Method for visualizing hydraulic fracture propagation in dual-lateral hydraulic fracturing based on helical fiber monitoring

Abstract

This invention discloses a visualization method for fracture propagation in dual-well hydraulic fracturing based on helical optical fiber monitoring. First, an equidistant helical support is fabricated using 3D printing. The optical fiber is then attached to the support. Next, an artificial sample is cast using cement. Then, water injection fracturing is performed, and the strain of the optical fiber changes with time and fiber length is recorded. Using Matlab, the strain values ​​at different fiber lengths over time are mapped onto the helical optical fiber. Finally, strain abrupt change points on the fiber are extracted, and strain abrupt change points with similar times and orientations on the upper and lower helical optical fibers of the same wellbore are connected into lines. These lines are then connected into patches to form the fracture geometry. The patches are then displayed sequentially based on the time of occurrence of the strain abrupt change points, thereby visualizing the fracture propagation process. This invention, through a unique and reasonable optical fiber deployment method and an effective means of visualizing the fracture propagation process, can clearly and intuitively demonstrate the fracture formation process.

Description

Technical Field

[0001] This invention belongs to the field of distributed optical fiber monitoring technology, specifically involving dynamic monitoring and visualization interpretation of fracture propagation in physical simulation of hydraulic fracturing in petroleum engineering. Background Technology

[0002] In many fields such as rock mechanics, petroleum engineering, and building structures, crack propagation has a critical impact on the safety, stability, and durability of structures. For example, in oil extraction, reservoir crack propagation affects oil and gas production and extraction efficiency; crack development in rock structures can trigger geological disasters. Traditional crack monitoring technologies have significant limitations. Strain monitoring methods based on strain gauges and displacement sensors can only monitor single-point strain values, and are complex to install, have low spatial resolution, and are easily affected by environmental factors, leading to large deviations in measurement results. Ultrasonic detection and electromagnetic induction technologies based on acoustic and electromagnetic principles are limited by the characteristics of the medium, the complexity of the structure, and the conductivity of the monitored object, making it difficult to accurately and comprehensively monitor crack propagation. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a visualization method for the propagation of hydraulic fracturing fractures in dual wells based on spiral optical fiber monitoring. This method integrates 3D printing technology and distributed optical fiber monitoring technology, and uses equidistant spiral-shaped optical fibers to monitor the strain of hydraulic fractures throughout the entire process of fracturing model initiation and propagation with high precision. It can capture the strain information of each point inside the rock sample to the maximum extent.

[0004] The objective of this invention is achieved through the following technical solution: a visualization method for fracture propagation in dual-well hydraulic fracturing based on helical optical fiber monitoring, comprising the following steps:

[0005] The first step is to use 3D printing to print multiple spiral fiber optic supports with equal spacing between the spirals. The inner diameter of the spiral fiber optic support is larger than the wellbore diameter, and the outer diameter is smaller than the maximum size of the hydraulic fracturing sample.

[0006] Step 2, Optical Fiber Preparation and Pretreatment: Paste the single-mode bare optical fiber along the inner wall of the spiral optical fiber support; during pasting, leave a 3-5cm length of the free end of the single-mode bare optical fiber located in the center of the spiral optical fiber support and make a loop with a diameter of 0.5-1cm; leave a 300cm length of the free end of the single-mode bare optical fiber located on the outermost side of the spiral optical fiber support for connection with external optical fiber monitoring instruments.

[0007] Step 3, Artificial Sample Preparation and Fiber Optic Laying: Place two supports with attached optical fibers into the mold, with the two optical fibers aligned vertically; pass the artificial well shaft through the center of the two supports, with the bottom of the artificial well shaft close to the bottom of the mold and the top extending out of the mold; lead out the free end of the optical fiber for connection with external fiber optic monitoring instruments, then pour mixed mortar into the mold, let it stand for 24 hours, then demold it, and cure it for 30 days or more according to the relevant specifications for cement sample curing to obtain the sample;

[0008] Step 4: Fiber integrity monitoring and fiber parameter determination: Use a fiber optic fusion splicer to fusion the free end of the fiber to a fiber optic patch cord, and connect the fiber optic monitoring instrument through the fiber optic patch cord; create strain disturbance at the fiber optic access point on the sample surface, and confirm the effective monitoring length and monitoring position of the fiber optic through the fiber optic monitoring instrument.

[0009] Then, input the fiber optic monitoring parameters into the fiber optic monitoring instrument, and continue the experiment once everything is ready.

[0010] Step 5: Conduct hydraulic fracturing test: Hoist the sample into the confining pressure loading chamber of the true triaxial hydraulic fracturing system, connect the artificial wellbore on the sample to the injection line of the fracturing machine with a high-pressure connector, and debug the true triaxial hydraulic fracturing equipment and fiber optic monitoring instruments used for injection.

[0011] Triaxial stress is applied to the rock sample: fracturing fluid is injected into the artificial wellbore to form triaxial stress on the rock sample; at the same time as the fracturing fluid injection begins, the fiber optic monitoring instrument is started to record the strain response on the entire fiber optic cable, and the strain data at different times and distances on the spiral fiber optic cable are obtained; the strain data is a two-dimensional matrix, where each column corresponds to the strain data of all monitoring positions on the entire fiber optic cable within the monitoring range of a time point, and each row corresponds to the fiber optic strain value at a certain monitoring position at different time points;

[0012] Step 6: Constructing a spiral in Matlab: Based on the given arc length range θ min to θ max The arc length of the spiral fiber at each monitoring location is calculated using the integral function arcLengthIntegral, and the arc length is mapped to θ. min to θ max Within the range, the value of angle θ corresponding to each monitoring position is obtained;

[0013] After obtaining the angle θ at each monitoring position, the coordinates x and y of the spiral in the Cartesian coordinate system are calculated according to the basic formula for the conversion between polar coordinates and rectangular coordinates. At the same time, the z values ​​of the two spirals are set to construct the spiral in three-dimensional space.

[0014] Step 7: Data Import and Processing: Use MATLAB's load function to load the fiber strain data into the workspace, and begin to organize and expand the data to obtain the maximum strain value and the maximum value location index maxwz for each interval at each time.

[0015] Step 8: Constructing cracks based on strain abrupt change points: In the time series loop, when the maximum strain on the spiral fiber is detected to be significantly increased compared to the maximum strain in the previous time step, crack construction begins.

[0016] Step 9: Extract all monitoring locations, then connect the fracture points of the spiral optical fibers around the same wellbore to form line segments, then connect the line segments to form a surface. After all the line segments are connected, a fracture patch is formed. All the fracture patches together form a fracture surface. Then, display the fracture patches in chronological order to form the above-mentioned visualization of the dynamic expansion of hydraulic fracturing fractures.

[0017] The beneficial effects of this invention are as follows: The main objective of this invention is to overcome the difficulty in accurately visualizing the crack formation process and the strain distribution of rock samples during crack propagation research. The advantages of this invention are specifically reflected in the following aspects:

[0018] (1) By integrating 3D printing technology and distributed optical fiber monitoring technology, and using equidistant spiral-shaped optical fibers, the strain of hydraulic fractures during the entire process of initiation and propagation in the hydraulic model is monitored with high precision. This can capture the strain information of each point inside the rock sample to the maximum extent, providing a new characterization idea for in-depth analysis of the geometry and dynamic evolution of hydraulic fractures.

[0019] (2) Develop a crack propagation morphology inversion program based on fiber strain data. Based on the parameters of the spiral support (inner diameter, outer diameter and pitch, etc.) and the length position and strain intensity of the fiber strain abrupt change, characterize the three-dimensional crack geometry and evolution characteristics of the fracturing model, accurately interpret the characteristics of hydraulic fracturing initiation and propagation, and realize high-precision visualization characterization of three-dimensional spatial cracks in the fracturing model sample. Attached Figure Description

[0020] Figure 1 This is a flowchart of the present invention: a visualization method for fracture propagation in dual-well hydraulic fracturing based on spiral optical fiber monitoring.

[0021] Figure 2 This is a schematic diagram of the fiber optic support structure of the present invention;

[0022] Figure 3 This is a schematic diagram of the spiral fiber optic support layout according to the present invention;

[0023] Figure 4 This is a schematic diagram of the mold after the fiber optic bracket has been inserted;

[0024] Figure 5 A waterfall plot of strain response for monitoring with a spiral optical fiber;

[0025] Figure 6 The response curve of a spiral optical fiber;

[0026] Figure 7 A mapping diagram of strain response values ​​monitored by a spiral optical fiber;

[0027] Figure 8 For fracturing fracture morphology inversion based on strain response of helical optical fiber;

[0028] Figure 9 A visualization of the fractures in a dual-well hydraulic fracturing system. Detailed Implementation

[0029] This invention aims to overcome the shortcomings of existing strain monitoring methods by utilizing distributed fiber optic sensing technology to monitor strain in fracturing model specimens, thereby indirectly reflecting crack propagation dynamics. This results in a novel crack monitoring scheme for fracturing models based on fiber optic strain monitoring. The innovative deployment method, combined with the helical spatial position calculation equation, ensures that the fiber optic strain data accurately reflects the crack location and propagation dynamics, improving the accuracy of crack characterization in fracturing models. This invention enables precise monitoring and clear, intuitive visualization of the crack propagation process, providing a more accurate, convenient, and efficient technical means for research and engineering applications related to crack propagation in hydraulic fracturing in petroleum engineering. It possesses significant innovation, practicality, and application value.

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0031] like Figure 1 As shown, the present invention provides a method for visualizing fracture propagation in dual-well hydraulic fracturing based on helical optical fiber monitoring, comprising the following steps:

[0032] The first step is to use 3D printing to print multiple equally spaced spiral fiber optic brackets, such as... Figure 2 As shown; set the inner diameter d of the support according to the size of the rock sample (e.g., Figure 2 As shown in Figure 1), outer diameter D (as shown in Figure 1) Figure 2 (as shown in Figure 2) and pitch P (as shown in Figure 2) Figure 2 As shown in Figure 3), the inner diameter of the spiral fiber optic support should be larger than the wellbore diameter, and the outer diameter should be slightly smaller than the maximum size of the hydraulic fracturing specimen (the side length of the cubic specimen and the outer diameter of the cylindrical specimen; in this embodiment, a cubic specimen is used as an example). The fiber optic support is fabricated as an equidistant helix with n turns and a pitch of P, with a hollow region of diameter d at its center.

[0033] Step 2: Fiber Preparation and Pre-treatment: Attach the single-mode bare fiber along the inner wall of the spiral fiber optic bracket (the side of the bracket closest to the well shaft) using 502 super glue. During attachment, leave a 3-5cm free end of the single-mode bare fiber located at the center of the spiral fiber optic bracket and make a loop with a diameter of 0.5-1cm. This allows the light signal to be reflected back after reaching the fiber end, enabling the fiber optic monitoring instrument to detect a stronger signal and improving monitoring accuracy. Leave a 300cm free end of the single-mode bare fiber located on the outermost side of the spiral fiber optic bracket for connection to external fiber optic monitoring instruments. Figure 3 As shown; prepare two or more fiber optic brackets using this method;

[0034] Step 3: Artificial Sample Preparation and Fiber Optic Laying: Using a sample casting mold, a sample of a certain size (e.g., ...) is prepared.

[0035] (400mm×400mm×400mm). Place two supports with attached optical fibers into the mold, with the two fibers vertically aligned. The position and distance between the two supports can be determined based on the sample size and well length; generally, they are placed symmetrically, for example, at 1 / 4 and 3 / 4 of the mold height (the position is not strictly defined, as long as crack propagation can be monitored). Figure 4 As shown, 4, 5, and 6 represent the first layer of supports with attached optical fibers, the second layer of supports with attached optical fibers, and the artificial rock sample from the fracturing model, respectively. The artificial wellbore is inserted through the center of the two supports, with its bottom close to the bottom of the mold and its top extending beyond the mold (the total length of the wellbore is less than the side length of the rock core; if the mold side length is 400mm, the wellbore should be about 10cm from the bottom of the mold after being placed inside; this distance can be adjusted according to actual needs, ensuring that the bottom of the wellbore is inside the sample after pouring). Two artificial wellbores and optical fiber supports with attached optical fibers are prepared using the above method. The free end of the optical fiber is used for connection to an external optical fiber monitoring instrument. Then, mixed mortar is poured into the mold, taking care not to damage the optical fiber during pouring. After standing for 24 hours, the sample is demolded and cured for 30 days or more according to the relevant specifications for cement sample curing to obtain the final sample.

[0036] Step 4: Fiber Integrity Monitoring and Fiber Parameter Determination: After sample maintenance, the free end of the fiber optic cable is fused to a fiber optic patch cord using a fiber optic fusion splicer. The patch cord is then connected to a fiber optic monitoring instrument. Strain disturbances are created at the fiber optic insertion point on the sample surface, and the effective monitoring length and monitoring position of the fiber optic cable are confirmed using the fiber optic monitoring instrument. The fiber optic monitoring instrument monitors the signal along the entire fiber length. However, outside the sample, another section of fiber is connected to the monitoring instrument. Therefore, after arranging the fiber optic cable, before conducting the test, it is necessary to confirm the exact starting point of the fiber optic cable to determine the true embedded fiber length for more accurate monitoring results. The number of fiber optic patch cords required is the same as the number of spiral fiber optic supports; that is, each fiber on a spiral fiber optic support is a separate fiber optic channel.

[0037] Then, input the fiber optic monitoring parameters into the fiber optic monitoring instrument, including: selecting the fiber optic channel, fiber length, scanning range, sampling interval, starting distance, cutting-off distance, refractive index, spatial resolution, initial strain, strain coefficient, initial temperature, temperature coefficient, starting point of each channel, sensing resolution, sampling resolution, and scanning mode (single / continuous scan); after preparation, continue the experiment.

[0038] Step 5: Conduct hydraulic fracturing test: Hoist the sample into the confining pressure loading chamber of the true triaxial hydraulic fracturing system, connect the artificial wellbore on the sample to the fracturing machine injection line using a high-pressure connector, and debug the true triaxial hydraulic fracturing equipment and fiber optic monitoring instrument used for injection; apply triaxial stress to the rock sample: inject fracturing fluid into the artificial wellbore at a certain flow rate to form triaxial stress on the rock sample; at the same time as the fracturing fluid injection begins, start the fiber optic monitoring instrument to record the strain response along the entire fiber optic cable; during the test, the true triaxial hydraulic fracturing equipment collects the triaxial stress value, injection pressure, and total injected fluid volume of the sample in real time; when a sharp drop in injection pressure is observed, stop the injection and stop the signal acquisition of the true triaxial hydraulic fracturing equipment and fiber optic monitoring instrument.

[0039] Fiber optic monitoring instruments acquire strain data at different times and distances along a spiral optical fiber, storing it in MAT format. The strain data is a two-dimensional matrix, where each column corresponds to the strain data at all monitoring locations along the entire fiber within the monitoring range at a given time point, and each row corresponds to the fiber strain value at a specific monitoring location at different time points. Plotted on a coordinate system, this forms a spiral optical fiber monitoring strain response waterfall plot with time on the horizontal axis and distance on the vertical axis, as shown below. Figure 5 As shown, Figure 5 (a) and (b) are the strain response waterfall plots of the two optical fibers, respectively. Figure 5 (a) The corresponding response curve is as follows Figure 6 As shown.

[0040] Step 6: Constructing the helical fiber in Matlab: First, determine the key parameters of the helical fiber, including the pitch P, the number of turns n, and the maximum radius D. These parameters are known parameters determined in Step 1 (the same as the parameters of the helical fiber support with equidistant helical spacing); then define the arc length calculation function arcLengthFunc as follows:

[0041]

[0042] Where r(θ) is the helix radius corresponding to the rotation angle θ, and r′(θ) is the derivative of r(θ); α represents the starting angle for helix calculation, and β represents the ending angle for helix calculation.

[0043] Based on the given arc length range θ min to θ max The number of monitoring points is n, where n is the number of monitoring locations; the arc length of the spiral fiber at each monitoring location is calculated using the integral function arcLengthIntegral, and the arc length is mapped to θ. min to θ max Within the range, the value of angle θ corresponding to each monitoring position is obtained; the integral function arcLengthIntegral calculates the value from θ through numerical integration. min The arc length of the helix to a certain angle θ, at θ min to θ max Find the angle θ value within the range that corresponds to the arc length values ​​divided at equal intervals;

[0044] During the calculation, a sequence of arc length ratios from 0 to 1, arcLengths, is first created. Then, the arcLengthIntegral function is used to calculate the arc length of the spiral fiber at each monitoring location, and the arc length is normalized. Finally, the fminbnd function is used at a set θ. min to θ max Within the interval, find the θ value that minimizes the absolute value of the difference between the normalized arc length and the element in the arc length ratio sequence for each monitoring location, and use it as the angle θ for that monitoring location, thus realizing the transformation from arc length calculation to angle solution;

[0045] After obtaining the angle θ at each monitoring position, the coordinates x and y of the spiral in the Cartesian coordinate system are calculated according to the basic formula (2) for the conversion between polar coordinates and rectangular coordinates. At the same time, the z values ​​of the two spirals are set to construct the spiral in three-dimensional space:

[0046]

[0047] Step 7: Data Import and Processing: Use MATLAB's load function to load the fiber strain data into the workspace, and begin to organize and expand the data to obtain the maximum strain value and the maximum value location index maxwz for each interval at each time.

[0048] First, a new time series with equal intervals is generated. Then, the time series of the original fiber strain data is matched with the new time series. For missing data (time points that exist in the new time series but not in the original time series), the corresponding data rows in the new time series are filled with zeros. For time points that exist in both the original and new time series, the corresponding data values ​​from the original time series are copied to the new time series. The time intervals of the originally acquired data are not strictly equal, so data gaps may occur in the new time series. Common methods for filling missing data include directly filling with 0 and filling with the average of adjacent data. In this embodiment, filling with 0 is chosen.

[0049] Extract the strain values ​​sensed by the optical fiber at different locations and time points, and map these strain values ​​onto equidistant helices, such as... Figure 7 As shown, the original data contains strain values ​​at different monitoring locations at different time points. The location of the monitoring location corresponds to the location of the spiral length. It is only necessary to map the strain value to the corresponding length based on the location of the monitoring location. Then, iterate through each time period to obtain the strain value of each monitoring location on the equidistant spiral at different time points.

[0050] The entire optical fiber is divided into intervals based on the angle of the helix. Starting from the free end at the center of the helix, each 180° rotation of the helix constitutes an interval (idxCell), and the entire fiber contains nIntervals intervals. The fiber strain data is also correspondingly divided into nIntervals sub-matrices for subsequent analysis of strain characteristics in different regions. The entire angle range [θ] is... min θ max The array is also divided into nIntervals intervals. The find function is used to find the index of each interval and store it in the idxCell cell array idxCell{i}.

[0051] Call the processStressData function, which takes strain data strainValues ​​and angle interval index idxCell as input, finds the maximum value of strain data in each angle interval and returns the maximum value and its corresponding index.

[0052] The strain is processed using the function processStressData in conjunction with the predefined intervals idxCell. In the function processStressData, the strain value data matrix strainValues ​​for each interval is first obtained. Then, an output matrix modifiedData is initialized, which has the same size as the strain value data matrix for that interval and all elements in the matrix are 0. At the same time, two cell arrays maxIdx and maxwz are initialized to store the maximum strain value and the corresponding index for each interval, respectively.

[0053] Next, data processing is performed through two nested loops. The outer loop iterates through each interval index. For each interval, the corresponding index idxCell{i} is obtained first, and the array maxIdx{i} used to store the position of the maximum value of the interval at each time step and the array maxwz{i} used to store the index corresponding to the maximum value are initialized.

[0054] The inner loop, for each time step, extracts the data `currentData` for that interval from the data of the current time step. `currentData` is a vector containing the strain values ​​corresponding to all monitoring positions within that interval. The maximum strain value within that interval at the current time step is found using the `max` function and stored in `maxIdx{i}(t)`. The monitoring position corresponding to the maximum strain value is used as an index and stored in `maxwz{i}(t)`. Then, only the value of the monitoring position with the largest strain value is retained, and the strain values ​​of all other monitoring positions in that interval at the current time step are set to 0, thus completing the processing of the data for each interval. Then, the data for the next time step is processed until all time steps have been traversed.

[0055] The final processed data modifiedData is obtained, in which only the maximum strain value is retained for each interval at each time step, and the rest are 0, as well as the maximum value location index maxwz for each interval at each time step. After processing by the processStressData function, the processed data and the maximum value point index for each interval are obtained, providing key data support for subsequent operations based on monitoring location to connect cracks.

[0056] Step 8: Constructing Cracks Based on Strain Abrupt Points: In the time series loop, when a significant increase in the maximum strain on the helical fiber is detected at a certain time step compared to the maximum strain at the previous time step (the specific definition of this significant increase can be set according to the material used), crack construction begins; traverse the maximum value point index, obtain the corresponding coordinate point on the helix from the helical coordinate array using the index value, including the x, y, and z coordinates and the corresponding strain value, store the time, coordinate point, and strain value of the strain abrupt point in a new array, and map the strain value to the corresponding spatial position on the helix, with its color attribute corresponding to the magnitude of the strain value, and use the scatter3 function to mark an abrupt point; determine the orientation and occurrence time of the strain abrupt point on the helical fiber, if the orientation difference and time difference between two points are less than a preset threshold, connect the two strain abrupt points into a line segment, such as... Figure 8 As shown; then connect adjacent line segments to form a four-sided patch, and connect multiple patches in sequence according to the time sequence of the occurrence of strain abrupt change points, thereby forming a continuous curved surface and visually displaying the shape of the crack; the smaller the pitch of the spiral support, the narrower the connected patch, and the more refined the crack will be.

[0057] Step 9: Based on the single helical fiber monitoring and fracture inversion characterization method, extract the monitoring locations on all supports. Then, connect the fracture break points (i.e., points with large strain) of the helical fibers around the same wellbore to form line segments. Connect these line segments to form surfaces. After connecting all line segments, a fracture patch is formed. All fracture patches constitute the fracture surface. Then, display the fracture patches sequentially according to time sequence to form the above-mentioned visualization of the dynamic propagation of hydraulic fracturing fractures. Figure 9 As shown, Figure 9 This is a visualization of the hydraulic fracturing fractures in the dual-well configuration in this embodiment.

[0058] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A visualization method for fracture propagation in dual-well hydraulic fracturing based on spiral optical fiber monitoring, characterized in that, Includes the following steps: The first step is to use 3D printing to print multiple spiral fiber optic supports with equal spacing between the spirals. The inner diameter of the spiral fiber optic support is larger than the wellbore diameter, and the outer diameter is smaller than the maximum size of the hydraulic fracturing sample. Step 2, Optical Fiber Preparation and Pretreatment: Paste the single-mode bare optical fiber along the inner wall of the spiral optical fiber support; during pasting, leave a 3-5cm length of the free end of the single-mode bare optical fiber located in the center of the spiral optical fiber support and make a loop with a diameter of 0.5-1cm; leave a 300cm length of the free end of the single-mode bare optical fiber located on the outermost side of the spiral optical fiber support for connection with external optical fiber monitoring instruments. Step 3, Artificial Sample Preparation and Fiber Optic Laying: Place two supports with attached optical fibers into the mold, with the two optical fibers aligned vertically; pass the artificial well shaft through the center of the two supports, with the bottom of the artificial well shaft close to the bottom of the mold and the top extending out of the mold; lead out the free end of the optical fiber for connection with external fiber optic monitoring instruments, then pour mixed mortar into the mold, let it stand for 24 hours, then demold it, and cure it for 30 days or more according to the relevant specifications for cement sample curing to obtain the sample; Step 4: Fiber integrity monitoring and fiber parameter determination: Use fiber optic fusion splicing equipment to fusion splice the free end of the fiber to the fiber optic patch cord, and connect the fiber optic monitoring instrument through the fiber optic patch cord; Strain disturbances were created at the location where the optical fiber was inserted on the sample surface, and the effective monitoring length and monitoring location of the optical fiber were confirmed by an optical fiber monitoring instrument. Then, input the fiber optic monitoring parameters into the fiber optic monitoring instrument, and continue the experiment once everything is ready. Step 5: Conduct hydraulic fracturing test: Hoist the sample into the confining pressure loading chamber of the true triaxial hydraulic fracturing system, connect the artificial wellbore on the sample to the injection line of the fracturing machine with a high-pressure connector, and debug the true triaxial hydraulic fracturing equipment and fiber optic monitoring instruments used for injection. Applying triaxial stress to rock samples: Injecting fracturing fluid into artificial wellbores creates triaxial stress on the rock samples; Simultaneously with the injection of fracturing fluid, the fiber optic monitoring instrument is activated to record the strain response along the entire fiber optic cable, obtaining strain data at different times and distances along the spiral fiber optic cable. The strain data is a two-dimensional matrix, where each column corresponds to the strain data of all monitoring positions along the entire fiber optic cable within the monitoring range at a given time point, and each row corresponds to the fiber optic strain value at a certain monitoring position at different time points. Step 6: Constructing a spiral in MATLAB: Based on a given range of arc lengths arrive The arc length of the spiral fiber at each monitoring location is calculated using the integral function arcLengthIntegral, and the arc length is mapped to... arrive Within the range, the angle corresponding to each monitoring location is obtained. The value; The angle at each monitoring location was obtained. Then, the coordinates x and y of the spiral in the Cartesian coordinate system are calculated according to the basic formula for the conversion between polar coordinates and rectangular coordinates. At the same time, the z values ​​of the two spirals are set to construct the spiral in three-dimensional space. Step 7: Data Import and Processing: Use MATLAB's load function to load the fiber strain data into the workspace, and begin to organize and expand the data to obtain the maximum strain value and the maximum value location index maxwz for each interval at each time. Extract the strain values ​​perceived by the optical fiber at different locations and time points, and map the strain values ​​onto equidistant helices; The entire optical fiber is divided into intervals based on the angle of the spiral. The entire optical fiber contains nIntervals intervals. The entire angle range [ , Divide the data into nIntervals intervals and use the find function to find the index of each interval; The data is processed using the function processStressData in conjunction with the predefined intervals. The data is processed using two nested loops: the outer loop iterates through each interval index; the inner loop, for each time step, uses the max function to find the maximum strain value within the interval at the current time step, and uses the monitoring position corresponding to the maximum strain value as the index corresponding to the maximum strain value. Step 8: Constructing cracks based on strain abrupt change points: In the time series loop, when the maximum strain on the spiral fiber is detected to be significantly increased compared to the maximum strain in the previous time step, crack construction begins. Step 9: Extract all monitoring locations, then connect the fracture points of the spiral optical fibers around the same wellbore to form line segments, then connect the line segments to form surfaces. After all the line segments are connected, a fracture patch is formed. All fracture patches together form a fracture surface. Then, display the fracture patches in chronological order to form the above-mentioned visualization of the dynamic expansion of hydraulic fracturing fractures.

2. The method for visualizing fracture propagation in dual-well hydraulic fracturing based on helical optical fiber monitoring according to claim 1, characterized in that, The specific implementation method of the seventh step is as follows: First, generate a new time series with equal spacing, and then match the time series of the original fiber strain data with the new time series; for missing data, that is, time points that exist in the new time series but do not appear in the original time series, fill the corresponding data rows in the new time series with zeros; for time points that exist in both the original time series and the new time series, copy the corresponding data values ​​in the original time series to the new time series. Extract the strain values ​​perceived by the optical fiber at different locations and time points, and map the strain values ​​onto equidistant helices; The entire optical fiber is divided into intervals based on the angle of the helix. Starting from the free end at the center of the helix, each 180° rotation of the helix constitutes an interval idxCell. The entire optical fiber contains nIntervals intervals. The fiber strain data is correspondingly divided into nIntervals sub-matrices. The entire angle range [ , Divide the array into nIntervals intervals, use the find function to find the index of each interval, and store it in the idxCell cell array idxCell{i}; The strain is processed using the function processStressData in conjunction with the predefined intervals idxCell. In the function processStressData, the strain value data matrix for each interval is first obtained. Then, an output matrix modifiedData is initialized, which has the same size as the strain value data matrix for that interval and all elements in the matrix are 0. At the same time, two cell arrays maxIdx and maxwz are initialized to store the maximum strain value and the corresponding index for each interval, respectively. Next, data processing is performed through two nested loops. The outer loop iterates through each interval index. For each interval, the corresponding index idxCell{i} is obtained first, and the array maxIdx{i} used to store the position of the maximum value of the interval at each time step and the array maxwz{i} used to store the index corresponding to the maximum value are initialized. The inner loop extracts the data `currentData` for each time step from the data of the current time step. `currentData` is a vector containing the strain values ​​corresponding to all monitoring positions within the interval. The maximum strain value within the interval at the current time step is found using the `max` function and stored in `maxIdx{i}(t)`. The monitoring position corresponding to the maximum strain value is used as an index and stored in `maxwz{i}(t)`. Then, only the value of the monitoring position with the largest strain value is retained, and the strain values ​​of other monitoring positions in the interval at the current time step are set to 0, thus completing the processing of the data for each interval. Then, the data of the next time step is processed until all time steps have been traversed.

3. The method for visualizing fracture propagation in dual-well hydraulic fracturing based on helical optical fiber monitoring according to claim 1, characterized in that, The specific implementation method of the eighth step is as follows: traverse the index of the maximum value point, obtain the coordinate point on the corresponding spiral from the spiral coordinate array through the index value, including the x, y, z coordinates and the corresponding strain value, store the time, coordinate point and strain value of the strain mutation point in a new array, and map the strain value to the corresponding spatial position of the spiral line. Its color attribute corresponds to the magnitude of the strain value, and use the scatter3 function to mark a mutation point; determine the orientation and occurrence time of the strain mutation point on the spiral fiber. If the orientation difference and time difference of the two points are less than the preset threshold, connect the two strain mutation points into a line segment; then connect the adjacent line segments into a tetrahedral patch, and connect multiple patches in sequence according to the time order of the strain mutation points, thereby forming a continuous curved surface and intuitively displaying the shape of the crack.

Images