Hole-seam structure digital core construction method for simulating pore size of shale

Abstract

The invention provides a three-dimensional digital core reconstruction method capable of reflecting real shale pore structure characteristics and meeting pore scale numerical simulation connectivity requirements, which comprises the following steps of: firstly, acquiring a pore structure image according to a scanning electron microscope and a micro-nano CT (Computed Tomography); constructing a shale matrix digital core which is consistent with the porosity, permeability and pore size distribution of a real rock sample by adopting a method of combining a numerical value construction method and a physical experiment method; then establishing a digital core of the shale containing the micro-cracks according to the obtained spatial distribution characteristics of the micro-cracks; a matrix digital core and typical micro-crack distribution are combined to obtain a hole-crack structure digital core for pore scale simulation research. The method is reliable in principle, low in cost and accurate in reconstruction result, and solves the technical problems that a digital core obtained by adopting the prior art is poor in connectivity and cannot reflect typical pore characteristics of shale; the method can be used for researching reconstruction of different types of cores and seepage simulation established on a pore scale, and has a good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploration and development, and in particular to a method for constructing a digital core of a pore-fracture structure for shale pore scale simulation. Background Art

[0002] Digital cores can reflect the complex pore space of reservoir rocks and also show the solid skeleton characteristics of rocks. Using digital cores as a platform, numerical simulations of various physical properties of rocks (such as elasticity, conductivity, etc.) and gas-water / oil-water / oil-gas two-phase flow or oil-gas-water three-phase simulations can be performed. Therefore, the accuracy of the three-dimensional digital core model directly affects the reliability of the numerical simulation results.

[0003] Shale oil and gas reservoirs are usually characterized by deep burial, low matrix permeability, strong heterogeneity, high temperature and high pressure, well-developed micro-nano pores, and complex and diverse pore types and shapes. It is difficult and costly to obtain certain physical parameters of cores for this type of reservoir through physical experiments. The three-dimensional numerical reconstruction technology of cores has become an important means to obtain the physical parameters of cores for this reservoir, and is also an important basic support for pore scale simulation research. At present, CT scanning can obtain the real pore structure information of shale, but due to reasons such as image resolution and local heterogeneity of shale pore structure, the connectivity of the obtained digital cores is very poor, which cannot reflect the typical pore characteristics of shale, and it is also difficult to carry out seepage simulation on this basis.

[0004] Therefore, there is an urgent need for a digital core construction method for shale pore-scale simulation and reflecting the real shale pore-fracture structure characteristics. This method is of great significance for the study of shale imbibition and flowback mechanism, the optimization of shale oil and gas well flowback system, and the efficient development of shale oil and gas reservoirs. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a method for constructing a digital core of pore-fracture structure for shale pore scale simulation, which is as follows:

[0006] In a first aspect, a method for constructing a digital core of a pore-fracture structure for shale pore scale simulation is provided, comprising the following steps:

[0007] Obtain 2D SEM images and 3D CT images of real shale core structures, as well as real matrix porosity, real matrix permeability, real pore size distribution, and real fracture spatial distribution;

[0008] Based on the two-dimensional scanning electron microscope image and the three-dimensional CT image, the real matrix porosity, the real matrix permeability and the real pore size distribution are used as matrix physical property parameter constraints, and the shale matrix digital core is constructed by using the Markov chain-Monte Carlo numerical reconstruction method;

[0009] Based on 2D SEM images and 3D CT images, the spatial distribution characteristics of microfractures in shale matrix cores were obtained, and digital cores of shale containing microfractures were constructed.

[0010] The shale matrix digital core is coupled with the shale digital core containing microcracks to obtain a pore-fracture structure digital core for shale pore scale simulation.

[0011] Furthermore, based on the two-dimensional scanning electron microscope image and the three-dimensional CT image, the real matrix porosity, the real matrix permeability and the real pore size distribution are used as matrix physical property parameter constraints, and the Markov chain-Monte Carlo numerical reconstruction method is used to construct a shale matrix digital core, including:

[0012] Based on the two-dimensional scanning electron microscope image, the two-dimensional grayscale image of the scanning electron microscope is converted into a binary image by setting the segmentation threshold using a binarization algorithm, and the simulated matrix porosity in the binary image is made consistent with the difference between the real matrix porosity and the spatial pore structure porosity in the three-dimensional CT image.

[0013] Based on the 2D SEM images, the Markov chain-Monte Carlo numerical reconstruction method is used to reconstruct the digital core that meets the statistical characteristics of the 2D SEM images, and combined with the spatial pore structure in the 3D CT images, the shale matrix digital core is obtained.

[0014] Extract the pore structure of the digital core of the shale matrix, and remove the isolated pores to obtain the three-dimensional connected pore structure, so that the simulated matrix porosity and simulated pore size distribution of the digital core after removing the isolated pores are consistent with the real matrix porosity and real pore size distribution;

[0015] Based on the real matrix permeability, the discrete unified gas dynamics method is used to calculate the simulated matrix permeability of the shale matrix digital core, so that the simulated matrix permeability is consistent with the real matrix permeability.

[0016] Furthermore, the transition probability of the three-dimensional Markov chain is:

[0017] p(x ijk |{x lmn :(l,m,n)≠(i,j,k)})=p(x ijk |{x lmn :(l,m,n)∈N(ijk)})

[0018] Where: N(ijk) is the neighborhood of point (i,j,k), which is a 19-point neighborhood template system:

[0019]

[0020] Furthermore, the Markov chain-Monte Carlo numerical reconstruction method is used to reconstruct the digital core that meets the statistical characteristics of the two-dimensional scanning electron microscope image, including:

[0021] The autocorrelation function is introduced to verify the reliability of the Markov chain-Monte Carlo numerical reconstruction method, and its expression is:

[0022] Where: S(h) represents the value of the autocorrelation function; r i represents the coordinates of the i-th point; Z(r i ) represents r i The observed value at the point; Z(r i +h) means r i +h is the observation value at point; h represents the distance between the two observations.

[0023] Furthermore, when the discrete unified gas dynamics method is used to calculate the permeability of the shale matrix digital core, the distribution function f of each grid is first initialized. j and macro quantities, and then iteratively calculate the current time t according to the following steps n Physical quantities:

[0024] 1) According to Calculate t n At each grid center

[0025] 2) Calculate t n At +Δt / 2, all mesh interfaces

[0026] 3) Calculate t n The density ρ and velocity u at all mesh interfaces at +Δt / 2;

[0027] 4) Calculate t n The distribution function f at all mesh interfaces at time +Δt / 2 i , and repeat the above process until the flow reaches a stable state;

[0028] The permeability of the three-dimensional shale matrix digital core is calculated using a discrete unified gas dynamics method using pressure boundaries at the inlet and outlet boundaries.

[0029] Furthermore, the spatial distribution characteristics of microfractures in the shale matrix core are obtained based on the two-dimensional scanning electron microscope image and the three-dimensional CT image, and a digital core of shale containing microfractures is constructed, including:

[0030] Based on the 2D SEM images, the microcrack contour map was obtained by image processing;

[0031] The three-dimensional distribution map of cracks was obtained by micro-nano CT;

[0032] According to the three-dimensional distribution map of cracks, the crack distribution information is counted, including the length, width, number, inclination angle and occupied area of ​​the cracks;

[0033] Based on the statistical data of fracture distribution information, microfractures are reconstructed using a four-parameter random growth method to obtain digital cores of shale containing microfractures.

[0034] Furthermore, the microcracks are reconstructed using a four-parameter random growth method, which includes the following steps:

[0035] 1) According to the range of crack numbers obtained by statistics, a plurality of growth nuclei are randomly generated within the range of crack numbers;

[0036] 2) Determine the growth probability in eight directions based on the crack inclination angle;

[0037] 3) Based on the growth probability, the crack width is randomly generated in the eight directions of each growth core;

[0038] 4) Statistically check whether the randomly generated crack width is within the range of the crack width in the two-dimensional scanning electron microscope image, and whether the crack penetrates the porous medium. If so, the reconstruction of the microcrack is successful. If not, return to 3) until the generated crack width and crack penetration meet the requirements.

[0039] Furthermore, the shale matrix digital core is coupled with the shale digital core containing microfractures, and the coupling formula is as follows:

[0040]

[0041] In the above formula, Ω represents the digital core.

[0042] In a second aspect, an electronic device is provided, comprising: one or more processors; a storage device for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the method for constructing a digital core of a pore-fracture structure for shale pore-scale simulation provided in the first aspect.

[0043] In a third aspect, a computer-readable storage medium storing a computer program is provided, and when the computer program is executed by a processor, the method for constructing a digital core of a pore-fracture structure for shale pore-scale simulation provided in the first aspect is implemented.

[0044] It can be seen from the above technical solution that the beneficial technical effects of the present invention are as follows:

[0045] 1. The technical solution of the present invention solves the problem that the shale core constructed by the physical experimental method has poor connectivity and is not suitable for pore-scale seepage simulation. On the other hand, it also improves the problem that the physical property parameters of the digital core pore structure constructed by the numerical reconstruction method are inconsistent with the real core pore structure.

[0046] 2. The technical solution of the present invention has reliable principles, strong operability, low cost, and accurate reconstruction results, which solves the problem of inaccurate reconstruction of shale cores by the current numerical reconstruction method; the method is repeatable and can be used to study the reconstruction of different types of cores and seepage simulation based on the pore scale, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the prior art description. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0048] Figure 1 A schematic diagram of a digital core construction method according to an embodiment of the present invention;

[0049] FIG2( a ) is a schematic diagram of scanning a shale sample according to an embodiment of the present invention;

[0050] Figure 2(b) is the binary image of Figure 2(a);

[0051] Figure 3 A schematic diagram of a shale matrix digital core according to an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of a digital core of shale containing microfractures according to an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0054] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0055] Example

[0056] This embodiment provides a method for constructing a digital core of pore-fracture structure for shale pore scale simulation, such as Figure 1 As shown, the following steps are included:

[0057] S1. Obtain 2D SEM images and 3D CT images of real shale core structures, as well as real matrix porosity, real matrix permeability, real pore size distribution, and real fracture spatial distribution

[0058] With the help of scanning electron microscope, micro-nano CT machine, constant rate mercury injection instrument and nitrogen adsorption instrument testing equipment, physical experiments were carried out on real rock cores:

[0059] The real shale core samples obtained by drilling are used to obtain two-dimensional scanning electron microscope images. The rock sample scanning electron microscope images are determined using the industry standard "SY T 5162-1997 Scanning Electron Microscope Analysis Method for Rock Samples".

[0060] The three-dimensional CT image of the real shale core structure is obtained by micro-nano CT. The three-dimensional CT image is a computer tomography image, which contains the spatial pore structure obtained by CT scanning.

[0061] The true matrix porosity and matrix permeability are determined using the industry standard "GB / T 34533-2017 Determination of Shale Helium Porosity and Pulse Attenuation Permeability". The matrix permeability K can be calculated using the following formula:

[0062]

[0063] In the above formula: Q represents the flow rate through the core under the pressure difference Δp; A represents the cross-sectional area of ​​the core perpendicular to the flow direction, μ represents the viscosity of the fluid passing through the core, L represents the length of the core, and Δp represents the pressure difference before and after the fluid passes through the core;

[0064] The true pore size distribution is determined using the industry standard "NB / T 14008-2015 Determination of Shale Full Pore Size Distribution by Mercury Intrusion-Adsorption Combined Method". The true fracture spatial distribution is based on three-dimensional CT images, and the open source three-dimensional image processing software ParaView is used for visualization and statistical calculation of fracture spatial distribution.

[0065] S2: Based on the 2D SEM images and 3D CT images of the real shale core structure, the real matrix porosity, real matrix permeability and real pore size distribution are used as matrix physical property parameter constraints to construct the shale matrix digital core using the Markov chain-Monte Carlo numerical reconstruction method.

[0066] In a specific implementation manner, step S2 is implemented in the following manner:

[0067] S21. Based on the two-dimensional scanning electron microscope image, a binarization algorithm is used to convert the two-dimensional grayscale image of the scanning electron microscope into a binary image by setting a segmentation threshold, and the simulated matrix porosity in the binary image is made consistent with the difference between the real matrix porosity and the spatial pore structure porosity in the three-dimensional CT image.

[0068] S22. Based on the 2D SEM images, the Markov chain-Monte Carlo numerical reconstruction method is used to reconstruct the digital core that meets the statistical characteristics of the 2D SEM images, and combined with the spatial pore structure in the 3D CT images to obtain the shale matrix digital core

[0069] Specifically, the two-dimensional scanning electron microscope image is first traversed and scanned to obtain the transition probability, and then the voxel points are assigned values ​​using the Monte Carlo method based on the transition probability. Since the reconstruction of a digital core requires the acquisition of the complete probability distribution of the entire image, but it is almost impossible to achieve this due to the large sample space, the neighborhood concept is introduced in this embodiment, that is, it is assumed that the value of each arbitrary point only depends on the values ​​of the surrounding neighboring points.

[0070] For a certain point a, use the set C -a Represents all points other than point a, then there exists a neighborhood N of point a a , satisfying the following formula:

[0071] P(x a |x(C -a ))≈P(x a |x(N a )) (2)

[0072] The model of a three-dimensional Markov chain is:

[0073] p(x ijk |{x lmn :0<l<i,0<m<j,0<n<k})=p(x ijk |x i-1,j,k ,x i,j-1,k ,x i,j,k-1 ) (3)

[0074] In the above formula, (i, j, k) is the three-dimensional coordinate of a point in the sample space, and l, m, and n represent the coordinates in the x, y, and z directions respectively.

[0075] For any point (i, j, k) belonging to the sample space V, the joint probability function is:

[0076]

[0077] The transition probability of a three-dimensional Markov chain is:

[0078] p(x ijk |{xlmn :(l,m,n)≠(i,j,k)})=p(x ijk |{x lmn :(l,m,n)∈N(ijk)}) (5)

[0079] Where: N(ijk) is the neighborhood of point (i,j,k), which is point (i,j,k) and its 18 adjacent points, that is, a 19-point neighborhood template system:

[0080]

[0081] The real matrix porosity, matrix permeability, and real pore size distribution obtained in step S1 are used as prior information to constrain the probability distribution of the reconstruction process; based on the spatial pore structure of the CT scan, the conditional probability weighting factor is adjusted to generate the digital core; finally, the autocorrelation function is introduced to verify the reliability of the Markov chain-Monte Carlo numerical reconstruction method. The autocorrelation function reflects the probability that any two points in the image are in the same phase (skeleton or pore), and its expression is:

[0082]

[0083] Where: S(h) represents the value of the autocorrelation function; r i represents the coordinates of the i-th point; Z(r i ) represents r i The observed value at the point; Z(r i +h) means r i +h is the observation value at point; h represents the distance between the two observations.

[0084] S23, extract the pore structure of the digital core of the shale matrix, and remove the isolated pores to obtain the three-dimensional connected pore structure, ensuring that the simulated matrix porosity and simulated pore size distribution of the digital core after removing the isolated pores are consistent with the real matrix porosity and real pore size distribution

[0085] Due to the image segmentation and reconstruction algorithms themselves, isolated skeletons and isolated pores often appear in digital cores generated by different reconstruction methods. The existence of isolated skeletons will lead to redundant pore structures and some erroneous pore connection channels. Isolated pores will affect the microscopic seepage simulation results, and will also produce incorrect descriptions of the pore structure, number, pore size distribution and coordination number of the real core. In this embodiment, isolated skeletons and isolated pores are removed based on the seed filling method, that is, the same pixel value and the same position are used as the judgment conditions for the connected area, so as to merge adjacent voxels. When the number of elements in the merged set is less than a certain threshold, it can be identified as an isolated skeleton or pore and removed.

[0086] S24, based on the real matrix permeability, the simulated matrix permeability of the shale matrix digital core is calculated using the discrete unified gas dynamics method, so that the simulated matrix permeability is consistent with the real matrix permeability. Otherwise, steps S21 to S24 need to be repeated until the constructed shale matrix digital core is consistent with the real shale matrix in terms of matrix porosity, matrix permeability and pore size distribution.

[0087] The discrete unified gas dynamics method is used to calculate the digital core permeability of shale matrix. In the actual calculation, the distribution function f of each grid is first initialized. j and macro quantities, and then iteratively calculate the current time t according to the following steps n Physical quantities:

[0088] 1) According to Calculate t n At each grid center

[0089] 2) Calculate t n At +Δt / 2, all mesh interfaces

[0090] 3) Calculate t n The density ρ and velocity u at all mesh interfaces at +Δt / 2;

[0091] 4) Calculate t n The distribution function f at all mesh interfaces at time +Δt / 2 i , and repeat the above process until the flow reaches a stable state.

[0092] The inlet and outlet boundaries adopt pressure boundaries, and the discrete unified gas dynamics method is used to calculate the permeability K of the three-dimensional shale matrix digital core:

[0093]

[0094] In the above formula, μ represents the viscosity of the fluid passing through the core, φ represents the porosity, and L represents the distance between the inlet and outlet. represents the sum of all grids in the pore space, represents the sum of all directions of the grid, f i represents the distribution function in the i direction, c i represents the discrete velocity in the i direction, N represents the total number of grid points, and p in Indicates the inlet pressure, p out Indicates the outlet pressure.

[0095] S3. Obtain the spatial distribution characteristics of microfractures in shale matrix cores based on 2D SEM images and 3D CT images, and construct digital cores of shale containing microfractures

[0096] Based on the two-dimensional scanning electron microscope image, the micro-crack area of ​​the original scanning electron microscope image is obtained, and a micro-crack identification training data set is constructed. The image segmentation model is constructed through U2-net neural network training, and the image segmentation model is used to obtain the micro-crack contour map; the three-dimensional CT image obtained by micro-nano CT contains a three-dimensional distribution map of cracks; according to the three-dimensional distribution map of cracks, the crack distribution information is statistically analyzed, including the length, width, number of cracks, inclination angle and occupied area of ​​the cracks; based on the statistical data of the crack distribution information, the micro-cracks are reconstructed using the four-parameter random growth method to obtain the digital core of shale containing micro-cracks.

[0097] The microcracks are reconstructed using a four-parameter random growth method, which includes the following steps:

[0098] 1) According to the range of crack numbers obtained by statistics, a plurality of growth nuclei are randomly generated within the range of crack numbers;

[0099] 2) Determine the growth probability in eight directions based on the crack inclination angle;

[0100] 3) Based on the growth probability, the crack width is randomly generated in the eight directions of each growth core;

[0101] 4) Statistically check whether the randomly generated crack width is within the range of the crack width in the two-dimensional scanning electron microscope image, and whether the crack penetrates the porous medium. If so, the reconstruction of the microcrack is successful. If not, return to 3) until the generated crack width and crack penetration meet the requirements.

[0102] S4. Couple the reconstructed shale matrix digital core with the microfracture shale digital core to obtain the pore-fracture structure digital core for shale pore scale simulation

[0103] The digital core of the shale matrix obtained in step S2 is coupled with the digital core of the shale containing microfractures obtained in step S3. The coupling formula is as follows:

[0104]

[0105] In the above formula, Ω represents the digital core, and after coupling, the pore-fracture structure digital core for shale pore-scale simulation can be obtained.

[0106] For ease of understanding, the following examples are given:

[0107] A shale sample was collected from a certain area. According to step S1, the porosity of the rock sample was measured to be 5.10%, and the permeability was 0.0004 mD. An electron microscope image was obtained by scanning electron microscope. The porosity of the binarized image obtained at a threshold of 74 was 5.01%. The scanning image is shown in Figure 2(a) and the binarized image is shown in Figure 2(b).

[0108] According to step S2, the binarized image is used to obtain the conditional probabilities of three orthogonal directions by traversing the scan, and the three-dimensional shale matrix digital core is established based on the spatial pore structure of the CT scan using the three-dimensional MCMC algorithm, and a digital core with a size of 130×130×100 voxels is constructed. The pore structure of the digital core is extracted, and the isolated pores are removed to obtain the three-dimensional connected pore structure, such as Figure 3 As shown in Figure 1, the porosity of the digital core is 5.09%, which is only 0.01% lower than the matrix porosity of 5.10%. Figure 4 shown.

[0109] Compared with the prior art, the technical solution of the present invention solves the problem that the shale core constructed by the physical experimental method has poor connectivity and is not suitable for pore-scale seepage simulation. On the other hand, it also improves the problem that the physical property parameters of the digital core pore structure constructed by the numerical reconstruction method are inconsistent with the real core pore structure. The method is reliable in principle, highly operable, low in cost, and accurate in reconstruction results, which solves the problem of inaccurate reconstruction of shale cores by the current numerical reconstruction method; the method is repeatable and can be used to study the reconstruction of different types of cores and seepage simulation based on the pore scale, and has good application prospects.

[0110] In some embodiments, an electronic device is also provided, including: one or more processors; a storage device for storing one or more programs; when the one or more programs are executed by one or more processors, the one or more processors implement the method for constructing a digital core of a pore-fracture structure for shale pore-scale simulation as described above.

[0111] In some embodiments, a computer-readable storage medium storing a computer program is also provided. When the computer program is executed by a processor, the method for constructing a digital core of a pore-fracture structure for shale pore-scale simulation as described above is implemented.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A method for constructing a digital core of pore-fracture structure for shale pore scale simulation, characterized in that: The following steps are involved: Obtain 2D SEM images and 3D CT images of real shale core structures, as well as real matrix porosity, real matrix permeability, real pore size distribution, and real fracture spatial distribution; Based on the two-dimensional scanning electron microscope image and the three-dimensional CT image, the real matrix porosity, the real matrix permeability and the real pore size distribution are used as matrix physical property parameter constraints, and the shale matrix digital core is constructed by using the Markov chain-Monte Carlo numerical reconstruction method; Based on 2D SEM images and 3D CT images, the spatial distribution characteristics of microfractures in shale matrix cores were obtained, and digital cores of shale containing microfractures were constructed. The shale matrix digital core is coupled with the shale digital core containing microcracks to obtain a pore-fracture structure digital core for shale pore scale simulation.

2. The method for constructing a digital core of pore-fracture structure for shale pore scale simulation according to claim 1, characterized in that: Based on the two-dimensional scanning electron microscope image and the three-dimensional CT image, the real matrix porosity, the real matrix permeability and the real pore size distribution are used as matrix physical property parameter constraints, and the Markov chain-Monte Carlo numerical reconstruction method is used to construct a shale matrix digital core, including: Based on the two-dimensional scanning electron microscope image, the two-dimensional grayscale image of the scanning electron microscope is converted into a binary image by setting the segmentation threshold using a binarization algorithm, and the simulated matrix porosity in the binary image is made consistent with the difference between the real matrix porosity and the spatial pore structure porosity in the three-dimensional CT image. Based on the 2D SEM images, the Markov chain-Monte Carlo numerical reconstruction method is used to reconstruct the digital core that meets the statistical characteristics of the 2D SEM images, and combined with the spatial pore structure in the 3D CT images, the shale matrix digital core is obtained. Extract the pore structure of the digital core of the shale matrix, and remove the isolated pores to obtain the three-dimensional connected pore structure, so that the simulated matrix porosity and simulated pore size distribution of the digital core after removing the isolated pores are consistent with the real matrix porosity and real pore size distribution; Based on the real matrix permeability, the discrete unified gas dynamics method is used to calculate the simulated matrix permeability of the shale matrix digital core, so that the simulated matrix permeability is consistent with the real matrix permeability.

3. The method for constructing a digital core of pore-fracture structure for shale pore scale simulation according to claim 2, characterized in that: The transition probability of a three-dimensional Markov chain is: p(x ijk |{x lmn :(l,m,n)≠(i,j,k)})=p(x ijk |{x lmn :(l,m,n)∈N(ijk)}) Where: N(ijk) is the neighborhood of point (i,j,k), which is a 19-point neighborhood template system:

4. The method for constructing a digital core of pore-fracture structure for shale pore scale simulation according to claim 2, characterized in that: The Markov chain-Monte Carlo numerical reconstruction method is used to reconstruct the digital core that meets the statistical characteristics of the two-dimensional scanning electron microscope image, including: The autocorrelation function is introduced to verify the reliability of the Markov chain-Monte Carlo numerical reconstruction method, and its expression is: Where: S(h) represents the value of the autocorrelation function; r i represents the coordinates of the i-th point; Z(r i ) represents r i The observed value at the point; Z(r i +h) means r i +h is the observation value at point; h represents the distance between the two observations.

5. The method for constructing a digital core of pore-fracture structure for shale pore scale simulation according to claim 2, characterized in that: When using the discrete unified gas dynamics method to calculate the permeability of shale matrix digital core, the distribution function f of each grid is initialized first. j and macro quantities, and then iteratively calculate the current time t according to the following steps n Physical quantities: 1) According to Calculate t n At each grid center 2) Calculate t n At +Δt / 2, all mesh interfaces 3) Calculate t n The density ρ and velocity u at all mesh interfaces at +Δt / 2; 4) Calculate t n The distribution function f at all mesh interfaces at time +Δt / 2 i , and repeat the above process until the flow reaches a stable state; The permeability of the three-dimensional shale matrix digital core is calculated using a discrete unified gas dynamics method using pressure boundaries at the inlet and outlet boundaries.

6. The method for constructing a digital core of pore-fracture structure for shale pore scale simulation according to claim 2, characterized in that: Based on 2D SEM images and 3D CT images, the spatial distribution characteristics of microfractures in shale matrix cores are obtained, and digital shale cores containing microfractures are constructed, including: Based on the 2D SEM images, the microcrack contour map was obtained by image processing; The three-dimensional distribution map of cracks was obtained by micro-nano CT; According to the three-dimensional distribution map of cracks, the crack distribution information is counted, including the length, width, number, inclination angle and occupied area of ​​the cracks; Based on the statistical data of fracture distribution information, microfractures are reconstructed using a four-parameter random growth method to obtain digital cores of shale containing microfractures.

7. The method for constructing a digital core of pore-fracture structure for shale pore scale simulation according to claim 6, characterized in that: The microcracks are reconstructed using a four-parameter random growth method, which includes the following steps: 1) According to the range of crack numbers obtained by statistics, a plurality of growth nuclei are randomly generated within the range of crack numbers; 2) Determine the growth probability in eight directions based on the crack inclination angle; 3) Based on the growth probability, the crack width is randomly generated in the eight directions of each growth core; 4) Statistically check whether the randomly generated crack width is within the range of the crack width in the two-dimensional scanning electron microscope image, and whether the crack penetrates the porous medium. If so, the reconstruction of the microcrack is successful. If not, return to 3) until the generated crack width and crack penetration meet the requirements.

8. The method for constructing a digital core of pore-fracture structure for shale pore scale simulation according to claim 1, characterized in that: The shale matrix digital core is coupled with the shale digital core containing microfractures, and the coupling formula is as follows: In the above formula, Ω represents the digital core.

9. An electronic device, characterized in that: include: one or more processors; A storage device for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method for constructing a digital core of pore-fracture structure for shale pore-scale simulation as described in any one of claims 1 to 8.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for constructing a digital core of pore-fracture structure for shale pore scale simulation according to any one of claims 1 to 8 is implemented.

Images