Fracture characterization method and device based on two-dimensional sheet fracturing and layer-by-layer three-dimensional reconstruction

Abstract

The present application relates to the technical field of unconventional oil and gas reservoir fracturing development and rock physics experiment, and is a fracture characterization method and device based on two-dimensional slice fracturing and layer-by-layer three-dimensional reconstruction. The latter includes a core two-dimensional slice preparation module, a two-dimensional slice layer-by-layer fracturing experiment module, a fracture imaging and digital processing module, and a three-dimensional fracture network reconstruction module. The present application carries out two-dimensional slicing of the same core and layer-by-layer fracturing experiments under the same experimental conditions, eliminates the physical property difference interference between different cores caused by rock heterogeneity, and makes the fracture initiation pressure and expansion morphology reproducible. By converting three-dimensional core fracturing experiments into two-dimensional slice layer-by-layer fracturing experiments, the experimental device and operation process are simplified, the dependence on three-dimensional imaging monitoring equipment is reduced, the cost of core fracturing experiments is reduced, and the operation efficiency is improved. The present application has the characteristics of accurate characterization, repeatability and low cost.

Description

Technical Field

[0001] This invention relates to the field of fracturing development of unconventional oil and gas reservoirs and rock physics experimental technology, and is a method and apparatus for fracture characterization based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction. Background Technology

[0002] Fracture morphology is a crucial parameter characterizing the effectiveness of fracturing in unconventional oil and gas reservoirs. Its initiation location, propagation path, spatial distribution, and complexity directly determine the fracturing volume, flow channel connectivity, and ultimate oil and gas production. Therefore, rapidly and accurately obtaining the development morphology and spatial structure of fracturing fractures is a key foundation for conducting research on fracturing mechanisms, optimizing fracturing parameter design, and evaluating fracturing effectiveness. Currently, the main technical means for obtaining fracture development morphology include laboratory physical simulation experiments and numerical simulation methods. Among these, laboratory core fracturing physical simulation experiments, by applying stress to cores and injecting fracturing fluid under laboratory conditions, can visually reflect the initiation, propagation, and evolution characteristics of fractures in a controlled environment. This is an important tool for studying the formation mechanism of complex fracture networks and validating numerical models, and has been widely used in academia and engineering.

[0003] However, due to the heterogeneity of rock materials and limitations in experimental techniques, existing three-dimensional core fracturing physical simulation methods have significant limitations in terms of three-dimensional fracture characterization and experimental repeatability. First, natural rocks are generally highly heterogeneous; even cores from the same block or adjacent layers exhibit significant differences in mineral composition, pore structure, and natural fracture distribution. After fracturing experiments, the core structure suffers irreversible damage, making it impossible to conduct repeated experiments under the same initial conditions. This results in severely insufficient repeatability and lateral comparability of experimental results, making it difficult to eliminate the random effects of rock heterogeneity. Second, the preparation process for three-dimensional core fracturing experiments is cumbersome, costly, and time-consuming, making it difficult to meet the practical needs of multi-parameter comparisons and large-scale systematic studies. Third, the internal structure of fractures is extremely complex, placing stringent demands on the detailed characterization of fracture networks. Existing studies typically combine acoustic emission monitoring, CT scanning, and nuclear magnetic resonance imaging for characterization, but these methods all face inherent technical bottlenecks in practical applications. For example, acoustic emission technology mainly inverts the location of fracture activity by capturing elastic wave events generated by rock fracturing. The results are mostly discrete event points, which makes it difficult to accurately depict the true geometry of continuous fractures. Furthermore, its ability to identify micro-cracks or non-brittle fracture processes is extremely limited, and it is highly susceptible to background noise interference. While imaging technologies such as CT can provide high-resolution three-dimensional structural information, the scanning speed is relatively slow, making it difficult to capture the transient process of rapid fracture propagation during fracturing. In addition, the equipment purchase and maintenance costs are huge, and the experimental environment requirements are extremely strict, which greatly limits their widespread integration and application in conventional high-pressure fracturing simulation devices.

[0004] Meanwhile, numerical simulation methods also face significant challenges in predicting fracture morphology. These methods heavily rely on the accuracy of rock constitutive models, fracture criteria, and related input parameters, which are often difficult to obtain or effectively calibrate under actual complex geological conditions. In particular, existing numerical models still exhibit considerable uncertainty in describing the interactions of multiple fractures and the intertwined extension of natural and artificial fractures in complex heterogeneous media, leading to significant deviations between simulation results and actual hydraulic fracturing fracture morphology.

[0005] In summary, both traditional indoor physical simulation and numerical simulation methods suffer from insurmountable systemic defects in areas such as detailed characterization of three-dimensional fracture morphology, repeatability of experimental results, and cost control. These technical bottlenecks make it difficult for researchers to obtain high-fidelity, comparable three-dimensional fracture evolution data, severely restricting the in-depth understanding of complex fracturing mechanisms and the reliability of fracturing effect evaluation, and greatly hindering the further optimization and large-scale application of fracturing technology for unconventional oil and gas reservoirs. Summary of the Invention

[0006] This invention provides a method and apparatus for characterizing fractures based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction, which overcomes the shortcomings of the prior art. It can effectively solve the problems of poor experimental repeatability, difficulty in fine three-dimensional characterization of fractures, high cost and low efficiency of existing three-dimensional core fracturing physical simulation due to rock heterogeneity, as well as the problems of existing monitoring methods.

[0007] One of the technical solutions of this invention is achieved through the following measures: a fracture characterization method based on two-dimensional thin-slice fracturing and layer-by-layer three-dimensional reconstruction, comprising: selecting a complete core sample of the target block, marking and recording the original spatial orientation information on the surface of the core sample, testing the basic physical properties and natural fracture characteristics of the core sample; cutting the core sample into several two-dimensional thin slices along the length direction according to a preset thickness, and preparing thin-slice samples by grinding and sealing; and numbering and marking the thin-slice samples according to the original spatial order of each two-dimensional thin slice in the core sample.

[0008] Under the same experimental conditions, a thin-slice sample was installed in the center of the clamping cavity of the planar fracturing device each time, and a confining pressure was uniformly applied to it in the circumference to simulate formation stress. Fracturing loading was carried out by constant pressure injection until the two-dimensional thin slice initiated and formed a stable propagating fracture. During the fracturing process, the fracturing pressure change curve, fracture initiation characteristics and propagation characteristics were recorded in real time. After the thin-slice sample was fracturing, the next numbered thin-slice sample was replaced, and the above installation and fracturing steps were repeated until all thin-slice samples had completed the fracturing experiment.

[0009] After fracturing, orthophoto images of the surface of each thin-section sample are acquired. After standardization preprocessing, image binarization, and filtering and denoising, the crack boundaries and center lines are extracted. Geometric parameters, including crack length, orientation angle, number of branches, and distribution range, are quantitatively extracted to generate vectorized crack data. The crack data of each two-dimensional thin section are standardized and stored in a unified format, and a spatial index relationship is established by combining the numbering and thickness information of the two-dimensional thin sections.

[0010] Based on the spatial index relationship of each thin section sample, interlayer feature matching and registration alignment are performed on the vectorized crack data of each two-dimensional thin section to complete the spatial correction between adjacent two-dimensional thin sections; interlayer topological connection and interpolation extension are performed on cracks with corresponding relationships to reconstruct the continuous morphology of cracks in three-dimensional space and generate a three-dimensional crack network model of the core sample.

[0011] The following are further optimizations and / or improvements to the above-mentioned technical solution: After generating the three-dimensional fracture network model, the analysis can also include spatial feature analysis of the fractures: based on the three-dimensional fracture network model, key structural parameters including fracture volume, fracture network connectivity and fracture spatial density, and fracture propagation range are quantitatively calculated; and the fracture propagation mechanism is analyzed and the fracturing effect is evaluated based on the calculated parameters.

[0012] The above-mentioned method, based on the spatial indexing relationship of each thin section sample, performs interlayer feature matching and registration alignment on the vectorized fracture data of each two-dimensional thin section to complete the spatial correction between adjacent two-dimensional thin sections. This can include: treating each two-dimensional thin section as a discrete slice layer in the core sample, establishing a three-dimensional spatial coordinate system based on the spatial indexing relationship, and determining the layer coordinates of each two-dimensional thin section in three-dimensional space; correcting the interlayer position through the original spatial orientation information, and using a rigid transformation model or an affine transformation model to spatially align the planar coordinates of the two-dimensional thin sections; introducing an iterative nearest point algorithm to optimize the registration results, controlling the interlayer registration error within a single pixel, and providing an accurate spatial reference for subsequent fracture topological connections.

[0013] The aforementioned interlayer topological connection of corresponding cracks may include: segmenting the vectorized crack data into multiple discrete crack segments by dividing the continuous crack centerline; extracting local geometric features of each crack segment, including centroid location, main orientation angle, centerline length, and average aperture calculated based on crack boundaries; and determining the spatial connectivity of crack segments through a weighted comprehensive similarity based on multiple geometric features, wherein the comprehensive similarity calculation formula is: in, The overall similarity of the crack segments; These are the weighting coefficients corresponding to each geometric feature. ; For positional similarity, To determine the similarity of the directional angles, For length similarity, For opening similarity; set a similarity threshold. S 0, if the overall similarity between the two crack segments is 0. S ≥ S If the similarity is 0, then the two are determined to be different sections of the same three-dimensional crack, and a topological correspondence is established; if the comprehensive similarity of the two crack segments is 0, then the two crack segments ... S < S When the value is 0, it is determined to be a non-connected crack.

[0014] After establishing the topological correspondence, spatial interpolation is performed on the crack morphology between adjacent two-dimensional thin sections to construct a continuous geometric structure of the crack in three-dimensional space. This may include setting a high similarity threshold. S h ,and S h > S 0, for overall similarity S ≥ S h For high-matching crack segments, a continuous crack surface is constructed using three-dimensional linear interpolation. A one-to-one correspondence is established between the endpoints, bifurcation points, and key points on the crack centerline and crack boundary. The coordinates of the upper-layer feature points are set as follows: The coordinates of the corresponding feature points in the lower layer are: Arbitrary height between floors The coordinates of the interpolation point at that location are ,in: in, The thickness of a single-layer two-dimensional sheet is given by x and y, which represent the horizontal and vertical coordinates of the two-dimensional sheet plane, respectively, and z represents the height coordinate in three-dimensional space. All corresponding feature points are interpolated and connected sequentially to generate a continuous crack profile surface between layers.

[0015] The above refers to the overall similarity S satisfy S 0≤ S < S h For the mid-matching fracture segment, the spatial interpolation extension employs a curvature interpolation method with similarity constraints, which may include: using the fracture mechanics laws of hydraulic fracture propagation in the rock medium and the geostress constraint laws as boundary conditions to limit the morphological range of interlayer fracture transition, and accordingly setting the maximum allowable curvature for fracture propagation as a reference. Let the curvature of the interpolation curve be... ,satisfy ,in, SThe comprehensive similarity between crack segments between adjacent two-dimensional thin sections is used. The lower the similarity, the greater the allowable interpolation curvature, in order to adapt to the continuous transition of complex crack segments including crack turning and bifurcation, so that the generated three-dimensional cracks can satisfy the interlayer geometric correspondence while conforming to the physical mechanism of crack propagation in the real hydraulic fracturing process.

[0016] The aforementioned generation of vectorized crack data, combined with thin section numbering and thickness information to establish a spatial index relationship, may include: establishing a crack vectorized data structure based on the extracted crack boundaries and centerlines, assigning crack length, orientation angle, number of branches, and distribution range as attribute information to the corresponding crack vector entities, thereby generating vectorized crack data; using the thin section specimen number as a hierarchical index identifier in the z-axis direction, calculating the z-axis spacing between adjacent thin sections based on the thickness of each thin section specimen, and storing the vectorized crack data hierarchically according to the hierarchical index identifier and z-axis spacing to construct a spatial index relationship.

[0017] The aforementioned cutting of the core sample into several two-dimensional thin slices along its length according to a preset thickness may include: using a high-precision wire cutting device to cut the core sample into two-dimensional thin slices with a thickness of 1 to 3 mm, and the thickness error of the thin slices not exceeding [a certain value]. During the cutting process, the cutting order and circumferential angle of each two-dimensional sheet are kept aligned according to the original spatial orientation information to ensure spatial orientation matching during three-dimensional reconstruction.

[0018] The above-mentioned uniform application of confining pressure in the circumference to simulate formation stress and constant pressure injection for fracturing loading may include: placing the thin-section sample in the center of the clamping cavity of the planar fracturing device, applying a preset confining pressure to it in a uniform circumferential loading manner, the preset confining pressure being a uniform constraint pressure simulating the in-situ stress conditions of the target formation; setting a simulated wellbore at the center of the planar fracturing device, and continuously injecting fracturing fluid into the thin-section sample through the simulated wellbore at a preset injection pressure in a constant pressure injection manner until the thin-section sample initiates fracturing and forms a stable propagating fracture.

[0019] The second technical solution of the present invention is achieved through the following measures: a fracture characterization device based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction, comprising: a core two-dimensional thin-section preparation module, a two-dimensional thin-section layer-by-layer fracturing experiment module, a fracture imaging and digital processing module, and a three-dimensional fracture network reconstruction module.

[0020] The core 2D thin section preparation module is used to select complete core samples from the target block, mark and record the original spatial orientation information on the surface of the core sample, test the basic physical properties and natural fracture characteristics of the core sample, cut the core sample into several 2D thin sections along the length direction according to the preset thickness, and prepare thin section samples by grinding and plastic sealing; and number and mark the thin section samples according to the original spatial order of each 2D thin section in the core sample.

[0021] The two-dimensional thin-slice layer-by-layer fracturing experimental module is used to install one thin-slice sample at a time in the center of the clamping cavity of the planar fracturing device under the same experimental conditions, and uniformly apply confining pressure to it in the circumference to simulate formation stress; constant pressure injection is used for fracturing loading until the two-dimensional thin slice initiates fracturing and forms a stable propagating fracture; the fracturing pressure change curve, fracturing initiation characteristics and propagation characteristics are recorded in real time during the fracturing process; after the thin-slice sample is fracturing, the next numbered thin-slice sample is replaced, and the above installation and fracturing steps are repeated until all thin-slice samples have completed the fracturing experiment.

[0022] The crack imaging and digitization module is used to acquire orthophoto images of the cracks on the surface of each thin-section sample after fracturing. After standardized preprocessing, image binarization, and filtering and denoising, the crack boundaries and center lines are extracted. Geometric parameters, including crack length, orientation angle, number of branches, and distribution range, are quantitatively extracted to generate vectorized crack data. The crack data of each two-dimensional thin section is stored in a standardized format and a spatial index relationship is established by combining the numbering and thickness information of the two-dimensional thin sections.

[0023] The three-dimensional fracture network reconstruction module is used to perform interlayer feature matching and registration alignment of the vectorized fracture data of each two-dimensional thin section according to the spatial index relationship of each thin section sample, and to complete the spatial correction between adjacent two-dimensional thin sections; it performs interlayer topological connection and interpolation extension on fractures with corresponding relationships, reconstructs the continuous morphology of fractures in three-dimensional space, and generates a three-dimensional fracture network model of the core sample.

[0024] This invention cuts the same whole rock core sample into two-dimensional thin sections and conducts layer-by-layer fracturing experiments under the same boundary constraints and injection conditions. By utilizing the continuous material and physical properties of adjacent two-dimensional thin sections, the interference of physical property differences caused by rock heterogeneity between different rock cores is eliminated, so that the obtained fracture initiation pressure and propagation morphology are consistent, and the reproducibility and comparability of experimental results are improved.

[0025] By acquiring orthophoto images of the fractures after fracturing each two-dimensional thin section and performing image standardization preprocessing, the digital extraction of fracture geometric details and branch morphology was achieved. By quantifying and analyzing the fracture geometric parameters and establishing a vectorized data structure, and combining the numbering and thickness information of the two-dimensional thin sections to establish a spatial index, the standardized storage and spatial coordinate positioning of the two-dimensional fracture data of each layer were achieved.

[0026] By topologically connecting the corresponding cracks between adjacent thin sections based on spatial indexing relationships and performing interpolation extensions in conjunction with mechanical constraints, an equivalent mapping from two-dimensional fracturing results to a three-dimensional spatial crack network structure was achieved. This yielded the continuous evolution morphology and network connectivity characteristics of cracks equivalent to the fracturing experiment of a whole three-dimensional rock core.

[0027] By transforming the three-dimensional core fracturing experiment into two-dimensional thin-section layer-by-layer fracturing and three-dimensional reconstruction, the experimental setup and operation process are simplified, the dependence on three-dimensional imaging equipment is reduced, the cost of fracturing experiments is lowered, and the experimental cycle is shortened. It has the characteristics of accurate characterization, strong repeatability and low cost. Attached Figure Description

[0028] Appendix Figure 1 The flowchart shows the crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction in Embodiments 1 to 9 of the present invention.

[0029] Appendix Figure 2 This is a schematic diagram of the preparation of two-dimensional thin sheets and thin sheet samples in Examples 1 and 8 of the present invention.

[0030] Appendix Figure 3 This is a schematic diagram of the confining pressure loading and liquid injection structure of the thin sheet sample in Examples 1 and 9 of the present invention.

[0031] Appendix Figure 4 This is a schematic diagram of the layer-by-layer reconstruction of the three-dimensional crack network in Embodiments 1 and 3 of the present invention.

[0032] Appendix Figure 5 This is a schematic diagram of the crack characterization device based on two-dimensional thin-sheet fracturing and layer-by-layer three-dimensional reconstruction in Embodiment 10 of the present invention.

[0033] The codes in the attached figures are as follows: 1 is the clamping mechanism; 2 is the simulated wellbore; 3 is the two-dimensional thin section; 4 is the epoxy resin sealing layer; 201 is the core two-dimensional thin section preparation module; 202 is the two-dimensional thin section layer-by-layer fracturing experiment module; 203 is the fracture imaging and digital processing module; and 204 is the three-dimensional fracture network reconstruction module. Detailed Implementation

[0034] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0035] The present invention will be further described below with reference to embodiments and accompanying drawings: Example 1: As shown in the attached document Figures 1 to 4 As shown, the crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction includes: S1: Select a complete core sample from the target block, mark and record the original spatial orientation information on the surface of the core sample, and test the basic physical properties and natural fracture characteristics of the core sample.

[0036] During the process, a complete core sample from the target block is first selected as the experimental object and processed into a regular columnar structure, such as a cylinder or a square prism. In this embodiment, a standard cylinder with a diameter of 50 mm and a length of 200 mm is used. The use of a cylinder facilitates compatibility with conventional coring processes and basic physical property testing equipment, and it has isotropic characteristics in circumferential stress, which is beneficial for uniformly applying confining pressure during fracturing.

[0037] After processing, the original spatial orientation information is marked and recorded on the outer surface of the core sample to ensure spatial consistency during subsequent 2D thin section 3 cutting, fracturing, and 3D reconstruction. The original spatial orientation information includes: vertical orientation—marking the top / bottom direction of the core and the corresponding vertical stratigraphic sequence, used to ensure that the longitudinal stacking order of the cut 2D thin sections 3 is consistent with its position within the core sample; horizontal stress orientation—marking the directions of the maximum and minimum horizontal principal stresses of the corresponding strata, ensuring that the confining pressure loading direction of the 2D thin section fracturing experiment matches the stress field direction of the strata where the core sample is located; and circumferential positioning marks—uniformly etched baselines along the axial direction on the outer circumferential surface of the core sample, used for circumferential alignment of each 2D thin section 3 after cutting, and to ensure spatial orientation matching of each 2D thin section 3 during 3D fracture reconstruction.

[0038] After recording the initial spatial orientation information, the intact core sample was placed in a constant temperature drying oven at 40℃ for 24 hours. Once the core mass stabilized, it was removed and weighed. Then, basic physical property and natural fracture characteristic tests were conducted on the core sample. These tests included, but were not limited to: mineral composition analysis, pore structure testing, P-wave and S-wave velocity measurements (for converting rock mechanical parameters), and observation of natural fracture characteristics. These tests obtained the initial physical parameters and natural fracture development status of the core sample, providing fundamental data support for subsequent analysis of fracturing experiment results and evaluation of fracture propagation mechanisms.

[0039] S2: Cut the core sample into several two-dimensional thin slices 3 along the length direction according to the preset thickness, and make thin slice samples by grinding and sealing; number and mark the thin slice samples according to the original spatial order of each two-dimensional thin slice 3 in the core sample.

[0040] During use, the core sample is first cut into two-dimensional thin slices 3 (i.e., two-dimensional core slices or slices) with a thickness of 1 mm along the axial direction, and the thickness error of the slices is ensured to be no more than 1 mm. To avoid z-axis coordinate distortion introduced during interlayer interpolation calculations in 3D reconstruction. After cutting, the surface of the two-dimensional thin sheet 3 is polished step by step with sandpaper of 50 to 200 grit to remove burrs and uneven areas generated during cutting, improve the surface flatness of the two-dimensional thin sheet 3, ensure that the surface state of each two-dimensional thin sheet 3 is consistent, and avoid stress concentration or fracturing fluid leakage caused by surface roughness during fracturing experiments.

[0041] The polished two-dimensional thin slices 3 are placed in a pressure mold in sequence, and each two-dimensional thin slice 3 is encapsulated with epoxy resin to form a thin slice sample (i.e., a two-dimensional core thin slice sample). However, at the position of the simulated wellbore 2 of the corresponding plane fracturing test device, the top center of the two-dimensional thin slice 3 needs to be reserved with a fluid injection hole that is compatible with the simulated wellbore. This position is not encapsulated so that the fracturing fluid can directly contact the two-dimensional thin slice 3 through the simulated wellbore 2.

[0042] During the encapsulation process, a uniform pressure of 2 MPa to 3.5 MPa is applied into the mold to promote the full penetration of epoxy resin into the microporous structure of the rock, forming a stable and solidified epoxy resin encapsulation layer 4. This improves the overall strength and integrity of the thin-film sample and prevents the two-dimensional thin film 3 from disintegrating during fracturing loading. After encapsulation and curing, the overall thickness of the thin-film sample is approximately 10 mm, meeting the mechanical stability and operational requirements of subsequent two-dimensional planar fracturing experiments.

[0043] Finally, each thin section specimen was numbered sequentially according to the spatial order of the two-dimensional thin section 3 in the core sample, and the aforementioned original orientation marks (such as top and bottom directions, circumferential baselines, etc.) were clearly marked on the outer surface (or side) of the sealed specimen. By simultaneously retaining the numbering and orientation marks, it was ensured that each two-dimensional thin section 3 specimen possessed both independent fracturing experimental physical strength and precise spatial coordinate identity, providing a spatial logical basis for establishing spatial index relationships and three-dimensional reconstruction of subsequent interlayer fracture data.

[0044] S3: Under the same experimental conditions, a thin sample is taken each time and installed in the center of the clamping cavity of the planar fracturing device, and a confining pressure is uniformly applied to it in the circumferential direction to simulate the formation stress.

[0045] The planar fracturing device used in the above technical solution mainly includes a clamping mechanism 1, a simulated wellbore 2, a confining pressure loading system, a fluid injection system, and a loading control unit.

[0046] In use, a single thin sample is installed in the center of the clamping cavity of the planar fracturing device, and the pre-set injection hole on the top surface of the thin sample is aligned with the simulated wellbore 2 at the center of the planar fracturing device. The simulated wellbore 2 is then sealed and inserted into the injection hole.

[0047] A clamping mechanism 1 is provided in the clamping cavity. The clamping mechanism 1 applies constraint pressure (i.e., confining pressure) to the thin-section sample from the circumference through surface contact to simulate the in-situ confining pressure conditions of the strata where the core sample is located. In this embodiment, the preset value of the confining pressure is 10 MPa. The loading control unit controls the confining pressure loading system to gradually increase the constraint pressure of the clamping mechanism 1 on the thin-section sample, so that the thin-section sample is in contact with the inner wall of the clamping mechanism 1, ensuring the uniformity of stress and the stability of boundary conditions of the thin-section sample during the fracturing experiment.

[0048] Throughout the fracturing process, the loading control unit controls and monitors the constraint pressure, fracturing fluid injection rate, injection pressure, and loading path in real time to ensure that each thin-slice sample completes the two-dimensional fracturing experiment under consistent boundary conditions and experimental parameters (i.e., under the same experimental conditions). This improves the repeatability and reliability of the two-dimensional thin-slice fracturing experiment and provides a comparable experimental data basis for the subsequent comparative analysis of fracture morphology characteristics between two-dimensional thin-slices and interlayer three-dimensional reconstruction.

[0049] The above technical solution is based on two-dimensional thin sectioning of the same whole core sample and layer-by-layer fracturing experiments under the same experimental conditions. Since the thickness of the two-dimensional thin section 3 (millimeters) is much smaller than the length of the core sample (decimeters), the material and physical properties of adjacent two-dimensional thin sections 3 are continuous and have the same mechanical and material conditions. This eliminates the interference of the differences in physical properties between different core samples on the experimental results, and makes the obtained fracture initiation pressure, direction and distribution morphology consistent, thus improving the repeatability and comparability of the experimental results.

[0050] S4: Fracturing loading is performed using constant pressure injection until the two-dimensional thin sheet initiates fracturing and forms a stable propagating fracture; the fracturing pressure change curve, fracturing initiation characteristics and propagation characteristics are recorded in real time during the fracturing process.

[0051] After the boundary constraint pressure reaches the preset value and stabilizes, the injection system uses simulated fracturing fluid as the fracturing medium and employs a constant pressure injection method for fracturing loading; the fracturing fluid is continuously injected into the thin-film sample through the simulated wellbore 2. In this embodiment, the injection pressure of the fracturing fluid can be set to 8 MPa.

[0052] During loading, the fracturing fluid injection continues until the thin-film sample exhibits significant fracturing initiation and forms a stable propagating crack. Throughout this process, pressure sensors installed in the injection system record the injection pressure variation curves in real time. By analyzing these pressure variation curves, and through a comprehensive analysis of the initiation and propagation characteristics, the fracturing behavior of the two-dimensional thin-film 3 during fracturing can be accurately determined. During this process, the loading control unit precisely controls and monitors the constraint pressure, injection rate, injection pressure, and loading path in real time.

[0053] Fracture initiation and propagation characteristics are core dynamic parameters characterizing fracture development behavior during hydraulic fracturing. Among them, fracture initiation characteristics include fracture initiation pressure, the time of initiation, the orientation of the initiation location relative to the injection hole, and the abrupt change characteristics of the pressure curve at the time of initiation; propagation characteristics include the pressure change law during fracture propagation, the main direction and deflection behavior of fracture propagation, the timing and number of branch fractures, the dynamic changes in fracture propagation rate, fracture length and distribution range, as well as complex evolution behaviors such as fracture turning, bifurcation, and fracture arrest.

[0054] S5: After the fracturing of the thin sheet sample is completed, replace it with the next numbered thin sheet sample and repeat steps S3 to S4 until all thin sheet samples have completed the fracturing test.

[0055] To ensure the comparability of experimental results from various 2D thin sections, the same confining pressure conditions, constant pressure injection method, and loading path were strictly followed for the fracturing and loading processes of all thin section samples, and consistent experimental parameter settings were maintained—that is, the experiments were conducted under identical experimental conditions. This effectively eliminated interference caused by fluctuations in experimental conditions, greatly improved the repeatability and reliability of the experimental data, and enabled the fracture characteristics independently obtained from each 2D thin section to accurately reflect the heterogeneous evolution of the core layers, laying a solid data foundation for subsequent accurate matching and 3D reconstruction of interlayer fractures.

[0056] S6: Obtain orthophoto images of the surface of each thin-slice sample after fracturing. After standardization preprocessing, image binarization, and filtering for noise reduction, extract the crack boundaries and center lines.

[0057] After the fracturing experiment on the two-dimensional thin section 3 is completed, high-resolution imaging of the crack morphology on the surface of each two-dimensional thin section 3 is first performed. In actual use, high-precision two-dimensional imaging equipment can be used to acquire orthophoto images of the cracks on the surface of the two-dimensional thin section 3. High-precision imaging equipment can be high-resolution optical imaging equipment, electron microscopes, two-dimensional scanning electron microscopes, or CT scanning equipment, etc. The imaging resolution needs to be better than 0.05 to 0.1 mm to ensure complete recording of crack geometric details (especially tiny branch cracks).

[0058] After acquiring the original surface orthophoto images of cracks in each thin section sample, standardized image preprocessing is performed on them, which may include image grayscale processing, contrast enhancement and background correction, in order to eliminate the interference of uneven illumination and the original texture of the rock surface on crack identification during the imaging process.

[0059] The preprocessed image is then binarized using an adaptive threshold segmentation method to accurately distinguish the crack target from the background area. Next, median filtering is used to remove isolated noise points and non-crack features from the binary image, such as tiny bubbles or natural isolated pores on the surface of the sealing resin.

[0060] Finally, based on the processed clear binary image, an edge detection algorithm is used to extract the crack boundary and centerline structure, thereby achieving accurate identification of the crack geometry and spatial distribution features on the 2D thin section 3. This series of image processing steps effectively removes imaging noise and background interference, achieving accurate extraction of crack geometric features, thus providing a high-quality 2D data foundation for subsequent accurate matching and 3D reconstruction of interlayer cracks.

[0061] S7: Quantitatively extract geometric parameters including crack length, orientation angle, number of branches and distribution range to generate vectorized crack data; standardize and store the crack data of each two-dimensional thin section 3 in a unified format, and establish a spatial index relationship by combining the numbering mark and thickness information of the two-dimensional thin section 3.

[0062] Based on the extraction of fracture boundaries and centerlines, and using the three-dimensional spatial coordinate system of the core sample, the geometric parameters of the fractures are digitally extracted and quantitatively analyzed to construct the topological structure of the fracture centerline (fracture skeleton). The extracted geometric parameters include, but are not limited to, fracture length, fracture orientation angle, number of fracture branches, and fracture propagation range. Based on these parameters, a vectorized data structure for the fractures is established, achieving the conversion of fracture data from pixel-level to vector-level.

[0063] Through the above vectorization extraction, the spatial resolution of the crack reaches 10 to 20 μm, which can obtain two-dimensional geometric information of the crack initiation location, propagation path and branch structure.

[0064] Then, the vectorized crack data of each two-dimensional thin section 3 are standardized and stored according to a unified data format. At the same time, a spatial index relationship is established by combining the numbering mark and thickness information (z-axis direction) of each thin section sample, and the spatial coordinates corresponding to the two-dimensional crack data of each layer are assigned, providing the input data basis for the subsequent three-dimensional reconstruction of interlayer cracks.

[0065] S8: Based on the spatial index relationship of each thin-section sample, perform interlayer feature matching and registration alignment on the vectorized crack data of each two-dimensional thin section 3 to complete the spatial correction between adjacent two-dimensional thin sections 3.

[0066] Based on the fracture vectorized data structure and spatial index relationship established in step S7, according to the numbering and thickness information of each two-dimensional thin section 3, the acquired two-dimensional fracture data of each layer are accurately positioned and stacked in the three-dimensional spatial coordinate system to restore the relative spatial position of each two-dimensional thin section 3 in the original core sample (the state of the core sample before cutting).

[0067] For crack features on adjacent 2D thin sections 3, spatial similarity matching is performed by combining their spatial coordinates, crack orientation angles, number of branches, and other geometric parameters. For successfully matched cracks in adjacent layers, spatial interpolation algorithms (such as linear interpolation, distance-weighted interpolation, or morphological interpolation) are used to connect breakpoints and fit surfaces to recover the continuous evolution trajectory of cracks in the uncut region between layers.

[0068] Finally, the two-dimensional fracture data of all layers are fused to generate a three-dimensional fracture network model that can fully reflect the spatial distribution, morphological bifurcation, and network connectivity of the internal hydraulic fracturing fractures, thereby achieving high-precision reconstruction of the three-dimensional spatial fracture development characteristics from multi-slice two-dimensional hydraulic fracturing experimental data.

[0069] S9: Perform interlayer topological connection and interpolation extension on the corresponding cracks to reconstruct the continuous morphology of the cracks in three-dimensional space and generate a three-dimensional crack network model of the core sample.

[0070] After completing the above spatial registration and alignment, interlayer topological connection and interpolation extension are performed, namely: based on the spatial index and matching results of crack data of each layer of two-dimensional thin slice 3, for cracks with spatial correspondence between adjacent two-dimensional thin slices 3, the topological association of cracks in the direction perpendicular to the plane of two-dimensional thin slice 3 (z-axis direction) is established by analyzing the direction angle, endpoint spatial coordinates and branch structure of cracks in adjacent layers.

[0071] Spatial interpolation algorithms are used to extend and fit surfaces to fracture breakpoints between adjacent 2D thin sections. For fracture segments with corresponding relationships in adjacent thin sections, interpolation extension is performed based on their spatial location and geometric morphology to construct a continuous surface or volume structure of the fracture in 3D space. For complex fractures with multi-level bifurcation or deflection, multi-path matching and topological connection are performed in conjunction with the fracture propagation direction. At the same time, mechanical constraints are introduced, namely, the fracture mechanics law of hydraulic fracture propagation in rock medium and the geostress constraint law are used as boundary conditions to limit the morphological range of interlayer fracture transition, so that the generated 3D fractures not only satisfy the interlayer geometric correspondence, but also conform to the physical mechanism of the actual hydraulic fracturing process.

[0072] The aforementioned interpolation and topological connection processes compensate for the missing fractures in the uncut areas between layers caused by slice thickness, restoring and reconstructing the continuous evolution morphology of fractures in three-dimensional space. Two-dimensional fracture data from each layer are integrated through topological connections and interpolation extensions to generate a three-dimensional fracture network model of the core sample that reflects the spatial distribution, morphological bifurcation, and network connectivity characteristics of the internal hydraulic fracturing fractures.

[0073] By introducing three-dimensional reconstruction technology, the fracture information formed by three-dimensional fracturing of each two-dimensional thin section is superimposed and correlated according to its original spatial order. Without conducting three-dimensional core fracturing experiments, the equivalent mapping of two-dimensional fracturing results to three-dimensional spatial fracture network structure can be achieved, obtaining the final fracture structure information equivalent to a three-dimensional whole-block core fracturing experiment. This enables a holistic characterization of fracture initiation location, propagation path, orientation, distribution range, and spatial complexity, meeting the needs of quantitative analysis of fracture networks.

[0074] This invention cuts the same whole rock core sample into two-dimensional thin slices 3 and conducts layer-by-layer fracturing experiments under the same boundary constraints and injection conditions. By utilizing the continuous material and physical properties of adjacent two-dimensional thin slices 3, the interference of physical property differences caused by rock heterogeneity between different rock cores is eliminated, so that the obtained fracture initiation pressure and propagation morphology are consistent, and the reproducibility and comparability of experimental results are improved.

[0075] By acquiring orthophoto images of the fractures after fracturing each two-dimensional thin plate 3 and performing image standardization preprocessing, the digital extraction of fracture geometric details and branch morphology was achieved. By quantifying and analyzing the fracture geometric parameters and establishing a vectorized data structure, and by combining the numbering and thickness information of the two-dimensional thin plate 3 to establish a spatial index, the standardized storage and spatial coordinate positioning of the two-dimensional fracture data of each layer were achieved.

[0076] By topologically connecting the corresponding cracks between adjacent thin sections based on spatial indexing relationships and performing interpolation extensions in conjunction with mechanical constraints, an equivalent mapping from two-dimensional fracturing results to a three-dimensional spatial crack network structure was achieved. This yielded the continuous evolution morphology and network connectivity characteristics of cracks equivalent to the fracturing experiment of a whole three-dimensional rock core.

[0077] By transforming the three-dimensional core fracturing experiment into a mode that combines two-dimensional thin-section layer-by-layer fracturing with three-dimensional reconstruction, the experimental process is simplified, the dependence on three-dimensional imaging equipment is reduced, the experimental cost is lowered, and the experimental cycle is shortened. It has the characteristics of accurate characterization, strong repeatability, and controllable cost.

[0078] The above-mentioned crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction can be further optimized and / or improved according to actual needs: Example 2: As an optimization of the above example, after generating the three-dimensional fracture network model, the method further includes spatial feature analysis of the fractures: based on the three-dimensional fracture network model, key structural parameters including fracture volume, fracture network connectivity and fracture spatial density, and fracture propagation range are quantitatively calculated; based on the calculated parameters, the fracture propagation mechanism is analyzed and the fracturing effect is evaluated, thereby providing quantitative data support for the design and optimization of reservoir fracturing schemes.

[0079] Example 3: As an optimization of the above examples, as shown in the appendix Figure 4 As shown, the step of performing interlayer feature matching and registration alignment on the vectorized crack data of each two-dimensional thin section 3 based on the spatial index relationship of each thin section sample to complete the spatial correction between adjacent two-dimensional thin sections 3 includes: Each two-dimensional thin section 3 is regarded as a discrete slice layer in the core sample. Based on the spatial index relationship of the two-dimensional thin sections 3, such as the numbering mark (slicing order) and single layer thickness of the two-dimensional thin sections 3, a three-dimensional spatial coordinate system is established to determine the layer coordinates of each two-dimensional thin section 3 in three-dimensional space.

[0080] The z-axis of the three-dimensional spatial coordinate system is the thickness direction of the two-dimensional thin section 3, and the axial direction of the core sample before cutting coincides with the z-axis of the three-dimensional spatial coordinate system.

[0081] The interlayer positions are corrected using the original spatial orientation information, and the planar coordinates of the two-dimensional thin sheet 3 are spatially aligned using a rigid transformation model or an affine transformation model.

[0082] In this embodiment, the boundary contour features of the two-dimensional thin slice 3 and the preset circumferential reference line (i.e., the original spatial orientation information) are used to perform initial correction on the relative position between layers. The planar coordinates of each two-dimensional thin slice 3 are uniformly transformed into the three-dimensional spatial coordinate system by using a rigid transformation model or an affine transformation model to achieve initial spatial alignment.

[0083] Based on the initial alignment, an iterative nearest-point algorithm is introduced to optimize the registration results, controlling the inter-layer registration error to within a single pixel, thus providing an accurate spatial reference for subsequent crack topology connections.

[0084] By iteratively optimizing the nearest point algorithm, the slicing processing error, image distortion, and residual system deviation in the initial alignment process of the two-dimensional thin slice 3 can be effectively eliminated, and the interlayer registration error can be strictly controlled within a single pixel, thereby greatly improving the interlayer alignment accuracy and providing an accurate spatial reference for the subsequent interlayer topological connection of cracks and the reconstruction of three-dimensional structures.

[0085] Example 4: As an optimization of the above embodiments, the step of performing interlayer topological connections on cracks with corresponding relationships includes: The vectorized crack data is segmented, dividing the continuous crack centerline into multiple discrete crack segments; the local geometric features of each crack segment are extracted, including the centroid position, main orientation angle, centerline length, and average aperture calculated based on the crack boundary.

[0086] The spatial connectivity of crack segments is determined by a weighted comprehensive similarity based on multiple geometric features. The formula for calculating the comprehensive similarity is as follows: in, The overall similarity of the crack segments; These are the weighting coefficients corresponding to each geometric feature. ; For positional similarity, To determine the similarity of the directional angles, For length similarity, For opening similarity; set a similarity threshold. S 0, if the overall similarity between the two crack segments is 0. S ≥ S If the similarity is 0, then the two are determined to be different sections of the same three-dimensional crack, and a topological correspondence is established; if the comprehensive similarity of the two crack segments is 0, then the two crack segments ... S < S When the value is 0, it is determined to be a non-connected crack.

[0087] In the above technical solution, when determining the spatial connectivity between two crack segments in adjacent two-dimensional thin plates 3, it is necessary to first calculate the similarity of the local geometric features of the two crack segments, specifically: Position similarity is calculated based on the planar Euclidean distance between the centroids of the two crack segments. The smaller the distance, the higher the similarity. The calculation formula is: in, d The distance between the centroids of the two crack segments is the planar distance. d 0 represents the distance baseline threshold; Based on the difference in the main strike angle of the two fracture segments Calculate the similarity of the direction angle The calculation formula is: in, The value range is from 0° to 90°; Length similarity is calculated based on the relative difference in the centerline lengths of the two crack segments. The calculation formula is: in, These represent the skeleton lengths of two crack segments in two adjacent layers; The aperture similarity is calculated based on the relative difference in the average aperture of the two crack segments. The calculation formula is: in These represent the skeleton lengths of two crack segments in two adjacent layers.

[0088] In this embodiment, Set similarity thresholds of 0.4, 0.3, 0.2, and 0.1 respectively. When the overall similarity of the two crack segments S When the value is ≥0.65, the two are determined to be different sections of the same three-dimensional crack, and a topological correspondence is established; if the value is below 0.65, they are determined to be unconnected cracks.

[0089] By using the above-mentioned comprehensive similarity determination method with weighted multiple geometric features, we can overcome the limitations of single feature matching (such as relying solely on centroid position or orientation angle) in complex crack networks, which is prone to misjudgment. This method can more accurately and objectively establish the true topological correspondence between cracks in three adjacent two-dimensional thin plates, providing a reliable topological foundation for high-precision reconstruction of three-dimensional crack networks.

[0090] Example 6: As an optimization of the above examples, after establishing the topological correspondence, spatial interpolation is performed on the crack morphology between adjacent two-dimensional thin slices 3 to construct a continuous geometric structure of the crack in three-dimensional space, including: setting a high similarity threshold. S h ,and S h > S 0, for overall similarity S ≥ S h For high-matching crack segments, a continuous crack surface is constructed using three-dimensional linear interpolation. A one-to-one correspondence is established between the endpoints, bifurcation points, and key points on the crack centerline and crack boundary. The coordinates of the upper-layer feature points are set as follows: The coordinates of the corresponding feature points in the lower layer are: Arbitrary height between floors The coordinates of the interpolation point at that location are ,in: in, The thickness of a single-layer two-dimensional sheet 3 is the z-axis distance between two adjacent two-dimensional sheets 3. x and y represent the horizontal and vertical coordinates of the two-dimensional sheet 3 plane, respectively, and z represents the height coordinate in three-dimensional space. The coordinates of the feature points of each height section between layers are calculated using the above formula. All corresponding feature points are interpolated and connected in sequence to generate a continuous crack profile surface between layers.

[0091] By introducing this three-dimensional linear interpolation extension method, the lack of crack morphology data in the uncut area between layers due to slice thickness is effectively compensated, and the smooth transition and continuous geometric reconstruction of high-matching crack segments between layers in three-dimensional space are realized, laying the foundation for constructing a high-fidelity three-dimensional crack network model.

[0092] Example 6: As an optimization of the above examples, for the comprehensive similarity S satisfy S 0≤ S < S h In the mid-matching fracture segment, the spatial interpolation extension employs a curvature interpolation method with similarity constraints, including: using the fracture mechanics laws of hydraulic fracture propagation in the rock medium and the geostress constraint laws as boundary conditions to limit the morphological range of interlayer fracture transition, and accordingly setting the maximum allowable curvature for fracture propagation as the reference value. Let the curvature of the interpolation curve be... ,satisfy ,in, SThe comprehensive similarity is the ratio of the crack segments between three adjacent two-dimensional thin sections. The lower the similarity, the greater the allowable interpolation curvature, so as to adapt to the continuous transition of complex crack segments including crack turning and bifurcation, so that the generated three-dimensional cracks can satisfy the interlayer geometric correspondence while conforming to the physical mechanism of crack propagation in the real hydraulic fracturing process.

[0093] By using the curvature interpolation method with similarity constraints, the generated three-dimensional cracks not only satisfy the interlayer correspondence at the geometric level, but also conform to the mechanical mechanism of crack propagation in the real hydraulic fracturing process at the physical level, thereby improving the realism and rationality of the three-dimensional reconstruction of complex crack structures.

[0094] Example 7: As an optimization of the above embodiment, the generation of vectorized crack data, combined with the thin section number and thickness information to establish a spatial index relationship, includes: establishing a crack vectorized data structure based on the extracted crack boundary and centerline, assigning crack length, orientation angle, number of branches and distribution range as attribute information to the corresponding crack vector entity, thereby generating vectorized crack data; using the number of the thin section sample as the hierarchical index identifier in the z-axis direction, calculating the z-axis spacing between adjacent thin sections based on the thickness of each thin section sample, and storing the vectorized crack data hierarchically according to the hierarchical index identifier and z-axis spacing to construct a spatial index relationship.

[0095] By establishing a spatial index relationship by combining vectorized crack data with thin section numbering and thickness information, the structured storage and three-dimensional spatial coordinate positioning of crack information in two-dimensional thin section 3 (slice) were realized, providing standardized basic data support for subsequent inter-layer registration and alignment and three-dimensional topology reconstruction.

[0096] Example 8: As an optimization of the above embodiments, as shown in the appendix Figure 2 As shown, the step of cutting the core sample into several two-dimensional thin slices 3 along the length direction according to a preset thickness includes: using a high-precision wire cutting device to cut the core sample into two-dimensional thin slices 3 with a thickness of 1 to 3 mm, and the thickness error of the thin slices does not exceed... During the cutting process, the cutting order and circumferential angle of each two-dimensional sheet 3 are kept aligned according to the original spatial orientation information to ensure spatial orientation matching during three-dimensional reconstruction.

[0097] By using this setup, compared to conventional disc slicers, high-precision wire cutting equipment, such as diamond wire cutting machines, can effectively reduce mechanical vibration and frictional heat during the cutting process, preventing secondary breakage of the core sample or inducing surface microcracks, thereby ensuring the integrity of the original structure of the two-dimensional thin section 3.

[0098] By setting it this way, the preset thickness of the single two-dimensional sheet 3 is controlled between 1 and 3 mm, and the sheet thickness error does not exceed [the specified value]. To avoid reducing interlayer spatial resolution due to excessive thickness, which would prevent the accurate capture of subtle crack turning and bifurcation features during subsequent 3D reconstruction, and to prevent non-crack propagation-related artificial fracturing due to insufficient thickness and low mechanical strength, the thickness error must be strictly controlled within a certain range. The reason for this is to prevent distortion of the z-axis (height) coordinate system due to uneven thickness of each layer during the inter-layer interpolation calculation in the subsequent 3D reconstruction, and to ensure the true scale and calculation accuracy of the 3D crack network model.

[0099] During the cutting process, a specialized positioning clamp can be used to hold the core sample, ensuring that the cutting trajectory maintains a fixed relative position with the baseline on the outer periphery of the core sample. This ensures that the baseline can be uniformly transferred to each two-dimensional thin section 3. After each two-dimensional thin section 3 is cut, it is immediately numbered and marked according to its order of detachment from the core sample (i.e., vertical stratigraphy), and the top / bottom direction is indicated. This ensures that the spatial order and top / bottom direction of each two-dimensional thin section 3 are completely consistent with its corresponding position in the core sample before cutting, thus providing a high-precision spatial orientation matching basis for subsequent fracture imaging, interlayer feature matching, and three-dimensional reconstruction.

[0100] Example 9: As an optimization of the above embodiments, as shown in the appendix Figure 3 As shown, the step of uniformly applying confining pressure in the circumferential direction to simulate formation stress and performing fracturing loading using a constant pressure injection method includes: placing the thin-sheet sample in the center of the clamping cavity of the planar fracturing device, applying a preset confining pressure to it in a circumferentially uniform loading method, wherein the preset confining pressure is a uniform constraint pressure simulating the in-situ stress conditions of the target formation; setting a simulated wellbore 2 at the center of the planar fracturing device, and continuously injecting fracturing fluid into the thin-sheet sample through the simulated wellbore 2 in a constant pressure injection method according to a preset injection pressure until the thin-sheet sample initiates fracturing and forms a stable propagating fracture.

[0101] By using a loading method of circumferential uniform confining pressure and central constant pressure injection fracturing, the initiation and propagation characteristics of hydraulic fractures under real geostress conditions can be accurately reproduced in a two-dimensional plane, ensuring the consistency of the experimental boundary conditions of each thin section sample and providing a reliable physical basis for subsequent comparison of interlayer fracture data and three-dimensional reconstruction.

[0102] Depending on the requirements, the preset confining pressure can be in the range of 8 to 12 MPa; the preset injection pressure can be in the range of 10 to 16 MPa.

[0103] Example 10: As attached Figure 4 , 5 As shown, the fracture characterization device based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction includes: a core two-dimensional thin-section preparation module 201, a two-dimensional thin-section layer-by-layer fracturing experiment module 202, a fracture imaging and digital processing module 203, and a three-dimensional fracture network reconstruction module 204.

[0104] The core two-dimensional thin section preparation module 201 is used to select complete core samples from the target block, mark and record the original spatial orientation information on the surface of the core sample, test the basic physical properties and natural fracture characteristics of the core sample, cut the core sample into several two-dimensional thin sections 3 along the length direction according to the preset thickness, and prepare thin section samples by grinding and plastic sealing; and number and mark the thin section samples according to the original spatial order of each two-dimensional thin section 3 in the core sample.

[0105] The two-dimensional thin-slice layer-by-layer fracturing test module 202 is used to, under the same experimental conditions, take one thin-slice sample at a time and install it in the center of the clamping cavity of the planar fracturing device, and apply a uniform confining pressure to it in the circumference to simulate formation stress; use constant pressure injection to perform fracturing loading until the two-dimensional thin slice initiates fracturing and forms a stable propagating fracture; record the fracturing pressure change curve, fracturing initiation characteristics and propagation characteristics in real time during the fracturing process; after the thin-slice sample is fracturing, replace it with the next numbered thin-slice sample, and repeat the above installation and fracturing steps until all thin-slice samples have completed the fracturing test.

[0106] The crack imaging and digitization processing module 203 is used to acquire orthophoto images of the surface of each thin-section sample after fracturing. After standardization preprocessing, image binarization and filtering denoising, the crack boundary and center line are extracted. Geometric parameters including crack length, orientation angle, number of branches and distribution range are quantitatively extracted to generate vectorized crack data. The crack data of each two-dimensional thin section 3 are stored in a standardized format and a spatial index relationship is established by combining the numbering mark and thickness information of the two-dimensional thin section 3.

[0107] The three-dimensional fracture network reconstruction module 204 is used to perform interlayer feature matching and registration alignment of the vectorized fracture data of each two-dimensional thin section 3 according to the spatial index relationship of each thin section sample, and to complete the spatial correction between adjacent two-dimensional thin sections 3; to perform interlayer topological connection and interpolation extension of fractures with corresponding relationships, to reconstruct the continuous morphology of fractures in three-dimensional space, and to generate a three-dimensional fracture network model of the core sample.

[0108] The crack characterization device based on multi-module collaboration provided by this invention has the following significant technical effects: This method eliminates heterogeneity interference, enabling comprehensive and repeatable studies of fracture morphology in the target block. The same core sample is divided into multiple 2D thin sections using a core 2D thin section preparation module. These sections are then used in conjunction with a 2D thin section layer-by-layer fracturing experiment module to perform layer-by-layer fracturing under identical boundary constraints and injection conditions. Utilizing the continuity of material and properties between adjacent thin sections, the method eliminates the interference caused by differences in physical properties due to rock heterogeneity between different core samples. Multiple sections of the same core sample are equivalent to multiple independent fracturing experiments, ensuring the consistency and reproducibility of experimental boundary conditions, and enabling a more thorough study of fracture initiation and propagation morphology in the target block.

[0109] It can obtain an equivalent complete three-dimensional fracture distribution. The fracture imaging and digitization module achieves standardized extraction of two-dimensional fracture data, and the three-dimensional fracture network reconstruction module performs spatial registration and topological reconstruction on the two-dimensional thin-section fracturing results, realizing an equivalent mapping from two-dimensional fracturing results to a three-dimensional spatial fracture network structure. Without the need for complex and expensive single-block three-dimensional core fracturing experiments, it is possible to obtain an equivalent complete and continuously evolving three-dimensional fracture distribution and network connectivity characteristics of a whole core sample.

[0110] This device lowers the experimental threshold and improves characterization efficiency. It transforms traditional three-dimensional core fracturing experiments into a mode that combines two-dimensional thin-section layer-by-layer fracturing with three-dimensional reconstruction, simplifying the hardware process, reducing dependence on high-end three-dimensional imaging and fracturing equipment, and significantly reducing experimental costs and shortening the experimental cycle while ensuring the accuracy of fracture spatial characterization.

[0111] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for characterizing fractures based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction, characterized in that... include: Select complete core samples from the target block, mark and record the original spatial orientation information on the surface of the core samples, and test the basic physical properties and natural fracture characteristics of the core samples. The core sample is cut into several two-dimensional thin slices along the length direction according to the preset thickness, and then polished and sealed to make thin slice specimens; the thin slice specimens are numbered and marked according to the original spatial order of each two-dimensional thin slice in the core sample. Under the same experimental conditions, a thin-slice sample was installed in the center of the clamping cavity of the planar fracturing device each time, and a confining pressure was uniformly applied to it in the circumference to simulate formation stress. Fracturing loading was carried out by constant pressure injection until the two-dimensional thin slice initiated and formed a stable propagating fracture. During the fracturing process, the fracturing pressure change curve, fracture initiation characteristics and propagation characteristics were recorded in real time. After the thin-slice sample was fracturing, the next numbered thin-slice sample was replaced, and the above installation and fracturing steps were repeated until all thin-slice samples had completed the fracturing experiment. After fracturing, orthophoto images of the surface of each thin-section sample are acquired. After standardization preprocessing, image binarization, and filtering and denoising, the crack boundaries and center lines are extracted. Geometric parameters, including crack length, orientation angle, number of branches, and distribution range, are quantitatively extracted to generate vectorized crack data. The crack data of each two-dimensional thin section are standardized and stored in a unified format, and a spatial index relationship is established by combining the numbering and thickness information of the two-dimensional thin sections. Based on the spatial index relationship of each thin section sample, interlayer feature matching and registration alignment are performed on the vectorized crack data of each two-dimensional thin section to complete the spatial correction between adjacent two-dimensional thin sections; interlayer topological connection and interpolation extension are performed on cracks with corresponding relationships to reconstruct the continuous morphology of cracks in three-dimensional space and generate a three-dimensional crack network model of the core sample.

2. The crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction according to claim 1, characterized in that, After generating the 3D crack network model, the process also includes spatial feature analysis of the cracks: Based on a three-dimensional fracture network model, key structural parameters, including fracture volume, fracture network connectivity, fracture spatial density, and fracture propagation range, are quantitatively calculated. Based on the calculated parameters, the fracture propagation mechanism is analyzed and the fracturing effect is evaluated. Or / and, the step of performing interlayer feature matching and registration alignment on the vectorized crack data of each two-dimensional thin section based on the spatial index relationship of each thin section specimen to complete the spatial correction between adjacent two-dimensional thin sections includes: Each two-dimensional thin section is regarded as a discrete slice layer in the core sample. A three-dimensional spatial coordinate system is established based on the spatial index relationship to determine the layer coordinates of each two-dimensional thin section in three-dimensional space. The interlayer positions are corrected by using the original spatial orientation information, and the planar coordinates of the two-dimensional thin section are spatially aligned using a rigid transformation model or an affine transformation model. An iterative nearest point algorithm is introduced to optimize the registration results, controlling the interlayer registration error within a single pixel, thus providing an accurate spatial reference for subsequent crack topological connections.

3. The crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction according to claim 1 or 2, characterized in that, The method of performing interlayer topological connections on cracks with corresponding relationships includes: The vectorized crack data is segmented, dividing the continuous crack centerline into multiple discrete crack segments; the local geometric features of each crack segment are extracted, including the centroid position, main orientation angle, centerline length, and average aperture calculated based on the crack boundary. The spatial connectivity of crack segments is determined by a weighted comprehensive similarity based on multiple geometric features. The formula for calculating the comprehensive similarity is as follows: in, The overall similarity of the crack segments; These are the weighting coefficients corresponding to each geometric feature. ; For positional similarity, To determine the similarity of the directional angles, For length similarity, For opening similarity; Set similarity threshold S 0, if the overall similarity between the two crack segments is 0. S ≥ S If the similarity is 0, then the two are determined to be different sections of the same three-dimensional crack, and a topological correspondence is established; if the comprehensive similarity of the two crack segments is 0, then the two crack segments ... S < S When the value is 0, it is determined to be a non-connected crack.

4. The crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction according to claim 3, characterized in that, After establishing the topological correspondence, spatial interpolation is performed on the crack morphology between adjacent two-dimensional thin sections to construct the continuous geometric structure of the crack in three-dimensional space, including: Set a high similarity threshold S h ,and S h > S 0, for overall similarity S ≥ S h For high-matching crack segments, a continuous crack surface is constructed using three-dimensional linear interpolation. A one-to-one correspondence is established between the endpoints, bifurcation points, and key points on the crack centerline and crack boundary. The coordinates of the upper-layer feature points are set as follows: The coordinates of the corresponding feature points in the lower layer are: Arbitrary height between floors The coordinates of the interpolation point at that location are ,in: in, The thickness of a single-layer two-dimensional sheet is given by x and y, which represent the horizontal and vertical coordinates of the two-dimensional sheet plane, respectively, and z represents the height coordinate in three-dimensional space. All corresponding feature points are interpolated and connected sequentially to generate a continuous crack profile surface between layers.

5. The crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction according to claim 4, characterized in that, For overall similarity S satisfy S 0≤ S < S h The spatial interpolation extension of the mid-matching crack segment employs a curvature interpolation method with similarity constraints, including: The fracture mechanics laws governing the propagation of hydraulic fractures in rock media, along with the in-situ stress constraint laws, are used as boundary conditions to limit the morphological range of interlayer fracture transitions. Based on this, a benchmark maximum curvature for allowable fracture propagation is set. Let the curvature of the interpolation curve be... ,satisfy ,in, S The comprehensive similarity between crack segments between adjacent two-dimensional thin sections is used. The lower the similarity, the greater the allowable interpolation curvature, in order to adapt to the continuous transition of complex crack segments including crack turning and bifurcation, so that the generated three-dimensional cracks can satisfy the interlayer geometric correspondence while conforming to the physical mechanism of crack propagation in the real hydraulic fracturing process.

6. The crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction according to claim 1, 2, 4, or 5, is characterized in that, The generation of vectorized crack data, combined with the section number and thickness information, establishes a spatial index relationship, including: Based on the extracted crack boundaries and centerlines, a crack vectorized data structure is established. Crack length, orientation angle, number of branches, and spread range are assigned as attribute information to the corresponding crack vector entities, thereby generating vectorized crack data. The numbering of the thin-section specimens is used as the hierarchical index identifier in the z-axis direction. The z-axis spacing between adjacent thin sections is calculated based on the thickness of each thin-section specimen. The vectorized crack data is stored hierarchically according to the hierarchical index identifier and the z-axis spacing to construct a spatial index relationship.

7. The crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction according to claim 3, characterized in that, The generation of vectorized crack data, combined with the section number and thickness information, establishes a spatial index relationship, including: Based on the extracted crack boundaries and centerlines, a crack vectorized data structure is established. Crack length, orientation angle, number of branches, and spread range are assigned as attribute information to the corresponding crack vector entities, thereby generating vectorized crack data. The numbering of the thin-section specimens is used as the hierarchical index identifier in the z-axis direction. The z-axis spacing between adjacent thin sections is calculated based on the thickness of each thin-section specimen. The vectorized crack data is stored hierarchically according to the hierarchical index identifier and the z-axis spacing to construct a spatial index relationship.

8. The crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction according to any one of claims 1, 2, 4, 5, or 7, characterized in that, The process of cutting the core sample into several two-dimensional thin slices along its length according to a preset thickness includes: The core samples were cut into two-dimensional thin sections with a thickness of 1 to 3 mm using a high-precision wire cutting device, and the thickness error of the thin sections did not exceed [a certain value]. During the cutting process, the cutting order and circumferential angle of each two-dimensional sheet are kept aligned according to the original spatial orientation information to ensure spatial orientation matching during three-dimensional reconstruction. Or / and, the application of confining pressure uniformly in its circumference to simulate formation stress, and the fracturing loading using a constant pressure injection method, includes: The thin-section sample is placed in the center of the clamping cavity of the planar fracturing device, and a preset confining pressure is applied to it in a circumferential uniform loading manner. The preset confining pressure is a uniform constraint pressure that simulates the in-situ stress conditions of the target formation. A simulated wellbore is set up at the center of the planar fracturing device. Fracturing fluid is continuously injected into the thin-film sample through the simulated wellbore at a constant pressure according to the preset injection pressure, until the thin-film sample initiates fracturing and forms a stable propagating fracture.

9. The crack characterization method based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction according to claim 6, characterized in that, The process of cutting the core sample into several two-dimensional thin slices along its length according to a preset thickness includes: The core samples were cut into two-dimensional thin sections with a thickness of 1 to 3 mm using a high-precision wire cutting device, and the thickness error of the thin sections did not exceed [a certain value]. During the cutting process, the cutting order and circumferential angle of each two-dimensional sheet are kept aligned according to the original spatial orientation information to ensure spatial orientation matching during three-dimensional reconstruction. Or / and, the application of confining pressure uniformly in its circumference to simulate formation stress, and the fracturing loading using a constant pressure injection method, includes: The thin-section sample is placed in the center of the clamping cavity of the planar fracturing device, and a preset confining pressure is applied to it in a circumferential uniform loading manner. The preset confining pressure is a uniform constraint pressure that simulates the in-situ stress conditions of the target formation. A simulated wellbore is set up at the center of the planar fracturing device. Fracturing fluid is continuously injected into the thin-film sample through the simulated wellbore at a constant pressure according to the preset injection pressure, until the thin-film sample initiates fracturing and forms a stable propagating fracture.

10. A crack characterization device based on two-dimensional thin-section fracturing and layer-by-layer three-dimensional reconstruction, characterized in that, include: The system includes a core 2D thin section preparation module, a 2D thin section layer-by-layer fracturing experiment module, a fracture imaging and digital processing module, and a 3D fracture network reconstruction module. The core 2D thin section preparation module is used to select complete core samples from the target block, mark and record the original spatial orientation information on the surface of the core sample, and test the basic physical properties and natural fracture characteristics of the core sample. The core sample is cut into several two-dimensional thin slices along the length direction according to the preset thickness, and then polished and sealed to make thin slice specimens; the thin slice specimens are numbered and marked according to the original spatial order of each two-dimensional thin slice in the core sample. The two-dimensional thin-slice layer-by-layer fracturing experimental module is used to, under the same experimental conditions, install one thin-slice sample at a time in the center of the clamping cavity of the planar fracturing device, and uniformly apply confining pressure to it in the circumference to simulate formation stress; fracturing loading is carried out by constant pressure injection until the two-dimensional thin slice initiates fracturing and forms a stable propagating fracture; during the fracturing process, the fracturing pressure change curve, fracturing initiation characteristics, and propagation characteristics are recorded in real time; after the thin-slice sample is fracturing, the next numbered thin-slice sample is replaced, and the above installation and fracturing steps are repeated until all thin-slice samples have completed the fracturing experiment. The crack imaging and digitization module is used to acquire orthophoto images of the cracks on the surface of each thin-section sample after fracturing. After standardization preprocessing, image binarization, and filtering and denoising, the crack boundaries and center lines are extracted. Geometric parameters, including crack length, orientation angle, number of branches, and distribution range, are quantitatively extracted to generate vectorized crack data. The crack data of each two-dimensional thin section is stored in a standardized format and a spatial index relationship is established by combining the numbering and thickness information of the two-dimensional thin sections. The three-dimensional fracture network reconstruction module is used to perform interlayer feature matching and registration alignment of the vectorized fracture data of each two-dimensional thin section according to the spatial index relationship of each thin section sample, and to complete the spatial correction between adjacent two-dimensional thin sections; it performs interlayer topological connection and interpolation extension on fractures with corresponding relationships, reconstructs the continuous morphology of fractures in three-dimensional space, and generates a three-dimensional fracture network model of the core sample.

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