A method for constructing a three-dimensional digital core model of irregular concave-convex shaped particles

Abstract

The application discloses a method for constructing a three-dimensional digital core model of irregular concave-convex particles, and comprises the following steps: S1, generating regular small balls with the same radius distribution based on the actual rock particle radius distribution and shape characteristics; S2, constructing a single particle with irregular concave-convex shape based on a single regular small ball; S3, constructing several regular small balls with different sizes into several irregular concave-convex particles by setting the modeling parameters of different regular small balls based on the construction method of the single particle with irregular concave-convex shape; and S4, simulating the deposition and compaction of the several irregular concave-convex particles in a three-dimensional space to obtain a digital core model with different pore structures. The modeling principle and process of the application have the advantages of easy understanding, controllable concave-convex shape, various results and the like, and lay a model foundation for carrying out oil and gas reservoir petrophysical analysis and modeling work.

Description

A method for constructing a three-dimensional digital core model of irregularly shaped particles Technical Field

[0001] This invention belongs to the field of deep-sea oil and gas reservoir exploration and development technology, specifically relating to a method for constructing a three-dimensional digital core model of irregularly shaped particles. Background Technology

[0002] The physical properties of reservoir rocks, such as porosity, permeability, and elastic modulus, are influenced by the morphological characteristics of the constituent mineral grains. Efficiently and realistically establishing numerous three-dimensional digital core models of mineral grains with complex, irregular shapes and varying degrees of concavity and convexity is crucial for reservoir rock physics research. Although digital core modeling plays an important role in many fields, simulating complex-shaped grains, even in two-dimensional space, remains extremely challenging. Currently, most studies use spherical grains, employing grain expansion and contraction techniques to construct spherical grains of different sizes. In addition, irregularly shaped grains, such as ellipsoids, disks, tetrahedrons, and polyhedra, are also frequently studied. However, these digital core modeling methods cannot construct digital core models with arbitrarily irregular, concave and convex shapes, and cannot effectively represent the shape characteristics of actual rock grains, thus limiting their application in studying rock physical properties. A key direction in the current development of digital rock technology is moving from the digital replication of single rock samples to intelligent generation based on geostatistical laws. This patent proposes a method that can flexibly control the morphological characteristics of particles, such as their concavity and convexity, providing rock physicists and engineers with a powerful rock physics modeling method. It can promote the establishment of the relationship between microstructure and macroscopic properties, and provide a basic model for the study of micro-mechanisms in the study of rock physics properties and the geophysical interpretation of oil and gas.

[0003] Existing technological solutions: The mineral grains in natural rocks are irregular. Most current research uses spherical grains, employing grain expansion and contraction techniques to construct spherical grains. In addition, irregularly shaped grains with fixed forms, such as ellipsoids, disks, tetrahedrons, and polyhedra, are also frequently studied. Simulations using the same spherical and fixed-shape grains cannot reflect the shape characteristics observed in natural rocks and cannot effectively calculate the effective physical property parameters of the reservoir.

[0004] Existing technical problems: Current research on digital core modeling of irregular particles mainly focuses on constructing non-spherical, regular-shaped particles, such as ellipsoids, disks, tetrahedrons, and polyhedra. While these methods can construct non-spherical particles, the shape remains specific and cannot create models with arbitrary degrees of irregularity. Furthermore, irregular, convex-concave particles better reflect the shapes of actual rock particles; these models typically exhibit convex characteristics, making it difficult to construct models with concave characteristics. To quantitatively study the influence of particle irregularity on rock physical properties, there is an urgent need to establish a three-dimensional digital core model with irregular particles and controllable convex-concave characteristics. Summary of the Invention

[0005] This invention aims to address the shortcomings of existing technologies and provides the following solutions:

[0006] A method for constructing a three-dimensional digital core model of irregularly shaped particles includes the following steps:

[0007] S1. Based on the actual rock particle radius distribution and shape characteristics, generate regular small spheres with the same radius distribution;

[0008] S2. Based on a single regular sphere, construct a single particle with an irregular concave-convex shape;

[0009] S3. By setting different modeling parameters for the regular spheres, based on the construction method of a single particle with an irregular concave-convex shape, several regular spheres of different sizes are constructed into several irregular concave-convex particles;

[0010] S4. Simulate the deposition and compaction diagenesis process of several irregular, uneven particles in three-dimensional space to obtain digital core models with different pore structures.

[0011] Preferably, the method for obtaining the regular small ball includes:

[0012] S11. Obtain rock particle samples, and obtain the particle radius distribution histogram of the actual rock based on CT scan analysis to obtain the actual rock particle radius distribution;

[0013] S12. Analyze the shape characteristics of the rock particles using images of the rock particle samples;

[0014] S13. Based on the actual rock particle radius distribution and the shape characteristics, construct the regular spheres with the same radius distribution.

[0015] Preferably, the method for obtaining a single particle with an irregular, uneven shape includes:

[0016] S21. By setting the azimuth angle, polar angle, and distance from the center of the ball, the specific location of the key point G inside the regular ball is determined;

[0017] S22. Establish a first straight line passing through the center point O of the sphere and the key point G, and establish a spatial plane perpendicular to the first straight line and passing through the key point G;

[0018] S23. Establish the relationship between the spatial plane and the sphere to clarify the mineral composition information outside the spatial plane;

[0019] S24. Repeat S21-S23, and control the number of cuts of the regular spheres by changing the number of key points G and the number of spatial planes, thereby changing the irregularity of the regular spheres and obtaining a single particle with an irregular concave-convex shape.

[0020] Preferably, the specific location of key point G is:

[0021] ;

[0022] ;

[0023] ;

[0024] Where α represents the azimuth angle, β represents the polar angle, r represents the distance of key point G from the center of the sphere, and (x,y,z) represents the coordinates of the key point.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention, by effectively performing key operations, including randomly determining key points G, determining the cross-section and number of cutting spheres, and determining the mineral composition outside the cross-section, can transform regular spheres into irregularly shaped particles with concave and convex shapes. This allows for the further simulation of rock compaction processes to create a three-dimensional digital core of these irregularly shaped particles. The modeling principles and processes of this invention offer several advantages, including ease of understanding, controllable concavity and convexity shapes, and diverse results, laying a foundation for petrophysical analysis and modeling of oil and gas reservoirs. The core objective of this method is to go beyond simple spherical or ellipsoidal models, more realistically simulating the morphological diversity of particles in actual rocks, thereby more accurately predicting the physical properties of reservoir rocks. Attached Figure Description

[0027] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 is a schematic diagram of the method flow according to an embodiment of the present invention;

[0029] Figure 2 is a flowchart of the modeling process for generating irregularly shaped particles based on a single regularly shaped sphere in an embodiment of the present invention;

[0030] Figure 3 is a schematic diagram of the transformation of regular small balls into irregular concave and convex particles and a three-dimensional digital core model in an embodiment of the present invention. Among them, (a) is the initial model of irregular particle modeling, (b) is a schematic diagram of multiple facets cutting small balls to form irregular particles, and (c) is a three-dimensional digital core model composed of multiple irregular particles.

[0031] Figure 4 shows three-dimensional digital core models with different porosities constructed based on regular small spheres in an embodiment of the present invention. Among them, (a) is the core model with a porosity of 40%, (b) is the core model with a porosity of 30%, (c) is the core model with a porosity of 20%, and (d) is the core model with a porosity of 10%.

[0032] Figure 5 shows the three-dimensional digital core model of irregular concave and convex particles constructed when the parameter k is 5 / 6 in the embodiment of the present invention. Among them, (a) is the core model with a porosity of 40%, (b) is the core model with a porosity of 30%, (c) is the core model with a porosity of 20%, and (d) is the core model with a porosity of 10%.

[0033] Figure 6 shows the three-dimensional digital core model of irregular concave and convex particles constructed when the parameter k is 2 / 3 in the embodiment of the present invention. Among them, (a) is the core model with a porosity of 40%, (b) is the core model with a porosity of 30%, (c) is the core model with a porosity of 20%, and (d) is the core model with a porosity of 10%.

[0034] Figure 7 shows the three-dimensional digital core model of irregular concave and convex particles constructed when the parameter k is 1 / 2 in the embodiment of the present invention. Among them, (a) is the core model with a porosity of 40%, (b) is the core model with a porosity of 30%, (c) is the core model with a porosity of 20%, and (d) is the core model with a porosity of 10%. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Example 1:

[0038] In this embodiment, as shown in Figure 1, a method for constructing a three-dimensional digital core model of irregularly shaped particles includes the following steps:

[0039] S1. Based on the actual rock particle radius distribution and shape characteristics, generate regular small spheres with the same radius distribution.

[0040] The method for obtaining regular spheres includes: S11. Obtaining rock particle samples and obtaining the histogram of actual rock particle radius distribution based on CT scan analysis to obtain the actual rock particle radius distribution; S12. Analyzing the shape characteristics of rock particles using images of rock particle samples; S13. Constructing regular spheres with the same radius distribution based on the actual rock particle radius distribution and shape characteristics.

[0041] In this embodiment, the actual rock particle radius and shape characteristics serve as the basis for digital core modeling of irregularly shaped particles. First, particle size variation is analyzed: rock particle samples are obtained, and histograms of the actual rock particle radius distribution are acquired based on CT scans or thin section analysis to obtain the actual rock particle radius distribution. Further calculations of particle size parameters, including mean, standard deviation, and sorting coefficient, are then performed to evaluate the variation pattern of rock particle size. Simultaneously, particle shape characteristics are analyzed. Parameters such as aspect ratio, irregularity, and roughness are quantified through image analysis to obtain shape characteristics. The degree of irregularity in particle shape is analyzed as a key feature, serving as the basis for establishing an equivalent model to the actual rock. Based on the actual rock particle radius distribution and shape characteristics, regular spheres with the same radius distribution are generated as the initial model for modeling irregularly shaped particles. Furthermore, parameters such as the actual rock particle aspect ratio, the degree of irregularity in the actual rock shape, and the degree of compaction of the actual rock serve as the basis for subsequent digital core modeling.

[0042] S2. Based on a single regular sphere, construct a single particle with an irregular concave and convex shape.

[0043] This step is the key to the entire technology. The proposed modeling method is used to construct a digital core model with varying degrees of irregularity. Here, we focus on describing the construction of the irregular uneven shape of a single particle. The process of constructing an irregular uneven particle based on a single sphere is shown in Figure 2.

[0044] Methods for obtaining individual particles with irregular, uneven shapes include:

[0045] S21. By setting the azimuth angle, polar angle, and distance from the center of the ball, determine the specific location of the key point G inside the regular ball.

[0046] In this embodiment, to create particles with irregular concave and convex properties, it is necessary to cut the sphere using a spatial plane and establish the relationship between the two. An important step is to determine the coordinate position of the key point G. First, a three-dimensional rectangular coordinate system is established with the center O of the sphere as the origin. Then, the position of the key point G is randomly determined as a key parameter for establishing the spatial plane (section). The key point is determined by three parameters: azimuth angle α, polar angle β, and distance r from the center of the sphere, as shown in point G (r, α, β) in Figure 3(a).

[0047] The azimuth angle α is randomly selected within the range of 0 to 360 degrees. In MATLAB programming, how can this random selection of the azimuth angle within the range of 0 to 360 degrees be implemented?

[0048] ;

[0049] Here, rand(0,1) represents generating random numbers uniformly distributed in the range [0,1).

[0050] The polar angle β is randomly selected within the range of -90 to 90 degrees. This can be implemented using MATLAB programming language.

[0051] ;

[0052] Wherein, unifrnd(-1,1) represents generating a uniformly distributed random number within the specified interval [-1,1].

[0053] The distance r of the key point G from the center of the sphere is randomly selected between the interval [0, R).

[0054] ;

[0055] Where R represents the radius of the ball, and k represents the parameter controlling the distance between the key point G and the center O of the ball. This parameter is in the interval (0,1) and is one of the parameters controlling the degree of irregularity of the ball.

[0056] The farther the key point G is from the center of the sphere, the smaller the area where the cut surface intersects with the sphere, and the less part of the sphere is removed; conversely, the farther away the key point G is from the center of the sphere, the larger the removed portion. Using three parameters—azimuth angle, polar angle, and distance from the center of the sphere—any point on the sphere can be determined, and each point has a corresponding coordinate position. This allows for subsequent modification of the sphere's shape, controlling its direction, position, and radius to transform it into an irregular, concave-convex shape.

[0057] Given that the keypoint's position in the spherical coordinate system is G(r, α, β), for ease of calculation, the spherical coordinates are converted to rectangular coordinates, and the keypoint's position in the rectangular coordinate system is calculated as G(x, y, z):

[0058] ;

[0059] ;

[0060] ;

[0061] In this context, α×π÷180 and β×π÷180 represent the conversion of degrees to radians in MATLAB calculations.

[0062] S22. Establish the first straight line passing through the center point O and the key point G, and establish a spatial plane perpendicular to the first straight line and passing through the key point G.

[0063] In this embodiment, given the coordinates of the sphere's center O and the key point G, a unique first straight line is established through these two points. A unique spatial plane (cutting plane) is then established through the key point G and perpendicular to this line; this cutting plane is defined as A, as shown in Figure 3(a). For a small sphere, any number of spatial planes (cutting planes) can be established to cut it. By controlling multiple cutting planes, the irregularity of the sphere can be modified. Generally, the more cutting planes there are, the more the sphere is cut, and the more irregular its shape, thus simulating the irregularity of actual rock particles. Figure 3(b) shows multiple cutting planes cutting a sphere to form irregular particles. Furthermore, the position of the cutting plane is closely related to the position of the key point G. The farther the key point G is from the sphere's center, the smaller the area where the cutting plane intersects the sphere, and the less of the sphere is removed; conversely, the closer the key point G is to the sphere's center, the larger the area removed. The azimuth and polar angle parameters can control the position of the cutting plane.

[0064] S23. Establish the relationship between the spatial plane and the sphere to clarify the mineral composition information outside the spatial plane.

[0065] In this embodiment, the voxels inside the initial sphere are defined as mineral components, represented by the number 1, and the voxels outside the sphere are defined as pore space, represented by the number 0. Along the direction of the key point G, the sphere is divided into two parts using the spatial plane A as a dividing line: the side containing the sphere center O is defined as the inner side, and the side not containing the sphere center O is defined as the outer side. In previous irregular particle digital core modeling, the outer side (the side not containing the sphere center O) was defined as 0, meaning that part of the voxel 1 of the sphere was removed by a cross-section, transforming it into pore space 0. The traditional definition only allows for convex particles, not concave ones. However, this modeling method cannot satisfy the shape characteristics of actual rocks, because rock particles are composed of irregularly shaped particles; simply representing actual rocks with convex particles is inaccurate. Therefore, the proposed method defines the outer side as either mineral component 1 or pore space 0, thus enabling the construction of digital core models with both convex and concave shapes. The dashed circle in Figure 3(b) illustrates the concave shape of the particles.

[0066] The mineral composition information outside the cut surface is defined as being controlled by the relationship between the cut surface A and the small sphere (i.e., outside the cut surface is defined as 0 or 1). By setting the distribution range, the proportion of 0 or 1 outside the cut surface can be controlled. First, a random number J is generated within the distribution range:

[0067] ;

[0068] Wherein, unifrn(a,b) represents generating a uniformly distributed random number J within the specified interval [a, b].

[0069] The proportion of out-of-section component information is controlled by customizing the value of c, which ranges from [a, b]. Then, the out-of-section value is controlled to be 0 or 1 by comparing the values ​​of J and c. The formula is as follows:

[0070] ;

[0071] ;

[0072] Wherein, voxel represents the voxel of the cross section; this formula means that if J≤c, the voxel of the cross section is set to pore space 0; if J>c, the voxel of the cross section is set to mineral component 1.

[0073] S24. Repeat S21-S23, and change the number of key points G and spatial planes to control the number of regular balls being cut, thereby changing the degree of irregularity of the regular balls and obtaining a single particle with an irregular concave and convex shape.

[0074] In this embodiment, the number of facets is one of the key parameters for transforming a regular sphere into an irregularly shaped particle. Theoretically, any number of facets can be created to cut a single sphere. By controlling the number of facets, the irregularity of the sphere can be modified. Generally, the more facets there are, the more the sphere is cut, and the more irregular it becomes, thus simulating the irregularity of actual rock particles. When all facets are set to 0, the sphere can only be transformed into an irregular convex particle; only when the facets are 0 or 1 can concave particles be formed. Increasing the number of facets and repeatedly performing steps ②-④ allows for the formation of irregularly shaped particles with both concave and convex forms, while also controlling the degree of irregularity, thereby creating a shape that more closely resembles the characteristics of actual rocks.

[0075] S3. By setting modeling parameters for different regular spheres, based on the construction method of a single particle with an irregular concave-convex shape, several regular spheres of different sizes are constructed into several irregular concave-convex particles.

[0076] In this embodiment, based on the actual particle shape characteristics of rocks and the proposed modeling method of transforming a single sphere into a concave-convex shaped particle, the modeling parameters of the next sphere can be controlled by controlling modeling parameters such as azimuth angle, polar angle, distance from the sphere center, key point G, spatial plane, external component information of the cross section, and number of cross sections, based on regular sphere particles of different sizes. By continuously repeating this process, a large number of particles with irregular concave-convex shapes can be established, and these particles are the basis for establishing a digital core model.

[0077] S4. Simulate the deposition and compaction diagenesis process of several irregular, uneven particles in three-dimensional space to obtain digital core models with different pore structures.

[0078] In this embodiment, the parameters changed in the modeling mainly include the shape characteristics of irregular particles and the depositional compaction characteristics of the rock during its formation. Deposition involves particles directly deposited in a specific three-dimensional space (length, width, and height), exhibiting stability in the direction of gravity. Compaction simulates the compaction and densification of particles under the gravity of overlying strata, forming tightly bonded rock. Based on a Matlab program, the deposition and compaction of irregular, uneven particles are simulated in three-dimensional space, thereby creating digital core models with different porosities and pore structures.

[0079] Based on research needs, the above methods and steps can be used to establish a large number of three-dimensional digital core models of granular rocks with different shapes and textures.

[0080] Concave particles can better represent the morphological characteristics of actual rock particles. Since few methods can effectively create concave particles, the biggest advantage of this method is its ability to create particles with irregular concave and convex shapes. Furthermore, by defining key points, the morphology of small spheres transformed into irregularly shaped particles can be better controlled, saving modeling time and allowing for control over the degree of irregularity. This better simulates the irregularity of rock particles in actual strata; for example, some rocks form well-rounded particles, while others are poorly rounded; some particles have more concave shapes, while others have more convex shapes; and the degree of irregularity also varies; shape parameters such as roundness, concavity / convexity, and aspect ratio also differ. This technique establishes complex three-dimensional digital core models by controlling modeling parameters.

[0081] Examples (Figures 4, 5, 6, and 7) demonstrate the modeling effectiveness of this method. For instance, by controlling the parameter k, irregularly shaped porous digital cores with varying concave and convex shapes can be formed. Figure 4 shows a 3D digital core model with different porosities built based on regular spheres. It can be seen that the mineral particles in the figure are regular spheres, and ϕ represents porosity. Figure 5 shows a 3D digital core model with irregularly shaped concave and convex particles built based on parameter k of 5 / 6. In this model, the mineral particles are no longer regular spheres but have become irregularly shaped, although their roundness is still relatively good. Figure 6 shows a 3D digital core model with irregularly shaped concave and convex particles built based on parameter k of 2 / 3, where the irregularity of the particles increases. Figure 7 shows a 3D digital core model with irregularly shaped concave and convex particles built based on parameter k of 1 / 2. In this model, the particle shape is even more irregular, with sharp edges and corners, poor roundness, and an overall more complex pore structure. These examples demonstrate that this method can controllably, cost-effectively, and efficiently build 3D digital core models with irregular concave and convex shapes.

[0082] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for constructing a three-dimensional digital core model of irregularly shaped particles, characterized in that, Includes the following steps: S1. Based on the actual rock particle radius distribution and shape characteristics, generate regular small spheres with the same radius distribution; S2. Based on a single regular sphere, construct a single particle with an irregular concave-convex shape; S3. By setting different modeling parameters for the regular spheres, based on the construction method of a single particle with an irregular concave-convex shape, construct several regular spheres of different sizes into several irregular concave-convex particles; S4. Simulate the deposition and compaction diagenesis process of several irregularly shaped particles in three-dimensional space to obtain digital core models with different pore structures; the method for obtaining a single particle with an irregularly shaped irregularity includes: S21. Determine the specific location of the key point G inside the regular sphere by setting the azimuth angle, polar angle, and distance from the center of the sphere; S22. Establish a first straight line passing through the center point O and the key point G, and establish a spatial plane perpendicular to the first straight line and passing through the key point G; S23. Set the relationship between the spatial plane and the sphere to clarify the mineral composition information outside the spatial plane; S24. Repeat S21-S23, and control the number of regular spheres being cut by changing the number of key points G and the number of spatial planes, thereby changing the irregularity of the regular spheres and obtaining a single particle with an irregularly shaped irregularity.

2. The method for constructing a three-dimensional digital core model of irregularly shaped particles according to claim 1, characterized in that, The relationship between the spatial plane and the sphere is established to clarify the mineral composition information outside the spatial plane. The proportion of composition information outside the cross-section is controlled by a custom value of c, with the c value ranging from [a, b]. Then, the value outside the cross-section is controlled to be 0 or 1 by judging the magnitude of the J value and the c value. The formula is expressed as: ； Where, voxel represents the voxel of the cross section; this formula means that if J≤c, the voxel of the cross section is set to pore space 0; if J>c, the voxel of the cross section is set to mineral component 1.

3. The method for constructing a three-dimensional digital core model of irregularly shaped particles according to claim 1, characterized in that, The specific location of key point G is: ； ； Where α represents the azimuth angle, β represents the polar angle, r represents the distance of key point G from the center of the sphere, and (x,y,z) represents the coordinates of the key point.

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