Research on device for fault slip, test method and preparation method of fault sample

Abstract

The application discloses a device for studying fault slip, a test method and a preparation method of a fault sample. The holder assembly of the device for studying fault slip can clamp the upper and lower ends of the fault sample. The fault slip sensor is located at the center position of the fault zone and is equidistantly arranged between the first slip detection part and the second slip detection part. The fault slip sensor is used for detecting the displacement of the first slip detection part and the second slip detection part when the upper plate bedrock and the lower plate bedrock are dislocated under a preset alternating stress. One end of the extensometer is fixed to the upper end of the holder assembly, and the other end can vertically move relative to the lower end of the holder assembly, and is used for detecting the axial compression deformation of the fault sample under the preset alternating stress. The fault compression measuring assembly is arranged on the surface of the fault sample and is used for detecting fault compression data when the fault zone is compressed under the preset alternating stress. The stress condition of the fault under different stress conditions can be restored, and the slip stability of the fault can be accurately evaluated.

Description

Technical Field

[0001] This invention relates to the field of gas storage technology, and in particular to an apparatus, testing method, and method for preparing fault samples for studying fault slip. Background Technology

[0002] Faults are among the most common geological structures, widely distributed across continental plates. In resource exploration and development, fault slippage often affects the accumulation and distribution of underground resources, as well as the sealing performance of traps. Faults play a crucial role in controlling reservoir development and distribution, and slippage can cause reservoir deformation, fracturing, or folding. For caprocks, fault slippage can cause stretching or compression, severely impacting their integrity and sealing performance. Faults are prone to stress concentration under multi-cycle alternating injection and production conditions, leading to sealing failure.

[0003] For the target areas of underground gas storage construction in China, the geological conditions are relatively poor, with significant burial depths, generally exceeding 3000m, numerous faults, complex geological structures, rapid sedimentary facies changes, poor reservoir properties, and strong heterogeneity. Analysis of the geological conditions of 27 existing gas storage facilities reveals that, with the exception of three salt cavern gas storage facilities, most are fault-prone gas reservoirs, such as Shuang 6 and Xiangguosi. Therefore, research on faults is a crucial component in the early-stage construction studies, scheme design, and pressurization / expansion processes.

[0004] The periodic, intense injection and extraction of natural gas into gas storage facilities leads to alternating changes in the regional geostress field, resulting in stress concentration at the fault sections. Since the rock masses within faults are generally weak and fractured, alternating stress easily causes fault slippage, leading to deformation of the caprock and reservoir rock masses, potentially triggering minor earthquakes. Fault slippage or rupture also affects fault sealing, and sealing failure can cause natural gas leaks. Natural gas from the storage facility leaking through the fault to the surface could cause fires, explosions, and environmental pollution, and even more serious consequences such as casualties, economic losses, and disruptions to downstream gas supply and social stability. Fault sealing failure not only hinders the increase of the upper operating pressure of gas storage facilities but also poses safety hazards to production and daily life. Therefore, research on fault slippage or rupture under alternating stress is of great significance to the development of gas storage facilities. Summary of the Invention

[0005] To accurately reproduce the stress conditions of real underground faults under different stress conditions and to more accurately assess the slip stability of faults, this invention provides an apparatus, testing method, and fault sample preparation method for studying fault slip, so as to evaluate the fault sealing performance and the site selection and pressurization operation of gas storage facilities.

[0006] In a first aspect, embodiments of the present invention provide an apparatus for studying fault slip, including a triaxial stress experimental apparatus and a clamping assembly, a first slip detection unit, a second slip detection unit, a fault slip sensor, an extensometer, and a fault compression measurement assembly disposed in the inner cavity of the triaxial stress experimental apparatus.

[0007] The clamping assembly is capable of clamping the upper and lower ends of the fault sample, wherein the fault sample includes an upper wall bedrock and a lower wall bedrock with a preset fault dip angle, and a fault zone connecting the upper wall bedrock and the lower wall bedrock.

[0008] The first slip detection unit is disposed on the surface of the hanging wall bedrock and is attached to the junction of the fault zone and the hanging wall bedrock;

[0009] The second slip detection unit is disposed on the surface of the footwall bedrock and is attached to the junction of the fault zone and the footwall bedrock;

[0010] The fault slip sensor is located at the center of the fault zone and is equidistantly disposed between the first slip detection unit and the second slip detection unit;

[0011] The triaxial stress testing device includes a loading mechanism, which is capable of applying a preset alternating stress to the fault sample.

[0012] The fault slip sensor is used to detect the displacement of the first slip detection part and the second slip detection part when the upper bedrock and the lower bedrock move under a preset alternating stress, and to obtain fault slip data.

[0013] One end of the extensometer is fixed to the upper end of the clamping assembly, and the other end can move vertically relative to the lower end of the clamping assembly. It is used to detect the axial compression deformation of the fracture sample under a preset alternating stress and obtain overall compression data.

[0014] The fault compression measurement component is disposed on the surface of the fault sample and is used to detect fault compression data when the fault zone is compressed under a preset alternating stress.

[0015] Optionally, the fault compression measurement assembly includes a first compression detection unit, a second compression detection unit, and a fault compression sensor;

[0016] The first slip detection unit is disposed on the surface of the hanging wall bedrock and is located close to the fault zone;

[0017] The second slip detection unit is disposed on the surface of the footwall bedrock and is located close to the fault zone;

[0018] The fault compression sensor is equidistantly disposed between the first compression detection unit and the second compression detection unit, and is used to detect the displacement of the first slip detection unit and the second slip detection unit when the fault zone is compressed under a preset alternating stress, so as to obtain the fault compression data.

[0019] Optionally, the clamping assembly includes a first clamping block and a second clamping block;

[0020] The first pressure block and the second pressure block are respectively connected to the upper and lower ends of the fracture sample, and the first pressure block, the second pressure block and the fracture sample are coaxially arranged.

[0021] Optionally, the first pressure block is circumferentially sleeved with the first fixing member;

[0022] The second pressure block is circumferentially sleeved with the second fixing member;

[0023] One end of the extensometer is connected to the first fixing member, and the other end passes through the second fixing member;

[0024] The extensometer is used to move vertically relative to the second fixing member when the fracture sample is compressed under a preset alternating stress, and to detect the moving distance to obtain overall compression data.

[0025] Optionally, the apparatus for studying fault slip further includes at least one set of acoustic emission sensor assemblies mounted on the surface of the fault sample;

[0026] Each acoustic emission sensor assembly includes a first acoustic emission sensor and a second acoustic emission sensor.

[0027] The first acoustic emission sensor is located on the upper bedrock, and the second acoustic emission sensor is located on the lower bedrock, with the first acoustic emission sensor and the second acoustic emission sensor on the same vertical line;

[0028] The first acoustic emission sensor and the second acoustic emission sensor are used to detect the acoustic signals generated by the fracture sample.

[0029] Optionally, the apparatus for studying fault slip may further include acoustic signal processing equipment;

[0030] The acoustic signal processing device is connected to the first acoustic emission sensor and the second acoustic emission sensor, and is used to receive the acoustic signals detected by the first acoustic emission sensor and the second acoustic emission sensor, and determine the slip stage of the fault sample based on the change amplitude of the acoustic signals.

[0031] Optionally, the apparatus for studying fault slip may further include data processing equipment;

[0032] The data processing device is connected to the loading mechanism, the fault slip sensor, the fault compression sensor, and the extensometer to acquire the value of the preset alternating stress, the fault slip data, the fault compression data, and the overall compression data, and calculates the friction coefficient of the fault sample based on the value of the preset alternating stress.

[0033] Secondly, embodiments of the present invention provide a testing method for studying fault slip, using the apparatus for studying fault slip described in the first aspect, comprising:

[0034] A first slip detection unit, a second slip detection unit, a fault slip sensor, and a fault compression measurement assembly are installed on the surface of the fault sample.

[0035] The surface of the fracture sample is sealed with a sealing material. After sealing, the fracture sample is connected to the clamp assembly.

[0036] One end of the extensometer is fixed to the upper end of the clamp assembly;

[0037] The clamping assembly is placed inside the cavity of the triaxial stress testing apparatus;

[0038] A preset alternating stress is applied to the fracture sample using a loading mechanism;

[0039] Under a preset alternating stress, the displacement of the first slip detection part and the second slip detection part is detected by the fault slip sensor to obtain fault slip data. The axial compression deformation of the fault sample under the preset alternating stress is detected by the extensometer to obtain overall compression data. Finally, the fault compression measurement component is used to detect the fault compression data.

[0040] Optionally, the preset alternating stress includes a preset axial compression and a preset confining compression;

[0041] The application of a preset alternating stress to the fracture sample using a loading mechanism includes:

[0042] Axial pressure and confining pressure are applied to the fault sample in an incremental manner until the applied axial pressure and confining pressure reach the preset axial pressure and preset confining pressure, respectively, and the preset axial pressure and preset confining pressure are continuously applied to the fault sample.

[0043] Optionally, the step of detecting the displacement of the first and second slip detection units using the fault slip sensor under a preset alternating stress to obtain fault slip data, detecting the axial compression deformation of the fault sample under the preset alternating stress using the extensometer to obtain overall compression data, and detecting the fault compression data using the fault compression measurement assembly, further includes:

[0044] Based on the preset axial pressure and preset confining pressure, the friction coefficient of the fault sample is calculated according to the following formula:

[0045]

[0046] In the above formula: σ n The normal stress experienced by the fracture sample;

[0047] τ is the shear stress experienced by the fault sample;

[0048] μ is the friction coefficient of the fault sample;

[0049] σ1, σ2, and σ3 are the first principal stress, the second principal stress, and the third principal stress, respectively. The value of the first principal stress is equal to the preset axial compression, and the values ​​of the second and third principal stresses are equal to the preset confining pressure.

[0050] Thirdly, embodiments of the present invention provide a method for preparing a tomographic sample, comprising:

[0051] Obtain rock cores from the target study area and fabricate a plunger;

[0052] Based on the preset fault dip angle, the plunger is cut from the center point, and the cut surface of the plunger is ground to obtain the hanging wall bedrock and the footwall bedrock.

[0053] The upper bedrock and the lower bedrock are bonded together using pre-mixed filling and casting materials, and the height formed by the filling and casting materials is consistent with the height of the preset fault zone. The solidified filling and casting materials serve as the fault zone to obtain a fault sample.

[0054] The beneficial effects of the above-mentioned technical solutions provided in the embodiments of the present invention include at least the following:

[0055] This invention provides an apparatus for studying fault slip. The apparatus includes a triaxial stress testing device and a clamping assembly, a first slip detection unit, a second slip detection unit, a fault slip sensor, an extensometer, and a fault compression measurement assembly disposed within the cavity of the triaxial stress testing device. The triaxial stress testing device includes a loading mechanism that can apply a preset alternating stress to the fault sample. By precisely controlling the application of the preset alternating stress by the loading mechanism, the frequency and amplitude of the alternating loading can be controlled to reproduce the stress condition of a real underground fault under different stress conditions, thereby more accurately assessing the slip stability of the fault.

[0056] By setting a first slip detection unit, a second slip detection unit, and a fault slip sensor on the surface of a fault sample, with the fault slip sensor located at the center of the fault zone and equidistantly positioned between the first and second slip detection units, the fault slip sensor can detect the positional changes of the first and second slip detection units in real time and record the dynamic slip data of the fault sample under alternating stress. The collected fault slip data can be further processed and analyzed, including the study of parameters such as displacement magnitude (slip distance) and slip velocity, as well as the identification of slip patterns, to assess the slip stability of the fault under alternating stress. This is of great significance for understanding the behavior mechanism of faults and the safe operation of gas storage facilities. Simultaneously, it can also be used to evaluate the fault sealing performance in relation to gas storage facility site selection and pressurization operation.

[0057] By installing components such as a first slip detection unit, a second slip detection unit, a fault slip sensor, an extensometer, and a fault compression measurement assembly on the surface of the fault sample, fault slip data, fault compression data, and overall compression data can be monitored. This provides a more comprehensive and accurate monitoring of the actual deformation of the fault compared to existing technologies, and offers more comprehensive and accurate data support for studying the behavior mechanism of faults under alternating stress.

[0058] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0059] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0060] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0061] Figure 1 This is a schematic diagram of a tomographic sample provided in an embodiment of the present invention;

[0062] Figure 2 This is a schematic diagram of the assembly of the fault sample with the first and second pressure blocks provided in an embodiment of the present invention;

[0063] Figure 3 This is a schematic diagram of a tomographic sample placed inside the triaxial stress testing apparatus according to an embodiment of the present invention;

[0064] Figure 4 A flowchart illustrating the testing method for studying fault slip provided in this embodiment of the invention;

[0065] Figure 5 This is a flowchart of the method for preparing a tomographic sample provided in an embodiment of the present invention;

[0066] Explanation of reference numerals in the attached figures:

[0067] 1. Upper footwall bedrock; 2. First slip detection unit; 3. Fault zone; 4. Second slip detection unit; 5. First compression detection unit; 6. Second compression detection unit; 7. Lower footwall bedrock; 8. Second acoustic emission sensor; 9. First acoustic emission sensor; 10. Second acoustic emission sensor; 11. First acoustic emission sensor; 12. First pressure block; 13. Second pressure block; 14. First fixing component; 15. Second fixing component; 16. Extensometer; 17. Triaxial stress testing device; 18. Confining pressure loading mechanism; 19. Axial pressure loading mechanism. Detailed Implementation

[0068] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0069] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," "far," "near," "front," and "rear," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0070] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0071] The inventors discovered that in existing technologies, a biaxial direct shear test method using cubic specimens excluding fault zones is generally employed to test fault slip and evaluate the mechanical slip stability of gas storage faults under alternating stress. However, the loading methods used in existing technologies differ significantly from the actual faults and their surrounding environment. Existing technologies often employ biaxial direct shear tests, which apply only biaxial stress to the specimen, while underground rocks are subjected to triaxial stress. Furthermore, activities such as earthquakes and oil and gas resource development subject faults to alternating stress.

[0072] To reconstruct the stress conditions of a true underground fault, Chinese Patent Publication No. CN112461668A discloses an experimental method for studying fault activation induced by hydraulic fracturing. The method involves measuring the average axial displacement of a rock sample using two position sensors mounted on the sample. Another sensor attached to a radial ring records the lateral displacement of the rock sample. However, although this method employs alternating loading, the recorded lateral displacement does not represent the distance of relative fault displacement.

[0073] Chinese Patent Publication No. CN117470896A discloses a device and method for conducting hydrodynamic coupling tests on structural surfaces containing filling materials. By using a 5TE sensor, a thin-film pressure sensor, and an acoustic emission sensor, it obtains "load-displacement" data of the rock slippage process for analysis of experimental results. However, the fault displacement data monitored by this method cannot represent the relative displacement of the fault.

[0074] To solve the above-mentioned technical problems, the inventors have developed a device, a testing method, and a method for preparing fault samples for studying fault slip, which can measure the slip data of faults under alternating stress in real time.

[0075] Example 1

[0076] See Figures 1-3 This embodiment proposes an apparatus for studying fault slip and uses a fault sample for experiments. The fault sample can be cylindrical and is prepared based on real bedrock. The fault sample includes hanging wall bedrock 1, footwall bedrock 7, and a fault zone 3 connecting the hanging wall bedrock 1 and footwall bedrock 7. The hanging wall bedrock 1 and footwall bedrock 7 have a preset fault dip angle. The apparatus of this embodiment includes a triaxial stress testing device 17 and a clamping assembly, a first slip detection unit 2, a second slip detection unit 4, a fault slip sensor (not shown in the figure), an extensometer 16, and a fault compression measurement assembly disposed in the cavity of the triaxial stress testing device 17. The clamping assembly can clamp the upper and lower ends of the fault sample to fix the fault sample and ensure the stability of the fault sample's position during the experiment.

[0077] The triaxial stress experimental apparatus 17 includes a loading mechanism that applies a preset alternating stress (including preset axial pressure and preset confining pressure) to the fault sample to reproduce the stress conditions of a real underground fault. The first slip detection unit 2, the second slip detection unit 4, and the fault slip sensor are all mounted on the surface of the fault sample, with the fault slip sensor located at the center of the fault zone 3 and equidistantly positioned between the first slip detection unit 2 and the second slip detection unit 4. The first slip detection unit 2 is located on the surface of the hanging wall bedrock 1 and is attached to the boundary between the fault zone 3 and the hanging wall bedrock 1. The second slip detection unit 4 is located on the surface of the footwall bedrock 7 and is attached to the boundary between the fault zone 3 and the footwall bedrock 7. Here, when the fault sample is cylindrical, the first slip detection unit 2, the second slip detection unit 4, and the fault slip sensor are all arc-shaped to ensure complete contact with the fault sample and guarantee measurement accuracy. One end of the extensometer 16 is fixed to the upper end of the clamping assembly, while the other end can move vertically relative to the lower end of the clamping assembly. When the hanging wall bedrock 1 and the footwall bedrock 7 shift under a preset alternating stress, the fault slip sensor can detect the displacement of the first slip detection unit 2 and the second slip detection unit 4, obtaining fault slip data. Simultaneously, the extensometer 16 can detect the overall compression data of the fault sample. In addition, a fault compression measurement component is provided on the surface of the fault sample. When the fault zone 3 is compressed under a preset alternating stress, the fault compression measurement component can detect the fault compression data.

[0078] In use, the first slip detection unit 2, the second slip detection unit 4, and the fault slip sensor are installed on the surface of the fault sample. The fault sample is fixed to the clamping assembly, and the clamping assembly and the fault sample are placed in the inner cavity of the triaxial stress experimental device 17. A preset alternating stress is applied to the fault sample by the loading mechanism. When the hanging wall bedrock 1 and the footwall bedrock 7 shift under the preset alternating stress, the first slip detection unit 2 and the second slip detection unit 4 will shift along with the hanging wall bedrock 1 and the footwall bedrock 7, respectively. The displacement of the first slip detection unit 2 and the second slip detection unit 4, detected by the fault slip sensor, reflects the displacement when the hanging wall bedrock 1 and the footwall bedrock 7 shift relative to each other, and is used as fault slip data. Simultaneously, under the action of a preset alternating stress, the fault sample will compress. During compression, the extensometer 16 will move vertically relative to the lower end of the clamping assembly. The extensometer 16 can measure the moving distance, which reflects the axial compressive deformation of the fault sample under the preset alternating stress, thus obtaining overall compression data. Under the action of the preset alternating stress, the fault zone 3 will also compress. At this time, the amount of compression generated by the fault zone 3 can be measured using the fault compression measurement assembly, thus obtaining fault compression data.

[0079] In this embodiment, by installing components such as the first slip detection unit 2, the second slip detection unit 4, the fault slip sensor (not shown in the figure), the extensometer 16, and the fault compression measurement assembly on the surface of the fault sample, fault slip data, fault compression data, and overall compression data are monitored. This provides a more comprehensive and accurate monitoring of the actual deformation of the fault compared to existing technologies, and provides more comprehensive and accurate data support for studying the behavior mechanism of the fault under alternating stress.

[0080] In this embodiment, for fault samples where the bedrock (i.e., the hanging wall bedrock 1 and the footwall bedrock 7 mentioned above) is weak rock (such as sandstone), when the fault sample is subjected to a preset alternating stress, the bedrock itself will deform due to the stress, which will interfere with the measurement of fault slip. In order to effectively avoid the deformation of the bedrock, firstly, by equidistantly placing the fault slip sensor between the first slip detection unit 2 and the second slip detection unit 4, it can be ensured that the fault sensor can accurately capture the relative displacement change between the two, so as to effectively avoid the measurement error caused by bedrock deformation. Secondly, by attaching the first slip detection unit 2 and the second slip detection unit 4 to the corresponding bedrock, it can be ensured that the first slip detection unit 2 and the second slip detection unit 4 slide together with the corresponding bedrock, thereby truly reflecting the displacement of the bedrock. Combining the above two points, the displacement measured by the fault sensor actually reflects the real displacement between the hanging wall bedrock 1 and the footwall bedrock 7 due to relative displacement, and can accurately reflect the actual situation of fault slip.

[0081] In this embodiment, by precisely controlling the loading mechanism to apply a preset alternating stress, the frequency and amplitude of the alternating loading can be controlled to reproduce the stress conditions of a real underground fault under different stress conditions, thereby more accurately assessing the slip stability of the fault. Fault slip sensors are used to detect the positional changes of the first slip detection unit 2 and the second slip detection unit 4 in real time, and to record the dynamic slip data of the fault sample under the preset alternating stress. The collected fault slip data can be further processed and analyzed, including the study of parameters such as the magnitude of displacement (slip distance) and slip velocity, as well as the identification of slip patterns, to assess the slip stability of the fault under the preset alternating stress. This is of great significance for understanding the behavior mechanism of faults and the safe operation of gas storage facilities. Simultaneously, it can also achieve the purpose of evaluating the fault sealing performance and the site selection and pressurization operation of gas storage facilities.

[0082] In one specific embodiment, see [reference] Figure 3The loading mechanism may include a confining pressure loading mechanism 18 and an axial pressure loading mechanism 19. The axial pressure loading mechanism 19 acts on the entire fault sample to apply a preset axial pressure to the fault sample. The confining pressure loading mechanism 18 is connected to the inner cavity of the triaxial stress test device 17 through a pipe and can deliver hydraulic oil at a preset pressure to provide a preset confining pressure to the fault sample, so as to restore the stress condition of the real fault underground and improve the accuracy of the experiment.

[0083] In one specific embodiment, see [reference] Figure 1 The fault compression measurement assembly includes a first compression detection unit 5, a second compression detection unit 6, and a fault compression sensor (not shown in the figure). The fault compression sensor is equidistantly positioned between the first compression detection unit 5 and the second compression detection unit 6. The first slip detection unit 2 is located on the surface of the hanging wall bedrock 1, close to the fault zone 3, and the second slip detection unit 4 is located on the surface of the footwall bedrock 7, close to the fault zone 3. When the fault sample is subjected to a preset alternating stress, the fault zone 3 will compress. The first compression detection unit 5 and the second compression detection unit 6 will displace along with the hanging wall bedrock 1 and the footwall bedrock 7, respectively. The fault compression sensor detects the displacement of the first slip detection unit 2 and the second slip detection unit 4. This displacement reflects the amount of compressive deformation of the fault zone 3 under the preset alternating stress, serving as fault compression data to accurately assess the deformation of the fault zone 3 under the preset alternating stress. Furthermore, by combining the preset alternating stress applied by the loading mechanism, the compression-slip relationship of the fault under different stress conditions can be studied, providing more comprehensive and accurate data support for studying the behavior mechanism of the fault under alternating stress.

[0084] In one specific embodiment, see [reference] Figure 2 The clamping assembly includes a first pressure block 12 and a second pressure block 13, which are respectively connected to the upper and lower ends of the fracture sample. The first pressure block 12, the second pressure block 13 and the fracture sample are coaxially arranged to avoid the fracture sample being subjected to eccentric force during the experiment, which would affect the fracture and sliding behavior of the fracture sample. This embodiment can ensure that the stress distribution inside the fracture sample is uniform, thereby improving the accuracy and reliability of the experiment.

[0085] In one specific embodiment, see [reference] Figure 2The first pressure block 12 is circumferentially sleeved on the first fixing member 14, and the second pressure block 13 is circumferentially sleeved on the second fixing member 15. One end of the extensometer 16 is connected to the first fixing member 14, and the other end passes through the second fixing member 15. When the fault sample is compressed under a preset alternating stress, the extensometer 16 will move vertically relative to the second fixing member 15. The extensometer 16 can measure the moving distance, which reflects the axial compression deformation of the fault sample under the preset alternating stress, serving as overall compression data. By setting the extensometer 16, the deformation of the fault sample under the preset alternating stress can be accurately measured to understand the mechanical properties of the fault sample, such as elastic modulus and yield strength, providing more comprehensive and accurate data support for studying the behavior mechanism of faults under alternating stress.

[0086] In one specific embodiment, see [reference] Figure 2 The apparatus of this embodiment further includes at least one set of acoustic emission sensor assemblies mounted on the surface of the fault sample. Each set of acoustic emission sensor assemblies includes a first acoustic emission sensor 11 and a second acoustic emission sensor 10. The first acoustic emission sensor 11 is disposed on the hanging wall bedrock 1, and the second acoustic emission sensor 10 is disposed on the footwall bedrock 7, with the first acoustic emission sensor 11 and the second acoustic emission sensor 10 aligned on the same vertical line. The first acoustic emission sensor 11 and the second acoustic emission sensor 10 are used to detect acoustic signals generated by the fault sample, which are typically caused by the propagation of microcracks, frictional slip, or other physical processes within the rock. It is worth noting that when multiple sets of acoustic emission sensor assemblies are provided, the acoustic emission sensor assemblies should be evenly distributed on the surface of the fault sample. For example, when three sets of acoustic emission sensor assemblies are provided and the fault sample is cylindrical, each set of acoustic emission sensor assemblies should be spaced 120° apart. Figure 1 The first acoustic emission sensor 9 and the second acoustic emission sensor 8 shown are the second set of acoustic emission sensor components, and the third set of acoustic emission sensor components is located behind the fracture sample in the figure.

[0087] Under stress, the fault sample deforms internally, fracturing and rapidly releasing strain energy, generating stress waves. These stress waves propagate through the rock material to the surface of the fault sample, causing minute surface displacements. Since the first acoustic emission sensor 11 and the second acoustic emission sensor 10 are respectively installed on the surfaces of the hanging wall bedrock 1 and the footwall bedrock 7, and are aligned vertically, they can capture the surface displacements caused by the stress waves emanating from the fault zone 3. This allows the acoustic signals to be collected and recorded by the first acoustic emission sensor 11 and the second acoustic emission sensor 10. Analysis of the collected acoustic signals allows determination of the slip stage of the fault sample (including three stages: stable stage, steady-slip stage, and stick-slip stage). Specifically:

[0088] During the stable phase, the fault sample is relatively stable with no obvious slippage, and the intensity of the acoustic signal is extremely low. During the steady-slip phase, the fault sample exhibits more slippage, which is stable and continuous without violent vibrations. Although the intensity of the acoustic signal increases slightly compared to the stable phase, it remains relatively low. During the stick-slip phase, the fault sample experiences severe instability, and the intensity of the acoustic signal increases dramatically. At this point, it can be concluded that the fault sample has slipped or fractured. Real-time monitoring of the acoustic signal using acoustic emission sensor components can promptly detect abnormal fault activity, serving as an effective early warning method.

[0089] In one specific embodiment, see [reference] Figure 1 and Figure 2 The apparatus in this embodiment also includes an acoustic signal processing device (not shown in the figure). The acoustic signal processing device is connected to the first acoustic emission sensor 11 and the second acoustic emission sensor 10. The acoustic signal processing device can receive the acoustic signals detected by the first acoustic emission sensor 11 and the second acoustic emission sensor 10, and determine the slip stage of the fault sample based on the change amplitude of the acoustic signal. By monitoring the change amplitude of the acoustic signal, the slip stage of the fault sample can be accurately determined. When the intensity of the acoustic signal suddenly increases, it often indicates that the fault sample is about to enter the stick-slip stage or has already slipped or fractured.

[0090] In one specific embodiment, see [reference] Figure 1 and Figure 2 The apparatus in this embodiment also includes a data processing device (not shown in the figure). The data processing device is connected to the loading mechanism, fault slip sensor, fault compression sensor, and extensometer 16. It receives signals from each sensor and extensometer 16 and can preprocess and store these signals. Preprocessing may include signal amplification, filtering, and noise reduction steps to ensure the accuracy and reliability of the data, thereby obtaining accurate fault slip data, fault compression data, overall compression data, and preset alternating stress values. Based on the preset alternating stress values, the friction coefficient of the fault sample is calculated, revealing the dynamic change of the friction coefficient under alternating stress, thus enabling a more accurate assessment of the sliding stability of the fault sample. The data stored in the data processing device can be used for further analysis and processing, such as plotting deformation curves, performing spectral analysis, and calculating mechanical parameters, to gain a deeper understanding of the mechanical behavior and fracture mechanism of the fault, as well as energy conversion during the sliding process.

[0091] Example 2

[0092] Based on the same inventive concept, see [reference] Figure 4 This embodiment proposes a testing method for studying fault slip, using the fault slip research apparatus described in Embodiment 1, including the following steps:

[0093] Step S1: Install the first slip detection unit, the second slip detection unit, the fault slip sensor, and the fault compression measurement assembly on the surface of the fault sample.

[0094] In one specific embodiment, the tomographic compression measurement assembly may include the first compression detection unit, the second compression detection unit, and the tomographic compression sensor described in Embodiment 1, and the first and second acoustic emission sensors may be disposed on the surface of the tomographic sample. Therefore, step S1 above may specifically include the following steps:

[0095] The first slip detection unit, the second slip detection unit, and the fault slip sensor are attached to the fault zone along the dip angle using adhesive.

[0096] The first compression probe, the second compression probe, and the fault compression sensor are attached to the axial direction of the fault sample.

[0097] Acoustic emission sensor arrays are uniformly arranged on the surface of the fault sample. The first and second acoustic emission sensors correspond one-to-one, and the distance between the first and second acoustic emission sensors and the end face of the fault sample is consistent.

[0098] Step S2: Seal the surface of the fracture sample with sealing material. After sealing, connect the fracture sample to the clamp assembly.

[0099] In step S2 above, when applying a preset alternating stress (including axial compression and confining pressure) to the fault sample using a loading mechanism, hydraulic oil is typically used for confining pressure loading. However, if the fault sample breaks in the later stages of the experiment, the hydraulic oil can enter the sample, affecting the experimental results. Therefore, sealing the surface of the fault sample with a sealing material can effectively isolate the sealing oil from the fault sample, ensuring the accuracy of the experimental data. It is worth noting that when sealing the fault sample, the aforementioned components, including the first slip detection unit, second slip detection unit, fault slip sensor, first compression detection unit, second compression detection unit, fault compression sensor, first acoustic emission sensor, and second acoustic emission sensor, should be exposed.

[0100] In one specific embodiment, the clamping assembly may include the first clamping block and the second clamping block as described in Embodiment 1, with the first fixing member circumferentially sleeved on the first clamping block and the second fixing member circumferentially sleeved on the second clamping block. Therefore, step S2 above may specifically include the following steps:

[0101] Insert the second fixing piece into the second pressure block, place the fracture sample on the upper end of the second pressure block, and then place the first pressure block on the upper end of the fracture sample. Use tape to fix the fracture sample to the joint between the first and second fixing pieces, or take two sections of heat shrink tubing and put them on the joint between the fracture sample and the first and second fixing pieces, and use a hot air gun to heat and shrink them for fixation. During the above fixing process, it should be ensured that the fracture sample is coaxially set with the first and second fixing pieces.

[0102] Structural adhesive is evenly applied to the air-exposed areas of the fault sample, as well as the contact areas between the first and second pressure blocks and the fault sample, using a glue gun to create a sealed environment for the fault sample and prevent the confining oil from contacting the sample.

[0103] Insert the first fixing member into the first pressure block, insert the extensometer through the second fixing member between the first and second fixing members, and connect the extensometer to the first fixing member.

[0104] Step S3: Place the clamping assembly into the inner cavity of the triaxial stress test apparatus.

[0105] Step S4: Apply a preset alternating stress to the fault sample using a loading mechanism.

[0106] In step S4 above, the preset alternating stress includes a preset axial compression and a preset confining pressure. The specific process of applying the preset alternating stress using a loading mechanism may include:

[0107] Axial and confining pressures are applied to the fault sample in an incremental manner until the applied axial and confining pressures reach the preset axial and confining pressures, respectively. The preset axial and confining pressures are then continuously applied to the fault sample.

[0108] Step S5: Under a preset alternating stress, the displacement of the first and second slip detection parts is detected by the fault slip sensor to obtain fault slip data. The axial compression deformation of the fault sample under the preset alternating stress is detected by the extensometer to obtain overall compression data. The fault compression data is then obtained by the fault compression measurement component.

[0109] After completing step S5 above, the dynamic change of the friction coefficient of the fault sample under alternating stress can be calculated using formulas, thereby enabling a more accurate assessment of the sliding stability of the fault sample:

[0110] Based on the preset axial pressure and preset confining pressure, the friction coefficient of the fault sample is calculated according to the following formula (1):

[0111]

[0112] In the above formula: σ n This represents the normal stress experienced by the fault sample.

[0113] τ is the shear stress experienced by the fault sample;

[0114] μ is the friction coefficient of the fault sample;

[0115] σ1, σ2, and σ3 are the first principal stress, the second principal stress, and the third principal stress, respectively. The value of the first principal stress is equal to the preset axial compression, and the values ​​of the second and third principal stresses are equal to the preset confining pressure.

[0116] Under alternating stress, the shear strength of a fault plane gradually decreases with the increase of the number of alternations. When the number of alternations increases to a certain value, the decrease in the shear strength of the fault plane gradually slows down and eventually tends to a constant value. If the shear stress on the fault plane exceeds its shear strength at this point, the fault plane will fracture. Monitoring the dynamic ratio of shear stress to normal stress during fault slip can quantitatively describe the potential slip trend of the fault, providing an effective way for assessing the stress state of faults in gas storage facilities and analyzing the potential hazards of active faults.

[0117] Example 3

[0118] Fault samples containing fault zones are essential for conducting laboratory tests on the aforementioned fault slip. However, the geological conditions of depleted oil and gas reservoirs, saline strata, and aquifer structures—which serve as targets for reservoir construction—are extremely complex. These geological formations typically contain well-developed fault systems, and some reservoirs are even directly sealed by faults. Furthermore, the high degree of fracturing and softness of the rock mass at fault locations often lead to core blockage and drill bit failure during core extraction. In addition, directly using natural underground rocks for testing presents difficulties in sample preparation and compromises test consistency. Therefore, in fault slip experimental research, self-prepared fault samples are frequently used for relevant tests.

[0119] The inventors discovered that in existing fault sample preparation processes, the fault samples used only include the hanging wall bedrock and the footwall bedrock. When the fault planes at the edges or inside the hanging wall and footwall bedrock do not meet the requirements, they are usually sanded to achieve a predetermined angle before being directly spliced ​​together for experiments. In reality, there is a certain degree of cementation between the fault zone and the hanging wall and footwall bedrock. Existing fault sample preparation methods do not take this into account, resulting in fault samples that differ significantly from the actual underground faults, and experimental data lacking accuracy and reliability.

[0120] To address the aforementioned problems, based on the same inventive concept, see [reference] Figure 5 This embodiment proposes a method for preparing a tomographic sample, which specifically includes the following steps:

[0121] Step s1: Obtain rock cores from the target study area and fabricate a plunger.

[0122] Step s2: Based on the preset fault dip angle, cut from the center point of the plunger and grind the cut surface of the plunger to obtain the hanging wall bedrock and the footwall bedrock.

[0123] In step s2 above, when grinding the cross-section of the plunger, attention should be paid to ensuring that the dip angles of the upper and lower bedrock sections are consistent.

[0124] Step s3: Use pre-mixed filling and casting material to bond the upper and lower bedrock together, and make the height of the filling and casting material consistent with the height of the preset fault zone. The solidified filling and casting material serves as the fault zone to obtain a fault sample.

[0125] In step s3 above, the filling material should be selected as a material with fluidity, relatively low viscosity, and the ability to solidify under certain conditions. The filling material can be one of cement mortar, gypsum, epoxy resin, or paraffin wax. In this embodiment, cement mortar is used as the filling material. The cement mortar is pre-mixed, and during the mixing process, the strength of the cement mortar needs to reach a preset strength, generally C30 strength cement mortar. The strength of the cement mortar is proportional to the anisotropy parameters of the rock core. Of course, cement mortars of different strengths can also be mixed to obtain multiple fault samples to study the failure characteristics and mechanical characteristics of fault zones with different strengths, providing a certain reference value for injection and extraction. When pouring the filling material, uniform pouring should be ensured to guarantee uniform fault zone thickness. After pouring, a 14-day curing period is performed to obtain fault samples.

[0126] For example, core samples were taken from the target study area, and a 50mm diameter plunger was drilled. Based on a preset fault dip angle, the plunger was cut at its center point. The cut surface of the plunger yielded the hanging wall bedrock and the footwall bedrock, ensuring a joint height (without fault zones) of 95mm between the two. Cement mortar, made from silicate cement and river sand, was used to bond the hanging wall and footwall bedrock. After 14 days of curing, a fault sample with a diameter of 50mm and a height of 100mm was obtained.

[0127] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. This disclosure 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 this disclosure is limited only by the appended claims. Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. An apparatus for studying fault slip, characterized in that, It includes a triaxial stress testing apparatus and a clamping assembly, a first slip detection unit, a second slip detection unit, a fault slip sensor, an extensometer, and a fault compression measurement assembly disposed in the inner cavity of the triaxial stress testing apparatus; The clamping assembly is capable of clamping the upper and lower ends of the fault sample, wherein the fault sample includes an upper wall bedrock and a lower wall bedrock with a preset fault dip angle, and a fault zone connecting the upper wall bedrock and the lower wall bedrock. The first slip detection unit is disposed on the surface of the hanging wall bedrock and is attached to the junction of the fault zone and the hanging wall bedrock; The second slip detection unit is disposed on the surface of the footwall bedrock and is attached to the junction of the fault zone and the footwall bedrock; The fault slip sensor is located at the center of the fault zone and is equidistantly disposed between the first slip detection unit and the second slip detection unit; The triaxial stress testing device includes a loading mechanism, which is capable of applying a preset alternating stress to the fault sample. The fault slip sensor is used to detect the displacement of the first slip detection part and the second slip detection part when the hanging wall bedrock and the footwall bedrock move under a preset alternating stress, and to obtain fault slip data. One end of the extensometer is fixed to the upper end of the clamping assembly, and the other end can move vertically relative to the lower end of the clamping assembly. It is used to detect the axial compression deformation of the fracture sample under a preset alternating stress and obtain overall compression data. The fault compression measurement component is disposed on the surface of the fault sample and is used to detect fault compression data when the fault zone is compressed under a preset alternating stress.

2. The apparatus for studying fault slip according to claim 1, characterized in that, The fault compression measurement assembly includes a first compression detection unit, a second compression detection unit, and a fault compression sensor; The first slip detection unit is disposed on the surface of the hanging wall bedrock and is located close to the fault zone; The second slip detection unit is disposed on the surface of the footwall bedrock and is located close to the fault zone; The fault compression sensor is equidistantly disposed between the first compression detection unit and the second compression detection unit, and is used to detect the displacement of the first slip detection unit and the second slip detection unit when the fault zone is compressed under a preset alternating stress, so as to obtain the fault compression data.

3. The apparatus for studying fault slip according to claim 1 or 2, characterized in that, The clamping assembly includes a first pressure block and a second pressure block; The first pressure block and the second pressure block are respectively connected to the upper and lower ends of the fracture sample, and the first pressure block, the second pressure block and the fracture sample are coaxially arranged.

4. The apparatus for studying fault slip according to claim 3, characterized in that, The first pressure block is circumferentially sleeved with the first fixing member; The second pressure block is circumferentially sleeved with the second fixing member; One end of the extensometer is connected to the first fixing member, and the other end passes through the second fixing member; The extensometer is used to detect the vertical movement of the fracture sample relative to the second fixing member when the fracture sample is compressed under a preset alternating stress, and to obtain the overall compression data.

5. The apparatus for studying fault slip according to claim 1 or 4, characterized in that, It also includes at least one set of acoustic emission sensor assemblies mounted on the surface of the fracture sample; Each acoustic emission sensor assembly includes a first acoustic emission sensor and a second acoustic emission sensor. The first acoustic emission sensor is located on the upper bedrock, and the second acoustic emission sensor is located on the lower bedrock, with the first acoustic emission sensor and the second acoustic emission sensor on the same vertical line; The first acoustic emission sensor and the second acoustic emission sensor are used to detect the acoustic signals generated by the fracture sample.

6. The apparatus for studying fault slip according to claim 5, characterized in that, It also includes sound signal processing equipment; The acoustic signal processing device is connected to the first acoustic emission sensor and the second acoustic emission sensor, and is used to receive the acoustic signals detected by the first acoustic emission sensor and the second acoustic emission sensor, and determine the slip stage of the fault sample based on the change amplitude of the acoustic signals.

7. The apparatus for studying fault slip according to claim 5, characterized in that, It also includes data processing equipment; The data processing device is connected to the loading mechanism, the fault slip sensor, the fault compression sensor, and the extensometer to acquire the value of the preset alternating stress, the fault slip data, the fault compression data, and the overall compression data, and calculates the friction coefficient of the fault sample based on the value of the preset alternating stress.

8. A testing method for studying fault slip, using the apparatus for studying fault slip as described in claims 1-7, characterized in that, include: A first slip detection unit, a second slip detection unit, a fault slip sensor, and a fault compression measurement assembly are installed on the surface of the fault sample. The surface of the fracture sample is sealed with a sealing material. After sealing, the fracture sample is connected to the clamp assembly. One end of the extensometer is fixed to the upper end of the clamp assembly; The clamping assembly is placed inside the cavity of the triaxial stress testing apparatus; A preset alternating stress is applied to the fracture sample using a loading mechanism; Under a preset alternating stress, the displacement of the first slip detection part and the second slip detection part is detected by the fault slip sensor to obtain fault slip data. The axial compression deformation of the fault sample under the preset alternating stress is detected by the extensometer to obtain overall compression data. Finally, the fault compression measurement component is used to detect the fault compression data.

9. The test method for studying fault slip according to claim 8, characterized in that, The preset alternating stress includes preset axial compression and preset confining compression; The application of a preset alternating stress to the fracture sample using a loading mechanism includes: Axial pressure and confining pressure are applied to the fault sample in an incremental manner until the applied axial pressure and confining pressure reach the preset axial pressure and preset confining pressure, respectively, and the preset axial pressure and preset confining pressure are continuously applied to the fault sample.

10. The test method for studying fault slip according to claim 9, characterized in that, The method further includes: under a preset alternating stress, using the fault slip sensor to detect the displacement of the first slip detection unit and the second slip detection unit to obtain fault slip data; using the extensometer to detect the axial compression deformation of the fault sample under the preset alternating stress to obtain overall compression data; and using the fault compression measurement component to detect the fault compression data. Based on the preset axial pressure and preset confining pressure, the friction coefficient of the fault sample is calculated according to the following formula: In the above formula: σ n The normal stress experienced by the fracture sample; τ is the shear stress experienced by the fault sample; μ is the friction coefficient of the fault sample; σ1, σ2, and σ3 are the first principal stress, the second principal stress, and the third principal stress, respectively. The value of the first principal stress is equal to the preset axial compression, and the values ​​of the second and third principal stresses are equal to the preset confining pressure.

11. A method for preparing a tomographic sample, characterized in that, include: Obtain rock cores from the target study area and fabricate a plunger; Based on the preset fault dip angle, the plunger is cut from the center point, and the cut surface of the plunger is ground to obtain the hanging wall bedrock and the footwall bedrock. The upper bedrock and the lower bedrock are bonded together using pre-mixed filling and casting materials, and the height formed by the filling and casting materials is consistent with the height of the preset fault zone. The solidified filling and casting materials serve as the fault zone to obtain a fault sample.

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