Quantitative evaluation method for multi-fracture temporary plugging efficiency of combined monitoring system using optical fiber and acoustic emission

Abstract

This invention relates to a method for quantitatively evaluating the temporary plugging efficiency of multiple fractures using a combined monitoring system of optical fiber and acoustic emission, belonging to the field of petroleum technology. The method includes using a hydraulic jet perforation device to perform hydraulic jet perforation operations at preset perforation locations through a simulated wellbore to form holes simulating on-site spiral or directional perforations, and recording perforation parameters; applying true triaxial stress to a true triaxial fracturing sample, and injecting fracturing fluid into the perforation holes through a simulated wellbore to perform multi-cluster fracturing; simultaneously and continuously acquiring near-wellbore fiber strain data, far-wellbore fiber strain data, acoustic emission event data, and injection pressure data during the fracturing process; using the near-wellbore fiber strain abrupt change moment in the near-wellbore fiber strain data as a time anchor point, and verifying it in conjunction with the spatiotemporal distribution in the acoustic emission event data to confirm the fracturing sequence of each perforation cluster, and estimating the fracture propagation rate based on far-wellbore fiber and acoustic emission inversion.

Description

Technical Field

[0001] This invention relates to the field of petroleum technology, and in particular to a quantitative evaluation method for the temporary plugging efficiency of multiple fractures using a combined monitoring system of optical fiber and acoustic emission. Background Technology

[0002] Hydraulic fracturing is a core technology for the economical development of unconventional reservoirs such as shale oil and gas and tight sandstone gas. With the increasing demands for reservoir stimulation volume, segmented multi-cluster fracturing technology has become mainstream, increasing the drainage area by simultaneously fracturing multiple fractures within a segment. However, the simultaneous propagation of multiple fractures often involves non-uniform fracturing initiation and competitive propagation, leading to some perforation clusters becoming ineffective or inefficient, severely restricting the fracturing stimulation effect. Temporary plugging technology, which involves injecting a plugging agent at the fracture opening of already fractured areas, forces subsequent fracturing fluid to redirect and open insufficiently fractured perforation clusters, and is an important means of achieving balanced propagation of multiple fractures. However, the mechanism of temporary plugging is complex, and key issues such as the plugging efficiency of the plugging agent, fracture redirection conditions, and timing remain unclear, requiring systematic research through high-precision physical simulation experiments.

[0003] True triaxial hydraulic fracturing physical simulation experiments can reproduce the three-dimensional stress state underground in a laboratory setting, and are an important approach to studying the mechanisms of fracture initiation and propagation. However, existing true triaxial fracturing physical model experiments have the following shortcomings in the study of multi-fracture initiation and propagation and temporary plugging of fracture openings: First, the completion method is out of touch with the actual field conditions. Existing experiments mostly involve open-hole fracturing or slotting, which cannot simulate real spiral perforation or directional perforation, resulting in significant deviations between the fracturing initiation pressure and fracture morphology and the actual situation.

[0004] Second, single monitoring methods are insufficient to accurately depict the initiation and propagation process of multiple fractures. Acoustic emission technology suffers from decreased positioning accuracy when multiple fractures initiate simultaneously; distributed fiber optic strain can only acquire one-dimensional information, making it difficult to simultaneously cover near-wellbore initiation and far-wellbore propagation.

[0005] Third, there is a lack of quantitative evaluation methods for temporary plugging efficiency. Existing experimental evaluations of temporary plugging effects mostly rely on post-pressure dissection observation or qualitative comparison of pressure curves, lacking a multi-index quantitative evaluation system based on real-time monitoring data, and thus lacking a basis for optimizing temporary plugging process parameters.

[0006] The above content is only used to help understand the technical solution of the present invention and does not represent an admission that the above content is prior art. Summary of the Invention

[0007] The main objective of this invention is to provide a quantitative evaluation method for the temporary plugging efficiency of multiple cracks using a combined monitoring system of optical fiber and acoustic emission, aiming to solve the aforementioned technical problems in the prior art.

[0008] To achieve the above objectives, this invention provides a method for quantitatively evaluating the temporary plugging efficiency of multiple fractures using a combined monitoring system of optical fiber and acoustic emission. The combined monitoring system includes a true triaxial fracturing sample, a simulated wellbore, near-wellbore and far-wellbore optical fibers, and a true triaxial hydraulic fracturing system. The simulated wellbore is pre-embedded within the true triaxial fracturing sample. The far-wellbore optical fibers are horizontally embedded on both sides of the simulated wellbore along the expected fracture propagation direction and located inside the true triaxial fracturing sample. The near-wellbore optical fibers are arranged axially along the outer wall of the simulated wellbore, forming strain measurement points at corresponding positions of each perforation cluster. The near-wellbore and far-wellbore optical fibers together form a dual-channel optical fiber monitoring structure. The true triaxial hydraulic fracturing system has pressure plates in all three directions, and multiple acoustic emission sensors are mounted on each pressure plate to form a combined monitoring system with the dual-channel optical fiber monitoring structure. The method includes: The hydraulic sandblasting perforation device is used to perform hydraulic sandblasting perforation operations at the preset perforation position through a simulated well shaft, so as to form holes that simulate the on-site spiral perforation or directional perforation, and the perforation parameters are recorded. True triaxial stress was applied to the true triaxial fracturing sample, and fracturing fluid was injected into the perforation hole through a simulated wellbore to carry out multi-cluster fracturing. During the fracturing process, near-wellbore fiber optic strain data, far-wellbore fiber optic strain data, acoustic emission event data and injection pressure data were collected simultaneously and continuously. Using the moment of abrupt strain change in near-wellbore fiber strain data as the time anchor point, and combining it with the spatiotemporal distribution in acoustic emission event data for verification, the fracture initiation sequence of each perforation cluster is confirmed, and the fracture propagation rate is estimated based on far-wellbore fiber and acoustic emission inversion; at the same time, the stress shadowing factor is calculated in real time according to the strain difference of each cluster of near-wellbore fiber to evaluate the balance of multi-fracture competitive propagation; and the timing of temporary plugging agent is determined based on the stress shadowing factor. At a predetermined time for the release of the temporary plugging agent, a pre-set concentration of temporary plugging agent is injected into the simulated wellbore. Based on the injection pressure before and after temporary plugging, the cumulative energy of acoustic emission events, and the strain change characteristics of the dual-channel fiber optic cable, a comprehensive evaluation model is established, including the temporary plugging turning efficiency, pressure amplification efficiency, energy efficiency, and opening degree improvement efficiency, to quantitatively evaluate the temporary plugging effect.

[0009] Preferably, in the quantitative evaluation method for the temporary plugging efficiency of the multi-crack system utilizing the combined monitoring system of optical fiber and acoustic emission, after the step of establishing a comprehensive evaluation model including temporary plugging turning efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency based on the injection pressure before and after temporary plugging, the cumulative energy of acoustic emission events, and the strain change characteristics of the dual-channel optical fiber, to quantitatively evaluate the temporary plugging effect, the method further includes: After the fracturing experiment is completed, the true triaxial fracturing specimen is dissected and observed post-fracturing to record the actual distribution and morphology of the temporary plugging agent at the fracture opening. The results are compared with the evaluation results of the comprehensive evaluation model, and the model parameters of the comprehensive evaluation model are corrected accordingly.

[0010] Preferably, in the quantitative evaluation method for the temporary plugging efficiency of the multi-fracture monitoring system utilizing optical fiber and acoustic emission, after the fracturing experiment, the true triaxial fracturing sample is dissected and observed post-fracturing to record the actual distribution location and morphology of the plugging agent at the fracture opening. This is compared with the evaluation results of the comprehensive evaluation model, and the steps for correcting the model parameters of the comprehensive evaluation model are fed back. Cut the rock sample along the preset cutting line, observe the residual morphology of the temporary plugging agent at the fracture opening and the fracture morphology under ultraviolet light, and count the actual number of newly formed fracture clusters N3; If the actual number of newly formed crack clusters N3 deviates from the number of newly formed perforation clusters N2 after temporary plugging by more than ±20%, the strain mutation threshold or the weighting coefficients of temporary plugging turning efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency in the comprehensive evaluation model are adjusted, and the comprehensive temporary plugging efficiency is recalculated until the deviation between N3 and N2 does not exceed ±20%.

[0011] Preferably, in the quantitative evaluation method for the temporary plugging efficiency of the multi-fracture system using the combined monitoring system of optical fiber and acoustic emission, the step of using the moment of abrupt change in near-wellbore optical fiber strain data as the time anchor point, combined with the spatiotemporal distribution in the acoustic emission event data for verification, to confirm the fracture initiation sequence of each perforation cluster includes: The strain time series of each measuring point near the wellbore is analyzed. When the strain at a certain measuring point exceeds the strain mutation threshold within ≤1 s, and the mutation time is consistent with the pressure drop or fluctuation time on the injection pressure curve, it is determined that the perforation cluster corresponding to that measuring point has fractured. The fracture initiation sequence of each perforation cluster is determined based on the fracture initiation time of the perforation cluster.

[0012] Preferably, in the quantitative evaluation method for the temporary plugging efficiency of the multi-fracture system using a combined monitoring system of optical fiber and acoustic emission, the estimation of the fracture propagation rate based on far-wellbore optical fiber and acoustic emission inversion includes: The propagation rate v = d / Δt is calculated using the difference Δt between the arrival time of the strain response of the far-well fiber and the fracture initiation time t0, and the distance d from the far-well fiber to the center line of the simulated wellbore.

[0013] Preferably, in the quantitative evaluation method for the temporary plugging efficiency of the combined monitoring system utilizing optical fiber and acoustic emission, the step of calculating the stress shadowing factor in real time based on the strain difference of each cluster of near-wellbore optical fibers to assess the equilibrium of competitive propagation of multiple fractures; and determining the timing of temporary plugging agent delivery based on the stress shadowing factor, includes: Take the maximum strain ε at each fractured cluster measuring point near the wellbore at the same time.max Minimum value ε min and average ε avg Calculate the stress shading factor SSI = (ε max -ε min ) / ε avg ; When SSI > 1.5, significant stress shadow competition is identified, and the time within 10–20 s after the SSI reaches its peak is determined as the time for the temporary plugging agent to be released.

[0014] Preferably, in the quantitative evaluation method for the multi-crack temporary plugging efficiency of the combined monitoring system utilizing optical fiber and acoustic emission, the step of establishing a comprehensive evaluation model that includes temporary plugging turning efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency based on the injection pressure before and after temporary plugging, the cumulative energy of acoustic emission events, and the strain change characteristics of the dual-channel optical fiber, to quantitatively evaluate the temporary plugging effect, includes: Based on the real-time strain curves at various measuring points near the wellbore, before the temporary plugging agent is applied, the number of fracturing perforation clusters N1 is identified and recorded, and the number of non-fracturing perforation clusters N0 is also recorded. total -N1, where N total This represents the total number of perforation clusters; After the temporary plugging agent is applied, continue to monitor the fiber strain and injection pressure near and far from the well. If the injection pressure increases significantly by ≥2MPa and a new fiber strain mutation point appears subsequently, the temporary plugging is considered to have been successfully reversed. Record the number N2 of new perforation clusters that fractured after the temporary plugging and the fracture time of each new cluster. Calculate the temporary blocking steering efficiency η N = (N2 / N0)×100%, when N0=0, η N It is 0%; Calculate the pressure amplification efficiency η P = (P post -P pre ) / P pre ×100%, P pre and P post These are the peak pressure values ​​before and after the administration of the temporary plugging agent; Calculate energy efficiency η based on the cumulative energy of acoustic emission events. E The total cumulative energy of acoustic emission events during the entire fracturing process is denoted as E. total The cumulative energy corresponding to the fracture cluster that occurred before the temporary blockage is denoted as E. before The cumulative energy corresponding to the newly formed fracture cluster after temporary closure is denoted as E. after Then η E = E after / (E total -E before )×100%; Fracture hydraulic aperture was inverted based on the amplitude of near-wellbore fiber strain abrupt change, and the aperture enhancement efficiency η was calculated. w ; A comprehensive evaluation model is constructed, and the overall congestion efficiency is: η comb =α·η N +β·η P +γ·η E +δ·η w ; Where α, β, γ, and δ are the weighting coefficients for temporary blocking steering efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency, respectively, and α+β+γ+δ=1.

[0015] Preferably, in the quantitative evaluation method for the multi-crack temporary plugging efficiency of the joint monitoring system utilizing optical fiber and acoustic emission, the method for determining the weight coefficients in the comprehensive evaluation model includes: Obtain η from at least two completed temporary damming experiments. N η P η E η w The four indicator values ​​form the original data matrix X = [x ij ], where i = 1,2,...,n is the number of experimental groups, and j = 1,2,3,4 corresponds to η respectively. N η P η E η w ; The original data matrix is ​​forward-oriented; the forward-oriented data is then normalized. Calculate the proportion f of the i-th group of experiments under the j-th indicator. ij The calculation formula is: (1) The information entropy value of the j-th indicator is calculated using the following formula: (2) The coefficient of variation for the j-th indicator is calculated using the following formula: (3) The initial weights w of each indicator are calculated using the coefficient of difference. j : (4) The four weights w1, w2, w3, w4 are assigned to the final weight coefficients α, β, γ, δ corresponding to the four indicators, respectively, and α+β+γ+δ=1. If the difference coefficient dj of a certain indicator If the value is less than 0.05, then set its minimum weight lower limit to 0.05, and adjust the weights of other indicators accordingly to keep the sum of 1. in, This represents the summation of the normalized values ​​of all samples in column j; k = 1 / ln(n) is a constant, when f ij When = 0, let f ij ·lnf ij = 0; d j This represents the information utility value of the j-th indicator; In equation (4), the denominator is the sum of the difference coefficients of all four indicators, ensuring that the initial weights meet the normalization condition. .

[0016] Preferably, in the quantitative evaluation method for the temporary plugging efficiency of the multi-crack system using the combined monitoring system of optical fiber and acoustic emission, the perforation pressure of the hydraulic sandblasting perforation device is not less than 40 MPa, the perforation method simulates at least one of spiral perforation, directional perforation and fixed-surface perforation, the perforation orifice diameter is 4-6 mm, and the orifice depth is 40-60 mm.

[0017] Preferably, in the quantitative evaluation method for the multi-crack temporary plugging efficiency of the combined monitoring system utilizing optical fiber and acoustic emission, the acoustic emission sensor employs a probe with a resonant frequency of 150 kHz; and / or, Each pressure plate has at least four acoustic emission sensors on each of its six surfaces, with a total of at least 24 channels and a sampling frequency of at least 5 MHz; and / or, The optical fiber is demodulated using an optical frequency domain reflectance demodulator with a spatial resolution of 1–2 mm and a sampling frequency of no less than 1 Hz.

[0018] The present invention has at least the following beneficial effects: This invention utilizes a hydraulic sandblasting perforation device to perform hydraulic sandblasting perforation operations at preset perforation locations through a simulated well shaft, thereby forming holes that simulate on-site spiral or directional perforations, and recording the perforation parameters. True triaxial stress was applied to the true triaxial fracturing sample, and fracturing fluid was injected into the perforation holes through a simulated wellbore for multi-cluster fracturing. During the fracturing process, near-wellbore fiber strain data, far-wellbore fiber strain data, acoustic emission event data, and injection pressure data were continuously acquired simultaneously. The moment of abrupt change in near-wellbore fiber strain data was used as the time anchor point, and the spatiotemporal distribution in the acoustic emission event data was used for verification to confirm the fracturing sequence of each perforation cluster. The fracture propagation rate was estimated based on the far-wellbore fiber and acoustic emission inversion. At the same time, the stress shadowing factor was calculated in real time based on the strain difference of each cluster in the near-wellbore fiber to evaluate the balance of multi-fracture competitive propagation. The timing of temporary plugging agent injection was determined based on the stress shadowing factor. At the determined time of temporary plugging agent injection, a preset concentration of temporary plugging agent was injected into the simulated wellbore. Based on the injection pressure before and after temporary plugging, the cumulative energy of acoustic emission events, and the strain change characteristics of dual-channel fiber, a comprehensive evaluation model was established, including temporary plugging turning efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency, to quantitatively evaluate the temporary plugging effect. This allows for the simulation of real spiral perforation and directional perforation, precisely depicting the initiation and propagation process of multiple cracks, and providing a quantitative evaluation method for temporary plugging efficiency.

[0019] Furthermore, by using hydraulic jet perforation, perforation completion conditions consistent with those in the field were achieved, overcoming the problem of significant differences in stress fields between traditional slotted or open-hole completion and field perforation completion. The simulation error of fracturing pressure was reduced from ±30% to ±8%.

[0020] Furthermore, through joint monitoring and spatiotemporal joint inversion of near-wellbore and far-wellbore dual-channel optical fiber and acoustic emission, the precise identification of the fracturing state and fracture propagation path of the perforation cluster was achieved, and the fracturing identification accuracy was improved to over 92%, which is about 30 percentage points higher than that of single optical fiber or single acoustic emission technology.

[0021] Furthermore, a multi-dimensional comprehensive evaluation model was established, which includes temporary plugging turning efficiency, pressure response coefficient, energy turning efficiency, and opening permeability enhancement efficiency. The information entropy weighting method was introduced to objectively determine the weighting coefficients, reducing the average deviation between the evaluation results of temporary plugging effect and the post-pressurization dissection results from ±35% to ±12%. This provides a scientific and reliable quantitative basis and correction mechanism for optimizing the experimental parameters of the temporary plugging process. Attached Figure Description

[0022] Figure 1 A schematic diagram of the joint monitoring system provided in an embodiment of the present invention; Figure 2 for Figure 1 Fiber optic arrangement diagrams for near-wellbore and far-wellbore sections in the intermediate sample; Figure 2 Image (a) is a schematic diagram of the overall fiber optic cable arrangement. Figure 2 (b) shows the arrangement of near-wellbore optical fibers. Figure 2 (c) shows the arrangement of optical fibers in the distant well. Figure 2Image d shows a complete rock sample image after near / far well fiber optic cable deployment; Figure 3 This is a diagram illustrating the installation process of a water jetting perforation device. Figure 4 This is an image showing the actual effect of the perforation. Figure 5 The optical fiber strain response diagram; Figure 6 The injection pressure curves are shown before and after the temporary plugging agent is added. Figure 7 A spatial distribution map of acoustic emission monitoring points; Figure 8 These are photographs showing the fracture morphology of a rock sample after compression.

[0023] 1-True triaxial fracturing specimen, 2-Simulated wellbore, 3-Fiber optic cable, 4-True triaxial hydraulic fracturing system, 5-Pressure plate.

[0024] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0025] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0026] In this embodiment of the invention, the term "and / or" describes the relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The character " / " generally indicates that the preceding and following associated objects have an "or" relationship.

[0027] It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0028] In this embodiment of the invention, the term "multiple" refers to two or more, and other quantifiers are similar.

[0029] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction of the component itself; similarly, for ease of understanding and description, "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the embodiments of the present invention to facilitate a better understanding of the invention. However, the technical solutions claimed in the present invention can be implemented even without these technical details and various variations and modifications based on the following embodiments. The division of the following embodiments is for ease of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with and referenced by each other without contradiction.

[0031] This invention provides a combined monitoring system comprising a true triaxial fracturing specimen, a simulated wellbore, near-wellbore optical fibers, far-wellbore optical fibers, and a true triaxial hydraulic fracturing system. The simulated wellbore is pre-embedded within the true triaxial fracturing specimen. The far-wellbore optical fibers are horizontally embedded on both sides of the simulated wellbore along the expected fracture propagation direction and located inside the true triaxial fracturing specimen. The near-wellbore optical fibers are arranged axially along the outer wall of the simulated wellbore, forming strain measurement points at corresponding positions of each perforation cluster. The near-wellbore and far-wellbore optical fibers together form a dual-channel optical fiber monitoring structure. The true triaxial hydraulic fracturing system has pressure plates in all three directions, and multiple acoustic emission sensors are mounted on each pressure plate to form a combined monitoring system with the dual-channel optical fiber monitoring structure.

[0032] Near-well fiber optic cables are arranged close to the outer wall of the simulated wellbore along its axial direction, forming strain measurement points at the corresponding positions of each perforation cluster; far-well fiber optic cables are horizontally buried inside the rock samples on both sides of the wellbore along the expected fracture propagation direction, with the distance from the centerline of the simulated wellbore set according to the preset fracture monitoring range.

[0033] The acoustic emission sensor uses a probe with a resonant frequency of 150 kHz. At least four sensors are arranged on each of the six surfaces of the pressure plate, with a total of at least 24 channels and a sampling frequency of at least 5 MHz. The optical fiber uses an optical frequency domain reflection demodulator with a spatial resolution of 1–2 mm and a sampling frequency of at least 1 Hz.

[0034] In some implementations, a cubic rock sample with a side length of 400 mm is used, taken from a natural shale outcrop. A through hole (40 mm in diameter and 350 mm in depth) is drilled in the center of the rock sample to install the simulated wellbore. The simulated wellbore is made of metal pipe (30 mm outer diameter and 24 mm inner diameter), with threads on the outside of the pipe wall to facilitate cement filling and consolidation with the well wall.

[0035] Near-wellbore optical fibers, using tight-buffered single-mode fiber (900 μm in diameter), are axially arranged along the outer wall of the simulated wellbore, tightly bonded to the outer wall, and solidified with cement. Strain measurement points are set at the corresponding depth positions of each perforation cluster, with one measurement point per perforation location. Far-wellbore optical fibers are horizontally embedded inside rock samples on both sides of the simulated wellbore along the expected fracture propagation direction, 120 mm from the centerline of the simulated wellbore (adjusted according to the preset monitoring range), and are also solidified with cement to ensure coordinated deformation between the fiber and the rock. The fiber leads out through the entrance of the simulated wellbore and connect to the OFDR demodulator. Please refer to [link to relevant documentation]. Figure 2 .

[0036] The acoustic emission sensors employ piezoelectric ceramic probes with a resonant frequency of 150 kHz, mounted inside the six pressure plates of the true triaxial system. Four sensors are arranged on each pressure plate, resulting in a total of 24 channels. The acoustic emission sensors are spring-loaded to the pressure plates, and Vaseline is used as the coupling agent. Signal lines are led out via shielded cables to the multi-channel acoustic emission acquisition system (sampling frequency 5 MHz, threshold 40 dB).

[0037] Two intermediate containers and a control valve assembly are installed between the fracturing pump and the simulated wellbore to switch the injection of temporary plugging agent solution at predetermined times.

[0038] Figure 1 The flowchart illustrates a method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission, which includes steps S1000 to S4000.

[0039] Step S1000: Using a hydraulic sandblasting perforation device, hydraulic sandblasting perforation is performed at a preset perforation location through a simulated well shaft to form holes simulating on-site spiral or directional perforations, and perforation parameters are recorded.

[0040] The hydraulic sandblasting perforation device adopts the principle of abrasive water jet, with a perforation pressure of not less than 40 MPa and a perforation time that can be adjusted according to the preset hole depth. It can achieve precise positioning perforation at any depth and orientation in the well barrel, simulating at least one of the perforation methods such as spiral perforation, directional perforation, and fixed-face perforation. The perforation hole diameter is 4-6 mm and the hole depth is 40-60 mm.

[0041] The jetting gun of the hydraulic sandblasting perforation device is lowered into the simulated wellbore to a predetermined depth. The nozzle is aligned with the predetermined perforation direction using a rotation and positioning mechanism. The high-pressure pump is activated, injecting a high-speed water jet (pressure 45 MPa, flow rate 12 L / min) containing abrasive (60-mesh quartz sand, concentration 5%–8%) onto the inner wall of the wellbore, eroding the rock to form perforations. The perforation time for a single perforation is 5–10 minutes, resulting in a perforation diameter of 4–6 mm and a depth of 40–60 mm. This example uses a 180° symmetrical perforation scheme, setting the number of perforation clusters to 4 clusters with a cluster spacing of 50 mm, for a total of 8 perforations. Please refer to [link to relevant documentation]. Figure 3 and Figure 4 .

[0042] In step S2000, true triaxial stress is applied to the true triaxial fracturing sample, and fracturing fluid is injected into the perforation hole through a simulated wellbore to carry out multi-cluster fracturing. During the fracturing process, near-wellbore fiber optic strain data, far-wellbore fiber optic strain data, acoustic emission event data, and injection pressure data are collected simultaneously and continuously.

[0043] The true triaxial fracturing sample was loaded into the true triaxial pressure chamber, and triaxial principal stresses (15 MPa vertically, 15 MPa horizontally at maximum, and 5 MPa horizontally at minimum) were applied according to the preset stress path. Fracturing fluid (viscosity 5 mPa·s, with 0.1% fluorescent tracer added for later observation) was injected into the wellbore at a constant flow rate (30 mL / min) using a servo pump to carry out multi-cluster fracturing.

[0044] During fracturing, the OFDR fiber optic strain demodulator continuously acquires strain data from near-wellbore and far-wellbore optical fibers, with a spatial resolution of 1 mm and a sampling frequency of 1 Hz; the acoustic emission system continuously records waveforms and calculates the three-dimensional coordinates of events in real time; and the pressure sensor records changes in injection pressure. All data are recorded with a unified timestamp via a synchronized clock.

[0045] Step S3000 uses the moment of abrupt strain change in near-wellbore fiber strain data as the time anchor point, and verifies it in conjunction with the spatiotemporal distribution in acoustic emission event data to confirm the fracture initiation sequence of each perforation cluster, and estimates the fracture propagation rate based on far-wellbore fiber and acoustic emission inversion; at the same time, it calculates the stress shadowing factor in real time according to the strain difference of each cluster of near-wellbore fiber to evaluate the balance of multi-fracture competitive propagation; and determines the time for releasing the temporary plugging agent based on the stress shadowing factor.

[0046] Specifically, the step of using the moment of strain abrupt change in near-wellbore fiber strain data as a time anchor point and verifying it in conjunction with the spatiotemporal distribution in acoustic emission event data to confirm the fracture initiation sequence of each perforation cluster includes: analyzing the strain time series of each measuring point in the near-wellbore fiber; when the strain at a certain measuring point exceeds the strain abrupt change threshold (e.g., 100 με) within ≤1 s, and the moment of abrupt change coincides with the pressure drop or fluctuation moment on the injection pressure curve, it is determined that the perforation cluster corresponding to that measuring point has fractured; and determining the fracture initiation sequence of each perforation cluster based on the fracture initiation time of the perforation cluster.

[0047] More specifically, the strain time series of each measuring point near the wellbore is analyzed. When the strain of a certain measuring point changes by more than 50 to 100 με within ≤1s, and the time of the change coincides with the time of pressure drop or fluctuation on the injection pressure curve, it is determined that the perforation cluster corresponding to that measuring point has been fractured. The fracture initiation efficiency is defined as the percentage of the actual number of fractured clusters to the total number of perforation clusters.

[0048] Using the moment of strain abrupt change in the near-wellbore fiber optic cable t0 as the time anchor point, a time window [t0-0.5 s, t0+0.5 s] is set, and acoustic emission events within this window are retrieved. If the spatial location of at least one acoustic emission event is ≤15 mm away from the Euclidean distance of the fiber optic cable abrupt change point, the effective initiation of the cluster is further confirmed.

[0049] The method for estimating the fracture propagation rate based on far-well fiber and acoustic emission inversion includes: using the difference Δt between the arrival time of the strain response of the far-well fiber and the fracture initiation time t0, and the distance d from the far-well fiber to the center line of the simulated wellbore, to calculate the propagation rate v = d / Δt.

[0050] The propagation rate *v* is used to verify the effectiveness of crack propagation: if *v* > 0 and the response time of the far-well fiber matches the acoustic emission event, then the crack has been confirmed to have effectively propagated to the far-well region. This cluster is counted in the effective crack initiation cluster count; if *v* = 0 or there is no response from the far-well fiber, then the cluster is determined to have only initiated near the well and has not effectively propagated. In calculating the crack initiation efficiency, this cluster is marked as an invalid propagation cluster and is not counted in the effective crack initiation cluster count.

[0051] The stress shadowing factor is calculated in real time based on the strain differences among near-wellbore fiber clusters to assess the equilibrium of multi-fracture competitive propagation. Based on the stress shadowing factor, the timing of temporary plugging agent application is determined, including taking the maximum strain ε at the measuring points of each fractured cluster near the wellbore fiber at the same time. max Minimum value ε min and average ε avg Calculate the stress shading factor SSI = (ε max -ε min ) / ε avgWhen SSI > 1.5, significant stress shadow competition is identified, and the time for temporary plugging agent is determined within 10–20 seconds after the SSI reaches its peak.

[0052] More specifically, the magnitude of the stress shadowing factor can determine whether the current crack propagation is uniform or highly uneven (i.e., the strength of the stress shadowing effect). When the stress shadowing factor is below a preset threshold, it indicates that the propagation of the main crack significantly inhibits adjacent cracks, forming a strong competitive relationship.

[0053] The timing of temporary plugging agent administration signifies that some fractures have over-proliferated while others are severely suppressed, limiting reservoir stimulation volume without intervention. The purpose of temporary plugging agent administration is to seal over-proliferated fractures (high-strain clusters), forcing the fracturing fluid to redirect and activating previously uninitiated or limited-proliferation fractures (low-strain clusters), thereby improving overall stimulation uniformity. Therefore, the optimal time for temporary plugging agent administration is considered to be within 10–20 seconds after the SSI reaches its peak.

[0054] In step S4000, at the determined time of temporary plugging agent release, a preset concentration of temporary plugging agent is injected into the simulated wellbore; and based on the injection pressure before and after temporary plugging, the cumulative energy of acoustic emission events, and the strain change characteristics of dual-channel optical fibers, a comprehensive evaluation model is established that includes temporary plugging turning efficiency, pressure amplification efficiency, energy efficiency, and opening degree improvement efficiency, in order to quantitatively evaluate the temporary plugging effect.

[0055] The steps described above, which involve establishing a comprehensive evaluation model based on the injection pressure before and after temporary clogging, the cumulative energy of acoustic emission events, and the strain change characteristics of the dual-channel optical fiber, including temporary clogging turning efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency, to quantitatively evaluate the effect of temporary clogging, include steps S4100 to S4700.

[0056] Step S4100, based on the real-time strain curves of each measuring point near the wellbore, identifies and records the number N1 of fractured perforation clusters before the temporary plugging agent is applied, and simultaneously records the number N0 of non-fractured perforation clusters. total -N1, where N total This represents the total number of perforation clusters.

[0057] After the temporary plugging agent is added in step S4200, the fiber strain and injection pressure near and far from the well continue to be monitored. If the injection pressure increases significantly by ≥2 MPa and a new fiber strain mutation point appears subsequently, the temporary plugging is determined to be successful and the direction is changed. Record the number N2 of new perforation clusters that fracture after the temporary plugging and the fracture time of each new cluster.

[0058] Step S4300 calculates the temporary blocking steering efficiency η N = (N2 / N0)×100%, when N0=0, η N It is 0%; Step S4400 calculates the pressure amplification efficiency η P = (P post -P pre ) / P pre ×100%, P pre and P post These are the peak pressure values ​​before and after the administration of the temporary plugging agent; Step S4500: Calculate the energy efficiency η based on the cumulative energy of acoustic emission events. E The total cumulative energy of acoustic emission events during the entire fracturing process is denoted as E. total The cumulative energy corresponding to the fracture cluster that occurred before the temporary blockage is denoted as E. before The cumulative energy corresponding to the newly formed fracture cluster after temporary closure is denoted as E. after Then η E = E after / (E total -E before )×100%; Step S4600 inverts the fracture hydraulic aperture based on the amplitude of near-wellbore fiber strain abrupt change and calculates the aperture enhancement efficiency η. w ; For each perforation cluster, the peak strain abrupt change Δε at the corresponding near-wellbore fiber optic measuring point at the moment of fracture initiation is taken. max (Unit: με), strain abrupt change Δε measured by near-wellbore fiber optic cable max There should be a linear proportional relationship between the crack opening displacement (i.e., aperture w) and the crack mean hydraulic aperture w can be obtained by using a semi-analytical model: ; In the formula, L is the effective sensing section length of the optical fiber (usually taken as 2 to 3 times the spatial resolution of the optical fiber, such as 5 mm), k is the dimensionless strain-aperture coupling coefficient, which needs to be determined through calibration experiments, and its value range is generally 100 to 800; the average aperture of each crack cluster before temporary plugging is denoted as w. pre The sum of the opening of the new cracks induced by the temporary plugging and the cracks that resume opening after the temporary plugging is denoted as w. post Then the opening degree increases the efficiency η w = (w post ) / w pre ×100% represents the proportion of the newly constructed and restored fracture conductivity aperture by temporary plugging relative to the total aperture of the original fracture system before plugging, reflecting the degree to which temporary plugging supplements and improves the conductivity of the fracture system; for multi-fracture systems, w pre and w post Take the sum of the affected crack openings before and after the temporary plugging, respectively. .

[0059] Step S4700 constructs a comprehensive evaluation model, and the comprehensive temporary congestion efficiency is: ηcomb =α·η N +β·η P +γ·η E +δ·η w ; Where α, β, γ, and δ are the weighting coefficients for temporary blocking steering efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency, respectively, and α+β+γ+δ=1.

[0060] The method for determining the weight coefficients in the comprehensive evaluation model includes: Obtain η from at least two completed temporary damming experiments. N η P η E η w The four indicator values ​​form the original data matrix X = [x ij ], where i = 1,2,...,n is the number of experimental groups, and j = 1,2,3,4 corresponds to η respectively. N η P η E η w ; The original data matrix is ​​positiveized; all indicators are of the larger the better type: if an indicator is negative or needs to be reversed, it is positiveized by taking the reciprocal or the difference. The positively oriented data is then normalized to eliminate dimensional differences between indicators. The formula is as follows: ; Among them, minx kj and maxx kj These are the minimum and maximum values ​​of the j-th indicator across all experimental groups, respectively. Calculate the proportion f of the i-th group of experiments under the j-th indicator. ij The calculation formula is: (1) The information entropy value of the j-th indicator is calculated using the following formula: (2) The coefficient of variation for the j-th indicator is calculated using the following formula: (3) The initial weights w of each indicator are calculated using the coefficient of difference. j : (4) The four weights w1, w2, w3, w4 are assigned to the final weight coefficients α, β, γ, δ corresponding to the four indicators, respectively, and α+β+γ+δ=1. If the difference coefficient dj of a certain indicator If the value is less than 0.05, then set its minimum weight lower limit to 0.05, and adjust the weights of other indicators accordingly to keep the sum of 1. in, This represents the summation of the normalized values ​​of all samples in column j; k = 1 / ln(n) is a constant, when f ij When = 0, let f ij ·lnf ij = 0; d j This represents the information utility value of the j-th indicator; In equation (4), the denominator is the sum of the difference coefficients of all four indicators, ensuring that the initial weights meet the normalization condition. .

[0061] After the fracturing experiment is completed in step S5000, the true triaxial fracturing sample is dissected and observed post-fracturing to record the actual distribution and morphology of the temporary plugging agent at the fracture opening. The results are compared with the evaluation results of the comprehensive evaluation model, and the model parameters of the comprehensive evaluation model are corrected accordingly.

[0062] Specifically, the rock sample was cut along the preset cutting line, and the residual morphology of the temporary plugging agent at the fracture opening and the fracture morphology were observed under ultraviolet light. The actual number of newly formed fracture clusters N3 was counted. If the actual number of newly formed fracture clusters N3 deviates from the number of newly formed perforation clusters N2 after temporary plugging by more than ±20%, then adjust the strain mutation threshold or adjust the weighting coefficients of temporary plugging turning efficiency, pressure amplification efficiency, energy efficiency, and aperture improvement efficiency in the comprehensive evaluation model, and recalculate η. comb Until the deviation between N3 and N2 does not exceed ±20%.

[0063] Example A cubic rock sample with a side length of 400 mm was taken from a natural shale outcrop. A through hole (40 mm in diameter and 350 mm in depth) was drilled in the center of the rock sample to install the simulated well casing. The simulated well casing was made of metal pipe (30 mm outer diameter and 24 mm inner diameter) with threads on the outside of the pipe wall to facilitate cement filling and consolidation with the well wall.

[0064] Near-wellbore optical fibers, using tight-buffered single-mode fiber (900 μm in diameter), are axially arranged along the outer wall of the simulated wellbore, tightly bonded to the outer wall, and solidified with cement. Strain measurement points are set at the corresponding depth positions of each perforation cluster, with one measurement point per perforation location. Far-wellbore optical fibers are horizontally embedded inside rock samples on both sides of the simulated wellbore along the expected fracture propagation direction, 120 mm from the centerline of the simulated wellbore (adjusted according to the preset monitoring range), and are also solidified with cement to ensure coordinated deformation between the fiber and the rock. The fiber leads out through the entrance of the simulated wellbore and connect to the OFDR demodulator. Please refer to [link to relevant documentation]. Figure 2 .

[0065] The acoustic emission sensors employ piezoelectric ceramic probes with a resonant frequency of 150 kHz, mounted inside the six pressure plates of the true triaxial system. Four sensors are arranged on each pressure plate, resulting in a total of 24 channels. The acoustic emission sensors are spring-loaded to the pressure plates, and Vaseline is used as the coupling agent. Signal lines are led out via shielded cables to the multi-channel acoustic emission acquisition system (sampling frequency 5 MHz, threshold 40 dB).

[0066] Two intermediate containers and a control valve assembly are installed between the fracturing pump and the simulated wellbore to switch the injection of temporary plugging agent solution at predetermined times.

[0067] The jetting gun of the hydraulic sandblasting perforation device is lowered into the simulated wellbore to a predetermined depth. The nozzle is aligned with the predetermined perforation direction using a rotation and positioning mechanism. The high-pressure pump is activated, injecting a high-speed water jet (pressure 45 MPa, flow rate 12 L / min) containing abrasive material (60-mesh quartz sand, concentration 5%–8%) onto the inner wall of the wellbore, eroding the rock to form perforations. The perforation time for a single perforation is 5–10 minutes, resulting in a perforation diameter of 4–6 mm and a depth of 40–60 mm. A 180° symmetrical perforation scheme is adopted, with 4 perforation clusters, a cluster spacing of 50 mm, and a total of 8 perforations. Please refer to [link to relevant documentation]. Figure 3 and Figure 4 .

[0068] The true triaxial fracturing sample was loaded into the true triaxial pressure chamber, and triaxial principal stresses (15 MPa vertically, 15 MPa horizontally at maximum, and 5 MPa horizontally at minimum) were applied according to the preset stress path. Fracturing fluid (viscosity 5 mPa·s, with 0.1% fluorescent tracer added for later observation) was injected into the wellbore at a constant flow rate (30 mL / min) using a servo pump to carry out multi-cluster fracturing.

[0069] During fracturing, the OFDR fiber optic strain demodulator continuously acquires strain data from near-wellbore and far-wellbore optical fibers, with a spatial resolution of 1 mm and a sampling frequency of 1 Hz; the acoustic emission system continuously records waveforms and calculates the three-dimensional coordinates of events in real time; and the pressure sensor records changes in injection pressure. All data are recorded with a unified timestamp via a synchronized clock.

[0070] Please see Figure 5 The strain time series at each measuring point of the optical fiber was processed in real time: 364 s after the injection began, tensile strain abrupt changes occurred simultaneously at 7280 mm, 7150 mm, and 6670 mm in the near-wellbore fiber, with amplitudes of 210 με, 195 με, and 85 με, respectively, all exceeding the preset threshold of 80 με. Using 364 s as the time anchor point t0, a time window [t0-0.5 s, t0+0.5 s] was set, and 12 acoustic emission location events were retrieved within this window. The Euclidean distances between the spatial coordinates of three of these events and the three fiber abrupt change locations were 8 mm, 11 mm, and 13 mm, respectively, all ≤15 mm. Therefore, joint inversion confirmed the effective initiation of three cracks HF1, HF2, and HF4. Combining the magnitude and energy of the acoustic emission events, the initiation sequence was determined to be HF2 (left side of the fourth cluster) → HF1 (right side of the second cluster) → HF4 (left side of the second cluster).

[0071] Crack propagation rate inversion: The strain was detected at 380 s at a distance of 120 mm from the far-wellbore fiber, corresponding to the crack initiation time of HF2 at 364 s. The propagation rate of HF2 was calculated as vleft = 120 mm / (380-364) s = 7.5 mm / s. The far-wellbore fiber on the right side responded at 385 s, suggesting a propagation rate of approximately 6.7 mm / s on the HF1 side.

[0072] Stress Shadowing Factor (SSI) Real-time Calculation: Continuous monitoring of strain evolution in fractured clusters. At 480 s, the strain values ​​of each fractured cluster in the near-wellbore fiber are as follows: ε max (HF1) = 400με, ε min (HF4) = 25με, ε avg =(400+195+25) / 3≈207με, calculated SSI = (400-25) / 207≈1.81, exceeding the set threshold of 1.5, indicating that the stress shadowing effect has significantly suppressed HF4 propagation. Further tracking showed that SSI reached a peak of 1.92 around 500 s, suggesting the application of a temporary plugging agent. The pump was stopped at 515 s to prepare for temporary plugging. Propagation efficiency assessment: At this time, the number of fracture clusters was 2 (the second and fourth clusters), and the fracture initiation efficiency = 2 / 4 = 50%.

[0073] The pump was stopped at 515s, and the intermediate container was switched to prepare for the injection of the temporary plugging agent. The formal injection of the temporary plugging agent (biodegradable fiber temporary plugging agent, concentration 2%) began at 765s. Due to the increased viscosity of the liquid carried by the temporary plugging agent and the effect of the temporary plugging agent entering the perforation orifice, the injection pressure rose slightly, reaching a maximum of 3.87MPa, and then the pressure dropped and fluctuated.

[0074] During the injection of the temporary plugging agent, the fiber optic waterfall plot showed that the strain band width and color at cracks HF1 and HF4 increased significantly, indicating that after the injection pressure was increased, the dominant crack HF1 expanded more significantly; while at HF2, it remained almost unchanged, indicating that HF1 became the dominant crack on the same side compared to HF2, and the stress shadow inhibited the expansion of HF2.

[0075] During the temporary plugging agent injection phase (770-790 s), the acoustic emission system detected several low-frequency events concentrated in the 30-48 kHz range, with energies more than twice the average energy. Simultaneously, the near-wellbore optical fiber exhibited brief compression pulses at the corresponding measuring points in the second and fourth clusters, with Δε ≈ -35 με. Joint analysis confirmed that the temporary plugging agent formed an initial bridging at the orifice of the second cluster at 782 s. The pressure only began to rise significantly after the bridging formed, verifying the accuracy of the bridging identification and its early warning function.

[0076] After 1500 s, the pressure rose sharply to 14.25 MPa (1704 s), and a new strain band with an amplitude of about 120 με appeared at the 6840 mm position of the optical fiber. A new crack HF3 was generated, and a response was detected at the corresponding position of the optical fiber at the far well 1706 s, confirming that the temporary plugging and diversion were successful.

[0077] Fracture hydraulic aperture inversion and aperture enhancement efficiency calculation: near-wellbore fiber strain peak Δε at fracture initiation max =280 με, effective sensing section length of the optical fiber L=5 mm, strain-aperture coupling coefficient k=185 (determined by calibration experiment), based on the simplified model w= k·Δε max ·L Estimate the initial average hydraulic aperture w pre = 185 × 280 × 10 -6 × 5 = 0.26 mm; HF3 crack initiation degree w after temporary plugging post = 185 × 120 × 10 -6 × 5 = 0.11 mm; while the suppressed HF4, due to the increase in pressure, has an opening of 0.08 mm (w pre_HF4 ) Restored to 0.15mm (w post_HF4 ), comprehensively evaluate the efficiency η of opening improvement w = / =(w post +w post_HF4 ) / (w pre +w pre_HF4 = (0.11 + 0.15) / (0.26 + 0.08) ×100% = 76.5%.

[0078] Energy diversion efficiency calculation: Calculate the cumulative acoustic emission energy E throughout the entire fracturing process. total=15600 (normalized units), cumulative energy E of the fractured clusters (HF1, HF2, HF4) before temporary plugging. before =10500, cumulative energy E of the new cluster HF3 after temporary blocking. after =1800, then η E = 1800 / (15600-10500)×100% = 35.3%.

[0079] Overall congestion efficiency: Calculate η using the entropy weight method with weights α=0.4, β=0.2, γ=0.2, and δ=0.2. comb = (0.4×50+0.2×268 +0.2×35.3+0.2×76.5 = 20+53.6+7.06+15.3) ×100%=95.96%. The overall efficiency is close to 96%, indicating that the temporary plugging effect is excellent, successfully activating the unopened clusters and significantly improving the flow conductivity of the fracture system.

[0080] After fracturing, the rock sample is cut along the pre-defined cutting line (in the direction of the wellbore axis). Under ultraviolet light, the residual morphology of the temporary plugging agent at the fracture opening and the distribution of fractures are visible. See also... Figure 8 The internal crack morphology is as follows: HF1 and HF4 are inclined cracks (double-winged) formed by the second cluster of perforations, with HF1 closer to the right perforation of the second cluster, and HF4 not close to the perforation. HF2 is a single-winged crack formed by the fourth cluster of perforations (consistent with the fiber optic results). The actual newly initiated crack shown in the dissection is HF3, located in the fourth cluster, which coincides with the 6840mm newly initiated crack point detected by the fiber optic monitoring. Please refer to [link to relevant documentation]. Figure 8 The results showed that the actual number of fracturing clusters was consistent with the monitoring results, and no adjustment of the threshold or weights was required, indicating that the model was reliable.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for quantitatively evaluating the temporary plugging efficiency of a multi-crack monitoring system utilizing a combined monitoring system of optical fiber and acoustic emission, characterized in that, The joint monitoring system includes a true triaxial fracturing sample, a simulated wellbore, near-wellbore optical fibers, far-wellbore optical fibers, and a true triaxial hydraulic fracturing system. The simulated wellbore is pre-embedded within the true triaxial fracturing sample. The far-wellbore optical fibers are horizontally embedded on both sides of the simulated wellbore along the expected fracture propagation direction and located inside the true triaxial fracturing sample. The near-wellbore optical fibers are arranged axially along the outer wall of the simulated wellbore, forming strain measurement points at corresponding positions of each perforation cluster. The near-wellbore and far-wellbore optical fibers together form a dual-channel optical fiber monitoring structure. The true triaxial hydraulic fracturing system has pressure plates in all three directions, and multiple acoustic emission sensors are installed on each pressure plate to form a joint monitoring system with the dual-channel optical fiber monitoring structure. The method includes: The hydraulic sandblasting perforation device is used to perform hydraulic sandblasting perforation operations at the preset perforation position through a simulated well shaft, so as to form holes that simulate the on-site spiral perforation or directional perforation, and the perforation parameters are recorded. True triaxial stress was applied to the true triaxial fracturing sample, and fracturing fluid was injected into the perforation hole through a simulated wellbore to carry out multi-cluster fracturing. During the fracturing process, near-wellbore fiber optic strain data, far-wellbore fiber optic strain data, acoustic emission event data and injection pressure data were collected simultaneously and continuously. Using the moment of abrupt strain change in near-wellbore fiber strain data as the time anchor point, and combining it with the spatiotemporal distribution in acoustic emission event data for verification, the fracture initiation sequence of each perforation cluster is confirmed, and the fracture propagation rate is estimated based on far-wellbore fiber and acoustic emission inversion; at the same time, the stress shadowing factor is calculated in real time according to the strain difference of each cluster of near-wellbore fiber to evaluate the balance of multi-fracture competitive propagation; and the timing of temporary plugging agent is determined based on the stress shadowing factor. At a predetermined time for the release of the temporary plugging agent, a pre-set concentration of temporary plugging agent is injected into the simulated wellbore. Based on the injection pressure before and after temporary plugging, the cumulative energy of acoustic emission events, and the strain change characteristics of the dual-channel fiber optic cable, a comprehensive evaluation model is established, including the temporary plugging turning efficiency, pressure amplification efficiency, energy efficiency, and opening degree improvement efficiency, to quantitatively evaluate the temporary plugging effect.

2. The method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission as described in claim 1, characterized in that, Following the step of establishing a comprehensive evaluation model that includes temporary clogging turning efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency based on the injection pressure before and after temporary clogging, the cumulative energy of acoustic emission events, and the strain change characteristics of the dual-channel optical fiber, to quantitatively evaluate the effect of temporary clogging, the following steps are also included: After the fracturing experiment is completed, the true triaxial fracturing specimen is dissected and observed post-fracturing to record the actual distribution and morphology of the temporary plugging agent at the fracture opening. The results are compared with the evaluation results of the comprehensive evaluation model, and the model parameters of the comprehensive evaluation model are corrected accordingly.

3. The method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission as described in claim 2, characterized in that, After the fracturing experiment is completed, the true triaxial fracturing specimen is dissected and observed post-fracturing to record the actual distribution and morphology of the temporary plugging agent at the fracture opening. This is compared with the evaluation results of the comprehensive evaluation model, and the steps for correcting the model parameters of the comprehensive evaluation model are fed back. Cut the rock sample along the preset cutting line, observe the residual morphology of the temporary plugging agent at the fracture opening and the fracture morphology under ultraviolet light, and count the actual number of newly formed fracture clusters N3; If the actual number of newly formed crack clusters N3 deviates from the number of newly formed perforation clusters N2 after temporary plugging by more than ±20%, the strain mutation threshold or the weighting coefficients of temporary plugging turning efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency in the comprehensive evaluation model are adjusted, and the comprehensive temporary plugging efficiency is recalculated until the deviation between N3 and N2 does not exceed ±20%.

4. The method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission as described in claim 1, characterized in that, The process of using the abrupt change in near-wellbore fiber strain data as a time anchor point, combined with the spatiotemporal distribution in acoustic emission event data for verification, confirms the fracture initiation sequence of each perforation cluster, including: The strain time series of each measuring point near the wellbore is analyzed. When the strain at a certain measuring point exceeds the strain mutation threshold within ≤1 s, and the mutation time is consistent with the pressure drop or fluctuation time on the injection pressure curve, it is determined that the perforation cluster corresponding to that measuring point has fractured. The fracture initiation sequence of each perforation cluster is determined based on the fracture initiation time of the perforation cluster.

5. The method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission as described in claim 1, characterized in that, The estimation of fracture propagation rate based on far-well fiber optic and acoustic emission inversion includes: The propagation rate v = d / Δt is calculated using the difference Δt between the arrival time of the strain response of the far-well fiber and the fracture initiation time t0, and the distance d from the far-well fiber to the center line of the simulated wellbore.

6. The method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission as described in claim 1, characterized in that, The stress shadowing factor is calculated in real time based on the strain difference of each cluster of near-wellbore optical fibers to evaluate the balance of competitive propagation of multiple fractures. Based on the stress shadowing factor, the timing of the temporary plugging agent is determined, including: Take the maximum strain ε at each fractured cluster measuring point near the wellbore at the same time. max Minimum value ε min and average ε avg Calculate the stress shading factor SSI = (ε max -ε min ) / ε avg ; When SSI > 1.5, significant stress shadow competition is identified, and the time for temporary plugging agent is determined within 10–20 seconds after the SSI reaches its peak.

7. The method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission as described in claim 1, characterized in that, The steps outlined in the text, based on the injected pressure before and after temporary clogging, the cumulative energy of acoustic emission events, and the strain changes in the dual-channel fiber, to establish a comprehensive evaluation model encompassing temporary clogging turning efficiency, pressure amplification efficiency, energy efficiency, and opening enhancement efficiency, in order to quantitatively evaluate the effectiveness of temporary clogging, include: Based on the real-time strain curves at various measuring points near the wellbore, before the temporary plugging agent is applied, the number of fracturing perforation clusters N1 is identified and recorded, and the number of non-fracturing perforation clusters N0 is also recorded. total -N1, where N total This represents the total number of perforation clusters; After the temporary plugging agent is added, continue to monitor the fiber strain and injection pressure near the well and far from the well. If the injection pressure increases significantly by ≥2 MPa and a new fiber strain mutation point appears subsequently, the temporary plugging is determined to be successful and the direction is changed. Record the number N2 of the new perforation clusters that fractured after the temporary plugging and the fracture time of each new cluster. Calculate the temporary blocking steering efficiency η N = (N2 / N0)×100%, when N0=0, η N It is 0%; Calculate the pressure amplification efficiency η P = (P post -P pre ) / P pre ×100%, P pre and P post These are the peak pressure values ​​before and after the administration of the temporary plugging agent; Calculate energy efficiency η based on the cumulative energy of acoustic emission events. E The total cumulative energy of acoustic emission events during the entire fracturing process is denoted as E. total The cumulative energy corresponding to the fracture cluster that occurred before the temporary blockage is denoted as E. before The cumulative energy corresponding to the newly formed fracture cluster after temporary closure is denoted as E. after Then η E = E after / (E total -E before )×100%; Fracture hydraulic aperture was inverted based on the amplitude of near-wellbore fiber strain abrupt change, and the aperture enhancement efficiency η was calculated. w ; A comprehensive evaluation model is constructed, and the overall congestion efficiency is: or comb =a·h N +b·h P +g·h E +d·h w ; Where α, β, γ, and δ are the weighting coefficients for temporary blocking steering efficiency, pressure amplification efficiency, energy efficiency, and opening improvement efficiency, respectively, and α+β+γ+δ=1.

8. The method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission as described in claim 7, characterized in that, The method for determining the weight coefficients in the comprehensive evaluation model includes: Obtain η from at least two completed temporary damming experiments. N η P η E η w The four indicator values ​​form the original data matrix X = [x ij ], where i = 1,2,...,n is the number of experimental groups, and j = 1,2,3,4 corresponds to η respectively. N η P η E η w ; The original data matrix is ​​forward-oriented; the forward-oriented data is then normalized. Calculate the proportion f of the i-th group of experiments under the j-th indicator. ij The calculation formula is: ；（1） The information entropy value of the j-th indicator is calculated using the following formula: ；（2） The coefficient of variation for the j-th indicator is calculated using the following formula: ；（3） The initial weights w of each indicator are calculated using the coefficient of difference. j : ；（4） The four weights w1, w2, w3, w4 are assigned to the final weight coefficients α, β, γ, δ corresponding to the four indicators, respectively, and α+β+γ+δ=1. If the difference coefficient dj of a certain indicator is less than 0.05, then its minimum weight is set to 0.05, and the weights of other indicators are adjusted accordingly to keep the sum of 1. in, This represents the summation of the normalized values ​​of all samples in column j; k = 1 / ln(n) is a constant, when f ij When = 0, let f ij ·lnf ij = 0; d j This represents the information utility value of the j-th indicator; In equation (4), the denominator is the sum of the difference coefficients of all four indicators, ensuring that the initial weights meet the normalization condition. .

9. The method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission as described in claim 1, characterized in that, The perforation pressure of the water jet perforation device is not less than 40 MPa, and the perforation method simulates at least one of spiral perforation, directional perforation and fixed-face perforation. The perforation orifice diameter is 4-6 mm and the orifice depth is 40-60 mm.

10. The method for quantitatively evaluating the temporary plugging efficiency of a multi-crack system using a combined monitoring system of optical fiber and acoustic emission as described in claim 1, characterized in that, The acoustic emission sensor employs a probe with a resonant frequency of 150 kHz; and / or, Each pressure plate has at least four acoustic emission sensors on each of its six surfaces, with a total of at least 24 channels and a sampling frequency of at least 5 MHz; and / or, The optical fiber uses an optical frequency domain reflectance demodulator with a spatial resolution of 1–2 mm and a sampling frequency of no less than 1 Hz.

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