Dry hot rock reservoir horizontal well fracturing fiber breakage early warning method based on DAS monitoring

Abstract

The invention discloses a dry hot rock reservoir horizontal well fracturing fiber breakage early warning method based on DAS monitoring, which comprises the following steps: firstly, collecting a vibration signal in a shaft through a DAS (Distributed Acoustic Wave Sensing) system, and carrying out wavelet threshold denoising, data segmentation and normalization processing to obtain preprocessed signal data; secondly, performing time-frequency analysis on the signal by adopting a short-time Fourier transform analysis method so as to identify energy distribution of different frequency bands and visualize a high-energy region, thereby identifying an abnormal broadband; then, phase wrapping detection is carried out, whether the signals exceed a dynamic range or not is verified, and the strain rate and histogram features of the phase signals are calculated; and finally, the standard deviation of the strain rate is evaluated through normal distribution modeling and maximum likelihood estimation, and once the standard deviation exceeds a set threshold value, fiber breakage risk early warning information is sent out. According to the method, the signal processing technology and the statistical analysis technology are effectively integrated, the safety of fracturing operation is improved, and meanwhile reliable technical support is provided for efficient development of the hot dry rock reservoir.

Description

Technical Field

[0001] The present invention belongs to the field of distributed fiber optic sensing (DFOS) for hydraulic fracturing of horizontal wells in enhanced geothermal system (EGS) hot dry rock reservoirs, and particularly relates to a method for warning of fiber breakage in horizontal well fracturing of hot dry rock reservoirs based on DAS monitoring. Background Art

[0002] In the construction of hydraulic fracturing of horizontal wells in EGS hot dry rock reservoirs, permanent optical fibers are often laid outside the casing in the wellbore for real-time monitoring. DAS is an important distributed fiber optic sensing method, which can obtain the vibration information of the whole well section under the condition of high sampling rate, so as to help the operator evaluate the effect of hydraulic fracturing, such as evaluating the geometric distribution and connectivity of the hydraulic fractures between the injection well and the production well. However, during the hydraulic fracturing operation, if the optical fiber is exposed within the perforation hole range, the high-speed injected fracturing fluid and / or proppant will directly erode the optical fiber, and the optical fiber is very likely to break under the action of erosive high-energy vibration; in addition, if the cementing quality is poor, the high-speed injection body of hydraulic fracturing may cause the cracking of the cement sheath, resulting in the breakage of the optical fiber cemented with the cement sheath. The breakage of the optical fiber will not only cause huge economic losses, but also lose the ability of subsequent production monitoring. Therefore, aiming at the fracture risk of the optical fiber outside the wellbore casing, how to identify and warn of the fiber breakage risk during the hydraulic fracturing operation based on the real-time DAS data has important application value. Summary of the Invention

[0003] In order to solve the problem that the strong vibration in the well during the hydraulic fracturing process may cause the optical fiber to break in the background art, the present invention aims to provide a method for warning of fiber breakage in horizontal well fracturing of hot dry rock reservoirs based on DAS monitoring, which is used to identify the precursors of optical fiber breakage and issue warnings in time during the hydraulic fracturing process. Specifically, three features, namely broadband signal, phase wrapping and continuously high amplitude (strain rate), are proposed as the precursor phenomena of fiber breakage, which can be used to help the operator capture the corresponding warning signals in time before the optical fiber breaks, so as to reasonably control the pumping parameters and adjust the fracturing construction plan, and reduce the risk of optical fiber breakage.

[0004] In order to solve the technical problems, the technical solution of the present invention is as follows:

[0005] A method for warning of fiber breakage in horizontal well fracturing of hot dry rock reservoirs based on DAS monitoring, the method comprising:

[0006] S1: Obtain the original vibration signal collected by the DAS demodulator, perform wavelet threshold denoising, data segmentation and normalization processing to obtain the preprocessed DAS signal data;

[0007] S2: For the preprocessed DAS signal data, use the short-time Fourier transform (STFT) to separate the energy distributions of different frequency bands. Use the output time-frequency spectrogram to visually judge the high-energy area, identify abnormal wide-frequency bands, and obtain the spectrum analysis result.

[0008] S3: For the preprocessed DAS signal data, first perform phase wrapping detection to determine the dynamic range of the DAS system. Detect whether phase wrapping occurs in the signals beyond the dynamic range, calculate the phase signal histogram, and observe whether abnormal peaks appear near the dynamic range. Then perform vibration amplitude calculation, calculate the fiber strain and strain rate respectively, and judge whether wrapping occurs through histogram analysis to obtain the phase wrapping detection result and strain rate data.

[0009] S4: Input the phase wrapping detection result and the calculated strain rate data obtained in step S3, perform normal distribution modeling, maximum likelihood estimation, and high-amplitude detection, and output the amplitude detection result and the estimated standard deviation of the strain rate.

[0010] S5: Based on the spectrum analysis result, phase wrapping detection result, and amplitude detection result, perform fiber breakage precursor identification and early warning information generation.

[0011] Further, step S1 includes:

[0012] Connect the permanent optical fiber arranged outside the wellbore casing to the DAS demodulator, continuously record the vibration signals at each position along the wellbore at a high time sampling rate, and obtain the original vibration signals along the entire length of the wellbore through the DAS demodulator; remove the environmental noise and demodulator noise interference through wavelet threshold denoising; then perform data segmentation, segment with a 2-second time window and spatial channels to form a three-dimensional data structure, i.e., time × depth × amplitude, and finally perform normalization to unify the data scales of different time windows and channels, and output the preprocessed DAS signal data.

[0013] Further, step S3 includes:

[0014] S301: Dynamic range and phase wrapping

[0015] The DAS system has an upper limit of the dynamic range. The phase signal of the optical fiber demodulator is usually limited between [-π, +π]. When the vibration energy exceeds this range, the measured phase signal will exhibit phase wrapping, and high-frequency spikes or discontinuous jumps will appear in the histogram or data distribution.

[0016] S302: Vibration amplitude

[0017] By comparing the vibration amplitudes and their distribution shapes at different positions in the well section, the high-energy abnormal interval can be quickly located.

[0018] To quantitatively analyze the vibration amplitude, assume that the phase signal after demodulation is denoted as If the fiber optic measurement gauge length is set to L, the strain can be obtained through the following approximate linear relationship:

[0019]

[0020] In DAS measurement, for the phase method DAS system, the measured phase φ(t) can be approximately regarded as a linear relationship with the strain rate Approximately regarded as a linear relationship:

[0021]

[0022] Among them, φ(t) is the phase value measured by the fiber optic sensor demodulator (unit: radian), defined in the range of [-π, +π]; C is a proportionality constant determined by the fiber material characteristics and the internal modulation coefficient of the demodulator; ε(t) is the strain of the optical fiber; L is the gauge length, with the unit of meter;

[0023] In actual hydraulic fracturing monitoring, the average strain rate within each time window Δt is defined as Then there is

[0024]

[0025] Among them, k is a normalization coefficient, which includes the aforementioned C and L, is the average strain rate of each time window;

[0026] S303: Phase wrapping and its histogram characteristics when exceeding the dynamic range

[0027] When the true φ(t) exceeds the range of [-π, +π], the phase measured by the demodulator will have a jump. At this time, the histogram will show the following characteristics: obvious peaks appear near -π and +π, and the probability distribution in the middle region decreases; this distribution characteristic can be regarded as reaching or exceeding the dynamic range limit of the DAS, and can be regarded as a precursor phenomenon of fiber breakage.

[0028] Furthermore, the step S4 specifically includes:

[0029] Assume the vibration strain rate obeys the normal distribution N(0, σ 2 ) within a certain time window, that is, the average value is 0 and the standard deviation is σ;

[0030] For the phase measurement of the demodulator, if it does not exceed the dynamic range, it can be written as formula (2). If when |φ| ≤ π, the phase measured by the demodulator is still the true value, but if |φ| > π, wrapping will occur and the measurement result will fall back to [-π, +π], resulting in a pile-up at ±π in the histogram;

[0031] By fitting the statistical distribution of the histogram, the estimated value of the optimal σ is obtained, and its inversion process is as follows:

[0032] Let f(φ) represent the probability distribution function PDF of the phase. If the dynamic range saturation is not reached, then:

[0033]

[0034] If there is phase wrapping, the measured phase φ m From φ m = φ mod(2π) mapped into [-π, +π], f(φ m ) can be expressed as the sum of the superposition probabilities for all φ k = φ m + 2πn;

[0035] By the maximum likelihood method, comparing the measured histogram with the theoretical distribution, the optimal σ is finally obtained, and the average strain rate amplitude can be deduced:

[0036]

[0037] Among them, is the standard deviation of the phase; and k·Δt is the proportionality coefficient for converting the phase to the strain rate, thereby establishing a correspondence between the order of magnitude of the micro-strain rate με / s and the safety threshold of the fiber optic amplitude. If maintains above a certain critical value A within a certain period of time, it is determined that there is a high risk of fiber breakage.

[0038] Compared with the prior art, the advantages of the present invention are as follows:

[0039] For horizontal wells with permanently installed optical fibers deployed outside the casing, during the hydraulic fracturing process of EGS hot dry rock reservoir development, the present invention can be used to help operators capture corresponding warning signals in time before the optical fiber breaks, thereby reasonably controlling the pumping parameters and adjusting the fracturing construction plan, greatly reducing the risk of optical fiber breakage and saving the additional cost of taking remedial measures. Brief Description of the Drawings

[0040] Figure 1 The technical roadmap of a method for warning of fiber breakage during fracturing of a horizontal well in a hot dry rock reservoir based on DAS monitoring according to the present invention;

[0041] Figure 2 The schematic diagram of optical fiber deployment according to the present invention;

[0042] Figure 3 The DAS waterfall diagram (the black dotted line indicates the depth of 2661m as the depth of fiber breakage);

[0043] Figure 4, the time-frequency spectrogram of the DAS raw signal at a depth of 2661m;

[0044] Figure 5 , the histogram of the phase numerical distribution of the DAS raw data;

[0045] Figure 6 , the comparative analysis chart of the DAS raw signal amplitude values (strain rate) at the fiber break (depth of 2661m) and the normal fracturing location (depth of 2625m). Specific Embodiments

[0046] The following describes the specific embodiments of the present invention in conjunction with the embodiments:

[0047] It should be noted that the structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0048] At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of clear narration, and are not used to limit the scope of implementation of the present invention. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope in which the present invention can be implemented.

[0049] Abbreviation and Definition of Key Terms:

[0050] DAS: Distributed Acoustic Sensing (Distributed Acoustic Sensing)

[0051] DFOS: Distributed Fiber Optic Sensing (Distributed Fiber Optic Sensing)

[0052] STFT: Short-Time Fourier Transform (Short-Time Fourier Transform)

[0053] PDF: Probability Distribution Function (Probability Distribution Function)

[0054] Hydraulic fracturing: An engineering operation of injecting high-pressure liquid into the formation to form fractures

[0055] Fiber break: The phenomenon of fiber optic breakage

[0056] Phase wrapping: The periodic jump phenomenon that occurs when the measured phase exceeds the range

[0057] Strain rate: The amount of strain change per unit time

[0058] Gauge length: The length of the basic spatial unit for fiber optic sensing measurement

[0059] Brillouin frequency shift: The scattering effect of light in a medium

[0060] Rayleigh scattering: The elastic scattering phenomenon of light in a medium

[0061] Dynamic range: The maximum signal range that the DAS system can measure

[0062] Permanently installed fiber optic deployment: Fibers consolidated in a cement casing

[0063] Demodulator: A device used to demodulate fiber optic sensing signals

[0064] Embodiment 1:

[0065] In view of the problem that strong wellbore vibrations during hydraulic fracturing may cause fiber optic breakage, the present invention provides a fiber breakage warning method based on DAS monitoring data, and proposes that three characteristics, namely broadband signals, phase wrapping, and continuously high amplitude (strain rate), are precursors to fiber breakage. This can help operators timely capture corresponding warning signals before the fiber breaks, thereby reasonably controlling the pumping parameters and adjusting the fracturing construction plan, and reducing the risk of fiber breakage.

[0066] Based on the real-time DAS data, the present invention analyzes the spectrum, phase change, and amplitude characteristics of each depth position over time during the hydraulic fracturing process. The technical route of the present invention is as Figure 1 shown:

[0067] The key technical steps of this method are as follows:

[0068] I. DAS signal acquisition and preprocessing

[0069] The permanently installed fiber optic deployed outside the wellbore casing is connected to the DAS demodulator, and the vibration signals at each position along the wellbore are continuously recorded at a high time sampling rate (10 kHz). The fiber optic deployment method is as Figure 2 shown. The vibration information along the entire length of the wellbore is obtained through the DAS system.

[0070] Perform preprocessing operations such as wavelet threshold denoising on the collected original DAS signals to remove the interference of environmental noise and demodulator noise.

[0071] Based on the known fiber optic deployment depth information, obtain the time-depth two-dimensional matrix of the DAS signal.

[0072] The original DAS data is sliced by time slices (every 2 seconds) and spatial channels (varying with fiber depth) to form three-dimensional data (time × depth × amplitude).

[0073] Normalization: Normalize the data of different channels and time windows numerically for subsequent unified processing.

[0074] II. Spectrum Analysis

[0075] For the preprocessed signal, use the short-time Fourier transform (STFT) time-frequency analysis method to separate the energy distributions of different frequency bands.

[0076] Use spectrogram and other methods to visually judge the high-energy region and identify abnormal wide-frequency bands. Under the interference of fiber breakage abnormal signals, the frequency bands corresponding to strong amplitudes on the spectrogram image contain low-frequency, medium-frequency, and high-frequency signals, forming a wide-frequency strong-amplitude feature.

[0077] III. Phase Wrapping Detection

[0078] (1) Dynamic Range and Phase Wrapping

[0079] In DAS measurement, the DAS system has an upper limit of dynamic range. The maximum measurable range of the demodulator for optical phase is usually between [-π, +π]. Once the vibration energy exceeds this range, the measured phase signal will exhibit a wrapping phenomenon (Phase Wrapping), and high-frequency spikes or discontinuous jumps will appear in the histogram or data distribution.

[0080] (2) Vibration Amplitude (Strain Rate)

[0081] By comparing the vibration amplitudes and their distribution shapes at different positions in the well section, the high-energy abnormal interval can be quickly located.

[0082] To quantitatively analyze the vibration amplitude, assume that the phase signal after demodulation is denoted as φ(t). If the fiber measurement gauge length is set to L, the strain can be obtained through the following approximate linear relationship:

[0083] ε(t) = kφ(t) (1)

[0084] In DAS measurement, when the fiber is affected by external vibration, it will cause changes in the Brillouin frequency shift or the phase of the Rayleigh scattering signal. Usually, for the phase method DAS system, the measured phase and the strain rate (microstrain / second) can be approximately regarded as a linear relationship:

[0085]

[0086] Where:

[0087] is the phase value measured by the fiber optic sensing demodulator (unit: radian), usually defined within the range of [-π, +π];

[0088] C is a proportionality constant determined by the characteristics of the fiber optic material and the internal modulation coefficient of the demodulator;

[0089] ε(t) is the strain of the optical fiber;

[0090] L is the gauge length, with the unit of meter.

[0091] In actual hydraulic fracturing monitoring, due to frequent formation vibrations and uneven vibration amplitudes, "strain rate" rather than "strain" is often concerned. If the average strain rate within each time window Δt is defined as then there is

[0092]

[0093] where:

[0094] k is the normalization coefficient, which includes the aforementioned C and L

[0095] is the average strain rate of each time window.

[0096] (3) Phase wrapping and its histogram characteristics when exceeding the dynamic range

[0097] When the true exceeds the range of [-π, +π], the phase measured by the demodulator will have a jump (wrapping phenomenon), like a "sawtooth" going back and forth between ±π. At this time, the histogram will show the following characteristics

[0098] There are obvious peaks near -π and +π;

[0099] The probability distribution in the middle region (such as near 0) decreases;

[0100] This distribution characteristic can be regarded as reaching or exceeding the dynamic range limit of DAS, and can be regarded as a precursor phenomenon of fiber breakage.

[0101] IV. Amplitude detection

[0102] Assume that the vibration strain rate obeys the normal distribution N(0, σ 2 ) within a certain time window, that is, the average value is 0 (no net offset) and the standard deviation is σ.

[0103] For the phase measurement of the demodulator, if it does not exceed the dynamic range, it can be written as formula 2. If when the phase measured by the demodulator is still the true value. However, if Wrapping will occur, and the measurement result will fall back to [-π, +π], resulting in accumulations in the histogram at ±π.

[0104] Based on this, the present invention can obtain an estimated value of the optimal σ by fitting the statistical distribution of the histogram. The inversion process is generally as follows:

[0105] Let represent the probability distribution function (PDF) of the phase. If the dynamic range saturation is not reached, then

[0106]

[0107] If there is phase wrapping, the measured phase is mapped from (here representing taking the remainder with respect to 2π) to [-π, +π]. can be expressed as the sum of the superposition probabilities for all (n is an integer).

[0108] By the maximum likelihood method, comparing the measured histogram with the theoretical distribution, the optimal σ is finally obtained. Once σ is determined, the average strain rate amplitude can be deduced:

[0109]

[0110] where is the standard deviation of the phase; and k·Δt is the proportionality coefficient for converting the phase to the strain rate. Furthermore, a corresponding relationship is established between the order of magnitude of the micro-strain rate με / s and the safe threshold of the fiber amplitude. If remains higher than a certain critical value A within a certain period of time (such as 30 s or a longer period), it is determined that there is a high risk of fiber breakage.

[0111] V. Fiber breakage risk warning

[0112] As described above, for each slice of the DAS raw data, real-time wideband signal recognition, phase wrapping analysis, and amplitude detection are carried out. If within a certain period of time (such as 600 s or a longer period), the DAS data at a certain depth simultaneously exhibits three characteristics: wideband, phase wrapping, and a continuously high amplitude (strain rate), it is determined that the data corresponding to this period and depth shows the precursor phenomenon of fiber breakage. A fiber breakage warning message (including time and depth) can be sent in a timely manner to prompt the fracturing operation personnel to pay attention to the DAS response at this depth, and it is recommended that the fracturing operation personnel take measures such as reducing the displacement, liquid volume, or even suspending the fracturing construction in combination with the on-site fracturing parameters (such as pressure, displacement, proppant concentration, etc.) to avoid fiber breakage.

[0113] Example 2:

[0114] Taking the hydraulic fracturing of a horizontal well and fiber optic monitoring of a certain EGS hot dry rock reservoir as an example, a permanently installed fiber optic cable outside the casing was deployed in this well, and the fiber optic cable was deployed in the cement sheath between the casing and the reservoir through a cementing operation. During the hydraulic fracturing operation, the fiber optic cable was connected to a ground DAS demodulator, and the fracturing vibration signal data of each section was recorded at a spatial sampling interval of 0.25 m, a gauge length of 1 m, and a temporal sampling frequency of 10 kHz.

[0115] Figure 3 The waterfall plot shows the DAS raw data of the third stage of fracturing in this well after being processed by the method of the present invention. It can be seen that the fracturing started around 1050 s, and the fiber optic cable broke at 7050 s. The depth of the break is at 2661 m indicated by the black dashed line. After the fiber optic cable broke at a depth greater than this, DAS data could not be recorded. In addition, the normalized amplitude indicates that the depth of the fiber optic cable break remained at a relatively high vibration intensity level from the start of the fracturing until the fiber optic cable broke.

[0116] According to the method and process described in the present invention, time-frequency spectrum analysis was respectively carried out to determine whether the frequency band width of the signal before the fiber optic cable break was relatively wide, phase wrapping analysis was carried out to determine whether there was a phase wrapping phenomenon in the signal before the fiber optic cable break, and whether the amplitude (strain rate) curve remained high before the fiber optic cable break. At the same time, the results of these three analyses can also be used to verify that the three features described in the present invention can be used as precursors of fiber optic cable breakage and the basis for issuing a warning of fiber optic cable breakage.

[0117] Figure 4 is for Figure 3 The time-frequency spectrum diagram is generated by performing time-frequency analysis based on the short-time Fourier transform (STFT) on the DAS raw signal (one-dimensional time series) at a depth of 2661 m in. It can be seen from the figure that the fracturing had not started before 1000 s, and the strong amplitude of the DAS signal was distributed within 2000 - 5000 Hz; when the normal fracturing started around 3000 s, the strong amplitude of the DAS signal was distributed in a relatively wide frequency band of 1000 - 5000 Hz; while in the time period before the fiber optic cable break, such as 6000 - 7050 s, the strong amplitude was distributed in a relatively wide frequency band of 0 - 5000 Hz; there were obvious differences in the frequency bandwidths of the DAS signals in the three time periods. Therefore, the wide-frequency feature can be used as a precursor feature of fiber optic cable breakage.

[0118] Figure 5 is for Figure 3 The phase value distribution histogram is generated by performing phase analysis on the DAS raw signal (one-dimensional time series) at a depth of 2661 m in. It can be seen from the figure that due to the fiber optic cable break at 7050 s, the phase distribution of the DAS data is no longer a normal distribution during normal fracturing, but there are a large number of abnormal phases near -π and +π, which indicates the occurrence of the phase wrapping phenomenon. Therefore, the phase wrapping phenomenon can be used as a precursor feature of fiber optic cable breakage.

[0119] Figure 6 Yes Figure 3 Comparative analysis of the amplitude values (strain rates) of the DAS raw signals (one-dimensional time series) at the optical fiber fracture point (depth of 2661 m) and the normal fracturing point (depth of 2625 m). It can be seen from the figure that the normal fracturing point (depth of 2625 m) maintains a relatively low amplitude level throughout the fracturing operation. The first strong amplitude distribution appears at the optical fiber fracture point (depth of 2661 m) between 3000 and 3500 s, and the maximum strain rate is 1300.0 με / s indicated by the black horizontal dotted line, but the time is relatively short and no optical fiber fracture occurs. However, at the optical fiber fracture point (depth of 2661 m) from 4000 s to 7050 s, the amplitude has been maintained at a relatively high level, and finally an optical fiber fracture occurs at the 7050 s moment (black vertical dotted line), and the maximum strain rate at the time of fracture is 2820.0 με / s indicated by the black horizontal dotted line. In addition, the strong amplitude from 7050 to 7500 s is due to the strong vibration caused by the fracture of the optical fiber while the end of the optical fiber is still recording the fracturing after the fiber breakage. Therefore, the continuous high amplitude (strain rate) curve before the optical fiber fracture can be used as a precursor feature of optical fiber fracture.

[0120] In summary, during the real-time monitoring of hydraulic fracturing DAS, for each slice of DAS raw data, real-time wideband signal recognition, phase wrapping analysis, and amplitude detection are carried out. The DAS data at a depth of 2661 m during the time period from 4000 s to 7050 s after the start of fracturing simultaneously exhibits three characteristics: wideband, phase wrapping, and high amplitude (strain rate). It is judged that the data corresponding to this time period and depth shows a precursor phenomenon of fiber breakage, and a fiber breakage warning message (including time and depth) is sent to the fracturing operation personnel in a timely manner, prompting the fracturing operation personnel to pay attention to the DAS response at this depth, and it is recommended that the fracturing operation personnel take measures such as reducing the displacement, liquid volume, or even suspending the fracturing construction in combination with on-site fracturing parameters (such as pressure, displacement, proppant concentration, etc.) to successfully avoid the occurrence of optical fiber fracture events.

[0121] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0122] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or means for implementing the functions specified in multiple blocks.

[0123] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means for implementing the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or means for implementing the functions specified in multiple blocks.

[0124] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operational steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or means for implementing the functions specified in multiple blocks.

[0125] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those of ordinary skill in the art.

[0126] Many other changes and modifications can be made without departing from the concept and scope of the present invention. It should be understood that the present invention is not limited to specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. A method for early warning of fiber breakage during hydraulic fracturing of horizontal wells in enhanced geothermal system (EGS) reservoirs based on DAS monitoring, characterized in that, The method includes: S1: Obtain the original vibration signals collected by the DAS demodulator, perform wavelet threshold denoising, data segmentation, and normalization processing to obtain the preprocessed DAS signal data; S2: For the preprocessed DAS signal data, use the short-time Fourier transform (STFT) to separate the energy distributions of different frequency bands, visually judge the high-energy areas using the output time-frequency spectrogram, identify abnormal wide-frequency bands, and obtain the spectrum analysis results; S3: For the preprocessed DAS signal data, first perform phase wrapping detection to determine the dynamic range of the DAS system, detect whether phase wrapping occurs for signals exceeding the dynamic range, calculate the phase signal histogram, observe whether abnormal peaks appear near the dynamic range, then calculate the vibration amplitude, calculate the fiber strain and strain rate respectively, and judge whether wrapping occurs through histogram analysis to obtain the phase wrapping detection results and strain rate data; S4: Input the phase wrapping detection results and the calculated strain rate data obtained in step S3, perform normal distribution modeling, maximum likelihood estimation, and high-amplitude detection, and output the amplitude detection results and the estimated strain rate standard deviation; S5: Based on the spectrum analysis results, phase wrapping detection results, and amplitude detection results, perform fiber breakage precursor identification and warning information generation.

2. The fiber breakage warning method for horizontal well fracturing of hot dry rock reservoir based on DAS monitoring according to claim 1, wherein, The step S1 includes: Connect the permanent fiber optic cable set outside the wellbore casing to the DAS demodulator, continuously record the vibration signals at each position along the wellbore at a high time sampling rate, and obtain the original vibration signals along the entire length of the wellbore through the DAS demodulator; remove environmental noise and demodulator noise interference through wavelet threshold denoising; then perform data segmentation, segment with a 2-second time window and spatial channels to form a three-dimensional data structure, i.e., time × depth × amplitude, and finally perform normalization to unify the data scales of different time windows and channels, and output the preprocessed DAS signal data.

3. A method for early warning of fiber breakage during hydraulic fracturing of horizontal wells in a hot dry rock reservoir based on DAS monitoring according to claim 1, characterized in that, The step S3 includes: S301: Dynamic range and phase wrapping The DAS system has an upper limit of the dynamic range. The phase signal of the fiber optic demodulator is usually limited between [-π, +π]. When the vibration energy exceeds this range, the measured phase signal will have phase wrapping, and high-frequency spikes or discontinuous jumps will appear in the histogram or data distribution; S302: Vibration amplitude By comparing the vibration amplitudes and their distribution shapes at different positions in the well section, the high-energy abnormal intervals can be quickly located; To quantitatively analyze the vibration amplitude, assume that the phase signal after demodulation is denoted as If the fiber optic measurement gauge length is set to L, the strain can be obtained through the following approximate linear relationship: In DAS measurement, for a phase-based DAS system, the measured phase φ(t) and the strain rate can be approximately regarded as a linear relationship: Among them, φ(t) is the phase value measured by the fiber optic sensing demodulator, defined within the range of [-π, +π]; C is a proportionality constant determined by the fiber material characteristics and the internal modulation coefficient of the demodulator; ε(t) is the strain of the fiber optic cable; L is the gauge length, with the unit of meter; In actual hydraulic fracturing monitoring, the average strain rate within each time window Δt is defined as Then there is where k is a normalization coefficient that includes the aforementioned C and L, is the average strain rate of each time window; S303: Phase wrapping and its histogram characteristics when exceeding the dynamic range When the true φ(t) exceeds the range of [-π, +π], the phase measured by the demodulator will have a jump. At this time, the histogram will show the following characteristics: obvious peaks appear near -π and +π, and the probability distribution in the middle region decreases; this distribution characteristic can be regarded as reaching or exceeding the dynamic range limit of the DAS, and can be regarded as a precursor phenomenon of fiber breakage.

4. A method for predicting fiber breakage during hydraulic fracturing of horizontal wells in a hot dry rock reservoir based on DAS monitoring according to claim 1, characterized in that, The step S4 specifically includes: Assume the vibration strain rate obeys the normal distribution N(0, σ 2 ) within a certain time window, that is, the mean value is 0 and the standard deviation is σ; For the phase measurement of the demodulator, if it does not exceed the dynamic range, it can be written as formula (2). If the phase measured by the demodulator is still the true value when |φ| ≤ π, but if |φ| > π, wrapping will occur and the measurement result will fall back to [-π, +π], resulting in accumulation at ±π in the histogram. By fitting the statistical distribution of the histogram, the estimated value of the optimal σ is obtained, and its inversion process is as follows: Let f(φ) represent the probability distribution function PDF of the phase. If the dynamic range saturation is not reached, then: If there is phase wrapping, the measured phase φ m From φ m = φ mod(2π) mapped into [-π, +π], f(φ m ) can be expressed as the sum of the superposition probabilities for all φ k = φ m + 2πn; By the maximum likelihood method, comparing the measured histogram with the theoretical distribution, the optimal σ is finally obtained, and the average strain rate amplitude can be deduced: Among them, is the standard deviation of the phase; and k·Δt is the proportionality coefficient for converting the phase into the strain rate, thereby establishing a correspondence between the order of magnitude of the micro-strain rate με / s and the safe threshold of the optical fiber amplitude. If maintains above a certain critical value A within a certain period of time, it is determined that there is a high risk of fiber breakage.

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