Shale damage monitoring and early warning method based on temperature and bedding angles

Abstract

The invention belongs to the technical field of shale mechanical property detection, and particularly discloses a shale damage monitoring and early warning method based on temperature and bedding angle, comprising the following steps: acquiring the bedding angle and actual temperature of shale; and according to the bedding angle and the actual temperature, calculating the total damage variable of the coupling effect of the temperature and the bedding angle on the rock damage, predicting the predicted compressive strength of the shale by using the damage model, and giving out an early warning when the predicted compressive strength exceeds an early warning threshold value. Under the synergistic effect of the temperature and the bedding angle, the influence of the shale mechanical property and the crack propagation mode is systematically studied, the U-shaped rule of the shale compressive strength under different bedding angles and high temperature conditions is provided, and a damage model comprehensively considering the influence of the temperature and the bedding angle is constructed. The influence of the temperature and the bedding angle on the compressive strength of the shale is quantitatively analyzed, and the damage state of the shale under the conditions of different temperatures and different bedding angles can be effectively predicted.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale mechanical property detection, and particularly relates to a shale damage monitoring and early warning method based on temperature and bedding angle. Background Art

[0002] As a typical layered sedimentary rock, shale has significant anisotropy, and its mechanical properties are affected by various factors. First, the bedding angle, that is, the angle between the bedding plane and the loading direction, as a basic structural feature of shale, directly affects mechanical parameters such as its compressive strength and elastic modulus. Second, the change in temperature will change the mineral composition and pore structure of shale, and thus affect its mechanical properties. In addition, the increase in water content will weaken the strength and stiffness of shale, and the change in loading rate will affect the stress-strain response of shale. In the study of shale mechanics, establishing a damage model for predicting compressive strength is crucial for engineering design and safety assessment.

[0003] Existing studies have analyzed the mechanical properties of shale at different bedding angles through uniaxial and triaxial compression tests. The results show that the bedding angle significantly affects the compressive strength and failure mode of shale. For example, when the bedding angle is 0° and 90°, the compressive strength of shale is relatively high, while at 45° and 60°, the compressive strength is significantly reduced. It is found that temperature has an important impact on the mechanical properties of shale. As the temperature rises, the compressive strength and elastic modulus of shale show different trends of change.

[0004] Although the above studies have revealed the influence of bedding angle and temperature on the mechanical properties of shale, most of them only consider a single factor (such as only analyzing the effect of temperature or bedding angle on the mechanical properties of shale), lacking a systematic study on the coupling effect of temperature and bedding angle. In addition, the existing damage models for predicting compressive strength have limited accuracy when considering the influence of multiple factors, and the prediction of the mechanical behavior of shale under high-temperature conditions is insufficient. Although the existing technology has discussed the tensile-shear failure mode of crack propagation, it has not been able to quantitatively describe the crack propagation path and dynamic evolution mechanism at different bedding angles. Most of the mechanical property prediction models in the existing technology only consider the influence of a single factor and have not constructed a damage prediction model that comprehensively considers multiple factors such as temperature and bedding angle. Summary of the Invention

[0005] Aiming at the above existing problems, the purpose of the present invention is to provide a shale damage monitoring and early warning method based on temperature and bedding angle, which constructs a damage model that comprehensively considers the influence of temperature and bedding angle, and can effectively predict the damage state of shale under different temperatures and different bedding angles.

[0006] The technical solution of the present invention is: a shale damage monitoring and early warning method based on temperature and bedding angle, comprising the following steps: Obtain the bedding angle and actual temperature of the shale, and calculate the total damage variable of the coupled action of temperature and bedding angle on shale damage according to the bedding angle and actual temperature.

[0007] According to the total damage variable of the coupled action of temperature and bedding angle on shale damage, use the damage model shown below to predict the predicted compressive strength of the shale.

[0008] , where represents the predicted compressive strength of the shale, represents the compressive strength under the reference conditions, represents the total damage variable of the coupled action of temperature and bedding angle on shale damage.

[0009] When the predicted compressive strength exceeds the warning threshold, issue a warning.

[0010] Furthermore, the calculation of the total damage variable of the coupled action of temperature and bedding angle on shale damage according to the bedding angle and actual temperature includes: Determine the bedding angle damage variable according to the bedding angle .

[0011] Determine the temperature damage variable according to the actual temperature .

[0012] Perform weighted summation on the variables, and obtain the total damage variable of the coupled action of temperature and bedding angle on shale damage according to the following formula.

[0013] , where , and both represent the weighting coefficients, represents the contribution of temperature to the overall damage, represents the contribution of the bedding angle to the overall damage, represents the actual temperature, represents the bedding angle.

[0014] Furthermore, the bedding angle damage variable is determined according to the following formula . The stress-strain relationship of the material can be expressed as The stress-strain relationship of the material can be expressed as The stress-strain relationship of the material can be expressed as The stress-strain relationship of the material can be expressed as The stress-strain relationship of the material can be expressed as The stress-strain relationship of the material can be expressed as The stress-strain relationship of the material can be expressed as The stress-strain relationship of the material can be expressed as The stress-strain relationship of the material can be expressed as

[0015] ; where represents the bedding angle, represents the minimum bedding damage value, Represents the maximum bedding damage value.

[0016] Furthermore, the actual temperature determines the damage variable according to the following formula .

[0017] ; where Represents the temperature damage coefficient, Represents the actual temperature, Represents the reference temperature.

[0018] Even further, the specific steps for determining the weighting coefficients of the weighted summation are as follows: Drill samples according to different bedding angles to obtain multiple shale samples. Apply axial loads to the multiple shale samples at different temperatures, and detect the acoustic characteristics during the shale damage and fracture processes. Calculate the weighting coefficients of the weighted summation.

[0019] Even further, the bedding angles are 0° to 90° respectively.

[0020] Even further, the specific steps for applying axial loads to the multiple shale samples are as follows: Enclose the shale samples in plastic-sealed tubes, and fix the acoustic emission monitoring device on the surface of the shale samples. Heat the shale samples, heat them to different temperature stages respectively, keep the temperature constant for one day after each target temperature stage is reached, and apply axial compressive loads in a displacement control mode. During the loading process, use the acoustic emission monitoring device to monitor the initiation and propagation of internal cracks in the samples in real time, and record the characteristic parameters of the acoustic emission signals.

[0021] Even further, the heating of the shale samples is carried out at a heating rate of 3°C per minute.

[0022] Even further, the loading rate of the axial compressive load is set to 0.1 mm / min.

[0023] Even further, the acoustic emission signals are analyzed according to the formula k = AF / RA. When k is greater than 50, it is determined as tensile failure, and when k is less than 50, it is determined as shear failure; RA represents the ratio of the rise time to the maximum amplitude of the acoustic emission signal, which is used to characterize the failure type, and AF represents the ratio of the ring count to the duration of the acoustic emission signal, which is used to evaluate the signal characteristics.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention systematically studies the influence of the combined action of temperature and bedding angle on the mechanical properties and crack propagation mode of shale, proposes the "U-shaped law" of the uniaxial compressive strength of shale under different bedding angles and high-temperature conditions, constructs a damage model that comprehensively considers the influence of temperature and bedding angle, quantitatively analyzes the influence of temperature and bedding angle on the uniaxial compressive strength of shale, and can effectively predict the damage state of shale under different temperature and different bedding angle conditions. Description of the Drawings

[0025] Figure 1 It is a graph showing the relationship between the uniaxial compressive strength and the bedding angle of different experimental groups in the experimental examples of the present invention.

[0026] Figure 2 It is a graph showing the change of the elastic modulus under different bedding angles in the experimental examples of the present invention.

[0027] Figure 3 It is the stress-strain curve under different bedding angles and temperature conditions in the experimental examples of the present invention.

[0028] Figures 4 to 6 It is a comparison graph of acoustic emission parameters under different bedding angles in the experimental examples of the present invention; among them, Figure 4 It is a comparison graph of the ring-down count parameters under different bedding angles; Figure 5 It is a comparison graph of the amplitude parameters under different bedding angles; Figure 6 It is a comparison graph of the energy parameters under different bedding angles.

[0029] Figure 7 It is the acoustic emission characteristics of tensile cracks and shear cracks under different bedding angles in the experimental examples of the present invention.

[0030] Figure 8 It is the acoustic emission mode of tensile failure and shear failure under different bedding angles and temperature in the experimental examples of the present invention.

[0031] Figure 9 It is a comparison graph of the number of acoustic emission events under different bedding angles and temperature in the experimental examples of the present invention. Detailed Embodiments

[0032] The following combines Figures 1 to 9 to describe the detailed embodiments of the present invention in detail. In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0033] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features; in the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0034] Embodiment A shale damage monitoring and early warning method based on temperature and bedding angle, comprising the following steps: Obtain the bedding angle and actual temperature of the shale, and calculate the total damage variable of the coupling effect of temperature and bedding angle on shale damage according to the bedding angle and actual temperature.

[0035] According to the total damage variable of the coupling effect of temperature and bedding angle on shale damage, use the damage model shown below to predict the predicted compressive strength of the shale.

[0036] , where represents the predicted compressive strength of the shale, represents the compressive strength under reference conditions, represents the total damage variable of the coupling effect of temperature and bedding angle on shale damage.

[0037] Issue an early warning when the predicted compressive strength exceeds the early warning threshold.

[0038] Preferably, calculating the total damage variable of the coupling effect of temperature and bedding angle on shale damage according to the bedding angle and actual temperature includes: Determine the bedding angle damage variable according to the bedding angle .

[0039] Determine the temperature damage variable according to the actual temperature .

[0040] Perform weighted summation on the variables, and obtain the total damage variable of the coupling effect of temperature and bedding angle on shale damage according to the following formula.

[0041] , where , and both represent weighting coefficients, represents the contribution of temperature to the overall damage, represents the contribution of the bedding angle to the overall damage, represents the actual temperature, represents the bedding angle.

[0042] Preferably, the bedding angle damage variable is determined according to the following formula 。

[0043] ; wherein, represents the bedding angle, represents the minimum bedding damage value, represents the maximum bedding damage value.

[0044] Preferably, the actual temperature determines the damage variable according to the following formula 。

[0045] ; wherein, represents the temperature damage coefficient, represents the actual temperature, represents the reference temperature.

[0046] Preferably, the specific steps for determining the weighting coefficient of the weighted summation are as follows: Drill samples according to different bedding angles to obtain multiple shale samples. Apply axial loads to the multiple shale samples at different temperatures, and detect the acoustic characteristics during the shale damage and fracture processes. Calculate the weighting coefficient of the weighted summation through calculation.

[0047] Preferably, the bedding angles are 0° to 90° respectively. Selecting the bedding angles within the full range of 0° to 90° can effectively ensure that the later obtained model is the optimal model. This is mainly because shale samples are comprehensively collected for each bedding angle to obtain the optimal and values.

[0048] Preferably, the specific steps for applying axial loads to the multiple shale samples are as follows: Enclose the shale samples in plastic-sealed tubes, and fix the acoustic emission monitoring device on the surface of the shale samples. Heat the shale samples, heat them to different temperature stages respectively, keep the temperature constant for one day after each target temperature stage is reached, and apply axial compressive loads in a displacement control mode. During the loading process, use the acoustic emission monitoring device to monitor the initiation and propagation of internal cracks in the samples in real time, and record the characteristic parameters of the acoustic emission signals.

[0049] Preferably, the shale samples are heated at a heating rate of 3°C per minute.

[0050] Preferably, the loading rate of the axial compressive load is set to 0.1 mm / min.

[0051] Preferably, the acoustic emission signal is analyzed according to the formula k = AF / RA. When k is greater than 50, it is determined as tensile failure, and when k is less than 50, it is determined as shear failure; RA represents the ratio of the rise time to the maximum amplitude of the acoustic emission signal, which is used to characterize the failure type, and AF represents the ratio of the ring count to the duration of the acoustic emission signal, which is used to evaluate the signal characteristics.

[0052] Experimental example Based on the shale damage monitoring and early warning method proposed in the embodiment, experiments are carried out. The specific steps are as follows: S1. Prepare shale samples.

[0053] The shale samples are selected from the Gulong shale oil block in the Q3 section of the Qingshankou Formation. This block has a carbonaceous shale formation rich in organic matter, ranging from grayish-black to dark gray, showing a significant layered structure, with complex interlayer intersections and weak cohesion, and is easily affected by weathering. The overall inclination angle of the formation is 60°, indicating that it has experienced a complex tectonic activity history.

[0054] To ensure the representativeness and consistency of the specimens, shale samples relatively stable and less disturbed in the deep formation are selected in the experiment. To study the influence of bedding angle on the mechanical properties and failure modes of shale, samples are drilled at bedding angles of 0°, 30°, 45°, 60° and 90° respectively, as Figure 1 shown. According to the standards of the International Society for Rock Mechanics (ISRM), the samples are processed into cylinders with a diameter of 25 mm and a length of 50 mm to ensure the standardization and repeatability of the test. By selecting different bedding angles, the influence of bedding on the damage and failure modes of shale under uniaxial compression conditions at in-situ temperature is systematically studied.

[0055] S2. Conduct an axial load experiment on the shale samples, detect the acoustic characteristics during the shale damage and fracture process, record the characteristic parameters of the acoustic emission signal, and obtain experimental data.

[0056] Among them, a mechanical testing device is used to apply an axial load to the shale samples, and an acoustic emission monitoring device is used to detect the acoustic characteristics during the shale damage and fracture process. The GCTS RTR-1500 shale mechanics testing system is adopted. This system has precise temperature and pressure control functions and can accurately apply an axial load. The temperature control system required in this system includes a high-temperature heating device and a high-precision temperature sensor, which are used to monitor and adjust the temperature during the experiment in real time. Among them, the temperature range of the high-temperature heating device is: from room temperature to 160 °C, and the accuracy of the high-precision temperature sensor is ±1 °C. The samples are encapsulated in plastic tubes to maintain temperature stability and avoid external interference. The temperature during the heating process is accurately controlled through a real-time monitoring system to avoid temperature fluctuations during the traditional preheating and constant temperature processes.

[0057] In this system, the acoustic emission monitoring system required adopts the DS-5 system of Beijing Ruandao Company to monitor the initiation and propagation process of internal cracks in shale in real time. The resonance frequency of the acoustic emission signal is 140 kHz, the gain of the preamplifier is set to 40 dB, and the signal acquisition threshold value is 35 dB. The signal characteristics such as ring count, cumulative event number and energy are mainly analyzed to reveal the acoustic behavior during the damage and fracture process of shale at in-situ temperature.

[0058] The shale sample is firmly installed in the GCTS RTR-1500 system. Six acoustic emission sensors are fixed on the sample surface through fixtures, and it is ensured that the wiring is correctly connected to the data acquisition system. The sample is heated by a real-time high-temperature system, and the heating rate is set to 3 °C / min. It is heated to three temperature stages of 100 °C, 130 °C and 160 °C respectively. After reaching the target temperature each time, it is kept at a constant temperature for one day to ensure that the sample is fully heated. Under the constant temperature condition, an axial compressive load is applied in the displacement control mode, and the loading rate is set to 0.1 mm / min to ensure the accurate capture of the stress-strain curve. During the loading process, the acoustic emission system monitors the initiation and propagation of internal cracks in the sample in real time and records the relevant acoustic emission signal characteristic parameters.

[0059] S3. Analyze the experimental data and draw experimental conclusions.

[0060] As Figure 1 , Figure 2 shown, the uniaxial compressive strength of shale shows a trend of "decreasing first and then increasing" with the change of bedding angle. At the bedding angles of 0° and 90°, the compressive strength reaches the maximum value, while it decreases significantly at the bedding angles of 45° and 60°. This reflects the influence of the interaction between the bedding direction and the loading direction on the internal microstructure and mechanical properties of shale. In addition, the elastic modulus of shale decreases significantly with the increase of bedding angle. At the bedding angle of 0°, the elastic modulus is the largest. As the bedding angle increases, especially at the angles of 45° and 60°, the stiffness decreases significantly, showing stronger plastic deformation characteristics.

[0061] As Figure 3 shown, at the bedding angles of 0° and 90°, the peak stress of shale is relatively high, especially exceeding 300 MPa at 100 °C and 130 °C. In contrast, at the bedding angles of 45° and 60°, with the increase of temperature, the peak stress decreases significantly. Especially in the combination of 160 °C and 45° angle, the strength decreases greatly and the plastic region expands.

[0062] As Figures 4 to 6As shown, the variation laws of acoustic emission parameters at different bedding angles indicate that among them, the acoustic emission parameters are ring count, amplitude, and energy. At low bedding angles, acoustic emission events are frequent and the energy release is strong, and cracks propagate smoothly along the bedding plane. For example, the low bedding angle is 0°. As the bedding angle increases, the number of acoustic emission events decreases and the energy release decreases. Especially at 90°, the acoustic emission signals are sparse and crack propagation is blocked. Among them, Figure 4 is the comparison diagram of ring count parameters at different bedding angles; Figure 5 is the comparison diagram of amplitude parameters at different bedding angles; Figure 6 is the comparison diagram of energy parameters at different bedding angles.

[0063] As Figure 7 shown, through the ratio of acoustic emission parameters, tensile failure and shear failure can be clearly distinguished. Among them, RA represents the ratio of the rise time of the acoustic emission signal to the maximum amplitude, which is used to characterize the failure type, and AF represents the ratio of the ring count of the acoustic emission signal to the duration, which is used to evaluate the signal characteristics. When the AF / RA ratio exceeds the critical value k = 50, it is determined as tensile failure; when it is lower than 50, it is shear failure. At different bedding angles, the failure mode transitions from tensile to shear. Especially at bedding angles of 30°, 45°, and 60°, the shear failure increases significantly.

[0064] As Figure 8 shown, at bedding angles of 0° and 90°, tensile failure is dominant, while at angles of 30°, 45°, and 60°, the shear failure increases significantly. Under high-temperature conditions, especially at a bedding angle of 60°, the proportion of shear failure is the highest, further verifying the synergistic effect of bedding angle and temperature on the failure mode.

[0065] As Figure 9 shown, the number of acoustic emission events at different bedding angles shows that the number of events is the highest at a bedding angle of 60° and the lowest at 90°. When the temperature increases, the number of acoustic emission events reaches a peak at medium bedding angles. The medium bedding angles are from 45° to 60°, indicating that the combination of high temperature and medium bedding angles is more likely to trigger complex failure modes.

[0066] S4. Establish a damage model based on the experimental conclusions.

[0067] To accurately predict the influence of temperature and bedding angle on the compressive strength of shale, based on the shale damage mechanics theory, a damage model considering the influence of temperature and bedding angle is established. This model is fitted through experimental data and can predict the compressive strength of shale under different temperature and different bedding angle conditions. The different temperatures are specifically 100 °C, 130 °C, and 160 °C, and the different bedding angles are specifically 0°, 30°, 45°, 60°, and 90°.

[0068] According to the theory of continuum damage mechanics, internal damage occurs in materials under external loading, resulting in a reduction in the effective load-bearing area.

[0069] Define the traditional damage variable D1 as: . Where D1 represents the traditional damage variable, A represents the effective load-bearing area after damage, and A0 represents the initial load-bearing area.

[0070] The stress-strain relationship of the material can be expressed as: . Where σ represents stress, E represents the elastic modulus, represents strain.

[0071] Temperature affects shale damage by causing microcrack propagation and mineral phase transformation through thermal stress. The temperature damage variable is calculated according to the following formula.

[0072] ; where, represents the temperature damage variable, represents the temperature damage coefficient, represents the actual temperature, represents the reference temperature.

[0073] The bedding angle affects the anisotropic mechanical behavior of shale. The bedding angle damage variable is calculated according to the following formula.

[0074] ; where, represents the bedding angle damage variable, represents the bedding angle, represents the minimum bedding damage value, represents the maximum bedding damage value.

[0075] The newly designed formula for the bedding angle damage variable is used to describe the effect of the bedding angle on shale damage. The formula combines the sine and cosine functions of the bedding angle with the minimum bedding damage value and the maximum bedding damage value to introduce a continuous influence model for the bedding angle, reflecting the non-linear effect of angle change on damage. This formula can accurately quantify the effect of the bedding angle on shale damage, overcoming the shortcomings of the lack of systematic and precise quantification of the effect of the bedding angle in the existing technology. Most of the existing technologies deal with the effect of the bedding angle relatively simply or inaccurately, and fail to consider the continuous and non-linear effect of the complex change of the bedding angle on shale damage.

[0076] Calculate the total damage variable of the coupling effect of temperature and bedding angle on shale damage according to the following formula.

[0077] , where, , Denote the total damage variable representing the coupled effect of temperature and bedding angle on shale damage, and both represent the weighting coefficients, represents the contribution of temperature to the overall damage, represents the contribution of bedding angle to the overall damage, represents the temperature damage variable, represents the bedding angle damage variable.

[0078] The predicted compressive strength of shale is predicted using the damage model shown below.

[0079] , where represents the predicted compressive strength of shale, i.e., the compressive strength of shale under the temperature damage variable and bedding angle damage variable, represents the compressive strength under the reference condition.

[0080] By innovatively expressing the coupling relationship between the temperature damage variable and the bedding angle damage variable , two weighting coefficients and are defined, representing the contributions of temperature and bedding angle to the overall damage respectively. Through the two weighting coefficients, the effects of temperature and bedding angle are quantified into an overall damage model. This weighted synthesis model can flexibly combine the different effects of temperature and bedding angle and determine their relative contributions based on experimental data. This innovation fills the gap in the existing technology of lacking a multi-factor coupling model, can more accurately predict the mechanical properties of shale under complex conditions, and provides a more scientific and accurate prediction tool for the mechanical behavior under the comprehensive influence of high temperature and bedding angle.

[0081] To accurately predict the compressive strength of shale at different temperatures and different bedding angles, through uniaxial compression tests on shale samples under different temperature conditions and combined with experimental analysis of the influence of bedding angle, the following key parameters are obtained: the reference temperature is 0 °C, the compressive strength under the reference condition is 120 MPa, the temperature damage coefficient is 0.004 °C -1 , the minimum bedding damage value is 0.05, the maximum bedding damage value is 0.55, and after calculation, , then the total damage variable representing the coupled effect of temperature and bedding angle on shale damage.

[0082] S5. Predict the predicted compressive strength of shale at different temperatures and different bedding angles according to the damage model, and issue a warning when the predicted compressive strength exceeds the warning threshold.

[0083] For the first time, the synergistic effect of temperature and bedding angle was systematically studied, the "U-shaped law" was proposed to describe the change of compressive strength at different bedding angles, and a damage model for predicting the compressive strength considering the influence of temperature and bedding angle was established. Through this innovative method, the limitation of ignoring the interaction of multiple factors in existing research was overcome. According to the experimental results, the compressive strength of shale shows a "U-shaped" distribution with the change of bedding angle. Specifically: when the bedding angle is 0° and 90°, the compressive strength of shale reaches the maximum value. When the bedding angle is 45° and 60°, the compressive strength decreases significantly.

[0084] This shows that the bedding angle has a significant influence on the compressive strength of shale. At certain angles, such as 45° and 60°, due to the influence of temperature, the compressive strength will decrease.

[0085] The "U-shaped law" is reflected through experimental data and mechanical property analysis. Specifically reflected in the following content: Analysis of experimental results: Figure 1 It shows the relationship diagram between the uniaxial compressive strength and the bedding angle of different experimental groups. This diagram shows the influence of the bedding angle on the compressive strength, presenting the "U-shaped law". Experimental data show that shale has a high compressive strength at bedding angles of 0° and 90°, while at bedding angles of 45° and 60°, the compressive strength decreases significantly.

[0086] An experimental scheme covering different temperatures and different bedding angles was designed, comprehensively covering the temperature and bedding angle changes that may be encountered under actual geological conditions, so as to obtain more accurate experimental data.

[0087] By optimizing the positioning accuracy of acoustic emission signals and the method for discriminating failure modes, a quantitative monitoring method for crack propagation combining acoustic emission signal characteristics was proposed, providing more efficient and reliable technical support for real-time monitoring and failure warning.

[0088] A damage model for predicting the compressive strength considering the influence of temperature and bedding angle was constructed, and the accuracy of this damage model was verified through experimental data. Compared with the existing technology, it can make accurate predictions under complex conditions. Through detailed sample preparation, precise experimental equipment and procedures, comprehensive experimental result analysis, and mathematical modeling based on damage mechanics theory, the compressive strength of shale under different temperature and different bedding angle conditions can be effectively predicted. The verification results of the damage model show that the warning method has high accuracy, providing reliable theoretical support and scientific basis for the evaluation of shale mechanical behavior in shale oil extraction.

[0089] It should be noted that: Step S3 is the part for analyzing experimental data, which includes the experimental measurement of the mechanical properties of shale under different temperatures and different bedding angles. The mechanical properties specifically include compressive strength, elastic modulus, stress-strain curve, etc. Through the analysis of these experimental data, the parameters of the model are fitted. Among them, the parameters of the model such as temperature damage coefficient, bedding damage parameter, etc., and provide a basis for the construction of the damage model in the subsequent step S4. The damage model in step S4 is fitted through the experimental conclusions in step S3 and the accuracy of the prediction is verified according to the experimental conclusions.

[0090] For the first time, the synergistic effect of temperature and bedding angle was systematically studied, the "U-shaped law" was proposed to describe the change of compressive strength under different bedding angles, and a damage model for predicting compressive strength considering the influence of temperature and bedding angle was established. Through this innovative method, the limitation of ignoring the interaction of multiple factors in existing research was overcome.

[0091] The experimental scheme covering different temperatures and different bedding angles comprehensively covers the temperature and bedding angle changes that may be encountered under actual geological conditions, so as to obtain more accurate experimental data.

[0092] By optimizing the positioning accuracy of acoustic emission signals and the method for discriminating failure modes, a quantitative monitoring method for crack propagation combining the characteristics of acoustic emission signals was proposed, providing more efficient and reliable technical support for real-time monitoring and failure warning.

[0093] The specific embodiments described above further elaborate on the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and do not limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A shale damage monitoring and early warning method based on temperature and bedding angle, characterized in that, It includes the following steps: Obtain the bedding angle and actual temperature of the shale, and calculate the total damage variable of the coupled action of temperature and bedding angle on shale damage according to the bedding angle and actual temperature; According to the total damage variable of the coupled action of temperature and bedding angle on shale damage, use the damage model shown below to predict the predicted compressive strength of the shale; ； Among them, represents the predicted compressive strength of shale, represents the compressive strength under reference conditions, represents the total damage variable of the coupled effect of temperature and bedding angle on shale damage; Issue a warning when the predicted compressive strength exceeds the warning threshold; The calculating the total damage variable of the coupled action of temperature and bedding angle on shale damage according to the bedding angle and actual temperature includes: Determine the bedding angle damage variable according to the bedding angle ; Determine the temperature damage variable according to the actual temperature ; Perform weighted summation on the variables, and obtain the total damage variable of the coupled action of temperature and bedding angle on shale damage according to the following formula; , where , and both represent weighting coefficients, represents the contribution of temperature to the overall damage, represents the contribution of bedding angle to the overall damage, represents the actual temperature, represents the bedding angle; The bedding angle determines the bedding angle damage variable according to the following formula ; ; wherein, represents the bedding angle, represents the minimum bedding damage value, represents the maximum bedding damage value; The actual temperature determines the damage variable according to the following formula ; ; wherein, represents the temperature damage coefficient, represents the actual temperature, represents the reference temperature.

2. The shale damage monitoring and early warning method based on temperature and bedding angle according to claim 1, wherein, The specific steps for determining the weighting coefficient of the weighted summation are: Drill samples according to different bedding angles to obtain multiple shale samples; Apply axial loads to multiple shale samples at different temperatures, detect the acoustic characteristics during the shale damage and fracture process, and calculate the weighting coefficient of the weighted summation through calculation.

3. The shale damage monitoring and early warning method based on temperature and bedding angle according to claim 2, wherein, The bedding angle range is 0° to 90°.

4. The shale damage monitoring and early warning method based on temperature and bedding angle according to claim 2, characterized in that, The specific steps for applying axial loads to multiple said shale samples are: Seal the shale sample in a plastic-sealed tube, and fix the acoustic emission monitoring device on the surface of the shale sample; Heat the shale sample, heat it to different temperature stages respectively, keep it at a constant temperature for one day after reaching each target temperature stage, and apply an axial compressive load in a displacement control mode; During the loading process, use the acoustic emission monitoring device to monitor the initiation and propagation of internal cracks in the sample in real time, and record the characteristic parameters of the acoustic emission signal.

5. The shale damage monitoring and early warning method based on temperature and bedding angle according to claim 4, characterized in that, The heating of the said shale sample is carried out at a heating rate of 3°C per minute.

6. The shale damage monitoring and early warning method based on temperature and bedding angle according to claim 4, characterized in that The loading rate of the axial compressive load is set to 0.1 mm / min.

7. The shale damage monitoring and early warning method based on temperature and bedding angle as claimed in claim 4, wherein The acoustic emission signal is analyzed according to the formula k = AF / RA. When k is greater than 50, it is determined as tensile failure. When k is less than 50, it is determined as shear failure; RA represents the ratio of the rise time of the acoustic emission signal to the maximum amplitude, which is used to characterize the failure type. AF represents the ratio of the ring count of the acoustic emission signal to the duration, which is used to evaluate the signal characteristics.

Images