Proppant conveying numerical simulation method based on high-fidelity rough crack structured grid

Abstract

The invention relates to a propping agent conveying numerical simulation method based on a high-fidelity rough crack structured grid, and the method comprises the following steps: S1, obtaining rock plate crack rough surface point cloud data based on a 3D laser scanning technology, and constructing a crack rough surface model according to the point cloud data; s2, based on a group of corresponding crack rough surface models, defining the minimum width of a coupling crack, and constructing a simulated three-dimensional entity comprising a group of crack rough surfaces; and S3, after structured mesh generation is carried out on the simulated three-dimensional entity constructed in the step S2, propping agent conveying numerical simulation is carried out. According to the method, the morphology of the rough surface of the crack is reserved to the maximum extent through boundary point cloud data finishing, the rough crack geometric model is subdivided by adopting the structured grid, the real rough crack morphology can be restored, and the calculation precision and the calculation efficiency are further improved.

Description

Technical Field

[0001] The invention relates to the field of oil and gas field development engineering, and in particular to a proppant transport numerical simulation method based on a high-fidelity rough fracture structured grid. Background Art

[0002] During the hydraulic fracturing of unconventional oil and gas reservoirs, the rock matrix undergoes significant tension and shear damage under the strong drive of high-pressure fluids, thus shaping a series of fracture walls with diverse roughness. The movement characteristics of proppant particles are directly regulated by the roughness of the fracture walls, and their migration and sedimentation are highly complex and uncertain, resulting in a unique distribution pattern and laying form of proppants in the fractures. This process not only finely regulates the support structure of the fracture, but also ultimately determines the fracture diversion efficiency and the long-term production capacity of oil and gas wells, which is of vital importance to improving the efficiency and economic benefits of oil and gas resource extraction.

[0003] In order to deeply explore the influence of the rough surface of the fracture on the dynamic behavior of the proppant particles, the numerical simulation technology of solid-liquid multiphase flow is often used. The first step of this process is to construct a geometric model of the rough fracture and mesh it. At present, the methods for constructing the rough fracture surface mainly include the JRC (Joint Roughness Coefficient) method, the spectral function method and the point cloud data reconstruction method based on 3D laser scanning. Among them, the JRC method relies on the empirical division of the linear characteristics of the fracture to characterize the rough fracture surface; the spectral function law digitally reconstructs the rough fracture surface through statistical parameters and filtering analysis. However, neither of these two methods can restore the rough morphology of the fracture more realistically. The point cloud data reconstruction method based on 3D laser scanning can truly restore the rough morphology of the fracture through high-precision point cloud data, showing good adaptability and broad application prospects in rough fracture geometric modeling. However, for fracture surfaces with a large degree of roughness (large surface tortuosity and roughness), the rough fracture surface patch and geometric model cannot be generated due to too many singular points in the point cloud data. In addition, the existing technology currently mainly uses unstructured grids to segment irregular rough crack geometric models, which are far inferior to structured grids in terms of calculation accuracy and calculation efficiency. Summary of the invention

[0004] In order to overcome the problems in the prior art, the present invention provides a method for numerical simulation of proppant transport based on high-fidelity rough fracture structured grids. To achieve the above purpose, the present invention provides the following solutions:

[0005] A method for numerical simulation of proppant transport based on high-fidelity rough fracture structured grids, comprising the following steps:

[0006] S1. Obtaining point cloud data of the rough surface of the rock slab crack based on 3D laser scanning technology, and constructing a rough surface model of the crack according to the point cloud data;

[0007] S2, based on a set of corresponding crack rough surface models, defining the minimum width of the coupled cracks, and constructing a simulated three-dimensional entity including a set of crack rough surfaces;

[0008] S3. After performing structured meshing on the simulated three-dimensional entity constructed in step S2, a proppant transport numerical simulation is performed.

[0009] A further technical solution is that step S1 includes

[0010] The point cloud data is imported into the processing software, and denoising, packaging, mesh repair, surface patch construction, grid construction, and surface fitting are performed in sequence.

[0011] A further technical solution is to set the maximum number of triangles to no less than 250,000 when encapsulating; and to set the resolution to 100 when constructing the grid.

[0012] A further technical solution is that when an error message "there are intersecting surfaces" appears during the surface fitting step, return to the point cloud data state, check and delete the singular points on the four edges, and use curvature and boundary hole filling methods to fill the missing parts on the four edges with single holes.

[0013] A further technical solution is that the minimum width of the coupling crack defined in step S2 includes

[0014] The .iges format files of the upper and lower crack rough surface models obtained in step S1 are simultaneously imported into the Auto CAD software, and the upper and lower crack rough surface models are respectively subjected to a "union" operation to obtain two independent crack rough surface entities. The upper and lower crack rough surface entities are ensured to be in a coupled state through a "rotation" operation, and the minimum width of the coupled crack is defined through "translation" and "distance measurement" operations.

[0015] A further technical solution is that the minimum width of the rough crack is defined as 1.6 mm in step S2.

[0016] A further technical solution is that the step S3 also includes

[0017] The simulated three-dimensional entity constructed in step S2 is imported into the processing software, and mesh repair, flow area construction, flow inlet / outlet and crack wall definition, point-line-surface association of flow area and rough cracks, and structured mesh generation are performed in sequence.

[0018] On the other hand, the present invention provides a proppant transport numerical simulation system based on a high-fidelity rough fracture structured grid, comprising the following modules:

[0019] A crack rough surface point cloud data acquisition module is used to acquire the point cloud data of the crack rough surface of the rock plate using 3D laser scanning technology, and construct a crack rough surface model according to the point cloud data;

[0020] A simulated three-dimensional entity construction simulation is used to adopt a set of corresponding crack rough surface models, define a minimum width of coupled cracks, and construct a simulated three-dimensional entity including a set of crack rough surfaces;

[0021] The proppant transport numerical simulation module is used to perform structured grid division processing on the constructed simulated three-dimensional entity and perform proppant transport numerical simulation.

[0022] On the other hand, the present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that when the processor executes the computer program, the steps of the method for numerical simulation of proppant transport based on a high-fidelity rough fracture structured grid as described in any one of the above claims are implemented.

[0023] On the other hand, the present invention provides a computer-readable storage medium having a computer program stored thereon, characterized in that when the computer program is executed by a processor, the steps of the method for numerical simulation of proppant transport based on a high-fidelity rough fracture structured grid as described in any one of the above claims are implemented.

[0024] The present invention has the following advantages: The present invention provides a numerical simulation method for proppant transport based on a high-fidelity rough fracture structured grid, which retains the morphology of the rough surface of the fracture to the greatest extent through boundary point cloud data trimming, wherein the rough fracture geometric model is divided using a structured grid, which can restore the true rough fracture morphology, and further improves the calculation accuracy and efficiency compared to the simulation method in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 It is a schematic diagram of the method flow of the present invention;

[0027] Figure 2 is a crack rough surface model in an embodiment of the present invention;

[0028] Figure 3Schematic diagram of the relative positions of three entities before cutting in an embodiment of the present invention;

[0029] Figure 4 A three-dimensional solid image of a rough crack after sectioning in an embodiment of the present invention;

[0030] Figure 5 is a structured grid diagram of a rough fracture surface in an embodiment of the present invention;

[0031] Figure 6 This is a numerical simulation diagram of proppant transport in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0033] The object of the present invention is to provide a method for numerical simulation of proppant transport based on a high-fidelity rough fracture structured grid. In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0034] In the prior art, when the point cloud data reconstruction method of 3D laser scanning is used to restore the rough morphology of cracks, if there are too many singular points in the point cloud data, it will lead to the inability to restore the rough crack surface and geometric model. In addition, the performance of unstructured grids in terms of calculation accuracy and efficiency needs to be improved.

[0035] Based on this, Figure 1 As shown, the present invention provides a proppant transport numerical simulation method based on a high-fidelity rough fracture structured grid, comprising the following steps:

[0036] S1. Obtaining point cloud data of the rough surface of the rock slab crack based on 3D laser scanning technology, and constructing a rough surface model of the crack according to the point cloud data;

[0037] Specifically, for a split or sheared rock slab, two corresponding rough crack surfaces can be obtained, for example, a first crack surface and a second crack surface (i.e., two corresponding surfaces of a crack). 3D laser scanning technology (such as a high-resolution optical three-dimensional camera, scanner, etc.) can be used to scan the two corresponding rough crack surfaces respectively to obtain the original three-dimensional geometric data images of the two rough crack surfaces, and the elevation point cloud data is represented by spatial points (x, y, z). A coordinate system is established in space, and the xy plane is the reference horizontal plane passing through the lowest point of the crack surface. The z value represents the height value of the point on the crack surface. Each point on the crack surface is represented by (x, y, z), so the rough surface point cloud data of the rock slab can be obtained.

[0038] Specifically, the rough surface point cloud data of the rock slab obtained based on 3D laser scanning technology is imported into the Geomagic Studio software, and the steps of noise reduction, packaging, mesh repair, surface patch construction, grid construction, surface fitting, etc. are performed in sequence. The final rough surface model generated without error is exported in .iges format for use in constructing rough surface entities.

[0039] Specifically, the point cloud data is subjected to noise reduction and packaging, and the maximum number of triangles is set to no less than 250,000 during packaging; the resolution is set to 100 during grid construction.

[0040] If an error message "There are intersecting surfaces" appears during the surface fitting step, return to the point cloud data state, check and delete the singular points on the four edges, use curvature and boundary hole filling methods to fill the missing parts on the four edges with single holes, re-encapsulate and mesh repair them, and then perform encapsulation, mesh repair, surface patch construction, grid construction, surface fitting, etc. in sequence. In this step, by trimming the boundary point cloud data, compared with trimming the global point cloud data, the rough morphology of the crack can be retained to the greatest extent, so that the simulation results are more consistent with the actual situation.

[0041] S2, based on a set of corresponding crack rough surface models, defining the minimum width of the coupled cracks, and constructing a simulated three-dimensional entity including a set of crack rough surfaces;

[0042] Specifically, according to a set of corresponding crack roughness models (such as Figure 2 As shown, that is, the first crack seam surface and the second crack seam surface corresponding to a crack located at the upper and lower positions thereof), the upper and lower .iges format crack rough surface models obtained in step S1 are simultaneously imported into the Auto CAD software, and the upper and lower rough surface models are respectively subjected to a "union" operation to obtain two independent crack rough surface entities.

[0043] The longitudinal elevation difference between the first crack surface and the second crack surface is the crack width. Therefore, the "rotation (3DROTATE)" operation is used to ensure that the upper and lower crack rough surface entities are in a coupled state. The "translation (M)" and "distance measurement (DIST)" operations can be used to define the minimum width of the coupled crack. In the embodiment of the present invention, the minimum width of the rough crack is defined as 1.6 mm.

[0044] It should be noted that when performing the "DIST" operation, it is necessary to ensure that the distance between two rough surface entities is non-negative.

[0045] Specifically, when constructing a simulated three-dimensional entity, it is necessary to create a cuboid with a certain height (the height direction is consistent with the crack width direction) and a length and width slightly smaller than the minimum length and width of the rough surface entity. Figure 3 As shown in the figure, the cuboid and the upper and lower rough surface models are sliced ​​to obtain a rough crack three-dimensional entity (such as Figure 4 The height of the cuboid should be more than twice the width of the crack, and the length-width plane of the cuboid cannot exceed the length and width of the rough surface when cut.

[0046] S3. After performing structured meshing on the simulated three-dimensional entity constructed in step S2, a proppant transport numerical simulation is performed.

[0047] Specifically, the rough fracture model in .stl format in step S2 is imported into the ICEM software, and the steps of mesh repair (the repair error can be set to 0.01), flow area construction, flow inlet / outlet and fracture wall definition, point-line-surface association between flow area and rough fracture, and mesh generation are performed in sequence.

[0048] It should be noted that the structured meshing is performed on the associated geometry. During meshing, the minimum crack width is not less than 0.2 mm and the mesh scaling ratio is set to 1.05 or 1. Assuming that the node spacing is Δx, Δy, and Δz respectively, the coordinates (x ijk ,y ijk ,z ijk ) is expressed as:

[0049]

[0050] Where (x0, y0, z0) is the coordinate of the first node.

[0051] In a specific embodiment of the present invention, the minimum grid sizes in the length, width and height directions of the crack are set to 1, 0.4 and 1 mm respectively, and the grid scaling ratios in the three directions are 1.05, 1 and 1.05 respectively, to obtain a rough crack structured grid (such as Figure 5The rough fracture structured grid is exported in .msh format. The .msh format is imported into the computational fluid dynamics software, and the computational fluid dynamics-discrete element method is used to perform numerical simulation of fluid-solid coupled proppant transport (as shown in Figure 6 As shown in Figure 2 ). Since the narrow fracture wall has a strong interference effect on the migration of proppant particles, the calculation needs to adopt a drag model that takes into account the wall capture effect:

[0052]

[0053] In the formula, F D is the drag force; ls is the solid-liquid phase momentum exchange coefficient; subscripts l and s refer to the liquid phase and solid phase respectively; U is the movement velocity; α is the phase fraction; ρ is the density; d is the particle size; C D is the drag coefficient, Re s is the particle Reynolds number, and h is the distance from the particle to the crack wall.

[0054] The present invention provides a proppant transport numerical simulation method based on a high-fidelity rough fracture structured grid, in which the morphology of the fracture rough surface is retained to the greatest extent through boundary point cloud data trimming, and the rough fracture geometric model is segmented using a structured grid, which has the advantages of high-fidelity simulation of the fracture rough surface, high calculation accuracy and efficiency.

[0055] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for numerical simulation of proppant transport based on high-fidelity rough fracture structured grids, comprising the following steps: S1. Obtaining point cloud data of the rough surface of the rock slab crack based on 3D laser scanning technology, and constructing a rough surface model of the crack according to the point cloud data; S2. Based on a set of corresponding crack rough surface models, a minimum width of coupled cracks is defined, and a simulated three-dimensional entity including a set of crack rough surfaces is constructed; S3. After performing structured meshing on the simulated three-dimensional entity constructed in step S2, a proppant transport numerical simulation is performed.

2. According to the proppant transport numerical simulation method of claim 1, the step S1 comprises importing the point cloud data into processing software, and sequentially performing denoising, packaging, mesh repair, surface patch construction, grid construction, and surface fitting.

3. According to the proppant transport numerical simulation method of claim 2, the maximum number of triangles is set to be no less than 250,000 during packaging.

4. According to the proppant transport numerical simulation method of claim 2, when an error message "there are intersecting surfaces" appears in the surface fitting step, the point cloud data state is returned to check and delete the singular points on the four edges, and the missing parts on the four edges are filled with single holes using curvature and boundary hole filling methods.

5. The method for numerical simulation of proppant transport according to claim 1, wherein the minimum width of the coupled fracture is defined in step S2 as follows: Import the .iges format files of the upper and lower crack rough surface models obtained in step S1 into the Auto CAD software at the same time, perform the "union" operation on the upper and lower crack rough surface models respectively, and obtain two independent crack rough surface entities. The "rotation" operation is used to ensure that the upper and lower crack rough surface entities are in a coupled state, and the minimum width of the coupled crack is defined by the "translation" and "distance measurement" operations.

6. The proppant transport numerical simulation method according to claim 5, wherein the minimum width of the rough fracture defined in step S2 is 1.6 mm.

7. The proppant transport numerical simulation method according to claim 1, wherein step S3 further comprises: The simulated three-dimensional entity constructed in step S2 is imported into the processing software, and mesh repair, flow area construction, flow inlet / outlet and crack wall definition, point-line-surface association of flow area and rough cracks, and structured mesh generation are performed in sequence.

8. A proppant transport numerical simulation system based on high-fidelity rough fracture structured grid, including the following modules: A crack rough surface point cloud data acquisition module is used to acquire the point cloud data of the crack rough surface of the rock plate using 3D laser scanning technology, and construct a crack rough surface model according to the point cloud data; A simulated three-dimensional entity construction simulation is used to adopt a set of corresponding crack rough surface models, define a minimum width of coupled cracks, and construct a simulated three-dimensional entity including a set of crack rough surfaces; The proppant transport numerical simulation module is used to perform structured grid division processing on the constructed simulated three-dimensional entity and perform proppant transport numerical simulation.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the steps of the proppant transport numerical simulation method described in any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the proppant transport numerical simulation method described in any one of claims 1 to 8 are implemented.

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