Testing device and method for measuring deep ground stress gradient based on rock thermal spalling

Abstract

The invention discloses a testing device and method for measuring deep ground stress gradient based on rock thermal spalling. The testing device comprises a high-temperature heat source device, an in-situ response monitoring device, a pushing mechanism and a data processing center, the high-temperature heat source device heats the surfaces of rocks with different depths, and the in-situ response monitoring device synchronously acquires corresponding data in situ, so that the direct measurement of rock thermal spalling behavior difference caused by different ground stress is particularly sensitive to a deep ground high-stress area, errors caused by multi-parameter and multi-step indirect calculation are avoided, and the accuracy of rock thermal spalling behavior difference measurement is improved. The precision of measured data is effectively improved; the pushing mechanism adjusts the positions and orientations of the high-temperature heat source device and the in-situ response monitoring device, multi-directional measurement under the same depth is achieved, then the maximum horizontal principal stress direction is directly determined, the result is more visual and reliable, and subsequent excavation design or other tests on rocks are facilitated. In addition, the whole testing process does not need packing and is not affected by drilling fluid, and finally, the deep ground stress gradient is accurately and efficiently measured.

Description

Technical Field

[0001] This invention belongs to the field of geological exploration and rock mechanics technology, specifically a testing device and method for measuring deep-ground stress gradient based on rock thermal exfoliation. Background Technology

[0002] Accurately obtaining the magnitude, direction, and gradient of the deep geostress field is a crucial prerequisite for oil and gas exploration and development, hot dry rock mining, nuclear waste geological disposal, deep mining, and large-scale underground engineering construction. Currently, the main in-situ stress measurement methods include hydraulic fracturing, acoustic emission (Kaiser effect), borehole collapse, and strain relief methods.

[0003] Hydraulic fracturing is currently the most widely used method, but one of its assumptions is that the rock is an isotropic linear elastic body and that the stress perpendicular to the borehole direction is the minimum principal stress. These assumptions often do not hold true in complex geological environments. Furthermore, under extremely high stress conditions, packer setting is difficult, resulting in a low test success rate. Acoustic emission methods exhibit large results dispersion and heavily rely on high-quality core samples. Borehole collapse methods can only provide indirect information about stress direction. All of the above existing methods suffer from low testing accuracy in deep geostress testing.

[0004] Rock thermal exfoliation is a phenomenon in which thin layers of rock buckle and detach under high-temperature heat flow, eventually intruding into the rock. Existing theoretical and experimental studies indicate that the presence of geostress significantly affects the critical temperature or critical heat flux density required to induce thermal exfoliation, and that the intermediate principal stress plays a decisive role in controlling the entire process of thermal exfoliation. In other words, current research only qualitatively establishes a relationship between geostress and the critical temperature of rock thermal exfoliation. Furthermore, this relationship has not yet been utilized in techniques for quantitatively measuring geostress.

[0005] Therefore, the research direction of this invention is to provide a new testing device and method that can establish a quantitative relationship between thermal exfoliation and deep geostress, and use thermal exfoliation to measure geostress data at different depths in situ, thereby accurately obtaining the deep geostress gradient. The entire testing process has the advantages of being direct and efficient. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a testing device and method for measuring deep-ground stress gradient based on rock thermal exfoliation, which can effectively solve the aforementioned technical problems.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a testing device for measuring deep stress gradient based on rock thermal exfoliation, comprising a high-temperature heat source device, an in-situ response monitoring device, a pushing mechanism, and a data processing center; the high-temperature heat source device and the in-situ response monitoring device are both mounted on the pushing mechanism. The high-temperature heat source device is used to generate a high-energy-density heat flow and locally focus heating the rock surface; the in-situ response monitoring device is used to simultaneously monitor the temperature field changes, exfoliation process images, and acoustic emission signals in the heating area of ​​the high-temperature heat source device; the pushing mechanism is used to adjust the position and orientation of the high-temperature heat source device and the in-situ response monitoring device underground, so that the high-temperature heat source device and the in-situ response monitoring device can heat the required area and monitor data; the data processing center is located on the ground or in the mine, and is connected to the high-temperature heat source device, the in-situ response monitoring device, and the pushing mechanism. It is used to control the output power and time of the high-temperature heat source system and to control the position and orientation adjustment of the high-temperature heat source device and the in-situ response monitoring device by the pushing mechanism. At the same time, it can receive the data collected by the in-situ response monitoring device, analyze and process it, and determine the deep rock stress gradient.

[0008] Furthermore, the high-temperature heat source device is an adjustable high-power laser. This structure facilitates precise control of the heating temperature.

[0009] Furthermore, the in-situ response monitoring device includes a high-speed infrared thermal imager, a high-speed camera, and an acoustic emission monitoring group; the high-speed infrared thermal imager is used for non-contact measurement of the temperature field distribution and changes in the heated area; the high-speed camera, in conjunction with a coaxial or lateral illumination source, is used to record the morphological and dynamic characteristics of the rock spalling process in the heated area; the acoustic emission monitoring group is used to collect elastic wave signals generated by rock spalling in the heated area to obtain the starting time of rock spalling.

[0010] Furthermore, the pushing mechanism includes a pushing arm and a rotating mechanism. The rotating mechanism is mounted on one end of the pushing arm and can rotate 360° relative to the pushing arm. The rotating mechanism is provided with multiple support rods, which are used to place the high-temperature heat source device and the in-situ response monitoring device, respectively. During measurement, one end of the pushing arm drives the rotating mechanism to extend to the required measurement depth. After the rotating mechanism rotates, it makes the high-temperature heat source device and the in-situ response monitoring device face the required measurement position.

[0011] Furthermore, the data processing center is connected to the high-temperature heat source device, the in-situ response monitoring device, and the pushing mechanism via a cable bus. Using a cable bus ensures the stability of data transmission between the data processing center and various downhole components, as well as guarantees power supply requirements.

[0012] The working method of the above-mentioned testing device for measuring deep-ground stress gradient based on rock thermal exfoliation includes the following steps:

[0013] S1: Laboratory calibration: Rock samples were obtained from the target area, and different gradients of geostress were applied to the rock samples in a true triaxial pressure chamber. The rock samples were heated using a high-temperature heat source device, and the heating data was obtained using an in-situ response monitoring device. The critical temperature of thermal exfoliation of the rock samples under different geostress conditions was obtained, and then a functional relationship model between the geostress value and the critical temperature of thermal exfoliation of the rock sample was established.

[0014] S2: Downhole testing: The testing device is lowered to the target depth in the borehole, shaft, or tunnel. The position and orientation of the high-temperature heat source device and the in-situ response monitoring device are adjusted by the pushing mechanism until the required heating area is reached and then stopped. Then, the high-temperature heat source device is controlled to heat the heating area, and the data of the heating area is collected synchronously by the in-situ response monitoring device until the rock thermal spalling is detected and the heating process is stopped, and the critical heating temperature at this time is obtained.

[0015] S3: Data Inversion: Substitute the critical heating temperature of the rock at the current depth and orientation obtained in step S2 into the functional relationship model established in step S1, and invert the calculation to obtain the in-situ stress value at the heating point.

[0016] S4: Gradient calculation: Keep the orientation constant, change the test depth, repeat steps S2 and S3 to obtain the ground stress values ​​at different depths in the same orientation, and then fit the gradient law of the change of ground stress with depth in the same orientation.

[0017] Furthermore, the functional relationship model in step S1 is specifically: σ = f(q, p), where σ is the geostress, q is the critical heating temperature, and p is the rock physical and mechanical parameters of the rock sample.

[0018] Furthermore, in step S2, the high-temperature heat source device heats the rock surface at a temperature below the melting point of the rock in the current heating area. This ensures that the rock does not directly melt without thermal spalling due to excessively high heating temperature.

[0019] Furthermore, step S4 also includes: keeping the test depth constant, changing the orientation, and repeating steps S2 and S3 to obtain the geostress values ​​at different orientations at the same depth. Based on the magnitude of the critical heating temperature for inducing thermal spalling at different orientations, the direction in which the lowest critical heating temperature is most likely to cause thermal spalling on the rock heating surface is determined. This direction is perpendicular to the direction of the maximum horizontal principal stress, thereby determining the direction of the maximum horizontal principal stress at the same depth. Determining this direction facilitates subsequent rock excavation design and other tests.

[0020] Compared with existing technologies, the present invention combines a high-temperature heat source device, an in-situ response monitoring device, a pushing mechanism, and a data processing center, which has the following advantages:

[0021] 1. Directness and high sensitivity: This invention uses a high-temperature heat source device to heat the surface of rocks at different depths, while an in-situ response monitoring device simultaneously measures and acquires corresponding data during the heating process. This direct measurement of the differences in rock thermal exfoliation behavior caused by different ground stresses is particularly sensitive to deep, high-stress areas, avoiding errors caused by indirect calculations involving multiple parameters and steps, and effectively improving the accuracy of data acquisition.

[0022] 2. Precisely obtain the direction of the maximum principal stress: The present invention adjusts the position and orientation of the high-temperature heat source device and the in-situ response monitoring device through the pushing mechanism, thereby realizing multi-directional measurement at the same depth. Then, the direction of the maximum horizontal principal stress is directly determined according to the measured critical heating temperature of thermal exfoliation. The result is more intuitive and reliable, which is convenient for subsequent rock excavation design or other tests.

[0023] 3. Applicable to complex environments: The entire testing process of this invention does not require isolation and is not affected by drilling fluid, which has obvious advantages in high-stress hard rock environments where traditional hydraulic fracturing methods are difficult to implement.

[0024] 4. Accurate monitoring data: The in-situ response monitoring device of the present invention can simultaneously acquire thermal, visual and acoustic multimodal information during the heating process. After mutual verification, the starting time of peeling can be accurately obtained, and then the critical heating temperature can be obtained.

[0025] 5. One well can be used for multiple purposes: The boreholes or logging used for exploration in this invention do not require special setup and can be used for boreholes or logging that use other logging technologies; or the boreholes or logging constructed in this test can be used for other logging technologies in the future. This not only makes construction simpler, but also provides more comprehensive stratigraphic information for the required exploration area by combining multiple different logging technologies. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure after the testing device is set up in this invention.

[0027] Figure 2 This is a flowchart of the testing method of the present invention.

[0028] Figure 3 This is a schematic diagram of the "ground stress-critical temperature" relationship curve obtained from laboratory calibration in an embodiment of the present invention.

[0029] In the diagram: 1-Data processing center, 2-Cable bus, 3-Push mechanism control box, 4-Push arm, 5-High-speed camera, 6-High-speed infrared thermal imager, 7-Rotating mechanism, 8-Acoustic emission sensor, 9-Adjustable high-power laser. Detailed Implementation

[0030] The present invention will be further described below.

[0031] like Figure 1 As shown, a testing device for measuring deep stress gradient based on rock thermal exfoliation includes a high-temperature heat source device, an in-situ response monitoring device, a pushing mechanism, and a data processing center 1. Both the high-temperature heat source device and the in-situ response monitoring device are mounted on the pushing mechanism. The high-temperature heat source device generates a high-energy-density heat flow and locally focuses heat on the rock surface. The in-situ response monitoring device synchronously monitors the temperature field changes, exfoliation process images, and acoustic emission signals in the heating area of ​​the high-temperature heat source device. The pushing mechanism adjusts the position and orientation of the high-temperature heat source device and the in-situ response monitoring device underground, enabling them to heat and monitor the required area. The data processing center 1, located on the ground or in a mine, is connected to the high-temperature heat source device, the in-situ response monitoring device, and the pushing mechanism. It controls the output power and time of the high-temperature heat source system and the position and orientation adjustment of the high-temperature heat source device and the in-situ response monitoring device by the pushing mechanism. Simultaneously, it receives and analyzes the data collected by the in-situ response monitoring device to determine the deep rock stress gradient.

[0032] As an improvement of the present invention, the high-temperature heat source device is an adjustable high-power laser 9. This structure facilitates precise control of the heating temperature. The in-situ response monitoring device includes a high-speed infrared thermal imager 6, a high-speed camera 5, and an acoustic emission monitoring group; the high-speed infrared thermal imager 6 is used for non-contact measurement of the temperature field distribution and changes in the heating area; the high-speed camera 5, in conjunction with a coaxial or side-illumination light source, is used to record the morphological and dynamic characteristics of the rock spalling process in the heating area; the acoustic emission monitoring group consists of at least one acoustic emission sensor 8, used to collect the elastic wave signals generated by the rock spalling in the heating area to obtain the starting time of the rock spalling.

[0033] As another improvement of the present invention, the pushing mechanism includes a pushing arm 4 and a rotating mechanism 7. The rotating mechanism 7 is mounted on one end of the pushing arm 4 and can rotate 360° relative to the pushing arm. The rotating mechanism 7 has multiple support rods for placing the high-temperature heat source device and the in-situ response monitoring device, respectively. The pushing mechanism control box 3 receives instructions from the data processing center 1 to control the pushing arm 4 and the rotating mechanism 7. During measurement, the data processing center 1 controls the pushing arm 4 to drive the rotating mechanism 7 to extend to the required measurement depth via the pushing mechanism control box 3. After the data processing center 1 controls the rotating mechanism 7 to rotate, the high-speed camera 5 and the high-speed infrared thermal imager 6 in the high-temperature heat source device and the in-situ response monitoring device are oriented towards the required measurement position, while the acoustic emission sensor 8 is coupled to the rock wall surrounding the measurement position. The pushing arm 4 contains a cavity to achieve a through-link connection of the cable bus 2. The data processing center 1 is connected to the high-temperature heat source device, the in-situ response monitoring device, and the pushing mechanism via the cable bus 2. The use of the cable bus 2 ensures the stability of data transmission between the data processing center and various components downhole, as well as guarantees power supply requirements.

[0034] The aforementioned high-temperature heat source device, in-situ response monitoring device, push mechanism, and data processing center 1 are all existing equipment or structures that can be directly purchased from the market. This invention does not improve their structure but only utilizes their functions to achieve the corresponding inventive purpose.

[0035] like Figure 2 As shown, the working method of the above-mentioned testing device for measuring deep-ground stress gradient based on rock thermal exfoliation includes the following steps:

[0036] S1: Laboratory Calibration: Rock samples were obtained from the target area. Different gradients of geostress were applied to the rock samples in a true triaxial pressure chamber. A high-temperature heat source was used to heat the rock samples, and in-situ response monitoring was employed to acquire heating data. The critical thermal exfoliation temperature of the rock samples under different geostress conditions was obtained, such as... Figure 3 As shown, a functional relationship model between the geostress value and the critical thermal exfoliation temperature of the rock sample is established, specifically: σ = f(q, p), where σ is the geostress, q is the critical heating temperature, and p is the rock physical and mechanical parameters of the rock sample.

[0037] S2: Downhole Testing: The testing device is lowered to the target depth in the borehole, shaft, or tunnel. The position and orientation of the high-temperature heat source device and the in-situ response monitoring device are adjusted by the pushing mechanism until the desired heating area is reached. Then, the high-temperature heat source device is controlled to heat the heating area, while the in-situ response monitoring device synchronously collects data on the heating area until thermal spalling of the rock is detected, at which point the heating process stops and the critical heating temperature is obtained. The specific process is as follows: the high-speed infrared thermal imager 6 continuously records the temperature changes in the heating area, while the high-speed camera 5 continuously captures images of the heating area. The acoustic emission monitoring group is attached to the heating area. When the acoustic emission monitoring group collects elastic wave signals, and the high-speed camera 5 captures an image of thermal spalling in the heating area, the data processing center 1 compares and analyzes the two data to determine the starting time of rock spalling. The temperature of the heating area at that moment is determined based on the temperature data continuously fed back by the high-speed infrared thermal imager 6, and this temperature is determined as the critical heating temperature. The high-temperature heat source device heats the rock surface at a temperature below the melting point of the rock in the current heating area. This ensures that the rock does not become molten directly without thermal spalling due to excessive heating temperature.

[0038] S3: Data Inversion: Substitute the critical heating temperature of the rock at the current depth and orientation obtained in step S2 into the functional relationship model established in step S1, and invert the calculation to obtain the in-situ stress value at the heating point.

[0039] S4: Gradient Calculation: Keeping the orientation constant and changing the test depth, repeat steps S2 and S3 to obtain the geostress values ​​at different depths in the same orientation. Then, fit the gradient law of geostress variation with depth in the same orientation. Alternatively, keeping the test depth constant and changing the orientation, repeat steps S2 and S3 to obtain geostress values ​​at different orientations in the same depth. Based on the critical heating temperature for induced thermal spalling in different orientations, the direction with the lowest critical heating temperature is where thermal spalling of the rock surface is most likely to occur. This direction is perpendicular to the direction of the maximum horizontal principal stress, thus determining the direction of the maximum horizontal principal stress at the same depth. Determining this direction facilitates subsequent rock excavation design and other tests.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A testing device for measuring deep-ground stress gradient based on rock thermal exfoliation, characterized in that, This includes a high-temperature heat source device, an in-situ response monitoring device, a push mechanism, and a data processing center; Both the high-temperature heat source device and the in-situ response monitoring device are mounted on the pushing mechanism. The high-temperature heat source device is used to generate a high-energy-density heat flow and to locally focus the heating of the rock surface. The in-situ response monitoring device is used to simultaneously monitor the temperature field changes, peeling process images and acoustic emission signals in the heating area of ​​the high-temperature heat source device. The pushing mechanism is used to adjust the position and orientation of the high-temperature heat source device and the in-situ response monitoring device underground, so that the high-temperature heat source device and the in-situ response monitoring device can heat the required area and monitor data. The data processing center is located on the ground and is connected to the high-temperature heat source device, the in-situ response monitoring device, and the pushing mechanism. It is used to control the output power and time of the high-temperature heat source system and to control the position and orientation of the high-temperature heat source device and the in-situ response monitoring device by the pushing mechanism. At the same time, it can receive the data collected by the in-situ response monitoring device, analyze and process it, and determine the geostress gradient of the deep rock.

2. The testing device for measuring deep-ground stress gradient based on rock thermal exfoliation according to claim 1, characterized in that, The high-temperature heat source device is an adjustable high-power laser.

3. The testing device for measuring deep-ground stress gradient based on rock thermal exfoliation according to claim 1, characterized in that, The in-situ response monitoring device includes a high-speed infrared thermal imager, a high-speed camera, and an acoustic emission monitoring group; the high-speed infrared thermal imager is used for non-contact measurement of the temperature field distribution and changes in the heated area; the high-speed camera is used to record the morphological and dynamic characteristics of the rock exfoliation process in the heated area. The acoustic emission monitoring group is used to collect elastic wave signals generated by rock spalling in the heated area to obtain the starting time of rock spalling.

4. The testing device for measuring deep-ground stress gradient based on rock thermal exfoliation according to claim 1, characterized in that, The pushing mechanism includes a pushing arm and a rotating mechanism. The rotating mechanism is mounted on one end of the pushing arm and can rotate 360° relative to the pushing arm. The rotating mechanism is equipped with multiple support rods, which are used to place the high-temperature heat source device and the in-situ response monitoring device, respectively. During measurement, one end of the pushing arm drives the rotating mechanism to extend to the required measurement depth. After the rotating mechanism rotates, it makes the high-temperature heat source device and the in-situ response monitoring device face the required measurement position.

5. The testing device for measuring deep-ground stress gradient based on rock thermal exfoliation according to claim 1, characterized in that, The data processing center is connected to the high-temperature heat source device, the in-situ response monitoring device, and the pushing mechanism via a cable bus.

6. A method for operating the testing device for measuring deep-ground stress gradient based on rock thermal exfoliation according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Laboratory calibration: Rock samples were obtained from the target area, and different gradients of geostress were applied to the rock samples in a true triaxial pressure chamber. The rock samples were heated using a high-temperature heat source device, and the heating data was obtained using an in-situ response monitoring device. The critical temperature of thermal exfoliation of the rock samples under different geostress conditions was obtained, and then a functional relationship model between the geostress value and the critical temperature of thermal exfoliation of the rock sample was established. S2: Downhole test: Lower the test device to the target depth, adjust the position and orientation of the high-temperature heat source device and the in-situ response monitoring device through the pushing mechanism until the required heating area is reached and then stop; then control the high-temperature heat source device to heat the heating area, and at the same time use the in-situ response monitoring device to collect data of the heating area until the rock thermal spalling is detected and the heating process is stopped, and the critical heating temperature at this time is obtained. S3: Data Inversion: Substitute the critical heating temperature of the rock at the current depth and orientation obtained in step S2 into the functional relationship model established in step S1, and invert the calculation to obtain the in-situ geostress value at the heating point. S4: Gradient calculation: Keep the orientation constant, change the test depth, repeat steps S2 and S3 to obtain the ground stress values ​​at different depths in the same orientation, and then fit the gradient law of the change of ground stress with depth in the same orientation.

7. The working method according to claim 6, characterized in that, The functional relationship model in step S1 is specifically: σ=f(q,p), where σ is the geostress, q is the critical heating temperature, and p is the rock physical and mechanical parameters of the rock sample.

8. The working method according to claim 6, characterized in that, In step S2, the high-temperature heat source device heats the rock surface at a temperature below the melting point of the rock in the current heating area.

9. The working method according to claim 6, characterized in that, Step S4 further includes: keeping the test depth unchanged, changing the orientation, repeating steps S2 and S3 to obtain the ground stress values ​​at different orientations at the same depth, and determining the direction of the maximum horizontal principal stress at the same depth based on the magnitude of the critical heating temperature for induced thermal exfoliation at different orientations.

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