mechanism and adjusting the fracturing strategy accordingly. (2) This invention verifies and optimizes the fracturing scheme through indoor experiments in advance, which can identify the most effective fracturing parameters before actual application, reduce the number of trial and error in on-site operation, reduce the waste of resources and time, thereby reducing the overall mining cost and reducing potential environmental hazards, such as reducing groundwater pollution and surface disturbance, thus making it more environmentally friendly.

[0016] In summary, this invention enables real-time and comprehensive observation of the formation and propagation of cracks within experimental rock samples; it is applicable to the rock mechanics and petroleum engineering industries, and is used to simulate and monitor the cracking and crack propagation process of experimental rock samples. Attached Figure Description

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0018] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the fracturing fluid storage device in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the linear drive element and the tubing sleeve in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the structure of Embodiment 2 of the present invention.

[0019] In the diagram: 1-Detection and imaging system, 2-Servo control hydraulic system, 3-Cooling device, 4-Hydraulic oil storage device, 5-Fracturing fluid storage device, 51-Outer shell, 52-Moving rod, 53-Fracturing fluid, 6-Fracturing pipe, 7-Transparent pressure chamber, 8-Radioactive detection probe, 9-Base, 10-Pressure plate, 11-Protective seat, 12-Fixed seat, 13-Linear drive element, 131-Piston rod, 14-Tube clamp, 15-Horizontal flow pump, 16-Experimental sample, 17-Loading frame, 18-Computer control system, 19-High pressure pipeline, 20-Confined pressure oil pipeline, 21-Axial load oil pipeline. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the conventional triaxial hydraulic fracturing visualization experimental apparatus, system, and experimental method described herein are preferred embodiments and are only used for illustration and explanation of the present invention, and do not constitute a limitation thereof.

[0021] Example 1: Visual experimental setup for conventional triaxial hydraulic fracturing like Figures 1-3 As shown, this embodiment includes a transparent pressure chamber 7, an experimental sample 16, a tracer assembly, a loading system, and a loading frame 17.

[0022] The transparent pressure chamber 7 is fixed inside the loading frame 17 and located in the center of the loading frame 17. In this embodiment, the transparent pressure chamber 7 is made of polycarbonate material, which does not affect observation and can withstand high pressure. Of course, the transparent pressure chamber 7 can also be made of other transparent materials, such as high-strength glass. A fixing seat 12 is fixed at both the top and bottom of the transparent pressure chamber 7, and the fixing seat 12 is sealed to the transparent pressure chamber 7.

[0023] like Figure 1 As shown, the transparent pressure chamber 7 is hollow inside, and the experimental sample 16 is placed inside the transparent pressure chamber 7. A base 9 is fixed to both the top and bottom of the experimental sample 16. A pressure plate 10 is placed between the base 9 and the fixing seat 12. A groove extending vertically is provided at the top of the experimental sample 16, and a fracturing tube 6 is placed inside the groove. In this embodiment, the experimental sample 16 is a cylindrical rock sample with dimensions of 50mm × 100mm, where 50mm is the diameter of the experimental sample 16 and 100mm is the height of the experimental sample 16. According to the standards of the International Society for Petrology, the parallelism of the upper and lower surfaces of the experimental sample 16 is controlled to 0.5mm, and the flatness of the sidewall surface is controlled to 0.1mm. The groove at the top of the experimental sample 16 has a diameter Φ = 6mm and a height H = 50mm. The fracturing tube 6 is bonded to the groove of the experimental sample 16. It should be noted that in this embodiment, the experimental sample 16 is wrapped with a transparent heat shrink tubing to prevent the residue from falling into the transparent pressure chamber 7 after the experimental sample 16 is fractured, and to facilitate the removal of the experimental sample 16 after the fracture test.

[0024] The tracer assembly is used to monitor fracture propagation. The tracer assembly includes a liquid delivery component, a high-pressure pipeline 19, a fracturing fluid storage device 5, and a radioactive detection probe 8.

[0025] In this embodiment, the liquid delivery component uses a conventional horizontal flow pump 15. The output end of the liquid delivery component is connected to the input end of the fracturing fluid storage device 5 via a high-pressure pipe 19. The output end of the fracturing fluid storage device 5 is also connected to the fracturing pipe 6 via a high-pressure pipe 19. Here, the high-pressure pipe 19 passes through the pressure plate 10 located at the top and is threadedly connected to the top of the fracturing pipe 6. Figure 2 As shown, the fracturing fluid storage device 5 includes a housing 51 and a movable rod 52. The movable rod 52 is slidably and sealed within the housing 51. The fracturing fluid 53 is stored in the cavity on the left side formed by the housing 51 and the movable rod 52. The fracturing fluid 53 contains a radioactive tracer, which here refers to a radioactive isotope tracer. Figure 1 As shown, the radioactive detection probe 8 is mounted on the transparent pressure chamber 7 and is used to track the fracturing fluid 53. In use, the horizontal flow pump 15 injects liquid into the cavity on the right side of the chamber formed by the outer casing 51 and the movable rod 52. The liquid pushes the movable rod 52 to the left, thereby injecting the fracturing fluid 53 into the fracturing tube 6 at the top of the experimental sample 16. When the experimental sample 16 is fractured by the fracturing fluid 53 containing the radioactive isotope tracer injected through the fracturing tube 6, the radioactive isotope tracer penetrates the fracture and is tracked by the radioactive detection probe 8.

[0026] In this embodiment, eight radioactive detection probes 8 are provided, with four on each side of the transparent pressure chamber 7. The four radioactive detection probes 8 on each side are spaced apart to comprehensively and in real time monitor the formation and propagation of cracks. Of course, the number of radioactive detection probes 8 can also be set to two, four, or other numbers according to actual needs.

[0027] The loading system includes a first loading unit and a second loading unit, such as... Figure 1 , 3As shown, the first loading part is a linear drive element 13. In this embodiment, the linear drive element 13 adopts a hydraulic piston cylinder in the prior art. The output end of the linear drive element 13 is connected to the pressure plate 10 at the bottom of the experimental specimen 16, that is, the piston rod 131 passes through the fixed seat 12 at the bottom and is fixedly connected to the pressure plate 10, which is used to apply axial stress to the experimental specimen 16. The second loading part includes a hydraulic oil storage device 4 and an oil pipeline. The input end of the oil pipeline is connected to the hydraulic oil storage device 4, and the output end of the oil pipeline extends into the space between the transparent pressure chamber 7 and the experimental specimen 16, which is used to apply confining pressure to the experimental specimen 16. In this embodiment, a cooling device 3 is provided above the hydraulic oil storage device 4 to ensure a stable and continuous supply of high-pressure liquid. The cooling device 3 is prior art and will not be described in detail here. In this embodiment, the oil pipeline includes a confining pressure oil pipeline 20 and an axial load oil pipeline 21. The input end of the linear drive element 13 is connected to the hydraulic oil storage device 4 through the axial load oil pipeline 21. When the hydraulic oil enters the linear drive element 13, it pushes the piston rod 131 to move upward and applies axial stress to the experimental sample 16.

[0028] To prevent the piston rod 131 from damaging the fixed seat 12 at the bottom when it moves, a protective seat 11 is sealed at the bottom of the transparent pressure chamber 7 in this embodiment. The protective seat 11 and the fixed seat 12 are in contact with the side inside the transparent pressure chamber 7. That is, the protective seat 11 is fixed to the bottom inside the transparent pressure chamber 7. The piston rod 131 passes through the fixed seat 12 and the protective seat 11 and is fixedly connected to the pressure plate 10.

[0029] In this embodiment, two confining pressure oil delivery pipes 20 are provided. When hydraulic oil enters the space between the transparent pressure chamber 7 and the experimental specimen 16 through the two confining pressure oil delivery pipes 20, confining pressure is applied to the experimental specimen 16, which is the radial pressure. In this embodiment, one of the two confining pressure oil delivery pipes 20 extends into the left cavity formed by the transparent pressure chamber 7 and the experimental specimen 16, and the other extends into the right cavity formed by the transparent pressure chamber 7 and the experimental specimen 16. In order to fix the confining pressure oil delivery pipe 20, a pipe clamp 14 is provided on the fixing seat 12 at the bottom of the transparent pressure chamber 7 at the position corresponding to the confining pressure oil delivery pipe 20. The pipe clamp 14 vertically penetrates the protective seat 11 and is used to fix the output end of the confining pressure oil delivery pipe 20. Here, the output end refers to the end of the confining pressure oil delivery pipe 20 that extends into the transparent pressure chamber 7.

[0030] In this embodiment, the horizontal flow pump 15 pumps liquid into the fracturing fluid storage device 5, causing the movable rod 52 to move to the left, allowing the fracturing fluid 53 containing the radioactive isotope tracer to flow into the experimental sample 16. The radioactive detection probe 8 then tracks the flow, enabling monitoring of fracture formation and propagation. The hydraulic oil storage device 4 drives the piston rod 131 in the hydraulic piston cylinder to move upward, applying axial stress to the experimental sample 16. The hydraulic oil storage device 4 also supplies hydraulic oil through the confining pressure oil supply pipe 20 between the transparent pressure chamber 7 and the experimental sample 16, applying confining pressure to the experimental sample 16.

[0031] This embodiment can apply triaxial stress to the experimental specimen 16 and observe the dynamic failure process and deformation of the internal structure of the rock under stress in real time.

[0032] Example 2: Visual Experimental System for Conventional Triaxial Hydraulic Fracturing like Figure 4 As shown, this embodiment includes a computer control system 18, a detection imaging system 1, a servo control hydraulic system 2, and also includes Embodiment 1.

[0033] The radioactive detection probe 8 is electrically connected to the input terminal of the detection imaging system 1, the output terminal of the detection imaging system 1 is electrically connected to the input terminal of the computer control system 18, the output terminal of the computer control system 18 is electrically connected to the input terminal of the servo control hydraulic system 2, and the output terminal of the servo control hydraulic system 2 is electrically connected to the input terminal of the hydraulic oil storage device 4.

[0034] The radioactive detection probe 8 is used in conjunction with the detection imaging system 1 to acquire dynamic three-dimensional images of the fracturing process. The detection imaging system 1 is connected to the servo-controlled hydraulic system 2. The detection imaging system 1 includes a control panel and a radioactive detection platform. The radioactive detection probe 8 transmits monitoring data to the radioactive detection platform via a communication cable to achieve real-time monitoring.

[0035] The output of the computer control system 18 is also electrically connected to the input of the liquid delivery component (i.e., the horizontal flow pump 15). The computer control system 18 controls the pressure loading and the injection rate of the fracturing fluid 53 through dedicated software, and processes and stores the collected data in real time. Here, dedicated software refers to the triaxial hydraulic fracturing control system.

[0036] Since the computer control system 18, the detection and imaging system 1, and the servo control hydraulic system 2 are all existing technologies, their internal structure and working principle will not be described in detail in this embodiment.

[0037] This embodiment enables real-time observation and recording of rock fracture propagation under triaxial stress and hydraulic fracturing, achieving three-dimensional imaging of dynamic fracture propagation and providing an important experimental tool for the study of hydraulic fracturing mechanisms. The introduction of the radioactive detection probe 8 and the detection imaging system 1 also allows for real-time monitoring and visualization of changes in the internal microstructure of the rock.

[0038] Example 3: Visual Experimental Method for Conventional Triaxial Hydraulic Fracturing This embodiment uses Embodiment 2, and includes the following steps: S1. Start the servo-controlled hydraulic system 2. The servo-controlled hydraulic system 2 drives the first loading part to work. The first loading part applies axial stress to the test specimen 16, so that the piston rod 131 of the hydraulic piston cylinder applies axial pressure to the test specimen 16, so that the pressure plate 10 presses the test specimen 16, ensuring that the test specimen 16 is fixed between the two pressure plates 10.

[0039] S2. Restart the servo-controlled hydraulic system 2. First, drive the second loading unit to work, so that the hydraulic oil in the hydraulic oil storage device 4 enters the space between the transparent pressure chamber 7 and the test specimen 16 through the confining pressure oil pipeline 20, and applies confining pressure to the test specimen 16 until the confining pressure is loaded to the experimental design value, that is, the confining pressure is loaded to the minimum horizontal principal stress. Second, drive the first loading unit to work, and apply axial stress to the test specimen 16 until the axial stress is also loaded to the experimental design value, that is, the axial stress is loaded to the vertical stress.

[0040] S3. The computer control system 18 is used to start the liquid delivery device, that is, the horizontal flow pump 15 is working, and the fracturing fluid 53 containing the radioactive tracer in the fracturing fluid storage device 5 is input into the experimental sample 16. S4. Start the detection imaging system 1, display the flow spread data and three-dimensional image of the fracturing fluid 53 transmitted in real time by the radioactive detection probe 8 on the detection imaging system 1; and record the stress, strain and injection pressure data through the data acquisition system in the detection imaging system 1. S5. Inject fracturing fluid 53 into the test sample 16 at a constant rate until the test sample 16 is fractured; after the test sample 16 is fractured, stop injecting fracturing fluid 53, release the confining pressure and axial stress, turn off the radioactivity detection probe 8, take out the test sample 16, and the experiment ends. S6. Use the computer control system 18 to process and analyze the data collected in step S4, observe the real-time stress-strain curves and crack propagation images during the fracturing process, and analyze the experimental results.

[0041] In this embodiment, the monitoring data obtained by the detection and imaging system 1 using radioactive isotope tracers has three-dimensional characteristics, which can directly realize the real-time dynamic expansion of hydraulic fractures in three-dimensional space. This eliminates the need for reprocessing the sample after fracturing and reprocessing the post-fracturing rock sample photos in the traditional experimental process, making it more accurate and eliminating the problem of human interference with the actual situation of the fractures.

[0042] It should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above 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 visualization experimental apparatus for conventional triaxial hydraulic fracturing, characterized in that, include: A transparent pressure chamber with a hollow interior. A fixed base is fixed at both the top and bottom of the transparent pressure chamber, and the fixed base is sealed to the transparent pressure chamber. The experimental specimen is placed inside a transparent pressure chamber. A base is fixed at both the top and bottom of the experimental specimen. A pressure plate is placed between the base and the fixed seat. A groove extending vertically is provided at the top of the experimental specimen, and a fracturing tube is placed in the groove. The tracer assembly, used to monitor fracture propagation, includes a fluid delivery system, a high-pressure pipeline, a fracturing fluid storage device, and a radioactive detection probe. The output end of the fluid delivery system is connected to the input end of the fracturing fluid storage device via a high-pressure pipeline, and the output end of the fracturing fluid storage device is connected to the fracturing pipe via a high-pressure pipeline. The fracturing fluid in the fracturing fluid storage device contains a radioactive tracer, and the radioactive detection probe is mounted on a transparent pressure chamber to track the fracturing fluid. The loading system includes a first loading part and a second loading part. The first loading part is a linear drive element, the output end of which is connected to a pressure plate at the bottom of the test specimen to apply axial stress to the test specimen. The second loading part includes a hydraulic oil storage device and an oil pipeline. The input end of the oil pipeline is connected to the hydraulic oil storage device, and the output end of the oil pipeline extends into the space between the transparent pressure chamber and the test specimen to apply confining pressure to the test specimen.

2. The visualization experimental apparatus for conventional triaxial hydraulic fracturing according to claim 1, characterized in that, Multiple radioactive detection probes are provided and are spaced apart on the side wall of the transparent pressure chamber.

3. The visualization experimental apparatus for conventional triaxial hydraulic fracturing according to claim 2, characterized in that, The bottom of the transparent pressure chamber is sealed with a protective seat, which contacts the fixed seat on the side inside the transparent pressure chamber.

4. The visualization experimental apparatus for conventional triaxial hydraulic fracturing according to claim 3, characterized in that, An oil pipe clamp is installed on the fixed base at the bottom of the transparent pressure chamber, corresponding to the position of the oil pipeline. The oil pipe clamp penetrates vertically through the protective base and is used to fix the output end of the oil pipeline.

5. The conventional triaxial hydraulic fracturing visualization experimental apparatus according to any one of claims 1-4, characterized in that, The transparent pressure chamber is made of polycarbonate material.

6. The visualization experimental apparatus for conventional triaxial hydraulic fracturing according to claim 5, characterized in that, It also includes a loading frame, with a transparent pressure chamber fixed inside the loading frame.

7. A visualization experimental system for conventional triaxial hydraulic fracturing, characterized in that, It includes a computer control system, a detection and imaging system, a servo control hydraulic system, and a conventional triaxial hydraulic fracturing visualization experimental device according to any one of claims 1 to 6; The radioactive detection probe is electrically connected to the input of the detection imaging system, the output of the detection imaging system is electrically connected to the input of the computer control system, the output of the computer control system is electrically connected to the input of the servo control hydraulic system, the output of the servo control hydraulic system is electrically connected to the input of the hydraulic oil storage device, and the output of the computer control system is electrically connected to the input of the liquid delivery component.

8. A visual experimental method for conventional triaxial hydraulic fracturing, characterized in that, The method employs the visualization experimental system for conventional triaxial hydraulic fracturing as described in claim 7, and includes the following steps: S1. Start the servo-controlled hydraulic system. The servo-controlled hydraulic system drives the first loading part to work. The first loading part applies axial stress to the experimental sample, so that the pressure plate presses the experimental sample tightly. S2. Restart the servo-controlled hydraulic system. First, drive the second loading unit to work, so that the hydraulic oil in the hydraulic oil storage device enters the space between the transparent pressure chamber and the test sample through the oil pipeline, and applies confining pressure to the test sample until the confining pressure is loaded to the experimental design value. Second, drive the first loading unit to work, and apply axial stress to the test sample until the axial stress is also loaded to the experimental design value. S3. Activate the liquid delivery system to input the fracturing fluid containing the radioactive tracer from the fracturing fluid storage device into the test sample; S4. Activate the detection imaging system to display the flow spread data and three-dimensional image of the fracturing fluid transmitted in real time by the radioactive detection probe; and record the stress, strain and injection pressure data through the data acquisition system of the detection imaging system. S5. Inject fracturing fluid into the test specimen at a constant rate until the test specimen is fractured; after the test specimen is fractured, stop injecting fracturing fluid, release the confining pressure and axial stress, turn off the radioactivity detection probe, remove the test specimen, and the experiment ends. S6. Use a computer control system to process and analyze the data collected in step S4, observe the real-time stress-strain curves and crack propagation images during the fracturing process, and analyze the experimental results.

Images