Rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement method and device

Abstract

The invention provides a rock true triaxial liquid nitrogen circulating fracturing strain and temperature measuring method and device.The rock true triaxial liquid nitrogen circulating fracturing strain and temperature measuring method comprises the steps that a rock sample is obtained, and initialization calibration is conducted on the measuring device; performing liquid nitrogen fracturing operation on the rock sample, and collecting fracturing data in a fracturing process in real time; the fracturing data comprises a DIC image, an infrared thermogram and acoustic emission data; performing data processing on the fracturing data, and constructing a three-dimensional crack network of the rock sample; and in combination with the three-dimensional crack network of the rock sample, establishing a correlation coefficient matrix of the temperature gradient and the strain rate, and determining the contribution degree of low-temperature embrittlement to strain localization. According to the invention, the interference of a low-temperature environment on optical measurement can be avoided, the data processing effect is improved, and the problem of poor measurement precision in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of rock fracturing detection, and in particular to a method and device for measuring strain and temperature of rock true triaxial liquid nitrogen circulation fracturing. Background Art

[0002] Fracturing technology plays a significant role in resource extraction. Compared to hydraulic fracturing, waterless fracturing avoids water pollution and reservoir damage. It also prevents formations containing soft, sticky minerals from absorbing water and expanding, potentially blocking migration pathways. Furthermore, compared to nitrogen fracturing, liquid nitrogen has a wider range of applications. Under normal pressure, liquid nitrogen can reach a temperature of -196°C, with a vaporization expansion temperature of 21°C. Pure nitrogen has an expansion ratio of 696 times, generating enormous pressure within a confined space. Furthermore, liquid nitrogen has a latent heat of vaporization of 5.56 kJ / mol, absorbing a significant amount of surrounding heat upon vaporization. Since most formations contain water, when rock comes into contact with liquid nitrogen, the water in the rock's pores rapidly freezes as the liquid nitrogen vaporizes, absorbing heat. The water-to-ice phase transition results in a volume expansion of approximately 9%, theoretically generating frost heave forces of up to hundreds of megapascals. In addition, as a consumable material, liquid nitrogen has the advantages of simple preparation and wide source of raw materials. In rock mass cyclic fracturing, liquid nitrogen can be used as an economical and efficient refrigeration and permeability-enhancing medium.

[0003] True triaxial testing is considered a key laboratory test for evaluating fracturing efficiency because it can accurately reproduce the mechanical failure behavior of rock under original in-situ stress conditions. Digital image correlation (DIC) and infrared technology can further capture various microscopic parameters of rock. However, due to the low temperature effects of liquid nitrogen, which can cause window deformation and frost, DIC cannot directly observe specimens undergoing liquid nitrogen treatment, making it impossible to fully replicate the loading process.

[0004] There is currently no effective solution to the problem of poor measurement accuracy in existing related technologies. Summary of the Invention

[0005] The present invention provides a rock true triaxial liquid nitrogen circulation fracturing strain and temperature measurement method and device, which are used to solve the defect of poor measurement accuracy in existing related technologies and realize real-time acquisition and deep fusion of multimodal data.

[0006] The present invention provides a method for measuring strain and temperature of rock during true triaxial liquid nitrogen cyclic fracturing, comprising: Obtain rock samples and initialize and calibrate the measuring device; Performing liquid nitrogen fracturing on the rock sample and collecting fracturing data in real time during the fracturing process; the fracturing data includes DIC images, infrared thermal images, and acoustic emission data; Processing the fracturing data to construct a three-dimensional crack network of the rock sample; Combined with the three-dimensional crack network of the rock sample, a correlation coefficient matrix between temperature gradient and strain rate is established to determine the contribution of low-temperature embrittlement to strain localization.

[0007] According to the present invention, a method for measuring strain and temperature of rock by true triaxial liquid nitrogen cyclic fracturing is provided, wherein a rock sample is obtained, comprising: Obtaining a sample rock block, and cutting the sample rock block into a preset shape; Prefabricating a slit on the surface of the sample rock block; the slit is used for injecting liquid nitrogen; A micro resistance wire is pre-embedded on the surface of the sample rock block, and black and white matte speckle and high emissivity coating are sprayed to obtain the rock sample.

[0008] According to a rock true triaxial liquid nitrogen cyclic fracturing strain and temperature measurement method provided by the present invention, initialization and calibration of the measurement device are performed, including: placing the rock sample in the measuring device and applying an initial confining pressure; Acquire the initial state reference image during the confining pressure application process.

[0009] According to a rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement method provided by the present invention, liquid nitrogen fracturing operation is performed on the rock sample, and fracturing data during the fracturing process is collected in real time, including: Perform liquid nitrogen fracturing operations according to preset procedures and simultaneously collect fracturing data; When the acoustic emission energy exceeds the threshold, the high-speed acquisition mode is executed.

[0010] According to a rock true triaxial liquid nitrogen cyclic fracturing strain and temperature measurement method provided by the present invention, data processing is performed on the fracturing data to construct a three-dimensional crack network of the rock sample, including: Performing distortion correction on the DIC image using a pre-built distortion prediction model; The DIC speckle pattern in the frosted area is interpolated and reconstructed using a deep learning image restoration network with a U-Net architecture. performing emissivity compensation and non-uniformity correction on the infrared thermal image, and aligning the timestamps of the infrared thermal image and the DIC image by spline interpolation; The DIC strain field and the infrared thermal map are unified into the specimen global coordinate system through affine transformation, and the three-dimensional crack network of the rock sample is generated by combining the DIC strain concentration area, the infrared low temperature area and the acoustic emission positioning point.

[0011] According to a method for measuring strain and temperature during true triaxial liquid nitrogen cyclic fracturing of rock provided by the present invention, a correlation coefficient matrix between temperature gradient and strain rate is established in combination with the three-dimensional crack network of the rock sample to determine the contribution of low-temperature embrittlement to strain localization, including: determining a crack initiation point of the rock sample during the fracturing process; determining a crack growth rate based on the DIC image of the rock sample; A correlation coefficient matrix between temperature gradient and strain rate is constructed, and the contribution of low-temperature embrittlement of the rock sample to strain localization is determined.

[0012] The present invention further provides a rock true triaxial liquid nitrogen cyclic fracturing strain and temperature measurement device, which is used to implement the rock true triaxial liquid nitrogen cyclic fracturing strain and temperature measurement method described in the first aspect, comprising: True triaxial pressure chamber, used to load rock samples and conduct liquid nitrogen fracturing experiments; a liquid nitrogen injection device, used for injecting liquid nitrogen into the true triaxial pressure chamber; Data acquisition system, used to collect real-time fracturing data during the fracturing process; A digital control storage system, used for processing and storing the fracturing data; A high-speed channel is used for data transmission between the touch storage system and the data acquisition system.

[0013] According to the present invention, a rock true triaxial liquid nitrogen cyclic fracturing strain and temperature measurement device is provided. The liquid nitrogen injection device includes a liquid nitrogen tank, the outlet of the liquid nitrogen tank is connected to a booster pump via a pipeline, the output end of the booster pump is connected to a liquid nitrogen buffer via a pipeline, and the liquid nitrogen buffer is connected to the true triaxial pressure chamber via a pipeline; the pipeline is provided with an electronically controlled valve; The liquid nitrogen injection device further comprises a pressure maintainer, an output end of the pressure maintainer is provided with a reverse discharge valve, and the reverse discharge valve is connected to the true triaxial pressure chamber.

[0014] According to a rock true triaxial liquid nitrogen cyclic fracturing strain and temperature measurement device provided by the present invention, the true triaxial pressure chamber includes a thermal insulation and pressure insulation layer, an air flotation vibration isolation platform is arranged inside the thermal insulation and pressure insulation layer, an observation window is arranged on the side of the thermal insulation and pressure insulation layer, a loading device is arranged inside the thermal insulation and pressure insulation layer, and a liquid nitrogen injection port and a first synchronous controller are arranged on the side of the thermal insulation and pressure insulation layer.

[0015] According to a rock true triaxial liquid nitrogen circulation fracturing strain and temperature measurement device provided by the present invention, the digital control storage system includes a wireless control switchboard and a high-speed storage array connected by signals; The data acquisition system includes a constant temperature box, in which a high-speed camera and an infrared thermal imager are arranged. The high-speed camera and the infrared thermal imager are both provided with a second synchronization controller.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a true triaxial liquid nitrogen cyclic fracturing strain and temperature measurement method for rock. This method utilizes active defrosting techniques, such as pre-embedded micro-resistance wires on the rock specimen surface and an annular heating film installed on the window exterior, along with a U-Net architecture deep learning image restoration network algorithm. This method interpolates and reconstructs DIC speckle patterns in frosted areas, preventing frost buildup on the specimen surface caused by liquid nitrogen injection. This improves DIC speckle recognition and infrared temperature measurement accuracy, enabling optical measurement in low-temperature environments. Furthermore, this method utilizes online real-time calibration (capturing calibration plate images in real time during loading) to dynamically correct camera calibration parameters. Furthermore, elastic compensation based on a distortion prediction model established based on the window stress-strain relationship is used to reversely correct the DIC displacement field, addressing DIC image distortion caused by window deformation under high-pressure loading. This method also employs interpolation synchronization and event-driven triggering to align data timestamps, achieving multimodal data time synchronization. Furthermore, by utilizing a sapphire window with active defrosting, this method overcomes interference with optical measurement caused by the extreme conditions of -196°C and 50 MPa in liquid nitrogen fracturing experiments, achieving high-precision and high-efficiency optical measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is a flow chart of the rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement method provided by the present invention; Figure 2 This is a structural block diagram of the rock true triaxial liquid nitrogen circulation fracturing strain and temperature measurement device provided by the present invention; Figure 3 2 is a schematic structural diagram of a liquid nitrogen injection device according to an embodiment of the present invention; Figure 4 2 is a schematic structural diagram of a true triaxial pressure chamber according to an embodiment of the present invention; Figure 5 1 is a schematic structural diagram of a numerical control storage system according to an embodiment of the present invention; Figure 6 Schematic diagram of the structure of the data acquisition system in an embodiment of the present invention.

[0019] Reference numerals: 1: Liquid nitrogen injection device; 11: Liquid nitrogen tank; 12: Electronically controlled valve; 13: Booster pump; 14: Backflow valve; 15: Liquid nitrogen buffer; 16: Pressure maintainer; 2: True triaxial pressure chamber; 21: Liquid nitrogen injection port; 22: Loading device; 23: Insulation and pressure layer; 24: First synchronous controller; 25: Observation window; 26: Air-float vibration isolation table; 3: CNC storage system; 31: Wireless control switchboard; 32: High-speed storage array; 4: High-speed channel; 5: Data acquisition system; 51: Second synchronous controller; 52: High-speed camera; 53: Infrared thermal imager; 54: Constant temperature chamber. DETAILED DESCRIPTION

[0020] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0021] The present invention provides a method for measuring strain and temperature of rock true triaxial liquid nitrogen cyclic fracturing. Figure 1 The flowchart of the rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement method provided by the present invention is as follows: Figure 1 As shown, the method includes the following steps: Step S101, obtaining a rock sample and initializing and calibrating the measuring device; Step S102, performing liquid nitrogen fracturing operation on the rock sample and collecting fracturing data in real time during the fracturing process; the fracturing data includes DIC images, infrared thermal images and acoustic emission data; Step S103, processing the fracturing data to construct a three-dimensional crack network of the rock sample; Step S104 , combining the three-dimensional crack network of the rock sample, establishing a correlation coefficient matrix between temperature gradient and strain rate, and determining the contribution of low-temperature embrittlement to strain localization.

[0022] In this method, the rock sample required for the experiment is first prepared, and the measurement device used for the experiment is initialized and calibrated to facilitate subsequent calibration of basic parameters such as speckle distribution and surface temperature baseline. The rock sample is then placed in the measurement device and subjected to liquid nitrogen fracturing. Fracturing data is collected in real time during the fracturing process. This fracturing data includes DIC images, infrared thermal images, and acoustic emission data. DIC images characterize the rock sample's full-field displacement, principal strain, and shear strain; infrared thermal images characterize the rock sample's surface temperature distribution, the location of the low-temperature diffusion front, and temperature gradients; and acoustic emission data characterize the rock sample's fracture time, energy, and location coordinates. The fracturing data is then processed to reconstruct a three-dimensional crack network with an accuracy of less than or equal to 0.1 mm. Finally, a correlation coefficient matrix between temperature gradient and strain rate is constructed based on the three-dimensional crack network to determine the contribution of low-temperature embrittlement to strain localization. Through the initial calibration of the measurement device and the multimodal fracturing data acquisition, interference from the low-temperature environment on optical measurements is avoided, data processing is improved, and the poor measurement accuracy currently encountered in related technologies is addressed.

[0023] In some embodiments, step S101, obtaining a rock sample, includes: obtaining a sample rock block and cutting the sample rock block into a preset shape; pre-fabricating a slit on the surface of the sample rock block; the slit is used to inject liquid nitrogen; pre-embedding a micro resistance wire on the surface of the sample rock block, and spraying a black and white matte speckle pattern and a high emissivity coating to obtain a rock sample.

[0024] For example, a uniform and complete sample rock block is cut into several rectangular samples with a length-width-height ratio of 1:1:2 and pre-cut slits are prepared for injection of liquid nitrogen. Then, a power density of 0.5 W / cm is pre-embedded on the surface of the sample rock block. 2 The micro-resistance wire is then sprayed with black and white matte speckle with a diameter of 0.1-0.3 mm and a coverage of 50%-70% (the base is a low-temperature resistant epoxy resin that can withstand temperatures from -200°C to 150°C). Finally, a high-emissivity coating (such as Nextel Velvet Coating811-21, with an emissivity of 0.97) is sprayed on the surface of the sample rock to ensure the accuracy of infrared temperature measurement.

[0025] In some embodiments, step S101, initializing and calibrating the measuring device, includes: placing a rock sample in the measuring device and applying an initial confining pressure; and collecting an initial state reference image during the confining pressure application process.

[0026] Before initial calibration, the optical path of the measuring device needs to be calibrated. Specifically, a laser collimator is used to calibrate the observation angles of the high-speed camera (DIC camera) and the infrared thermal imager to ensure that the center of the field of view coincides with the center of the sample surface. Then, the prefabricated rock sample is installed in the true triaxial pressure chamber, the calibration plate is installed on the inner wall of the true triaxial pressure chamber, and the acoustic emission sensor is installed around the rock sample. Then, the initial confining pressure is applied to 、 ,in, represents the maximum principal stress, represents the intermediate principal stress, Finally, the DIC camera and infrared thermal imager are started to collect the initial state reference image for subsequent calibration of basic parameters such as speckle distribution and surface temperature baseline.

[0027] In some embodiments, step S102, performing liquid nitrogen fracturing operation on the rock sample and collecting fracturing data in real time during the fracturing process, includes: performing the liquid nitrogen fracturing operation according to a preset program and synchronously collecting fracturing data; when the acoustic emission energy exceeds a threshold, executing a high-speed acquisition mode.

[0028] For example, the liquid nitrogen injection device is started, and the fracturing process is performed according to the preset program (such as pressure 10 MPa, pressure release after 5 minutes, and 3 cycles), and the DIC camera is triggered synchronously to record the full-field displacement U x and U y , principal strain and , shear strain Start the infrared thermal imager to record the surface temperature distribution, low temperature diffusion front position and temperature gradient of the rock sample The acoustic emission sensor is activated to record the rock sample's fracture time, energy, and location coordinates. During the loading process, a calibration plate image is captured in real time to dynamically adjust the DIC camera calibration parameters. When the acoustic emission energy exceeds a threshold, all equipment is forced into high-speed acquisition mode. High-speed acquisition mode requires a DIC camera frame rate exceeding 1000 fps and an infrared thermal imager frequency exceeding 100 Hz. All fracturing data is stored in a CNC storage system using a high-speed acquisition card (such as the NI PXIe-5172, with a sampling rate of 1 GB / s).

[0029] In some embodiments, step S103 processes the fracturing data to construct a three-dimensional crack network of the rock sample, including: performing distortion correction on the DIC image through a pre-built distortion prediction model; interpolating and reconstructing the DIC speckle in the frosted area through a deep learning image restoration network with a U-Net architecture; performing emissivity compensation and non-uniformity correction on the infrared thermal image, and aligning the timestamps of the infrared thermal image and the DIC image through a spline interpolation method; unifying the DIC strain field and the infrared thermal image to the global coordinate system of the specimen through an affine transformation, and combining the DIC strain concentration area, the infrared low-temperature area and the acoustic emission positioning point to generate a three-dimensional crack network of the rock sample.

[0030] In this embodiment, the deep learning image restoration network using a U-Net architecture utilizes a neural network with hidden layers. Before use, the network is fed several original images without speckle coverage. Then, speckle is overlaid on the original images, allowing the network to establish a connection between the images before and after the speckle coverage. When the speckle-covered image is fed back into the network, the inverse operation is performed, using the hidden layers to restore the original image.

[0031] For example, the DIC image is corrected for distortion based on the distortion prediction model established based on the calibration plate parameters and the stress-strain relationship of the window, and the DIC speckle in the frosted area is interpolated and reconstructed using a deep learning image restoration network with a U-Net architecture. At the same time, the infrared thermal image is subjected to emissivity compensation, non-uniformity correction, and cubic spline interpolation to align it with the timestamp of the DIC image. Then, the DIC strain field (coordinate system XY) and the infrared thermal image (coordinate system X'-Y') are unified to the global coordinate system of the specimen through affine transformation. The DIC strain concentration area, infrared low-temperature area, and acoustic emission positioning point are combined to reconstruct a three-dimensional crack network with an accuracy of ≤0.1mm.

[0032] In some embodiments, step S104, combining the three-dimensional crack network of the rock sample, establishing a correlation coefficient matrix between the temperature gradient and the strain rate, and determining the contribution of low-temperature embrittlement to strain localization, including: determining the crack initiation point of the rock sample during the fracturing process; determining the crack propagation rate in combination with the DIC image of the rock sample; constructing a correlation coefficient matrix between the temperature gradient and the strain rate, and determining the contribution of low-temperature embrittlement of the rock sample to strain localization.

[0033] For example, when DIC monitors local strain concentration ( ) and the infrared display temperature drops sharply ( ), it is determined to be the crack initiation point, and then the crack growth rate is calculated according to the following formula:

[0034] Where Vc represents the crack growth rate, represents the DIC tracking of the crack tip displacement, Indicates the time interval between adjacent frames. Finally, the temperature gradient is established and strain rate The correlation coefficient matrix of is used to analyze the contribution of low-temperature embrittlement to strain localization.

[0035] In summary, this method utilizes active defrosting techniques, including pre-embedded microresistance wires on the rock specimen surface and an annular heating film installed on the window exterior, along with a U-Net architecture deep learning image inpainting network algorithm. This method interpolates and reconstructs DIC speckle patterns from frosted areas, preventing frost buildup on the specimen surface caused by liquid nitrogen injection. This improves DIC speckle recognition and infrared temperature measurement accuracy, enabling optical measurements in low-temperature environments. Furthermore, this method utilizes online real-time calibration (capturing calibration plate images in real time during loading) to dynamically correct camera calibration parameters. Furthermore, elastic compensation, based on a distortion prediction model based on the window stress-strain relationship, reversely corrects the DIC displacement field, addressing DIC image distortion caused by window deformation under high-pressure loading. This method also employs interpolation synchronization and event-driven triggering to align data timestamps, achieving multimodal data time synchronization. Furthermore, this method, through its active defrosting sapphire window design, overcomes the interference with optical measurements caused by the extreme conditions of -196°C and 50 MPa in liquid nitrogen fracturing experiments, achieving high-precision and high-efficiency optical measurements.

[0036] The present invention also provides a rock true triaxial liquid nitrogen circulation fracturing strain and temperature measurement device. The rock true triaxial liquid nitrogen circulation fracturing strain and temperature measurement device provided by the present invention is described below. The rock true triaxial liquid nitrogen circulation fracturing strain and temperature measurement device described below and the rock true triaxial liquid nitrogen circulation fracturing strain and temperature measurement method described above can be referenced to each other. Figure 2 This is a structural block diagram of the rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement device provided by the present invention, such as Figure 2 As shown, the device includes: True triaxial pressure chamber 2, used to load rock samples and conduct liquid nitrogen fracturing experiments; Liquid nitrogen injection device 1, used to inject liquid nitrogen into the true triaxial pressure chamber; Data acquisition system 5, used for real-time acquisition of fracturing data during the fracturing process; A numerical control storage system 3, used for processing and storing fracturing data; High-speed channel 4 is used for data transmission between the touch storage system and the data acquisition system.

[0037] Figure 3 Schematic diagram of the structure of the liquid nitrogen injection device in the embodiment of the present invention. Figure 3As shown, in some embodiments, the liquid nitrogen injection device 1 includes a liquid nitrogen tank 11, the outlet of the liquid nitrogen tank 11 is connected to a booster pump 13 via a pipeline, the output end of the booster pump 13 is connected to a liquid nitrogen buffer 15 via a pipeline, and the liquid nitrogen buffer 15 is connected to the true triaxial pressure chamber 2 via a pipeline; an electrically controlled valve 12 is provided on the pipeline; the liquid nitrogen injection device 1 also includes a pressure maintainer 16, and a reverse valve 14 is provided at the output end of the pressure maintainer 16, and the reverse valve 14 is connected to the true triaxial pressure chamber 2.

[0038] Figure 4 FIG. 1 is a schematic structural diagram of a true triaxial pressure chamber according to an embodiment of the present invention. Figure 4 As shown, in some embodiments, the true triaxial pressure chamber 2 includes a thermal insulation and pressure-insulating layer 23, an air-floating vibration isolation platform 26 is arranged inside the thermal insulation and pressure-insulating layer 23, an observation window 25 is arranged on the side of the thermal insulation and pressure-insulating layer 23, a loading device 22 is arranged inside the thermal insulation and pressure-insulating layer 23, and a liquid nitrogen injection port 21 and a first synchronous controller 24 are arranged on the side of the thermal insulation and pressure-insulating layer 23.

[0039] In this embodiment, the observation window 25 is a circular observation window made of sapphire glass with a diameter of about 100 mm, a thickness of about 10 mm, a light transmittance of more than 95%, and a pressure resistance of more than 50 MPa. A ring-shaped heating film is installed on the outside of the observation window 25 to achieve active defogging. The vibration isolation frequency of the air-floating vibration isolation table 26 is above 10 Hz, which can eliminate the interference of the press vibration on the optical measurement. In some of these embodiments, Figure 5 As shown, Figure 5 3 is a schematic structural diagram of a numerical control storage system in an embodiment of the present invention. The numerical control storage system 3 includes a wireless control switchboard 31 and a high-speed storage array 32 connected by signals. Figure 6 Schematic diagram of the structure of the data acquisition system in the embodiment of the present invention. Figure 6 As shown, the data acquisition system 5 includes a constant temperature box 54 , in which a high-speed camera 52 and an infrared thermal imager 53 are arranged. Both the high-speed camera and the infrared thermal imager 53 are provided with a second synchronization controller 51 .

[0040] In this embodiment, the data acquisition system 5 uses a DIC camera calibrated by a laser collimator and an infrared thermal imager 53 that matches the surface emissivity of the sample. It is also equipped with a long working distance microscope lens and a multi-device synchronization controller developed based on a field programmable gate array (FPGA) that can synchronize the DIC camera, infrared thermal imager 53 and liquid nitrogen injection timing through transistor-transistor logic (TTL) signals.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for measuring strain and temperature of rock true triaxial liquid nitrogen cyclic fracturing, characterized in that: include: Obtain rock samples and initialize and calibrate the measuring device; Performing liquid nitrogen fracturing on the rock sample and collecting fracturing data in real time during the fracturing process; the fracturing data includes DIC images, infrared thermal images, and acoustic emission data; Processing the fracturing data to construct a three-dimensional crack network of the rock sample; Combined with the three-dimensional crack network of the rock sample, a correlation coefficient matrix between temperature gradient and strain rate is established to determine the contribution of low-temperature embrittlement to strain localization.

2. The rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement method according to claim 1 is characterized in that: Obtain rock samples, including: Obtaining a sample rock block, and cutting the sample rock block into a preset shape; Prefabricating a slit on the surface of the sample rock block; the slit is used for injecting liquid nitrogen; A micro resistance wire is pre-embedded on the surface of the sample rock block, and black and white matte speckle and high emissivity coating are sprayed to obtain the rock sample.

3. The rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement method according to claim 1, characterized in that: Initialize and calibrate the measuring device, including: placing the rock sample in the measuring device and applying an initial confining pressure; Acquire the initial state reference image during the confining pressure application process.

4. The rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement method according to claim 1, characterized in that: Performing liquid nitrogen fracturing on the rock sample and collecting fracturing data in real time during the fracturing process includes: Perform liquid nitrogen fracturing operations according to preset procedures and simultaneously collect fracturing data; When the acoustic emission energy exceeds the threshold, the high-speed acquisition mode is executed.

5. The rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement method according to claim 1, characterized in that: Processing the fracturing data to construct a three-dimensional crack network of the rock sample includes: Performing distortion correction on the DIC image using a pre-built distortion prediction model; The DIC speckle pattern in the frosted area is interpolated and reconstructed using a deep learning image restoration network with a U-Net architecture. performing emissivity compensation and non-uniformity correction on the infrared thermal image, and aligning the timestamps of the infrared thermal image and the DIC image by spline interpolation; The DIC strain field and the infrared thermal map are unified into the specimen global coordinate system through affine transformation, and the three-dimensional crack network of the rock sample is generated by combining the DIC strain concentration area, the infrared low temperature area and the acoustic emission positioning point.

6. The rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement method according to claim 1, characterized in that: Combined with the three-dimensional crack network of the rock sample, a correlation coefficient matrix between temperature gradient and strain rate is established to determine the contribution of low-temperature embrittlement to strain localization, including: determining a crack initiation point of the rock sample during the fracturing process; determining a crack growth rate based on the DIC image of the rock sample; A correlation coefficient matrix between temperature gradient and strain rate is constructed, and the contribution of low-temperature embrittlement of the rock sample to strain localization is determined.

7. A rock true triaxial liquid nitrogen cyclic fracturing strain and temperature measurement device, used to implement the rock true triaxial liquid nitrogen cyclic fracturing strain and temperature measurement method according to any one of claims 1 to 6, characterized in that: include: A true triaxial pressure chamber (2) for loading rock samples and conducting liquid nitrogen fracturing experiments; A liquid nitrogen injection device (1) for injecting liquid nitrogen into the true triaxial pressure chamber; A data acquisition system (5) for collecting real-time fracturing data during the fracturing process; A numerical control storage system (3), used for processing and storing the fracturing data; A high-speed channel (4) is used for data transmission between the touch storage system and the data acquisition system.

8. The rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement device according to claim 7, characterized in that: The liquid nitrogen injection device (1) comprises a liquid nitrogen tank (11), the outlet of the liquid nitrogen tank (11) is connected to a booster pump (13) via a pipeline, the output end of the booster pump (13) is connected to a liquid nitrogen buffer (15) via a pipeline, and the liquid nitrogen buffer (15) is connected to the true triaxial pressure chamber (2) via a pipeline; an electric control valve (12) is provided on the pipeline; The liquid nitrogen injection device (1) further comprises a pressure maintainer (16), an output end of the pressure maintainer (16) being provided with a backflow valve (14), and the backflow valve (14) being connected to the true triaxial pressure chamber (2).

9. The rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement device according to claim 7, characterized in that: The true triaxial pressure chamber (2) comprises a heat-insulating and pressure-insulating layer (23), an air-floating vibration isolation platform (26) is provided inside the heat-insulating and pressure-insulating layer (23), an observation window (25) is provided on the side of the heat-insulating and pressure-insulating layer (23), a loading device (22) is provided inside the heat-insulating and pressure-insulating layer (23), and a liquid nitrogen injection port (21) and a first synchronous controller (24) are provided on the side of the heat-insulating and pressure-insulating layer (23).

10. The rock true triaxial liquid nitrogen cycle fracturing strain and temperature measurement device according to claim 7, characterized in that: The numerical control storage system (3) includes a wireless control switchboard (31) and a high-speed storage array (32) connected by signals; The data acquisition system (5) includes a constant temperature box (54), a high-speed camera (52) and an infrared thermal imager (53) are arranged in the constant temperature box (54), and a second synchronization controller (51) is arranged on both the high-speed camera and the infrared thermal imager (53).

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