CN115356363B - Pore structure characterization method based on wide ion beam polishing-scanning electron microscope - Google Patents
Pore structure characterization method based on wide ion beam polishing-scanning electron microscope Download PDFInfo
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- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
- G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
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- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
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- G01N15/088—Investigating volume, surface area, size or distribution of pores; Porosimetry
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Abstract
The invention discloses a pore structure characterization method based on a wide ion beam polishing-scanning electron microscope, which comprises the following steps: step 100, cutting a core sample to obtain a sample sheet, and preprocessing the sample sheet to obtain a tungsten-plated polished surface; step 200, sequentially scanning and splicing the tungsten plating polished surfaces of the sample thin plate by using a scanning electron microscope to form a panoramic image; step 300, screening pores and dividing mineral types based on a threshold segmentation method to form a pore layer and a mineral type layer respectively; step 400, performing superposition analysis on the pore layer and the mineral type layer, and predicting the porosity of the large-size three-dimensional columnar sample based on the porosity of the two-dimensional microscopic image; the method for intuitively researching the pore morphology, pore size distribution and connectivity in each mineral phase on the surface of a large-area rock sample has the advantages of less core consumable and accurate porosity prediction, and can be widely applied to research of reservoir physical property evaluation and diagenetic effect.
Description
Technical Field
The invention relates to the technical field of petroleum engineering, in particular to a pore structure characterization method based on a wide ion beam polishing-scanning electron microscope.
Background
Pores are the basic reservoir space in which fluids reside in the rock, and the connectivity of pore size ranges and pore structures control the flow and transport of fluids in the reservoir. In order to quantify the relationship among porosity, reservoir capacity and seepage characteristics in a reservoir, quantitative characterization of pore structure is particularly important.
In recent years, mercury intrusion porosimetry, low-pressure nitrogen or carbon dioxide adsorption methods are widely used for characterization of pore structures, but these methods are based on the assumption of simplified pore geometry and lack visual information about pore morphology and connectivity. Furthermore, the presence and distribution of pores may be related to a particular mineral phase, whereas fluid invasion techniques act on the rock as a whole, failing to obtain relevant information.
With the development of imaging technology, scanning electron microscopy is gradually capable of providing high-resolution images for the study of nanopores, while wide ion beam polishing technology (Broad ion beam milling, abbreviated as BIB) can prepare a millimeter-sized flat and crack-free and scratch-free sample surface, and combining the two can provide a method for qualitatively and quantitatively characterizing the pore structure of a sample in a relatively large area (square millimeter scale).
Disclosure of Invention
The invention aims to provide a pore structure characterization method based on a wide ion beam polishing-scanning electron microscope, which combines the scanning electron microscope and the wide ion beam polishing technology to qualitatively and quantitatively characterize a sample pore structure so as to solve the technical problems that an idealized pore morphology model is adopted in the prior art, the obtained pore structure parameters are few, and finally, the comprehensive and accurate characterization of the rock pore structure is difficult.
In order to solve the technical problems, the invention specifically provides the following technical scheme:
a pore structure characterization method based on a wide ion beam polishing-scanning electron microscope comprises the following steps:
step 200, sequentially scanning the tungsten plating polished surface of the sample thin plate by using a scanning electron microscope, and splicing according to the scanning sequence to form a panoramic image;
step 300, screening pores and dividing mineral types based on a threshold segmentation method to respectively form a pore layer and a mineral type layer;
and 400, overlapping the pore layer and the mineral type layer, analyzing the porosity and pore structure parameters of different types of minerals, and predicting the porosity of the large-size three-dimensional columnar sample based on the porosity of the two-dimensional microscopic image.
Further, in step 200, scanning the tungsten-plated polished surface of the sample sheet by using a scanning electron microscope specifically includes:
the scanning electron microscope generates related signals by emitting high-energy electron beams to the tungsten plating polished surface, wherein the high-energy electron beams interact with atoms on the surface of the sample;
the secondary electron detector collects secondary electrons to obtain pore and microstructure information of the sample;
the method comprises the steps that a back scattering electron detector collects back scattering electrons to obtain mineral type and distribution information of a sample;
the energy dispersion X-ray spectrometer collects characteristic X-rays to obtain element abundance information of the sample.
Further, the sample sheet is scanned using a scanning electron microscope equipped with a secondary electron detector, a back-scattered electron detector and an energy dispersive X-ray spectrometer, with at least 10% image overlap between adjacent images of each scan.
Further, the specific steps of stitching the scanned images according to the scanning sequence are as follows:
defining overlapping areas according to the overlapping degree of the images, obtaining markers in the overlapping areas of each image through visual identification, and marking each marker;
matching the identified markers on different images, splicing in an overlapping area according to a matching result, and carrying out stretching or compression correction on the images in a certain range by taking the adjacent markers as references in the splicing process so as to finish seamless splicing;
and after the seamless stitching is completed, performing secondary correction on the stitching pattern by using pixel units to form a panoramic image.
Further, in step 300, the specific steps of the threshold segmentation-based screening are:
threshold segmentation is carried out on a panoramic image obtained by a secondary electron detector, pores and solid phases are distinguished according to the difference of gray values, boundaries of the pores are outlined, and the pores are screened out from the panoramic image to form a pore layer;
threshold segmentation is carried out on a panoramic image obtained by the back scattering electron detector, a solid phase is divided into different mineral types according to different gray values, boundaries of each mineral type are outlined to screen different minerals from the panoramic image to form a mineral type image layer, and meanwhile, element distribution diagrams obtained by the energy dispersion X-ray spectrometer are utilized to verify distribution of different types of minerals on a two-dimensional plane.
Further, the pore layer and the mineral type layer are overlapped, the porosity of each type of mineral is calculated, and the pore structure parameters of each type of mineral are recorded.
Further, the pore structure parameters include pore morphology, pore size distribution, and connectivity;
wherein the pore morphology comprises a short axial length W, a long axial length L, an area A, a perimeter P and a roundness of 4pi A/P 2 Elongation 1-W/L.
Further, the specific method for comparing the pore size distribution characteristics in panoramic images with different sizes comprises the following steps:
assuming that the pore sizes of panoramic images of different sizes are all divided into i groups from small to large in an exponential manner, wherein the i-th group (b i ，b i+1 ) Group spacing b i And b i+1 ＝2b i ；
Pair (b) i ，b i+1 ) Frequency N of occurrence of intra-range voids i By group distance b i And an area S of the panoramic image mosaic Normalized by the product of (2), if the normalized pore frequency N i /(b i ·S mosaic ) Area S of corresponding aperture pore The distribution of pore sizes is considered to have self-similarity if the following exponential relationship is satisfied:
wherein i is a measurement constant, i is not less than 1, D is an index of the index relationship, and C is a constant.
Further, assuming that the minimum interlayer spacing of the clay mineral is μ, and extrapolating the equivalent pore diameter to μ by using the exponential relationship obtained by panoramic image analysis, the obtained porosity is just within the porosity range of the measured large-size columnar sample.
Further, when dividing based on gray values in threshold segmentation, firstly counting the frequency of the gray values, arranging the gray values according to the size sequence of the gray values, and determining the demarcation value or demarcation interval of the adjacent gray values according to the aggregation interval of the gray values;
setting adjacent demarcation values or gray values between demarcation intervals as an effective interval, and carrying out homogenization treatment on each effective interval so as to obtain contour division on the whole panoramic image for re-correction;
wherein, the demarcation interval is much smaller than the effective interval.
Compared with the prior art, the invention has the following beneficial effects:
the invention can realize pore structure characterization and mineral composition analysis of a relatively large-area sample, and analyze the pore structure of each mineral one by one; by utilizing the index relation between the normalized pore frequency and the pore area, the porosity of the large-size columnar sample can be predicted based on the porosity of the two-dimensional microscopic image, the three-dimensional sample is not required to be measured one by one, the operation controllability is strong, and the complexity is low.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It will be apparent to those skilled in the art from this disclosure that the drawings described below are merely exemplary and that other embodiments may be derived from the drawings provided without undue effort.
FIG. 1 is a flow chart of pore structure characterization based on a wide ion beam polish-scanning electron microscope.
Fig. 2 is a pore size distribution diagram of calcite (a) and clay mineral (b) in the present embodiment.
FIG. 3 shows normalized pore frequencies N in calcite and clay minerals in the present embodiment i /(b i ·S mosaic ) And pore area S pore Relationship between them.
FIG. 4 is a graph of the cumulative total porosity distribution after extrapolation in this embodiment.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the invention, the basic flow comprises four aspects, namely sample preparation (including pretreatment of the sample), image acquisition, image processing and analysis of pore results, in sequence of processing. As shown in fig. 1, to better illustrate the characterization method, the present invention provides a pore structure characterization method based on a wide ion beam polishing-scanning electron microscope, which includes the following steps:
and 100, cutting the core sample to obtain a sample sheet, and sequentially carrying out sand paper polishing, wide ion beam polishing and tungsten plating on any surface of the sample sheet to obtain a tungsten-plated polished surface.
The core sample is processed by cutting, sanding, wide ion beam polishing and tungsten plating, and the specific method comprises the following steps:
first, a piece of about 1X 1cm was cut from a Cobourg limestone core using a diamond saw blade 3 The left and right sample thin plates, and one surface of the sample thin plate is primarily polished by using diamond abrasive paper;
secondly, placing the sample sheet after manual polishing on a wide ion beam polishing machine with the model JEOL SM-09010, polishing the sample sheet for 8 hours under 6kV accelerating voltage, wherein a high angle is formed between the wide ion beam and the sample sheet;
finally, a polished sample sheet was uniformly coated with a layer of tungsten and scanned under a scanning electron microscope model Zeiss Supra 55.
In the foregoing, the side of the sample sheet cut with little or no cracks is selected as much as possible to avoid crack propagation or formation of new cracks during subsequent sanding and polishing.
The signals obtained during this scanning process include secondary electrons (secondary electron, SE2 for short), backscattered electrons (backscatter electron, BSE for short) and characteristic X-rays, which are analyzed by an energy dispersive X-ray spectrometer to obtain an energy dispersive X-ray (EDX for short).
And 200, sequentially scanning the tungsten plating polished surface of the sample thin plate by using a scanning electron microscope, and splicing according to the scanning sequence to form a panoramic image.
The scanning of the tungsten plating polished surface of the sample sheet by using the scanning electron microscope specifically comprises the following steps:
scanning electron microscopy produces a correlated signal by emitting a beam of energetic electrons onto the tungsten-plated polished surface, which interact with atoms on the surface of the sample.
The secondary electron detector collects secondary electrons to obtain pore and microstructure information of the sample;
the method comprises the steps that a back scattering electron detector collects back scattering electrons to obtain mineral type and distribution information of a sample;
the energy dispersion X-ray spectrometer collects characteristic X-rays to obtain element abundance information of the sample.
And scanning the sample thin plate by using a scanning electron microscope provided with a secondary electron detector, a back scattering electron detector and an energy dispersion X-ray spectrometer, wherein at least 10% of images are overlapped between adjacent images scanned each time, and 10% -20% of images are generally selected so as to better realize the positioning and alignment treatment of the adjacent images in splicing software.
The method comprises the steps of partially overlapping images, wherein certain microstructure features are enabled to be simultaneously displayed on two adjacent images, so that the images are conveniently spliced, in the embodiment, the acquired hundreds of images are spliced by adopting Autopano giga2.6 software, the images can be spliced in order in the splicing process, the images are spliced successively according to the scanning sequence, and the splicing mode is as follows:
defining overlapping areas according to the overlapping degree of the images, obtaining markers in the overlapping areas of each image through visual identification, and marking each marker;
matching the identified markers on different images, splicing the images in an overlapping area according to a matching result, and carrying out stretching or compression correction on the images in a certain range by taking the adjacent markers as references in the splicing process so as to finish seamless splicing;
and after the seamless stitching is completed, performing secondary correction on the stitching pattern by using pixel units to form a panoramic image.
In this embodiment, in order to improve the stitching efficiency and avoid malformation of the stitched panoramic image, firstly, coarse stretching is performed by using a marker to enable the scanned image to be stitched quickly to form seamless connection, and then, the stitched image is corrected twice by a pixel unit to form a complete panoramic image accurate to the pixel unit, and it is to be noted that, in the stitching process, image malformation caused by stretching or compression is unavoidable, in this embodiment, the foregoing problem is solved mainly in two ways, and in the first way, a line with the marker itself or a marker adjacent to or in a region as a reference is corrected as a standard, so that stitching of a deformed image is guaranteed as much as possible; the second way is to perform image complementation by means of overlapping area images.
In the present embodiment, the area of the finally formed panoramic image is about 1mm 2 The aperture containing 10 pixel areas is considered the "identifiable" smallest aperture, the equivalent circular aperture having a diameter of 52nm.
And 300, screening pores and dividing mineral types based on a threshold segmentation method to respectively form a pore layer and a mineral type layer.
The specific steps of the threshold segmentation screening are as follows:
threshold segmentation is carried out on the panoramic image obtained by the secondary electron detector, pores and solid phases are separated according to different gray values, boundaries of the pores are outlined, and the pores are screened out from the panoramic image to form a pore layer;
threshold segmentation is carried out on a panoramic image obtained by a back scattering electron detector, a solid phase is divided into different mineral types according to different gray values, boundaries of each mineral type are outlined to screen out different mineral types from the panoramic image to form a mineral type image layer, and meanwhile, element distribution diagrams obtained by an energy dispersion X-ray spectrometer are utilized to verify distribution of each mineral type on a two-dimensional plane.
In the foregoing, both the identification of the pores and the division of the mineral types are dependent on the gradation identification, however, in actual operation, since gradation values of the pores and the different types of minerals are uncertain and may vary within a certain range, it is often difficult to determine a division point or a division section (a transition zone exists) of the gradation values during actual processing, which is disadvantageous for threshold division of the pores and the mineral types.
In order to solve the above-described problem, in the present invention, when dividing based on gray values in threshold division, since the pores and mineral basic features at the same sampling position are considered to be similar, the division value or division section is determined based on the frequency at which the same gray value appears.
The concrete mode is as follows:
firstly, counting the frequency of gray values, arranging the gray values according to the size sequence of the gray values, and determining the demarcation value or demarcation interval of adjacent gray values according to the aggregation interval of the gray values;
setting the gray value between adjacent demarcation values or demarcation intervals as an effective interval, and carrying out homogenization processing on each effective interval so as to obtain contour division on the whole panoramic image for re-correction.
In the foregoing, each active region corresponds to either an aperture or a solid phase, or a mineral type, depending mainly on the panoramic image taken in the secondary electron detector, the backscattered electron detector.
In order to effectively distinguish, the proportion of the boundary is reduced as far as possible, and the boundary interval is far smaller than the effective interval.
In this embodiment, the SE2 image is thresholded using ArcMap software, and the pores are separated from the solid phase (solid matter including minerals and other constituent components) according to the gray scale values. After the separation of the pores and the solid phase is completed, the boundary of the pores is outlined by the space analysis tool carried by the Arcmap software through polygons, and in this way, the pores can be rapidly and automatically screened from the image.
To increase accuracy, after the autofilter is completed, all pore boundaries need to be manually checked and further editing is required for small number of erroneous segmentations.
Similarly, the BSE images were thresholded in ArcMap software, and Cobourg limestone mineral types were classified into calcite, dolomite, quartz, clay minerals, and pyrite according to the difference in gray scale values, and EDX images corresponding to the BSE images were used to further verify the distribution of each mineral phase on a two-dimensional plane.
Such as: the distribution area of pyrite in the BSE image corresponds to the enrichment area of iron and sulfur elements in the EDX image.
And 400, overlapping the pore layer and the mineral type layer, analyzing the porosities and the pore parameters of different types of minerals, and predicting the porosities of the large-size three-dimensional columnar sample based on the porosities of the two-dimensional microscopic images.
And superposing the pore layer and the mineral type layer, calculating the porosity of each type of mineral, and recording pore structure parameters of various minerals.
Further, the pore structure parameters include pore morphology, pore size distribution and connectivity, and the connectivity analysis of the pores is limited to the connectivity between adjacent pores in a two-dimensional plane.
Wherein the pore morphology comprises a short axial length W, a long axial length L, an area A, a perimeter P and a roundness of 4pi A/P 2 Elongation 1-W/L.
In order to classify the pore sizes, the pore sizes are all divided exponentially from small to large into i groups, where the i-th group (b i ，b i+1 ) Group spacing b i And b i+1 ＝2b i As shown in fig. 2. It is emphasized here that in order to compare the distribution characteristics of the pore sizes in panoramic images of different sizes, the normalization process is performed in the same way, the specific manner of which is further described below.
When pore sizes are all divided exponentially from small to large into groups, the ratio of (b) i ，b i+1 ) Frequency of pore occurrence N within a range i By group distance b i And an area S of the panoramic image mosaic Normalized by the product of (2), observing the normalized pore frequency N i /(b i ·S mosaic ) Area S of corresponding aperture pore The relationship between them is considered to have self-similarity if the following exponential relationship is satisfied, where the exponential relationship is:
wherein i is a measurement constant, i is not less than 1, D is an index of the index relationship, and C is a constant.
In this embodiment, a reasonable minimum pore diameter range needs to be considered in combination with the mineral composition and mineral internal structure of the actual rock sample when extrapolated using the exponential relationship of normalized pore frequency to pore area. In order to predict the porosity range of large-size columnar samples, helium porosimetry needs to be introduced for measurement.
The porosity of each type of mineral is firstly verified, and the porosity prediction based on the two-dimensional image is verified to be consistent with the laboratory test result. In fig. 3, r is calculated using the formula y= -2.59x-1.32 2 =0.99, the cumulative porosity at 1nm of the clay mineral of Cobourg limestone was calculated; also, the formula y= -1.93x-3.51, r 2 The method comprises the steps of (1) calculating the cumulative porosity of calcite of Cobourg limestone at 1nm, analyzing other types of minerals one by one according to the steps to obtain the cumulative porosity of all types of minerals, and finally verifying that the total porosity obtained by a two-dimensional image is identical with the porosity of a three-dimensional sample tested in a laboratory, wherein the method can be used for effectively predicting.
For helium porosimetry, the diameter of the smallest aperture into which helium can theoretically enter is 0.26nm, while the equivalent diameter of the smallest aperture "identifiable" by the wide ion beam polish-scanning electron microscopy technique is 52nm. The clay minerals in rock generally have the smallest pore size, the clay minerals of Cobourg limestone are mainly composed of illite and illite mixed layers, the smallest inter-layer distance of clay minerals of this type of TOT is 1 in nm (only the clay minerals in rock are of a layered structure, generally possess the smallest pore size, i.e. the smallest inter-layer distance, the present study assumes that the lower limit value of the rock pore size is determined by the smallest inter-layer distance of clay minerals. In order to compare the porosities obtained by the imaging method and the helium porosimeter, the porosities of calcite and clay mineral respectively under the current resolution are obtained firstly, the sum of the porosities accounts for more than 99% of the total porosity, the equivalent pore diameter is extrapolated to 1nm by utilizing the index relation obtained by image analysis so as to predict the pore frequency in a smaller pore diameter range, and the sum of the accumulated porosities of the calcite and the clay mineral is calculated on the basis of the calculated sum, and the sum is just in the porosity range of a large-size columnar sample measured by the helium porosimeter (as shown in figure 4, wherein the intersection point of two parallel dotted lines and the ordinate axis represents the porosity range of the large-size columnar sample measured by the helium porosimeter).
By combining the above, compared with the traditional mercury intrusion porosimetry, low-pressure nitrogen or carbon dioxide adsorption method, the method for intuitively researching the pore morphology, pore size distribution and connectivity is provided based on the pore structure characterization of the wide ion beam polishing-scanning electron microscope.
The invention can realize pore structure characterization and mineral composition analysis of samples in a large area range (several square millimeters), and analyze the pore structure of each mineral one by one.
In addition, the invention can predict the porosity of the large-size columnar sample based on the porosity of the two-dimensional microscopic image by utilizing the exponential relation of the normalized pore frequency and the pore area.
The invention can realize pore structure characterization and mineral composition analysis on a relatively large-area sample, and analyze the pore structure of each mineral one by one; by utilizing the index relation between the normalized pore frequency and the pore area, the porosity of the large-size columnar sample can be predicted based on the porosity of the two-dimensional microscopic image, the three-dimensional sample is not required to be measured one by one, the operation controllability is strong, and the complexity is low.
The above embodiments are only exemplary embodiments of the present application and are not intended to limit the present application, the scope of which is defined by the claims. Various modifications and equivalent arrangements may be made to the present application by those skilled in the art, which modifications and equivalents are also considered to be within the scope of the present application.
Claims (7)
1. The pore structure characterization method based on the wide ion beam polishing-scanning electron microscope is characterized by comprising the following steps of:
step 100, cutting a core sample to obtain a sample sheet, and sequentially carrying out sand paper polishing, wide ion beam polishing and tungsten plating on any surface of the sample sheet to obtain a tungsten plating polished surface;
step 200, sequentially scanning the tungsten plating polished surface of the sample thin plate by using a scanning electron microscope, and splicing according to the scanning sequence to form a panoramic image;
step 300, screening pores and dividing mineral types based on a threshold segmentation method to respectively form a pore layer and a mineral type layer;
the specific steps of the threshold segmentation screening are as follows:
threshold segmentation is carried out on a panoramic image obtained by a secondary electron detector, pores and solid phases are distinguished according to the difference of gray values, boundaries of the pores are outlined, and the pores are screened out from the panoramic image to form a pore layer;
threshold segmentation is carried out on a panoramic image obtained by a back scattering electron detector, a solid phase is divided into different mineral types according to different gray values, boundaries of each mineral type are outlined to screen different minerals from the panoramic image to form a mineral type image layer, and meanwhile, element distribution diagrams obtained by an energy dispersion X-ray spectrometer are utilized to verify distribution of different types of minerals on a two-dimensional plane;
overlapping the pore layer and the mineral type layer, calculating the porosity of each type of mineral, and recording pore structure parameters of each type of mineral;
step 400, overlapping the pore layer and the mineral type layer, analyzing the porosity and pore structure parameters of different types of minerals, and predicting the porosity of a large-size three-dimensional columnar sample based on the porosity of a two-dimensional microscopic image;
the specific method for comparing the pore size distribution characteristics in panoramic images with different sizes comprises the following steps:
counting the areas of all pores in panoramic images with different sizes, and distributing all pores into i groups from small to large according to the pore areas;
wherein assigned to the ith group (b) i ，b i+1 ) The frequency of the pores in the porous material is N i Group i (b) i ，b i+1 ) Group spacing b i And b i+1 ＝2b i ，b i Is the pore area, N i Average area of individual pores is S pore ；
Pair (b) i ，b i+1 ) Frequency N of occurrence of intra-range voids i By group distance b i And an area S of the panoramic image mosaic Normalized by the product of (2), if the normalized pore frequency N i /(b i ·S mosaic ) Average pore area S with group i pore The distribution of pore areas is considered to have self-similarity if the following exponential relationship is satisfied:
wherein i is a measurement constant, i is not less than 1, D is an index of the index relationship, and C is a constant.
2. The method of claim 1, wherein in step 200, scanning the tungsten-plated polished surface of the sample sheet with the scanning electron microscope comprises:
the scanning electron microscope generates related signals by emitting high-energy electron beams to the tungsten plating polished surface, wherein the high-energy electron beams interact with atoms on the surface of the sample;
the secondary electron detector collects secondary electrons to obtain pore and microstructure information of the sample;
the method comprises the steps that a back scattering electron detector collects back scattering electrons to obtain mineral type and distribution information of a sample;
the energy dispersion X-ray spectrometer collects characteristic X-rays to obtain element abundance information of the sample.
3. The method of claim 2, wherein the sample sheet is scanned using a scanning electron microscope equipped with a secondary electron detector, a back-scattered electron detector and an energy dispersive X-ray spectrometer, and wherein at least 10% of the images overlap between adjacent images of each scan is maintained.
4. The pore structure characterization method based on the wide ion beam polishing-scanning electron microscope according to claim 3, wherein the specific steps of stitching the scanned images according to the scanning sequence are as follows:
defining overlapping areas according to the overlapping degree of the images, obtaining markers in the overlapping areas of each image through visual identification, and marking each marker;
matching the identified markers on different images, splicing the images in an overlapping area according to a matching result, and carrying out stretching or compression correction in a certain range on the images by taking the adjacent markers as references in the splicing process so as to finish seamless splicing;
and after the seamless stitching is completed, performing secondary correction on the stitching pattern by using pixel units to form a panoramic image.
5. The method for characterizing a pore structure based on a wide ion beam polish-scan electron microscope according to claim 4, wherein the pore structure parameters include pore morphology, pore size distribution and connectivity;
wherein the pore morphology comprises a short axial length W, a long axial length L, an area A, a perimeter P and a roundness of 4pi A/P 2 Elongation 1-W/L.
6. The method for characterizing a pore structure based on a wide ion beam polishing-scanning electron microscope according to claim 5, wherein the obtained porosity is just within the measured porosity range of a large-sized columnar sample by setting the minimum interlayer spacing of clay minerals to μ and extrapolating the equivalent pore diameter to μ by using an exponential relationship obtained by panoramic image analysis.
7. The method for characterizing a pore structure based on a wide ion beam polish-scanning electron microscope as defined in claim 4,
when dividing based on gray values in threshold segmentation, firstly counting the frequency of the gray values, arranging the gray values according to the size sequence of the gray values, and determining the demarcation value or demarcation interval of adjacent gray values according to the aggregation interval of the gray values;
setting adjacent demarcation values or gray values between demarcation intervals as an effective interval, and carrying out homogenization treatment on each effective interval so as to obtain contour division on the whole panoramic image for re-correction;
wherein, the demarcation interval is much smaller than the effective interval.
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