Quantitative evaluation and optimization method for hydraulic fracture temporary plugging and steering effect under true triaxial

Abstract

The present application relates to the field of oil and gas field development and hydraulic fracturing technology, especially to a true triaxial hydraulic fracture temporary plugging and steering effect quantitative evaluation and optimization method, comprising applying three-directional ground stress to obtain a rock sample experiment carrier, screening initial fracturing data to construct a primary fracture benchmark data set, preparing a temporary plugging mixed solution, collecting pressure parameters to form a temporary plugging monitoring data set, switching to pure fracturing fluid to carry out secondary fracturing after the in-joint pressure is stable, collecting related data to obtain a secondary fracturing monitoring data set, using industrial CT scanning after the experiment is completed to establish a fracture three-dimensional morphology data set, calculating a comprehensive steering effect index based on the four types of data sets, calibrating a critical pressure increment and a critical stress difference through multiple experiments, iteratively solving optimal parameters and reproducing the experiment to verify the optimization range, and outputting a field temporary plugging and fracturing standardized scheme. The true triaxial hydraulic fracture temporary plugging and steering effect quantitative evaluation and optimization method can improve the quantitative evaluation efficiency.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development and hydraulic fracturing technology, and in particular to a method for quantitative evaluation and optimization of the effect of temporary plugging and redirection of hydraulic fractures under true triaxial conditions. Background Technology

[0002] Unconventional oil and gas reservoirs such as shale oil and gas and tight oil and gas have poor physical properties, with air permeability generally below 0.1 mD and porosity less than 10%, resulting in weak oil and gas flow capacity. Industrial development generally adopts hydraulic fracturing to construct a fracture network within the formation to improve production capacity. In-fracture temporary plugging and diversion is a core technology to increase the complexity of the fracture network and expand the reservoir stimulation volume. After the initial fracturing forms primary fractures, this technology introduces fiber and particulate temporary plugging agents into the fractures to form a high-resistance sealing zone, raising the net pressure within the fractures and forcing the formation to initiate and extend new fractures in a new direction. This technology is widely used in multi-cluster fracturing of horizontal wells and repeated fracturing of old wells.

[0003] True triaxial hydraulic fracturing physical simulation is a core indoor research method for revealing the mechanism of hydraulic fracture propagation and temporary plugging diversion. The complete set of equipment includes a cubic rock sample loading chamber, a simulated wellbore, an intermediate container for temporary plugging agent, a three-dimensional independent stress loading system, and a multi-channel data acquisition system. The conventional experimental procedure is to first pump fracturing hydraulic fluid to open the rock sample to form primary fractures, and then pump in a fluid mixed with temporary plugging agent. The secondary diversion of the fracture is achieved by relying on temporary plugging and pressure buildup.

[0004] Current methods rely solely on qualitative observation of crack morphology or single indicators such as modified area and fractal dimension to evaluate the effectiveness of temporary plugging. However, the redirection effect of temporary plugging includes multiple dimensions such as sealing capacity, new crack initiation capacity, crack propagation range, and crack network complexity. A single indicator cannot fully represent the true effect, and data from different experimental groups lack cross-comparison. Only the final crack morphology after temporary plugging is observed, without establishing a baseline for comparison between the primary crack and the secondary redirected crack. The data from the two process stages of plugging and redirection are fragmented, and the monitoring methods are limited, making it impossible to distinguish whether the new crack is caused by the pressure buildup from temporary plugging. Whether a crack can be effectively redirected depends on whether the pressure increase within the crack after temporary plugging reaches a critical value. However, current technologies rely solely on theoretical calculations to derive the critical pressure increase and critical horizontal stress difference, without forming a unified quantitative judgment method adapted to true triaxial indoor experiments. Although it is known that horizontal stress difference and the degree of development of natural cracks affect the redirection effect, there are no experimentally calibrated critical thresholds, resulting in a disconnect between theoretical calculations and indoor experimental data. Summary of the Invention

[0005] Technical objective: In order to overcome the shortcomings of the existing technology, this invention provides a method for quantitative evaluation and optimization of the temporary plugging and turning effect of hydraulic fractures under true triaxial conditions.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for quantitative evaluation and optimization of the temporary plugging and diversion effect of hydraulic fractures under true triaxial conditions, comprising the following steps:

[0007] S1, Obtain standard cubic rock samples;

[0008] The corresponding geostress loads were independently applied to the standard cubic rock sample in three orthogonal directions to obtain the rock sample test carrier. A fixed continuous constant flow rate was preset, and fracturing fluid was continuously pumped into the rock sample test carrier according to the fixed continuous constant flow rate. The initial comparison baseline of the original fracture was screened to obtain the original fracture benchmark dataset.

[0009] S2, Prepare the temporary plugging mixture injection solution;

[0010] According to a fixed continuous constant flow rate, a temporary plugging mixed injection fluid is pumped into the rock sample experimental carrier that has generated primary fractures inside, and a complete monitoring dataset of the temporary plugging stage is obtained. Then, pure fracturing fluid without any temporary plugging solid particles is switched to, and pure fracturing fluid is continuously pumped into the rock sample experimental carrier according to a fixed continuous constant flow rate to carry out secondary fracturing and fracture creation operations, and a complete monitoring dataset of the secondary fracturing stage is obtained. The three-dimensional morphological feature dataset of the fracture is collected by industrial CT three-dimensional reconstruction imaging.

[0011] S3, obtain a standardized construction plan based on the dataset;

[0012] By performing full-dimensional data quantification, the comprehensive steering effect index, critical pressure rise, and critical stress difference are obtained. Based on the comprehensive steering effect index, critical pressure rise, and critical stress difference, closed-loop parameter optimization is performed to obtain a standardized on-site temporary plugging steering fracturing construction plan that includes critical control indicators and is adapted to the target reservoir.

[0013] Preferably, S1 includes S101, which detects the vertical, maximum horizontal, and minimum horizontal triaxial geostress of the target reservoir;

[0014] The in-situ triaxial stress parameters of the reservoir were obtained, and standard cubic rock samples were acquired. A simulated wellbore was prefabricated inside the standard cubic rock samples and acoustic emission probes and pipeline pressure sensors were installed.

[0015] A standard cubic rock sample with all monitoring sensors installed is placed into a true triaxial independent pressure loading system. Based on the in-situ triaxial stress parameters of the reservoir, corresponding geostress loads are applied independently to the standard cubic rock sample in three orthogonal directions to obtain a rock sample experimental carrier that can completely replicate the real stress state of the underground reservoir.

[0016] A constant-speed, constant-pressure pump was used to perform constant-speed pump-controlled injection operation on the prefabricated wellbore of the rock sample test carrier. The time-series pressure signal was continuously collected in real time by a pressure sensor pre-installed on the injection pipeline.

[0017] Acoustic emission signals of crack propagation were collected by multi-channel acoustic emission probes deployed on the surface of the rock sample experimental carrier, and spatial positioning data of acoustic emission were obtained based on the crack propagation acoustic emission signals.

[0018] Preferably, S1 includes S102, which is a preset fixed continuous constant displacement;

[0019] Based on a fixed continuous flow rate, fracturing fluid was continuously pumped into the rock sample experimental carrier to obtain primary fracture extension data.

[0020] Preferably, S1 includes S103, which sets a preset threshold for crack extension;

[0021] When the original fracture extension data reaches the fracture extension threshold, the operation of continuously pumping fracturing fluid into the rock sample test carrier is stopped.

[0022] The time-series pressure data, acoustic emission spatial positioning data, and native crack propagation data obtained by converting the time-series pressure signal are stored and then uniformly collected to obtain the real-time monitoring data to be measured.

[0023] Redundant and interfering data related only to temporary plugging agent injection and secondary fracturing process are removed from the real-time monitoring data to be tested, and only the original fracture characteristics without temporary plugging interference generated in the primary fracturing stage are retained.

[0024] The primary fracture features obtained by collection and screening are used to establish the initial comparison baseline for initial hydraulic fracturing. Based on the initial comparison baseline, the primary fracture benchmark dataset is obtained. The primary fracture benchmark dataset includes four types of modeling parameters: initial fracturing pressure, initial stable fracture propagation pressure, initial fracture spatial orientation and morphology, and spatial distribution of acoustic emission events corresponding to the initial fracture propagation.

[0025] Preferably, S2 includes S201, selecting a temporary plugging agent of a preset type, preset particle size, and preset mass concentration and mixing it thoroughly with fracturing fluid to prepare a temporary plugging mixed injection solution;

[0026] Based on a fixed, continuous, constant discharge rate, a temporary plugging mixture was pumped into the rock sample experimental carrier with pre-existing primary fractures. During the entire pumping process of the temporary plugging mixture, the stable pressure inside the fracture at the beginning of the temporary plugging injection, the peak pressure increase during the temporary plugging process, the stable pressure inside the fracture at the end of the temporary plugging, the duration of pressure maintaining above 80% of the peak value, and the total injection time of the temporary plugging liquid were continuously collected to obtain a complete monitoring dataset for the temporary plugging stage.

[0027] Preferably, S2 includes S202, which detects the pressure change characteristics within the fissures of the rock sample experimental carrier;

[0028] The pressure change characteristics inside the fracture are obtained, and a pressure change threshold is preset. If the pressure change characteristics inside the fracture remain stable and the pressure change characteristics inside the fracture are less than or equal to the pressure change threshold, the temporary plugging agent delivery pipeline is closed and pure fracturing fluid without any temporary plugging solid particles is switched.

[0029] Based on a fixed continuous flow rate, pure fracturing fluid was continuously pumped into the rock sample experimental carrier to carry out secondary fracturing operations. The peak pressure of secondary fracture initiation, the stable propagation pressure of secondary fracture, the increase in initiation pressure relative to the pressure in the stable fracture at the end of the temporary plugging period of secondary fracture, and the spatial distribution of acoustic emission events corresponding to the propagation of secondary fracture were extracted and collected to obtain a complete monitoring dataset of the secondary fracturing stage.

[0030] Preferably, S2 includes S203, after the secondary fracturing process is completely completed, the rock sample experimental carrier prepared in the early stage is taken out as a whole from the true triaxial independent pressure loading system, and the industrial CT three-dimensional reconstruction imaging method is used to measure the projected area of ​​the primary fracture generated in the primary fracturing process, the effective extension length of the primary fracture, the reference azimuth angle of the primary fracture, and the projected area of ​​the secondary fracture and the extension azimuth angle of the secondary fracture generated in the secondary fracturing process.

[0031] Based on the reference azimuth of the primary crack and the propagation azimuth of the secondary crack, the spatial turning angle between the primary crack and the secondary crack is calculated.

[0032] The box-counting method was used to perform fractal calculations on the overall fracture network image within the rock sample experimental carrier to obtain the fractal dimension of the fracture network. The projected area of ​​the primary fracture, the effective extension length of the primary fracture, the reference azimuth angle of the primary fracture, the projected area of ​​the secondary fracture generated by the secondary fracturing process, the extension azimuth angle of the secondary fracture, the spatial turning angle, and the fractal dimension of the fracture network were collected to obtain a three-dimensional morphological feature dataset of the fracture.

[0033] Preferably, S3 includes S301, which involves performing hierarchical statistics on four-dimensional indicators—plugging efficiency, deflection initiation, deflection propagation, and fracture network complexity—based on the original fracture baseline dataset, the complete monitoring dataset of the temporary plugging stage, the complete monitoring dataset of the secondary fracturing stage, and the fracture three-dimensional morphological feature dataset, to obtain four-dimensional quantitative evaluation indicators.

[0034] Preferably, S3 includes S302, where a preset index corresponds to a weighting coefficient;

[0035] Based on the weight coefficients corresponding to the indicators, the four-dimensional quantitative evaluation indicators are weighted and summed to obtain the comprehensive turning effect index;

[0036] Multiple sets of control true triaxial experiments with different lithologies and different stress differences were conducted to obtain the control true triaxial experiment results. The experimental pressure and stress data were statistically analyzed to obtain the critical pressure rise and critical stress difference.

[0037] Preferably, S3 includes S303, acquiring various temporary blockage construction parameters, using the various temporary blockage construction parameters as independent variables and the comprehensive steering effect index as dependent variable, fitting and modeling the correspondence between parameters and evaluation index to obtain a construction parameter effect response model;

[0038] The critical pressure rise and critical stress difference are set as hard constraints. With the goal of maximizing the comprehensive steering effect index, the construction parameter effect response model is iteratively optimized to obtain the optimal combination of construction parameters.

[0039] The entire true triaxial simulation experiment was reproduced based on the optimal combination of construction parameters. The optimization effect was compared and verified by combining the critical pressure rise, critical stress difference and comprehensive turning effect index. The optimization gain was quantified and finally output as a standardized construction plan for on-site temporary plugging turning fracturing that includes critical control indicators and is adapted to the target reservoir.

[0040] The beneficial effects of this invention are:

[0041] 1. The method for quantitative evaluation and optimization of the temporary plugging and diversion effect of hydraulic fractures under true triaxial conditions provided by this invention calculates four quantitative indicators—plugging efficiency, diversion and fracture initiation capability, diversion and expansion degree, and fracture network complexity—in a hierarchical manner using a native fracture baseline dataset, a temporary plugging monitoring dataset, a secondary fracturing monitoring dataset, and a fracture three-dimensional morphological feature dataset. A unified comprehensive diversion effect index is obtained through weighted averaging, overcoming the shortcomings of existing technologies that rely solely on single indicators such as modified area and fractal dimension for qualitative evaluation. This method can comprehensively characterize the true effect of temporary plugging and diversion from multiple dimensions, including plugging, fracture initiation, expansion, and fracture network complexity. Evaluation results from different experimental groups and under different reservoir conditions have a unified quantitative standard, making them more comparable.

[0042] 2. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions provided by this invention simultaneously collects full data on pressure, acoustic emission, and fracture extension during the initial fracturing stage. It then removes interference information related to temporary plugging to construct a native fracture baseline dataset as a unified reference standard. Subsequently, it distinguishes between native fractures and newly redirected fractures by comparing temporary plugging and secondary fracturing data with the baseline data. This solves the problem of existing technologies that only observe the final fracture and cannot distinguish whether new fractures are generated by temporary plugging pressure buildup or randomly activated by natural fractures. It can accurately quantify the reservoir stimulation gain brought by the temporary plugging agent itself, and the attribution analysis is supported by scientific data.

[0043] 3. The quantitative evaluation and optimization method for the temporary plugging and diversion effect of hydraulic fractures under true triaxial conditions provided by this invention obtains the critical threshold for temporary plugging and diversion that can be directly applied based on statistical analysis of real experimental data through multiple sets of true triaxial experiments with varying lithology and varying horizontal stress differences. This eliminates the drawback of the disconnect between theoretical calculations and indoor simulation experimental results, and provides a unified and quantifiable experimental basis for judging whether the temporary plugging and diversion is successful.

[0044] 4. The quantitative evaluation and optimization method for the temporary plugging and diversion effect of hydraulic fracture under true triaxial conditions provided by this invention has built-in critical pressure rise and critical stress difference control indicators obtained from indoor experimental calibration in the final output construction plan. During field construction, the temporary plugging and diversion can be judged by real-time monitoring of the bottom hole pressure rise to determine whether the temporary plugging and diversion has met the standards. At the same time, it is equipped with a complete set of parameters such as the optimal temporary plugging agent concentration and injection rate verified by experiments, which directly guides the adjustment of the temporary plugging and diversion fracturing process in the field, effectively improving the success rate of the temporary plugging and diversion construction. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0046] Figure 1 This is a flowchart illustrating the steps of the present invention. Detailed Implementation

[0047] The following is in conjunction with the appendix Figure 1 The principles and features of the present invention are described, and the examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0048] Please see Figure 1 The present invention provides a method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions, comprising the following steps:

[0049] S1, Obtain standard cubic rock samples; S1 includes:

[0050] S101 detects the vertical, maximum horizontal, and minimum horizontal triaxial geostress of the target reservoir;

[0051] S102, preset fixed continuous constant displacement;

[0052] S103; Preset crack extension threshold;

[0053] The corresponding geostress loads were independently applied to the standard cubic rock sample in three orthogonal directions to obtain the rock sample test carrier. A fixed continuous constant flow rate was preset, and fracturing fluid was continuously pumped into the rock sample test carrier according to the fixed continuous constant flow rate. The initial comparison baseline of the original fracture was screened to obtain the original fracture benchmark dataset.

[0054] S2, preparation of the temporary plugging mixture injection solution; S2 includes:

[0055] S201, Select a temporary plugging agent of preset type, preset particle size, and preset mass concentration and mix it thoroughly with fracturing fluid to prepare a temporary plugging mixed injection solution;

[0056] S202, to detect the pressure change characteristics inside the fracture of the rock sample experimental carrier;

[0057] According to a fixed continuous constant flow rate, a temporary plugging mixed injection fluid is pumped into the rock sample experimental carrier that has generated primary fractures inside, and a complete monitoring dataset of the temporary plugging stage is obtained. Then, pure fracturing fluid without any temporary plugging solid particles is switched to, and pure fracturing fluid is continuously pumped into the rock sample experimental carrier according to a fixed continuous constant flow rate to carry out secondary fracturing and fracture creation operations, and a complete monitoring dataset of the secondary fracturing stage is obtained. The three-dimensional morphological feature dataset of the fracture is collected by industrial CT three-dimensional reconstruction imaging.

[0058] S3, obtain a standardized construction plan based on the dataset;

[0059] S301. Based on the original fracture baseline dataset, the complete monitoring dataset of the temporary plugging stage, the complete monitoring dataset of the secondary fracturing stage, and the fracture three-dimensional morphological feature dataset, the four-dimensional indicators of plugging efficiency, fracture initiation, fracture propagation, and fracture network complexity are hierarchically statistically analyzed to obtain four-dimensional quantitative evaluation indicators.

[0060] S302, preset indicator corresponding weight coefficient;

[0061] By performing full-dimensional data quantification, the comprehensive steering effect index, critical pressure rise, and critical stress difference are obtained. Based on the comprehensive steering effect index, critical pressure rise, and critical stress difference, closed-loop parameter optimization is performed to obtain a standardized on-site temporary plugging steering fracturing construction plan that includes critical control indicators and is adapted to the target reservoir.

[0062] Please see Figure 1 S101, detect the vertical, maximum horizontal and minimum horizontal triaxial stress of the target reservoir, obtain the in-situ triaxial stress parameters of the reservoir, obtain standard cubic rock samples, prefabricate a simulated wellbore inside the standard cubic rock samples and install acoustic emission probes and pipeline pressure sensors.

[0063] A standard cubic rock sample with all monitoring sensors installed is placed into a true triaxial independent pressure loading system. Based on the in-situ triaxial stress parameters of the reservoir, corresponding geostress loads are applied independently to the standard cubic rock sample in three orthogonal directions to obtain a rock sample experimental carrier that can completely replicate the real stress state of the underground reservoir.

[0064] A constant-speed, constant-pressure pump was used to perform constant-speed pump-controlled injection operation on the prefabricated wellbore of the rock sample test carrier. The time-series pressure signal was continuously collected in real time by a high-precision pressure sensor pre-installed on the injection pipeline.

[0065] Acoustic emission signals of fracture propagation are collected by multi-channel acoustic emission probes deployed on the surface of rock sample test carriers. Based on the acoustic emission signals of fracture propagation, acoustic emission spatial positioning data is obtained. For example, triaxial stress detection: reservoir hydraulic fracturing stress testing method is adopted, which is a common technology for in-situ stress detection in existing oilfields. If the vertical stress of the target shale reservoir measured by the downhole stress testing instrument is σ1=35MPa, the maximum horizontal stress is σ2=30MPa, and the minimum horizontal stress is σ3=25MPa, the in-situ triaxial stress parameters of the reservoir are obtained. Standard cubic rock sample processing: rock precision CNC machine tool, such as existing rock sample preparation equipment, is used to process 300mm×300mm standard shale rock samples. Wellbore and sensor deployment: CNC drilling equipment is used to prefabricate the wellbore. R15α type acoustic emission probe, such as commercial oil and gas simulation experimental sensors, and 0~100MPa high-precision pressure transmitter, with an accuracy of 0.1%FS, such as existing pipeline pressure detection standard equipment.

[0066] S102, preset with a fixed continuous constant discharge rate, continuously pumps fracturing fluid into the rock sample experimental carrier according to the fixed continuous constant discharge rate to obtain primary fracture extension data; True triaxial independent pressure loading system: large-size true triaxial physical simulation test machine, such as the mainstream equipment for existing shale fracturing indoor simulation, three-channel independent hydraulic loading, constant speed and constant pressure pump: a programmable metering pump for oil and gas experiments, used for constant speed fluid injection, time-series pressure signal acquisition: pressure transmitter with high-speed data acquisition instrument, such as existing pressure time-series acquisition equipment, outputs pressure time sequence in real time, acoustic emission spatial positioning: multi-channel acoustic emission acquisition system, such as existing mature fracture monitoring equipment, obtains acoustic emission spatial positioning data through P-wave time difference positioning algorithm, primary fracture extension data: synchronously integrates pressure curves and the number of acoustic emission events to comprehensively characterize the fracture extension scale.

[0067] S103; A preset fracture extension threshold is set. When the original fracture extension data reaches the fracture extension threshold, the operation of continuously pumping fracturing fluid into the rock sample test carrier is stopped.

[0068] The time-series pressure data, acoustic emission spatial positioning data, and native crack propagation data obtained by converting the time-series pressure signal are stored and uniformly collected to obtain the real-time monitoring data to be measured.

[0069] Redundant and interfering data related only to temporary plugging agent injection and secondary fracturing process are removed from the real-time monitoring data to be tested, and only the original fracture characteristics without temporary plugging interference generated in the primary fracturing stage are retained.

[0070] The primary fracture features obtained from the collection and screening are used to establish an initial comparison baseline for initial fracturing. Based on the initial comparison baseline, a primary fracture benchmark dataset is obtained. The primary fracture benchmark dataset includes four types of fixed parameters: initial fracturing pressure, initial stable fracture propagation pressure, initial fracture spatial orientation and morphology, and spatial distribution of acoustic emission events corresponding to initial fracture propagation. The fracture extension threshold is: the number of new acoustic emission events ≤ 5 in 60 seconds, and the pressure stability range fluctuation ≤ 0.5 MPa. As derived from experimental experience in shale examples, when the fracture has fully extended to a stable state, the fracture propagation activity is greatly reduced, and the pressure does not fluctuate significantly. This is used as the initial fracturing cessation standard to avoid excessive fracturing that damages the integrity of the rock sample. For example, the triaxial stress of shale reservoirs was tested at 35MPa / 30MPa / 25MPa; 300mm cubic shale samples were processed, a 12mm simulated wellbore was drilled in the center, 16 R15α acoustic emission probes were placed on the 6 sides of the sample, and a high-precision pressure transmitter was installed in the injection pipeline; the sample was loaded into a true triaxial testing machine and loaded at a rate of 0.5MPa / s to match the triaxial stress of the reservoir; a programmable metering pump injected slickwater at a fixed constant flow rate of 100mL / min, the pressure transmitter collected the time-series pressure every second, and the acoustic emission system located the fracture points in real time; The number of acoustic emission events and pressure fluctuations were simultaneously counted as primary fracture extension data. When the number of new acoustic emissions ≤5 and the pressure fluctuation ≤0.5MPa was monitored for 60 consecutive seconds, the extension threshold was reached and fluid injection was stopped. The data acquisition instrument collected time-series pressure data, acoustic emission location data, and fracture extension data to form real-time monitoring data to be measured. Subsequent temporary plugging and secondary fracturing irrelevant data were removed, and only the initial fracture creation data was retained. The initial fracture pressure of 42.5MPa, the propagation pressure of 28MPa, the fracture orientation, and the acoustic emission distribution were statistically obtained to generate the primary fracture baseline dataset.

[0071] S201, select a pre-set type, pre-set particle size, and pre-set mass concentration of temporary plugging agent and fracturing fluid, mix them thoroughly to prepare a temporary plugging mixture injection fluid; pump the temporary plugging mixture injection fluid into a rock sample test carrier with pre-existing primary fractures according to a fixed continuous constant flow rate; continuously collect data on the stable pressure within the fracture at the beginning of the temporary plugging injection, the peak pressure rise during the temporary plugging process, the stable pressure within the fracture at the end of the temporary plugging, the duration of pressure maintaining above 80% of the peak value, and the total injection time of the temporary plugging fluid during the entire pumping process, and compile a complete monitoring dataset for the temporary plugging stage; (e.g., stirring of the temporary plugging mixture: with stirring function) The equipment includes a container, standard equipment for true triaxial experiments, and an existing temporary plugging agent preparation device. Pressure acquisition during the temporary plugging stage is achieved using a high-precision pressure transmitter and high-speed data acquisition instrument, as explained earlier, continuously recording the pressure within the fracture. The type of temporary plugging agent is, for example, a fiber-particle composite temporary plugging agent. The particle size is adapted to the micro-fractures in shale. The preset mass concentration is 1.0%. In a single-factor control experiment, a concentration of 0.5% is insufficient for plugging, and 2.0% easily causes pipeline blockage; 1.0% is the baseline control concentration. The carrying fluid is selected from the initial fracturing slickwater, matching the sand-carrying medium used in on-site construction. Add slickwater carrying liquid to the intermediate mixing container, add a pre-set 1.0% concentration fiber-particle composite temporary plugging agent, stir for 5 minutes until uniformly suspended, maintain a constant discharge rate of 100 mL / min, and pump the temporary plugging mixture into the shale rock sample with the formed primary fracture. The pressure acquisition instrument continuously records the following throughout the process: the stable pressure in the fracture at the start of pumping is 28 MPa, the peak pressure increase is 10.5 MPa, the stable pressure at the end of the temporary plugging is 35 MPa, the duration of maintaining the peak pressure above 80% is 55 s, and the total injection time is 120 s. Collect all pressure time-series records to generate a complete monitoring dataset for the temporary plugging stage.

[0072] S202, detect the pressure change characteristics inside the fracture of the rock sample test carrier; obtain the pressure change characteristics inside the fracture, preset the pressure change threshold, if the pressure change characteristics inside the fracture remain stable and the pressure change characteristics inside the fracture are less than or equal to the pressure change threshold, then close the temporary plugging agent delivery pipeline and switch to pure fracturing fluid that does not contain any temporary plugging solid particles.

[0073] Based on a fixed, continuous, constant flow rate, pure fracturing fluid is continuously pumped into the rock sample experimental carrier to carry out secondary fracturing operations. The peak initiation pressure of the secondary fracture, the stable propagation pressure of the secondary fracture, the increase in initiation pressure relative to the stable fracture pressure at the end of the temporary plugging stage, and the spatial distribution of acoustic emission events corresponding to the secondary fracture propagation are extracted and compiled into a complete monitoring dataset for the secondary fracturing stage. Fracture pressure change detection: A high-precision pipeline pressure transmitter outputs a continuous pressure curve in real time. The pressure fluctuation amplitude per unit time is automatically calculated by data acquisition software. Existing mature algorithms for pressure fluctuation quantification are used. Pure fracturing delivery: A dual-path switching injection pipeline is used. The switching device is standard for true triaxial experiments and is existing equipment. Pressure change threshold: Fracture pressure fluctuation ≤ 0.3 MPa within 10 seconds. If the pressure curve characteristics are collected, the fracture pressure enters a stable range after the temporary plugging agent completes the sealing. Small fluctuations are only pump pulsations. Fluctuations exceeding 0.3 MPa indicate that the temporary plugging has not achieved stable sealing, and the injection of temporary plugging fluid needs to continue. The system continuously reads the intra-fracturing pressure data output by the pressure transmitter. The software calculates the pressure fluctuation amplitude every 10 seconds. When the fluctuation of three consecutive sets of data is ≤0.3MPa, it is determined that the stability threshold is met. The temporary plugging agent delivery is shut off through the dual-path switching pipeline, and pure slickwater without solid particles is switched to maintain a constant flow rate of 100mL / min for secondary fracturing. The system automatically extracts the secondary fracture pressure of 36.2MPa, the secondary propagation pressure of 30MPa, the pressure increase at the end of the relative temporary plugging period of 1.2MPa, and the distribution of acoustic emission points in the secondary fracture. All parameters are collected to generate a complete monitoring dataset for the secondary fracturing stage.

[0074] S2 includes S203. After the secondary fracturing process is completely completed, the rock sample experimental carrier prepared in the early stage is taken out as a whole from the true triaxial independent pressure loading system. Using industrial CT three-dimensional reconstruction imaging, the projected area of ​​the primary fracture generated in the primary fracturing process, the effective extension length of the primary fracture, the reference azimuth angle of the primary fracture, and the projected area of ​​the secondary fracture generated in the secondary fracturing process and the extension azimuth angle of the secondary fracture are measured respectively.

[0075] Based on the reference azimuth of the primary crack and the propagation azimuth of the secondary crack, the spatial turning angle between the primary crack and the secondary crack is calculated.

[0076] The box-counting method was used to perform fractal calculations on the overall fracture network image within the rock sample experimental carrier to obtain the fractal dimension of the fracture network. The projected area of ​​the primary fracture, the effective extension length of the primary fracture, the reference azimuth angle of the primary fracture, the projected area of ​​the secondary fracture generated by the secondary fracturing process, the extension azimuth angle of the secondary fracture, the spatial turning angle, and the fractal dimension of the fracture network were collected to obtain a three-dimensional morphological feature dataset of the fracture. Industrial CT three-dimensional reconstruction imaging: An industrial micron-level CT scanning system, a mature and universally applicable device for indoor three-dimensional fracture characterization, was used to scan the rock sample to obtain a three-dimensional grayscale image of the internal fracture. Fracture size and orientation measurement: CT-compatible three-dimensional image measurement software and existing commercial fracture parameter extraction tools were used. Turning angle calculation: The software has a built-in angle solving algorithm; the angle between two sets of fracture azimuth angles is automatically calculated. Fractal dimension calculation: A dedicated image processing program for the box-counting method and an industry-standard tool for calculating fracture network complexity were used. The theoretical maximum turning angle is fixed at 90°. The minimum fractal dimension of a simple double-wing fracture is 1.05, and the maximum fractal dimension of a complex fracture network is 1.75. A large amount of historical CT statistical data on shale fractures was used, representing a commonly used value range in the industry. After all secondary fracturing procedures are completed, the shale sample is removed from the true triaxial testing machine and sent to an industrial CT scanner for a complete scan, measuring the area of ​​the primary fracture at 185 cm². 2 Length, reference azimuth angle 0°, secondary crack area 98cm² 2 The azimuth angle is extended to 35°, the spatial turning angle is automatically calculated by the software to be 35°, and the box dimension program calculates the fractal dimension of the overall crack network to be 1.42; all parameters such as area, length, azimuth angle, turning angle and fractal dimension are collected to generate a three-dimensional morphological feature dataset of cracks.

[0077] S302, preset the weight coefficients corresponding to the indicators, and perform a weighted summation of the four-dimensional quantitative evaluation indicators based on the weight coefficients corresponding to the indicators to obtain the comprehensive turning effect index;

[0078] Multiple sets of controlled true triaxial experiments were conducted with different lithologies and different horizontal stress differences. The results of the controlled true triaxial experiments were obtained, and the experimental pressure and stress data were statistically analyzed to obtain the critical pressure rise and critical stress difference. Four-dimensional indexes and weighted calculations were performed using a Python data analysis program, which is a common tool for processing existing oil and gas experimental data. The controlled true triaxial experiments were conducted using the same set of true triaxial simulation testing machine, with only the lithology adjusted. Multiple sets of parallel tests were carried out for shale or sandstone and horizontal stress differences (5MPa / 9MPa / 12MPa). For example, the weight range of the four indexes is 0.15~0.40, and 0.25 is selected. If the sealing, fracturing, propagation, and fracture complexity are equally important in shale reservoir evaluation, and the sealing effect is emphasized, the weight of the sealing index can be increased to 0.4, and the others can be decreased, with the sum always being 1, to adapt to different reservoir evaluation focuses. Four datasets—primary fracture baseline, temporary plugging monitoring, secondary fracturing monitoring, and fracture morphology—were imported into the data analysis program. The following calculations were performed sequentially: plugging efficiency 0.172 (temporary plugging efficiency index = (peak pressure increase / initial fracture stable propagation pressure) × (peak pressure maintenance time / total injection time of temporary plugging fluid)); fracturing initiation capacity 14.8% (direction initiation capacity index = [(initial fracturing pressure − secondary fracture initiation peak pressure) / initial fracturing pressure] × 100%); propagation degree 0.304 (direction propagation degree index = (secondary fracture projected area / primary fracture projected area) × (sin fracture turning angle / sin theoretical maximum turning angle), where the theoretical maximum turning angle is fixed at 90°); and fracture network complexity 5. 2.9%, the complexity index of the crack network = [(fractal dimension of crack network − minimum fractal dimension of simple double-wing crack) / (maximum fractal dimension of complex crack network − minimum fractal dimension of simple double-wing crack)] × 100%, where the minimum fractal dimension of simple double-wing crack is 1.0~1.1, and the maximum fractal dimension of complex crack network is 1.6~1.8; the four-dimensional index, if weighted with equal weight of 0.25, yields a comprehensive steering effect index of 0.288; multiple sets of horizontal stress difference gradient parallel experiments are set up, and the pressure rise of all successful steering experiment groups is extracted. If the minimum value of 9.8MPa is defined as the critical pressure rise, the horizontal stress difference-comprehensive index curve is plotted. The maximum stress difference of 12MPa corresponding to the comprehensive index ≥ 0.6 is the critical stress difference.

[0079] S3 includes S303, which involves acquiring various temporary blockage construction parameters, using the various temporary blockage construction parameters as independent variables and the comprehensive steering effect index as dependent variables, fitting and modeling the correspondence between parameters and evaluation indexes to obtain a construction parameter effect response model.

[0080] The critical pressure rise and critical stress difference are set as hard constraints. With the goal of maximizing the comprehensive steering effect index, the construction parameter effect response model is iteratively optimized to obtain the optimal combination of construction parameters.

[0081] The entire true triaxial simulation experiment was reproduced based on the optimal combination of construction parameters. The optimization effect was compared and verified by combining the critical pressure rise, critical stress difference, and comprehensive turning effect index. The optimization gain was quantified, and the final output included a standardized construction plan for on-site temporary plugging turning fracturing that was adapted to the target reservoir and included critical control indicators. Response surface fitting: Multivariate regression data analysis software, a mature tool for modeling existing experimental data; Iterative optimization algorithm: Open source programs of genetic algorithm or particle swarm optimization algorithm, a general intelligent algorithm for oil and gas parameter optimization; Verification experiment: A complete set of true triaxial simulation experimental equipment was used to reproduce the complete experimental process described above; The critical pressure rise of 9.8 MPa and the critical stress difference of 12 MPa were used as hard constraints. The critical threshold of shale reservoir calibrated by multiple sets of control experiments must meet the experimental results corresponding to the optimized parameters; otherwise, effective fracture turning cannot be achieved on-site. Two core construction parameters, temporary plugging agent concentration and injection rate, were selected as independent variables, and the comprehensive diversion effect index was selected as the dependent variable. Based on seven sets of single-factor experimental data, a response surface model was fitted and constrained for optimization: the optimization results corresponded to an experimental pressure increase ≥ 9.8 MPa and a horizontal stress difference ≤ 12 MPa. The optimal concentration of 1.4% and the optimal injection rate of 158 mL / min were obtained by iterative solution with the goal of maximizing the comprehensive index. The entire set of true triaxial experiments was completely reproduced using these optimal parameters. The comprehensive index of the verification group was calculated to be 0.342, compared to 0.288 in the baseline group, with a quantitative optimization gain of 19%. By integrating the critical pressure increase of 9.8 MPa, the critical stress difference of 12 MPa, and the optimal temporary plugging parameters, a standardized construction scheme for on-site temporary plugging and diversion adapted to this shale reservoir was output.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A quantitative evaluation and optimization method for the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions, characterized by: Includes the following steps: S1, Obtain standard cubic rock samples; The corresponding geostress loads were independently applied to the standard cubic rock sample in three orthogonal directions to obtain the rock sample test carrier. A fixed continuous constant flow rate was preset, and fracturing fluid was continuously pumped into the rock sample test carrier according to the fixed continuous constant flow rate. The initial comparison baseline of the original fracture was screened to obtain the original fracture benchmark dataset. S2, Prepare the temporary plugging mixture injection solution; According to a fixed continuous constant flow rate, a temporary plugging mixed injection fluid is pumped into the rock sample experimental carrier that has generated primary fractures inside, and a complete monitoring dataset of the temporary plugging stage is obtained. Then, pure fracturing fluid without any temporary plugging solid particles is switched to, and pure fracturing fluid is continuously pumped into the rock sample experimental carrier according to a fixed continuous constant flow rate to carry out secondary fracturing and fracture creation operations, and a complete monitoring dataset of the secondary fracturing stage is obtained. The three-dimensional morphological feature dataset of the fracture is collected by industrial CT three-dimensional reconstruction imaging. S3, obtain a standardized construction plan based on the dataset; By performing full-dimensional data quantification, the comprehensive steering effect index, critical pressure rise, and critical stress difference are obtained. Based on the comprehensive steering effect index, critical pressure rise, and critical stress difference, closed-loop parameter optimization is performed to obtain a standardized on-site temporary plugging steering fracturing construction plan that includes critical control indicators and is adapted to the target reservoir.

2. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions as described in claim 1, characterized in that: S1 includes S101, which detects the vertical, maximum horizontal, and minimum horizontal triaxial geostress of the target reservoir. The in-situ triaxial stress parameters of the reservoir were obtained, and standard cubic rock samples were acquired. A simulated wellbore was prefabricated inside the standard cubic rock samples and acoustic emission probes and pipeline pressure sensors were installed. A standard cubic rock sample with all monitoring sensors installed is placed into a true triaxial independent pressure loading system. Based on the in-situ triaxial stress parameters of the reservoir, corresponding geostress loads are applied independently to the standard cubic rock sample in three orthogonal directions to obtain a rock sample experimental carrier that can completely replicate the real stress state of the underground reservoir. A constant-speed, constant-pressure pump was used to perform constant-speed pump-controlled injection operation on the prefabricated wellbore of the rock sample test carrier. The time-series pressure signal was continuously collected in real time by a pressure sensor pre-installed on the injection pipeline. Acoustic emission signals of crack propagation were collected by multi-channel acoustic emission probes deployed on the surface of the rock sample experimental carrier, and spatial positioning data of acoustic emission were obtained based on the crack propagation acoustic emission signals.

3. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions as described in claim 2, characterized in that: S1 includes S102, which is a preset fixed continuous constant displacement. Based on a fixed continuous flow rate, fracturing fluid was continuously pumped into the rock sample experimental carrier to obtain primary fracture extension data.

4. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions as described in claim 3, characterized in that: S1 includes S103, which is a preset threshold for crack extension to meet the standard. When the original fracture extension data reaches the fracture extension threshold, the operation of continuously pumping fracturing fluid into the rock sample test carrier is stopped. The time-series pressure data, acoustic emission spatial positioning data, and native crack propagation data obtained by converting the time-series pressure signal are stored and then uniformly collected to obtain the real-time monitoring data to be measured. Redundant and interfering data related only to temporary plugging agent injection and secondary fracturing process are removed from the real-time monitoring data to be tested, and only the original fracture characteristics without temporary plugging interference generated in the primary fracturing stage are retained. The primary fracture features obtained by collection and screening are used to establish the initial comparison baseline for initial hydraulic fracturing. Based on the initial comparison baseline, the primary fracture benchmark dataset is obtained. The primary fracture benchmark dataset includes four types of modeling parameters: initial fracturing pressure, initial stable fracture propagation pressure, initial fracture spatial orientation and morphology, and spatial distribution of acoustic emission events corresponding to the initial fracture propagation.

5. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions as described in claim 4, characterized in that: S2 includes S201, which involves selecting a temporary plugging agent of a preset type, preset particle size, and preset mass concentration and mixing it thoroughly with fracturing fluid to prepare a temporary plugging mixed injection solution. Based on a fixed, continuous, constant discharge rate, a temporary plugging mixture was pumped into the rock sample experimental carrier with pre-existing primary fractures. During the entire pumping process of the temporary plugging mixture, the stable pressure inside the fracture at the beginning of the temporary plugging injection, the peak pressure increase during the temporary plugging process, the stable pressure inside the fracture at the end of the temporary plugging, the duration of pressure maintaining above 80% of the peak value, and the total injection time of the temporary plugging liquid were continuously collected to obtain a complete monitoring dataset for the temporary plugging stage.

6. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions as described in claim 5, characterized in that: S2 includes S202, which detects the pressure change characteristics within the fissures of the rock sample experimental carrier; The pressure change characteristics inside the fracture are obtained, and a pressure change threshold is preset. If the pressure change characteristics inside the fracture remain stable and the pressure change characteristics inside the fracture are less than or equal to the pressure change threshold, the temporary plugging agent delivery pipeline is closed and pure fracturing fluid without any temporary plugging solid particles is switched. Based on a fixed continuous flow rate, pure fracturing fluid was continuously pumped into the rock sample experimental carrier to carry out secondary fracturing operations. The peak pressure of secondary fracture initiation, the stable propagation pressure of secondary fracture, the increase in initiation pressure relative to the pressure in the stable fracture at the end of the temporary plugging period of secondary fracture, and the spatial distribution of acoustic emission events corresponding to the propagation of secondary fracture were extracted and collected to obtain a complete monitoring dataset of the secondary fracturing stage.

7. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions as described in claim 6, characterized in that: S2 includes S203, after the secondary fracturing process is completely completed, the rock sample experimental carrier prepared in the early stage is taken out as a whole from the true triaxial independent pressure loading system, and the industrial CT three-dimensional reconstruction imaging method is used to measure the projected area of ​​the primary fracture generated in the primary fracturing process, the effective extension length of the primary fracture, the reference azimuth angle of the primary fracture, and the projected area of ​​the secondary fracture and the extension azimuth angle of the secondary fracture generated in the secondary fracturing process. Based on the reference azimuth of the primary crack and the propagation azimuth of the secondary crack, the spatial turning angle between the primary crack and the secondary crack is calculated. The box-counting method was used to perform fractal calculations on the overall fracture network image within the rock sample experimental carrier to obtain the fractal dimension of the fracture network. The projected area of ​​the primary fracture, the effective extension length of the primary fracture, the reference azimuth angle of the primary fracture, the projected area of ​​the secondary fracture generated by the secondary fracturing process, the extension azimuth angle of the secondary fracture, the spatial turning angle, and the fractal dimension of the fracture network were collected to obtain a three-dimensional morphological feature dataset of the fracture.

8. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions as described in claim 7, characterized in that: S3 includes S301, which involves performing hierarchical statistics on four-dimensional indicators—plugging efficiency, directional fracture initiation, directional fracture propagation, and fracture network complexity—based on the original fracture baseline dataset, the complete monitoring dataset of the temporary plugging stage, the complete monitoring dataset of the secondary fracturing stage, and the fracture three-dimensional morphological feature dataset, to obtain four-dimensional quantitative evaluation indicators.

9. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions as described in claim 8, characterized in that: S3 includes S302, where a preset index corresponds to a weighting coefficient; Based on the weight coefficients corresponding to the indicators, the four-dimensional quantitative evaluation indicators are weighted and summed to obtain the comprehensive turning effect index; Multiple sets of control true triaxial experiments with different lithologies and different stress differences were conducted to obtain the control true triaxial experiment results. The experimental pressure and stress data were statistically analyzed to obtain the critical pressure rise and critical stress difference.

10. The method for quantitative evaluation and optimization of the temporary plugging and redirection effect of hydraulic fractures under true triaxial conditions as described in claim 9, characterized in that: S3 includes S303, which involves acquiring various temporary blockage construction parameters, using the various temporary blockage construction parameters as independent variables and the comprehensive steering effect index as dependent variables, fitting and modeling the correspondence between the parameters and the evaluation index to obtain a construction parameter effect response model. The critical pressure rise and critical stress difference are set as hard constraints. With the goal of maximizing the comprehensive steering effect index, the construction parameter effect response model is iteratively optimized to obtain the optimal combination of construction parameters. The entire true triaxial simulation experiment was reproduced based on the optimal combination of construction parameters. The optimization effect was compared and verified by combining the critical pressure rise, critical stress difference and comprehensive turning effect index. The optimization gain was quantified and finally output as a standardized construction plan for on-site temporary plugging turning fracturing that includes critical control indicators and is adapted to the target reservoir.

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