Digital rock core three-dimensional reconstruction method containing pore and mineral distribution

Abstract

The invention provides a digital rock core three-dimensional reconstruction method containing pore and mineral distribution, and relates to the field of oil-gas exploration and development. The three-dimensional reconstruction method of the digital rock core containing pore and mineral distribution comprises the following steps: (1) marking positioning information on a sample; (2) acquiring pore three-dimensional information of the rock core sample; (3) obtaining a mineral analysis cross section; (4) carrying out QEMSCAN quantitative analysis; and (5) establishing a three-dimensional mineral model. According to the method, a multi-element three-dimensional mineral model of pore and mineral distribution is established, so that reservoir characterization and rock parameter simulation are better carried out, and a basis is provided for later reservoir evaluation and favorable exploration area selection.

Description

Technical Field

[0001] The invention relates to the field of oil and gas exploration and development, and in particular to a three-dimensional reconstruction method of a digital core including pores and mineral distribution. Background Art

[0002] The establishment of three-dimensional rock models is mostly binary rock models, that is, only the mineral particles and pore structures are distinguished. Although there have been preliminary explorations of three-dimensional mineral models, their application is limited. At present, there is no effective means to reconstruct digital core models that include pore information and mineral distribution.

[0003] At present, the reconstruction of three-dimensional rock models based on experimental means mainly obtains two-dimensional grayscale images of rock samples through X-ray CT scanning and focused ion beam-scanning electron microscopy, and then uses specific algorithms to reconstruct the two-dimensional images in three dimensions. When building a three-dimensional rock model based on the X-ray CT scanning method, the rock sample is completely non-destructive, and other types of experiments can be carried out after the scan. However, this method can only use grayscale to reflect the density of minerals and cannot identify mineral components. Although the focused ion beam scanning electron microscope can be combined with the energy spectrum to identify limited minerals, this method has a very small field of view and is only suitable for nanoscale pore characterization. The sample size is at the millimeter level, and it cannot reflect the heterogeneity of the reservoir macroscopically, and cannot achieve digital three-dimensional reconstruction at the core level.

[0004] CN115078422A discloses a method for establishing a three-dimensional mineral model, including: selecting a rock sample, placing it in a CT scanner to obtain an X-ray CT scan to obtain an image, and performing three-dimensional reconstruction to generate a three-dimensional rock model; preparing the rock sample into a rock thin section sample for quantitative analysis of mineral composition to obtain a two-dimensional image of mineral distribution; searching for an image identical to the two-dimensional image of mineral distribution in the three-dimensional rock model, calibrating the same mineral particles in the three-dimensional rock model, determining the mineral components represented by different grayscale values, selecting an area with the same grayscale value in the three-dimensional rock model according to the grayscale value of the calibrated area, calibrating and filling the mineral components, and after the mineral components are filled, the three-dimensional mineral model is established. However, the grayscale value in the CT result of the invention only reflects the density of the mineral distribution area, and there may be multiple minerals or a mixture of multiple minerals at similar densities, which are difficult to distinguish in the grayscale image, and even if there are mineral analysis results, it is difficult to calibrate.

[0005] Therefore, it is urgent to establish a three-dimensional reconstruction method for digital cores that includes pore information and mineral distribution to truly reflect the reservoir rock composition and physical properties.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a method for three-dimensional reconstruction of digital cores including pores and mineral distribution, so as to solve the problem that in the prior art, three-dimensional digital reconstruction of cores can only reflect mineral particles in grayscale images but cannot truly reflect mineral components, thereby truly reflecting the reservoir rock composition and physical properties, so as to accurately carry out oil and gas reservoir evaluation work.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] In a first aspect, the present invention provides a method for three-dimensional reconstruction of a digital core including pores and mineral distribution, the method comprising the following steps:

[0010] (1) Sample marking and positioning information: a linear notch is cut along the height direction on the cylindrical surface of the cylindrical rock sample as the positioning line of the mineral analysis section;

[0011] (2) Obtaining 3D pore information of core samples: Performing X-ray CT scanning on the positioned cylindrical rock samples to obtain a 3D grayscale image of the rock, and then reconstructing and processing the image to obtain a 3D grayscale image model of the rock;

[0012] (3) Obtaining the mineral analysis section: The cylindrical rock sample with CT scan information is cut into several sample slices along the direction of the circular cross section, and then each sample slice is injected with glue, ground, polished and carbon-plated in turn to obtain several cross-section samples to be tested;

[0013] (4) QEMSCAN quantitative analysis: The surface of each cross-section sample to be tested is scanned using the scanning electron microscope mineral quantitative evaluation system, the distribution of mineral components on the two-dimensional image is quantitatively analyzed, and the two-dimensional image of each cross-section sample to be tested is output;

[0014] (5) Establishing a three-dimensional mineral model: The two-dimensional images of each cross-sectional sample to be measured are registered according to the positioning lines to obtain cross-sectional mineral images that are aligned and of the same size, and then the two-dimensional images are reconstructed into three dimensions through a multi-faceted reconstruction method.

[0015] Preferably, in step (1), the cylindrical rock sample is processed into a cylindrical shape by rock samples.

[0016] Preferably, the diameter of the cross section of the cylindrical rock sample is 2.5 to 3.0 cm.

[0017] Preferably, the length of the cylindrical rock sample is 4.5 to 5.5 cm (there is no strict requirement on the sample size, but the longer the length, the more cross sections need to be prepared to ensure accuracy).

[0018] Preferably, in step (1), the positioning process also includes a mark for supplementing the positioning information:

[0019] Marking characteristic sedimentary phenomenon information points on samples from which sedimentary phenomena can be identified, and numbering these information points; wherein the sedimentary phenomenon information points include any one or a combination of at least two of minerals, bedding, laminations, or various sedimentary structural features;

[0020] Or, physical positioning information is produced on a sample where deposition phenomena are difficult to identify, and these information points are numbered; wherein the production method includes using cutting and / or laser engraving.

[0021] Preferably, in step (2), the CT scanning specifically includes the following steps:

[0022] The positioned cylindrical rock sample is placed in a CT scanner for X-ray CT scanning to obtain an X-ray CT scanning grayscale three-dimensional image and an engineering file output by the CT scanner;

[0023] The engineering files output by the CT scanner are analyzed by Amira 3D software to obtain a grayscale three-dimensional image model of a rock composed of minerals and pores of different densities.

[0024] Preferably, in step (2), the process of obtaining the three-dimensional pore information of the core sample also includes extracting pore information and / or positioning information:

[0025] Identify and mark positioning lines, sedimentary phenomenon information points and / or physical positioning information in the rock grayscale three-dimensional image model, extract the three-dimensional model of pores and positioning information points in the generated rock grayscale three-dimensional image model, and output it as a universal editable three-dimensional format file through Amira 3D software.

[0026] Preferably, in step (3), the number of cuts of the same cylindrical rock sample is at least 10.

[0027] Preferably, in step (3), the thickness of the sample slice obtained by cutting is 4 to 5 mm.

[0028] Preferably, in step (3), the specific process of glue injection, grinding, polishing and carbon plating is as follows:

[0029] (a) Glue injection: Place the sample piece inside the mold coated with a release agent, then pour the mixture of epoxy resin and curing agent. After the glue layer is cured, take out the sample piece;

[0030] (b) grinding: using a metallographic grinder to first coarsely grind the sample after the injection of glue, and then finely grind it to remove the glue layer on the surface to be scanned of the sample piece;

[0031] (c) Polishing: Use a short-napped polishing disc to polish the side of the ground sample containing the ore in sections;

[0032] (d) Carbon coating: The polished sample is subjected to carbon coating treatment to form a carbon film layer.

[0033] Preferably, in step (a), the thickness of the adhesive layer is 10 to 15 mm (this range depends on the situation of the sample stage).

[0034] Preferably, in step (b), the coarse grinding is performed by wet grinding using an MD-Piano220 grinding disc, with a force of 15 to 25 N, a rotation speed of 200 to 300 rpm, and a time of 0.5 to 2 min.

[0035] Preferably, in step (b), the fine grinding is performed by wet grinding using an MD-piano1200 grinding disc, with a force of 10 to 15 N, a rotation speed of 150 to 250 rpm, and a time of 0.5 to 2 min.

[0036] Preferably, in step (c), the segmented polishing is as follows: the segmented operation is performed according to the gradually decreasing particle size of the diamond suspension from 5 μm, 3 μm, and 1 μm, the pressure of each polishing section is independently < any value of 10N (the pressure applied for polishing should be less than that for coarse grinding and fine grinding, as mentioned above, the fine grinding pressure is 10-15N, and the polishing pressure is <10N), the rotation speed of each polishing section is independently 100-200 rpm, and the polishing time of each section is independently 4-5 min.

[0037] Preferably, in step (d), the thickness of the carbon film layer is 5-10 nm.

[0038] Preferably, in step (4), the QEMSCAN quantitative analysis is specifically:

[0039] Using the scanning electron microscope mineral quantitative evaluation system, a high-energy electron beam is used to scan the surface of each cross-section sample to be tested along a preset raster scanning pattern to collect BSE data;

[0040] At each scanning point, by comparing the collected X-ray and BSE data (the X-ray here is the X-ray emitted by the energy dispersive spectrometer (EDS) of Qemscan, which is used to identify the elemental composition scanned by the X-ray intensity of EDS, and BSE refers to backscattered electrons, both of which must be collected) with the mineral phase information in the reference mineral library, mineral identification is performed on each scanning point, and finally the verification results of all scanning information points are summarized and output as a two-dimensional image.

[0041] Preferably, in step (4), the working mode of the scanning electron microscope mineral quantitative evaluation system is backscattering mode imaging;

[0042] Preferably, in step (4), the scanning parameters are set as follows: parameter speed voltage is 10-20 kV, working distance is 10-15 mm, and resolution is 10-15 μm.

[0043] Preferably, in step (5), the process of establishing the three-dimensional mineral model further includes:

[0044] Before inputting the pore information obtained by X-ray CT scanning, the three-dimensional pore information already contained in the three-dimensional mineral model needs to be deleted.

[0045] Preferably, in step (5), the process of establishing the three-dimensional mineral model further includes:

[0046] According to the grayscale distribution of the X-ray CT scan, the positioning line of the cylindrical section, the position of the positioning line in the electron microscope scanning analysis results of the mineral quantitative analysis, and the relative positions of different minerals, the rock grayscale three-dimensional image model with pore information obtained in step (2) is fitted with the three-dimensional mineral model obtained in step (5) to obtain a three-dimensional reconstruction model of the digital core.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The mineral composition of the three-dimensional model obtained by the digital core three-dimensional reconstruction method including pores and mineral distribution of the present invention is based on the actual detection results. The longitudinal accuracy depends on the number of analysis sections and the number of quantitative grindings, and can reach up to about 10 μm. The plane analysis accuracy can reach 1 μm.

[0049] (2) The digital core three-dimensional reconstruction method including pore and mineral distribution described in the present invention combines the three-dimensional pore information obtained by CT and the three-dimensional mineral composition information obtained by in-situ mineral analysis, and its accuracy is better than that of existing technical means.

[0050] (3) The method for three-dimensional reconstruction of digital cores including pore and mineral distribution described in the present invention solves the problem that the establishment of conventional three-dimensional rock models can only characterize a binary model of pores and solid mineral particles, and establishes a multivariate three-dimensional mineral model of standard pores and major minerals, thereby better performing reservoir characterization and rock parameter simulation, providing a basis for later reservoir evaluation and selection of favorable exploration areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0052] Figure 1 This is the appearance of the cylindrical rock sample provided in Example 1.

[0053] Figure 2 Appearance diagram of a cylindrical rock sample with positioning marks provided in Example 1.

[0054] Figure 3 This is a two-dimensional grayscale image of the X-ray CT scan provided in Example 1.

[0055] Figure 4 This is the three-dimensional reconstruction image of the X-ray CT scan provided in Example 1.

[0056] Figure 5 This is a result diagram of extracting pore three-dimensional distribution information from the three-dimensional reconstruction image of the X-ray CT scan provided in Example 1.

[0057] Figure 6 This is a cross-sectional view of the mineral analysis of the cylindrical rock sample provided in Example 1 after cutting.

[0058] Figure 7 This is a cross-sectional view of the sample to be tested after carbon plating provided in Example 1.

[0059] Fig. 8A This is the result of the quantitative analysis of the mineral micro-area of ​​the cross section of sample 11 provided in Example 1 by scanning electron microscopy.

[0060] Figure 8B for Fig. 8A The quantitative analysis results of the corresponding minerals in the analysis results of the 11th sample cross section.

[0061] Fig. 9 A three-dimensional mineral model is obtained for Example 1. DETAILED DESCRIPTION

[0062] Unless otherwise defined herein, scientific and technical terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear, however, in the case of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, unless otherwise stated, the use of "or" means "and / or". In addition, the use of the term "including" and other forms is non-limiting.

[0063] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0064] It should be noted that specific details are described in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in a variety of other ways different from those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0065] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0066] In a first aspect, the present invention provides a method for three-dimensional reconstruction of a digital core including pores and mineral distribution, the method comprising the following steps:

[0067] (1) Sample marking and positioning information: a linear notch is cut along the height direction on the cylindrical surface of the cylindrical rock sample as the positioning line of the mineral analysis section;

[0068] (2) Obtaining 3D pore information of core samples: Performing X-ray CT scanning on the positioned cylindrical rock samples to obtain a 3D grayscale image of the rock, and then reconstructing and processing the image to obtain a 3D grayscale image model of the rock;

[0069] (3) Obtaining the mineral analysis section: The cylindrical rock sample with CT scan information is cut into several sample slices along the direction of the circular cross section, and then each sample slice is injected with glue, ground, polished and carbon-plated in turn to obtain several cross-section samples to be tested;

[0070] (4) QEMSCAN quantitative analysis: The surface of each cross-section sample to be tested is scanned using the scanning electron microscope mineral quantitative evaluation system, the distribution of mineral components on the two-dimensional image is quantitatively analyzed, and the two-dimensional image of each cross-section sample to be tested is output;

[0071] (5) Establishing a three-dimensional mineral model: The two-dimensional images of each cross-sectional sample to be measured are registered according to the positioning lines to obtain cross-sectional mineral images that are aligned and of the same size, and then the two-dimensional images are reconstructed into three dimensions through a multi-faceted reconstruction method.

[0072] In the present invention, a method for three-dimensional reconstruction of digital cores containing pore information and mineral distribution is provided, including: preparing regular rock samples, placing them in a CT scanner to obtain X-ray CT scanning grayscale images, performing three-dimensional reconstruction to generate a three-dimensional rock model, and extracting three-dimensional pore information; cutting the rock sample into multiple sections in equal parts to carry out scanning electron microscope rock mineral micro-area quantitative analysis, and obtaining two-dimensional images of mineral distribution of all sections; using all the two-dimensional images of mineral distribution of the sections to carry out three-dimensional reconstruction of multi-faceted two-dimensional images, and establish a three-dimensional model of mineral composition; inputting the three-dimensional pore information obtained by CT scanning into the three-dimensional model of mineral composition, and finally obtaining a three-dimensional digital core model containing pore information and mineral distribution. The present invention establishes a multivariate three-dimensional mineral model of pore and mineral distribution, so as to better perform reservoir characterization and rock parameter simulation, and provide a basis for later reservoir evaluation and selection of favorable exploration areas.

[0073] As an optional embodiment, in step (1), the cylindrical rock sample is processed into a cylindrical shape by a rock sample.

[0074] As an optional embodiment, in step (1), the diameter of the cross section of the cylindrical rock sample is 2.5 to 3.0 cm, for example, it can be 2.5 cm, 2.6 cm, 2.8 cm, 2.8 cm, 2.9 cm, 3.0 cm, etc., and the length of the cylindrical rock sample is 4.5 to 5.5 cm, for example, it can be 4.5 cm, 4.6 cm, 4.8 cm, 5.0 cm, 5.2 cm, 5.4 cm, 5.5 cm, etc.

[0075] It should be noted that most rock samples are irregular in shape. Therefore, after selecting the rock sample to be tested, it is necessary to process it into a cylindrical shape. The size should be based on the convenience of CT scanning and mineral scanning electron microscope mineral micro-area quantitative analysis. It is generally recommended to prepare a regular cylinder with a diameter of 2.5 to 3 cm and a length of about 5 cm.

[0076] As an optional implementation, in step (1), the positioning process further includes a mark for supplementing the positioning information:

[0077] Marking characteristic sedimentary phenomenon information points on samples from which sedimentary phenomena can be identified, and numbering these information points; wherein the sedimentary phenomenon information points include any one or a combination of at least two of minerals, bedding, laminations, or various sedimentary structural features;

[0078] Or, physical positioning information is produced on a sample where deposition phenomena are difficult to identify, and these information points are numbered; wherein the production method includes using cutting and / or laser engraving.

[0079] It should be noted that in step (1), the sample needs to be marked with positioning information so that it can be used as the positioning point of the QEMSCAN mineral quantitative analysis section in step (4). That is, the sample is positioned on a regular cylindrical sample with a diameter of 2.5 to 3 cm and a length of about 5 cm. A linear notch is cut along the height of the cylindrical edge of the cylindrical sample, and the notch corresponding to the cut is used as the positioning point of the mineral analysis section in step (4). The method for determining the section position is shown in step (4).

[0080] It should be noted that, as a supplement to the positioning information, it is also necessary to select several sedimentary phenomenon information points with certain characteristics on the sample, including characteristic minerals, bedding, laminae and various sedimentary structural features, mark them and number them. For samples where it is difficult to identify enough sedimentary phenomena as positioning marks, physical positioning information can be produced, such as using cutting, laser engraving, etc. to produce positioning mark information points, mark them and number them.

[0081] It should be noted that the marked positioning information points or the marks made should avoid the segmentation position of the analysis interface in step (4).

[0082] As an optional implementation, in step (2), the CT scanning specifically includes the following steps:

[0083] The positioned cylindrical rock sample is placed in a CT scanner for X-ray CT scanning to obtain an X-ray CT scanning grayscale three-dimensional image and an engineering file output by the CT scanner;

[0084] The engineering files output by the CT scanner are analyzed by Amira 3D software to obtain a grayscale three-dimensional image model of a rock composed of minerals and pores of different densities.

[0085] It should be noted that the prepared rock sample is placed in a CT scanner for X-ray CT scanning, and the grayscale three-dimensional image of the X-ray CT scanning and the engineering file output by the CT scanner are obtained. The obtained X-ray CT scanning three-dimensional engineering file is analyzed by Amira 3D software to obtain a grayscale three-dimensional image model of the rock composed of minerals and pores of different densities. The notch cutting lines, sedimentary features or produced marking points with positioning information are identified and marked in the grayscale three-dimensional image model, and the three-dimensional model of pores and positioning information points is extracted in the generated three-dimensional rock model, and output to a general editable three-dimensional format file (including but not limited to .STL, .OBJ, .FBX, .DAE and other formats) through Amira 3D.

[0086] It should be noted that the analysis accuracy depends on the sample size and production needs. Taking the recommended size of 2.5 to 3 cm in diameter and about 5 cm in length as an example, the recommended analysis accuracy is 10 to 15 μm.

[0087] As an optional implementation, in step (2), the process of obtaining the three-dimensional pore information of the core sample also includes extracting pore information and / or positioning information:

[0088] Identify and mark positioning lines, sedimentary phenomenon information points and / or physical positioning information in the rock grayscale three-dimensional image model, extract the three-dimensional model of pores and positioning information points in the generated rock grayscale three-dimensional image model, and output it as a universal editable three-dimensional format file through Amira 3D software.

[0089] As an optional embodiment, in step (3), the number of cuts of the same cylindrical rock sample is at least 10, for example, it can be 10, 11, 12, 13, 14, 15, 16, 18, 20, etc.

[0090] As an optional embodiment, in step (3), the thickness of the cut sample piece is 4 to 5 mm, for example, it can be 4 mm, 4.2 mm, 4.4 mm, 4.5 mm, 4.6 mm, 4.8 mm, 5 mm, etc.

[0091] It should be noted that the cylindrical sample with CT scanning results and positioning information marked is cut along the circular cross section to obtain the mineral analysis section, and the cutting interval is determined according to the required analysis accuracy. Taking the recommended example, the cutting interval is about 4 to 5 mm. As mentioned above, at least 10 sections of the same cylinder are obtained for mineral quantitative analysis. Before cutting the section, first locate it on a regular cylindrical sample with a diameter of 2.5 to 3 cm and a length of about 5 cm, and cut a line along the height of the cylinder at the edge of the cylindrical sample as a positioning point.

[0092] As an optional implementation, in step (3), the specific process of glue injection, grinding, polishing and carbon plating is as follows:

[0093] (a) Glue injection: Place the sample piece inside the mold coated with a release agent, then pour the mixture of epoxy resin and curing agent. After the glue layer is cured, take out the sample piece;

[0094] (b) grinding: using a metallographic grinder to first coarsely grind the sample after the injection of glue, and then finely grind it to remove the glue layer on the surface to be scanned of the sample piece;

[0095] (c) Polishing: Use a short-napped polishing disc to polish the side of the ground sample containing the ore in sections;

[0096] (d) Carbon coating: The polished sample is subjected to carbon coating treatment to form a carbon film layer.

[0097] As an optional embodiment, in step (a), the thickness of the adhesive layer is 10 to 15 mm, for example, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, etc.

[0098] As an optional embodiment, in step (b), the coarse grinding is: wet grinding with water using an MD-Piano220 grinding disc, with a force of 15 to 25 N (for example, 15 N, 16 N, 18 N, 20 N, 22 N, 24 N, 25 N, etc.), a rotation speed of 200 to 300 rpm (for example, 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, etc.), and a time of 0.5 to 2 min (for example, 0.5 min, 0.6 min, 0.8 min, 1 min, 1.2 min, 1.4 min, 1.6 min, 1.8 min, 2 min, etc.).

[0099] As an optional embodiment, in step (b), the fine grinding is: wet grinding with water using an MD-piano1200 grinding disc, with a force of 10 to 15 N (for example, 10 N, 11 N, 12 N, 13 N, 14 N, 15 N, etc.), a rotation speed of 150 to 250 rpm (for example, 150 rpm, 160 rpm, 180 rpm, 200 rpm, 220 rpm, 240 rpm, 250 rpm, etc.), and a time of 0.5 to 2 min (for example, 0.5 min, 0.6 min, 0.8 min, 1 min, 1.2 min, 1.4 min, 1.6 min, 1.8 min, 2 min, etc.).

[0100] As an optional embodiment, in step (c), the segmented polishing is: the segmented operation is performed according to the diamond suspension particle size gradually decreasing from 5μm, 3μm, and 1μm, the pressure of each polishing section is less than 10N (for example, it can be 9.9N, 9N, 8N, 7N, 6N, 5N, 4N, 3N, 2N, 1N, etc.), the rotation speed of each polishing section is independently 100-200rpm (for example, it can be 100rpm, 120rpm, 140rpm, 160rpm, 180rpm, 200rpm, etc.), and the time of each polishing section is independently 4-5min (for example, it can be 4min, 4.2min, 4.4min, 4.5min, 4.6min, 4.8min, 5min, etc.).

[0101] As an optional implementation, in step (d), the thickness of the carbon film layer is 5 to 10 nm, for example, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc.

[0102] As an optional implementation, in step (4), the QEMSCAN quantitative analysis is specifically:

[0103] Using the scanning electron microscope mineral quantitative evaluation system, a high-energy electron beam is used to scan the surface of each cross-section sample to be tested along a preset raster scanning pattern to collect BSE data;

[0104] At each scanning point, mineral identification is performed on each scanning point by comparing the collected X-ray and BSE data with the mineral phase information in the reference mineral library. Finally, the identification results of all scanning information points are summarized and output as a two-dimensional image.

[0105] It should be noted that the obtained mineral analysis section uses QEMSCAN mineral analysis technology to scan the sample surface along a preset raster scanning pattern using a high-energy electron beam. At each scanning point, the mineral identification is performed on each scanning point by comparing the collected X-ray and BSE data with the mineral phase information in the reference mineral library. Finally, the verification results of all scanning information points are summarized and output as a two-dimensional image. Among them, the analysis accuracy depends on the sample size and production needs. The analysis accuracy of the same sample should be the same or similar to the CT scanning analysis accuracy. Taking the recommended size of 2.5-3cm in diameter and about 5cm in length as an example, the recommended analysis accuracy is 10-15μm.

[0106] As an optional implementation, in step (4), the working mode of the scanning electron microscope mineral quantitative evaluation system is backscattering mode imaging;

[0107] As an optional embodiment, in step (4), the scanning parameters are set as follows: parameter speed voltage is 10-20 kV (for example, it can be 10 kV, 12 kV, 14 kV, 15 kV, 16 kV, 18 kV, 20 kV, etc.), working distance is 10-15 mm (for example, it can be 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, etc.), resolution is 10-15 μm (for example, it can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.).

[0108] As an optional implementation, in step (5), the establishment of a three-dimensional mineral model is specifically:

[0109] A three-dimensional mineral model was established based on the quantitative analysis results of multiple cross-sectional minerals. Since the sizes of the obtained mineral images were not the same, no registration was performed between the cross-sections. Therefore, the cross-sectional images were first registered according to the reserved positioning ports to obtain cross-sectional mineral images that were aligned and of the same size (row and column numbers). The two-dimensional images were then reconstructed into three dimensions using the multi-plane reconstruction (MPR) technology to complete the establishment of a three-dimensional mineral model.

[0110] It should be noted that the process of establishing a three-dimensional mineral model includes image segmentation and three-dimensional reconstruction. The image segmentation refers to the image segmentation of different mineral components and pores in the mineral quantitative analysis image to facilitate subsequent image processing and analysis. The three-dimensional reconstruction refers to: using the positioning information point (notch position) feature matching of the two-dimensional image to perform image registration, and converting non-equal resolution image data into equal resolution data through interpolation technology, thereby completing three-dimensional reconstruction, and obtaining the three-dimensional reconstructed mineral three-dimensional model through image rendering and reorganization. The mineral three-dimensional model is output as a general editable three-dimensional format file (including but not limited to .STL, .OBJ, .FBX, .DAE and other formats) through Amira3D software, and the format used should be consistent with step (3).

[0111] As an optional implementation, in step (5), the process of establishing the three-dimensional mineral model further includes:

[0112] Before inputting the pore information obtained by X-ray CT scanning, the three-dimensional pore information already contained in the three-dimensional mineral model needs to be deleted;

[0113] As an optional implementation, in step (5), the process of establishing the three-dimensional mineral model further includes:

[0114] According to the grayscale distribution of the X-ray CT scan, the positioning line of the cylindrical section, the position of the positioning line in the electron microscope scanning analysis results of the mineral quantitative analysis, and the relative positions of different minerals, the rock grayscale three-dimensional image model with pore information obtained in step (2) is fitted with the three-dimensional mineral model obtained in step (5) to obtain a three-dimensional reconstruction model of the digital core.

[0115] It should be noted that since the three-dimensional mineral model obtained in step (5) already contains the three-dimensional pore information indirectly obtained by two-dimensional mineral image registration and interpolation, these pore information must be deleted before inputting the CT three-dimensional pore information. In addition, the 3D pore model obtained by CT can be fitted with the mineral three-dimensional model according to the grayscale distribution of CT, the positioning points of the cylindrical section, the notch position in the electron microscope scanning analysis results of the mineral quantitative analysis, and the relative positions of different minerals to obtain the final digital core three-dimensional reconstruction model.

[0116] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0117] The following embodiments take a certain layer of heterogeneous limestone-dolomite in the Sichuan Basin as an example.

[0118] Example 1

[0119] This embodiment provides a method for three-dimensional reconstruction of a digital core including pores and mineral distribution, the method specifically comprising the following steps:

[0120] S1. Sample marking positioning information:

[0121] Select rock samples and process them into cylindrical regular samples with a diameter of about 2.7 cm and a length of about 5.0 cm (such as Figure 1 As shown); Position the cylindrical sample, cut a linear notch along the height of the cylinder on the edge of the cylindrical sample, and mark the surface crack position (as shown in Figure 2 shown).

[0122] S2. Obtaining 3D pore information of core samples:

[0123] Place the sample on the turntable of the CT scanning equipment, ensuring that the sample is fixed and centered. Set the scanning parameters: adjust the X-ray source voltage, magnification and other parameters according to the characteristics of the sample (such as density, size, etc.) to obtain the best CT scanning image. Taking a 1-inch diameter cylindrical sample with an analysis accuracy of 15 microns as an example, the scanning operation is a spiral system, the scanning speed is 175mm / s, the scanning voltage is 140kV, the scanning power is 15W, and the voxel resolution is 15μm; the original typical two-dimensional CT slice has 2600 layers, each layer is 1700×1700 voxels. Start the scanning process, and the sample rotates at a constant speed in the range of -180° to 180°. After each rotation of a certain angle, X-rays irradiate the sample to obtain a projection image (such as Figure 3 and Figure 4 shown).

[0124] Import the acquired series of projection images into the reconstruction software of the micro-CT, and input the number of projection images, tube voltage, sample-to-detector distance, spatial pixels and other related parameters according to the prompts for reconstruction. Process the reconstructed CT images, including noise reduction, grayscale transformation, median filtering, binarization and image segmentation, to extract the information and parameters of the microstructure. Use software such as Avizo Fire 8.0 to process the images and extract the information and parameters of the microstructure (such as Figure 5 shown).

[0125] S3. Obtain mineral analysis section:

[0126] The cylindrical sample with CT scan results was positioned and cut along the circular cross section to obtain the mineral analysis section. The cutting interval was 4 mm. 11 cross sections were obtained for the cylindrical sample (such as Figure 6 After injection of glue, grinding, polishing and carbon coating, the cross section to be tested for mineral analysis is prepared. The specific operation method is as follows:

[0127] (a) Glue injection:

[0128] In order to prevent the sample from being broken by force during the grinding and polishing process, glue injection should be carried out first. Glue injection is generally made by fully mixing epoxy resin with curing agent and pouring it into the inside of the mold with the sample placed and coated with a release agent. The surface to be analyzed should be placed at the bottom to facilitate later grinding and polishing. The size of the mold should be based on the size of the sample table or storage table of the mineral scanning equipment. Taking the original sample with a diameter of 1 inch (about 25mm) as an example, a 30mm round storage table can be selected in the Qemscan scanning system. Therefore, the sample size after glue injection and curing should be 30mm in diameter (such as Figure 7 After the sample is completely cured, remove the injected sample from the mold.

[0129] (b) Grinding:

[0130] Use a metallographic grinder to grind the injected sample so that the sample analysis surface is completely exposed from the injection. First, use the MD-Piano220 grinding disc for wet grinding (rough grinding), with a force of 20N, a speed of 250rpm, and a grinding time of 1min; after rough grinding, use the MD-piano1200 grinding disc for wet grinding (fine grinding), with a force of 12N, a speed of 200rpm, and a grinding time of 1min. Grinding is based on the analysis surface being smooth and flawless. If the result is not ideal, repeat the above steps.

[0131] (b) Sectioning:

[0132] The polishing procedure is only for the side of the sample block containing ore to ensure that the sample surface is smooth, free of bubbles and scratches. A short-neck polishing disc is used for polishing, and the diamond suspension particle size is gradually reduced from 5μm, 3μm, and 1μm for segmented operation. The polishing pressure of each segment is 15N, the speed is 150rpm, and the polishing time is 4-5min. During the preparation process, spraying diamond suspension and lubricating fluid on the grinding disc at a certain time interval can ensure uniform grinding of minerals of different properties on the contact surface of the sample block. After each polishing stage is completed, the grinding surface of the clean sample block must be gently rinsed with clean water or detergent, and then the surface of the sample block must be gently dipped with a dust-free cloth to absorb the moisture on the surface of the sample block, and the sample block is slowly blown dry with an air gun to ensure that there is no polishing residue and other contaminants on the surface of the sample block.

[0133] (d) Carbon plating:

[0134] Before scanning, QEMSCAN samples must be treated with carbon spraying to make the sample surface conductive, thereby eliminating the influence of surface charging on morphology observation and focusing, and obtaining normal images and analysis results. Place the sample block and the brass indicator block in the sample stage of the high vacuum coater, so that the surface of the sample block and the surface of the brass block are at the same horizontal position to observe the thickness of the carbon film. When the carbon spraying is completed, the carbon spraying of the sample is detected through the transparent vacuum chamber of the coater. The sample that has completed the carbon spraying treatment can be placed in the QEMSCAN for scanning and analysis. Be careful not to touch the surface of the sample when taking the sample to avoid damaging the carbon film layer.

[0135] S4. QEMSCAN quantitative analysis:

[0136] The prepared cross-section sample to be tested was placed on the sample stage of the scanning equipment and fixed. The sample stage carrying the sample to be tested was loaded into the sample chamber of the Qemscan micro-area mineral scanning system. The system working mode was selected as backscattering mode imaging. The parameters were set to 15 kV, Spot 6.5, working distance 13 mm, and resolution 15 μm. The 11 sample cross-sections obtained were analyzed to quantitatively analyze the distribution of mineral components on the two-dimensional image ( Fig. 8A and Figure 8B shown).

[0137] S5. Establishing a three-dimensional mineral model:

[0138] A three-dimensional mineral model was established based on the quantitative analysis results of the 11 cross-sectional minerals. Since the sizes of the obtained mineral images were not the same and the cross-sections were not registered, the cross-sectional images were first registered according to the reserved positioning ports to obtain cross-sectional mineral images that were aligned and of the same size (row and column numbers), and then the two-dimensional images were reconstructed in three dimensions using multi-plane reconstruction (MPR) technology. A three-dimensional mineral model was established to generate a perspective view of the three-dimensional mineral. (e.g. Fig. 9 shown).

[0139] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for three-dimensional reconstruction of digital core including pore and mineral distribution, characterized in that: The method for three-dimensional reconstruction of digital core including pore and mineral distribution comprises the following steps: (1) Sample marking and positioning information: a linear notch is cut along the height direction on the cylindrical surface of the cylindrical rock sample as the positioning line of the mineral analysis section; (2) Obtaining 3D pore information of core samples: Performing X-ray CT scanning on the positioned cylindrical rock samples to obtain a 3D grayscale image of the rock, and then reconstructing and processing the image to obtain a 3D grayscale image model of the rock; (3) Obtaining the mineral analysis section: The cylindrical rock sample with CT scan information is cut into several sample slices along the direction of the circular cross section, and then each sample slice is injected with glue, ground, polished and carbon-plated in turn to obtain several cross-section samples to be tested; (4) QEMSCAN quantitative analysis: The surface of each cross-section sample to be tested is scanned using the scanning electron microscope mineral quantitative evaluation system, the distribution of mineral components on the two-dimensional image is quantitatively analyzed, and the two-dimensional image of each cross-section sample to be tested is output; (5) Establishing a three-dimensional mineral model: The two-dimensional images of each cross-sectional sample to be measured are registered according to the positioning lines to obtain cross-sectional mineral images that are aligned and of the same size, and then the two-dimensional images are reconstructed into three dimensions through a multi-faceted reconstruction method.

2. The method for three-dimensional reconstruction of digital cores including pore and mineral distribution according to claim 1, characterized in that: In step (1), the cylindrical rock sample is processed into a cylindrical shape by a rock sample; Preferably, the diameter of the cross section of the cylindrical rock sample is 2.5 to 3.0 cm.

3. The method for three-dimensional reconstruction of digital cores including pore and mineral distribution according to claim 1 or 2, characterized in that: In step (1), the positioning process also includes a mark for supplementing the positioning information: Marking characteristic sedimentary phenomenon information points on samples from which sedimentary phenomena can be identified, and numbering these information points; wherein the sedimentary phenomenon information points include any one or a combination of at least two of minerals, bedding, laminations, or various sedimentary structural features; Or, physical positioning information is produced on a sample where deposition phenomena are difficult to identify, and these information points are numbered; wherein the production method includes using cutting and / or laser engraving.

4. The method for three-dimensional reconstruction of digital cores including pore and mineral distribution according to claim 1, characterized in that: In step (2), the CT scan specifically includes the following steps: The positioned cylindrical rock sample is placed in a CT scanner for X-ray CT scanning to obtain an X-ray CT scanning grayscale three-dimensional image and an engineering file output by the CT scanner; The engineering files output by the CT scanner are analyzed by Amira 3D software to obtain a grayscale three-dimensional image model of a rock composed of minerals and pores of different densities.

5. The method for three-dimensional reconstruction of digital cores including pore and mineral distribution according to claim 1 or 4, characterized in that: In step (2), the process of obtaining the three-dimensional pore information of the core sample also includes extracting pore information and / or positioning information: Identify and mark positioning lines, sedimentary phenomenon information points and / or physical positioning information in the rock grayscale three-dimensional image model, extract the three-dimensional model of pores and positioning information points in the generated rock grayscale three-dimensional image model, and output it as a universal editable three-dimensional format file through Amira3D software.

6. The method for three-dimensional reconstruction of digital cores including pore and mineral distribution according to claim 1 or 4, characterized in that: In step (3), the number of cuts of the same cylindrical rock sample is at least 10; Preferably, in step (3), the thickness of the sample slice obtained by cutting is 4 to 5 mm; Preferably, in step (3), the specific process of glue injection, grinding, polishing and carbon plating is as follows: (a) Glue injection: Place the sample piece inside the mold coated with a release agent, then pour the mixture of epoxy resin and curing agent. After the glue layer is cured, take out the sample piece; (b) grinding: using a metallographic grinder to first coarsely grind the sample after the injection of glue, and then finely grind it to remove the glue layer on the surface to be scanned of the sample piece; (c) Polishing: Use a short-napped polishing disc to polish the side of the ground sample containing the ore in sections; (d) Carbon coating: The polished sample is subjected to carbon coating treatment to form a carbon film layer.

7. The method for three-dimensional reconstruction of digital cores including pore and mineral distribution according to claim 6, characterized in that: In step (a), the thickness of the adhesive layer is 10 to 15 mm; Preferably, in step (b), the coarse grinding is: wet grinding with a MD-Piano220 grinding disc, with a force of 15 to 25 N, a rotation speed of 200 to 300 rpm, and a time of 0.5 to 2 min; Preferably, in step (b), the fine grinding is: using MD-piano1200 grinding disc for wet grinding, with a force of 10 to 15 N, a rotation speed of 150 to 250 rpm, and a time of 0.5 to 2 min; Preferably, in step (c), the segmented polishing is performed by gradually decreasing the particle size of the diamond suspension to 5 μm, 3 μm, and 1 μm, the pressure of each segment polishing is less than 10 N, the rotation speed of each segment polishing is independently 100 to 200 rpm, and the time of each segment polishing is independently 4 to 5 min; Preferably, in step (d), the thickness of the carbon film layer is 5-10 nm.

8. The method for three-dimensional reconstruction of digital cores including pore and mineral distribution according to claim 1, characterized in that: In step (4), the QEMSCAN quantitative analysis is specifically as follows: Using the scanning electron microscope mineral quantitative evaluation system, a high-energy electron beam is used to scan the surface of each cross-section sample to be tested along a preset raster scanning pattern to collect BSE data; At each scanning point, mineral identification is performed on each scanning point by comparing the collected X-ray and BSE data with the mineral phase information in the reference mineral library. Finally, the identification results of all scanning information points are summarized and output as a two-dimensional image.

9. The method for three-dimensional reconstruction of digital core including pore and mineral distribution according to claim 1, characterized in that: In step (4), the working mode of the scanning electron microscope mineral quantitative evaluation system is backscattering mode imaging; Preferably, in step (4), the scanning parameters are set as follows: parameter speed voltage is 10-20 kV, working distance is 10-15 mm, and resolution is 10-15 μm.

10. The method for three-dimensional reconstruction of digital core including pore and mineral distribution according to claim 1, characterized in that: In step (5), the process of establishing the three-dimensional mineral model also includes: Before inputting the pore information obtained by X-ray CT scanning, the three-dimensional pore information already contained in the three-dimensional mineral model needs to be deleted; Preferably, in step (5), the process of establishing the three-dimensional mineral model further includes: According to the grayscale distribution of the X-ray CT scan, the positioning line of the cylindrical section, the position of the positioning line in the electron microscope scanning analysis results of the mineral quantitative analysis, and the relative positions of different minerals, the rock grayscale three-dimensional image model with pore information obtained in step (2) is fitted with the three-dimensional mineral model obtained in step (5) to obtain a three-dimensional reconstruction model of the digital core.

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