Hydraulic fracture fracturing monitoring system, method and device based on optical fiber monitoring

Abstract

The invention relates to the technical field of rock mechanics and petroleum and natural gas engineering, and particularly discloses a hydraulic fracture fracturing monitoring system, method and device based on optical fiber monitoring, and the system comprises a hydraulic fracturing simulation platform which is used for applying three-dimensional stress to a hydraulic fracturing test piece so as to simulate a stratum stress environment; the fracturing fluid injection device is used for injecting pre-prepared fracturing fluid into the test piece, so that a crack in the test piece expands; a plurality of strain sensor groups embedded in the test piece in the preparation process of the test piece; the optical fiber sensing demodulation device is used for collecting strain data detected by the plurality of strain sensor groups; and the data processing device is in communication connection with the optical fiber sensing demodulation device and is used for acquiring the strain data and processing the strain data so as to determine real-time state data of crack expansion in the test piece. According to the scheme, the fracture strain can be monitored in real time, and the accuracy and controllability of the hydraulic fracturing process are improved.

Description

Technical Field

[0001] This specification relates to the technical fields of rock mechanics and oil and gas engineering, and particularly to a hydraulic fracture fracturing monitoring system, method and device based on optical fiber monitoring. Background Art

[0002] The hydraulic fracturing technology is an important means for increasing oil and gas production. Its core is to generate fractures in the reservoir through high-pressure liquid, thereby improving the oil and gas flow channels. However, the fracture morphology (including width, length and height) directly determines the fracturing effect, and the monitoring of fracture strain is an important means to understand the dynamic fracture propagation process and optimize the fracturing design.

[0003] Traditional monitoring technologies mainly include the flexibility method, acoustic emission technology, potential method, etc. Although these methods can provide certain monitoring results for fracture propagation, their limitations are as follows: First, these methods usually rely on simplified assumptions, have high requirements for sensor layout, low test accuracy, and it is difficult to accurately describe the real fracture behavior in complex reservoirs; in addition, these methods are vulnerable to the influence of parameter uncertainties when dealing with complex geological conditions, resulting in large deviations in results.

[0004] Existing fracture prediction methods mainly rely on numerical simulation and model estimation, but these methods cannot directly reflect the real-time dynamic changes of fractures during the propagation process. How to accurately simulate the hydraulic fracturing process under experimental conditions and perform high-precision monitoring on complex fracture morphologies still has many technical difficulties.

[0005] In response to the above problems, no effective solution has been proposed yet. Summary of the Invention

[0006] Embodiments of this specification provide a hydraulic fracture fracturing monitoring system, method and device based on optical fiber monitoring to accurately simulate the hydraulic fracturing process under experimental conditions and perform high-precision monitoring on complex fracture morphologies.

[0007] Embodiments of this specification provide a hydraulic fracture fracturing monitoring system based on optical fiber monitoring, including:

[0008] A hydraulic fracturing simulation platform for applying triaxial stress to a hydraulic fracturing specimen to simulate the formation stress environment;

[0009] A fracturing fluid injection device for injecting the pre-configured fracturing fluid into the specimen to cause fractures to propagate in the specimen;

[0010] Multiple strain sensor groups, at least including a first FBG strain sensor group with an axial direction parallel to the crack propagation direction of the specimen and a second FBG strain sensor group with an axial direction perpendicular to the crack propagation direction; the multiple strain sensor groups are embedded in the specimen during the preparation process of the specimen;

[0011] An optical fiber sensing demodulation device for collecting the strain data detected by the multiple strain sensor groups;

[0012] A data processing device, communicatively connected to the optical fiber sensing demodulation device, for obtaining the strain data and processing the strain data to determine the real-time state data of crack propagation in the specimen.

[0013] In one embodiment, the multiple strain sensor groups further include:

[0014] A third FBG strain sensor group with an axial direction inclined to the crack propagation direction.

[0015] In one embodiment, the system further includes:

[0016] A distributed optical fiber temperature sensor, distributed inside the specimen, for monitoring the temperature field change during crack propagation; and / or,

[0017] An acoustic emission monitoring device, arranged around the specimen, for monitoring the acoustic emission signals during crack propagation.

[0018] In one embodiment, the data processing device is specifically configured to:

[0019] Calculate the crack length of crack propagation based on the first strain data detected by the first FBG strain sensor group; calculate the crack height of crack propagation based on the second strain data detected by the second FBG strain sensor group; calculate the crack propagation speed according to the crack lengths at multiple moments.

[0020] The embodiments of this specification provide a hydraulic fracture fracturing monitoring method based on optical fiber monitoring. The method is based on the hydraulic fracture fracturing monitoring system described in any of the above embodiments. The method includes:

[0021] Control the hydraulic fracturing simulation platform to apply triaxial stress to the hydraulic fracturing specimen to simulate the formation stress environment;

[0022] Control the fracturing fluid injection device to inject fracturing fluid into the hydraulic fracturing specimen so that cracks propagate in the specimen;

[0023] Obtain strain data detected by multiple strain sensor groups; the strain data at least includes first strain data detected by a first FBG strain sensor group and second strain data detected by a second FBG strain sensor group;

[0024] Calculate the crack length based on the first strain data; calculate the crack height based on the second strain data;

[0025] Calculate the crack propagation speed according to the crack lengths at multiple moments.

[0026] In one embodiment, the method further includes:

[0027] Obtain third strain data detected by a third FBG strain sensor group;

[0028] Generate a crack propagation path based on the first strain data, the second strain data, and / or the third strain data.

[0029] In one embodiment, the method further includes:

[0030] Obtain the stress data applied by the hydraulic fracturing simulation platform and the liquid injection rate of the fracturing fluid injection device;

[0031] Analyze the influence of the liquid injection rate and the stress data on crack propagation based on the first strain data, the second strain data, the stress data, and the liquid injection rate.

[0032] In one embodiment, the method further includes:

[0033] Monitor whether abnormal conditions occur during crack propagation; the abnormal conditions include at least one of the following: the change in the propagation speed exceeds a preset range, the propagation direction changes suddenly, or the temperature change exceeds a preset range;

[0034] Generate an abnormal signal when abnormal conditions occur during crack propagation;

[0035] Control the hydraulic fracturing simulation platform to adjust the triaxial stress or control the fracturing fluid injection device to adjust the liquid injection rate based on the abnormal signal.

[0036] An embodiment of this specification also provides a hydraulic fracture fracturing monitoring device based on optical fiber monitoring. The device is based on the hydraulic fracture fracturing monitoring system described in any of the above embodiments. The device includes:

[0037] A first control module, configured to control the hydraulic fracturing simulation platform to apply triaxial stress to the hydraulic fracturing specimen to simulate the formation stress environment;

[0038] A second control module, configured to control a fracturing fluid injection device to inject fracturing fluid into the hydraulic fracturing specimen, so that fractures expand in the specimen;

[0039] An acquisition module, configured to acquire strain data detected by a plurality of strain sensor groups; the strain data at least includes first strain data detected by a first FBG strain sensor group and second strain data detected by a second FBG strain sensor group;

[0040] A first calculation module, configured to calculate the fracture length based on the first strain data; calculate the fracture height based on the second strain data;

[0041] A second calculation module, configured to calculate the fracture propagation speed according to the fracture lengths at multiple moments.

[0042] An embodiment of this specification further provides a computer device, including a processor and a memory for storing processor-executable instructions. When the processor executes the instructions, the steps of the hydraulic fracture fracturing monitoring method based on optical fiber monitoring described in any of the above embodiments are implemented.

[0043] An embodiment of this specification further provides a computer-readable storage medium, on which computer instructions are stored. When the instructions are executed, the steps of the hydraulic fracture fracturing monitoring method based on optical fiber monitoring described in any of the above embodiments are implemented.

[0044] In an embodiment of this specification, a hydraulic fracture fracturing monitoring system based on optical fiber monitoring is provided. The hydraulic fracturing simulation platform can apply triaxial stress to the hydraulic fracturing specimen to simulate the formation stress environment. The fracturing fluid injection device can inject the pre-configured fracturing fluid into the specimen, so that fractures expand in the specimen. During the preparation process of the specimen, a plurality of strain sensor groups are buried in the specimen. The plurality of sensor groups at least include a first FBG strain sensor group and a second FBG strain sensor group whose axial directions are parallel and perpendicular to the fracture propagation direction respectively; the optical fiber sensing demodulation device collects the strain data detected by the plurality of strain sensor groups; the data processing device is communicatively connected to the optical fiber sensing demodulation device, and can acquire and process the strain data to determine the real-time state data of the fracture propagation in the specimen. In the above solution, by detecting strain data with FBG strain sensors, the high sensitivity, real-time performance and anti-interference ability of the detection can be ensured. It can not only dynamically capture the strain characteristics of fracture propagation, but also achieve high-precision reconstruction of the three-dimensional strain field in the case of multi-point layout, significantly improving the monitoring accuracy and reliability. Further, by arranging FBG strain sensor groups at multiple angles in the specimen, the fracture propagation characteristics shown during the fracture propagation process can be dynamically captured, realizing real-time dynamic monitoring of the dynamic expansion of hydraulic fractures, especially suitable for real-time monitoring of complex fracture networks in reservoirs, and providing an important experimental method for the mechanism of hydraulic fracture propagation. Brief Description of the Drawings

[0045] The drawings described herein are provided to further understand the present specification, form a part of the present specification, and do not limit the present specification. In the drawings:

[0046] Figure 1 A schematic structural diagram of a hydraulic fracture fracturing monitoring system based on optical fiber monitoring in an embodiment of the present specification is shown;

[0047] Figure 2 A flowchart of a hydraulic fracture fracturing monitoring method based on optical fiber monitoring in an embodiment of the present specification is shown;

[0048] Figure 3 A schematic diagram of the overall specimen and optical fiber layout in an embodiment of the present specification is shown;

[0049] Figure 4 A flowchart of a hydraulic fracture fracturing monitoring device based on optical fiber monitoring in an embodiment of the present specification is shown;

[0050] Figure 5 A schematic diagram of a computer device in an embodiment of the present specification is shown. Detailed Embodiments

[0051] The principles and spirit of the present specification will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are provided only to enable those skilled in the art to better understand and then implement the present specification, and do not limit the scope of the present specification in any way. On the contrary, these embodiments are provided to make the disclosure of the present specification more thorough and complete, and to convey the scope of the present disclosure fully to those skilled in the art.

[0052] Those skilled in the art know that the embodiments of the present specification can be implemented as a system, a device, a method, or a computer program product. Therefore, the disclosure of the present specification can be specifically implemented in the following forms, namely: complete hardware, complete software (including firmware, resident software, microcode, etc.), or a combination of hardware and software.

[0053] An embodiment of the present specification provides a hydraulic fracture fracturing monitoring system based on optical fiber monitoring. Figure 1 A schematic structural diagram of a hydraulic fracture fracturing monitoring system based on optical fiber monitoring in an embodiment of the present specification is shown. As Figure 1 shown, the hydraulic fracture fracturing monitoring system based on optical fiber monitoring in the embodiment of the present specification may include: a hydraulic fracturing simulation platform 101, a fracturing fluid injection device 102, a plurality of strain sensor groups 103, an optical fiber sensing demodulation device 104, and a data processing device 105.

[0054] The hydraulic fracturing simulation platform 101 can be used to apply triaxial stress to the hydraulic fracturing specimen to simulate the formation stress environment. Specifically, the hydraulic fracturing simulation platform 101 can be a true triaxial hydraulic fracturing simulation platform 101, which applies triaxial stress to simulate the formation stress environment. The pressure loading process can be increased step by step to simulate the in-situ stress changes at different reservoir depths.

[0055] In one embodiment, the hydraulic fracturing simulation platform 101 can simulate a more complex stress environment, such as cyclic loading stress, to simulate the periodic stress changes experienced by the formation during long-term exploitation; it can also simulate non-uniform stress distribution to better fit the non-uniformity of stress in the actual formation.

[0056] In one embodiment, stress monitoring sensors are provided on the hydraulic fracturing simulation platform 101 or the hydraulic fracturing specimen to real-time monitor the stress value applied to the specimen and feedback the data to the data processing device 105. When the stress value shows abnormal fluctuations, the system can automatically adjust the stress loading to ensure the stability and accuracy of the simulation environment.

[0057] The fracturing fluid injection device 102 is used to inject the pre-configured fracturing fluid into the specimen, causing cracks to propagate in the specimen. A flow sensor can be provided in the fracturing fluid injection device 102 to real-time detect the injection rate and feedback the data to the data processing device 105.

[0058] In one embodiment, in addition to injecting the pre-configured fracturing fluid, the fracturing fluid injection device 102 can also regulate parameters such as the properties of the fracturing fluid and the injection rate. For example, the fracturing fluid injection device 102 can adjust the injection rate and / or viscosity, density, etc. of the fracturing fluid according to the real-time state of crack propagation to better control the crack propagation direction and propagation speed.

[0059] During the preparation of the specimen, multiple strain sensor groups 103 can be buried in the specimen. The multiple strain sensor groups 103 at least include a first FBG strain sensor group and a second FBG strain sensor group. FBG is Fiber Bragg Grating. The first FBG strain sensor group can include multiple FBG strain sensors with the fiber axial direction parallel to the crack propagation direction of the specimen. The second FBG strain sensor group can include multiple FBG strain sensors with the fiber axial direction perpendicular to the crack propagation direction. In one embodiment, high-precision FBG strain sensors can be used to improve the measurement accuracy of strain data. At the same time, redundant sensor design can be added so that the system can still normally obtain strain data when some sensors fail. In addition, sensor groups can be added at different depths and positions to more comprehensively monitor the strain changes during crack propagation.

[0060] The fiber optic sensing demodulation device 104 is used to collect the strain data detected by multiple strain sensor groups 103. In one embodiment, a multi-channel demodulation function can be added so that the fiber optic sensing demodulation device 104 can demodulate the data of multiple sensor groups simultaneously, improving the monitoring efficiency of the system. The demodulation process of the fiber optic sensing demodulation device 104 for FBG strain sensors mainly converts the optical wavelength change caused by strain into recognizable electrical signals or data. Specifically, the stable light source (such as a broadband light source or a laser with a specific wavelength) equipped in the fiber optic sensing demodulation device 104 emits an optical signal with a certain spectral range. This optical signal enters the optical fiber and is transmitted to the FBG strain sensor. After the optical signal reaches the FBG strain sensor, the light with a specific wavelength (Bragg wavelength) that satisfies the Bragg condition will be reflected back, and the light of the remaining wavelengths will continue to be transmitted. The Bragg wavelength is related to the grating period and the effective refractive index of the fiber core of the FBG. When the FBG strain sensor is affected by external strain, the grating period and the effective refractive index change, causing the Bragg wavelength to shift, and it is approximately linearly related to the strain. The optical signal reflected by the FBG returns along the original optical fiber and enters the fiber optic sensing demodulation device 104. In the demodulation device, first, it passes through an optical coupler or circulator to guide the reflected optical signal to the subsequent processing unit to achieve the separation of optical signals in different directions. The reflected optical signal enters the wavelength detection module, and using methods such as the interference principle or spectral analysis, the offset of the Bragg wavelength is accurately measured. The measured wavelength offset is processed through algorithms and circuits for signal amplification, filtering, analog-to-digital conversion, etc., and is converted into corresponding strain data.

[0061] The data processing device 105 is communicatively connected to the fiber optic sensing demodulation device 104, and is used to obtain the strain data and process the strain data to determine the real-time status data of crack propagation in the specimen. The data processing device 105 can determine the real-time status data of the crack in the specimen in the propagation direction and in the direction perpendicular to the propagation direction based on the strain data obtained by multiple groups of FBG strain sensors. Among them, the real-time status data can include at least one of the following: crack propagation length, crack propagation width, crack propagation speed, crack propagation path, etc.

[0062] In the above embodiment, by using FBG strain sensors to detect strain data, it is possible to ensure high sensitivity, real-time performance, and anti-interference ability of the detection. It can not only dynamically capture the strain characteristics of crack propagation, but also achieve high-precision reconstruction of the three-dimensional strain field in the case of multi-point layout, significantly improving the accuracy and reliability of monitoring. Further, by arranging multi-angle FBG strain sensor groups in the specimen, it is possible to dynamically capture the crack propagation characteristics exhibited during the crack propagation process, realize real-time dynamic monitoring of the dynamic propagation of hydraulic fractures, especially suitable for real-time monitoring of complex fracture networks in reservoirs, and provide an important experimental method for the mechanism of hydraulic fracture propagation.

[0063] In some embodiments of this specification, the multiple strain sensor groups 103 further include: a third FBG strain sensor group with its axial direction inclined to the crack propagation direction.

[0064] During the actual hydraulic fracture fracturing process, the crack propagation direction does not always follow the preset parallel or perpendicular directions. It may be affected by various complex factors such as formation heterogeneity and uneven stress distribution, showing an inclined propagation path. The third FBG strain sensor group can capture the strain change information of the crack in the inclined direction, making up for the deficiency of monitoring only relying on the parallel and perpendicular direction sensor groups. Thus, it can achieve more comprehensive and accurate monitoring of the crack in three-dimensional space and obtain more complete crack propagation data. In one embodiment, the third FBG strain sensor group includes multiple FBG sensors with an inclination angle of 45°. By setting the first FBG strain sensor group, the second FBG strain sensor group, and the third FBG strain sensor group, a three-dimensional strain monitoring network can be formed. One more group of sensors in different directions can provide more dimensional data. Through the comprehensive analysis and mutual verification of these data, the errors and uncertainties that may be brought by single-direction monitoring can be reduced, and the accuracy and reliability of calculating crack propagation parameters (such as length, height, propagation speed, etc.) can be improved. For example, when the crack shows complex branches or twists, the data of the third FBG strain sensor group can help more accurately judge the true propagation situation of the crack and avoid misjudging the crack morphology. When conducting data analysis, the data of the third FBG strain sensor group provides more input variables for the analysis model. Through the mining and analysis of these multi-dimensional data, more in-depth research can be carried out, such as establishing a more accurate crack propagation prediction model, analyzing the influence weights of different factors on crack propagation, etc., further enhancing the data analysis ability and application value of the monitoring system.

[0065] In some embodiments of this specification, the system further includes: a distributed fiber optic temperature sensor, which is distributed inside the specimen and is used to monitor the temperature field change during the crack propagation process.

[0066] During the hydraulic fracture fracturing process, the temperature field change data monitored by the distributed fiber optic temperature sensor can provide valuable information in many aspects for the crack propagation process.

[0067] In one embodiment, the temperature field change data monitored by the distributed fiber optic temperature sensor can be used to determine the crack initiation location. When a crack begins to initiate, local deformation and friction occur in the stress concentration area inside the rock, which may lead to abnormal temperature changes in this area. By monitoring the temperature field change, when it is found that the temperature at a certain position inside the specimen suddenly rises or an abnormal temperature gradient appears, it may indicate that a crack starts to form here. For example, at the weak part of the rock, the stress concentration intensifies the friction between rock particles, generating heat and causing the temperature to rise, thus providing an important clue for determining the crack initiation location.

[0068] In another embodiment, the temperature field change data monitored by the distributed fiber optic temperature sensor can be used to determine the crack initiation location. During the crack propagation process, the fracturing fluid will flow along the crack, and factors such as the heat exchange between the fracturing fluid and the rock and the energy loss during the flow process will cause changes in the temperature field. Generally speaking, the direction of crack propagation is the direction of fracturing fluid flow, and the flow of the fracturing fluid will cause specific characteristics in the temperature distribution in this direction. By analyzing the change trend of the temperature field, such as the extension direction of the area with temperature rise, the crack propagation direction can be inferred. For example, if the temperature continuously rises in a certain direction and shows a certain gradient change, then it is very likely that the crack is propagating along this direction.

[0069] In yet another embodiment, the distribution characteristics of the temperature field can reflect the crack morphology. For example, when the crack shows a branched propagation, the flow rate and velocity of the fracturing fluid in different branches may be different, which will lead to differences in the temperature field distributions corresponding to each branch. By analyzing the non-uniformity of the temperature field, information such as whether the crack branches, the number of branches, and the general trend of the branches can be inferred. In addition, for the change in crack width, the temperature field can also provide certain information. In a relatively wide crack, the flow of the fracturing fluid is relatively smooth, and the temperature distribution may be relatively uniform; while at a relatively narrow crack, more heat loss may occur due to the increased resistance to the flow of the fracturing fluid, resulting in abnormal temperature distribution.

[0070] In still another embodiment, the ΔT value in the formula (such as formula (3) in the following text) for calculating the strain value in the area where the FBG strain sensor grating is located can be corrected by using the temperature field inside the specimen monitored in real time by the distributed fiber optic temperature sensor, so as to eliminate the influence of temperature drift.

[0071] In some embodiments of this specification, the system further includes: an acoustic emission monitoring device, which is arranged around the specimen and is used to monitor the acoustic emission signals during the crack propagation process.

[0072] During the crack propagation process, the breaking of chemical bonds, friction, etc. inside the rock will generate elastic waves, that is, acoustic emission signals. The device can capture these signals by being arranged around the specimen. From the perspective of the crack initiation stage, the acoustic emission monitoring device can detect weak acoustic emission signals when the crack just begins to form and before it causes obvious strain or temperature changes, thus warning of the occurrence of cracks earlier and providing key information for studying the initial state of the cracks. During the crack propagation process, the characteristics of acoustic emission signals, such as intensity, frequency, and distribution, are closely related to the propagation speed, direction, and morphology of the cracks. For example, when the crack propagates rapidly, the frequency and intensity of the acoustic emission signals may increase; by analyzing the acoustic emission signals at different positions, the propagation direction of the crack can be inferred. For complex crack morphologies, such as the formation of branched cracks, the acoustic emission monitoring device can help determine the number and position of crack branches by capturing the signal changes. In addition, the signals obtained by the acoustic emission monitoring device can also be verified and supplemented with the data of other monitoring means (such as strain sensors, temperature sensors). For example, the acoustic emission can be used to locate the crack initiation point, and combined with the FBG strain field data, a spatio-temporal fusion crack propagation model can be constructed. When the strain sensor detects a strain change, combining with the acoustic emission signal can more accurately determine whether this strain change is caused by crack propagation or other factors. By comprehensively analyzing various monitoring data, the process and mechanism of crack propagation can be understood more comprehensively and deeply, improving the accuracy and reliability of hydraulic fracture monitoring.

[0073] In some embodiments of the present specification, the data processing device 105 is specifically configured to: calculate the crack length of crack propagation based on the first strain data detected by the first FBG strain sensor group; calculate the crack height of crack propagation based on the second strain data detected by the second FBG strain sensor group; calculate the crack propagation speed according to the crack lengths at multiple moments.

[0074] Specifically, the axial direction of the first FBG strain sensor group is parallel to the crack propagation direction of the specimen, and the strain data detected by it is related to the deformation of the crack in the length direction. Based on the linear relationship between strain and length change in the elastic deformation stage of the material, etc., by analyzing and processing these strain data, the length of crack propagation can be deduced. The axial direction of the second FBG strain sensor group is perpendicular to the crack propagation direction, and the strain data detected by it is related to the change of the crack in the height direction, and the crack height can be calculated accordingly. By obtaining the crack length data at different moments, calculating the difference in crack lengths between adjacent moments, and dividing by the corresponding time interval, the average propagation speed of the crack during this time period can be obtained. The crack length, height, and propagation speed are key parameters describing the crack propagation state. The data processing device 105 can accurately calculate these parameters, providing direct and important data support for subsequent analysis of the crack propagation process, evaluation of the fracturing effect, and optimization of the fracturing process, etc.

[0075] This embodiment of the present specification also provides a hydraulic fracture fracturing monitoring method based on optical fiber monitoring, and the method is based on the hydraulic fracture fracturing monitoring system based on optical fiber monitoring described in any of the above embodiments. Figure 2 The flowchart of the hydraulic fracture fracturing monitoring method based on optical fiber monitoring in an embodiment of the present specification is shown. Although the present specification provides method operation steps or device structures as shown in the following embodiments or drawings, more or fewer operation steps or module units may be included in the method or device based on routine or non-creative labor. In steps or structures where there is no necessary causal relationship logically, the execution order of these steps or the module structure of the device is not limited to the execution order or module structure described in the embodiments of the present specification and shown in the drawings. When the method or module structure is applied to an actual device or terminal product, it can be executed sequentially or in parallel according to the method or module structure connection shown in the embodiments or drawings (for example, in an environment of parallel processors or multi-threaded processing, or even a distributed processing environment).

[0076] Specifically, as Figure 2 shown, the hydraulic fracture fracturing monitoring method provided by an embodiment of the present specification may include the following steps:

[0077] Step S201, controlling the hydraulic fracturing simulation platform to apply triaxial stress to the hydraulic fracturing specimen to simulate the formation stress environment.

[0078] The method in this embodiment can be applied to a computer device. In this embodiment, the computer device may be the data processing device in the above-mentioned hydraulic fracture fracturing monitoring system based on optical fiber monitoring. It can control the hydraulic fracturing simulation platform to apply triaxial stress to the hydraulic fracturing specimen to simulate the formation stress environment.

[0079] Corresponding stress values, including vertical stress, maximum horizontal principal stress, and minimum horizontal principal stress, can be input into the control system of the hydraulic fracturing simulation platform according to the actual stress parameters of the target formation. Start the loading system of the simulation platform, and slowly and evenly apply triaxial stress to the hydraulic fracturing specimen through a hydraulic cylinder or a mechanical loading device. During the loading process, use high-precision pressure sensors to monitor the stress magnitude in each direction in real time and feedback the data to the control system. When the stress value approaches the set value, the control system automatically adjusts the loading speed to achieve precise stress application. By simulating the real formation stress environment, the experimental results are more reliable and practical, providing a more realistic basic condition for subsequent crack propagation research and helping to accurately analyze the crack propagation law and influencing factors in the formation.

[0080] Step S202, control the fracturing fluid injection device to inject fracturing fluid into the hydraulic fracturing specimen, causing cracks to propagate in the specimen.

[0081] The pre-prepared fracturing fluid can be injected into a high-pressure storage tank. The fracturing fluid can be transported to the specimen by controlling a high-pressure pump. A flow control valve, a pressure sensor, and a temperature sensor are installed in the injection pipeline to precisely control the injection rate, pressure, and temperature of the fracturing fluid. According to experimental requirements, different injection schemes can be preset. For example, when injecting in segments, set the injection rate and time for each stage; when injecting in pulses, set the frequency and amplitude of the pulses. Monitor various parameters during the injection process in real time and record the data. Use the high-pressure pump to provide power to make the fracturing fluid enter the specimen under pressure, overcoming the tensile strength of the rock, thereby triggering crack propagation. By controlling the injection parameters, different fracturing construction conditions can be simulated to study their effects on crack propagation.

[0082] Step S203, obtain the strain data detected by multiple strain sensor groups; the strain data at least includes the first strain data detected by the first FBG strain sensor group and the second strain data detected by the second FBG strain sensor group.

[0083] The strain data detected by multiple strain sensor groups can be obtained from an optical fiber sensing demodulation device. Specifically, use an optical fiber sensing demodulator to connect the first FBG strain sensor group and the second FBG strain sensor group respectively. The sampling frequency and data acquisition time of the demodulator can be set to ensure that the changes in the strain data can be accurately captured. During the data acquisition process, monitor the working state of the sensors in real time to ensure the stability and reliability of the data. At the same time, perform preliminary filtering on the collected data to remove noise interference.

[0084] Step S204, calculate the crack length based on the first strain data; calculate the crack height based on the second strain data.

[0085] Specifically, according to the principles of material mechanics and elasticity mechanics, a mathematical model between the strain data and the crack length and height can be established. The first strain data can be substituted into the crack length calculation model, and through integration or other mathematical methods, the length of the crack in the propagation direction can be calculated. Similarly, the second strain data can be substituted into the crack height calculation model to calculate the height of the crack in the vertical direction. During the calculation process, consider the mechanical parameters and boundary conditions of the rock to ensure the accuracy of the calculation results. Based on the relationship between the deformation of the rock during the stress process and the crack propagation, the geometric parameters of the crack are inferred from the strain data. Use the mathematical model to quantify the relationship between physical quantities, thereby realizing the calculation of the crack length and height.

[0086] Step S205, calculate the crack propagation speed according to the crack lengths at multiple moments.

[0087] Multiple time nodes can be selected to record the crack length data corresponding to each time node. By calculating the difference in crack lengths between adjacent time nodes and dividing it by the time interval, the average propagation speed of the crack during this time period can be obtained. To more accurately reflect the changing trend of the crack propagation speed, the moving average method or other data smoothing methods can be used to process the calculation results. At the same time, analyze the relationships between the crack propagation speed and factors such as time, stress, and fracturing fluid parameters, and plot the relevant curves. Calculating the crack propagation speed can help understand the dynamic process of crack propagation, analyze the influence of different factors on the crack propagation speed, provide a basis for optimizing fracturing construction parameters, contribute to controlling crack propagation, and improving the fracturing effect.

[0088] In the above embodiments, by arranging a multi-angle FBG strain sensor group in the specimen, the crack propagation characteristics exhibited during the crack propagation process can be dynamically captured, realizing the real-time monitoring of the dynamic propagation of hydraulic fractures. It is especially suitable for the real-time monitoring of complex fracture networks in reservoirs, providing an important experimental method for the mechanism of hydraulic fracture propagation. There are rigorous steps in aspects such as the simulation experiment environment, data acquisition and analysis. The beneficial effects brought about are reflected in multiple dimensions such as accuracy, comprehensiveness, and practicality, which are of great significance to the research and engineering application of hydraulic fracturing. By precisely applying triaxial stress through the hydraulic fracturing simulation platform, the formation stress environment is realistically simulated, making the experimental conditions highly consistent with the actual formation. This enables the cracks to propagate under a stress state close to the real situation, and the experimental results can accurately reflect the real propagation law and influencing factors of the cracks in the formation, laying a reliable foundation for subsequent research and analysis, and greatly enhancing the credibility and application value of the research conclusions. The precise control of the fracturing fluid injection device allows for flexible setting of the injection rate, pressure, temperature, and diverse injection schemes. This helps to deeply explore the propagation characteristics of cracks under different injection conditions. Researchers can thereby find the most suitable fracturing construction parameters, optimize the fracturing construction plan, improve the fracturing effect, increase oil and gas production, and enhance the economic benefits of the project. By using an optical fiber sensing demodulator to obtain the strain data of multiple strain sensor groups, key data for calculating the geometric parameters of the cracks is provided. These data accurately reflect the mechanical behavior during the crack propagation process. Combined with the monitoring of other parameters such as temperature and pressure, a multi-dimensional data system is constructed, providing rich information for in-depth analysis of the crack propagation pattern, process, and internal mechanism, and helping to comprehensively master the crack propagation law. Calculating the crack length, height, and propagation speed based on the strain data realizes the quantification of the crack propagation degree and scale. These quantitative indicators visually display the fracturing effect, helping researchers and engineers quickly judge whether the fracturing construction meets the expected goals, promptly adjust the construction strategy, and ensure the smooth progress of the fracturing project. Analyzing the relationship between the crack propagation speed and factors such as time, stress, and fracturing fluid parameters can reveal the dynamic process and internal law of crack propagation. This provides a scientific basis for optimizing the fracturing construction parameters, enabling engineers to effectively control the crack propagation during actual operation, improving the fracturing effect, reducing construction risks, and promoting the development and application of hydraulic fracturing engineering technology

[0089] In some embodiments of this specification, the method further includes: obtaining third strain data detected by a third FBG strain sensor group; generating a crack propagation path based on the first strain data, the second strain data, and / or the third strain data.

[0090] Specifically, during the actual hydraulic fracture fracturing process, the fracture propagation direction is complex and does not only extend parallel or perpendicular to the prefabricated fracture propagation direction. The third FBG strain sensor group can capture the strain changes in the inclined direction. Combined with the first and second strain data, it can comprehensively monitor the fracture propagation in three-dimensional space, make up for the deficiencies of single-direction monitoring, and provide more complete fracture propagation information. Generating a fracture propagation path based on the three groups of strain data can accurately present the extension trajectories of the fractures in different directions. By analyzing the strain data at different times, the propagation trend of the fractures under complex stresses can be understood, providing a key basis for studying the fracture propagation mechanism, which is of great significance for optimizing the fracturing process. Multiple groups of data can be mutually verified and supplemented to reduce monitoring errors and uncertainties. The strain data in different directions reflect the fracture propagation state from multiple angles. Comprehensive analysis can more accurately judge the fracture propagation situation, avoid misjudgment caused by single data, and improve the credibility of the monitoring results.

[0091] Specifically, the first strain data detected by the first FBG strain sensor group, the second strain data detected by the second FBG strain sensor group, and the third strain data detected by the third FBG strain sensor group can be filtered first. Since in the actual monitoring process, sensor data may be interfered by various noises, such as electromagnetic interference, environmental vibration, etc., using filters (such as low-pass filters, band-pass filters, etc.) can remove these noises and improve the data quality. Data calibration is carried out. According to the calibration parameters of the sensors and the known standard strain values, the collected strain data is corrected to ensure the accuracy of the data. At the same time, the data of different sensor groups are time-synchronized because there may be slight time differences in the actual acquisition process. Through time synchronization, the consistency of subsequent analysis can be ensured. The mathematical relationship between strain and displacement can be established according to the principles of material mechanics. For fracture propagation in three-dimensional space, the strain data in three directions (parallel, perpendicular, and inclined to the fracture propagation direction) need to be considered separately and converted into displacement components. Using geometric relationships and trigonometric functions, the displacement components in each direction are synthesized to obtain the actual displacement of the fracture in three-dimensional space. At the initial state of the specimen, the starting position point of the fracture is determined. Usually, the starting position of the fracture can be determined according to the experimental setup or pre-made marks. According to the converted displacement data, at each monitoring moment, the displacement of the fracture endpoint relative to the starting position is calculated to determine the position point of the fracture at that moment. The fracture position point data at multiple monitoring moments are collected, and curve fitting algorithms (such as the least squares method, spline interpolation method, etc.) are used to fit these position points. According to the fitted curve, a fracture propagation path is generated. The fracture propagation path can be visualized using drawing software or programming tools (such as the Matplotlib library in Python, Matlab, etc.) to intuitively display the fracture propagation process in three-dimensional space.

[0092] In some embodiments of this specification, the method further includes: obtaining stress data applied by the hydraulic fracturing simulation platform and the liquid injection rate of the fracturing fluid injection device; analyzing the influence of the liquid injection rate and the stress data on fracture propagation based on the first strain data, the second strain data, the stress data, and the liquid injection rate.

[0093] After that, the generated fracture propagation path can also be optimized based on the temperature field change data monitored by the distributed optical fiber temperature sensor and the acoustic emission signal data monitored by the acoustic emission monitoring device. For example, areas with large temperature field changes may indicate active areas of fracture propagation, and positions with strong acoustic emission signals may correspond to the tips or rupture points of fractures. Combining this information with the strain data can more accurately determine the fracture propagation path and eliminate some incorrect paths caused by data noise or abnormal conditions. The mechanical properties of the rock and geological structure information can also be combined to verify the rationality of the fracture propagation path. Different mechanical properties of the rock and geological structures will affect the propagation direction and morphology of fractures. By considering these factors, the fracture propagation path can be further optimized to make it more in line with the actual situation.

[0094] In some embodiments of this specification, the method further includes: monitoring whether abnormal conditions occur during fracture propagation; the abnormal conditions include at least one of the following: the change in the propagation speed exceeds a preset range, the propagation direction undergoes a sudden change, or the temperature change exceeds a preset range; generating an abnormal signal when abnormal conditions occur during fracture propagation; controlling the hydraulic fracturing simulation platform to adjust the triaxial stress or controlling the fracturing fluid injection device to adjust the liquid injection rate based on the abnormal signal.

[0095] Specifically, a high-precision data acquisition system can be utilized to continuously collect strain data of multiple strain sensor groups, temperature data of distributed fiber optic temperature sensors, and / or acoustic emission signal data of acoustic emission monitoring devices at a set frequency. By applying data analysis algorithms, the crack propagation speed can be calculated in real time, the propagation direction can be analyzed, and the temperature change can be monitored. For example, by comparing the crack length data at adjacent time points and combining the time interval to calculate the propagation speed; judging the propagation direction based on the change trend of strain data in different directions; and monitoring the temperature data in real time to observe its change. Before the experiment starts, reasonable preset ranges can be set for the crack propagation speed, the change in propagation direction, and the temperature change according to the experimental purpose, rock properties, and past experience. For example, the normal range of the crack propagation speed is set to 0.5 - 1.5 cm per minute, the change in the propagation direction within 10 degrees is normal, and the temperature change not exceeding 5 degrees Celsius per hour is normal. During the data processing, the parameters obtained from real-time calculation and analysis can be compared with the preset ranges to determine whether an abnormality occurs. When the change in the crack propagation speed exceeds the preset range, the propagation direction undergoes a sudden change (such as exceeding the set 10-degree change range), or the temperature change exceeds the preset range, an abnormality judgment mechanism is triggered.

[0096] After receiving the abnormal signal, the central processing unit of the control system generates corresponding control instructions according to the preset control strategy. For example, if the propagation speed is too fast, an instruction to reduce the injection rate of the fracturing fluid is generated; if the propagation direction undergoes a sudden change, an instruction to adjust the three-dimensional stress distribution is generated. After receiving the control instructions, the actuators of the hydraulic fracturing simulation platform and the fracturing fluid injection device quickly adjust the three-dimensional stress or the injection rate. For example, the fracturing fluid injection device reduces the injection rate by 20% by adjusting the flow control valve; the hydraulic fracturing simulation platform changes the distribution of the three-dimensional stress by adjusting the pressure of the hydraulic system. During the adjustment process, the device real-time feeds back the adjusted parameter values to the control system to confirm whether the adjustment is successful. By monitoring in real time and processing abnormal situations promptly, safety accidents such as specimen rupture and equipment damage caused by out-of-control crack propagation can be avoided, ensuring the safety of experimental personnel and equipment. Abnormal situations are promptly detected and corrected to ensure that the experiment is carried out under stable and controllable conditions, avoiding interference of abnormal factors with experimental data, and improving the reliability and accuracy of experimental data. The analysis and processing of abnormal situations help to deeply understand the laws and influencing factors of crack propagation, provide a basis for optimizing the experimental plan and fracturing process, and improve the experimental efficiency and practical application effect. The entire abnormal monitoring and processing process is automated, reducing manual intervention, improving the response speed and control accuracy of the experiment, and enhancing the intelligent level of the experiment.

[0097] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other, and the differences between each embodiment and other embodiments are emphasized. Specifically, reference can be made to the descriptions of the relevant embodiments of the foregoing related processing, and details will not be repeated here.

[0098] The above describes specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in a different order than in the embodiments and still achieve the desired results. Additionally, the processes depicted in the figures do not necessarily require the specific order or sequential order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0099] The above method will be described below in conjunction with a specific embodiment. However, it should be noted that this specific embodiment is only for better explaining this specification and does not constitute an improper limitation to this specification.

[0100] A hydraulic fracture fracturing monitoring method based on optical fiber monitoring is provided in this specific embodiment. The method in this specific embodiment is based on the monitoring system described in any of the above embodiments. Figure 3 This is a schematic diagram of the overall specimen and optical fiber layout in this specific embodiment, showing the installation positions of the sensors in the specimen and the optical fiber layout.

[0101] The implementation steps of the hydraulic fracture fracturing monitoring method based on optical fiber monitoring in this specific embodiment are specifically introduced as follows:

[0102] Step 1, configure the wellbore 302 and the prefabricated fracture at the end of the wellbore 302. Simulate that a circular hard plastic sheet (natural fracture sheet 303) with a specific diameter is connected to the end of the wellbore 302 so as to simulate an existing natural fracture after the specimen 301 solidifies. Prepare a hydraulic fracturing concrete specimen 301, and bury several groups of FBG strain sensors (including the first FBG strain sensor group 304 and the second FBG strain sensor group 305) into the specimen 301 in directions parallel and perpendicular to the expected propagation path of the prefabricated fracture in the specimen 301 during the preparation process of the specimen 301.

[0103] Step 2, place the specimen 301 in a true triaxial testing machine and apply triaxial stress to simulate the formation stress environment. The pressure loading process needs to be increased step by step to simulate the in-situ stress changes at different reservoir depths.

[0104] Step 3, start the high-pressure liquid injection system, set a predetermined pump speed, and induce the propagation of the main fracture by pressure through injecting the pre-configured fracturing fluid, and record the dynamic changes of the pump pressure and strain over time through the FBG optical fiber and external sensors.

[0105] Step 4: Continuously pump fracturing fluid into the specimen until it ruptures over time. Stop pumping, unload the pressure and confining pressure, and remove the specimen.

[0106] Step 5: Use a fiber Bragg grating (FBG) sensing demodulator to collect data from the FBG sensors. Combine the results of multi-point monitoring to plot the crack propagation path and the curve of width change. Calculate the crack propagation speed based on the relationship between the FBG grating wavelength and strain, and analyze the influence on crack propagation by setting different liquid injection rates and pressures.

[0107] In the above Step 5, the calculation process for processing the FBG sensor data is as follows:

[0108] During the experiment, the fiber Bragg grating strain sensor embedded in the specimen can emit broadband light of multiple wavelengths and receive the Bragg reflected light wave reflected back after being modulated by the grating area of the fiber Bragg grating strain sensor. The reflected Bragg light wave is:

[0109] λ = 2nΛ (1)

[0110] Where: λ is the reflected Bragg wavelength (nm); n is the effective refractive index of the fiber core, and Λ is the grating period.

[0111] By calculating the spectral information such as the light wave wavelength and intensity collected by the FBG strain sensor, the change in the light wave wavelength returned by the sensor during the experiment is calculated, so as to obtain the strain value in the area where the FBG strain sensor grating is located:

[0112] Δλ = λ - λ 0 (2)

[0113] Δλ(ε,T) = K ε Δε + K T ΔT (3)

[0114] Where: λ is the reflected Bragg wavelength (nm); λ 0 is the initial reflected Bragg wavelength (nm); K ε is the strain optical sensitivity coefficient; K T is the temperature optical sensitivity coefficient (℃ / με); ε g is the strain change value in the grating area of the FBG strain sensor; ΔT is the temperature change value (℃).

[0115] In one embodiment, during the experiment, the room temperature of the experimental environment is kept constant all the time, so ΔT is 0.

[0116] Considering that the experimental environment temperature will fluctuate, therefore, a distributed fiber optic temperature sensor can be set inside the specimen to monitor the temperature field change during crack propagation and correct the ΔT value in formula (3) to eliminate the influence of temperature drift.

[0117] If the fiber Bragg grating and the intermediate layer are always in linear elastic deformation, the strain transfer theory can be used to calculate and derive the formula for the average strain transfer rate of the fiber optic sensor from the strain value in the grating area:

[0118]

[0119] In the formula: ε m is the strain value of the matrix; l is the grating area length (mm) of the FBG strain sensor; r m is the distance (μm) from the axis of the FBG strain sensor to the matrix; r g is the radius (μm) of the fiber Bragg grating; E g , E c are the elastic moduli (GPa) of the fiber Bragg grating and the intermediate layer respectively; μ is the Poisson's ratio of the intermediate layer.

[0120] In this specific embodiment, the specimen is placed in a true triaxial testing machine, and triaxial stresses are applied to simulate the formation stress environment. The pressure loading process needs to be increased step by step to simulate the in-situ stress changes at different reservoir depths. The high-pressure liquid injection system is started, and the main crack is induced to expand by injecting liquid pressure, and the dynamic changes of the crack morphology over time are recorded. The fiber Bragg grating sensing demodulator is used to collect the data of the FBG sensor, and the crack propagation path and width change curve are plotted in combination with the multi-point monitoring results. According to the relationship between the FBG grating wavelength and strain, the crack propagation speed is calculated, and the influence of different injection rates and pressures on crack propagation is analyzed.

[0121] Based on the same inventive concept, an apparatus for monitoring hydraulic fracture fracturing based on fiber optic monitoring is also provided in the embodiments of this specification. The apparatus is based on the system for monitoring hydraulic fracture fracturing based on fiber optic monitoring described in any of the above embodiments, as described in the following embodiments. Since the principle of solving problems by the apparatus for monitoring hydraulic fracture fracturing based on fiber optic monitoring is similar to that of the method for monitoring hydraulic fracture fracturing based on fiber optic monitoring, the implementation of the apparatus for monitoring hydraulic fracture fracturing based on fiber optic monitoring can refer to the implementation of the method for monitoring hydraulic fracture fracturing based on fiber optic monitoring, and the repeated parts will not be described again. Hereinafter, the term "unit" or "module" may be a combination of software and / or hardware that can achieve a predetermined function. Although the apparatus described in the following embodiments is preferably implemented in software, implementation in hardware, or a combination of software and hardware is also possible and contemplated. Figure 4 is a structural block diagram of the apparatus for monitoring hydraulic fracture fracturing based on fiber optic monitoring in the embodiments of this specification, as Figure 4 shown, including: a first control module 401, a second control module 402, an acquisition module 403, a first calculation module 404, and a second calculation module 405. The structure will be described below.

[0122] The first control module 401 is used to control the hydraulic fracturing simulation platform to apply triaxial stress to the hydraulic fracturing specimen to simulate the formation stress environment.

[0123] The second control module 402 is used to control the fracturing fluid injection device to inject fracturing fluid into the hydraulic fracturing specimen, so that cracks expand in the specimen.

[0124] The acquisition module 403 is used to acquire strain data detected by multiple strain sensor groups; the strain data at least includes first strain data detected by the first FBG strain sensor group and second strain data detected by the second FBG strain sensor group.

[0125] The first calculation module 404 is used to calculate the crack length based on the first strain data; calculate the crack height based on the second strain data.

[0126] The second calculation module 405 is used to calculate the crack propagation speed according to the crack lengths at multiple moments.

[0127] In some embodiments of the present specification, the device further includes a third calculation module, and the third calculation module is used to: acquire third strain data detected by a third FBG strain sensor group; generate a crack propagation path based on the first strain data, the second strain data and / or the third strain data.

[0128] In some embodiments of the present specification, the device further includes an analysis module, and the analysis module is used to: acquire the stress data applied by the hydraulic fracturing simulation platform and the liquid injection rate of the fracturing fluid injection device; analyze the influence of the liquid injection rate and the stress data on crack propagation based on the first strain data, the second strain data, the stress data and the liquid injection rate.

[0129] In some embodiments of the present specification, the device further includes an anomaly detection module, and the anomaly detection module is used to: monitor whether abnormal conditions occur in crack propagation; the abnormal conditions include at least one of the following: the change in the propagation speed exceeds a preset range, the propagation direction changes suddenly, or the temperature change exceeds a preset range; when abnormal conditions occur in crack propagation, generate an abnormal signal; control the hydraulic fracturing simulation platform to adjust the triaxial stress or control the fracturing fluid injection device to adjust the liquid injection rate based on the abnormal signal.

[0130] The embodiments of the present specification also provide a computer device, which can be specifically referred to Figure 5Schematic diagram of the composition structure of a computer device for the fiber-optic monitoring-based hydraulic fracture fracturing monitoring method provided in the embodiments of this specification. Specifically, the computer device may include an input device 51, a processor 52, and a memory 53. Among them, the memory 53 is used to store instructions executable by the processor. When the processor 52 executes the instructions, the steps of the fiber-optic monitoring-based hydraulic fracture fracturing monitoring method described in any of the above embodiments are implemented.

[0131] In this embodiment, the input device may specifically be one of the main devices for information exchange between a user and a computer system. The input device may include a keyboard, a mouse, a camera, a scanner, a light pen, a handwriting input board, a voice input device, etc.; the input device is used to input raw data and programs for processing these data into the computer. The input device may also obtain and receive data transmitted from other modules, units, and devices. The processor may be implemented in any suitable manner. For example, the processor may take the form of, for example, a microprocessor or a processor and a computer-readable medium storing computer-readable program code (such as software or firmware) executable by the (micro)processor, logic gates, switches, an application specific integrated circuit (ASIC), a programmable logic controller, and a form embedded microcontroller, etc. The memory may specifically be a memory device used to store information in modern information technology. The memory may include multiple levels. In a digital system, as long as it can store binary data, it can be a memory; in an integrated circuit, a circuit with a storage function without a physical form is also called a memory, such as RAM, FIFO, etc.; in a system, a storage device with a physical form is also called a memory, such as a memory module, a TF card, etc.

[0132] In this embodiment, the functions and effects specifically implemented by this computer device may be explained in comparison with other embodiments and will not be elaborated here.

[0133] This specification also provides a computer storage medium for the fiber-optic monitoring-based hydraulic fracture fracturing monitoring method. The computer storage medium stores computer program instructions, and when the computer program instructions are executed, the steps of the fiber-optic monitoring-based hydraulic fracture fracturing monitoring method described in any of the above embodiments are implemented.

[0134] In this embodiment, the above storage medium includes, but is not limited to, Random Access Memory (RAM), Read-Only Memory (ROM), Cache, Hard Disk Drive (HDD), or Memory Card. The memory can be used to store computer program instructions. The network communication unit can be set according to the standards specified by the communication protocol and is used for the interface of network connection communication.

[0135] In this embodiment, the functions and effects specifically implemented by the program instructions stored in the computer storage medium can be explained by comparison with other embodiments and will not be elaborated here.

[0136] Obviously, those skilled in the art should understand that the above-mentioned modules or steps of the embodiments of this specification can be implemented by a general-purpose computing device. They can be concentrated on a single computing device or distributed on a network composed of multiple computing devices. Optionally, they can be implemented by program codes executable by the computing device. Thus, they can be stored in the storage device and executed by the computing device. And in some cases, the steps shown or described can be executed in a different order than here, or they can be separately fabricated into individual integrated circuit modules, or multiple modules or steps among them can be fabricated into a single integrated circuit module to implement. In this way, the embodiments of this specification are not limited to any specific combination of hardware and software.

[0137] It should be understood that the above description is for illustrative purposes and not for limitation. By reading the above description, many embodiments and many applications other than the provided examples will be obvious to those skilled in the art. Therefore, the scope of this specification should not be determined with reference to the above description, but should be determined with reference to the full scope of the foregoing claims and the equivalents of these claims.

[0138] The above are only the preferred embodiments of this specification and are not used to limit this specification. For those skilled in the art, the embodiments of this specification can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included within the protection scope of this specification.

Claims

1. A hydraulic fracture monitoring system based on optical fiber monitoring, characterized in that: include: Hydraulic fracturing simulation platform, used to apply triaxial stress to hydraulic fracturing specimens to simulate the formation stress environment; A fracturing fluid injection device, used to inject pre-configured fracturing fluid into the test piece to expand the cracks in the test piece; A plurality of strain sensor groups, including at least a first FBG strain sensor group whose axial direction is parallel to the crack extension direction of the specimen and a second FBG strain sensor group whose axial direction is perpendicular to the crack extension direction; the plurality of strain sensor groups are embedded in the specimen during the preparation of the specimen; An optical fiber sensing demodulation device, used for collecting strain data detected by the plurality of strain sensor groups; A data processing device is connected to the optical fiber sensing demodulation device for acquiring the strain data and processing the strain data to determine the real-time state data of the crack extension in the specimen.

2. The hydraulic fracture monitoring system based on optical fiber monitoring according to claim 1, characterized in that: The plurality of strain sensor groups further include: A third FBG strain sensor group has an axial direction inclined to the crack propagation direction.

3. The hydraulic fracture monitoring system based on optical fiber monitoring according to claim 1, characterized in that: Also includes: Distributed optical fiber temperature sensors are distributed inside the test piece and are used to monitor the temperature field changes during the crack expansion process; and / or, The acoustic emission monitoring device is arranged around the test piece and is used to monitor the acoustic emission signal during the crack expansion process.

4. The hydraulic fracture monitoring system based on optical fiber monitoring according to claim 1, characterized in that: The data processing device is specifically used for: The crack length of the crack extension is calculated based on the first strain data detected by the first FBG strain sensor group; the crack height of the crack extension is calculated based on the second strain data detected by the second FBG strain sensor group; and the crack extension speed is calculated according to the crack lengths at multiple moments.

5. A method for monitoring hydraulic fractures based on optical fiber monitoring, characterized in that: The method is based on the hydraulic fracture monitoring system based on optical fiber monitoring according to any one of claims 1 to 4, and the method comprises: Control the hydraulic fracturing simulation platform to apply triaxial stress to the hydraulic fracturing specimen to simulate the formation stress environment; Controlling a fracturing fluid injection device to inject fracturing fluid into the hydraulic fracturing specimen, so that cracks in the specimen expand; Acquire strain data detected by a plurality of strain sensor groups; the strain data at least includes first strain data detected by a first FBG strain sensor group and second strain data detected by a second FBG strain sensor group; Calculate the crack length based on the first strain data; calculate the crack height based on the second strain data; The crack extension rate is calculated based on the crack lengths at multiple times.

6. The method for monitoring hydraulic fractures using optical fiber monitoring according to claim 5, characterized in that: Also includes: Acquiring third strain data detected by a third FBG strain sensor group; A crack propagation path is generated based on the first strain data, the second strain data and / or the third strain data.

7. The method for monitoring hydraulic fractures by optical fiber monitoring according to claim 5, characterized in that: Also includes: Acquiring stress data applied by the hydraulic fracturing simulation platform and injection rate of the fracturing fluid injection device; Based on the first strain data, the second strain data, the stress data and the injection rate, influences of the injection rate and the stress data on crack extension are analyzed.

8. The method for monitoring hydraulic fractures using optical fiber monitoring according to claim 5, characterized in that: Also includes: Monitor whether the crack expansion has any abnormal situation; the abnormal situation includes at least one of the following: the expansion speed changes beyond a preset range, the expansion direction changes suddenly, or the temperature changes beyond a preset range; When abnormal conditions occur in crack expansion, an abnormal signal is generated; Based on the abnormal signal, the hydraulic fracturing simulation platform is controlled to adjust the three-dimensional stress or the fracturing fluid injection device is controlled to adjust the injection rate.

9. A hydraulic fracture monitoring device based on optical fiber monitoring, characterized in that: The device is based on the hydraulic fracture monitoring system based on optical fiber monitoring according to any one of claims 1 to 4, and the device comprises: The first control module is used to control the hydraulic fracturing simulation platform to apply three-dimensional stress to the hydraulic fracturing specimen to simulate the formation stress environment; A second control module is used to control the fracturing fluid injection device to inject fracturing fluid into the hydraulic fracturing specimen, so that the cracks in the specimen expand; An acquisition module, used for acquiring strain data detected by a plurality of strain sensor groups; the strain data at least includes first strain data detected by a first FBG strain sensor group and second strain data detected by a second FBG strain sensor group; A first calculation module, configured to calculate a crack length based on the first strain data; and a crack height based on the second strain data; The second calculation module is used to calculate the crack expansion speed according to the crack lengths at multiple moments.

10. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the instructions are executed by a processor, the steps of the method according to any one of claims 5 to 8 are implemented.

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