Rock crack surface damage deformation experimental device and experimental method thereof

Abstract

The embodiment of the invention provides a rock crack surface damage deformation experimental device and an experimental method thereof. The rock crack surface damage deformation experimental device comprises a clamping device, a heating assembly, a pressure applying assembly, an injection assembly and a detection assembly. The clamp holder is provided with a cavity and two flow channels, the cavity is used for accommodating a rock to be measured and separating the rock to be measured between the two flow channels, and each flow channel is communicated with the outside and the cavity; the heating assembly is arranged on the clamping device; the pressure applying assembly is arranged in the cavity; the injection assembly communicates with the runner; the detection assembly is provided with a plurality of measuring parts which are sequentially arranged in the fluid flowing direction, and each measuring part at least can measure the dependent variable of the rock to be measured at the position where the measuring part is located in real time. According to the scheme, a reliable basis can be provided for deeply researching the strain characteristics and the deformation mechanism of the high-temperature rock subjected to low-temperature impact, and specific data of crack deformation caused by low-temperature impact and evolution of related deformation in the injection-production process of the enhanced geothermal system can be conveniently defined.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of experimental devices, in particular to a rock crack surface damage deformation experimental device and an experimental method thereof. BACKGROUND

[0002] An enhanced geothermal system (EGS) is a system that uses high-pressure fluid to fracture a dense rock mass and form an artificial fracture network by drilling into a hot dry rock mass at 150-400℃. These fractures convert the originally impermeable hot dry rock into a man-made heat reservoir that allows the circulating working medium to continuously absorb heat, thereby realizing the economic exploitation of low-permeability high-temperature rock mass.

[0003] In the related art, the experimental exploration of the deformation mechanism of high-temperature rock cracks under low-temperature impact is usually completed by analyzing the data such as the fracture toughness and elastic modulus of the rock after the experiment, or discussing the crack morphology of the rock after the experiment. However, the change mechanism of the thermal stress of high-temperature rock under low-temperature impact cannot be monitored in real time, and it is not clear how much the crack surface deforms under the action of low-temperature impact, which is not conducive to establishing the relevant constitutive model and numerical model of crack deformation. SUMMARY

[0004] The rock crack surface damage deformation experimental device and the experimental method thereof provided by the embodiments of the present application are used to solve the problem that in the experimental exploration of the deformation mechanism of high-temperature rock cracks under low-temperature impact in the related art, the change mechanism of the thermal stress of high-temperature rock under low-temperature impact cannot be monitored in real time, and it is not conducive to establishing the relevant constitutive model and numerical model of crack deformation.

[0005] In a first aspect, the embodiments of the present application provide a rock crack surface damage deformation experimental device, comprising:

[0006] A holder having a cavity and two flow channels, the cavity being used to accommodate a rock to be tested and to separate the rock to be tested between the two flow channels, and each flow channel being communicated between the outside and the cavity;

[0007] A heating assembly arranged in the holder and used to adjust the temperature in the cavity;

[0008] A pressure applying assembly arranged in the cavity and used to apply confining pressure to the rock to be tested;

[0009] An injection assembly communicated with the flow channels and used to inject fluid into the cavity and make the fluid flow from one flow channel to another flow channel through the cavity; and

[0010] A detection assembly having a plurality of measurement units, the plurality of measurement units being embedded in the rock to be tested, the plurality of measurement units being arranged in sequence along the fluid flow direction, and each measurement unit being capable of measuring the strain of the rock to be tested at the position in real time.

[0011] In some embodiments, the detection assembly comprises a distributed optical fiber having a measuring section extending into the cavity and embedded in the rock to be measured, and a fiber processing device connected to the distributed optical fiber for acquiring measuring data of the distributed optical fiber in real time.

[0012] The measuring points constitute the measuring section.

[0013] In some embodiments, the measuring section is further capable of measuring temperature and pressure of the location.

[0014] In some embodiments, the pressure applying assembly comprises an elastic sleeve and a pressurizing device, the elastic sleeve is arranged in the cavity and located between the two flow channels, the inner side of the elastic sleeve is used for accommodating the rock to be measured, and the elastic sleeve has a sandwiched cavity, and the pressurizing device is connected to the sandwiched cavity for adjusting the pressure in the sandwiched cavity.

[0015] In some embodiments, the holder comprises a barrel and two sealing heads, the inner cavity of the barrel constitutes the cavity, both ends of the barrel in the axial direction are open, and the two sealing heads are located at both ends of the barrel in the axial direction, at least one of the sealing heads is movable along the axial direction of the barrel and can be maintained at any position in the movable stroke, and the sealing head can extend into the barrel in the movable stroke.

[0016] The elastic sleeve is located in the barrel, and the axial direction of the elastic sleeve coincides with the axial direction of the barrel.

[0017] In some embodiments, the inner cavity of the barrel has a connected mounting section and two guide sections, the inner diameter of the mounting section is larger than that of the guide sections, and the two guide sections are located at both ends of the mounting section in the axial direction.

[0018] The holder further comprises two conical sleeves, the two conical sleeves are located in the mounting section and arranged at both ends of the mounting section in the axial direction, the inner wall of the conical sleeve is flush with the guide section, and the outer wall of the conical section is tapered in the direction of approaching the other conical section.

[0019] The elastic sleeve is located in the mounting section, and both ends of the axial direction of the elastic sleeve are arranged between the outer wall of the conical sleeve and the inner wall of the mounting section, and the sealing head can extend into the elastic sleeve through the guide section in the movable stroke.

[0020] In some embodiments, the inner wall of the barrel is provided with internal threads, the outer wall of the sealing head is provided with external threads, and the sealing head is threadedly connected to the barrel.

[0021] In some embodiments, the sealing head comprises an adjusting sleeve and a core plug, an outer wall of the adjusting sleeve is provided with external threads and is threadedly connected with the barrel, the core plug is arranged in the adjusting sleeve, the core plug extends out of the adjacent adjusting sleeve near one end of the other core plug and is formed with an abutting platform, and an outer diameter of the abutting platform is greater than an inner diameter of the adjusting sleeve.

[0022] In some embodiments, two flow channels are respectively formed in the two core plugs; and / or,

[0023] The core plug further has a wire channel capable of communicating the outside with the inner cavity of the barrel, and the wire channel is arranged for the cable of the measuring unit.

[0024] In addition, the application further provides an experimental method using the rock crack surface damage deformation experimental device, comprising the steps of:

[0025] Step S1: drilling a rock to be measured of a preset size, and splitting the drilled rock to be measured into two half rock plates to form a crack;

[0026] Step S2: cutting an installation groove at a preset distance from the crack surface of the half rock plate, placing a plurality of measuring units in the installation groove in sequence along the extension direction of the installation groove, and filling a sealing agent into the installation groove;

[0027] Step S3: misaligning and closing the two half rock plates and pairing them, heating the paired two half rock plates to a specified experimental temperature, and maintaining the specified experimental temperature for a preset time;

[0028] Step S4: placing the paired two half rock plates into the cavity of the clamping device after maintaining the temperature for the preset time, and arranging the extension direction of the installation groove to be parallel to the arrangement direction of the two flow channels;

[0029] Step S5: starting the heating assembly to maintain the paired two half rock plates at the specified experimental temperature, and starting the pressure applying assembly to apply confining pressure to the paired two half rock plates;

[0030] Step S6: starting the injection assembly to inject the low-temperature fluid into the flow channel at a preset rate, and acquiring the strain measured by the plurality of measuring units in real time.

[0031] The rock crack surface damage deformation experimental device provided by the embodiment of the present application first forms a self-supporting crack on the rock to be measured before the experiment, then embeds a plurality of measuring parts in the rock to be measured in turn, heats the rock to be measured to a specified experimental temperature, and keeps the temperature for a preset time. Then the rock to be measured after keeping warm is placed in the cavity of the clamping device and placed between the two flow channels, and the layout direction of the plurality of measuring parts is arranged parallel to the layout direction of the two flow channels, so that the measuring path of the measuring part coincides with the flow direction of the fluid flowing through the rock to be measured. Then start the heating assembly and the pressure applying assembly, maintain the temperature of the rock to be measured at the specified experimental temperature by the heating assembly; and apply a predetermined confining pressure to the rock to be measured by the pressure applying assembly, simulate the real environment of hot dry rock on the ground, and improve the experimental precision.

[0032] Then start the injection assembly to drive the low-temperature fluid into the cavity of the clamping device. Since the rock to be measured is located between the two flow channels, when the low-temperature fluid is injected into the cavity of the clamping device through one flow channel, the low-temperature fluid can flow to the other flow channel through the crack of the rock to be measured, ensuring that the low-temperature fluid effectively contacts the rock to be measured.

[0033] In this way, the experimental device in the present application can obtain the strain of the rock to be measured in the flow direction of the fluid in real time through the plurality of measuring parts, so that the deformation of the crack during the injection and production process can be monitored in real time, continuously and distributedly, and the thermal strain-time relationship curve of the rock at different crack surface positions (i.e. near the injection end, the middle of the crack, and near the outflow end) can be obtained, which facilitates the study of the thermal strain evolution process of high-temperature rock after being impacted by low-temperature and the independent influence law of temperature action (low-temperature impact) on crack deformation.

[0034] And the plurality of measuring parts simultaneously obtain stress data of a large number of measuring points, which can be continuously monitored for a long time, and the stress changes are recorded without interruption, providing rich data for studying the stress change trend of hot dry rock under the action of cold water at different stages. In addition, high spatial resolution stress data can be provided in combination with the positions of the measuring points, which provides a reliable basis for in-depth study of the strain characteristics and deformation mechanism of high-temperature rock after being impacted by low-temperature, and facilitates the determination of the specific data of crack deformation caused by low-temperature impact and the evolution of related deformation during the injection and production process of the enhanced geothermal system. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate an embodiment consistent with the present application and, together with the specification, serve to explain the principles of the application.

[0036] Figure 1 The experimental flowchart of the rock crack surface damage deformation experimental device (two half-cylinder rock plates are respectively provided with a group of detection assemblies) when detecting rock provided by an embodiment of the present application;

[0037] Figure 2 The experimental flowchart of the rock crack surface damage deformation experimental device (two half-cylinder rock plates are respectively provided with a group of detection assemblies) when detecting rock provided by an embodiment of the present application;Figure 1 Schematic diagram of the middle gripper and a set of detection components;

[0038] Figure 3 For Figure 1 Schematic diagram of the middle gripper;

[0039] Figure 4 For Figure 3 Cross-sectional view of the middle gripper, the elastic sleeve and the two semicylindrical rock plates;

[0040] Figure 5 For Figure 4 Cross-sectional view of the middle cylinder and the elastic sleeve;

[0041] Figure 6 For Figure 5 Cross-sectional view of the middle cylinder;

[0042] Figure 7 For Figure 3 Cross-sectional view of the middle plug;

[0043] Figure 8 Structure diagram of three groups of to-be-tested cores provided by an embodiment of the present application;

[0044] Figure 9 Strain result diagram of the experimental method using the rock crack surface damage deformation experimental device in an embodiment of the present application.

[0045] Reference signs:

[0046] 1, gripper; 1a, cavity; 1b, flow channel; 11, cylinder; 111, mounting section; 112, guide section; 12, plug; 121, adjusting sleeve; 122, core plug; 122a, wiring channel; 123, pressing table; 123a, transition groove; 13, conical sleeve; 14, connecting pipeline; 141, back pressure valve; 142, hand pump; 143, measuring cup; 144, measuring balance; 15, compression nut;

[0047] 2, heating component; 21, heating film;

[0048] 3, pressure applying component; 31, elastic sleeve;

[0049] 4, injection component;

[0050] 5, detection component; 51, distributed optical fiber; 511, measurement point; 52, optical fiber processing device;

[0051] 6, pressure sensor;

[0052] 7, temperature sensor;

[0053] 8. Rock to be tested; 81. Semi-cylindrical rock slab; 81a. Installation groove; 81b. Crack; 811. Crack surface; 82. Fluid injection end; 83. Fluid outflow end.

[0054] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0055] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0056] In related technologies, experimental studies on the deformation mechanism of high-temperature rock cracks caused by low-temperature impact are mostly completed by analyzing data such as fracture toughness and elastic modulus of the rock after the experiment, or discussing the crack morphology of the rock after the experiment. They cannot monitor the thermal stress change mechanism of high-temperature rock caused by low-temperature impact in real time, nor do they know the specific data of the deformation caused by low-temperature impact on cracks. In particular, they do not know how much the crack surface deforms under the action of low-temperature impact, which is not conducive to establishing relevant constitutive models and numerical models of crack deformation.

[0057] Therefore, the experimental device and method for testing surface damage and deformation of rock fractures disclosed in this application can monitor the deformation of fractures in real time and continuously in a distributed manner during the injection and production process, and obtain the thermal strain-time relationship curves of the rock at different fracture surface positions (i.e. near the injection end, the middle of the fracture, and near the outflow end). This facilitates the study of the thermal strain evolution process of high-temperature rocks after being subjected to low-temperature impact, and clarifies the independent influence law of temperature (low-temperature impact) on fracture deformation.

[0058] Please see Figure 1 and Figure 2The experimental apparatus for surface damage deformation of rock crack 81b provided in this application includes a clamp 1, a heating component 2, a pressure application component 3, an injection component 4, and a detection component 5. The clamp 1 has a cavity 1a and two flow channels 1b. The cavity 1a is used to accommodate the rock to be tested 8 and to separate the rock to be tested 8 between the two flow channels 1b. Each flow channel 1b is connected to the outside and the cavity 1a. The heating component 2 is located in the clamp 1 and is used to adjust the temperature inside the cavity 1a. The pressure application component 3 is located inside the cavity 1a and is used to apply confining pressure to the rock to be tested 8. The injection component 4 is connected to the flow channels 1b and is used to inject fluid into the cavity 1a and to make the fluid flow from one flow channel 1b through the cavity 1a to the other flow channel 1b. The detection component 5 has multiple measuring parts, which are embedded in the rock to be tested 8. The multiple measuring parts are arranged sequentially along the fluid flow direction, and each measuring part can at least measure the strain of the rock to be tested 8 at its location in real time.

[0059] In this application, before conducting the experiment, a self-supporting crack 81b is first formed on the rock 8 to be tested. Then, multiple measuring parts are sequentially embedded into the rock 8. The rock 8 is then heated to a specified experimental temperature and held at that temperature for a preset time. The heated rock 8 is then placed in the cavity 1a of the clamp 1 and positioned between two flow channels 1b. Simultaneously, the multiple measuring parts are arranged parallel to the direction of the two flow channels 1b, ensuring that the measuring paths of the measuring parts coincide with the flow direction of the fluid passing through the rock 8. The heating assembly 2 and the pressure application assembly 3 are then activated. The heating assembly 2 maintains the temperature of the rock 8 at the specified experimental temperature, while the pressure application assembly 3 applies a preset confining pressure to the rock 8, simulating the real environment of hot, dry rock underground and improving experimental accuracy.

[0060] Then, the injection component 4 is activated, driving the cryogenic fluid into the cavity 1a of the holder 1. Since the rock to be tested 8 is located between the two flow channels 1b, when cryogenic fluid is injected into the cavity 1a of the holder 1 through one flow channel 1b, the cryogenic fluid can flow through the crack 81b of the rock to be tested 8 to the other flow channel 1b, ensuring that the cryogenic fluid effectively contacts the rock to be tested 8.

[0061] Thus, the experimental setup in this scheme can acquire the strain of the rock under test 8 in the direction of fluid flow in real time through multiple measuring units, thereby enabling real-time, continuous, and distributed monitoring of the deformation of the fracture 81b during the injection and production process. This allows for obtaining thermal strain-time relationship curves of the rock at different fracture surface 811 positions (i.e., near the injection end, the middle of the fracture 81b, and near the outflow end), facilitating the study of the thermal strain evolution process of high-temperature rock after being subjected to low-temperature impact, and clarifying the independent influence of temperature (low-temperature impact) on the deformation of the fracture 81b.

[0062] Furthermore, multiple measurement units simultaneously acquire stress data from a large number of measurement points, enabling long-term continuous monitoring and uninterrupted recording of stress changes. This provides abundant data for studying the stress change trends of hot dry rocks under the action of cold water at different stages. In addition, it can combine the location of measurement point 511 to provide high spatial resolution stress data, providing a reliable basis for in-depth research on the strain characteristics and deformation mechanisms of high-temperature rocks after being subjected to low-temperature impacts. This facilitates the clarification of specific data on the deformation of crack 81b caused by low-temperature impacts and the evolution of related deformations during the injection and production process of enhanced geothermal systems.

[0063] It should be noted that the detection component 5 can be configured as multiple sensors arranged separately; or it can be configured as multiple sensors integrated into the same carrier and embedded in the rock 8 to be tested. It should be understood that the above sensors are high-temperature resistant sensors, specifically, they can be configured as high-temperature strain gauge sensors, surface acoustic wave strain sensors based on lanthanum gallium silicate thin films, or other types of sensors.

[0064] In one embodiment, the detection component 5 includes a distributed optical fiber 51 and an optical fiber processing device 52. The distributed optical fiber 51 has a measuring section that extends into the cavity 1a and is embedded in the rock to be tested 8. The measuring section is provided with multiple measuring points 511 along the fluid flow direction. The optical fiber processing device 52 is connected to the distributed optical fiber 51 and is used to acquire the measurement data of the distributed optical fiber in real time. The measuring points 511 constitute a measuring unit.

[0065] In this embodiment, a distributed optical fiber 51 is embedded in the rock 8 to be tested. The distributed optical fiber 51 sensor can continuously measure stress changes along the length of the optical fiber, providing high spatial resolution stress data and accurately capturing minute stress changes, such as at the millimeter or centimeter level. This allows the strain in the rock along the transmission path sensed by the distributed optical fiber 51 to be converted into an electrical signal. The optical fiber processing device 52 then interprets the evolution of the strain field and other detection data to obtain thermal strain-time relationship curves at different locations on the rock's fracture surface 811.

[0066] It should be noted that the fiber optic processing device 52 can employ a fiber optic demodulation system, an optical frequency domain reflectometer, or a synchronous distributed temperature and strain sensor. Specifically, in this scheme, the fiber optic processing device 52 employs a fiber optic demodulation system to interpret the evolution results of the strain field and other detection data. Furthermore, the distributed optical fiber 51 is a high-temperature resistant fiber, such as a glass-based high-temperature resistant fiber or a crystal-based high-temperature resistant fiber.

[0067] Furthermore, it should be noted that the fiber optic demodulation system employs distributed fiber optic sensing technology based on optical frequency domain reflection (OFDR) for real-time and accurate measurement of the global strain field of the rock sample. When an optical fiber is subjected to strain, its refractive index and geometry change, resulting in phase changes in the light propagating within the fiber. OFDR technology transmits light signals of different frequencies into the fiber and measures the frequency and phase changes of the reflected light. Based on these changes, it determines the strain at various points along the fiber, thereby achieving high-precision, continuous, distributed measurement of rock strain and capturing strain information over a wider range.

[0068] In one embodiment, the measuring unit can also measure the temperature and pressure at the location.

[0069] In this embodiment, the measuring unit can simultaneously measure the strain, temperature, and pressure at its location, realizing comprehensive monitoring of multiple physical quantities. By analyzing the interrelationships between different physical quantities, the experiment can gain a deeper understanding of the evolution of the thermodynamic properties and mechanical behavior of hot dry rocks, providing a more accurate basis for optimizing hot dry rock development schemes and improving development efficiency.

[0070] It should be noted that in this scheme, the stress, temperature, and pressure of the dry hot rock under test are simultaneously measured using a distributed optical fiber 51. It should be understood that the distributed optical fiber 51 can obtain strain, temperature, and pressure based on multi-parameter coupling analysis using Brillouin frequency shift. The frequency shift of the Brillouin scattered light is affected by both strain and temperature, and through specific experimental calibration and algorithms, the data for these two parameters can be separated first.

[0071] Building upon this foundation, by combining the effects of pressure on the structure of the carrier in which the optical fiber is located, the pressure can be further derived. Furthermore, high-precision demodulation technology enhances the reliability of synchronous measurements. High-precision equipment such as optical frequency domain reflectometers (OFDRs) can achieve millimeter-level spatial resolution, accurately capturing minute deformations of the optical fiber caused by pressure and strain, as well as changes in the scattered light characteristics due to temperature. OFDRs can analyze the combined signals of Rayleigh or Brillouin scattering to accurately extract distributed data of temperature and strain, and then calculate the pressure distribution based on a pre-set structural mechanics model, ensuring the accuracy of synchronous measurement of the three parameters and meeting the monitoring needs of precision scenarios.

[0072] In one embodiment, please refer to Figure 3 , Figure 4 and Figure 5 The pressure application component 3 includes an elastic sleeve 31 and a pressurizing device. The elastic sleeve 31 is located in the cavity 1a and between two flow channels 1b. The inner side of the elastic sleeve 31 is used to accommodate the rock 8 to be tested, and the elastic sleeve 31 has a sandwich cavity. The pressurizing device is connected to the sandwich cavity and is used to adjust the pressure in the sandwich cavity.

[0073] In this embodiment, after the rock to be tested 8 is placed in the inner space of the elastic sleeve 31, a high-pressure fluid is applied to the interlayer space of the elastic sleeve 31 through a pressurizing device. This compresses the rock to be tested 8 through the elastic sleeve 31. Based on the soft characteristics of the elastic sleeve 31, it can fit well against the periphery of the rock to be tested 8, thereby applying a relatively uniform confining pressure to the rock to be tested 8, simulating the real pressure environment of the rock to be tested 8. Specifically, a circumferential pressure of 1~2MPa is applied to the rock to be tested through the elastic sleeve 31.

[0074] It should be noted that the pressurizing equipment is a high-pressure fluid source, including a high-pressure storage tank, a compressor pump, and delivery pipelines. High-pressure fluid is delivered into the elastic sleeve 31 through the delivery pipelines, and the pressure within the elastic sleeve 31 can be adjusted and maintained at a preset value. Furthermore, the elastic sleeve 31 is made of a high-temperature resistant flexible material, selected based on the experimental temperature. Specifically, the elastic sleeve 31 can be made of fluororubber, high-temperature silicone rubber, polyimide (PI)-based elastomers, or metal-based elastic materials.

[0075] In one embodiment, please refer to Figure 3 and Figure 4 The clamp 1 includes a cylinder 11 and two sealing heads 12. The inner cavity of the cylinder 11 forms a cavity 1a. The two ends of the cylinder 11 are open in the axial direction. The two sealing heads 12 are located at the two ends of the cylinder 11 in the axial direction. At least one sealing head 12 can move along the axial direction of the cylinder 11 and can be maintained at any position in the moving stroke. The sealing head 12 can extend into the cylinder 11 in the moving stroke. The elastic sleeve 31 is located in the cylinder 11, and the axial direction of the elastic sleeve 31 coincides with the axial direction of the cylinder 11.

[0076] In this embodiment, the open end of the cylinder 11 can be opened or closed by the movable sealing head 12. Simultaneously, axial pressure can be applied to the test rock 8 by adjusting the position of the sealing head 12, ensuring relatively uniform pressure throughout and further improving measurement accuracy. It should be noted that in this embodiment, both sealing heads 12 can move relative to the cylinder 11 along its axial direction and maintain their moved positions, demonstrating good flexibility.

[0077] In one embodiment, please refer to Figure 5 and Figure 6The inner cavity of the cylinder 11 has a connected mounting section 111 and two guide sections 112. The inner diameter of the mounting section 111 is larger than the inner diameter of the guide sections 112. The two guide sections 112 are located at both ends of the axial direction of the mounting section 111. The clamp 1 also includes two conical sleeves 13. The two conical sleeves 13 are located in the mounting section 111 and are located at both ends of the axial direction of the mounting section 111. The inner wall of the conical sleeve 13 is flush with the guide section 112, and the outer wall of the conical section is gradually tapered in the direction close to the other conical section. The elastic sleeve 31 is located in the mounting section 111, and the two ends of the elastic sleeve 31 are located between the outer wall of the conical sleeve 13 and the inner wall of the mounting section 111. The sealing head 12 can extend into the elastic sleeve 31 through the guide section 112 during its active stroke.

[0078] In this embodiment, the two sealing heads 12 can extend from the two guide sections 112 into the elastic sleeves 31 of the mounting section 111 to press against both ends of the rock 8 to be tested inside the elastic sleeves 31, thus clamping the rock 8. Then, high-pressure fluid is introduced into the interlayer cavity of the elastic sleeve 31. At this time, the elastic sleeve 31 expands and fills the gap between the conical sleeve 13 and the inner wall of the mounting section 111, thereby enabling the elastic sleeve 31 to fit tightly against the outer wall of the conical sleeve 13 and the outer wall of the sealing head 12, ensuring that the space where the rock 8 is located is effectively isolated from the outside world, avoiding adverse effects of the outside world on the measurement environment, and improving the experimental accuracy.

[0079] It should be understood that the outer wall of at least one end of the plugging head 12 that extends into the elastic sleeve 31 is flush with the inner wall of the guide section 112 and the conical sleeve 13, further ensuring that the plugging head 12 can fit tightly against the inner wall of the elastic sleeve 31.

[0080] In addition, it should be noted that the movement of the sealing head 12 can be configured as a hydraulic cylinder or pneumatic cylinder driven form, or other forms.

[0081] In one embodiment, the inner wall of the cylinder 11 is provided with internal threads, and the outer wall of the sealing head 12 is provided with external threads and is threadedly connected to the cylinder 11.

[0082] In this embodiment, the position of the sealing head 12 in the axial direction of the cylinder 11 is adjusted by rotating the sealing head 12. Furthermore, the sealing head 12 remains stationary in its original position when no external force is applied, resulting in a simple and reliable structure. It should be noted that to improve the stability of the sealing head 12 after position adjustment, the thread between the cylinder 11 and the sealing head 12 is set as a self-locking thread to prevent the sealing head 12 from being passively rotated due to axial force. It should be understood that the lead angle of the self-locking thread is smaller than the equivalent friction angle of the thread pair; when axial force is applied, the frictional torque between the threads is greater than the unlocking torque generated by the axial force, preventing automatic relative rotation due to the axial force.

[0083] In one embodiment, please refer to Figure 4and Figure 7 The sealing head 12 includes an adjusting sleeve 121 and a core plug 122. The outer wall of the adjusting sleeve 121 is provided with external threads and is threadedly connected to the cylinder 11. The core plug 122 is inserted into the adjusting sleeve 121. One end of the core plug 122 near another core plug 122 extends out of the adjacent adjusting sleeve 121 and forms a pressing platform 123. The outer diameter of the pressing platform 123 is larger than the inner diameter of the adjusting sleeve 121.

[0084] In this embodiment, during assembly, the core plug 122 is fitted into the adjusting sleeve 121, with the end of the core plug 122 equipped with the pressing platform 123 facing the guide section 112, and then the adjusting sleeve 121 is rotated and tightened. Since the outer diameter of the pressing platform 123 is larger than the outer diameter of the adjusting sleeve 121, during the tightening process of the adjusting sleeve 121, the adjusting sleeve 121 can drive the pressing platform 123 to move towards the installation section 111, and both pressing platforms 123 will eventually press against the core to be tested. In this solution, the sealing head 12 is set as a separate adjusting sleeve 121 and core plug 122, which can form a certain gap between the adjusting sleeve 121 and the core plug 122; thus, when the core plug 122 is used to push the high-temperature rock to be tested 8 into the elastic sleeve 31, it can play a certain heat insulation role and prevent the experimental personnel from being burned when rotating the adjusting sleeve 121. It should be noted that in this scheme, the outer wall surface of the adjusting sleeve 121, the outer wall surface of the pressing platform 123, the inner wall surface of the conical sleeve 13, and the inner wall surface of the guide section 112 are flush.

[0085] In one embodiment, two flow channels 1b are formed in two core plugs 122 respectively; and / or, the core plug 122 also has a wiring channel 122a, which can connect to the inner cavity of the outer cylinder 11, and the wiring channel 122a is for the cable of the measuring unit to pass through.

[0086] In this embodiment, two flow channels 1b are respectively installed on two core plugs 122, allowing the cryogenic fluid to flow from one end of the rock to be tested 8 to the other end along the axial direction, covering the crack 81b path of the rock to be tested 8. This also facilitates the removal of the core plugs 122 for regular cleaning and unblocking of the flow channels 1b, preventing blockage. It should be noted that in this design, a PTFE gasket is provided at the outer port of the flow channel 1b. The PTFE gasket reduces the pore space and provides a certain degree of elasticity, allowing the liquid to pass through while simultaneously achieving pressurization.

[0087] Furthermore, in this scheme, the wiring channel 122a can also be located on the core plug 122. Thus, after removing the heated rock 8 embedded with the distributed optical fiber 51, one end of the distributed optical fiber 51 is first passed through the cylinder 11, and then the two ends of the optical fiber are respectively passed through the wiring channels 122a of the two core plugs 122. Then, the two sets of core plugs 122 and adjusting sleeves 121 are sequentially assembled onto the cylinder 11. When the adjusting sleeve 121 is rotated, the core plug 122 will not rotate synchronously with the adjusting sleeve 121, thereby preventing the optical fiber in the core plug 122 from rotating or twisting, ensuring the normal operation of the optical fiber. Moreover, during the tightening of the adjusting sleeve 121, the optical fiber at the end can be pulled outwards using a tool, ensuring the sealing head 12 seals properly, while also preventing the optical fiber from being squeezed.

[0088] It should be noted that the external port of the wiring channel 122a is also equipped with a PTFE gasket. The PTFE gasket reduces the space in the hole and provides a certain degree of elasticity, thus sealing the optical fiber. Then, a clamping nut 15 is installed at the outer port of the wiring channel 122a, and the optical fiber passes through the clamping nut 15. The clamping nut 15 is then connected to the core plug 122, ensuring that the optical fiber port of the core plug 122 is neither liquid nor air-permeable.

[0089] In one embodiment, each of the pressing platforms 123 is provided with a transition groove 123a on the side near the other pressing platform 123, and the inner ports of the flow channel 1b and the wiring channel 122a are connected to the corresponding transition groove 123a.

[0090] In this embodiment, the transition groove 123a serves as a transition space between the optical fiber and the fluid, preventing the optical fiber from being damaged by the pressure platform 123 and the rock 8 due to misalignment between the channel and the mounting groove 81a on the rock 8. Simultaneously, it ensures sufficient fluid contact with the crack 81b, improving fluid flow efficiency. It should be understood that the core plug 122 and the pressure platform 123 are integrally connected, and the flow channel 1b and the wiring channel 122a simultaneously penetrate the corresponding core plug 122 and pressure platform 123. In one embodiment, each core plug 122 is provided with two wiring channels 122a to correspond to the measurement of two half-rock slabs.

[0091] In addition, it should be noted that the heating component 2 can be configured as fuel heating or electric heating. When fuel heating is used, a combustion chamber interlayer can be provided at the location of the cylinder 11 corresponding to the installation section 111.

[0092] In one embodiment, the heating assembly 2 includes multiple sets of heating films 21, which are located in the mounting section 111 and arranged sequentially along the axial direction of the cylinder 11. Each set of heating films 21 surrounds the periphery of the cylinder 11 and is electrically connected to the control unit.

[0093] In this embodiment, due to the flow sequence of the cryogenic fluid during the injection of the tested rock 8, the heat dissipation at the injection end of the tested rock 8 is greater than that at the outlet end. Therefore, multiple sets of heating films 21 are sequentially arranged, allowing independent temperature control of corresponding areas via these films. That is, the power output of each heating film 21 can be dynamically adjusted by the control unit based on the local temperature feedback from the measuring unit, ensuring the uniformity and stability of the core temperature field. Dynamically adjusting the power output of each heating film 21 can quickly compensate for local temperature drops, avoiding strain measurement errors caused by uneven temperature gradients. This provides a more reliable experimental basis for the thermal stress analysis of crack 81b deformation and enhances the repeatability of experimental data.

[0094] It should be understood that the heating film 21 can be set as a high-temperature metal-based heating film 21, a semiconductor high-temperature heating film 21 or a special carbon-based heating film 21 to meet the actual environmental temperature simulation requirements of dry hot rock from 150℃ to 400℃.

[0095] Furthermore, it should be noted that the injection component 4 can be configured as a high-precision peristaltic pump with constant pressure feedback, a servo-controlled plunger pump equipped with a preset constant pressure and constant speed module, or other equipment. Specifically, in this solution, the injection component 4 adopts a dual-cylinder constant speed and constant pressure pump, supporting constant speed (precisely controllable flow rate) and constant pressure (stable pressure output) modes, and can inject cryogenic fluid at different rates according to experimental requirements. Specifically, in one embodiment, the fluid used is cryogenic water with a constant temperature, and the injection rate ranges from 5 to 45 ml / min.

[0096] In one embodiment, a connecting pipe 14 is connected to the flow channel 1b corresponding to the fluid outlet 83. A temperature sensor 7, a pressure sensor 6, and a back pressure valve 141 are installed on the connecting pipe 14. The back pressure valve 141 is connected to a hand-cranked pump 142, which can be used to pump fluid. After the experiment, the flow channel 1b is cleaned. The back pressure valve 141 allows the fluid to flow towards the measuring cup 143. In addition, the output end of the connecting pipe 14 is introduced into the measuring cup 143 so that the measuring cup 143 can be weighed by a measuring balance 144 during the experiment.

[0097] It should be understood that, in order to achieve precise control of the heating component 2, the pressurizing component 3, and the injection component 4, temperature sensors 7 are independently provided for the corresponding cylinder 11 and heating film 21, and pressure sensors 6 are independently provided for the corresponding elastic sleeve 31. Simultaneously, pressure sensors 6 and temperature sensors 7 are independently provided for the fluid pipeline of the dual-cylinder constant-speed and constant-pressure pump.

[0098] Furthermore, this application also provides an experimental method using the above-mentioned rock crack 81b surface damage deformation experimental apparatus, comprising the following steps:

[0099] Step S1: Drill a rock 8 of a preset size to be tested, and split the drilled rock 8 into two half-rock slabs to form crack 81b;

[0100] In this step, a granite core of a predetermined size is drilled to fit the inner space of the elastic sleeve 31. It should be understood that, based on the elastic deformation advantage of the elastic sleeve 31, cores of various sizes can be processed for comparative experiments. The core size is set to be smaller than the size of the transition groove 123a. Preferably, to improve the uniformity of confining pressure, a cylindrical core is drilled. In one embodiment, a granite core with a diameter of 100 mm and a height of 200 mm is drilled. The drilled rock 8 to be tested is then divided into two semi-cylindrical slabs 81 to facilitate the formation of a crack 81b between the two semi-cylindrical slabs 81.

[0101] Specifically, in this step, the core can be split in half along the axis using a wire cutting device, and three-dimensional carving technology can be applied to polish each core to create a realistic and identical seam surface 811 morphology.

[0102] Step S2: Cut an installation groove 81a at a preset distance from the joint surface 811 of the half-rock slab, place multiple measuring parts in the installation groove 81a in sequence along the extension direction of the installation groove 81a, and then fill the installation groove 81a with sealant.

[0103] In this step, for each semi-cylindrical rock slab 81, an installation groove 81a is cut at a predetermined distance from the joint surface 811 to accommodate multiple measuring units. The arrangement direction of the multiple measuring units is set to be the same as the extension direction of the installation groove 81a. After the measuring units are placed, the optical fiber is sealed with a sealant to prevent the optical fiber embedded in the rock from being affected by fluids or other external factors, thereby improving measurement accuracy. It should be noted that when conducting multiple sets of core comparison experiments, please refer to [the relevant documentation / reference]. Figure 8 In one embodiment, three sets of core samples to be tested are selected, each with a radius R of 50 mm and a height H of 100 mm. Installation grooves 81a are respectively opened at distances d1, d2, and d3 from the joint surface 811, where d1, d2, and d3 are 10 mm, 15 mm, and 20 mm respectively. Furthermore, in this design, a high-strength epoxy resin is used as the sealant. Sealing the installation grooves 81a with this high-strength epoxy resin reduces measurement interference factors.

[0104] Specifically, distributed fiber optic strain sensors 51 are arranged inside the crack to monitor the strain field during low-temperature impact. Furthermore, by conducting comparative experiments with multiple sets of different groove depths, the strain values ​​of crack 81b at different groove depths can be obtained. Comparative analysis of multiple sets of measurements improves the accuracy of measuring the deformation law of crack 81b under temperature effects (low-temperature impact).

[0105] It should be understood that the opening and closing, shearing, and other strains of the seam surface 811 will be transmitted through the rock slab body to the side opposite to the mounting groove 81a of the seam surface 811, causing synchronous micro-deformation in the area of ​​the mounting groove 81a. After the distributed optical fiber 51 (such as Bragg grating FBG, optical frequency domain reflectance OFDR fiber) is embedded in the mounting groove 81a, it is closely attached to the rock slab. The deformation of the rock slab will cause the optical fiber to be stretched or compressed, resulting in changes in the optical fiber signal (wavelength, phase). By demodulation, parameters such as strain, temperature, and pressure can be inferred.

[0106] Step S3: Close and pair the two half-rock plates in a staggered manner, then heat the paired half-rock plates to the specified experimental temperature and maintain the specified experimental temperature for a preset time.

[0107] In this step, the joint surface 811 of the split semi-cylindrical rock slab 81 itself has certain rough protrusions, and after three-dimensional carving and polishing, it forms the shape of a real crack. When the two semi-cylindrical rock slabs 81 are matched by a certain size misalignment, the misalignment causes the rough protrusions (such as rock particles and micro-joints) on the fracture surface of the rock slabs to interlock with each other, forming a mechanical lock similar to saw teeth, which counteracts the closing tendency of crack 81b, so that the joint surface 811 of the two semi-cylindrical rock slabs 81 is not completely attached. The contact point is concentrated to bear the ground stress or its own weight, and the dispersed stress prevents crack 81b from being completely compressed.

[0108] Thus, after misalignment, crack 81b is not completely closed, forming an irregular connecting channel. The interlocking structure prevents the channel from collapsing, satisfying the fluid circulation requirements of the self-supporting crack 81b. Specifically, in this scheme, the two semi-cylindrical rock plates 81 are axially misaligned by 1-2 mm before closing, ensuring uniform core ring pressure while forming the self-supporting crack 81b. It should be understood that the misalignment can be achieved through the pressure difference between the elastic sleeve 31 and the two core plugs 122.

[0109] In this step, the two paired semi-cylindrical rock slabs 81 are heated to a specified experimental temperature. Specifically, the high-temperature resistant optical fiber and the rock are placed in a heating chamber and heated together to the specified experimental temperature, and the temperature is maintained for more than 24 hours to ensure that the temperature inside and outside the entire rock is at the specified experimental temperature. The specified experimental temperature range for the rock in this experiment is 200~400℃.

[0110] Step S4: After the preheating time is set, place the two half-rock plates that are paired into the cavity 1a of the clamp 1, and arrange the extension direction of the mounting groove 81a parallel to the layout direction of the two flow channels 1b.

[0111] In this step, when the two uniformly heated semi-cylindrical rock plates 81 are placed into the cavity 1a of the clamp 1, the extension direction of the mounting groove 81a is kept the same as the layout direction of the two flow channels 1b, so that multiple measuring units can measure the strain of the rock at various points in the direction of fluid flow.

[0112] Specifically, in this scheme, the optical fiber is laid out along the axial direction of the semi-cylindrical rock plate 81, so that multiple measurement points 511 on the optical fiber correspond to various locations along the axial direction of the rock core, which facilitates obtaining the thermal strain-time relationship curves of different rock fracture surfaces 811 positions (i.e. near the injection end, the middle of the crack 81b, and near the outflow end).

[0113] Step S5: Activate heating component 2 to maintain the two paired half-rock plates at the specified experimental temperature, and activate pressure application component 3 to apply confining pressure to the two paired half-rock plates;

[0114] In this step, a confining pressure of 1~2MPa is applied to the core using the clamp 1, and the core is heated and maintained at the specified experimental temperature using the heating component 2 to simulate the real environment of the core and improve the accuracy of the experiment.

[0115] Step S6: Start the injection component 4, inject cryogenic fluid into the flow channel 1b at a preset rate, and acquire the strain measured by multiple measuring units in real time.

[0116] In this step, after the core is maintained at the specified experimental temperature in the holder 1, the injection component 4 is activated. Within the same set of experiments, a constant-speed and constant-pressure cryogenic fluid is injected into the cavity 1a of the holder 1 through the injection component 4, and the strain data under cryogenic impact is acquired in real time through the measuring unit. Furthermore, when conducting multiple sets of experiments, comparative analysis can be performed, and multiple sets can be injected with cryogenic fluid at different rates; specifically, a dual-cylinder constant-speed and constant-pressure pump is used to inject fluid at different rates (the temperature is kept constant at 20℃).

[0117] In one embodiment, please refer to Figure 9 The graph shows the experimental time on the horizontal axis, the fiber length on the vertical axis, and the strain magnitude on the color axis. Tensile strain is positive and compressive strain is negative. The larger the absolute value, the greater the strain.

[0118] according to Figure 9 As shown in the figure, in this embodiment, the location range of the fiber-optic positioning core is approximately 3.38~3.48m, where 3.48m is the fluid injection end 82 (water inlet) and 3.38m is the fluid outflow end 83 (water outlet). The information in the figure shows that the strain of the entire core is relatively uniform at the beginning of the experiment. After water injection, the strain at the water inlet changes first due to the time difference in fluid contact, and because of the temperature difference experienced at the water inlet during this stage, the strain generated is greater than that in the middle section. As time changes, the core temperature at the water inlet gradually decreases, and the strain caused by the fluid impact on the hot dry rock gradually decreases. The low-temperature fluid gradually comes into contact with the high-temperature rock in the middle section, causing the strain in the middle section to increase. Since the low-temperature fluid has made sufficient contact with the high-temperature core, the subsequent fluid temperature rise cannot create a sufficient temperature difference with the water outlet to generate strain. Furthermore, the fiber optic cable is fixed to the core, and after being subjected to compressive strain at the water inlet and the middle section, the water outlet exhibits a certain value of tensile strain.

[0119] Experimental results show that the experimental setup and method presented here can provide a reliable basis for in-depth research on the strain characteristics and deformation mechanism of high-temperature rocks after low-temperature impact. Furthermore, it can clarify the specific data on the deformation of crack 81b caused by low-temperature impact during the injection and production process of enhanced geothermal systems, and how the related deformation evolves. This scheme can solve the problem that existing enhanced geothermal system injection and production processes cannot monitor rock stress changes under low-temperature impact in real time, and clarifies the amount of deformation of crack 81b caused by low-temperature impact during the injection and production process of enhanced geothermal systems, as well as how the deformation evolves and is generated.

[0120] This application proposes an experimental method and procedure for using distributed optical fiber 51 to monitor stress changes in high-temperature rocks with a single crack 81b under low-temperature impact. This enables continuous monitoring of thermal stress changes in high-temperature rocks under low-temperature impact at a microscale, allowing the experiment to gain a deeper understanding of the evolution of thermodynamic properties and mechanical behavior of hot dry rocks, and providing a more accurate basis for optimizing hot dry rock development schemes and improving development efficiency.

[0121] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. An experimental apparatus for surface damage and deformation of rock cracks, characterized in that, include: The clamp has a cavity and two flow channels. The cavity is used to hold the rock to be tested and to separate the rock to be tested between the two flow channels. Each flow channel is connected to the outside and the cavity. A heating assembly, disposed in the clamp, is used to adjust the temperature inside the cavity; A pressure-applying component, located within the cavity, is used to apply confining pressure to the rock under test; An injection assembly, connected to the flow channels, is used to inject fluid into the cavity and to allow fluid to flow from one of the flow channels through the cavity to the other flow channel; and The detection component has multiple measuring units, which are embedded in the rock to be tested. The multiple measuring units are arranged sequentially along the fluid flow direction, and each measuring unit can at least measure the strain of the rock to be tested at its location in real time.

2. The experimental apparatus for surface damage and deformation of rock cracks according to claim 1, characterized in that, The detection component includes a distributed optical fiber and an optical fiber processing device. The distributed optical fiber has a measuring section that extends into the cavity and is embedded in the rock to be tested. The measuring section has multiple measuring points arranged along the fluid flow direction. The optical fiber processing device is connected to the distributed optical fiber and is used to acquire the measurement data of the distributed optical fiber in real time. The measurement points constitute the measurement unit.

3. The experimental apparatus for surface damage and deformation of rock cracks according to claim 1, characterized in that, The measuring unit can also measure the temperature and pressure at its location.

4. The experimental apparatus for surface damage and deformation of rock cracks according to claim 1, characterized in that, The pressure application assembly includes an elastic sleeve and a pressurizing device. The elastic sleeve is disposed in the cavity and located between the two flow channels. The inner side of the elastic sleeve is used to accommodate the rock to be tested, and the elastic sleeve has a sandwich cavity. The pressurizing device is connected to the sandwich cavity and is used to adjust the pressure in the sandwich cavity.

5. The experimental apparatus for surface damage and deformation of rock cracks according to claim 4, characterized in that, The clamp includes a cylinder and two sealing heads. The inner cavity of the cylinder forms the cavity. The two ends of the cylinder are open in the axial direction. The two sealing heads are located at the two ends of the cylinder in the axial direction. At least one sealing head can move along the axial direction of the cylinder and can be maintained at any position during the movement. The sealing head can extend into the cylinder during the movement. The elastic sleeve is located inside the cylinder, and the axial direction of the elastic sleeve coincides with the axial direction of the cylinder.

6. The experimental apparatus for surface damage and deformation of rock cracks according to claim 5, characterized in that, The inner cavity of the cylinder has a connected mounting section and two guide sections. The inner diameter of the mounting section is larger than the inner diameter of the guide sections, and the two guide sections are located at both ends of the axial direction of the mounting section. The clamp also includes two conical sleeves, which are located at the mounting section and at both ends of the mounting section in the axial direction. The inner wall of the conical sleeve is flush with the guide section, and the outer wall of the conical section is tapered towards the other conical section. The elastic sleeve is located in the mounting section, and the two ends of the elastic sleeve in the axial direction are located between the outer wall of the conical sleeve and the inner wall of the mounting section. The sealing head can extend into the elastic sleeve through the guide section during its active stroke.

7. The experimental apparatus for surface damage and deformation of rock cracks according to claim 5, characterized in that, The inner wall of the cylinder is provided with internal threads, and the outer wall of the sealing head is provided with external threads, and is threadedly connected to the cylinder.

8. The experimental apparatus for surface damage and deformation of rock cracks according to claim 7, characterized in that, The plugging head includes an adjusting sleeve and a core plug. The outer wall of the adjusting sleeve is provided with external threads and is threadedly connected to the cylinder body. The core plug is inserted into the adjusting sleeve. One end of the core plug near another core plug extends out of the adjacent adjusting sleeve and forms a pressing platform. The outer diameter of the pressing platform is larger than the inner diameter of the adjusting sleeve.

9. The experimental apparatus for surface damage and deformation of rock cracks according to claim 8, characterized in that, The two flow channels are respectively formed in the two core plugs; and / or, The core plug also has a wiring channel that connects the outside to the inner cavity of the cylinder, and the wiring channel is for the cable of the measuring unit to pass through.

10. An experimental method using the rock fracture surface damage deformation experimental apparatus according to any one of claims 1-9, characterized in that, Including the following steps: Step S1: Drill a rock sample of a preset size and split the sampled rock sample into two half-rock slabs to form a crack; Step S2: Cut an installation groove at a preset distance from the joint surface of the half-rock slab, place multiple measuring parts in the installation groove in sequence along the extension direction of the installation groove, and then fill the installation groove with sealant. Step S3: Close and pair the two half-rock plates in a staggered manner, then heat the paired half-rock plates to the specified experimental temperature and maintain the specified experimental temperature for a preset time. Step S4: After the pre-set heat preservation time, place the two half-rock plates that are paired into the cavity of the clamp, and arrange the extension direction of the mounting groove parallel to the layout direction of the two flow channels. Step S5: Activate the heating component to maintain the two paired half-rock plates at the specified experimental temperature, and activate the pressure application component to apply confining pressure to the two paired half-rock plates; Step S6: Start the injection component to inject cryogenic fluid into the flow channel at a preset rate, and acquire the strain measured by multiple measuring units in real time.

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