Rock core radial deformation measuring system and measuring method
The core radial deformation measurement system and method have solved the problems of complex, time-consuming and error-prone existing in-situ stress measurement, and have achieved rapid and accurate core elastic deformation measurement, providing a reliable in-situ stress reference for deep energy mining.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-03-27
AI Technical Summary
Existing methods for measuring geostress are complex, time-consuming, and prone to large errors, making it difficult to quickly and accurately measure the elastic deformation of rock cores, which affects deep energy extraction.
A core radial deformation measurement system was adopted, including a main frame, a rotating shaft, a drive device, a rotation controller, and a data acquisition unit. Combined with a CT scanning imaging unit, the core was sealed and preserved, and radial deformation was tested multiple times to eliminate interference from microcracks. The horizontal stress difference was calculated by combining the ultrasonic pulse method and rock mechanical parameters.
It enables rapid and accurate measurement of the true elastic deformation of rock cores, simplifies operation, reduces errors, provides reliable geostress references, and provides a basis for deep energy mining.
Smart Images
Figure CN121739965A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of geostress measurement technology, and in particular to a core radial deformation measurement system and method. Background Technology
[0002] In-situ stress is the initial stress existing in the Earth's crust and rock mass. It is one of the important physical properties of the solid Earth and a root cause of rock mass deformation, instability, and failure, while also affecting the extraction of deep energy sources such as oil, shale gas, and hot dry rock. For shale gas and hot dry rock reservoir development, the magnitude of differential stress is a key fundamental parameter for fracture system construction and fracture propagation into a network. Currently, in-situ stress measurement mainly relies on boreholes and core sampling, such as the elastic recovery method (ASR) of core samples. This method estimates the three-dimensional principal stress by testing the inelastic deformation of the core sample after it is removed from the stress environment. However, the operation procedure is complex, there are many interfering factors, and it is time-consuming (at least 7 days, and up to a month), making it difficult to quickly promote and apply on a large scale.
[0003] After core samples are extracted, they undergo both elastic and inelastic deformation. Elastic deformation largely recovers after drilling, making it difficult to measure and utilize. Furthermore, stress concentration at the bottom of the borehole and the weight of the drill pipe can cause micro-cracks in the core, and the temperature difference before and after core extraction further promotes their development. These micro-cracks interfere with the measurement of the core's dimensions, making it impossible to accurately obtain the true amount of elastic deformation. Simultaneously, existing methods for measuring the diameter deformation of cylindrical cores do not eliminate the interference from micro-cracks, resulting in large assessment errors and limiting the widespread application of core elastic deformation measurement. Summary of the Invention
[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a core radial deformation measurement system and method, which solves the technical problems of complex operation, long time consumption, and large errors in existing geostress measurement methods, and enables rapid and accurate measurement of horizontal geostress in rock masses.
[0005] To achieve the above objectives, the present invention provides the following technical solution.
[0006] A core radial deformation measurement system includes a main frame, a rotating shaft, a drive device, a rotation controller, and a data acquisition unit;
[0007] The rotating shaft is rotatably mounted on the main frame. The rotating shaft includes a driving shaft and a driven shaft arranged in parallel at intervals. A support area for placing rock cores is formed between the driving shaft and the driven shaft.
[0008] The driving device is a variable speed motor, and the output end of the variable speed motor is connected to the drive shaft for driving the drive shaft to rotate.
[0009] The rotation controller is electrically connected to the variable speed motor and is used to control the rotational speed of the variable speed motor;
[0010] The data acquisition unit includes a transmitting probe, a receiving probe, a data acquisition controller, and a computer. The transmitting probe and the receiving probe are respectively fixed at both ends of the main frame and are arranged opposite each other on both sides of the rotating shaft. The transmitting probe is used to transmit detection signals in the direction of the receiving probe, and the receiving probe is used to receive detection signals after passing through the rock core.
[0011] The data acquisition controller is electrically connected to the transmitting probe and the receiving probe respectively, and is used to control the transmission and reception of detection signals; the computer is electrically connected to the data acquisition controller, and is used to receive detection signals and process them to obtain the outer contour information and radial deformation of the rock core.
[0012] Furthermore, the core radial deformation measurement system also includes a CT scanning imaging unit, which includes a rotating stage, an X-ray emitter, and an image acquisition instrument. The rotating stage is used to place the core, the X-ray emitter and the image acquisition instrument are arranged opposite each other and are located on opposite sides of the rotating stage, and the image acquisition instrument is used to acquire cross-sectional images of the core to statistically analyze the cumulative width of microcracks.
[0013] Furthermore, the transmitting probe is a green LED light source transmitting probe, and the receiving probe is a CCD receiving probe; the data acquisition unit includes one or two pairs of the transmitting probe and the receiving probe.
[0014] Furthermore, the surfaces of the drive shaft and the driven shaft are provided with an anti-slip and wear-resistant layer.
[0015] Furthermore, the measurement method of the core radial deformation measurement system includes the following steps:
[0016] S1: After the core is removed from the borehole, it should be sealed immediately to prevent water loss, and a marking line should be drawn parallel to the axis of the core.
[0017] S2: Place the sealed rock core between the active shaft and the driven shaft of the radial deformation measurement system for rock cores according to any one of claims 1-4. Control the variable speed motor to drive the active shaft to rotate through the rotation controller, causing the rock core to rotate synchronously. Start the data acquisition unit, transmit detection signals through the transmitting probe, and receive the outer contour information of the rock core collected by the probe. Test a single radial position of a single rock core for at least 3-4 cycles, and test at least 2 radial positions of a single rock core. After processing, obtain the maximum radial deformation d of the rock core. max and minimum radial deformation d min ;
[0018] S3: The development and distribution characteristics of microfractures in the core were evaluated using the ultrasonic pulse method. P-wave velocity distribution curves were obtained at different azimuths of the cylindrical surface. Based on these curves, the azimuth angle α2 of the trough of the sinusoidal curve with the minimum velocity relative to the marker line was determined. This azimuth angle α2 is perpendicular to the long axis of the microfracture and d. min The radial included angle α is the same;
[0019] S4: The core was scanned using a CT scanning imaging unit, and the cumulative width of multiple sets of microfractures at different radial positions of the core was statistically analyzed. The microfractures included random microfractures and induced microfractures. The average value c0 of the cumulative width of multiple sets of induced microfractures was taken.
[0020] S5: According to formula c 0-ma x = c0 × cosα, c 0-min =c0×sinα, the induced microcracks in d are calculated. max Cumulative width c in the direction 0-max and d min Cumulative width c in the direction 0-min Then, using formula d 0-max =d max -c 0-max d 0-min =d min -c 0-min The true radial deformation d caused by elastic stress recovery in the rock core was obtained. 0-max and d 0-mi n;
[0021] S6: Conduct rock mechanics tests using the rock core from step S1 or a nearby rock core to obtain the Young's modulus E and Poisson's ratio v of the rock;
[0022] S7: The maximum horizontal principal stress S is calculated according to the formula. hmax With minimum horizontal principal stress S hmin The difference, wherein the formula is:
[0023]
[0024] Furthermore, in step S3, the rotation orientation of the ultrasonic pulse method is consistent with the rotation orientation of the rock core in step S2, that is, both are counterclockwise or clockwise.
[0025] Furthermore, in step S1, the sealed packaging uses a foil-sealed bag.
[0026] Furthermore, in step S2, before testing, it is necessary to ensure that the cylindrical surface of the rock core is smooth, has a regular shape, and is free of obvious joints.
[0027] The beneficial effects of this invention are as follows:
[0028] 1. The core radial deformation measurement system of the present invention has a reasonable structural design. The core is supported by the cooperation of the active shaft and the driven shaft. The variable speed motor can be adapted to cores of different diameters to adjust the speed. The data acquisition unit can accurately collect the core outer contour information. The CT scanning imaging unit can effectively count the cumulative width of microcracks, providing accurate parameters for subsequent calculations.
[0029] 2. The measurement method of this invention avoids the influence of water loss by sealing and preserving the rock core, and ensures the reliability of the data by testing the radial deformation multiple times. It combines ultrasonic pulse method and CT scanning imaging to eliminate the interference of micro-cracks, accurately obtains the true elastic deformation of the rock core, and finally calculates the horizontal geostress difference through rock mechanical parameters. It is simple to operate, short in time, and has small error. It can be quickly and widely promoted and applied, providing a reliable geostress reference for deep energy mining. Attached Figure Description
[0030] Figure 1 This is a schematic diagram of the radial elastic deformation of the rock core in an embodiment of the present invention;
[0031] Figure 2 This is a schematic diagram of the core radial deformation measurement system in an embodiment of the present invention;
[0032] Figure 3 This is a schematic diagram illustrating the development and distribution characteristics of microfractures within the rock core in an embodiment of the present invention;
[0033] Figure 4 This is a schematic diagram of the structure of the CT scanning imaging unit in an embodiment of the present invention;
[0034] Figure 5 This is a schematic diagram of a core cross-section image obtained by CT scanning in an embodiment of the present invention;
[0035] Figure 6 This is a graph showing the relationship between core diameter and P-wave velocity in an embodiment of the present invention;
[0036] Figure 7 This is a flowchart illustrating the method for measuring horizontal geostress in rock mass using brittle rock cores in an embodiment of the present invention.
[0037] Reference numerals in the attached figures: 1-Emitting probe; 2-Driven shaft; 3-Rock core; 4-Drive shaft; 5-Variable speed motor; 6-Receiving probe; 7-Main frame; 8-Rotation controller; 9-Computer; 10-Data acquisition controller; 11-X-ray emitter; 12-Image acquisition instrument; 13-Rotating stage; 14-Section; 15-Random microcrack; 16-Induced microcrack. Detailed Implementation
[0038] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0039] In the description of this invention, the terms “center,” “upper,” “lower,” “left,” “right,” “vertical,” “horizontal,” “inner,” and “outer,” etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used 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. Therefore, they should not be construed as limitations on this invention.
[0040] The terms “first” and “second” are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0041] In the description of this invention, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0042] like Figure 2As shown, the core radial deformation measurement system of the present invention includes a main frame 7, a rotating shaft, a drive device, a rotation controller 8, and a data acquisition unit. The rotating shaft is rotatably mounted on the main frame 7 and includes a drive shaft 4 and a driven shaft 2 arranged in parallel at intervals. A support area for placing the core 3 is formed between the drive shaft 4 and the driven shaft 2. The drive shaft 4 and the driven shaft 2 jointly support the core 3, ensuring the stable rotation of the core 3. The drive device is a variable speed motor 5, and the output end of the variable speed motor 5 is connected to the drive shaft 4 for driving the drive shaft 4 to rotate, thereby driving the core 3 to rotate synchronously. The rotation controller 8 is electrically connected to the variable speed motor 5 and can adjust the speed of the variable speed motor 5 according to the diameter of the core 3 to achieve the optimal measurement effect. The data acquisition unit includes a transmitting probe 1 and a receiving probe 6. The data acquisition controller 10 and computer 9, the transmitting probe 1 and the receiving probe 6 are respectively fixed at both ends of the main frame 7, and are arranged opposite each other on both sides of the rotation axis. The transmitting probe 1 is a green LED light source transmitting probe, used to emit green LED light source towards the receiving probe 6. The receiving probe 6 is a CCD receiving probe, used to receive the light source signal after passing through the rock core 3. The data acquisition controller 10 is electrically connected to the transmitting probe 1 and the receiving probe 6 respectively, and is used to control the transmission and reception of the light source signal. The computer 9 is electrically connected to the data acquisition controller 10, and is used to receive the light source signal and process it to obtain the outer contour information and radial deformation of the rock core 3. The data acquisition unit can be equipped with one or two pairs of transmitting probes 1 and receiving probes 6 to adapt to the measurement requirements of rock cores 3 of different specifications.
[0043] The system also includes a CT scanning imaging unit (such as...) Figure 4 As shown, the CT scanning imaging unit includes a rotating stage 13, an X-ray emitter 11, and an image acquisition device 12. The rotating stage 13 is used to place the rock core 3. The X-ray emitter 11 and the image acquisition device 12 are arranged opposite to each other and are located on both sides of the rotating stage 13. The image acquisition device 12 is used to acquire cross-sectional images of the rock core 3 in order to calculate the cumulative width of microcracks.
[0044] The surfaces of the drive shaft 4 and the driven shaft 2 are provided with anti-slip and wear-resistant layers, which can increase the friction between them and the rock core 3, prevent the rock core 3 from slipping during rotation, and extend the service life of the rotating shaft.
[0045] The method for measuring horizontal stress in rock mass using brittle rock cores of the present invention comprises the following steps: S1: After the rock core 3 is removed from the borehole, it is immediately sealed in a tin foil bag to prevent the rock core 3 from losing water and shrinking, which would affect the measurement results; then, a marking line L is drawn parallel to the axis of the rock core 3 to locate the rotation angle of the rock core 3. The cylindrical surface of the test rock core 3 should be smooth, regularly shaped, and free of obvious joints. S2: Place the sealed rock core 3 between the active shaft 4 and the driven shaft 2 of the above-mentioned rock core radial deformation measurement system. Control the variable speed motor 5 through the rotation controller 8 to drive the active shaft 4 to rotate, thereby driving the rock core 3 to rotate synchronously. Start the data acquisition unit. The data acquisition controller 10 sends a command to the transmitting probe 1. The transmitting probe 1 emits a green LED light source towards the receiving probe 6. Since the rock core 3 blocks part of the light source, the receiving probe 6 cannot receive the light source blocked by the rock core 3, thus forming a light-free area. The width of this area is the instantaneous diameter of the rock core 3. Test the single radial position of a single rock core 3 for at least 3-4 cycles. Test the single radial position of a single rock core 3 for at least 2 cycles. After removing abnormal data with significant numerical fluctuations, take the average value of the remaining data. After processing, obtain the maximum radial deformation d of the rock core 3. max and minimum radial deformation d min S3: The development and distribution characteristics of microfractures in core 3 are evaluated using the ultrasonic pulse method. The rotation orientation is consistent with that of core 3 in step S2 (both are counterclockwise or clockwise). During the ultrasonic pulse method test, a P-wave is emitted radially through core 3. The receiving probe receives the waveform signal, amplifies, collects, and processes it to obtain the P-wave velocity distribution curves at different orientations of the cylindrical surface. Based on the P-wave velocity distribution curves, the azimuth angle α2 of the trough of the sine curve with the minimum velocity relative to the marker line L is determined. This azimuth angle α2 is perpendicular to the long axis direction of the microfracture and d. min The radial angle α is the same. S4: Place the rock core 3 on the rotary table 13 of the CT scanning imaging unit. When the marker line L is directly opposite the X-ray emitter 11, the image acquisition instrument 12 starts recording. The rotary table 13 rotates in the same direction as in step S2. The image acquisition instrument 12 obtains a cross-sectional image of the rock core 3 through image magnification, enhancement, and interpretation. The cumulative width of multiple sets of micro-fractures at different radial positions of the rock core 3 is statistically analyzed. The micro-fractures include random micro-fractures 15 and induced micro-fractures 16. The average value c0 of the cumulative width of multiple sets of induced micro-fractures 16 is taken. S5: According to formula c 0-max =c0×cosα,c 0-min =c0×sinα, the induced microcrack 16 is calculated in d max Cumulative width c in the direction 0-max and d min Cumulative width c in the direction 0-min Then, using formula d 0-max =d max -c 0-max d0-min =d min -c 0-min The true radial deformation d caused by elastic stress recovery in core 3 was obtained. 0-max and d 0-min S6: Conduct rock mechanics tests using core 3 or a core from nearby samples obtained in step S1 to obtain the Young's modulus E and Poisson's ratio v. S7: Calculate the maximum horizontal principal stress S using the formula. hmax With minimum horizontal principal stress S hmin The difference, where the formula is:
[0046]
[0047] Among them, S hman The maximum horizontal principal stress; S hmin The minimum horizontal principal stress; E is Young's modulus; v is Poisson's ratio; d max The maximum radial deformation of core 3; d min This represents the minimum radial deformation of core 3.
[0048] According to classical elasticity theory, for an isotropic cylindrical rock core 3 drilled vertically, the in-situ stress on the core 3 is immediately relieved. The initial diameter of the cylindrical rock core 3 after detaching from the crustal stress field and before elastic deformation recovery is d0, and at this point, the cross-section 14 of the core 3 is a true circle. After stress relief, the core 3 will undergo elastic deformation, the amount of which is proportional to the level of relieved in-situ stress, such as... Figure 1 So, for a vertical borehole, in Figure 1 Under mid-plane stress conditions, the maximum horizontal principal stress S hmax and minimum horizontal principal stress S hmin Under the deformation mode of core 3 upon release, tensile strain will be generated in the plane of core 3 perpendicular to the borehole axis, as shown in Formula 1-2.
[0049]
[0050] Where, ε max For S hmax The maximum tensile strain in the direction, ε min For S hmin The minimum tensile strain in the direction, Sv is the vertical principal stress, E is the Young's modulus of the rock, and v is the Poisson's ratio of the rock.
[0051] in addition,
[0052]
[0053] Where, d max For the direction of the maximum core diameter 3, d minLet d0 be the diameter of the cylindrical core 3 before elastic recovery, and d0 be the diameter of the circle before elastic recovery. Clearly, the cross-section 14 of the cylindrical core 3 after elastic deformation recovery is an ellipse with its major axis being d. max The minor axis is d min ,like Figure 1 As shown. Solving the above equations (1) to (4), we can obtain the formula for calculating the difference of horizontal principal stresses.
[0054]
[0055] Since d0 is in the denominator, its magnitude is approximately equal to d. min Furthermore, the magnitude is relatively large compared to the diameter deformation difference. Therefore, in formula (6), d0 can be used to replace d. min In this case, the horizontal differential stress value can be obtained by measuring the maximum and minimum diameters of the cylindrical rock core 3 after elastic recovery, as well as the rock's elastic parameters E and v, using the following formula:
[0056]
[0057] However, as mentioned above, after the cylindrical rock core 3 is extracted from the deep rock mass, induced microfractures 16 will inevitably be generated inside it, caused by the concentration of horizontal differential stress in the crust. If the horizontal differential stress is large, this phenomenon will be very significant and cannot be ignored. Therefore, we must assess and determine the cumulative width of the induced microfractures 16, and the effect of the cumulative width on d. max and d min The impact.
[0058] According to rock mechanics and elasticity theories, the microcracks caused by thermal stress in core 3 are mostly randomly distributed without a dominant orientation. However, the microcracks generated by tensile stress concentration at the bottom of the borehole have a consistent, dominant orientation, approximately parallel to the maximum principal stress. However, determining the differential stress requires precise measurement of the radial deformation of core 3, especially for hard rock. max -d min Often only a few micrometers wide, it is essential to accurately assess the impact of the cumulative width of microcracks on the deformed elliptical cross-section.
[0059] The method used in this invention can effectively solve this problem.
[0060] First, after core 3 is removed from the borehole, a radial deformation test should be conducted as soon as possible. Before the test, to avoid shrinkage caused by water loss, core 3 should be stored in a sealed foil bag. The cylindrical surface of the test core 3 should be as smooth, regularly shaped, and without obvious joints as possible.
[0061] Then, radial deformation measurements were performed on core 3. Before the test, a marking line L was drawn parallel to the axial direction of core 3. Figure 2 The rock core 3 is placed on a rotating shaft, which consists of a drive shaft 4 and a driven shaft 2. The drive shaft 4 is connected to a variable speed motor 5, which can select different constant speeds according to the diameter of the rock core 3. The rotation controller 8 is activated and a fixed speed is set. When the mark line L of the rock core 3 reaches a certain fixed position, the acquisition software on the computer 9 is started. At this time, the data acquisition unit is connected to the CCD measurement system installed on the main frame 7. The measurement system consists of a transmitting probe 1 and a receiving probe 6. Depending on the diameter of the test rock core 3, the CCD measurement system can be selected as one or two pairs. The transmitting probe 1 emits a green LED light source, which is projected onto the measurement area of the cylindrical rock core 3 to measure the geometric parameters of the outer contour of the rock core 3, that is, the change in the circumferential diameter of the rock core 3 after deformation recovery. The relevant data is imported into the computer 9 in real time.
[0062] For a single core 3, test at a single radial position for 3-4 cycles, or test at more than 2 radial positions for a single core 3. Finally, remove outlier data (values with significant fluctuations or large differences), and average the remaining data. At this point, the overall radial deformation value d of core 3 can be easily obtained from the curve. max and d min The radial deformation curve of core 3 exhibits a sinusoidal distribution, and d can be obtained. max The azimuth angle α1 relative to the position of the marker line L.
[0063] Subsequently, the development and distribution characteristics of microfractures in core 3 were assessed using the ultrasonic pulse method, such as... Figure 3 Core 3 is the same core 3 as the previous one. The ultrasonic controller module 1 connects to and controls the acoustic wave emitting probe 1. At the start of the test, a P-wave is emitted. The P-wave passes radially through core 3 and is detected by the ultrasonic receiving probe 6. The ultrasonic receiving probe 6 amplifies the waveform signal through module 2 and transmits it to the waveform collector in module 3. Finally, module 4 processes and analyzes the signal to obtain the P-wave velocity distribution curves at different orientations of the cylindrical surface. The P-wave velocity test also starts from the marked line L and uses the same rotational orientation as the radial deformation measurement, such as counterclockwise or clockwise.
[0064] For cylindrical core 3 with predominantly oriented microfractures, the P-wave velocity distribution along the circumference of core 3 follows a sinusoidal curve; for core 3 with randomly distributed microfractures, the circumferential P-wave velocity distribution on the cylindrical core 3 is essentially linear. Since randomly distributed microfractures are generally closed fractures, and their orientation is random and isotropic, the radial deformation d... max and d minThe impact is negligible. Parallel to the direction of the induced fracture, the P-wave velocity is the highest and the radial deformation is the lowest, while perpendicular to the direction of the induced fracture, the P-wave velocity is the lowest and the radial deformation is the highest.
[0065] The azimuth angle α2 of the trough of the sinusoidal curve with minimum velocity relative to the marked line L can be easily obtained from the P-wave velocity curve. At this point, it can be preliminarily verified that α1 is not equal to α2 because it is caused by both elastic deformation recovery due to differential stress and the opening of microcracks, and this angular difference cannot be ignored. Figure 6 .
[0066] Subsequently, CT scan imaging was used to statistically determine the cumulative width of multiple microcracks at different radial locations. The implementation system is as follows: Figure 4 As shown. Core 3 is placed on the rotating stage 13. Core 3 is the same as the previously mentioned core 3. When the marker line L of core 3 is aligned with the X-ray emitter 11, the image acquisition instrument 12 begins recording. The rotation direction of the rotating stage 13 remains the same as the previous test procedure. The image acquisition instrument 12 obtains the following results through image magnification, enhancement, and interpretation: Figure 5 The cross-section 14 of core 3 shown can be used to depict the development of microfractures within the cross-section 14. The microfractures consist of random microfractures 15 and stress-induced microfractures 16. The contribution of microfractures to the radial deformation of core 3 is isotropic; therefore, the stress-induced microfractures 16 are primarily statistically analyzed. Since the tensile stress-induced microfractures 16 are mostly in an open state to varying degrees, the cumulative width of the induced microfractures 16 within the cross-section 14 can be statistically analyzed using interpretation software. Multiple CT scans were performed at the same location as the radial deformation test, and the average value c0 of the cumulative fracture width was finally taken. Simultaneously, the long axis direction of the induced microfractures 16 and the d-axis direction can be measured. min The radial angle α. In terms of magnitude, α = α2 ≠ α1.
[0067] It is easy to see that the cumulative width of stress-induced microcracks 16 is related to d max and d min The deformation contribution c 0-max and c 0-min The following formulas (8) and (9) are used to calculate the results respectively:
[0068] c 0-max =c0×cosα (8)
[0069] c 0-min =c0×sinα (9)
[0070] Furthermore, the true radial deformation of core 3 caused by elastic stress recovery can be obtained, as shown in formulas (10) and (11).
[0071] d 0-max =dmax -c 0-max (10)
[0072] d 0-min =d min -c 0-min (11)
[0073] Finally, using the test core 3 and its nearby core 3, rock mechanics tests were conducted to obtain Young's modulus E and Poisson's ratio v. At this point, according to formula (7), S... hmax -S hmin The formula for calculating the true value (12) is as follows:
[0074]
[0075] This concludes the method and specific procedures for determining differential stress using in-situ core sampling from boreholes. The flowchart of these steps is shown below. Figure 7 As shown.
[0076] The method for measuring differential stress using rock cores provided by this invention measures the width of microcracks in the rock core 3. When calculating the radial deformation of the rock core 3, the width of the microcracks is included, making the calculation of the radial deformation of the rock core 3 more accurate, reducing errors, and ensuring that the final data can be used normally under any circumstances. This enables the measurement of elastic deformation of the rock core 3 to be widely applied.
Claims
1. A core radial deformation measurement system, characterized in that, It includes a main frame, a rotating shaft, a drive unit, a rotation controller, and a data acquisition unit; The rotating shaft is rotatably mounted on the main frame. The rotating shaft includes a driving shaft and a driven shaft arranged in parallel at intervals. A support area for placing rock cores is formed between the driving shaft and the driven shaft. The driving device is a variable speed motor, and the output end of the variable speed motor is connected to the drive shaft for driving the drive shaft to rotate. The rotation controller is electrically connected to the variable speed motor and is used to control the rotational speed of the variable speed motor; The data acquisition unit includes a transmitting probe, a receiving probe, a data acquisition controller, and a computer. The transmitting probe and the receiving probe are respectively fixed at both ends of the main frame and are arranged opposite each other on both sides of the rotating shaft. The transmitting probe is used to transmit detection signals in the direction of the receiving probe, and the receiving probe is used to receive detection signals after passing through the rock core. The data acquisition controller is electrically connected to the transmitting probe and the receiving probe respectively, and is used to control the transmission and reception of detection signals; the computer is electrically connected to the data acquisition controller, and is used to receive detection signals and process them to obtain the outer contour information and radial deformation of the rock core.
2. The core radial deformation measurement system according to claim 1, characterized in that, It also includes a CT scanning imaging unit, which includes a rotating stage, an X-ray emitter, and an image acquisition device. The rotating stage is used to place the rock core, the X-ray emitter and the image acquisition device are arranged opposite each other and are located on opposite sides of the rotating stage, and the image acquisition device is used to acquire cross-sectional images of the rock core to calculate the cumulative width of microfractures.
3. The core radial deformation measurement system according to claim 1, characterized in that, The transmitting probe is a green LED light source transmitting probe, and the receiving probe is a CCD receiving probe; the data acquisition unit includes one or two pairs of the transmitting probe and the receiving probe.
4. The core radial deformation measurement system according to claim 1, characterized in that, The surfaces of the drive shaft and the driven shaft are provided with anti-slip and wear-resistant layers.
5. The measurement method of the core radial deformation measurement system according to claim 1, characterized in that, Includes the following steps: S1: After the core is removed from the borehole, it should be sealed immediately to prevent water loss, and a marking line should be drawn parallel to the axis of the core. S2: Place the sealed rock core between the active shaft and the driven shaft of the radial deformation measurement system for rock cores according to any one of claims 1-4. Control the variable speed motor to drive the active shaft to rotate through the rotation controller, causing the rock core to rotate synchronously. Start the data acquisition unit, transmit detection signals through the transmitting probe, and receive the outer contour information of the rock core collected by the probe. Test a single radial position of a single rock core for at least 3-4 cycles, and test at least 2 radial positions of a single rock core. After processing, obtain the maximum radial deformation d of the rock core. max and minimum radial deformation d min ; S3: The development and distribution characteristics of microfractures in the core were evaluated using the ultrasonic pulse method. P-wave velocity distribution curves were obtained at different azimuths of the cylindrical surface. Based on these curves, the azimuth angle α2 of the trough of the sinusoidal curve with the minimum velocity relative to the marker line was determined. This azimuth angle α2 is perpendicular to the long axis of the microfracture and d. min The radial included angle α is the same; S4: The core was scanned using a CT scanning imaging unit, and the cumulative width of multiple sets of microfractures at different radial positions of the core was statistically analyzed. The microfractures included random microfractures and induced microfractures. The average value c0 of the cumulative width of multiple sets of induced microfractures was taken. S5: According to formula c 0-ma x = c0 × cosα, c 0-min =c0×sinα, the induced microcracks in d are calculated. max Cumulative width c in the direction 0-max and d min Cumulative width c in the direction 0-min Then, using formula d 0-max =d max -c 0-max d 0-min =d min -c 0-min The true radial deformation d caused by elastic stress recovery in the rock core was obtained. 0-max and d 0-mi n; S6: Conduct rock mechanics tests using the rock core from step S1 or a nearby rock core to obtain the Young's modulus E and Poisson's ratio v of the rock; S7: The maximum horizontal principal stress S is calculated according to the formula. hmax With minimum horizontal principal stress S hmin The difference, wherein the formula is:
6. The measurement method of the core radial deformation measurement system according to claim 5, characterized in that, In step S3, the rotation orientation of the ultrasonic pulse method is consistent with the rotation orientation of the rock core in step S2, that is, both are counterclockwise or clockwise.
7. The measurement method of the core radial deformation measurement system according to claim 5, characterized in that, In step S1, the sealed packaging uses a foil-sealed bag.
8. The measurement method of the core radial deformation measurement system according to claim 5, characterized in that, In step S2, before testing, it is necessary to ensure that the cylindrical surface of the rock core is smooth, the shape is regular, and there are no obvious joints.