Rock microcrack detection method

Abstract

The invention relates to the technical field of rock crack detection methods, in particular to a rock microcrack detection method. According to the rock micro-crack detection method, a rock sample is submerged in a set container containing a permeation staining solution, and the permeation staining solution comprises transparent high-permeability epoxy resin and an oil-soluble fluorescent staining agent which are mixed together; the set container is placed in vacuumizing equipment to be vacuumized till the vacuum degree is smaller than the set pressure intensity; selecting a specified cross section of the rock sample as an observation surface, and shooting the observation surface in an ultraviolet light environment; an image obtained through shooting is processed into a micro-crack grayscale image; and analyzing and counting parameters for representing microcrack characteristics in the microcrack grayscale image. According to the invention, deep penetration and physical locking of the rock microcracks can be realized, the cured epoxy resin can be firmly combined with the rock microcracks, the original state cannot be destroyed due to the processes of rock sample carrying, cutting sample preparation and the like, and real and comprehensive rock internal microcrack distribution data can be conveniently collected by multiple sections.

Description

Technical Field

[0001] This invention relates to the technical field of rock crack detection methods, and in particular to a method for detecting microcracks in rocks. Background Technology

[0002] Natural rocks, after being affected by geological processes and weathering, develop microcracks within their interiors. When subjected to more severe external disturbances, such as drilling, impact vibration, or high temperatures, the affected rocks will suffer some degree of damage. Due to differences in the inherent properties of the rock and the degree of impact, while some rocks exhibit directly observable cracks and fractures, the cracks in other rocks often exist in the form of microcracks. Related studies have shown that the development and distribution characteristics of microcracks within rocks have a significant impact on the rock's mechanical properties and permeability.

[0003] Because the microcracks are extremely small (crack width less than 0.1 mm) and the mineral composition of the rock itself is complex, the difference between the microcracks and the interfaces of different minerals is very small, making it difficult to effectively observe the distribution characteristics of microcracks in the rock using a single magnification method. Summary of the Invention

[0004] The purpose of this invention is to provide a method for detecting microcracks in rocks.

[0005] To address the aforementioned technical problems, this invention provides a method for detecting microcracks in rocks.

[0006] The rock microcrack detection method of the present invention includes:

[0007] Obtain rock samples;

[0008] The rock sample is submerged in a pre-designed container filled with a penetrating staining solution, which comprises a mixture of a transparent, highly permeable epoxy resin and an oil-soluble fluorescent staining agent.

[0009] The container is placed in a vacuum pump and evacuated until the vacuum level is less than or equal to the set pressure, and the evacuation time is greater than or equal to the first set time.

[0010] Completely cure the highly permeable epoxy resin in the specified container;

[0011] A designated section of the rock sample was selected as the observation surface, and the observation surface was photographed under ultraviolet light.

[0012] The captured images are processed into grayscale images of microcracks;

[0013] The parameters used to characterize the microcrack properties in the grayscale image of the microcrack were analyzed and statistically analyzed.

[0014] Furthermore, the high-permeability epoxy resin has a solid content of <30%, a viscosity of <3000 mPa / s, and a shrinkage rate of <2%.

[0015] Furthermore, the curing time of the highly permeable epoxy resin is not less than 2 hours.

[0016] Furthermore, the container is an open container, and the size of the open side is larger than the size of the closed side.

[0017] Further, the process of processing the captured image into a microcrack grayscale image includes:

[0018] The captured images are processed using an automatic threshold selection algorithm based on one-dimensional traversal comparison and a local adaptive thresholding algorithm based on two-dimensional traversal comparison, respectively.

[0019] The grayscale image of the microcrack is obtained by superimposing the separately processed images.

[0020] Furthermore, the volume of the permeation staining solution above the rock sample portion is greater than 5% of the rock sample volume.

[0021] Furthermore, before vacuuming, the pressure of the rock sample inside the set container is ≤101kPa, and the vacuum is evacuated to the set pressure of 5kPa, with the first set time being 2 hours.

[0022] Furthermore, selecting a designated section of the rock sample as the observation surface and photographing the observation surface includes:

[0023] Remove the rock sample from the container and remove the cured epoxy resin from the outside of the rock sample;

[0024] Cut the rock sample to obtain a specified cross section as the observation surface;

[0025] Rock samples with observation surfaces were placed in a fluorescent observation darkroom for imaging.

[0026] Furthermore, there are multiple observation surfaces, which are numbered in a set order, and the spatial distribution parameters of the multiple observation surfaces are recorded.

[0027] Furthermore, for the obtained microcrack grayscale images, the corresponding microcrack grayscale images are numbered according to the numbering order of multiple observation surfaces.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] Through the synergistic effect of highly permeable epoxy resin and oil-soluble fluorescent dye, deep penetration and physical locking of rock microcracks are achieved in a vacuum environment. The cured epoxy resin can firmly bond with the rock microcracks and will not be damaged by rock sample handling, cutting, or other processes, facilitating the acquisition of accurate and comprehensive data on the distribution of internal rock microcracks from multiple sections. The rigid phosphor formed after epoxy resin curing produces a high-intensity contrast signal under ultraviolet light excitation, resulting in a high grayscale difference between the microcracks and the mineral background. This lays the foundation for subsequent image processing and is beneficial for obtaining clearer images of rock microcracks. Attached Figure Description

[0030] Figure 1 This is a flowchart of an embodiment of the rock microcrack detection method of the present invention;

[0031] Figure 2 Color images obtained from rock samples processed by the rock microcrack detection method of the present invention;

[0032] Figure 3 To Figure 2 The grayscale image obtained after desaturating a color image;

[0033] Figure 4 This is a schematic representation of the area distribution of pixel value summation within the local adaptive threshold algorithm region in the rock microcrack detection method of the present invention;

[0034] Figure 5 This is a grayscale image of a rock sample microcrack obtained after processing by the rock microcrack detection method of the present invention.

[0035] Figure label:

[0036] 301. Rectangular region shown in grayscale image; 401. Pixel value distribution table; 402. Area table of pixel value summation; 501. Rectangular region shown in rock microcrack image. Detailed Implementation

[0037] The method for detecting microcracks in rocks according to the present invention will be described below with reference to schematic diagrams, which illustrate preferred embodiments of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention. Based on the teachings of this specification, those skilled in the art can form new technical solutions through cross-combinations of different implementation methods without creating technical contradictions; such modifications should all be considered to fall within the protection scope of this patent.

[0038] The serial numbers assigned to components in this document, such as "first," "second," etc., are merely used to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages). In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0039] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0040] In this application, unless otherwise expressly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium. Furthermore, the term "electrical connection" can be a direct electrical connection or an indirect electrical connection through an intermediate medium.

[0041] The invention is described more specifically by way of example in the following paragraphs with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description and claims. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0042] The inventors discovered that rock microcracks are extremely small, making it difficult to effectively stain deep within the rock using atmospheric pressure permeation staining. Even with water-soluble dyes combined with vacuum staining, some tiny cracks failed to penetrate effectively, and the dye did not adhere firmly to the rock cracks, easily damaging the original state during sample handling and cutting.

[0043] This invention proposes using a mixture of highly permeable epoxy resin and an oil-soluble fluorescent dye as a penetrating dyeing solution. Under vacuum, this solution can effectively penetrate rock microcracks. The cured epoxy resin firmly bonds to the rock microcracks, facilitating the collection of accurate and comprehensive data on the distribution of internal rock microcracks from multiple cross-sections.

[0044] The following is in conjunction with the instruction manual appendix. Figure 1 To be continued Figure 5 The present invention describes the method for detecting microcracks in rocks.

[0045] In some of these embodiments, such as Figure 1 As shown, the rock microcrack detection method includes:

[0046] S100: Obtain rock samples;

[0047] S200: Immerse the rock sample in a pre-designated container filled with a permeation staining solution, the permeation staining solution comprising a mixture of a highly permeable epoxy resin and an oil-soluble fluorescent staining agent.

[0048] S300: Place the set container in a vacuum pump and evacuate it until the vacuum level is less than or equal to the set pressure, and maintain the vacuuming time for a period of time greater than or equal to the first set time;

[0049] S400: Completely cure the high-permeability epoxy resin in the set container;

[0050] S500: Select a designated section of the rock sample as the observation surface and photograph the observation surface;

[0051] S600: Processes the captured image into a grayscale image with microcracks;

[0052] S700: Analyze and statistically analyze the parameters used to characterize the microcrack properties in the grayscale image of the microcrack.

[0053] Through the synergistic effect of highly permeable epoxy resin and oil-soluble fluorescent dye, deep penetration and physical locking of rock microcracks are achieved in a vacuum environment. The cured epoxy resin can firmly bond with the rock microcracks and will not be damaged by rock sample handling, cutting, or other processes, facilitating the acquisition of accurate and comprehensive data on the distribution of internal rock microcracks from multiple sections. The rigid phosphor formed after epoxy resin curing produces a high-intensity contrast signal under ultraviolet light excitation, resulting in a high grayscale difference between the microcracks and the mineral background. This lays the foundation for subsequent image processing and is beneficial for obtaining clearer images of rock microcracks.

[0054] In some embodiments, in step S200, the container is preferably an open container, and the size of the open side is larger than the size of the closed side.

[0055] Because the curing process of epoxy resin is exothermic and involves thermal expansion, and because cured epoxy resin has high strength, open containers with an open side larger than the closed side are less susceptible to damage from high temperatures and thermal expansion. This also facilitates removal of the cured epoxy resin from the container. Furthermore, it is preferable to manufacture the open container from a material that is heat-resistant and deformable.

[0056] In some embodiments, in step S200, the high-permeability epoxy resin has a solids content of <30%, a viscosity of <3000 mPa / s, and a shrinkage rate of <2%. This results in the epoxy resin having extremely low viscosity, extremely low shrinkage rate, and high permeability, making it easier to penetrate into the microcracks inside the rock.

[0057] Preferably, the curing time of the highly permeable epoxy resin is not less than 2 hours, so that the epoxy resin can fully penetrate into the microcracks inside the rock. If the curing time is too short, it will be difficult to fully penetrate the microcracks. Preferably, the epoxy resin is a two-component epoxy resin, so that the epoxy resin has a sufficiently long curing time. In other embodiments, epoxy resins with other components can be selected, provided that a sufficient curing time can be guaranteed.

[0058] To ensure the rock sample remains submerged in the permeation staining solution throughout the vacuuming process, in some embodiments, in step S200, the volume of the permeation staining solution above the rock sample should be greater than 5% of the rock sample volume. For rocks with high primary porosity, the volume of the permeation staining solution above the rock sample should be greater than 10% of the rock sample volume.

[0059] In some embodiments, in step S300, to evacuate the set container, the set container containing the rock sample and the penetrating staining agent is placed in the vacuum setting. Preferably, the pressure inside the set container before vacuuming is ≤101 kPa, and the vacuum is evacuated to the set pressure of 5 kPa for a first set time of 2 hours. That is, the vacuum is evacuated to a vacuum degree of no more than 5 kPa and maintained for at least 2 hours. The set container must be securely fixed inside the vacuum equipment to prevent solution spillage and damage to the equipment.

[0060] In order to fully cure the epoxy resin, in some embodiments, in step S400, the entire container is removed and placed in a constant temperature chamber set at 20-25°C or a laboratory at the same temperature for more than 6 hours to allow the penetrating dye containing the highly permeable epoxy resin to fully cure.

[0061] In some embodiments, step S500, selecting a designated section of the rock sample as the observation surface and photographing the observation surface, includes:

[0062] Remove the rock sample from the container and remove the cured epoxy resin from the outside of the rock sample;

[0063] Cut the rock sample to obtain a specified cross section as the observation surface;

[0064] Rock samples with observation surfaces were placed in a fluorescent observation darkroom for imaging.

[0065] Specifically, the observation surface needs to be planar to facilitate image generation and data statistics. To facilitate multi-location observation of the distribution characteristics of rock microcracks, rock sample cutting equipment can be used to cut the rock sample at multiple locations along the axial or radial direction to form multiple observation surfaces for collecting microcrack distribution data at different locations inside the rock sample.

[0066] Furthermore, the multiple observation surfaces are numbered in a certain order, and the spatial distribution parameters of the multiple observation surfaces are recorded to form an observation surface information record table. This facilitates the identification and numbering of the multiple microcrack grayscale images after obtaining the microcrack grayscale images of the multiple observation surfaces, thereby making it easier to analyze the spatial distribution characteristics of the rock sample microcracks.

[0067] During the imaging process, the rock sample is placed in a fluorescence observation darkroom equipped with ultraviolet irradiation. The observation port of the fluorescence observation darkroom must have a filter and an imaging port. The rock sample is placed with the observation surface facing upwards in the optimal observation position of the fluorescence observation darkroom, and the observation surface is photographed using a high-resolution device, and the image data is saved.

[0068] For images acquired through photography, they are usually... Figure 2 In the color image, the microcracks are difficult to distinguish due to interference from the background (i.e., the rock's own color) and their small size. The image obtained after conventional desaturation and grayscale processing is as follows: Figure 3 As shown, due to the influence of the background of the rock image, it is still not easy to clearly distinguish the microcracks.

[0069] Therefore, this application proposes to use an automatic threshold selection algorithm based on one-dimensional traversal comparison and a local adaptive threshold algorithm based on two-dimensional traversal comparison to process the captured images respectively, and then superimpose the processed images to obtain the grayscale image of the microcrack.

[0070] Specifically, in step S600, processing the captured image into a microcrack grayscale image includes:

[0071] S601: The captured images are processed using an automatic threshold selection algorithm based on one-dimensional traversal comparison and a local adaptive threshold algorithm based on two-dimensional traversal comparison, respectively.

[0072] S602: Superimpose the processed images to obtain the grayscale image of the microcrack.

[0073] In S601, the process of processing the captured image using a one-dimensional traversal comparison automatic threshold selection algorithm is as follows:

[0074] For the captured image, by traversing the image, the total number of pixels in the captured image is identified as S, and the total number of gray levels is L.

[0075] Pixels are numbered in a one-dimensional manner, where a pixel with a grayscale value of i is defined as q. i The quantity is S. i The value of i ranges from [0, L-1]. The pixel with grayscale value i is q. i The probability of occurrence F i It can be calculated using the following formula:

[0076]

[0077] Assuming that pixel value k in the image is the initial optimal threshold for separating rock microcracks from the rock image background, then pixels with grayscale values ​​in the range [0, k] represent rock microcracks and are designated as black; pixels with grayscale values ​​in the range [k, L-1] represent the rock image background and are designated as white. The corresponding probability P of the rock microcracks is then... crack for:

[0078]

[0079] The average gray value H of the rock microcracks crack The average gray value H of the rock image background backdrop for:

[0080]

[0081] The inter-class variance σ between the rock microcrack pixels and the rock background pixels is... 2 :

[0082] σ 2 =P crack (1-P crack (H) crack -H backdrop ) 2 (5)

[0083] When σ 2 When the threshold is maximized, the corresponding pixel value k is the optimal threshold, at which point the difference between the rock microcracks and the rock image background is greatest. All rock microcracks appear black, while the rock background image appears white, thus achieving grayscale processing of a color image.

[0084] Furthermore, in step S601, in order to avoid the problem of missing rock microcrack information in some areas due to the selection of the initial threshold in the automatic threshold selection algorithm, a local adaptive threshold algorithm based on local pixel comparison is used for correction, and the local adaptive threshold is calculated according to the local average intensity around each pixel.

[0085] Specifically, such as Figure 2 As shown, for the selected rectangular region T, the pixels are numbered in a two-dimensional manner, and the grayscale value of each pixel is q. ij Given a rectangle with length a and width b, divide the rectangular region T into m*n smaller rectangular regions t. ij ,For example Figure 3 The image shows a rectangular region 301 in a medium grayscale image.

[0086] Iterate through all pixels within region T and calculate the value of each small rectangular region t. ij The pixel grayscale values ​​are used to form a pixel value distribution table 401;

[0087] To ensure accuracy, the length and width of the rectangular region T are less than 1 / 10 of the crack width.

[0088] Starting from the top left corner, the area table 402 is obtained by summing the pixel values ​​within this region according to the following formula.

[0089]

[0090] Then any small rectangular region t in the lower right corner ij The average grayscale value of the center pixel is

[0091]

[0092] Reintroducing the small rectangular region t ij The grayscale values ​​q of each pixel in the original image ij The order is the same as q. ij-avg In comparison, the grayscale value range of the pixel is [0, q]. ij-avg [This represents microcracks in the rock, set to black; the pixel grayscale value range is [q] ij-avg [L-1] is the background of the rock image, set to white.

[0093] Finally, in step S602, the images processed by the two image processing methods are superimposed to obtain the image as shown below. Figure 5 The image shown is a grayscale image of microcracks in a rock sample. As an example, Figure 3 The final processing result of the image within the rectangular region 301 of the medium grayscale image is shown in the diagram. Figure 5 The image shows a rectangular region 501 with microcracks in medium-sized rocks.

[0094] After processing by an automatic threshold selection algorithm based on one-dimensional traversal comparison and a local adaptive threshold algorithm based on two-dimensional traversal comparison, a grayscale image of rock microcracks was obtained, which significantly reduced the interference of rock mineral colors on the crack image processing results.

[0095] If there are multiple grayscale images of microcracks in the rock sample, they are numbered one-to-one according to the sequential numbering of the recorded observation surfaces to facilitate the analysis of the spatial distribution characteristics of the microcracks in the rock sample.

[0096] In some embodiments, in step S700, the parameters used to characterize the microcrack properties in the grayscale image of the microcrack are analyzed and statistically analyzed.

[0097] Specifically, the parameters used to characterize the microcrack properties include, but are not limited to, the density, data, length, orientation, and fractal dimension of the microcracks on each observation surface. For statistical analysis, dedicated crack statistical analysis software or algorithms, such as the Particle and Crack Analysis System (PCAS), can be used.

[0098] Compared with the prior art, the present invention has at least the following beneficial effects:

[0099] Through the synergistic effect of highly permeable epoxy resin and oil-soluble fluorescent dye, deep penetration and physical locking of rock microcracks are achieved in a vacuum environment. The cured epoxy resin can firmly bond with the rock microcracks and will not be damaged by rock sample handling, cutting, or other processes, facilitating the acquisition of accurate and comprehensive data on the distribution of internal rock microcracks from multiple sections. The rigid phosphor formed after epoxy resin curing produces a high-intensity contrast signal under ultraviolet light excitation, resulting in a high grayscale difference between the microcracks and the mineral background. This lays the foundation for subsequent image processing and is beneficial for obtaining clearer images of rock microcracks.

[0100] Furthermore, by combining automatic threshold selection algorithm and local adaptive threshold algorithm for grayscale processing of rock microcrack images, the problem of large deviations in results caused by the susceptibility of single methods to the influence of rock mineral colors is effectively overcome.

[0101] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for detecting microcracks in rock, characterized by, The method comprises: obtaining a rock sample; immersing the rock sample in a set container containing a permeation dyeing solution, the permeation dyeing solution comprising transparent high-permeability epoxy resin and oil-soluble fluorescent dyeing agent mixed together; placing the set container in a vacuum extraction device to extract vacuum to a vacuum degree less than or equal to a set pressure, and maintaining the vacuum extraction time greater than or equal to a first set time; completely curing the high-permeability epoxy resin in the set container; selecting a designated cross-section of the rock sample as an observation surface and taking a photograph of the observation surface under ultraviolet light; processing the obtained image into a micro-crack grayscale image; analyzing and counting parameters in the micro-crack grayscale image for representing micro-crack characteristics.

2. The method of claim 1, wherein, The high-permeability epoxy resin has a solid content less than 30%, a viscosity less than 3000 mPa / s, and a shrinkage less than 2%.

3. The method of claim 1, wherein, The curing time of the high-permeability epoxy resin is not less than 2 hours.

4. The method of claim 1, wherein, The set container is an open container, and the size of the open side is greater than the size of the closed side.

5. The method of claim 1, wherein, The processing of the obtained image into a micro-crack grayscale image comprises: respectively processing the obtained image by using a one-dimensional traversal contrast automatic threshold selection algorithm and a two-dimensional traversal contrast local adaptive threshold algorithm; superimposing the images processed respectively to obtain the micro-crack grayscale image.

6. The method of claim 1, wherein, The volume of the permeation dyeing solution higher than the rock sample is greater than 5% of the volume of the rock sample.

7. The method of claim 1, wherein, The pressure in the set container before the vacuum extraction is less than or equal to 101 kPa, the set pressure after the vacuum extraction is 5 kPa, and the first set time is 2 hours.

8. The method of claim 1, wherein, The selection of the designated cross-section of the rock sample as the observation surface and the photographing of the observation surface comprise: taking out the rock sample from the set container and removing the epoxy resin cured outside the rock sample; cutting the rock sample to obtain the designated cross-section as the observation surface; placing the rock sample with the observation surface into a fluorescent observation dark box for photographing.

9. The method of claim 8, wherein, The observation surface has multiple observation surfaces, the multiple observation surfaces are numbered in a set order, and the spatial distribution parameters of the multiple observation surfaces are recorded.

10. The method of claim 9, wherein, The corresponding micro-crack grayscale images are numbered in the numbering order of the multiple observation surfaces.

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