Method for constructing irregular concave-convex particle three-dimensional digital core model

Abstract

The invention discloses a method for constructing a three-dimensional digital core model of irregular concave-convex particles, and the method comprises the following steps: S1, generating regular small balls with the same radius distribution based on the radius distribution and shape characteristics of actual rock particles; s2, constructing a single particle with an irregular concave-convex shape based on a single regular small ball; s3, by setting modeling parameters of different regular small balls, on the basis of a construction method of a single particle with an irregular concave-convex shape, constructing a plurality of irregular concave-convex particles by the regular small balls with different sizes; and S4, simulating deposition and compaction diagenesis processes of a plurality of irregular concave-convex particles in a three-dimensional space to obtain digital core models with different pore structures. The modeling principle and process have the advantages of being easy to understand, controllable in concave-convex shape, diverse in result and the like, and a model foundation is laid for oil and gas reservoir rock physical analysis and modeling work.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of deep-sea oil and gas reservoir exploration and development, and particularly relates to a method for constructing a three-dimensional digital core model of irregular concave-convex shape particles. BACKGROUND

[0002] The physical properties of reservoir rocks, such as porosity, permeability and elastic modulus, are affected by the morphological characteristics of the constituent mineral particles. Efficient and realistic establishment of a large number of three-dimensional digital core models of mineral particles with complex irregular shapes and different concave-convex properties is of great significance for reservoir rock physics research. Although digital core modeling plays an important role in many fields, simulation of complex shape particles still presents great difficulties, even in two-dimensional space. Most current researches use spherical particles, and the grain swelling and shrinking technique is used to construct particles of different sizes. In addition, irregular fixed shape particles, such as ellipsoids, discs, tetrahedrons and polyhedrons, are also commonly used. However, these digital core modeling methods cannot construct digital core models of arbitrary irregular concave-convex shapes, and cannot effectively represent the shape characteristics of actual rock particles, thus having deficiencies in studying rock physical properties. An important direction of current digital rock technology development is to shift from digital replication of a single rock sample to intelligent generation based on geological statistical rules. The present patent proposes a method for flexibly controlling the morphological characteristics of particles, such as concave-convex properties, and provides a powerful rock physics modeling method for rock physicists and engineers, which can promote the establishment of the relationship between microstructure and macroscopic properties, and provide a micro-mechanism research foundation model for studying rock physical properties and oil and gas geophysical interpretation.

[0003] Prior art solution: The mineral particles of natural rocks are irregular, and most current researches use spherical particles, and the grain swelling and shrinking technique is used to construct spherical particles. In addition, irregular fixed shape particles, such as ellipsoids, discs, tetrahedrons and polyhedrons, are also commonly used. The simulation using the same spherical particles and fixed shape particles cannot reflect the shape characteristics observed in natural rocks, and cannot effectively calculate the effective physical property parameters of the reservoir.

[0004] Prior art problems: Current irregular particle digital core modeling research mainly focuses on the construction of non-spherical regular shape particles, such as ellipsoids, discs, tetrahedrons and polyhedrons. These methods can construct non-spherical shape particles, but the shape is still specific, and cannot construct models of arbitrary irregular degree. In addition, irregular concave-convex shape particles are more consistent with the shape of actual rock particles, and these models usually have convex properties, and it is difficult to construct models with concave properties. In order to quantitatively study the influence of the irregular degree of particles on rock physical properties, it is urgent to establish a three-dimensional digital core model of irregular particles with controllable concave-convex 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 as follows:

[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 This is a schematic diagram of the method flow according to an embodiment of the present invention;

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

[0030] Figure 3This 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. (a) is the initial model for modeling irregular particles, (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 The three-dimensional digital core models with different porosities constructed based on regular small spheres in this embodiment of the invention are shown below. (a) is a core model with a porosity of 40%, (b) is a core model with a porosity of 30%, (c) is a core model with a porosity of 20%, and (d) is a core model with a porosity of 10%.

[0032] Figure 5 The three-dimensional digital core model of irregular concave and convex particles constructed in the embodiment of the present invention when the parameter k is 5 / 6 is shown. 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 The three-dimensional digital core model of irregular concave and convex particles constructed in the embodiment of the present invention when the parameter k is 2 / 3 is shown. 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 The three-dimensional digital core model of irregular concave and convex particles constructed in the embodiment of the present invention when the parameter k is 1 / 2 is shown. 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 Figure 1 As shown, 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 crucial to the entire technology. It involves constructing a digital core model with varying degrees of irregularity using the proposed modeling method. The focus here is on describing the construction of the irregular, uneven shape of a single grain. The process of constructing irregularly uneven grains based on a single sphere is as follows: Figure 2 As shown.

[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-convex properties, it is necessary to cut the sphere using a spatial plane and establish the relationship between the two. A crucial step is determining the coordinate position of the key point G. First, a three-dimensional Cartesian coordinate system is established with the sphere center O 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 sphere center, such as... Figure 3 Point G (r, α, β) in (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 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.

[0063] In this embodiment, given the coordinates of the sphere's center O and the coordinates of the key point G, a unique first straight line is established through these two points. A unique spatial plane (tangent plane) is then established through the key point G and perpendicular to this line; that is, a tangent plane is established to the sphere. This tangent plane is defined as A. Figure 3 As shown in (a), for a small sphere, any number of spatial planes (cutting planes) can be created to cut the sphere. 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 becomes, thus simulating the irregularity of actual rock particles. Figure 3 Figure (b) shows multiple cut surfaces cutting the sphere to form irregular particles. Furthermore, the position of the cut surface is closely related to the position of the key point G. 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 of the sphere is removed; conversely, the farther away the key point G is, the larger the removed portion. The azimuth and polar angle parameters can control the position of the cut surface.

[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 shape properties. Figure 3 The dashed circle in (b) shows that the particle has a concave shape.

[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] Through examples ( Figure 4 , Figure 5 , Figure 6 , Figure 7 The modeling effectiveness of this method is demonstrated, for example, by controlling the parameter k, a porous digital core of particles with irregular concave and convex shapes is formed. Figure 4 It is a three-dimensional digital core model with different porosities constructed based on regular small spheres. It can be seen that the mineral particles in the figure are regular small spheres, and ϕ in the figure represents porosity. Figure 5 This is a three-dimensional digital core model of irregularly shaped, uneven particles constructed based on parameter k of 5 / 6. In the figure, the mineral particles are no longer regular spheres but have become irregular shapes, although their roundness is still relatively good. Figure 6 This is a three-dimensional digital core model of irregular, uneven particles constructed based on parameter k being 2 / 3. The irregularity of the particles in the figure increases. Figure 7 This is a three-dimensional digital core model of irregularly shaped particles constructed based on a parameter k of 1 / 2. The particles in the image are more irregular in shape, with sharp edges and poor roundness, resulting in a more complex pore structure. These examples demonstrate that this method can controllably, cost-effectively, and efficiently construct three-dimensional digital core models with irregularly shaped particles.

[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, several regular spheres of different sizes are constructed into several irregular concave-convex particles; S4. Simulate the deposition and compaction diagenesis process of several irregular and uneven particles in three-dimensional space to obtain digital core models with different pore structures; The method for obtaining a single particle with an irregular, uneven shape includes: 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; 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; S23. Establish 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 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.

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: ； ； 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.

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.

Images