A method and apparatus for fracture characterization of a shale

Abstract

The present application relates to oil and gas field exploration and development technical field, disclose a kind of shale fracture characterization method and device, method includes: in simulated formation environment to shale is applied non-uniform stress field and maintains preset pressure and simulated formation environment is heated to preset temperature;Multiple scale fractures on shale are collected and based on the parameter of each fracture to obtain corresponding scale fracture index;Based on each fracture index and the parameter of multiple scale fractures to obtain multi-scale fracture comprehensive index;Based on multi-scale fracture comprehensive index, preset pressure, preset temperature and the initial pressure and initial temperature of simulated formation environment to obtain the multi-scale fracture evolution index of shale.The scheme presented in the present application can capture the initiation, propagation and connectivity behavior of nano, micro and macro scale fractures, and collect the parameters of each fracture to calculate the multi-scale fracture comprehensive index and evolution index, realizing the quantitative characterization of shale multi-scale fractures under in-situ temperature, pressure and stress conditions.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field exploration and development technology, specifically to a method and apparatus for characterizing fractures in shale. Background Technology

[0002] With the increasing demand for shale oil and gas resource development, hydraulic fracturing technology, as a core means of reservoir stimulation, has made the study of its fracture network formation mechanism and evolution law a key scientific issue. However, existing technologies for the dynamic characterization of multi-scale fractures in shale still have significant limitations: traditional indoor fracturing experimental devices mostly use static loading methods, which are difficult to accurately reflect the dynamic propagation behavior of fractures under the multi-field coupling effect of underground reservoirs; although numerical simulation methods can achieve multi-scale modeling, the lack of a cross-scale parameter transfer mechanism leads to insufficient accuracy in characterizing the dynamic evolution correlation of micro-meso-macro fracture networks. In addition, existing experimental devices generally lack the ability to accurately simulate high-temperature and high-pressure environments and formation stress conditions, and a quantitative index system for fracture morphology has not yet been established, which seriously restricts the reliability of fracturing scheme optimization and production prediction.

[0003] Therefore, developing a technology and method that can integrate in-situ dynamic evolution observation of multi-scale fractures, simulation of multi-physics field coupling effects, and quantitative characterization has become a critical technical bottleneck that needs to be overcome for the efficient development of shale gas. Summary of the Invention

[0004] This invention summarizes various aspects of the embodiments and should not be construed as limiting the claims. Other embodiments are contemplated based on the technology described herein, as will be apparent to those skilled in the art upon studying the following drawings and detailed descriptions, and these embodiments are intended to be included within the scope of this application.

[0005] In view of this, in order to overcome at least one aspect of the above-mentioned problems, embodiments of the present invention propose a method for characterizing fractures in shale, comprising the steps of: A non-uniform stress field is applied to shale in a simulated geological environment while maintaining a preset pressure, and the simulated geological environment is heated to a preset temperature. Parameters of fractures at multiple scales on the shale were collected, and the fracture index at the corresponding scale was obtained based on the parameters of each fracture. A multi-scale crack composite index is obtained based on each crack index and parameters of cracks at multiple scales. The multi-scale fracture evolution index of shale is obtained based on the multi-scale fracture comprehensive index, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment.

[0006] In some embodiments, collecting parameters of fractures at multiple scales on the shale and obtaining a fracture index at the corresponding scale based on the parameters of each fracture further includes: The elastic modulus, surface fractal dimension, crack density per unit area, length, and angle with the principal stress direction of the nanoscale cracks on the shale were collected, and the nanoscale crack index was obtained based on the elastic modulus, surface fractal dimension, and crack density per unit area of ​​the nanoscale cracks. The length, width, scanning area, number, and angle with the principal stress direction of the micron-scale cracks on the shale were collected, and the micron-scale crack index was obtained based on the length, width, scanning area, and number of the micron-scale cracks. The total number of acoustic emission events, average event energy, length, and angle with the principal stress direction of macroscopic fractures on the shale are collected, and the macroscopic fracture index is obtained based on the total number of acoustic emission events, average event energy, and volume of the shale.

[0007] In some embodiments, it also includes: The elastic modulus, surface fractal dimension, crack density per unit area, length, and angle with the principal stress direction of nanoscale cracks on the shale were collected using nanoindentation probes and atomic force microscope probes. The length, width, scanning area, number, and angle with the principal stress direction of micron-scale cracks on the shale were collected using the laser emitter of a laser confocal microscope. The total number of acoustic emission events, average event energy, length, and angle with the principal stress direction of macroscopic cracks on the shale were collected using an acoustic emission sensor array.

[0008] In some embodiments, a multi-scale crack composite index is obtained based on parameters of each crack index and cracks at multiple scales, further including: Obtain the first weight, second weight, and third weight; Determine the connectivity coefficients; The multi-scale crack comprehensive index is obtained based on the first weight and the nanoscale crack index, the second weight and the microscale crack index, the third weight and the macroscale crack index, and the connectivity coefficient.

[0009] In some embodiments, obtaining the first weight, the second weight, and the third weight further includes: Obtain the nanoscale fracture index, micrometer scale fracture index, and macroscale fracture index corresponding to the multiple shale formations; Multiple nanoscale crack indices, micrometer-scale crack indices, and macroscale crack indices were standardized separately. Based on the standardized data, the information entropy corresponding to the nanoscale crack index, micrometer scale crack index and macroscale crack index were calculated respectively. The first weight, the second weight, and the third weight are obtained based on the information entropy corresponding to the nanoscale crack index, the microscale crack index, and the macroscale crack index.

[0010] In some embodiments, determining the connectivity coefficient further includes: Determine the crack connectivity factor and the crack critical connectivity threshold; The connectivity coefficient is determined based on the crack connectivity factor and the crack critical connectivity threshold.

[0011] In some embodiments, determining the crack connectivity factor further includes: The crack connectivity factor is determined based on the length of each crack and the angle between it and the principal stress direction.

[0012] In some embodiments, determining the critical connectivity threshold of the crack further includes: Obtain the nanoscale fracture index, micrometer scale fracture index, and macroscale fracture index corresponding to the multiple shale formations; The development index is obtained based on the first weight, the second weight, the third weight, and the nanoscale fracture index, microscale fracture index, and macroscale fracture index corresponding to each shale. The critical connectivity threshold of the crack is determined based on the development index and the crack connectivity factor.

[0013] In some embodiments, the multi-scale fracture evolution index of shale is obtained based on the multi-scale fracture comprehensive index, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment, further including: Based on the preset pressure, initial pressure, preset temperature, and initial temperature corresponding to multiple shale formations, an independent variable matrix is ​​constructed, and the corresponding dependent variable matrix is ​​obtained. The independent variable matrix and the dependent variable matrix are calculated based on the least squares method of multiple linear regression to obtain the first weight coefficient and the second weight coefficient. The weighting coefficients are obtained based on the first weighting coefficient, the second weighting coefficient, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment; The multi-scale fracture evolution index of shale is obtained based on the multi-scale fracture comprehensive index and the weighting coefficient.

[0014] Based on the same inventive concept, according to another aspect of the present invention, embodiments of the present invention also provide an apparatus for characterizing fractures in shale, comprising: The in-situ condition simulation module is used to apply a non-uniform stress field to shale in a simulated formation environment and maintain a preset pressure, as well as to heat the simulated formation environment to a preset temperature. The dynamic monitoring module is used to collect parameters of cracks at multiple scales on the shale and obtain the crack index at the corresponding scale based on the parameters of each crack. The calculation module is used to obtain a multi-scale crack composite index based on each crack index and parameters of cracks at multiple scales. The quantitative characterization module is used to obtain the multi-scale fracture evolution index of shale based on the multi-scale fracture comprehensive index, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment.

[0015] The present invention has one of the following beneficial technical effects: The proposed solution can accurately simulate the multi-field coupling environment of the formation and capture the initiation, expansion and connectivity behavior of nanoscale fractures, microscale fractures and macroscale fractures. It can also collect the parameters of each fracture to calculate the comprehensive index and evolution index of multi-scale fractures, and realize the dynamic evolution of shale multi-scale fractures under in-situ temperature, pressure and stress conditions, and quantitative characterization. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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 embodiments can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart of a method for characterizing cracks in shale provided for embodiments of the present invention; Figure 2 A schematic diagram of an apparatus for characterizing fractures in shale, provided as an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0019] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0020] According to one aspect of the present invention, embodiments of the present invention provide a method for characterizing fractures in shale, such as... Figure 1 As shown, it may include the following steps: S1, applying a non-uniform stress field to the shale in a simulated formation environment while maintaining a preset pressure, and heating the simulated formation environment to a preset temperature; S2, collect parameters of fractures at multiple scales on the shale and obtain the fracture index at the corresponding scale based on the parameters of each fracture. S3, based on the parameters of each crack index and cracks at multiple scales, yields a multi-scale crack composite index. S4. Based on the multi-scale fracture comprehensive index, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment, the multi-scale fracture evolution index of shale is obtained.

[0021] The proposed solution can accurately simulate the multi-field coupling environment of the formation and capture the initiation, expansion and connectivity of nanoscale, microscale and macroscale fractures. It also collects the parameters of each fracture to calculate the comprehensive index and evolution index of multi-scale fractures, realizing the dynamic evolution of shale multi-scale fractures under in-situ temperature, pressure and stress conditions, and quantitative characterization.

[0022] In some embodiments, an arbitrary cubic shale sample (2mm×2mm×3mm) is selected, placed in a core holder, and the sealed chamber is filled with fluid simulating the formation environment. Simultaneously, a fluorescence injection system is activated to inject fluorescence. After the sample is completely filled with fluid, the stress gradients in the x, y, and z axes are independently adjusted using a true triaxial loading system to simulate the non-uniform stress field of the formation. Combined with an in-situ temperature-pressure coupling unit, the experimental environment is heated to the target reservoir temperature (80-150°C) and the pressure is maintained (20-50MPa).

[0023] The sealed chamber uses a multi-core fiber optic connector to connect the probe and laser to the sample inside. The multi-core fiber optic connector enables signal transmission and ensures the high airtightness of the sealed chamber. The sealed chamber has high sealing performance and is resistant to high temperature and high pressure. At the same time, all devices inside the sealed chamber are resistant to high temperature and high pressure.

[0024] During this process, the multi-scale crack dynamic monitoring module is activated simultaneously: the nanoindentation probe and the atomic force microscope probe scan the sample surface in real time to capture the initiation location of nanoscale cracks and changes in surface energy; the laser emitter of the laser confocal microscope tracks the three-dimensional propagation path and seepage efficiency of micron-scale cracks through the fluorescence injected into the sample; and the acoustic emission sensor array inverts the spatial distribution and dynamic propagation rate of macroscopic cracks through acoustic signals.

[0025] The in-situ multi-field coupled control module dynamically adjusts the stress loading rate, fluid injection pressure, and temperature and pressure parameters based on real-time monitoring data, forming a closed-loop control system of "monitoring-feedback-regulation." The data processing module establishes quantitative characterization parameters for fractures at various scales and combines them with fracture connectivity factors to generate a comprehensive multi-scale fracture index for shale using weighting coefficients. Simultaneously, it quantifies the evolution process of multi-scale shale fractures into a multi-scale fracture evolution index by incorporating temperature and pressure. This dynamic coupling of multiple physics fields enables accurate simulation and quantitative characterization of fracture evolution, significantly improving the controllability and characterization efficiency of complex fracture network formation.

[0026] In some embodiments, collecting parameters of fractures at multiple scales on the shale and obtaining a fracture index at the corresponding scale based on the parameters of each fracture further includes: The elastic modulus, surface fractal dimension, crack density per unit area, length, and angle with the principal stress direction of the nanoscale cracks on the shale were collected, and the nanoscale crack index was obtained based on the elastic modulus, surface fractal dimension, and crack density per unit area of ​​the nanoscale cracks. The length, width, scanning area, number, and angle with the principal stress direction of the micron-scale cracks on the shale were collected, and the micron-scale crack index was obtained based on the length, width, scanning area, and number of the micron-scale cracks. The total number of acoustic emission events, average event energy, length, and angle with the principal stress direction of macroscopic fractures on the shale are collected, and the macroscopic fracture index is obtained based on the total number of acoustic emission events, average event energy, and volume of the shale.

[0027] Specifically, nanoscale cracks are dominated by local mechanical properties and surface morphology. Furthermore, crack density reflects the degree of damage accumulation. Therefore, we define a parameter characterizing nanoscale cracks—the nanoscale crack index—using elastic modulus, surface fractal dimension, and crack density per unit area. The calculation formula is as follows:

[0028] Where D is the fractal dimension of the crack surface; Crack density per unit area (cracks / mm²) 2 E represents the local elastic modulus of nanoindentation (GPa); k1 and This is a normalization factor introduced to eliminate the units of the remaining parameters. GPa; strips / mm 2 .

[0029] Micrometer-scale fractures are the main channels for seepage, and their length and width directly determine fluid flow efficiency. A parameter characterizing micrometer-scale fractures, the Micrometer-Scale Fracture Index (SFI), is defined by selecting the fracture length, fracture width, and scanned area. The calculation formula is as follows:

[0030] in, Let be the length (μm) of the i-th crack. Let A be the width of the i-th crack (μm); and let A be the area of ​​the scanned region (μm). 2 ); n is the total number of cracks in the region.

[0031] The dynamic propagation of macroscopic cracks can be directly captured by acoustic emission signals, whose energy and frequency reflect the overall activity and damage scale of the crack network. A parameter characterizing micron-scale cracks, the Micron-Scale Crack Index (MFI), is defined using the total number of acoustic emission events and the average event energy. The calculation formula is as follows:

[0032] Where N is the total number of acoustic emission events; V is the average event energy (aJ); V is the sample volume (mm³). 3 k2 is the introduced normalization factor. aJ / mm 3 .

[0033] In some embodiments, it also includes: The elastic modulus, surface fractal dimension, crack density per unit area, length, and angle with the principal stress direction of nanoscale cracks on the shale were collected using nanoindentation probes and atomic force microscope probes. The length, width, scanning area, number, and angle with the principal stress direction of micron-scale cracks on the shale were collected using the laser emitter of a laser confocal microscope. The total number of acoustic emission events, average event energy, length, and angle with the principal stress direction of macroscopic cracks on the shale were collected using an acoustic emission sensor array.

[0034] Specifically, nanoscale cracks can be quantitatively characterized by obtaining the elastic modulus, surface fractal dimension, crack density per unit area, length, and angle with the principal stress direction of nanoscale cracks using nanoindentation probes and atomic force microscope probes, respectively. The length, width, scanning area, number, and angle with the principal stress direction of micron-sized cracks are obtained using the laser emitter of a laser confocal microscope to quantitatively characterize micron-sized cracks. Macroscale cracks are quantitatively characterized by the total number of acoustic emission events, average event energy, length, and angle with the principal stress direction of macroscopic cracks obtained by an acoustic emission sensor array.

[0035] By integrating a four-dimensional observation system consisting of a nanoindentation probe, an atomic force microscope, a laser confocal microscope, and an acoustic emission sensor array, the morphological features, propagation trajectory, and mechanical response of cracks at different scales can be captured in real time.

[0036] In some embodiments, a multi-scale crack composite index is obtained based on parameters of each crack index and cracks at multiple scales, further including: Obtain the first weight, second weight, and third weight; Determine the connectivity coefficients; The multi-scale crack comprehensive index is obtained based on the first weight and the nanoscale crack index, the second weight and the microscale crack index, the third weight and the macroscale crack index, and the connectivity coefficient.

[0037] Specifically, a parameter that can comprehensively characterize multi-scale fractures in shale can be defined by combining fracture connectivity: the Multi-Scale Fracture Index (MSFI), whose calculation formula is as follows:

[0038] Wherein, NFI is the nanoscale crack index; SFI is the microscale crack index; MFI is the macroscale crack index; CF is the crack connectivity factor; C is the critical connectivity threshold; and a, b, and c are weighting coefficients.

[0039] In some embodiments, obtaining the first weight, the second weight, and the third weight further includes: Obtain the nanoscale fracture index, micrometer scale fracture index, and macroscale fracture index corresponding to the multiple shale formations; Multiple nanoscale crack indices, micrometer-scale crack indices, and macroscale crack indices were standardized separately. Based on the standardized data, the information entropy corresponding to the nanoscale crack index, micrometer scale crack index and macroscale crack index were calculated respectively. The first weight, the second weight, and the third weight are obtained based on the information entropy corresponding to the nanoscale crack index, the microscale crack index, and the macroscale crack index.

[0040] Specifically, if there are m groups of shale sample data, the nanoscale fracture index in the j-th sample is: The micron-scale crack index is The macro-scale crack index is First, the data obtained from the NFI, SFI, and MFI indices of each shale were standardized:

[0041] Where g is the index number, g=1 is the nanoscale crack index, g=2 is the microscale crack index, and g=3 is the macroscale crack index. This represents the minimum value of the g-th index in the m-th sample group. The maximum value of the g-th index in the m-th sample group; The value is the standardized value, which takes the range [0, 1].

[0042] Based on the standardized data, calculate the weight of the g-th indicator in the j-th sample group. :

[0043] Based on specific gravity Calculate the information entropy of the g-th index. Information entropy reflects the information redundancy of an indicator. The smaller the entropy value, the greater the dispersion of the indicator's value, the more effective evaluation information it can provide, and the higher its weight should be; conversely, the larger the entropy value, the lower the weight. The calculation formula is:

[0044] in, The sample size normalization coefficient is the natural logarithm, which guarantees... ∈[0,1]; Let g be the information entropy of the g-th indicator. The closer the value is to 0, the greater the contribution of the indicator to the comprehensive evaluation of cracks.

[0045] Calculate the coefficient of difference for the g-th indicator. The coefficient of difference reflects the discriminative power of an indicator, and its formula is:

[0046] Normalizing the difference coefficients yields the entropy weights for each indicator. These weights satisfy non-negativity and normalization (a+b+c=1), as shown in the formula:

[0047] Finally, the weighting coefficients can be derived:

[0048]

[0049]

[0050] In some embodiments, determining the connectivity coefficient further includes: Determine the crack connectivity factor and the crack critical connectivity threshold; The connectivity coefficient is determined based on the crack connectivity factor and the crack critical connectivity threshold.

[0051] In some embodiments, determining the crack connectivity factor further includes: The crack connectivity factor is determined based on the length of each crack and the angle between it and the principal stress direction.

[0052] Specifically, the fracture connectivity factor (CF) is an important indicator characterizing the connectivity of fractures, and its calculation formula is as follows:

[0053] in, The length of the i-th crack (mm); θ is the angle between the crack and the principal stress direction; n is the total number of cracks.

[0054] In some embodiments, determining the critical connectivity threshold of the crack further includes: Obtain the nanoscale fracture index, micrometer scale fracture index, and macroscale fracture index corresponding to the multiple shale formations; The development index is obtained based on the first weight, the second weight, the third weight, and the nanoscale fracture index, microscale fracture index, and macroscale fracture index corresponding to each shale. The critical connectivity threshold of the crack is determined based on the development index and the crack connectivity factor.

[0055] Specifically, after obtaining the first weight, the second weight, and the third weight, the development index can be obtained using the first weight, the second weight, the third weight, and the corresponding nanoscale fracture index, microscale fracture index, and macroscale fracture index for each shale.

[0056] It can reflect the degree of crack development, and Reflecting the connectivity of the cracks, therefore the product of the two is... This method can comprehensively characterize the crack development of each group of samples and take their average value. It can reflect the overall characteristics of the entire batch of experimental samples and is the core statistic for calibrating the connectivity threshold C.

[0057] First, calculate the product of each group of samples. Then calculate their arithmetic mean:

[0058] Simultaneously calculate all samples Arithmetic mean:

[0059] Finally, the connectivity threshold C is obtained: .

[0060] In some embodiments, the multi-scale fracture evolution index of shale is obtained based on the multi-scale fracture comprehensive index, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment, further including: Based on the preset pressure, initial pressure, preset temperature, and initial temperature corresponding to multiple shale formations, an independent variable matrix is ​​constructed, and the corresponding dependent variable matrix is ​​obtained. The independent variable matrix and the dependent variable matrix are calculated based on the least squares method of multiple linear regression to obtain the first weight coefficient and the second weight coefficient. The weighting coefficients are obtained based on the first weighting coefficient, the second weighting coefficient, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment; The multi-scale fracture evolution index of shale is obtained based on the multi-scale fracture comprehensive index and the weighting coefficient.

[0061] Specifically, to quantitatively characterize the evolution of multi-scale fractures in shale, a new parameter is defined in conjunction with temperature and pressure: the Shale Multi-Scale Fracture Evolution Index (MSFEI). A higher MSFEI value indicates better fracture development during the evolution process. Its calculation formula is as follows:

[0062] in, The comprehensive index of multi-scale fractures in shale; T and P are the real-time monitored temperature and pressure values, respectively. and These are the initial temperature and pressure values, respectively. and These are the weighting coefficients.

[0063] and The calculation process is as follows: Converting the exponential form of the formula to logarithmic form and taking the logarithm of both sides, we get:

[0064] make , , , Then the formula simplifies to:

[0065] Right now

[0066] but Let this be the new dependent variable, denoted as The new linear model is

[0067] Suppose there are m sets of sample data, and in the j-th sample... for , for The corresponding dependent variable is .

[0068] Constructing the independent variable matrix dependent vector Weight coefficient vector .

[0069] Based on the principle of least squares method in multiple linear regression, the coefficient vector is calculated. Received The two elements are the weighting coefficients in the formula. .

[0070] The proposed solution simulates the fracture formation process under in-situ underground conditions, enabling the dynamic evolution and quantitative characterization of multi-scale fractures. It comprehensively considers various fracture formation mechanisms and differences in fracture evolution at different scales, and combines in-situ temperature and pressure, as well as fluid systems, to provide a more realistic simulation of fracture dynamic evolution. Simultaneously, it captures the initiation, propagation, and connectivity behaviors of nanoscale, microscale, and macroscale fractures, and collects parameters for each fracture to calculate a comprehensive multi-scale fracture index and evolution index. This achieves full-scale observation and quantitative characterization of the dynamic evolution of multi-scale fractures in shale under in-situ temperature, pressure, and stress conditions.

[0071] Based on the same inventive concept, according to another aspect of the present invention, embodiments of the present invention also provide an apparatus for characterizing fractures in shale, comprising: The in-situ condition simulation module is used to apply a non-uniform stress field to shale in a simulated formation environment and maintain a preset pressure, as well as to heat the simulated formation environment to a preset temperature. The dynamic monitoring module is used to collect parameters of cracks at multiple scales on the shale and obtain the crack index at the corresponding scale based on the parameters of each crack. The calculation module is used to obtain a multi-scale crack composite index based on each crack index and parameters of cracks at multiple scales. The quantitative characterization module is used to obtain the multi-scale fracture evolution index of shale based on the multi-scale fracture comprehensive index, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment.

[0072] Specifically, such as Figure 2 As shown, the in-situ condition simulation module is used to simulate in-situ stress, temperature, pressure, and fluid conditions in shale reservoirs, driving multi-scale fracture evolution. It can include a true triaxial stress loading system, an in-situ temperature-pressure coupling unit, a multiphase fluid injection system, and a sealing chamber. The true triaxial stress loading system can independently control stress loading in the x, y, and z axes, simulating formation vertical stress, horizontal stress, and shear force; the in-situ temperature-pressure coupling unit can accurately simulate reservoir temperature and pressure; the multiphase fluid injection system can simulate the injection process of formation fluids; and the sealing chamber is filled with formation fluids, exhibiting high sealing performance and resistance to high temperature and pressure.

[0073] The multi-scale fracture dynamic monitoring module is used to monitor the formation and propagation of fractures in shale at different scales (macroscale, micrometer scale, and nanoscale) in real time. It mainly includes a nanoindentation probe, an atomic force microscope probe, a fluorescence injector, a laser emitter, an acoustic emission sensor array, and a multi-core fiber optic connector. The nanoindentation probe and atomic force microscope probe are used to observe the formation and propagation of nanoscale fractures; the fluorescence injector injects fluorescence into the shale sample for the laser emitter to observe the fractures; the laser emitter observes the formation and propagation of micrometer-scale fractures; and the acoustic emission sensor array observes the formation and propagation of macroscale fractures. Nanoindentation probes are used to measure local mechanical properties and identify the initiation location of nanoscale cracks; atomic force microscopy is used to observe nanoscale surface morphology and capture the initial formation and surface energy changes of micro-cracks; laser emitters combined with fluorescence tracer technology are used to observe the three-dimensional morphology and seepage path of micron-scale cracks; acoustic emission sensor arrays can locate acoustic emission events of macroscopic crack propagation and invert crack spatial distribution and dynamic evolution rate; multi-core fiber optic through-cell connectors are used to extend probes and lasers into the interior of the sealed chamber to contact the sample, which can ensure signal transmission and the high airtightness of the sealed chamber.

[0074] The data processing and display module mainly includes a computer. The computer can control the startup and shutdown of each module and synchronously acquire data from various measuring instruments via a high-speed data acquisition card. It performs filtering, amplification, and other processing on the acquired signals, runs algorithms, and converts the raw data into parameters that can quantitatively characterize shale fractures. Simultaneously, it can display measurement results in real time, store these parameters, calculate quantitative indices for shale fractures, and includes a network communication unit supporting remote data transmission and control system operation. Ultimately, it achieves in-situ dynamic evolution and quantitative characterization of multi-scale shale fractures.

[0075] The computing module mainly consists of a computer. The computer can control the startup and shutdown of each module and synchronously acquire data from various measuring instruments via a high-speed data acquisition card. It processes the acquired signals through filtering and amplification, runs algorithms, and converts the raw data into parameters that can quantitatively characterize shale fractures. Simultaneously, it can display measurement results in real time, store these parameters, calculate quantitative indices for shale fractures, and includes a network communication unit supporting remote data transmission and control system operation. Ultimately, it achieves in-situ dynamic evolution and quantitative characterization of multi-scale shale fractures.

[0076] The multi-scale fracture quantitative characterization module is used to quantitatively characterize fractures at different scales and their evolution processes. This module mainly includes: using nanoindentation probes and atomic force microscope probes to obtain the elastic modulus, surface fractal dimension, and fracture density per unit area of ​​nanoscale fractures to quantitatively characterize them; using the laser emitter of a laser confocal microscope to obtain the total fracture length, average fracture width, and scanned area of ​​micrometer-scale fractures to quantitatively characterize them; using an acoustic emission sensor array to obtain the total number of acoustic emission events and average event energy of macroscopic fractures to quantitatively characterize macroscopic fractures; and combining the quantitative characterization results of fractures at different scales to finally obtain the comprehensive index and evolution index of multi-scale fractures in shale, thus achieving quantitative characterization of multi-scale fractures in shale.

[0077] In some embodiments, the device further includes an in-situ multi-field coupling control and synchronization triggering module. This module coordinates the coupling effects of stress, temperature, and fluid injection to ensure the synchronization of experimental conditions and the alignment of data timing. Figure 2 As shown, it mainly includes a multi-field coupling controller and a data synchronization acquisition unit. The multi-field coupling controller integrates the timing logic control of stress loading, temperature and pressure regulation, and fluid injection, and supports preset experimental procedures; the data synchronization acquisition unit is used to ensure the time consistency of acoustic emission signals, microscope images, and mechanical parameters.

[0078] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0079] It should be understood that, as used herein, the singular form “a” is intended to include the plural form as well, unless the context clearly supports an exception. It should also be understood that, as used herein, “and / or” refers to any and all possible combinations of one or more of the associated listed items.

[0080] The embodiment numbers disclosed in the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0081] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for characterizing fractures in shale, characterized in that, include: A non-uniform stress field is applied to shale in a simulated geological environment while maintaining a preset pressure, and the simulated geological environment is heated to a preset temperature. Parameters of fractures at multiple scales on the shale were collected, and the fracture index at the corresponding scale was obtained based on the parameters of each fracture. A multi-scale crack composite index is obtained based on each crack index and parameters of cracks at multiple scales. The multi-scale fracture evolution index of shale is obtained based on the multi-scale fracture comprehensive index, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment.

2. The method as described in claim 1, characterized in that, Collect parameters of fractures at multiple scales on the shale and obtain a fracture index for each scale based on the parameters of each fracture, further including: The elastic modulus, surface fractal dimension, crack density per unit area, length, and angle with the principal stress direction of the nanoscale cracks on the shale were collected, and the nanoscale crack index was obtained based on the elastic modulus, surface fractal dimension, and crack density per unit area of ​​the nanoscale cracks. The length, width, scanning area, number, and angle with the principal stress direction of the micron-scale cracks on the shale were collected, and the micron-scale crack index was obtained based on the length, width, scanning area, and number of the micron-scale cracks. The total number of acoustic emission events, average event energy, length, and angle with the principal stress direction of macroscopic fractures on the shale are collected, and the macroscopic fracture index is obtained based on the total number of acoustic emission events, average event energy, and volume of the shale.

3. The method as described in claim 2, characterized in that, Also includes: The elastic modulus, surface fractal dimension, crack density per unit area, length, and angle with the principal stress direction of nanoscale cracks on the shale were collected using nanoindentation probes and atomic force microscope probes. The length, width, scanning area, number, and angle with the principal stress direction of micron-scale cracks on the shale were collected using the laser emitter of a laser confocal microscope. The total number of acoustic emission events, average event energy, length, and angle with the principal stress direction of macroscopic cracks on the shale were collected using an acoustic emission sensor array.

4. The method as described in claim 2, characterized in that, A multi-scale fracture composite index is obtained based on each fracture index and parameters of fractures at multiple scales, further including: Obtain the first weight, second weight, and third weight; Determine the connectivity coefficients; The multi-scale crack comprehensive index is obtained based on the first weight and the nanoscale crack index, the second weight and the microscale crack index, the third weight and the macroscale crack index, and the connectivity coefficient.

5. The method as described in claim 4, characterized in that, Obtaining the first weight, second weight, and third weight further includes: Obtain the nanoscale fracture index, micrometer scale fracture index, and macroscale fracture index corresponding to the multiple shale formations; Multiple nanoscale crack indices, micrometer-scale crack indices, and macroscale crack indices were standardized separately. Based on the standardized data, the information entropy corresponding to the nanoscale crack index, micrometer scale crack index and macroscale crack index were calculated respectively. The first weight, the second weight, and the third weight are obtained based on the information entropy corresponding to the nanoscale crack index, the microscale crack index, and the macroscale crack index.

6. The method as described in claim 4, characterized in that, Determining the connectivity coefficients further includes: Determine the crack connectivity factor and the crack critical connectivity threshold; The connectivity coefficient is determined based on the crack connectivity factor and the crack critical connectivity threshold.

7. The method as described in claim 6, characterized in that, Determining the crack connectivity factor further includes: The crack connectivity factor is determined based on the length of each crack and the angle between it and the principal stress direction.

8. The method as described in claim 6, characterized in that, Determining the critical connectivity threshold of the crack further includes: Obtain the nanoscale fracture index, micrometer scale fracture index, and macroscale fracture index corresponding to the multiple shale formations; The development index is obtained based on the first weight, the second weight, the third weight, and the nanoscale fracture index, microscale fracture index, and macroscale fracture index corresponding to each shale. The critical connectivity threshold of the crack is determined based on the development index and the crack connectivity factor.

9. The method as described in claim 1, characterized in that, The multi-scale fracture evolution index of shale is obtained based on the multi-scale fracture comprehensive index, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment, further including: Based on the preset pressure, initial pressure, preset temperature, and initial temperature corresponding to multiple shale formations, an independent variable matrix is ​​constructed, and the corresponding dependent variable matrix is ​​obtained. The independent variable matrix and the dependent variable matrix are calculated based on the least squares method of multiple linear regression to obtain the first weight coefficient and the second weight coefficient. The weighting coefficients are obtained based on the first weighting coefficient, the second weighting coefficient, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment; The multi-scale fracture evolution index of shale is obtained based on the multi-scale fracture comprehensive index and the weighting coefficient.

10. An apparatus for characterizing fractures in shale, characterized in that, include: The in-situ condition simulation module is used to apply a non-uniform stress field to shale in a simulated formation environment and maintain a preset pressure, as well as to heat the simulated formation environment to a preset temperature. The dynamic monitoring module is used to collect parameters of cracks at multiple scales on the shale and obtain the crack index at the corresponding scale based on the parameters of each crack. The calculation module is used to obtain a multi-scale crack composite index based on each crack index and parameters of cracks at multiple scales. The quantitative characterization module is used to obtain the multi-scale fracture evolution index of shale based on the multi-scale fracture comprehensive index, the preset pressure, the preset temperature, and the initial pressure and initial temperature of the simulated formation environment.

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