Visual model, experimental device and method for three-dimensional fracture seepage research

Abstract

The invention discloses a visual model, an experimental device and a method for three-dimensional fracture seepage research. The method comprises a three-dimensional fracture medium model manufacturing method, a refractive index matching technology and a three-dimensional fracture model visual experimental technology based on surface laser scanning fluorescence imaging. The experimental device comprises a material for constructing a solid model by adopting a parameterized curved surface generation technology, a CT (Computed Tomography) rock core scanning method and the like, and a refractive index matching liquid material matched with the model, wherein the material is used for constructing the solid model by using a 3D (Three-Dimensional) printing technology. According to the method, a three-dimensional fracture model with natural characteristics is generated through parametric modeling, a three-dimensional transparent fracture solid model is constructed by utilizing a 3D printing technology, and then visualization of an internal structure and a seepage behavior of the three-dimensional fracture model is realized by combining a solid-liquid system refractive index matching technology. The experimental device breaks through limitations in multiple aspects of seepage model dimension, visualization degree, seepage velocity and the like in a three-dimensional fractured medium seepage experiment, and has the advantages of good experimental effect, simplicity in construction and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of fractured medium seepage, and in particular to a visualization model, an experimental device and a method for studying complex seepage and transmission mechanisms of three-dimensional fractured media. Background Art

[0002] Seepage in underground fractured rock masses is a common occurrence in natural and industrial processes, including water conservancy project construction and safe operation, groundwater pollution and remediation, and oil and gas resource extraction. The mechanism of seepage in fractured media has become a key scientific issue of shared concern in the fields of water conservancy, energy, environment, and geotechnical engineering. In-depth research on the microscopic seepage mechanisms and macroscopic patterns of fracture network seepage is crucial for preventing and controlling groundwater pollution and improving energy extraction efficiency.

[0003] Due to the opacity of geotechnical structures, the complex spatial distribution of fractures, and the limitations of experimental observation methods, direct and precise in situ prediction of microscopic seepage in porous rock is currently difficult. Therefore, indoor seepage visualization experiments are the primary means of studying the microscopic flow characteristics and mesoscopic mechanisms of seepage in fractured media. Current methods for conducting indoor microscopic seepage experiments in fractured media primarily include core visualization experiments, two-dimensional planar fracture network experiments, and other simulation model experiments. In addition, there are methods such as establishing three-dimensional fracture numerical simulation systems. Core sample seepage experiments can accurately characterize the complex multiphase seepage within the three-dimensional structure of underground pores and fractures. However, due to the opacity of cores, visualization of the seepage process requires the use of expensive equipment such as CT scans and MRI machines. Limited by equipment and experimental techniques, these studies have encountered problems such as slow scanning speed, limited scanning accuracy, and limited scan size. Two-dimensional planar fracture network experiments utilize transparent plane models combined with light transmission for observation. While these experiments offer advantages such as simple model construction, clear experimental results, and ease of observation, they are limited to two-dimensional experiments and cannot reflect true three-dimensional characteristics. Numerical simulations of three-dimensional fracture systems offer lower costs and enable comprehensive dynamic observation of seepage processes, but they are limited in their inability to reflect actual fluid motion within rock masses. Consequently, technological limitations have become a bottleneck in the study of microscopic seepage in fractured media, and overcoming the limitations of existing technologies is essential.

[0004] In summary, there are technical limitations in the study of multiphase seepage problems in fractured media. It is necessary to develop a three-dimensional fracture model visualization experimental device for studying the complex seepage and transmission mechanisms of three-dimensional fracture networks to solve the existing technical limitations. Summary of the Invention

[0005] The purpose of the present invention is to provide a visualization model, experimental device and method for three-dimensional fracture seepage research in response to the problems existing in the prior art.

[0006] To achieve the above object, the technical solution adopted by the present invention is: On the one hand, a visualization model for three-dimensional fracture seepage research is provided, wherein the visualization model includes a plurality of fracture surfaces and a transparent closed body connecting and wrapping the plurality of fracture surfaces, wherein fracture spaces are formed between adjacent fracture surfaces, and a plurality of fracture spaces are connected and communicated; an inlet cavity is provided at the end of the fracture space, and the inlet cavity is respectively connected to a plurality of injection ports, wherein the inlet cavity and the injection port are both located in the transparent closed body, and the injection port is communicated with the outside of the transparent closed body.

[0007] Although the visualization model has a simple external structure, it is internally provided with irregular fracture surfaces, forming interconnected fracture spaces. The fracture spaces can be used to inject experimental liquids. By selecting transparent materials, the seepage of the experimental liquid in the fracture spaces can be observed from the outside. This visualization model breaks through multiple technical bottlenecks in traditional three-dimensional fracture seepage experiments, such as limited model dimensions, insufficient visualization, and difficulty in observing seepage velocity. This makes this visualization model have the advantages of significant experimental effects and simplified operation procedures.

[0008] Furthermore, the transparent closed body is a cubic structure, and the number of the crack surfaces is four and they are arranged horizontally and vertically, with two crack surfaces in the same direction being arranged opposite to each other and staggered with crack surfaces arranged opposite to each other in the other direction.

[0009] Furthermore, each of the inlet cavities is connected to 2-5 of the injection ports respectively; the visualization model also includes an auxiliary injection plate connected to the transparent enclosure, the auxiliary injection plate being provided with a single injection plate inlet and multiple injection plate outlets, and the multiple injection plate outlets are respectively connected to multiple injection ports.

[0010] Furthermore, a method for making the visualization model includes the following steps: Design and generate three-dimensional fractured media simulation models; Based on the three-dimensional fracture medium simulation model, solid materials are selected, and a three-dimensional fracture medium solid model is constructed using 3D printing technology. After printing is completed, cleaning and trimming are performed to obtain the visualization model.

[0011] Furthermore, the structural feature construction method of the three-dimensional fracture medium simulation model includes one or more of a parameterized surface generation method, a CT scanning core method, and a random generation method based on statistics and fractal theory.

[0012] Furthermore, the method for generating the three-dimensional fracture medium simulation model includes the following steps: The fracture surface is simulated by parametric surface generation method, whose non-uniform geometric characteristics are controlled by discretized coordinate parameters to generate a reference rough surface; Performing an array copy operation on the generated reference rough plane, translating and copying the reference rough plane along the normal direction to form a parallel crack structure with a preset opening, and generating a three-dimensional single-group crack model; Based on the three-dimensional single-group fracture model, orthogonal reconstruction of the fracture structure is achieved through a three-dimensional spatial transformation matrix to form a cross-fracture framework with a spatial orthogonal distribution. Then, geometric fusion is implemented using a Boolean difference operation. During the operation, a geometric tolerance compensation algorithm is synchronously executed to eliminate microscopic gaps generated by digital modeling. Finally, surface fusion processing is performed on the cross nodes of the cross-fracture framework, and fluid channels are opened at each end of the cross-fracture framework, that is, the inlet cavity and the injection port are set to generate the three-dimensional fracture medium simulation model.

[0013] Furthermore, the solid materials required for 3D printing are all transparent photosensitive resins with a refractive index of 1.51 to 1.53.

[0014] On the other hand, an experimental device for three-dimensional fracture seepage research is provided, which uses the above-mentioned visualization model for three-dimensional fracture seepage research. The experimental device includes an experimental platform, on which the visualization model is set through an adjustable bracket, a high-speed camera is arranged on one side of the visualization model, and a rotatable and adjustable reflector is arranged on the other side. A laser generator is also provided on the experimental platform, and the laser generator is arranged toward the reflector; the experimental device also includes a host computer connected to the high-speed camera, and an injection pump electrically connected to the host computer, the injection pump is connected to the visualization model and injects liquid into the visualization model.

[0015] Furthermore, the experimental platform is provided with an electric turntable, on which the reflector is arranged, the intersection line of the surface laser generated by the laser generator and the reflective surface of the reflector, the central axis of rotation of the reflector and the central axis of rotation of the electric turntable are all coaxially arranged, and a filter is also provided in front of the lens of the high-speed camera, and the lens of the high-speed camera is aimed at the surface of the visualization model scanned by the laser.

[0016] An experimental method for studying three-dimensional fracture seepage, comprising the following steps: Install and debug the experimental device; Preparing liquid materials required for the experiment, wherein the liquid materials include a refractive index matching liquid, and fluorescent particles are mixed in the refractive index matching liquid; Slowly injecting the liquid material into the visualization model from the injection port until the crack space is filled with the liquid material; Turn on the laser generator, adjust the reflector so that the reflected laser light is tangent to the edge of the visualization model, and set the tangent position coordinates as the two end coordinates of the reciprocating motion; then set the rotation speed and number of cycles of the reflector; Placing the visualization model in a completely dark state, starting the high-speed camera, adjusting the shooting parameters of the high-speed camera, and performing black and white balance correction; Starting the injection pump and setting different injection speeds so that the flow field injected into the visualization model reaches stability within a preset time; The reflector starts to rotate, and the high-speed camera starts to take pictures, and stops after several cycles; The experimental images taken by the high-speed camera are exported and input into a three-dimensional reconstruction code for processing to obtain a three-dimensional point cloud model. The density of the points in the three-dimensional point cloud model is analyzed to obtain the visualized streamlines of the crack space in the visualization model. Several of the visualized streamlines constitute a three-dimensional cross-crack flow field in the three-dimensional space.

[0017] Compared with the existing technology, the beneficial effects of the present invention are: 1. Although the external structure of the visualization model is simple, it is provided with irregular crack surfaces inside to form a connected crack space, which can be used to inject experimental liquid. By selecting transparent materials, the seepage of the experimental liquid in the crack space can be observed from the outside; 2. This visualization model breaks through the multiple technical bottlenecks of traditional three-dimensional crack seepage experiments, such as limited model dimensions, insufficient visualization, and difficulty in observing seepage velocity, so that this visualization model has the advantages of significant experimental effects and simplified operation procedures; 3. Based on multiple technologies such as parametric modeling The model generation method can obtain a rough crack surface with natural characteristics, ensure the authenticity of the model's geometric morphology, and significantly simplify the modeling process of complex crack structures; 4. High-precision transparent solid model construction uses 3D printing technology to manufacture transparent solid models. The selected printing material is highly matched with the refractive index of the experimental liquid, which effectively eliminates the optical interference inside the model, ensures the imaging clarity of the seepage process, and greatly improves the experimental visualization level; 5. This model and method can be seamlessly integrated with the surface laser three-dimensional rotation scanning system, supporting all-round observation of the dynamic seepage process, and significantly reducing the experimental complexity of the study of the seepage and transmission mechanism of three-dimensional fracture media. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is an overall schematic diagram of a visualization model for three-dimensional fracture seepage research according to the present invention; Figure 2 Schematic diagram of a physical model of the three-dimensional crack visualization model of the present invention; Figure 3 Photos of the three-dimensional crack visualization model of the present invention before and after achieving refractive index matching; Figure 4 This is an experimental photo of the flow field visualization experiment of the three-dimensional fracture visualization model of the present invention; Figure 5 This is a schematic diagram of the three-dimensional fracture model seepage experimental device of the present invention: In the figure: 1. Visual model; 2. First injection port; 3. Second injection port; 4. Third injection port; 5. Fourth injection port; 6. Fracture surface; 7. Inlet cavity; 8. Experimental platform; 9. Reflector; 10. Electric turntable; 11. Laser generator; 12. Turntable controller; 13. Host computer; 14. High-speed camera; 15. Injection pump; 16. Adjustable bracket. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first," "second," etc., etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Example 1

[0021] like Figure 1 As shown, a visualization model for three-dimensional fracture seepage research, the visualization model 1 includes a plurality of fracture surfaces 6, and a transparent closed body connecting and wrapping the plurality of fracture surfaces, fracture spaces are formed between adjacent fracture surfaces 6, and a plurality of the fracture spaces are connected and communicated; an inlet cavity 7 is provided at the end of the fracture space, and the inlet cavity 7 is respectively connected to a plurality of injection ports, the inlet cavity 7 and the injection ports are both located in the transparent closed body, and the injection ports are communicated with the outside of the transparent closed body.

[0022] Although the visualization model 1 has a simple external structure, it is provided with irregular fracture surfaces 6 inside, forming a connected fracture space. The fracture space can be used to inject experimental liquid. By selecting a transparent material, the seepage of the experimental liquid in the fracture space can be observed from the outside. This visualization model breaks through multiple technical bottlenecks in traditional three-dimensional fracture seepage experiments, such as limited model dimensions, insufficient visualization, and difficulty in observing seepage velocity. This makes this visualization model have the advantages of significant experimental effects and simplified operation procedures.

[0023] The inlet cavity 7 is provided with a plurality of injection ports to facilitate the uniform entry of the experimental liquid into the crack space. These injection ports are used as both injection channels and discharge channels, allowing the experimental liquid to enter and exit.

[0024] Furthermore, the transparent enclosure is a cubic structure, and the crack surfaces are four arranged horizontally and vertically, with two crack surfaces in the same direction arranged opposite to each other and staggered with the crack surfaces arranged opposite to each other in the other direction to form a cross-shaped crack space.

[0025] For the visualization model 1 of the cube, after a cross-shaped crack space is set up inside it, multiple groups of injection ports are arranged on its four faces, namely the first injection port 2, the second injection port 3, the third injection port 4 and the fourth injection port 5, wherein the first injection port 2 and the second injection port 3 are set on opposite faces, and the third injection port 4 and the fourth injection port 5 are set on another opposite face; during the experiment, the injection ports on each face can be connected to the pipeline for use at the same time, or two opposite groups of injection ports can be blocked, leaving the other two groups of injection ports for use.

[0026] Furthermore, each of the inlet cavities 7 is connected to three of the injection ports respectively; the visualization model also includes an auxiliary injection plate connected to the transparent enclosure, the auxiliary injection plate being provided with a single injection plate inlet and multiple injection plate outlets, and the multiple injection plate outlets are respectively connected to multiple injection ports.

[0027] In order to facilitate the simultaneous injection of experimental liquids into each group of multiple injection ports, an auxiliary injection plate is set up. The auxiliary injection plate has only one injection plate inlet, which can be directly connected to a syringe or an injection pump for liquid injection. It has multiple injection plate outlets, which just correspond to each group of injection ports. In this way, each group of injection ports can be injected with liquid at the same time, which not only improves the injection efficiency and convenience, but also is conducive to the uniformity and stability of the injection.

[0028] The auxiliary injection plate is made of acrylic material and can be made transparent. The auxiliary injection plate can be pasted on the visualization model or fixed on the visualization model by screws. Example 2

[0029] This embodiment provides a method for making the visualization model in Embodiment 1, which includes the following steps: Step 1: Design and generate a three-dimensional fracture medium simulation model; Step 2: Based on the three-dimensional fracture medium simulation model, solid materials are selected and a three-dimensional fracture medium solid model is constructed using 3D printing technology. After printing, the model is cleaned and trimmed to obtain the visualization model.

[0030] By using a three-dimensional fracture visualization model (i.e., the three-dimensional fracture medium entity model), saturated sodium iodide liquid is used to achieve refractive index matching of the model, and a three-dimensional rotating surface laser scanning system is combined to achieve visualization of three-dimensional fracture seepage.

[0031] Furthermore, the three-dimensional fracture medium simulation model includes structural features and dimensional features, and its structural feature construction method includes one or more of a parametric surface generation method, a CT scanning core method, and a random generation method based on statistics and fractal theory.

[0032] The model generation method based on various technologies such as parametric modeling can obtain a rough crack surface with natural characteristics, ensuring the authenticity of the model's geometric morphology, while significantly simplifying the modeling process of complex crack structures.

[0033] The high-precision transparent solid model is constructed using 3D printing technology. The selected printing material is highly matched with the refractive index of the experimental liquid, which effectively eliminates optical interference (such as reflection and refraction) inside the model, ensures the imaging clarity of the seepage process, and greatly improves the level of experimental visualization.

[0034] This model and method can be seamlessly integrated with the surface laser three-dimensional rotation scanning system, supporting all-round observation of the dynamic seepage process and significantly reducing the experimental complexity of the study of seepage and transport mechanisms in three-dimensional fractured media.

[0035] Furthermore, the method for generating the three-dimensional fracture medium simulation model includes the following steps: Step 1: The fracture surface is simulated by a parametric surface generation method, whose non-uniform geometric features are controlled by discretized coordinate parameters to generate a reference rough surface; The specific implementation method is to generate the displacement field in the z-axis direction in the three-dimensional coordinate system: , Where s1 and s2 are dynamic frequency parameters (value range 0≤s1, s2≤1), and the amplitude coefficient 0.01 is used to constrain the magnitude of the z-axis fluctuation to avoid excessive distortion of the surface, ensuring that the generated surface maintains planar features at the macro level while exhibiting microscopic roughness.

[0036] Step 2: Perform an array replication operation on the generated reference rough plane, translate and replicate the reference rough plane along the normal direction to form a parallel crack structure with a preset opening, and generate a three-dimensional single-group crack model; the gap area formed between the two reference rough planes is the physical crack space, that is, the crack space.

[0037] Step 3: Based on the three-dimensional single-group fracture model, orthogonal reconstruction of the fracture structure is achieved through a three-dimensional spatial transformation matrix to form a cross-fracture framework with spatial orthogonal distribution; then, geometric fusion is performed using a Boolean difference operation, and a geometric tolerance compensation algorithm is synchronously executed during the operation process to eliminate microscopic gaps generated by digital modeling. Finally, surface fusion processing is performed on the cross nodes of the cross-fracture framework, and fluid channels are opened at each end of the cross-fracture framework, that is, the inlet cavity and the injection port are set to generate the three-dimensional fracture medium simulation model; Specifically, the original fracture group (i.e., the three-dimensional single-group fracture model) is first spatially replicated, and then a 90° rotation transformation around the normal axis is applied to form a cross-fracture framework with spatial orthogonal distribution; then, a Boolean difference operation is used to implement geometric fusion, defining the original fracture group as the subtracted entity and the rotated fracture group as the tool entity, and the interfering parts of the two three-dimensional single-group fracture models in the intersection area are accurately removed through spatial topological relationship calculation; during the operation, a geometric tolerance compensation algorithm is synchronously executed to eliminate the microscopic gaps generated by digital modeling; finally, NURBS surface fusion processing is performed on the cross-intersection nodes to ensure the geometric continuity of the fracture space channel in three-dimensional space, and to generate a three-dimensional cross-fracture medium simulation model that meets the requirements of multi-physics field coupling analysis.

[0038] Furthermore, the solid materials required for 3D printing are all transparent photosensitive resins with a refractive index of 1.51 to 1.53. The product name of the transparent photosensitive resin is C-UV 9400R, and its specific components include bisphenol A epoxy resin (30-60%), acrylate (10-35%) and sulfonium salt mixture (3-7%).

[0039] In order to better observe the seepage situation in the visualization model, not only a transparent material but also a suitable refractive index is required. The refractive index of the solid material of the model entity needs to be matched with the refractive index of the liquid material, that is, a refractive index matching liquid that can be used well with the visualization model is formulated.

[0040] More specifically, the generation of the above-mentioned three-dimensional fractured medium solid model is achieved through a complete process of parametric modeling - format conversion and repair - Boolean operation - 3D printing verification. The specific implementation steps are as follows: S1. Define core parameters and initialization: Establish a global parameter control system in the parametric modeling platform and define the key parameters affecting the surface roughness of the crack, including the spectral index β, frequency component range, and fractal dimension D.

[0041] The spectral exponent β was set to 0.5, corresponding to high-roughness scenarios. Adjusting β can control the severity of surface undulations. The frequency component range was set to 10, and the harmonic components were constrained to be distributed within the interval m, n ∈ [-10, 10] to balance computational efficiency and spectral integrity. To ensure experimental reproducibility, the random seed value was fixed at 1234 to ensure consistency in the generated random field.

[0042] Furthermore, according to the fractal theory, the relationship between the fractal dimension D and the spectrum index β is associated, and the fractal dimension calculation formula is defined as follows: When β = 0.5, the calculated fractal dimension D ≈ 3.75, indicating a highly complex surface morphology; when β = 1.8, D ≈ 3.1, corresponding to a relatively smooth surface structure.

[0043] S2. Create a random function (such as a Gaussian random function): define a two-dimensional Gaussian distribution under the Random Function node, with mean μ=0 and standard deviation σ=1; for a uniform random function, define the phase angle range as [0, 2π].

[0044] S3. Construct a visual parametric surface: Based on the Weierstrass-Mandelbrot fractal function, enter the surface generation expression in the formula editor: , Where, the value range of s1 and s2 is [0, 1]. The amplitude coefficient of 0.01 is used to constrain the amplitude of the z-axis fluctuation to avoid excessive distortion of the surface. The parameters s1 and s2 are dynamically adjusted by the slider controller with a step size accuracy of 0.01.

[0045] z(x,y) represents the surface height function, m and n are integer index variables with a value range of [-N,N], covering positive and negative frequency components to meet symmetry, N is the upper limit of the summation, determining the symmetry range of m and n ±N; b is the fractal roughness parameter, which controls the complexity of the surface details; g1(m,n) represents the random phase factor, which is used to generate random perturbations; u1(m,n) represents the random phase offset function, which further introduces randomness; cos(2π(ms1+ ns2) + u1(m, n)) represents the phase fluctuation term, which combines dynamic frequency and random offset; if condition: when m=0 or n=0, exclude the central term to avoid redundant calculation; the logical symbol "V" in the conditional judgment represents the logical "or", that is, the exclusion operation is triggered when m=0 or n=0.

[0046] S4. Perform geometry optimization and generate high-precision mesh NURBS surface optimization was performed with the number of control nodes set to 5000, the fitting tolerance set to 0.001 mm, the adaptive subdivision algorithm enabled, and the sharpness of the crack edges preserved. Finite element meshing was performed using free tetrahedral elements with a global maximum element size of 0.1 mm, and a three-layer boundary layer mesh was set at the crack edges. The STL file of the reference rough surface is obtained through the above operations. The STL file is exported in binary format with a resolution of 20,000 surfaces / mm², and unit calibration verification is performed (in millimeters).

[0047] S5. Convert formats and repair model topology STL file preprocessing: perform vertex welding and normal unification operations to eliminate duplicate vertices; model repair: repair holes and optimize the number of faces, retaining 90% of the face details; DWG format conversion: the unit is millimeter, retaining the layered structure of the model; obtain the DWG format rough surface of the reference rough surface.

[0048] Step 6: Combine the 3D models Basic model creation: draw a cube of 6 cm × 6 cm × 6 cm, and reserve a cavity of 3.5 cm × 3.5 cm × 4 cm inside; the three-dimensional single-group fracture model generation: import the rough plane in DWG format, copy the rough plane and shift it 2 mm along the z-axis, and cut the cube through Boolean difference operation to obtain the fracture space; Orthogonal fracture construction: The fracture structure (the three-dimensional single-group fracture model) is copied and rotated 90 degrees, and the Boolean difference operation is performed again to form a cross-fracture framework with spatial orthogonal distribution. Fluid channel processing: The Boolean difference operation is used to open a water diversion groove on the side of the cube (i.e., the inlet cavity and the injection port are set) to serve as a fluid channel; finally, a three-dimensional fracture medium simulation model is obtained.

[0049] S7. Export the three-dimensional fracture medium simulation model and print it: export it to a high-precision STL format with a unit of millimeter, and perform 3D printing on the obtained three-dimensional fracture medium simulation model to obtain a solid model. Example 3

[0050] This embodiment provides an experimental device for three-dimensional fracture seepage research. Figure 5As shown, the visualization model for three-dimensional fracture seepage research in Example 1 is used, and the experimental device includes an experimental platform 8, on which the visualization model 1 is set through an adjustable bracket 16, a high-speed camera 14 is arranged on one side of the visualization model 1, and a rotatable and adjustable reflector 9 is arranged on the other side. A laser generator 11 is also provided on the experimental platform 8, and the laser generator 11 is arranged toward the reflector 9; the experimental device also includes a host computer 13 connected to the high-speed camera 14, and an injection pump 15 electrically connected to the host computer 13, and the injection pump 15 is connected to the visualization model 1 and injects liquid into the visualization model 1.

[0051] Furthermore, an electric turntable 10 is provided on the experimental platform 8, and the reflector 9 is set on the electric turntable 10. The intersection of the surface laser generated by the laser generator 11 and the reflective surface of the reflector 9, the central axis of rotation of the reflector 9 and the central axis of rotation of the electric turntable 10 are all coaxially arranged. A filter is also provided in front of the lens of the high-speed camera 14, and the lens of the high-speed camera 14 is aimed at the surface of the visualization model 1 scanned by the laser.

[0052] The visualization model 1 is set on the adjustable bracket 16, and its support height and position can be adjusted according to actual needs; the laser generator 11 can be an argon ion laser, which can generate surface laser and irradiate the reflector 9; the reflector 9 is set on the electric turntable 10, and can adjust its direction in conjunction with the turntable controller 12 connected to it, and can also perform rotational motion under electric control; the filter is placed in front of the high-speed camera lens to filter out light of wavelengths other than the specific wavelength emitted after the visualization model is excited; the host computer is a computer, which is connected to these devices through cables, and parameter settings and operation settings can be performed on the computer.

[0053] An experimental method for three-dimensional fracture seepage research, combined with Figures 2 to 5 As shown, the experimental method includes the following steps: (1) Install and debug the experimental device; First, the three-dimensional visualization model 1 is installed on the adjustable bracket 16 of the test platform, and then the high-speed camera 14 is installed on the same horizontal axis as the visualization model 1. Then, the electric turntable 10 is installed on the side of the visualization model 1, and the reflector 9 is installed on the center of the electric turntable 10; then the laser generator 11 is installed on the rear side of the electric turntable 10, and the intersection of the surface laser generated by it and the reflecting surface of the reflector coincides with the rotation axis of the electric turntable 10, and the central axis of rotation of the reflector 9 coincides with the rotation axis of the electric turntable 10; the injection pump, high-speed camera, turntable controller, etc. are connected to the host computer through cables, and the output end of the injection pump is connected to the visualization model through a pipeline or the auxiliary injection plate.

[0054] (2) Prepare the liquid materials required for the experiment, wherein the liquid materials include a refractive index matching liquid, in which fluorescent particles are mixed; the refractive index matching liquid is a saturated aqueous solution of sodium iodide at 20°C, with a refractive index of 1.51, and then add an appropriate amount of fluorescent particles to prepare a solution containing fluorescent particles with a concentration of 3g / L.

[0055] In this example, 20 ml of deionized water was added in batches to 36.8 g of sodium iodide and stirred until completely transparent. Small amounts of sodium iodide were then gradually added and stirred until insoluble sodium iodide crystals appeared, thereby obtaining a saturated sodium iodide solution at room temperature. Subsequently, 0.06 g of fluorescent particles (Red Fluorescent Polymer Microspheres) were added to the prepared sodium iodide solution and stirred evenly. The amount of fluorescent particles used can be adjusted according to actual conditions.

[0056] (3) slowly injecting the liquid material into the visualization model from the injection port until the crack space is filled with the liquid material; In this embodiment, the third and fourth injection ports on the side of the visualization model are first sealed with transparent tape or a plug, and then a certain amount of refractive index matching liquid (for example, 50 ml of experimental liquid) added with fluorescent particles is drawn using an injector with a tube and a connector, and slowly injected at a low speed (for example, 5 ml / min) from the first injection port of the visualization model. The injection is stopped when liquid appears at the second injection port of the visualization model.

[0057] The specific operation of quantitatively measuring the volume of the refractive index matching liquid with fluorescent particles added is as follows: use an injector with a pipeline to pre-absorb the vacuumed refractive index matching liquid, exhaust the air in the injector and the pipeline by repeatedly sucking in slowly and quickly, and then absorb the corresponding volume of the refractive index matching liquid; install the injector on the injection pump, input the diameter and volume of the injector, set the injection volume and time, place the pipeline outlet close to the inlet below the three-dimensional fracture medium model, start the injection pump, and slowly inject a certain amount of refractive index matching liquid into the three-dimensional fracture medium model to realize the three-dimensional seepage process in the three-dimensional fracture medium model.

[0058] (4) Turn on the laser generator and adjust the reflector so that the reflected laser is exactly tangent to the edge of the visualization model, and set the tangent position coordinates as the two end coordinates of the round-trip motion; then set the rotation speed and number of cycles of the reflector, for example, the rotation speed is 5.00 mm / s, the number of cycles is 20, and the round-trip motion delay is 1000 ms and 2000 ms respectively.

[0059] (5) placing the visualization model in a completely dark state, starting the high-speed camera, adjusting the shooting parameters of the high-speed camera, and performing black and white balance correction; The experimental platform described in this embodiment is equipped with a blackout curtain. The blackout curtain is closed to put the visualization model in a completely dark state. The high-speed camera is started and adjusted to an appropriate shooting speed (60fps), shutter speed (1 / 60 s), and resolution (512×512). Black and white balance correction is performed to reduce noise.

[0060] (6) Start the injection pump and set different injection speeds (e.g., 20 ml / min, 30 ml / min) so that the flow field in the visualization model becomes stable within a preset time. For example, the liquid flow field in the visualization model becomes stable after 5 seconds of injection.

[0061] Through the operation of the host computer, the reflector starts to rotate and the high-speed camera starts to take pictures, and stops after about 20 cycles.

[0062] (7) The experimental image taken by the high-speed camera is exported and input into a three-dimensional reconstruction code for processing to obtain a three-dimensional point cloud model. The density of the points in the three-dimensional point cloud model is analyzed to obtain the visualization streamlines of the crack space in the visualization model. Several of the visualization streamlines constitute a three-dimensional cross-crack flow field in the three-dimensional space.

[0063] Through the experimental method of the present invention, a transparent fracture model is used as an experimental object, and on the basis of ensuring that the fracture geometry can reflect the rock fracture geometry, the visual observation of the internal seepage of the fracture medium is achieved.

[0064] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A visualization model for three-dimensional fracture seepage research, characterized by: The visualization model includes several crack surfaces and a transparent closed body connecting and wrapping the several crack surfaces, a crack space is formed between adjacent crack surfaces, and multiple crack spaces are connected and communicated; an inlet cavity is provided at the end of the crack space, and the inlet cavity is respectively connected to several injection ports, the inlet cavity and the injection port are both located in the transparent closed body, and the injection port is communicated with the outside of the transparent closed body.

2. The visualization model for three-dimensional fracture seepage research according to claim 1, characterized in that: The transparent closed body is a cubic structure, and the number of the crack surfaces is four and they are arranged horizontally and vertically. Two crack surfaces in the same direction are arranged opposite to each other and are staggered with the crack surfaces arranged opposite to each other in the other direction.

3. The visualization model for three-dimensional fracture seepage research according to claim 1, characterized in that: Each of the inlet cavities is connected to 2-5 of the injection ports respectively; the visualization model also includes an auxiliary injection plate connected to the transparent closed body, the auxiliary injection plate is provided with a single injection plate inlet and multiple injection plate outlets, and the multiple injection plate outlets are respectively connected to multiple injection ports.

4. The visualization model for three-dimensional fracture seepage research according to claim 1, characterized in that: A method for making the visualization model comprises the following steps: Design and generate three-dimensional fractured media simulation models; Based on the three-dimensional fracture medium simulation model, solid materials are selected, and a three-dimensional fracture medium solid model is constructed using 3D printing technology. After printing is completed, cleaning and trimming are performed to obtain the visualization model.

5. The visualization model for three-dimensional fracture seepage research according to claim 4, characterized in that: The structural feature construction method of the three-dimensional fracture medium simulation model includes one or more of a parameterized surface generation method, a CT scanning core method, and a random generation method based on statistics and fractal theory.

6. The visualization model for three-dimensional fracture seepage research according to claim 4, characterized in that: The method for generating the three-dimensional fracture medium simulation model comprises the following steps: The fracture surface is simulated by parametric surface generation method, whose non-uniform geometric characteristics are controlled by discretized coordinate parameters to generate a reference rough surface; Performing an array copy operation on the generated reference rough plane, translating and copying the reference rough plane along the normal direction to form a parallel crack structure with a preset opening, and generating a three-dimensional single-group crack model; Based on the three-dimensional single-group fracture model, orthogonal reconstruction of the fracture structure is achieved through a three-dimensional spatial transformation matrix to form a cross-fracture framework with a spatial orthogonal distribution. Then, geometric fusion is implemented using a Boolean difference operation. During the operation, a geometric tolerance compensation algorithm is synchronously executed to eliminate microscopic gaps generated by digital modeling. Finally, surface fusion processing is performed on the cross nodes of the cross-fracture framework, and fluid channels are opened at each end of the cross-fracture framework, that is, the inlet cavity and the injection port are set to generate the three-dimensional fracture medium simulation model.

7. The visualization model for three-dimensional fracture seepage research according to claim 4, characterized in that: The solid materials required for 3D printing are all transparent photosensitive resins with a refractive index of 1.51 to 1.

53.

8. An experimental device for three-dimensional fracture seepage research, characterized in that: A visualization model for three-dimensional fracture seepage research according to any one of claims 1 to 7 is used, and the experimental device includes an experimental platform, on which the visualization model is set through an adjustable bracket, a high-speed camera is arranged on one side of the visualization model, and a rotatable and adjustable reflector is arranged on the other side. A laser generator is also provided on the experimental platform, and the laser generator is arranged toward the reflector; the experimental device also includes a host computer connected to the high-speed camera, and an injection pump electrically connected to the host computer, and the injection pump is connected to the visualization model and injects liquid into the visualization model.

9. The experimental device for three-dimensional fracture seepage research according to claim 8, characterized in that: An electric turntable is provided on the experimental platform, the reflector is arranged on the electric turntable, the intersection line of the surface laser generated by the laser generator and the reflective surface of the reflector, the central axis of rotation of the reflector and the central axis of rotation of the electric turntable are all coaxially arranged, and a filter is also provided in front of the lens of the high-speed camera, and the lens of the high-speed camera is aimed at the surface of the visualization model scanned by the laser.

10. An experimental method for studying three-dimensional fracture seepage, characterized in that: The experimental device for three-dimensional fracture seepage research according to claim 8 is used, and the experimental method includes the following steps: Install and debug the experimental device; Preparing liquid materials required for the experiment, wherein the liquid materials include a refractive index matching liquid, and fluorescent particles are mixed in the refractive index matching liquid; Slowly injecting the liquid material into the visualization model from the injection port until the crack space is filled with the liquid material; Turn on the laser generator, adjust the reflector so that the reflected laser light is tangent to the edge of the visualization model, and set the tangent position coordinates as the two end coordinates of the reciprocating motion; then set the rotation speed and number of cycles of the reflector; Placing the visualization model in a completely dark state, starting the high-speed camera, adjusting the shooting parameters of the high-speed camera, and performing black and white balance correction; Starting the injection pump and setting different injection speeds so that the flow field injected into the visualization model reaches stability within a preset time; The reflector starts to rotate, and the high-speed camera starts to take pictures, and stops after several cycles; The experimental images taken by the high-speed camera are exported and input into a three-dimensional reconstruction code for processing to obtain a three-dimensional point cloud model. The density of the points in the three-dimensional point cloud model is analyzed to obtain the visualized streamlines of the crack space in the visualization model. Several of the visualized streamlines constitute a three-dimensional cross-crack flow field in the three-dimensional space.

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