Digital rock multi-attribute grid division method and system

Abstract

The invention discloses a digital rock multi-attribute grid division method and system, and belongs to the technical field of rock physical parameter numerical simulation. According to the method, the regular hexahedron mesh is processed to obtain the tetrahedral structure mesh, the tetrahedral structure mesh enables each phase to independently establish the mesh, and the characteristic that phase interfaces share nodes is ensured, so that the establishment process of the multi-phase mesh is more flexible and simpler, and the mesh establishment difficulty and efficiency are reduced. According to the method, the multi-attribute digital rock is divided into the multi-attribute tetrahedral unstructured grids, the grids can accurately reflect the fine structure of the digital rock, the number of units is greatly reduced compared with a traditional regular hexahedral grid, the efficiency of finite element numerical calculation is improved, and the calculation scale is improved. Therefore, the multi-attribute grid division method provided by the invention can solve the problems in the prior art, and can also be suitable for grid division of composite materials with more components and complex structures.

Description

Technical Field

[0001] The invention belongs to the technical field of numerical simulation of rock physical parameters, and relates to a digital rock multi-attribute grid division method and system. Background Art

[0002] With the increasing demand for energy, unconventional oil and gas resources are receiving more and more attention. The reservoir rock of oil and gas is a typical porous medium, and its macroscopic physical properties are affected by a variety of microscopic factors. Compared with conventional reservoirs, unconventional reservoirs have undergone a variety of geological processes such as sedimentation, burial and diagenesis. The reservoirs have lower porosity, stronger heterogeneity, and unclear oil and gas response characteristics, which makes evaluation difficult.

[0003] Traditional rock physics experiments are expensive and have a long experimental cycle. For complex reservoirs, rock physics experiments are even more challenging. Digital rock technology provides more abundant pore-scale microstructure information on the one hand, and can be used to simulate and analyze the changing laws of rock physical properties on the other hand. It breaks through the limitations of traditional rock physics experiments and has developed into an important method for pore structure analysis and rock physical response research.

[0004] However, in the finite element numerical simulation based on digital rock, hexahedral structure grids based on volume pixels are often used. However, due to the small size of the grid cells, this method leads to a huge number of grids, which seriously affects the computational efficiency. Take the digital rock with a pixel size of 1000×1000×1000 established by CT scanning with a resolution of 7.8 microns as an example. The actual rock sample corresponding to the digital rock has a size of 7.8×7.8×7.8 cubic millimeters, but when used for finite element simulation, the number of units in its hexahedral grid is as high as 1 billion. This greatly affects the computational efficiency and limits the improvement of the computational scale. Summary of the invention

[0005] The purpose of the present invention is to solve the problem in the prior art of finite element numerical simulation based on digital rock that the grid unit size is small, resulting in a huge number of grids and limited computing efficiency and scale, and to provide a digital rock multi-attribute grid division method and system.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A digital rock multi-attribute grid division method proposed in the present invention comprises the following steps:

[0008] Process the grayscale image of the rock sample CT scan to obtain three-dimensional digital rock with multiple physical properties;

[0009] Generate hexahedral structural grids of various phases based on three-dimensional digital rock with multiple physical attributes;

[0010] The tetrahedral structured grid is processed to obtain the tetrahedral structured grid, and the tetrahedral structured grid is converted into a tetrahedral unstructured grid to realize the multi-attribute grid division of digital rock.

[0011] Preferably, the grayscale image of the rock sample CT scan is filtered to obtain a filtered image; the grayscale features of the filtered image are segmented to obtain a three-dimensional digital rock with multiple physical properties.

[0012] Preferably, when performing filtering, three-dimensional Gaussian filtering or median filtering is used;

[0013] Gaussian filtering, select a Gaussian kernel of size 3×3×3, and take the target pixel as the central pixel of the template; the target pixel is obtained by weighted average of the grayscale values ​​of itself and other pixels in the neighborhood;

[0014] Median filtering, build a 3×3×3 mask template, take the target pixel as the center pixel of the template, arrange all the pixels in the template from small to large according to the grayscale value, select the grayscale value of the middle pixel in the grayscale value sequence, and assign this value to the target pixel.

[0015] Preferably, a regular hexahedral unit is established for each voxel in the three-dimensional digital rock with multiple attributes, and a regular hexahedral structure grid of each phase is generated;

[0016] The size of the grid unit of the regular hexahedron structure is the same as the actual size of the pixel, and the properties of the grid unit are consistent with the physical properties corresponding to the pixel.

[0017] Preferably, the steps of processing the regular hexahedral structure grid to obtain the tetrahedral structure grid are as follows:

[0018] Step 1: extract the nodes and unit surfaces located at the interfaces of different physical phases in the digital rock grid and construct a quadrilateral two-dimensional grid;

[0019] Step 2: Create a mask with 2×2×2 pixels, and calculate the number of phase types of 8 pixels in the mask;

[0020] Step 3: Calculate the displacement vector of the target node: If the number of phase types of the pixel in the mask is not equal to 2, the displacement vector is 0; if the number of phase types is equal to 2, the displacement vector n of the target node is calculated by respectively calculating the components n on the xy, yz, and xz planes. xy 、n yz 、n xz , and then sum to obtain;

[0021] Step 4: Move the target node to a new position along the displacement vector;

[0022] Step 5: Convert the hexahedral mesh into a tetrahedral structured mesh by using the unit splitting method. By inserting the unit splitting method of the diagonal edges, each hexahedral unit is split into five tetrahedral units, and then the hexahedral structured mesh is converted into a tetrahedral structured mesh.

[0023] Preferably, the direction of the displacement vector of each layer is the product of the sum of the vectors formed by the center origin and the nodes at the boundary of the two phases and the weight factor λ;

[0024]

[0025] Among them, G p is the pixel gray value, G min is the minimum value of pixel grayscale value, G min is the maximum value of the pixel grayscale value, γ is the comparison factor, when the grayscale range of the object corresponding to the pointed pixel is smaller than the grayscale range of another object, γ = 1, otherwise γ = -1.

[0026] Preferably, the tetrahedral structured grid is simplified by an edge collapse algorithm, and then the grid is fission-encrypted in the region with large curvature at the boundary of the physical phase by an adaptive grid algorithm to generate a tetrahedral unstructured grid.

[0027] The present invention proposes a digital rock multi-attribute grid division system, comprising:

[0028] An image preprocessing module, which is used to process the grayscale image of the rock sample CT scan to obtain a three-dimensional digital rock with multiple physical properties;

[0029] A structural grid acquisition module, which is used to generate a regular hexahedral structural grid of each phase based on the three-dimensional digital rock with multiple physical attributes;

[0030] The structured grid conversion module is used to process the regular hexahedral structured grid to obtain the tetrahedral structured grid, convert the tetrahedral structured grid into a tetrahedral unstructured grid, and realize the multi-attribute grid division of digital rock.

[0031] A computer device comprises a memory and a processor, wherein the memory stores a computer program and the processor implements the steps of a digital rock multi-attribute grid division method when executing the computer program.

[0032] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a digital rock multi-attribute grid division method.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention proposes a digital rock multi-attribute meshing method, which processes the regular hexahedral mesh to obtain the tetrahedral structure mesh. The tetrahedral structure mesh allows each phase to establish a mesh independently, and ensures the characteristics of common nodes at the phase interface, which can make the process of establishing the multi-phase mesh more flexible and simple, and reduce the difficulty and efficiency of meshing. The multi-attribute digital rock is divided into a multi-attribute tetrahedral unstructured grid, which can not only accurately reflect the fine structure of the digital rock, but also greatly reduce the number of units compared to the traditional regular hexahedral grid, which improves the efficiency of finite element numerical calculations and improves the scale of calculations. Therefore, the multi-attribute meshing method proposed in the present invention can solve the problems existing in the prior art, and can also be applied to the meshing of composite materials with many components and complex structures.

[0035] The digital rock multi-attribute grid division system proposed in the present invention realizes the digital rock multi-attribute grid division by dividing the system into an image preprocessing module, a structural grid acquisition module and a structural grid conversion module. The modularization concept is adopted to make each module independent of each other, which is convenient for unified management of each module. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 This is a flow chart of the digital rock multi-attribute grid partitioning method of the present invention.

[0038] Figure 2 This is a digital rock map of the Fontainebleau sandstone sample, a digital rock having two physical phase attributes of a quartz skeleton and pores, according to the present invention ((a) is a digital rock map of the Fontainebleau sandstone sample, a digital rock having a quartz skeleton; (b) is a digital rock map of the Fontainebleau sandstone sample, a digital rock having pores).

[0039] Figure 3 Schematic diagram of the hexahedral structure grid of the quartz skeleton and pores of the Fontainebleau sandstone digital rock sample of the present invention ((a) is a schematic diagram of the hexahedral structure grid of the quartz skeleton; (b) is a schematic diagram of the hexahedral structure grid of the pores).

[0040] Figure 4Schematic diagram of the mesh smoothing effect of the local quartz skeleton and pore interface of the Fontainebleau sandstone digital rock sample of the present invention ((a) is an image of 80x80 pixels; (b) is an image with reduced resolution to 8×8 for mesh smoothing, the step line is the unsmoothed boundary, and the other line is the smoothed boundary; (c) is an effect diagram of the boundary after mesh smoothing of the 8×8 pixel image in the 80×80 pixel image).

[0041] Figure 5 Schematic diagram of tetrahedral unstructured grid of quartz skeleton and pores of Fontainebleau sandstone digital rock sample of the present invention ((a) is a schematic diagram of tetrahedral unstructured grid of quartz skeleton; (b) is a schematic diagram of tetrahedral unstructured grid of pores).

[0042] Figure 6 This is a diagram of the digital rock multi-attribute grid division system of the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0046] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0047] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0048] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0050] The present invention proposes a digital rock multi-attribute grid division method, such as Figure 1 As shown, the following steps are included:

[0051] S1. Processing the grayscale image of the rock sample scanned by CT to obtain a three-dimensional digital rock with multiple physical properties;

[0052] The grayscale image of the rock sample CT scan is filtered to obtain a filtered image; the grayscale features of the filtered image are segmented to obtain a three-dimensional digital rock with multiple physical properties.

[0053] When performing filtering, use three-dimensional Gaussian filtering or median filtering;

[0054] Gaussian filtering, select a Gaussian kernel of size 3×3×3, and take the target pixel as the central pixel of the template; the target pixel is obtained by weighted average of the grayscale values ​​of itself and other pixels in the neighborhood;

[0055] Median filtering, build a 3×3×3 mask template, take the target pixel as the center pixel of the template, arrange all the pixels in the template from small to large according to the grayscale value, select the grayscale value of the middle pixel in the grayscale value sequence, and assign this value to the target pixel.

[0056] When image segmentation is performed based on the grayscale characteristics of each phase in the rock, the minerals and pores in the rock are divided into multiple phases according to the CT grayscale characteristics, such as two or more of pores, kaolinite, quartz, potassium feldspar, chlorite, etc.; the grayscale value G of each phase is determined p Range G min ≤G p ≤G max,Using image segmentation methods such as threshold and watershed, all pixels are classified according to physical phases, and corresponding physical phase labels are assigned to establish multi-attribute digital rocks.

[0057] S2, Generate hexahedral structure grids of each phase based on three-dimensional digital rock with multiple physical attributes;

[0058] A regular hexahedral unit is established for each voxel in the three-dimensional digital rock with multiple attributes, and a regular hexahedral structure grid of each phase is generated;

[0059] The size of the grid unit of the regular hexahedron structure is the same as the actual size of the pixel, and the properties of the grid unit are consistent with the physical properties corresponding to the pixel.

[0060] S3. Process the regular hexahedral structured grid to obtain a tetrahedral structured grid, convert the tetrahedral structured grid into a tetrahedral unstructured grid, and realize the multi-attribute grid division of digital rock.

[0061] The steps to process the regular hexahedral structure grid to obtain the tetrahedral structure grid are as follows:

[0062] Step 1: extract the nodes and unit surfaces located at the interfaces of different physical phases in the digital rock grid and construct a quadrilateral two-dimensional grid;

[0063] Step 2: Create a mask with 2×2×2 pixels, and calculate the number of phase types of 8 pixels in the mask;

[0064] Step 3: Calculate the displacement vector of the target node: If the number of phase types of the pixel in the mask is not equal to 2, the displacement vector is 0; if the number of phase types is equal to 2, the displacement vector n of the target node is calculated by respectively calculating the components n on the xy, yz, and xz planes. xy 、n yz 、n xz , and then sum to obtain;

[0065] The displacement vector n in the xy plane xy Take the displacement vector n of the target node on the xy, yz, xz plane as an example xy 、n yz 、n xz Calculation method: Divide the 8 pixels extracted by the mask into two layers, upper and lower, perpendicular to the z-axis direction, then n xy =(n xy ) 下层 +(n xy ) 上层 ; The direction of the displacement vector of each layer is the product of the sum of the vectors composed of the center origin and the nodes at the boundary of the two phases and the weight factor λ. The weight factor λ depends on the non-zero vector and the gray value of the pixel pointed to by G p Related, specific:

[0066] The direction of the displacement vector of each layer is the product of the sum of the vectors composed of the center origin and the nodes at the boundary of the two phases and the weight factor λ;

[0067]

[0068] Among them, G p is the pixel gray value, G min is the minimum value of pixel grayscale value, G min is the maximum value of the pixel grayscale value, γ is the comparison factor, when the grayscale range of the object corresponding to the pointed pixel is smaller than the grayscale range of another object, γ = 1, otherwise γ = -1.

[0069] Step 4: Move the target node to a new position along the displacement vector;

[0070] Step 5: Convert the hexahedral mesh into a tetrahedral structured mesh by using the unit splitting method. By inserting the unit splitting method of the diagonal edges, each hexahedral unit is split into five tetrahedral units, and then the hexahedral structured mesh is converted into a tetrahedral structured mesh.

[0071] The tetrahedral structured grid is simplified by the edge collapse algorithm, and then the adaptive grid algorithm is used to perform grid fission encryption on the area with large curvature at the boundary of the phase to generate a tetrahedral unstructured grid.

[0072] The digital rock multi-attribute grid establishment method proposed in this embodiment is applied to the Fontainebleau sandstone digital rock sample, and the specific steps are as follows:

[0073] Step 1: Read the grayscale image of the Fontainebleau sandstone rock CT scan

[0074] This embodiment uses a 3D CT image of a Fontainebleau sandstone rock sample with a point resolution of 5.4 microns and a size of 240*240*240 pixels. Figure 2 shown.

[0075] Step 2: Use median filtering method to filter the image

[0076] Create a 3×3×3 mask template, take the target pixel as the center pixel of the template, arrange all the pixels in the template from small to large according to the grayscale value, select the grayscale value of the middle pixel in the grayscale value sequence, and assign the value to the target pixel.

[0077] Step 3: Perform threshold segmentation based on the grayscale characteristics of each phase of the rock to create a three-dimensional digital rock with two phase attributes: quartz skeleton and pores.

[0078] The main phases of the Fontainebleau sandstone sample are quartz and pores. The grayscale value range of the quartz phase is determined to be 60-255, and the grayscale value range of the pore phase is 0-59. Using the watershed image segmentation method, all pixels are classified and assigned mineral labels, pores are 1, and quartz is 2. In this way, the digital rock with grayscale values ​​as voxel values ​​is converted into a multi-attribute digital rock with mineral labels as voxel values.

[0079] Step 4: Generate regular hexahedral structure grids for pores and quartz phases respectively

[0080] Each pixel of the digital rock with two physical properties is established as a regular hexahedral unit with a side length of 5.4 microns. The properties of the unit correspond to the mineral label corresponding to the pixel. The units formed by each pixel of the digital rock form a regular hexahedral structure grid. The generated hexahedral grid of the quartz skeleton and pores is as follows Figure 3 shown.

[0081] Step 5: Smooth the mesh at the interface between different phases

[0082] The steps are as follows:

[0083] ① Extract the nodes and unit surfaces located at the interface between quartz and pores in the digital rock grid and construct a quadrilateral two-dimensional grid.

[0084] ② Each node of the interface is taken as a target point that needs to be smoothed. A 2×2×2 pixel mask is established with the target point as the center point, and the number of phase types of the 8 pixels in the mask is calculated.

[0085] ③ Calculate the displacement vector of the target node. If the number of phase types of the pixel in the mask is not equal to 2, the displacement vector is 0; if the number of phase types is equal to 2, the displacement vector n of the target node is calculated by respectively calculating the components n on the xy, yz, and xz planes. xy 、n yz 、n xz , and then sum to obtain. The displacement vector n in the xy plane xy Take the displacement vector n of the target node on the xy, yz, xz plane as an example xy 、n yz 、n xz Calculation method: Divide the 8 pixels extracted by the mask into two layers, upper and lower, perpendicular to the z-axis direction, then n xy =(n xy ) 下层 +(n xy ) 上层; The direction of the displacement vector of each layer is the product of the sum of the vectors composed of the center origin and the nodes at the boundary of the two phases and the weight factor λ. The weight factor λ depends on the non-zero vector and the gray value of the pixel pointed to by G p Related, specific:

[0086]

[0087] γ is a comparison factor. When the grayscale range of the object phase corresponding to the pointed pixel is smaller than the grayscale range of another object phase, γ=1, otherwise γ=-1.

[0088] ④ Move the target node to the new position along the displacement vector.

[0089] Figure 4 The effect of the mesh smoothing algorithm on the interface between Fontainebleau quartz and pores.

[0090] Step 6: Convert the hexahedral mesh to a tetrahedral structured mesh

[0091] All the hexahedral elements in the grid are selected, and each hexahedral element is split into five tetrahedral elements by inserting the diagonal edge element splitting method in each element, thereby converting the hexahedral grid into a tetrahedral structured grid.

[0092] Step 7: Convert tetrahedral structured mesh to tetrahedral unstructured mesh

[0093] The tetrahedral structured grid is simplified by the edge collapse algorithm, and then the adaptive grid algorithm is used to perform mesh fission encryption on the area with large curvature at the boundary of the phase to generate a tetrahedral unstructured grid. The generated tetrahedral unstructured grid of the quartz skeleton and pores is shown in Figure 5 shown.

[0094] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

[0095] Comparative Example 1:

[0096] For the Fontainebleau sandstone sample selected in Example 1, a conventional regular hexahedral structure grid with voxels as units is established. The advantages of the grid establishment method proposed in the present invention are compared by comparing the parameters of the regular hexahedral structure grid divided by voxels as units and the tetrahedral non-structure grid divided by the method proposed in the present invention for the same sample, as well as the convergence speed, time consumption and calculation result deviation of the two grids in finite element calculation.

[0097] Taking the simulation of elastic deformation process as an example, two sets of grids were used to perform finite element numerical simulation under the same computing power. The simulation used COMSOL software platform, selected conjugate gradient iterative solver, relative tolerance of 1×10-4, and maximum number of iterations of 2000 times. The boundary conditions were: tensile deformation of ε33=0.001 along the normal strain direction of 33; shear deformation of τ31=0.001 along the tangent direction of 31. The calculation time, number of iterations and calculation results were statistically analyzed.

[0098] The results are shown in Table 1. It can be seen that the tetrahedral unstructured grid established by the digital rock grid division method proposed in the present invention can greatly shorten the calculation time and improve the calculation efficiency while ensuring the calculation accuracy.

[0099] Table 1 Comparison of parameters, calculation time and results of regular hexahedral structured grid and tetrahedral unstructured grid for Fontainebleau sandstone digital rock

[0100]

[0101]

[0102] The present invention proposes a digital rock multi-attribute grid partitioning system, such as Figure 6 As shown, it includes an image preprocessing module, a structure grid acquisition module and a structure grid conversion module;

[0103] The image preprocessing module is used to process the grayscale image of the rock sample CT scan to obtain a three-dimensional digital rock with multiple physical properties;

[0104] The structural grid acquisition module is used to generate a regular hexahedral structural grid of each phase based on the three-dimensional digital rock with multiple physical attributes;

[0105] The structured grid conversion module is used to process the regular hexahedral structured grid to obtain the tetrahedral structured grid, convert the tetrahedral structured grid into a tetrahedral unstructured grid, and realize the digital rock multi-attribute grid division.

[0106] The terminal device provided in an embodiment of the present invention comprises: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps in the above-mentioned method embodiments are implemented. Alternatively, when the processor executes the computer program, the functions of the modules / units in the above-mentioned device embodiments are implemented.

[0107] The computer program may be divided into one or more modules / units, and the one or more modules / units are stored in the memory and executed by the processor to accomplish the present invention.

[0108] The terminal device may be a computing device such as a desktop computer, a notebook, a PDA, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0109] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0110] The memory may be used to store the computer programs and / or modules, and the processor implements various functions of the terminal device by running or executing the computer programs and / or modules stored in the memory and calling the data stored in the memory.

[0111] If the module / unit integrated in the terminal device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0112] The digital rock multi-attribute grid division method proposed in the present invention has the following advantages:

[0113] 1) The digital rock multi-attribute grid establishment method provided by the present invention divides the multi-attribute digital rock into a multi-attribute tetrahedral unstructured grid. The grid can not only accurately reflect the fine structure of the digital rock, but also greatly reduce the number of units compared with the traditional regular hexahedral grid, which improves the efficiency of finite element numerical calculation and increases the scale of calculation.

[0114] 2) The digital rock multi-attribute grid establishment method provided by the present invention adopts a grid smoothing method based on gray value weight when smoothing the grid. After the hexahedral grid is smoothed at the boundary by a method based on gray value weight, the visualization effect of the grid is improved, the model quality is improved, the stability and reliability of the model are improved, and the efficiency and accuracy of subsequent numerical simulation and data processing are improved.

[0115] 3) The digital rock multi-attribute grid establishment method provided by the present invention establishes a tetrahedral grid by inserting faces after the boundary of the hexahedral grid is smoothed, so that each phase can establish a grid independently and ensure the characteristics of common nodes at the phase interface. This can make the multi-phase grid establishment process more flexible and simple, and reduce the difficulty and efficiency of grid establishment.

[0116] 4) The multi-attribute grid establishment method provided by the present invention can also be applied to the grid division of composite materials with multiple components and complex structures.

[0117] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A digital rock multi-attribute grid division method, characterized in that: The steps include: Process the grayscale image of the rock sample CT scan to obtain three-dimensional digital rock with multiple physical properties; Generate hexahedral structural grids of various phases based on three-dimensional digital rock with multiple physical attributes; The tetrahedral structured grid is processed to obtain the tetrahedral structured grid, and the tetrahedral structured grid is converted into a tetrahedral unstructured grid to realize the multi-attribute grid division of digital rock.

2. The digital rock multi-attribute grid division method according to claim 1 is characterized in that: The grayscale image of the rock sample CT scan is filtered to obtain a filtered image; the grayscale features of the filtered image are segmented to obtain a three-dimensional digital rock with multiple physical properties.

3. The digital rock multi-attribute grid division method according to claim 2 is characterized in that: When performing filtering, use three-dimensional Gaussian filtering or median filtering; Gaussian filtering, select a Gaussian kernel of size 3×3×3, and take the target pixel as the central pixel of the template; the target pixel is obtained by weighted average of the grayscale values ​​of itself and other pixels in the neighborhood; Median filtering, build a 3×3×3 mask template, take the target pixel as the center pixel of the template, arrange all the pixels in the template from small to large according to the grayscale value, select the grayscale value of the middle pixel in the grayscale value sequence, and assign this value to the target pixel.

4. The digital rock multi-attribute grid division method according to claim 1, characterized in that: A regular hexahedral unit is established for each voxel in the three-dimensional digital rock with multiple attributes, and a regular hexahedral structure grid of each phase is generated; The size of the grid unit of the regular hexahedron structure is the same as the actual size of the pixel, and the properties of the grid unit are consistent with the physical properties corresponding to the pixel.

5. The digital rock multi-attribute grid division method according to claim 1 is characterized in that: The steps to process the regular hexahedral structure grid to obtain the tetrahedral structure grid are as follows: Step 1: extract the nodes and unit surfaces located at the interfaces of different physical phases in the digital rock grid and construct a quadrilateral two-dimensional grid; Step 2: Create a mask with 2×2×2 pixels, and calculate the number of phase types of 8 pixels in the mask; Step 3: Calculate the displacement vector of the target node: If the number of phase types of the pixel in the mask is not equal to 2, the displacement vector is 0; if the number of phase types is equal to 2, the displacement vector n of the target node is calculated by respectively calculating the components n on the xy, yz, and xz planes. xy 、n yz 、n xz , and then sum to obtain; Step 4: Move the target node to a new position along the displacement vector; Step 5: Convert the hexahedral mesh into a tetrahedral structured mesh by using the unit splitting method. By inserting the unit splitting method of the diagonal edges, each hexahedral unit is split into five tetrahedral units, and then the hexahedral structured mesh is converted into a tetrahedral structured mesh.

6. The digital rock multi-attribute grid generation method according to claim 5, characterized in that: The direction of the displacement vector of each layer is the product of the sum of the vectors composed of the center origin and the nodes at the boundary of the two phases and the weight factor λ; Among them, G p is the pixel gray value, G min is the minimum value of pixel grayscale value, G min is the maximum value of the pixel grayscale value, γ is the comparison factor, when the grayscale range of the object corresponding to the pointed pixel is smaller than the grayscale range of another object, γ = 1, otherwise γ = -1.

7. The digital rock multi-attribute grid division method according to claim 1 is characterized in that: The tetrahedral structured grid is simplified by the edge collapse algorithm, and then the adaptive grid algorithm is used to perform grid fission encryption on the area with large curvature at the boundary of the phase to generate a tetrahedral unstructured grid.

8. A digital rock multi-attribute grid division system, characterized in that: include: An image preprocessing module, which is used to process the grayscale image of the rock sample CT scan to obtain a three-dimensional digital rock with multiple physical properties; A structural grid acquisition module, which is used to generate a regular hexahedral structural grid of each phase based on the three-dimensional digital rock with multiple physical attributes; The structured grid conversion module is used to process the regular hexahedral structured grid to obtain the tetrahedral structured grid, convert the tetrahedral structured grid into a tetrahedral unstructured grid, and realize the multi-attribute grid division of digital rock.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the digital rock multi-attribute grid division method as described in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the digital rock multi-attribute grid division method as described in any one of claims 1 to 7 are implemented.

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